What is the 'sweet spot' exactly? [Archive]

lightshedder

Saturday 28th April 2007, 04:44

I see frequent mention of the term, 'sweet spot', but I don't really know what's meant by it. Are people seeing an actual spot—a circle of clearness surrounded by a ring of relative obscurity—or are they using the term as a metaphor for the notional area of maximum sharpness?

Michael.

All levity aside (and I did enjoy the lighter aspects of this thread), this is a topic of some interest to me, as the "sweet spot" of the Zeiss Victory FLs has come in for a lot of criticism on this forum.

At Zeiss, we define a "zone of critical sharpness" which surrounds the center of the field and is measured in degrees to either side of center, as an angle similar to field of view, or sometimes, less accurately, as a % of the visible field. That is what I have assumed people mean by "sweet spot".

However, continuing observations on the narrowness of the FL sweet spot when compared to the competing models on this forum has lead me to suspect that others are using the term differently.

We measure the zone of critical sharpness by taking photographs through the binocular eyepiece of a wall-sized resolution chart through a collimating lens that places the chart at apparent infinity.

In our experience the zone of critical sharpness in most binoculars has a fairly sharp demarcation or edge. The resolution lines do not just generally fade into indistinctness as you move toward the edge of the field. They are critically sharp, or so our eye tells us, out away from the center a good ways, and then rapidly transition to indistinct blurs.

When we measure the FLs against the competition on in this test, we find that they maintain sharpness further out toward the edge of the field than any of the competing models accept one, and that the "boundary" where they resolution lines become unacceptably fuzzy is closer to the edge of the field than any but that one competing model.

When we look at the one model that has a wider zone of critical sharpness than the FLs, we see that the it is nowhere in its field as sharp as the FLs are at the center of their field. The wider zone was achieved, apparently, by sacrificing some center field resolution (not an acceptable trade-off as far as we are concerned).

On the other hand, because the boundary of our zone of critical sharpness is closer to the edge of the field, sharpness decreases more rapidly beyond the zone than in the competing models. Another way of saying that is: Competing models are no sharper at the absolute edge of the field than the FLs, but, because the zone of unacceptable sharpness is wider, the transition appears more gradual.

Again, we are not relying on impressions for any of this, or on our visual memories. We have photographic records for each binocular which we can compare side by side.

As it happens, I was personally involved in the design of this test procedure during the development of the FLs and our Conquest binoculars, specifically because we wanted to insure that our products produce the widest possible zone of critical sharpness.

So, if others are using the term "sweet spot" to describe some other effect or observation, then I'd like to see an accurate description of it.

Otherwise I am at a loss to understand the difference in perception expressed here when people complain about the narrow sweet spot of the FLs.

Stephen Ingraham

jaymoynihan

Saturday 28th April 2007, 05:13

[QUOTE=lightshedder;873086]...At Zeiss, we define a "zone of critical sharpness" which surrounds the center of the field and is measured in degrees to either side of center, as an angle similar to field of view, or sometimes, less accurately, as a % of the visible field. That is what I have assumed people mean by "sweet spot". ...QUOTE]

You should post this whole comment in that long thread re the FL's in the Zeiss section

jay

Alexis Powell

Saturday 28th April 2007, 05:54

This thread would seem to be the perfect place for me to share my thoughts/questions on sweet spots, eye-placement sensitivity, and the Zeiss FL. I made an earlier post in the middle of the thread titled "Mixed thoughts on new 8*42 FL" (http://www.birdforum.net/showthread.php?t=81855) but no one responded. I'm just going to copy what I wrote there below in hopes that this time it will be found more interesting/contentious/relevant.... Here's what I stated/asked:

*************
One of the things about the FL line that continues to bother me is the disaparity in experience that users report w/respect to off-axis sharpness. Many who try the FL notice much astigmatism and edge-softness whereas others claim the sharpness along the edge is as good or better than any. Steve Ingraham, whose assessments I generally find trustworthy claimed on the Z-birding site that the off-axis resolution of the 8x32 FL is superior to all top-end competitors except the Nikon 8x32 LXL. This claim seems absurd given the experience of myself and many other users, so what is going on?

I own the 8x32 FL and generally describe it to prospective buyers as having much more astigmatism and a smaller sweet spot than the Swarovski EL and the Leica models (I've tried almost a dozen 8x32 FL units and they are all like mine, so it isn't a matter of unit to unit variability), but perhaps that is an oversimplification. The Zeiss does have more astigmatism than the Swarovski EL and Leicas. It also has a flatter field, so depending on how you judge edge sharpness, it might indeed seem to be similarly sharp toward the edges of the view when focused on a centered target. Personally, I prefer field curvature to astigmatism because that way I can dart my eye around the view more freely (it's nice to be able to correct the image focus/sharpness either by repositioning the object in the FOV or by refocusing, rather than just the former).

It is in characterizing the size of the sweet spot that I think things are more complicated. What I've noticed about the 8x32 FL from early on is that it seems much more sensitive to eye-positioning than other binoculars. Compounding this problem is the fact that the very large eyecups can force users with big noses to tend to set the IPD too wide. Also, as a glasses user, I find the eyecup design makes it more difficult to position the oculars relative to my eyes as consistently and precisely as I can with other binos because when twisted down, the eyecups are very slippery/hard and flat. What seems to be true, is that if my eyes are positioned perfectly, and remain so even as I dart my vision around the FOV, the 8x32 FL has much better edge sharpness than I generally perceive when using them in a sloppier fashion. When binos have a smaller exit pupil and shorter eye-relief, I am in the habit of sliding them around to change my eye positioning VERY SLIGHTLY to make it easier to alternately see what is above, below, left, and right of the center (to look at the edges of the FOV) without experiencing black-out. All the other binos that I own are fairly insensitive to this decentering (I can be WAY off with the Leica, Swarovski, Nikon, or even my Zeiss 7x42 Classics), but what happens in the 8x32FL is a MASSIVE INCREASE in the amount of astigmatic distortion.

I'd be interested to know if those of you who understand the physics of optics can explain my experience and/or why some eyepieces would be more prone to astigmatism with slight eye-decentering than others.
*************
--AP

Pileatus

Saturday 28th April 2007, 14:30

The funny thing about optical science is that some schmuck always shows up mumbling, "I just don't see it that way". I'm absolutely convinced that some designers have deliberately optimized centerfield sharpness at the expense of edge sharpness. Off-axis "softness" is so evident in Zeiss and Leica models I'm surprised there's a discussion about it. It's really a question of how much one can tolerate.

John

elkcub

Saturday 28th April 2007, 21:25

Hi Steve,

Not to detract from the seriousness of the discussion, but I have to chuckle a bit in this case. Let me step aside to briefly tell a story. About 30 ys. ago NASA and the FAA entered into a program to reduce aircraft over-flight noise. A mix of technology improvements such as engine noise suppression, modified approach and takeoff angles, as well as routing pattern changes were made to accomplish this. In the test areas engineering noise levels were clearly reduced, … but quite often public complaints increased. It turned out that reducing physical noise is not exactly the same as reducing psychological “noisiness.” As the overall noise level was reduced, what had been only moderately noisy flights stood out as being quite loud. Engineers were working on an absolute basis; but the humans were responding on a relative basis.

Applying this to binoculars’ suggests that the “sweet spot” is a perception that is based on relative relationships within the framework of each binoculars’ view, not absolute differences between the views of various binoculars. As an illustration not far from what you’ve already described, consider two hypothetical binoculars, A and B. Binocular A has uniform but “acceptable” sharpness over its entire field (this is hypothetical, remember). Binocular B has a much higher sharpness in the center that drops off monotonically to a level, which although still acceptable, is below A’s sharpness at the edge. Further assume that it’s all worked out so that the average sharpness over the whole field is the same for both binoculars.

Binocular A will not really have a sweet spot, because there is no gradient, but it will probably be described as having a large sweet spot from edge to edge. Binocular B will have a sweet spot, — the border of which will be dependent on the peak sharpness at the center and the shape of the gradient to the edge. The observer probably (I’m guessing) will develop the percept of an annulus at some radial distance based on his ability to detect relative changes in sharpness, let’s say, using some idiosyncratic psychophysical just-noticeable-difference (JND) criterion. Paradoxically, then, the better the center sharpness, the shorter the radial distance will be to the inner ring of the annulus, because that’s where a sharpness change can be detected. The “sweet spot” size, unfortunately, will be inversely related to engineering success at the center. Moreover, those points within the outer annulus may be judged as unacceptable, even though similar points in binocular A are acceptable.

I believe this is sort of the situation you’re in. Is there a way around it? Not really, unless Zeiss deliberately decreases center performance to get a larger perceived sweet spot. The beauty of all this for me, of course, is that although I can't prove a word of it, it has a satisfying glow of truthiness. ;)

Blue skies,
Ed

Alexis Powell

Sunday 29th April 2007, 01:14

...Applying this to binoculars suggests that the “sweet spot” is a perception that is based on relative relationships within the framework of each binoculars’ view, not absolute differences between the views of various binoculars...
...I believe, this is sort of the situation you’re in. Is there a way around it? Not really, unless Zeiss deliberately decreases center performance to get a larger perceived sweet spot...

It's a cute story, but is most certainly NOT relevant (or accurate) for explaining (or describing) my observations of Zeiss FL optical characteristics or what I mean by sweet spot. For me, the size of the sweet spot is NOT something to do with relative relationships between the optical performance at different distances from the center field. Rather, it is defined by how well the overall sharpness of the bino holds up off center. It is something that I can see using resolution targets. The Zeiss 8x32 FL always has more astigmatism than its Leica, Swarovski, and Nikon counterparts, but its off-axis performance is actually quite excellent AS LONG AS one's eyes are well centered on the exit pupil. However, its (otherwise beautifully color neutral and low CA) view is SEVERELY DEGRADED by astigmatism, especially off center, when one's eyes are not centered perfectly--line targets fuzz out, fine print becomes impossible to read less than halfway to the edge of the field, and touching up the focus accomplishes nothing. In contrast, even when one's eyes are WELL off center using the Swarovski 8x32 EL or Leica 8x32 Ultra/Trinovid, the off-center field remains quite sharp and it can be brought into reasonably good focus (text that is a smeared blur in the Zeiss is easy to read). So the Zeiss provides a stunning view, but one that is easily compromised. If one were accustomed to the robust optical performance of the others and treated the Zeiss as the others (perhaps a bit sloppy with eye-centering, especially in field use) it would be easy to conclude that the Zeiss FL had MUCH more astigmatism and a MUCH smaller sweet spot than the others. In a manner of speaking, or rather, use, it does. I'd like to know why.
--AP

jaymoynihan

Sunday 29th April 2007, 01:30

...the Zeiss provides a stunning view, but one that is easily compromised.

Assuming your experience is accurate, ( and I have no basis to judge/compare, since i have not examined the FL in detail), this be would a major step backward. I hope Zeiss takes care of it. My 2 Zeisses (8x30 and 7x42 classics) have wide "sweet spots" with very easy, forgiving eye placement.

elkcub

Sunday 29th April 2007, 04:01

Hi Alexis,

What I'm addressing is what accounts for the perception of a "sweet spot," which I've suggested may derive from the sharpness profile, i.e., the sharpness from the center to the edge. Sharpness in my lingo is inversely related to blur size, probably the square of blur size if this psychophysical function were known in detail. Just because a system produces the percept of a "sweet spot," doesn't say much of anything about its comparative sharpness to other systems.

Incidentally, I wasn't completely facetious in post #7. I don't know how much consideration is given to off-axis viewing in the design process, but to my experience all binoculars are equally sensitive in birding tasks that demand the ultimate performance. I have never found a binocular to be comfortable in use without the IPD being set just so, in spite of of several books saying that large exit pupils allow more leeway for an imprecise setting. I'd be happy to be wrong about that, but so far it's just been assertions, not theoretical or empirical proof. I might agree that large EPs make it easier to find the correct setting, but I would still encourage roof manufacturers to provide an IPD scale. Maybe Zeiss will take the lead on that.

I've said enough already ...

Blue skies,
Ed

Alexis Powell

Sunday 29th April 2007, 04:34

I understand the airplane sound story and why relative differences were important to perception in that case, but as I wrote before it isn't applicable to the comparison I'm making. The greatest centerfield sharpness in the world isn't going to interfere with my ability to read fine print off-axis, but astigmatism will/does! If I'm wrong about that, then I applaud the brilliant designers at Nikon, Leica, Swarovski (and other companies) who have designed their binos with low centerfield resolution such that I, with far better than average corrected vision, am able to see the same details in the fuzzy centerfield of their binos that I can with the stupendously sharp Zeiss, but I can also enjoy a large percentage of such apparent sharpness (with refocusing, to correct for field curvature) nearer the edges of the field.

One more point, dealing with sensitivity to eye-decentering is not so simple as getting the IPD set correctly. Even after that is done, it is possible to hold the binos too high, low, slightly diagonal, shifted left, shifted right, etc such that the oculars and eyes are not perfectly aligned.
--AP

kabsetz

Sunday 29th April 2007, 11:20

I have been following this thread with quite some interest and have almost jumped in a couple of times, but have been unsure of exactly how to approach the issue of the sweet spot in the present context. I'm no more sure about it now, but will write up some thoughts anyway.

Firstly, to Alexis, the prime reason I did not respond to your postings on Zeiss FL sweet spot and off-axis astigmatism in March was that I thought you expressed yourself very clearly and, compared with my own experience and impressions, were esentially correct in your observations and conclusions. So, I thought it wouldn't add anything valuable if I would come in.

Now, to get back to this thread. I'm very grateful for Steve Ingraham for his activity and contributions, but I'm also just a little concerned that his postings are, deliberately or not, attempting to redefine the terms of the conversation. In what follows, I'll have direct quotes from Steve's post in this thread placed in square brackets, with my comments, for whatever they are worth, following each quote.

[At Zeiss, we define a "zone of critical sharpness" which surrounds the center of the field and is measured in degrees to either side of center, as an angle similar to field of view, or sometimes, less accurately, as a % of the visible field. That is what I have assumed people mean by "sweet spot".]

This is pretty much how I have used the term "sweet spot" in my Alula reviews and postings. When I have made measurements of binoculars' off-axis performance, I have visually observed line-pair resolution targets at different distances off-center, and related the figures thus obtained to the subjective field of view. I no longer recal when I first saw the term "sweet spot" used in conjunction with binoculars, or even if have seen anyone use it before I first used it myself, but in my mind I have paralleled it to the term as used when speaking of tennis racquets, where I understand it to mean the relative size of the area of the strings which gives the player good control of the ball.

[However, continuing observations on the narrowness of the FL sweet spot when compared to the competing models on this forum has lead me to suspect that others are using the term differently.]

While it is possible that some people do use the term differently, I believe that a large majority on this forum use it in a very similar way to Zeiss or myself.

[We measure the zone of critical sharpness by taking photographs through the binocular eyepiece of a wall-sized resolution chart through a collimating lens that places the chart at apparent infinity. ...

In our experience the zone of critical sharpness in most binoculars has a fairly sharp demarcation or edge. The resolution lines do not just generally fade into indistinctness as you move toward the edge of the field. They are critically sharp, or so our eye tells us, out away from the center a good ways, and then rapidly transition to indistinct blurs.

When we measure the FLs against the competition on in this test, we find that they maintain sharpness further out toward the edge of the field than any of the competing models accept one, and that the "boundary" where they resolution lines become unacceptably fuzzy is closer to the edge of the field than any but that one competing model.]

This is very interesting, and probably highlights the difficulties of designing a truly outstanding binocular. Photographing a resolution target through the eyepiece must certainly be an integral part of a good design procedure, but the problem remains that the human eye is a dynamic and self-adjusting system. As has been pointed out in numerous threads on edge resolution, field-flatteners etc, our eyes can (to a greater or lesser amount, depending on our age and physiology) adjust to field curvature (the change of focus as one moves from the center of the field towards the edge), but cannot adjust to astigmatism at all. Also, it is not really possible to look off-center in a binocular image without moving the eye, whereby the alignment of the eye's lens to the eyepiece lens always changes. I was also a bit confused by the phrase: "they are critically sharp, or so our eye tells us" in conjunction with the photo tests. Does this refer to looking at the photos or looking through the binoculars with our eyes only?

[When we look at the one model that has a wider zone of critical sharpness than the FLs, we see that the it is nowhere in its field as sharp as the FLs are at the center of their field. The wider zone was achieved, apparently, by sacrificing some center field resolution (not an acceptable trade-off as far as we are concerned).]

Here, in the above quote, I'm reading an attempt to define the issue as an unavoidable compromise between superior center field resolution vs. superior sweet spot size/edge-of-field resolution, and I feel that some caution is needed. Firstly, having tested many-many binoculars (though certainly not as many as Steve or the Zeiss engineers) I feel that while Steve's assertion that the Zeiss showed superior centerfield sharpness is reasonable for the binoculars they had in the lab that day, the conclusion that he draws that this is due to the field-flattener is far less so. Also, I cannot help but to think that in a manufacturer's lab, the sample of their own product they measure is likely to be a very good one, whereas the sample of the competing models are more likely to be random or, at best, chosen from a batch of only a few. Very, very few of the binoculars I have tested have been free enough of optical manufacturing or assembly defects to allow me to say for sure that their resolution was limited by their opto-mechanical design and not by these random factors. Steve does not say which models he is referring to, but between the lines one can assume he means the Nikon HG series. Now, the best 8x42 FL I have measured did indeed have slightly higher centerfield resolution than the best Nikon 8x42 HG (L), but when it comes to 8x32, I have measured higher resolution figures for the Nikon than for the Zeiss. The last time I took a closer, booster-assisted look at a number of top-class roof binoculars, the highest-resolving and most aberration-free one happened to be a Swarovski 8.5x42 EL which was significantly better than the Zeiss models available at that moment, but the next time I do a similar test the results might very well be different. Likewise, I have measured a Nikon 10x42 SE (which has a field-flattener and very low off-axis astigmatism and a large sweet spot) that had a center-field resolution barely equaled (but not exceeded) by the best Zeiss 10x samples I have seen. In none of the cases could I say that less-than-stellar resolution was a result of "sacrificing some center field resolution" in the design brief.

[On the other hand, because the boundary of our zone of critical sharpness is closer to the edge of the field, sharpness decreases more rapidly beyond the zone than in the competing models. Another way of saying that is: Competing models are no sharper at the absolute edge of the field than the FLs, but, because the zone of unacceptable sharpness is wider, the transition appears more gradual.]

This is a nice hypothesis that appeals to our rational mind, but again I'm doubtful about its truthfulness. Firstly, in relatively aberration-free top-class 8x32-42 binoculars, the centerfield resolution is easily twice what the eye can directly utilize. Although we can nevertheless perceive one binocular as sharper than another, I very much doubt that these differences would radically alter our perception of the quality of the off-axis performance which is, even in the best of the field-flattener designs, significantly worse than centerfield sharpness. It also needs to be pointed out that the astigmatism/field curvature ratio is highly relevant here.

[Again, we are not relying on impressions for any of this, or on our visual memories. We have photographic records for each binocular which we can compare side by side.]

Who can argue with that? I certainly cannot, and since I also don't have the time now, will leave it at that.

Kimmo

hinnark

Sunday 29th April 2007, 18:16

Alexis,

unfortunately I can´t give you an explanation about your difficulties with the view through a 8x32 Zeiss FL. I only can confirm that I made very similar experiences like you with both 8x32 and 10x32 Zeiss FLs. I´m not sure if this has somethig to do with astigmatism. I found the off center astigmatism in the 7x and 8x42 mm Zeiss FLs even worse than within the 32mm FL bins. But ease of view or relaxed viewing through those 42mm is much more comfortable and like the other top bins. I´m also pretty sure that there´s no relationship to IPD. The 32 mm Zeiss FLs are pretty extreme bins. Very short objective focal length, the widest FOV in its class, very close focus and pretty long eye relief. Maybe this construction has to pay in a way we don´t know for those otherwise extreme performances. In other words: extreme construction like this could need an extreme degree of precision while in production that is pretty hard within reach in the real world. The only idea I have that someone of us should do a very careful star test of these bins. Perhaps sample variation plays also a role here. Do you come to same results, with and without eye glasses?

Kimmo: I agree in every single word.

Steve

Tero

Sunday 29th April 2007, 19:51

However, its (otherwise beautifully color neutral and low CA) view is SEVERELY DEGRADED by astigmatism, especially off center, when one's eyes are not centered perfectly--line targets fuzz out, fine print becomes impossible to read less than halfway to the edge of the field, and touching up the focus accomplishes nothing.
sounds like every binocular I have ever owned ;)

I do have a piece of optics that do work better than that:my glasses

elkcub

Sunday 29th April 2007, 21:45

The notional concepts I mentioned earlier were primarily designed to address Steve Ingraham's general comment:

However, continuing observations on the narrowness of the FL sweet spot when compared to the competing models on this forum has lead me to suspect that others are using the term differently.

Naturally, I've been talking about psychological constructs rather than physical ones, where it's generally believed that psycho-physical functions tie the two worlds together. So, yes, I have every reason to think Steve's suspicion is correct. Most people talk from the perspective of what they perceive rather than what optical engineers measure, and occasionally the two don't quite jibe. I'm not talking specifically about Zeiss products either (don't own any yet), but on a more general basis.

It should be added that I greatly appreciate and fully accept the results Kimmo, Alexis, Steve, and many others have reported. It's reassuring that there is so much agreement about physical facts, to which I can add absolutely nothing. |:$|

Blue skies,
Ed

Sancho

Monday 30th April 2007, 00:01

Robert/Seattle, I´m on board, "eyebox" I like. Jay Moynihan, I think now I understand, I have a pair of Leica compacts that are superb but they are not forgiving in terms of eye placement, in fact quite the contrary.

elkcub

Monday 30th April 2007, 00:11

[At Zeiss, we define a "zone of critical sharpness" which surrounds the center of the field and is measured in degrees to either side of center, as an angle similar to field of view, or sometimes, less accurately, as a % of the visible field. That is what I have assumed people mean by "sweet spot".]

This is pretty much how I have used the term "sweet spot" in my Alula reviews and postings. When I have made measurements of binoculars' off-axis performance, I have visually observed line-pair resolution targets at different distances off-center, and related the figures thus obtained to the subjective field of view. I no longer recal when I first saw the term "sweet spot" used in conjunction with binoculars, or even if have seen anyone use it before I first used it myself, but in my mind I have paralleled it to the term as used when speaking of tennis racquets, where I understand it to mean the relative size of the area of the strings which gives the player good control of the ball. ...
Kimmo

Kimmo,

I always thought the "sweet spot" was the best point of impact on a baseball bat, and never really could understand how it applied to a visual area. But, now I do.

Although you seem to have first applied the phrase to binoculars, and agree with Steve's reference to it as a "zone of critical sharpness," when measured by resolution targets, the way I read it you attribute Zeiss' findings to possibly being non-representative. Please take no offense, but this is rather disturbing since just about everything suffers from sampling variation, and what is to guarantee that specimens used in your lab aren't also non-representative in some way?

Which leads me to related questions (possibly rhetorical). I'd like to ask why Zeiss would appeal to this kind of empirical photographic measurement, when they have, no doubt, the best optical software in the world to compute blur fields and model critical sharpness zones? Moreover, assuming their quality assurance folks know all about manufacturing tolerances, why not compute sampling footprints as well? Empirical comparisons just seem so soft in the hard engineering world. ;)

Finally, some concerns about method. If the assumption is that the eye is always optimally aligned with the optics, and never moves, then taking a static picture makes sense. However, the eye rotates in its orbit in order to bring diffenent parts of the field to the retinal fovea. This being the case, the retinal projection is not well simulated by a static picture, the differences being quite complicated in terms of the blur fields. I need some hand holding as to why we're not barking up the wrong tree.

I hope nothing I've said has offended anyone.

Blue skies,
Ed

Pileatus

Monday 30th April 2007, 04:20

<snip>
Finally, some concerns about method. If the assumption is that the eye is always optimally aligned with the optics, and never moves, then taking a static picture makes sense. However, the eye rotates in its orbit in order to bring diffenent parts of the field to the retinal fovea. This being the case, the retinal projection is not well simulated by a static picture, the differences being quite complicated in terms of the blur fields. I need some hand holding as to why we're not barking up the wrong tree.

I hope nothing I've said has offended anyone.

Blue skies,
Ed

BINGO! Ed wins the posting prize of the day.
As I've said many times...we too often dismiss or, at best, fail to account for the human eye in all its wonder. If this is a contest between a scientific photograph and the customer's eye, the customer wins each and every time.

John

PS
I bolded and underlined Ed's comments for emphasis.

kabsetz

Monday 30th April 2007, 10:18

Ed,

Thanks for responding and rest assured I'm not in the least offended by your comments.

I'll try to clarify some more, as my post was pretty longwinded and I wrote it under some time constraints so it ended up being a bit less precisely worded than I would have liked.

[QUOTE=elkcub;874847]Kimmo,

the way I read it you attribute Zeiss' findings to possibly being non-representative. Please take no offense, but this is rather disturbing since just about everything suffers from sampling variation, and what is to guarantee that specimens used in your lab aren't also non-representative in some way?]

I am fully aware that whatever testing I do is statistically non-representative in the sense that the sample sizes, rigorousness of methodology, test sample selection method etc. do not allow for quantifiable analyses of predictable median quality or such. Thus, I cannot say that a certain unit would exhibit a "representative level of quality." However, I have enough experience by now to dare to say that a representative real-world sample of many high-end binoculars is not as good as the design would allow, and an assertion that a certain binocular offers superior centerfield sharpness over a certain other binocular - when made as a sweeping statement based on lab tests in a reputable manufacturers lab - thus becomes misleading rather than illuminating. Meanwhile, I would like to reiterate what I have said in my Zeiss FL reviews: The use of fluoride glass (as well as "ED" or "UD" lens elements as used by some other manufacturers) does, to my eyes, increase the perceived sharpness of the image when compared to other binoculars without the extra color-correction measures but with the same measured boosted line-pair resolution.

[Which leads me to related questions (possibly rhetorical). I'd like to ask why Zeiss would appeal to this kind of empirical photographic measurement, when they have, no doubt, the best optical software in the world to compute blur fields and model critical sharpness zones? Moreover, assuming their quality assurance folks know all about manufacturing tolerances, why not compute sampling footprints as well? Empirical comparisons just seem so soft in the hard engineering world. ;)]

Good question, Ed. Steve is the one who could answer this question, not me, but I can make a couple of guesses. Firstly, it really does seem to be very hard to design and manufacture a really good binocular. If it weren't, we'd be getting them for a fraction of the current cost. This always becomes very clear when we see the annual introduction of brand X's new top model which "offers the very best attainable image quality" for less than 2/3 the cost of the big four's offerings. When it comes to the quality assurance folks and manufacturing tolerances, I believe that by and large these people have an honestly-held but overly optimistic opinion of what kind of quality level will still be seen by the users' eyes as "just as good" as the optimally faultless samples.

[Finally, some concerns about method. If the assumption is that the eye is always optimally aligned with the optics, and never moves, then taking a static picture makes sense. However, the eye rotates in its orbit in order to bring diffenent parts of the field to the retinal fovea. This being the case, the retinal projection is not well simulated by a static picture, the differences being quite complicated in terms of the blur fields. I need some hand holding as to why we're not barking up the wrong tree.]

I'm fully with you on this. This is what I thought when reading Steve's account of their photographic "proof" that Zeiss FL's have just as good if not better edge resolution and sweet spot size than competing models. However, I would guess that when designing optics, the engineers need more than just penciled-down visual impression records to go by, and that is why I acknowledged that these kinds of photographic tests (or some similar method that removes the hard-to-tame human component from the equation) may be an essential part of the process. For it to produce useful and reliable results, the correllation between such tests and the visual impressions a user gets when viewing with the product needs to be well enough understood, and although I'm sure that Zeiss has worked as hard as they can to achieve this, the simple fact that there is so much disagreement on the results shows that they still have some hard work ahead.

Kimmo

mak

Monday 30th April 2007, 10:38

Kimmo, I appreciate that your post was considerably more informative, than the 2 comments, marked in brackets, which I would like to comment on.

(I cannot help but to think that in a manufacturer's lab, the sample of their own product they measure is likely to be a very good one, whereas the sample of the competing models are more likely to be random or, at best, chosen from a batch of only a few).

What about independent testing in labs and the average result taken from random samples, If these figures are available to the manufacturers, eg. stray light, transmission, zone (fov/sq rt2) then this type of testing, would give a fair and honest overview of optical performance, and a good starting point when looking at ways to improve on future products.

(Steve does not say which models he is referring to),
I do not think that a manufacturer or employee will disclose the findings of competitors optical performance, as it is "not the done thing", but if you perform well in the majority of tests, then surely each manufacturer can be pleased with their current optical design.

As each individual is different, then no binocular will be agreeable to all, that is why the best advise must be...look with an open mind, pro x manufacture users will in most cases see the positives and comment on the negatives for competitor products.

iporali

Monday 30th April 2007, 11:59

are they using the term as a metaphor for the notional area of maximum sharpness?
As I interpret it, it is when your eyes are coincident with the center of the focal point projected by the occular lenses, and is the sum of such considerations as exit pupil size, eye relief and interpupilary adjustment of the lenses.

In my experience these two features may sometimes be mutually exclusive.

The Nikon's HG and SE models (with "field-flattener elements") have a very large "notional area of maximum sharpness", but they are very demanding for a precise eye-placement.

In addition to the ER and exit pupil size a very important factor for "forgiving eye placement" is a NARROW apparent field of view. A wide FOV and long ER together are the main reason for irritating black shadows (blackouts), which occur when the eye is too close to the eyepiece.

Best regards,

Ilkka

elkcub

Monday 30th April 2007, 20:06

Kimmo,
I furiously agree with every aspect of your response on post #35.

John,
Your post #34 is the first time I've ever been quoted about my BS on BF. Many thanks. Keep those quotes coming. ;)

Joking aside, though, I think this discussion highlights the difference between measuring the binocular vs the perceptions resulting from it. To quote Kimmo (once again), the "... correlation between such tests and the visual impressions a user gets when viewing with the product needs to be well enough understood..." To quote John: "If this is a contest between a scientific photograph and the customer's eye, the customer wins each and every time."

Broadly speakiing, resolution of the dichotomy lies in the arcane and underappreciated area of psychophysics, but that might delay profitability for (quite) a while.

Blue skies,
Ed

Leif

Monday 30th April 2007, 21:54

I am with Alexis Powell on this. The Zeiss has more aberrations at the field edge, whereas a binocular such as the Swarovski 8x42 EL has edge curvature. So in the latter case the eye can refocus, and compensate. That is why a photographic test is not completely representative, though it does serve to quantify the problem.

There has been so much grumbling here over the Zeiss FL 8x42 (and others in the range) that I checked mine at the weekend while birding. The sweet spot was pretty wide to my eyes, but definitely not on a par with the Swarovski 8.5x42 EL or the Nikon 8x42 HG (though the latter has a narrower FOV). It is IMO grossly misleading to refer to it as a small sweet spot. It is actually quite large, though noticeably less than the best (taking into account allowing the eye to refocus to compensate for field curvature).

I have to admit that the Zeiss FL view is not as easy as the Nikon HG one, but I prefer it.

My opinion has always been that each binocular on the market has its own characteristics, and those of us who are prone to the optical equivalent of navel gazing - the rather wonderful French word is "nombrilisme" - have to take care to find one that best matches our own prejudices. It is easier for most people. |;|

Cloudy Skies (we desperately need some rain here in the UK).

Robert / Seattle

Tuesday 1st May 2007, 02:34

... My opinion has always been that each binocular on the market has its own characteristics, and those of us who are prone to the optical equivalent of navel gazing - the rather wonderful French word is "nombrilisme" - have to take care to find one that best matches our own prejudices. ...

And I have come to the opinion that any of the "alpha" binoculars, in the absence of any of the others in a side-to-side comparison, will produce results well in excess of any reasonable expectation -- Especially if the name of the manufacturer is removed from the test sample!

elkcub

Tuesday 1st May 2007, 05:10

Leif

Tuesday 1st May 2007, 08:50

And I have come to the opinion that any of the "alpha" binoculars, in the absence of any of the others in a side-to-side comparison, will produce results well in excess of any reasonable expectation -- Especially if the name of the manufacturer is removed from the test sample!

On that I disagree. I find that many produce far more chromatic aberration than I feel comfortable with, though most people do not notice it. I know that some have expressed disquiet at the edge softness of the Zeiss FL which to me is minor.

Sancho

Tuesday 1st May 2007, 23:46

Thanks for the new word "nombrilisme", Leif, I think I shall use it nonchalantly in conversation whenever I get the chance. So anyway guys, what is the Sweet Spot, then, exactly? (No, I really am only joking.....)

Robert / Seattle

Tuesday 1st May 2007, 23:54

On that I disagree. I find that many produce far more chromatic aberration than I feel comfortable with, though most people do not notice it. I know that some have expressed disquiet at the edge softness of the Zeiss FL which to me is minor.

I trust your judgement, but am curious. What optics did you use 10 years ago, were you satisfied, and how would they compare to today's "alphas"?

elkcub

Wednesday 2nd May 2007, 00:14

Sancho

Wednesday 2nd May 2007, 00:59

A binoculars' navel. :'D
Sometimes Old Sancho yearns for the days when binoculars were a pair of tubes with glass in for seeing things that were far away;). (Certainly would have a far healthier bank balance if I'd maintainted that attitude....)

Leif

Wednesday 2nd May 2007, 11:53

I trust your judgement, but am curious. What optics did you use 10 years ago, were you satisfied, and how would they compare to today's "alphas"?

Nikon 8x40 porros, cost £70 used. I am still impressed by the performance given the price, but others see only the strong off-axis astigmatism. As a birding tool they are brilliant: decent brightness, rugged, okay contrast, very wide field (for searching) and low chromatic aberration. But ... they have a lot of flaws. Still, they prove that you do not have to spend a large sum to do birding. I am sure there are other binoculars from other manufacturers that are as good, or perhaps even better. I long ago became a fan of porros, mainly as a result of Stephan Ingraham's writings online.

IMO the Zeiss 8x40 FL which I use is no better than the Nikon 8x32 SE which I also own. In fact, in many respects the SE is better. But, it gets very stiff in cold weather, has black out issues, a smaller exit pupil, and is not waterproof.

andytyle

Friday 28th December 2007, 14:57

After reading these posts, I am left with a distinct feeling that the "sweet spot" can mean whatever you want it to mean.

Given that (as Kimmo has suggested on another thread), most if not all instruments used for birding are probably not diffraction limited, then the "sweet spot" is not really definable - in a true sense, except to say that the area at and around the centre of the field of view is likely to be the sharpest.....that's all you can say really.
To an optician, it is a term that may mean the same as "diffraction limited field", i.e. the area of the field (around and at centre) where aberrations are not larger than the Airy disc, hence, the image is said to be limited only by diffraction. My guess is that many objective lenses used in high quality spotting scopes and the odd few binoculars may well be diffraction limited at field centre (and some of the surrounding field), but internal focusing lenses and prisms mess things up somewhat.
Just because a part of the field is not quite diffraction limited does not mean it does not appear sharp, because we are using low powers, even in spotting scopes, but the lack of diffraction limited instruments within the entire birding market makes it more difficult to define things like "sweet spot". I guess, as some of you have already said, that the area of the field that appears sharp (when the eye is central at the eyepiece) can be labelled the "sweet spot". This just leaves eyepiece design as a culprit for the reduced sweet spot, and quite often will be the main culprit for poor usable field.
I wonder how long it will be before some of the high quality manufacturers start going to China, as they can make Nagler type eyepieces a lot cheaper than the Germans, Austrians or Japanese. Naglers have been made in Taiwan for many years anyway, so the quality is possible. I once sold a Leitz 30mm 2" eyepiece with an 84 degree field for astronomy, it was superior to the Nagler 31mm, and just shows that it can be done. It is possible to make binoculars to a standard where the potentially diffraction limited field really is diffraction limited, but it is very expensive. Very few people would be prepared to pay the retail price for such instruments - unless they are made in China under strict quality control checks.

andytyle

Tero

Friday 28th December 2007, 16:05

I think most people refer to sweet spot as the area in focus, if is clearly different from an area just outside of it. A gradual decrease in quality is more difficult to label.

andytyle

Friday 28th December 2007, 16:37

Quote 'I think most people refer to sweet spot as the area in focus, if is clearly different from an area just outside of it. A gradual decrease in quality is more difficult to label.'

Do you mean depth of focus here, or are you talking about the portion of the angular field of view that appears sharp?

andytyle

Tero

Friday 28th December 2007, 17:51

sharp

andytyle

Saturday 29th December 2007, 14:01

Quote: 'sharp'

Right, so the area where aberrations are at their minimum. Either the diffraction limited field or the area of the field that is closest to being diffraction limited.

This all fits in neatly with what has been discussed before on another thread regarding consistency. The "sweet spot" will thus vary, not only from model to model, but even between inconsistent samples of the same model. This may explain why one user of a particular instrument may find a sweet spot to be greater in area than another user. They have extremes of the inconsistency scale.

andytyle

henry link

Saturday 29th December 2007, 16:03

Perhaps a reasonable definition of the "sweet spot" in binoculars would be that area of the field in which the smallest details that can be resolved are limited only by the eyesight acuity of the viewer. Outside the sweet spot the smallest visible details would be limited by the off-axis aberrations of the binocular's optics. It would be very rare to find a binocular with diffraction limited resolution in the center of the field (except when severely stopped down) but that's not necessary since the magnification is so low. It's also rare to find a binocular so poor that it's resolution in the center isn't substantially better than eyesight acuity.

In the same instrument the size of the sweet spot will probably vary a bit with light level since changing the effective focal ratio of the objective will change the off-axis aberrations in the eyepiece. Those with very high acuity are penalized by seeing a somewhat smaller sweet spot than those with poorer acuity. Those with wide focus accomodation see a larger sweet spot in binoculars in which the dominate off-axis aberration is field curvature. Just how the pupil is positioned when looking off-axis also has a large influence on visible off-axis aberrations and the size of the sweet spot. For those reasons I've come to the conclusion that precisely measuring the sweet spot is hopeless. It will never be quite the same for all people and all conditions. I think it's a concept most safely applied to the obvious extremes; binoculars with unusually large or unusually small sweet spots.

andytyle

Saturday 29th December 2007, 16:33

Quote: 'It would be very rare to find a binocular with diffraction limited resolution in the center of the field (except when severely stopped down) but that's not necessary since the magnification is so low.'

So, if we accept that a binocular being manufactured to a standard where a diffraction limited area at centre-field is very rare, (lets say the prisms are the problem in higher quality binoculars where the objectives may well be of good enough quality). The "sweet spot" is thus not a universal concept, because of, as you say, area of OG being used because of pupil size, individual user acuity etc. So perhaps it is meaningless to even mention it.
However, the problem is that visual acuity is a factor in every case of using an optical instrument, to some extent. The only way to determine whether concepts like "sweet spot" are meaningful, is to treat each instrument as a black box.
Its that test bench thing again. All else is opinion and interpretation.

andytyle

Leif

Saturday 29th December 2007, 17:31

I think we can assume an average acuity, and hence assume that an average binocular has to have a resolution better than that to appear sharp. I think most people tend to have acuity not far from the average (though often with eyeglasses). And in practice a binocular does not even have to be that sharp off axis in order to give the impression of a wide 'sweet spot'. It's when the off axis image gets really soft that the illusion falls apart, and we complain of a narrow usable field. And in some instruments the resolution versus distance from the field centre falls off gradually, whereas in others it falls away rapidly.

And don't forget that most people use binoculars hand held, and the natural vibrations from the hands will reduce the effective resolution. So really it is a case of the off-axis image being sharp enough to give the illusion of sharp everywhere. Few really are sharp at the field edges.

etudiant

Saturday 29th December 2007, 17:35

This discussion begs the question of what quality standards are being applied by the binocular manufacturers. Can anyone offer some input as to what range of optical deviation is considered acceptable by the manufacturers? Judging by the fluctuations in "sweet spot" size discussed above, it is implied that the tails of the performance curve can be quite wide. That should be readily apparent if several units of each individual model are tested. Has anyone any knowledge of such tests?

Leif

Saturday 29th December 2007, 18:35

This discussion begs the question of what quality standards are being applied by the binocular manufacturers. Can anyone offer some input as to what range of optical deviation is considered acceptable by the manufacturers? each individual model are tested. Has anyone any knowledge of such tests?

Like all of these things, the manufacturer tries to get the best overall balance within the budget. Clearly Zeiss consider CA correction more important than the field edges, whereas Swarovski focus (sic) consider the field edges more important. Although I have not tried the new Leica HD binoculars, I expect they have a wide sweet spot and excellent CA correction. But look at the price!

andytyle

Sunday 30th December 2007, 01:26

Quote: 'I think we can assume an average acuity, and hence assume that an average binocular has to have a resolution better than that to appear sharp. I think most people tend to have acuity not far from the average (though often with eyeglasses).'

What is meant by average acuity? Not sure what is meant by 'hence assume that an average binocular has to have a resolution better than that to appear sharp'

andytyle

Alexis Powell

Sunday 30th December 2007, 04:46

The "sweet spot" is thus not a universal concept, because of, as you say, area of OG being used because of pupil size, individual user acuity etc. So perhaps it is meaningless to even mention it.

The term "sweet spot" was never intended to be a precisely defined quantity that is subject to absolute measure, it's just a quick way of making relative comparisons between binoculars. Typically, the term is used when discussing the relative merits of two binoculars that differ greatly in field of view. For example, "Model A has a very wide field of view but the sweet spot is so small, I'd rather have model B because although it has a narrower FOV the sweet spot is much wider."

--AP

Surveyor

Sunday 30th December 2007, 05:11

Quote:

What is meant by average acuity?
andytyle

Hello Andy, Happy New Year

I think the term “average visual acuity” for bino resolution test is based on the Snellin test chart used by optometrists. For 20/20 vision the chart uses a 5 arc minute high character like E with the elements spaced a 1 arc minute apart like the top, bottom and center of the E with the white lines comprising the 5 alternate 1 minute elements. This means that if 20/20 were considered average vision, the 60 seconds would be average resolution for discerning the lines elements. The photo types use 120 seconds for line pairs. Engineering types like me use 60 seconds and single lines.

The current ISO standard for exit pupils larger than 4.5 mm is 60/power for object space.

Kimmo and others recommend a resolution of at least twice as good for very sharp images.

As an example, I have 20/20 left and 20/25 right eye vision. My right eye visual acuity is about 75 arc seconds or visus of .8 (this is pretty much confirmed by resolution chart viewing). So for me, twice the visual acuity would be about 40 arc seconds in image space or, in the case of 10x bins, 4 arc second observed resolution capability. So I would hopefully be able to resolve Group 6 Element 1 at 400 mm on a USAF resolution chart.

In the case of a 10x32 this would be close to the Dawes limit so I would not expect to get to twice visual acuity. The ISO standard for 10x32 would call for resolution better than 9.38 arc seconds.

Have a good day.
Ron

elkcub

Sunday 30th December 2007, 05:52

The term "sweet spot" was never intended to be a precisely defined quantity that is subject to absolute measure, it's just a quick way of making relative comparisons between binoculars. Typically, the term is used when discussing the relative merits of two binoculars that differ greatly in field of view. For example, "Model A has a very wide field of view but the sweet spot is so small, I'd rather have model B because although it has a narrower FOV the sweet spot is much wider." --AP

One of the issues with "sweet spot" is that FOV tends to get involved. Your statement is a good example, — and as usual I come away perplexed. A fixed retinal projection area affording a high level of visual acuity (as Henry described) probably would be perceived as relatively small within a wide field and relatively large within a narrow field. Assuming that to be a perceptual fact, I don't follow how one can compare the merits of two binoculars on this basis.

Elk

Leif

Sunday 30th December 2007, 10:40

I don't follow how one can compare the merits of two binoculars on this basis.

You just describe what you see.

Pileatus

Sunday 30th December 2007, 13:02

You just describe what you see.
Precisely!

henry link

Sunday 30th December 2007, 16:22

I prefer to estimate the sweet spot size as an area of apparent field in degrees. A 30 degree sweet spot is the same size in any binocular no matter how wide or narrow the total apparent field may be.

I think all of us who have experienced various sweet spot sizes in the field recognize that the concept is generally valid if not precisely measurable. After using many binoculars and trying to measure their sweet spots I've formed my own personal set of loose standards based on how my pupils tend to roam about within the field. For me a binocular with a sweet spot of 20 degrees or less will certainly be unpleasant to use because my gaze will frequently stray out of the sharp area. A sweet spot of 35 degrees or more will never cause any problems, but I've seen sweet spots that wide in only a few binoculars that use so called "field flatteners" in the eyepieces. Somewhere between 25 and 30 degrees seems to be the threshold between comfort and discomfort in the field for me. To that I would add that binoculars in which off-axis astigmatism is the dominant aberration limiting the size of the sweet spot tend to be more unpleasant for me to use than binoculars in which field curvature dominates.

elkcub

Sunday 30th December 2007, 21:42

... A 30 degree sweet spot is the same size in any binocular no matter how wide or narrow the total apparent field may be.
...

Precisely, — although it may also be perceived as smaller within a larger apparent field.

I was thinking along similar lines, and tempted to write that when the SS is defined as the largest angle within which a criterion level of acuity can be maintained, its size should be inversely related to observable head motions. I'm glad to hear your experience tends to confirm this, as does mine.

elkcub

Sunday 30th December 2007, 22:47

...A sweet spot of 35 degrees or more will never cause any problems, but I've seen sweet spots that wide in only a few binoculars that use so called "field flatteners" in the eyepieces. Somewhere between 25 and 30 degrees seems to be the threshold between comfort and discomfort in the field for me.

Just to follow up on this important point, your angular estimate jibes quite well with how the eye/head normally work. In general, there is a built in coupling between eye motion and head motion. Considering the lateral dimension (vertical is similar), the tendency to move the head increases as ocular rotation approaches 20˚ from center, and becomes compelling thereafter due to facial geometry, particularly the nose. So, the range of what seems "natural," would be captured by about 35˚, i.e., ±17.5˚, of the apparent field. Below approx. 25˚, i.e., ±12.5˚, more head motions would be required than are "natural," and there might well be increasing unpleasantness associated with that.

My reason for capitalizing on your comments is that this aspect of binocular assessment is, in many ways, more approachable within the framework of bio/behavioral science than optical science, per se. In that light, this aspect of design may also be more important than first imagined.

Elk

The attachment is taken from Human Engineering Design Data Digest, MIL-STD-1472.

Alexis Powell

Monday 31st December 2007, 00:36

I prefer to estimate the sweet spot size as an area of apparent field in degrees.

Exactly! And such comparisons do not require that the angle be measured. When two binos are compared side by side, it is easy to see which renders a larger amount of a large object in pleasing focus/image quality. The field of view does not complicate such comparisons.

--AP

andytyle

Monday 31st December 2007, 18:56

Quote: 'In the case of a 10x32 this would be close to the Dawes limit so I would not expect to get to twice visual acuity. The ISO standard for 10x32 would call for resolution better than 9.38 arc seconds.'

Ron

HNY

This is often where the difficulty lies with meaningful discussions around binocular and scope resolutions, and what individuals prefer to use as a test.
With my background, diffraction is the bottom line. An instrument can be tested to see whether it meets the resolution limit set by Rayleigh or Dawes, and as such can be described as being limited only by diffraction. Similarly, I can place an instrument on a testbench and look at the figure, or perhaps use an optical interferometer. This will enable a fairly safe assessment of whether the instrument will meet the diffraction limit of that aperture or not, or even what level of contrast can be expected that is due to figure. 99.9 times out of 100, if an instrument is tested for diffraction limit afterwards, the assessment proves correct. Sure, individual acuity may interfere with diffraction testing, but at higher powers this is less likely.
Then we get into the more murky area of bar charts and Snellin charts, or even sinusoidal testing with tests of lowering contrast. I say murky because with a testbench, interfering obstructions such as the eye (acuity, diameter of pupil etc), play much less of a role so the test results are much less open to interpretation.
Internal reflections can reduce centre-field contrast, but do not (usually) affect a diffraction limit test.

The problem with just describing "what you see" as another has suggested, is that the results can not be trusted. There are simply too many variables - exit pupil versus eyepupil, aberrations in the observer's eye, environment - heat conditions. Then we have to trust that the observer can accurately judge what is 25 degrees or so in a 60 or 70 degree apparent field. The state of health of the individual also makes a difference.
Here's an example. A 90mm Meade Maksutov Cassegrain is used as a spotting scope. The observer wishes to test the "sweet spot" with a favourite eyepiece - lets say a converted 21mm Leica eyepiece. At about 60X he decides to use an evenly illuminated brick wall as a target. An internal reflection creates unfocused diffuse light at the focal plane. The amount of diffuse light creates a condition where the boundary between the central area of sharp detail and where it ceases to be sharp becomes a little blurred. He estimates about 30% of the central field is satisfactory. Now he adds a dewshield (lens shade) of about 5" length. When he looks again, contrast has improved quite notably, and the sharp area of the field has risen to about 35%.
A decade or so ago, I used a pair of old Swarovski 8X30 SLC binoculars frequently for birdwatching. I used to take around with me a pair of homemade lens shades in the form of black painted 3" long cardboard rolls. In certain conditions they reduced internal reflections dramatically, improving contrast considerably, and making detail away from the centre of the image visible.

As an engineer you will appreciate the importance of scientific and objective testing and information. We can all judge by our own standards, but then there are as many standards as judges.
For me, a proper testbench method is the only meaningful method for assessing any real optical aspect of an instrument. Other than that, point sources in darkness at least allow the condition where the exit pupil is the defining pupil.

andytyle

Leif

Monday 31st December 2007, 22:57

The problem with just describing "what you see" as another has suggested, is that the results can not be trusted. There are simply too many variables - exit pupil versus eyepupil, aberrations in the observer's eye, environment - heat conditions. Then we have to trust that the observer can accurately judge what is 25 degrees or so in a 60 or 70 degree apparent field. The state of health of the individual also makes a difference.

I have to disagree with you. I have no objection to having objective tests, but IMO an experienced observer can reach an assessment of an instrument that often surpasses the results of tests.

For example, some instruments behave fine when tested for resolution and contrast, but in certain situations they fall to pieces. That fact would not be picked up by most tests despite the fact that the tests are far more accurate, precise and objective than any human observer. As you say, "there are simply too many variables".

I will give you an example. The Zeiss 8x30 Classic binocular is a very fine instrument, and can give lovely views. But use it at dusk, and you may see serious flare that interferes with observations. The Swarovski 8x5.42 EL is another very fine instrument, but in some circumstances it can exhibit substantial CA both on an off axis, and I find that objectionable. Admittedly many if not most users do not seem to notice the CA, but it exists and I do not not like it. In other words, it is very hard if not impossible to design a set of tests which gives an accurate assessment of an instrument.

Getting back to the sweet spot, in some instruments such as the Swarovski 8.5x42 EL, the image degrades gracefully away from the optical axis, and is still okay at the edge. In the Nikon 8x42 HG the image is remarkably good to the edge. No doubt in some others the image is almost perfect to half way to the edge, then degrades rapidly. So how do we rate each instrument? Do we favour a slow graceful decline, or do we favour no decline to half way to the edge, followed by a rapid decline? Clearly the choice is subjective. I suppose we could draw graphs showing resolution as a function of angle from the axis, and allow the reader to decide. But would that really give them a good feel for the instrument?

Or we would just describe what we see, and when several people start saying the same sort of thing, we can be reasonably confident that a) the observer is a reasonable judge and b) the observed behaviour is characteristic of a given model and not just one sample. Alternatively just try the instrument for yourself and ignore other peoples prejudices.

kabsetz

Tuesday 1st January 2008, 12:18

I’d like to add just a few comments to the nice and lively discussion going on this resurrected thread.

First, to Andytyle concerning mainly the following quote as well as what you say in post #68:

[So, if we accept that a binocular being manufactured to a standard where a diffraction limited area at center-field is very rare, (lets say the prisms are the problem in higher quality binoculars where the objectives may well be of good enough quality). The "sweet spot" is thus not a universal concept, because of, as you say, area of OG being used because of pupil size, individual user acuity etc. So perhaps it is meaningless to even mention it.
However, the problem is that visual acuity is a factor in every case of using an optical instrument, to some extent. The only way to determine whether concepts like "sweet spot" are meaningful, is to treat each instrument as a black box.
Its that test bench thing again. All else is opinion and interpretation.]

As the discussion between S.I. (in post #19) and Alexis, Elk, myself and others shows, current test bench procedures do not seem to be quite universal enough in their applicability to average (or exceptional) users’ perceptions. The test bench procedures used by Zeiss seem perfectly reasonable on the face of it, but when the hard proof they provide is uncorroborated or contradicted by the end users’ experiences, I find I cannot easily dismiss more subjective evaluations in their favor. So, even if a “sweet spot” is not easily quantifiable or is precisely quantifiable only for a particular individual under particular viewing conditions, I still find it a useful concept. In fact, much the same arguments as presented against the SS could be leveled against visually measuring edge-of-field resolution in general. For a user, it does matter how far off-axis and how easily one can look and still perceive a satisfyingly sharp image. If a reviewer or a user discusses these factors, it can (and should) certainly be called opinion and interpretation, but for another user it may nevertheless be highly valuable and sometimes (unfortunately) more valid than a full lab report of hard data when the procedure for obtaining the data turns out to miss (or misrepresent) some important aspects of real human use.

Another brief comment concerning your bracketed sentence about problems in higher quality binoculars. Although prisms can sometimes be the main culprit, I find (based on booster-assisted point source evaluation of visible aberrations) that the most common cause for less-than-optimum optical performance is misalignment of elements in the optical train. At least for the top manufacturers and their binoculars, prism manufacturing tolerances seem to be “good enough” not to introduce marked aberrations. With telescopes, the situation is not quite so good (because the magnifications are higher), but with binoculars usually the only prism-induced artifact I see is a very thin diagonal line of light splitting the image of a bright point source if I view the point source in darkness or near darkness and place the point source on the prism roof edge.

Next, just briefly, to Surveyor,

[In the case of a 10x32 this would be close to the Dawes limit so I would not expect to get to twice visual acuity. The ISO standard for 10x32 would call for resolution better than 9.38 arc seconds.]

The Dawes limit is based on double-point-source separation, and since the Snellen visus is based on single-line width, a 10x32 can in fact provide twice visual acuity for all but the very most fortunate among humankind. The real boosted resolution limit of the best 10x32’s I have measured is just under 2 arc seconds in single-line width, so you still have plenty of margin left.

Lastly, I can just quote Henry as I find almost nothing to add to his summary in post # 64,

[I prefer to estimate the sweet spot size as an area of apparent field in degrees. A 30 degree sweet spot is the same size in any binocular no matter how wide or narrow the total apparent field may be.

I think all of us who have experienced various sweet spot sizes in the field recognize that the concept is generally valid if not precisely measurable. After using many binoculars and trying to measure their sweet spots I've formed my own personal set of loose standards based on how my pupils tend to roam about within the field. For me a binocular with a sweet spot of 20 degrees or less will certainly be unpleasant to use because my gaze will frequently stray out of the sharp area. A sweet spot of 35 degrees or more will never cause any problems, but I've seen sweet spots that wide in only a few binoculars that use so called "field flatteners" in the eyepieces. Somewhere between 25 and 30 degrees seems to be the threshold between comfort and discomfort in the field for me. To that I would add that binoculars in which off-axis astigmatism is the dominant aberration limiting the size of the sweet spot tend to be more unpleasant for me to use than binoculars in which field curvature dominates.

Perhaps a reasonable definition of the "sweet spot" in binoculars would be that area of the field in which the smallest details that can be resolved are limited only by the eyesight acuity of the viewer. Outside the sweet spot the smallest visible details would be limited by the off-axis aberrations of the binocular's optics.]

I’m wondering if, just for practical purposes, we might try to come up with some kind of consensus definition of sweet spot parameters, at least between those of us who are interested in using such a subjective concept and measurement. I think that Henry’s definition in the last quoted paragraph is perhaps a bit too stringent, especially considering that for testing for the area limited only by the viewer’s eyesight acuity we will have the binocular tripod-mounted but for general viewing usually not. To come up with an alternative suggestion, I would have to do more testing, but I could imagine it would be something like considering the sweet spot as the area of the subjective field where resolution has not dropped by more than one element on the USAF chart.

Kimmo

andytyle

Tuesday 1st January 2008, 17:35

Quote: 'I have to disagree with you. I have no objection to having objective tests, but IMO an experienced observer can reach an assessment of an instrument that often surpasses the results of tests.'

Really, how? How does the subjective assessment of an instrument surpass the accuracy of measured results?

'For example, some instruments behave fine when tested for resolution and contrast, but in certain situations they fall to pieces.'

Can you give me a further example other than the ones you gave?
The two examples you gave - the Zeiss 8X30 flaring is (I presume you are talking about an internal reflection) something that can be seen in other light conditions besides dusk, and can be shown on a test bench. The Swarovski, I would suggest, has the chromatic aberration it has. The fact that some notice it and some not is the very point of this discussion. In one person's opinion it is objectionable, in anothers it is not. This then becomes a subjective assessment, not particularly useful. This makes the case for an objective test.

Any optical problem can be seen and often measured on a test bench, even chromatic aberration. Chromatic aberration can even be seen very easily on something as simple as a Ronchigram. A Koster's Prism interferometer can directly measure it.

'Getting back to the sweet spot, in some instruments such as the Swarovski 8.5x42 EL, the image degrades gracefully away from the optical axis, and is still okay at the edge. In the Nikon 8x42 HG the image is remarkably good to the edge. No doubt in some others the image is almost perfect to half way to the edge, then degrades rapidly. So how do we rate each instrument? Do we favour a slow graceful decline, or do we favour no decline to half way to the edge, followed by a rapid decline? Clearly the choice is subjective. I suppose we could draw graphs showing resolution as a function of angle from the axis, and allow the reader to decide. But would that really give them a good feel for the instrument?'

This paragraph doesn't make much sense. There is nothing subjective about it at all. We rate each instrument's "sweet spot" by measuring it. 'Slow graceful declines' is not a useful description. There will be a point within the field of view beyond which the image is not sharp. This can be demonstrated quite easily on a test bench, and furthermore, what the aberration is. This is not possible in the field.

'Describing what we see' is not good enough. It is OK for conversation between birders, or even chat on a forum, but little else. It is entirely subjective and not helpful when definitive and objective information is called for. 'Alternatively just try the instrument for yourself and ignore other peoples prejudices.' Fine, but isn't that what people do anyway? What we are talking about is whether we can agree on a universally acceptable test which will give an idea of which binoculars have the greatest "sweet spot" and whether this is consistent within each model.

andytyle

andytyle

Tuesday 1st January 2008, 18:10

Quote: 'As the discussion between S.I. (in post #19) and Alexis, Elk, myself and others shows, current test bench procedures do not seem to be quite universal enough in their applicability to average (or exceptional) users’ perceptions. The test bench procedures used by Zeiss seem perfectly reasonable on the face of it, but when the hard proof they provide is uncorroborated or contradicted by the end users’ experiences, I find I cannot easily dismiss more subjective evaluations in their favor. So, even if a “sweet spot” is not easily quantifiable or is precisely quantifiable only for a particular individual under particular viewing conditions, I still find it a useful concept. In fact, much the same arguments as presented against the SS could be leveled against visually measuring edge-of-field resolution in general. For a user, it does matter how far off-axis and how easily one can look and still perceive a satisfyingly sharp image. If a reviewer or a user discusses these factors, it can (and should) certainly be called opinion and interpretation, but for another user it may nevertheless be highly valuable and sometimes (unfortunately) more valid than a full lab report of hard data when the procedure for obtaining the data turns out to miss (or misrepresent) some important aspects of real human use.'

I agree entirely with the individuality of user perception of an image, but user perception is what it is. This may well be fine for most of us, we choose our instruments based upon how we find the optical performance. Nevertheless, the measured result on a testbench will give a definitive result (coma, astigmatism, LSA and HSA, Secondary spectrum, lateral colour, spherochromatism, distortion, field curvature). If a definitive test by a manufacturer on their own product or another testing is not particularly accurate, or if instruments are not consistent then it is not surprising that sometimes users prefer a subjective assessment. I would have to say that a testbench can reveal any optical issue, whether this issue is important to individual users, or whether the issue is objectionable in different circumstances, is quite another matter.

'Another brief comment concerning your bracketed sentence about problems in higher quality binoculars. Although prisms can sometimes be the main culprit, I find (based on booster-assisted point source evaluation of visible aberrations) that the most common cause for less-than-optimum optical performance is misalignment of elements in the optical train. At least for the top manufacturers and their binoculars, prism manufacturing tolerances seem to be “good enough” not to introduce marked aberrations. With telescopes, the situation is not quite so good (because the magnifications are higher), but with binoculars usually the only prism-induced artifact I see is a very thin diagonal line of light splitting the image of a bright point source if I view the point source in darkness or near darkness and place the point source on the prism roof edge.'

Yes, I should have mentioned that we should at least expect manufacturer's to align instruments properly - Quality Control again. Of course, assembly problems are often the biggest cause of errors, the entire image being comatic. My train of thought was more concerned with fabrication errors and their measurement - the Seidal aberrations (apart from on-axis coma). If we can't get the manufacturer's to up their game with regards to assembly QC, then all other talk of testing is somewhat academic (for accurate measuring).
Having said that, it is still possible to recognize the other Seidal aberrations even when on-axis coma dominates.

andytyle

andytyle

Tuesday 1st January 2008, 18:21

I should state (should have stated before) that my faith in a testbench giving me objective answers is through experience of how accurate predictions of performance are, based upon measured results. The results of tests on various instruments gives us an idea of exactly what the optical problems are, and thus what can be done about it. It should not necessarily be the deciding factor about which instrument to choose for personal use, there are many personal reasons why we choose. But it is useful to know because it gives us some power as consumers. We are always being told that the customer is always right. Well, here is a chance to see if that saying is right. If a product is sold as being 115mm long, and we measure it to be 113mm, are we wrong?

andytyle

Leif

Tuesday 1st January 2008, 19:12

AndyTyle: I do not doubt that measurements can be of use. For example, the amount of CA, the transmission, the centre field resolution, and the amount of scattered light are all interesting quantities, and they are measured by manufacturers. They can give an indication of quality as high transmission usually correlated to an optic of high optical quality. But such measurements are far from complete.

"the Zeiss 8X30 flaring is (I presume you are talking about an internal reflection) something that can be seen in other light conditions besides dusk, and can be shown on a test bench. "

That is most probably true but there are an awful lot of tests that you would have to perform to catch everything. Or alternatively you rely on a small set of tests and risk missing important aspects.

"Any optical problem can be seen and often measured on a test bench, even chromatic aberration. "

That is no doubt true but there are several issues. The first issue is choosing which tests to perform. There are an awful lot that you would have to carry out if you wanted to pick up everything. Unless of course you are simply interested in testing the instrument in one artificial situation on a test bench e.g. examination of a test subject with lighting from the front and to one side. The second issue is how to present and interpret the results. In other words, how do you convert figures into something meaningful.

And regarding flare, you would have to test the instrument with all kinds of lighting. You would for example have to test with light from above to check that there are not internal reflections in the objective cell which leads to flare in the visual field. I believe that Canon recalled the initial batch(es) of 24-105mm F4 L lenses due to internal flare resulting from reflections off an unpainted screw head inside the lens. The flare was only seen in specific lighting situations. It was picked up by users. I think Zeiss had an issue with flare inside the original Victory (not the current one) due to reflections. I recall being in a forest with a non Zeiss instrument, and suddenly seeing massive flare in my binoculars. The cause was a break in the canopy overhead, in an otherwise dark wood.

"This paragraph doesn't make much sense. There is nothing subjective about it at all. We rate each instrument's "sweet spot" by measuring it. 'Slow graceful declines' is not a useful description. There will be a point within the field of view beyond which the image is not sharp. "

Yes it does make sense, there is something subjective about it and 'Slow graceful declines' is a useful description, at least for me. The decline is not necessarily linear. Or graceful. The subjective comes in how to define what is acceptable or preferable.

For example, the Zeiss 8x42 FL binocular has (IMO) a decent sweet spot, but the image gets very soft towards the edge. Some people object strongly to this, and do not like the binocular, considering the sweet spot too narrow. Others such as me are more forgiving. However, the softness is in part due to field curvature. The human eye can of course to some degree correct for field curvature. So, how do you design a test to account for one instrument which has edge softness due purely to field curvature, and another which has edge softness due to field curvature and an aberration such as spherical or astigmatism? Do you assume they are comparable due to the same amount of softness in a test? Or do you favour the instrument whose edge softness is purely due to field curvature, and hence many/most users will be able to adjust their eyes to correct for it?

"'Describing what we see' is not good enough."

It looks like we will have to disagree on this. I would say that a brief description can be extremely informative, despite the subjectivity.

Photography is an area where huge amount of work has been done to assess optics from various manufacturers. Although MTF plots are useful they do not tell you everything, and often do not tell you about the most important aspects of a lens. One of the most respected lens reviewers is B. Rorslett, and the following might be of interest to you:

http://www.naturfotograf.com/lens_surv.html

Note that although he does take test photographs, his lens reviews are essentially short informative descriptions, not masses of data.And they are very useful.

mooreorless

Tuesday 1st January 2008, 21:43

I have read reviews by Kimmo and liked them a lot, as well as other's using USAF charts etc. and would say I have never read any review of binocular or spotting scope using what Andy describes. Telescopes maybe. I would much sooner be able to read what others say as well as test, than nothing at all. Why doesn't Andy post some of his reviews?
Regards,Steve

andytyle

Wednesday 2nd January 2008, 01:16

Quote: 'AndyTyle: I do not doubt that measurements can be of use. For example, the amount of CA, the transmission, the centre field resolution, and the amount of scattered light are all interesting quantities, and they are measured by manufacturers. They can give an indication of quality as high transmission usually correlated to an optic of high optical quality. But such measurements are far from complete.'

Not quite sure what you are saying here. Do you mean that manufacturer's tests of their own equipment are far from complete? Or do you mean that the variety of ways to test an optic still leaves an objective description of that optic far from complete? If its the former, then yes, it may well be true with some manufacturers. If its the latter then I'm sorry but it simply isn't true. ANY aspect of the performance of an optic can be seen on a testbench. Not only that, but better than it is seen in the field, because it can be controlled and quantified. Any stray light or condition where internal reflection or diffuse light can affect the image can be provided. All else simply requires collimated light.

'"the Zeiss 8X30 flaring is (I presume you are talking about an internal reflection) something that can be seen in other light conditions besides dusk, and can be shown on a test bench. "

That is most probably true but there are an awful lot of tests that you would have to perform to catch everything. Or alternatively you rely on a small set of tests and risk missing important aspects.'

No different to testing in any other condition. No important optical aspect is missed. The benefit on a testbench is that there is control, and hence greater accuracy for measuring. If this were not so, there would be no point in scientific bench tests of any kind, in any industry. Subjective assessments are just that, nothing more. Not useful because unlike a scientifically controlled test, a subjective assessment is not repeatable.........because its subjective.

'"Any optical problem can be seen and often measured on a test bench, even chromatic aberration. "

That is no doubt true but there are several issues. The first issue is choosing which tests to perform. There are an awful lot that you would have to carry out if you wanted to pick up everything. Unless of course you are simply interested in testing the instrument in one artificial situation on a test bench e.g. examination of a test subject with lighting from the front and to one side. The second issue is how to present and interpret the results. In other words, how do you convert figures into something meaningful.'

This paragraph is essentially a repeat of the points you made in the previous one.
The conversion of figures into something meaningful happens every time any optic is tested on an interferometer, thats what an interferometer does. It gives values to all the aberrations it tests for and then gives an RMS figure for the optic. The meaning is how the aberrations affect the image. That comes from a knowledge of what the aberrations are and what affect they have. Testbench testing and how the results correspond to performance is all very well known and practised in every professional optical shop virtually every day.

'And regarding flare, you would have to test the instrument with all kinds of lighting. You would for example have to test with light from above to check that there are not internal reflections in the objective cell which leads to flare in the visual field. I believe that Canon recalled the initial batch(es) of 24-105mm F4 L lenses due to internal flare resulting from reflections off an unpainted screw head inside the lens. The flare was only seen in specific lighting situations. It was picked up by users. I think Zeiss had an issue with flare inside the original Victory (not the current one) due to reflections. I recall being in a forest with a non Zeiss instrument, and suddenly seeing massive flare in my binoculars. The cause was a break in the canopy overhead, in an otherwise dark wood.'

Then this goes to show that satisfactory tests were not carried out by the manufacturers.....not that tests don't reveal all the errors you want them to reveal.

'"This paragraph doesn't make much sense. There is nothing subjective about it at all. We rate each instrument's "sweet spot" by measuring it. 'Slow graceful declines' is not a useful description. There will be a point within the field of view beyond which the image is not sharp. "

Yes it does make sense, there is something subjective about it and 'Slow graceful declines' is a useful description, at least for me. The decline is not necessarily linear. Or graceful. The subjective comes in how to define what is acceptable or preferable.'

I find this statement difficult to answer. I'm not sure what you are trying to say. Are you suggesting that we should prefer one type of boundary between what is diffraction limited (or near to diffraction limited) and what is not, and another type of boundary? Whichever, "slow and graceful" is hardly a term which has any meaning in a scientific sense, particularly in context with measuring a geometrical optical field.

'For example, the Zeiss 8x42 FL binocular has (IMO) a decent sweet spot, but the image gets very soft towards the edge. Some people object strongly to this, and do not like the binocular, considering the sweet spot too narrow. Others such as me are more forgiving. However, the softness is in part due to field curvature. The human eye can of course to some degree correct for field curvature.'

Only with extreme accomodation. Field curvature is normally bad enough to need re-focusing.

'So, how do you design a test to account for one instrument which has edge softness due purely to field curvature',

Simple, you measure focus shift from edge to centre.

'and another which has edge softness due to field curvature and an aberration such as spherical or astigmatism?'

One aberration will dominate, all three can be seen or measured using either interferometry, Foucault or Ronchi testing.

'Do you assume they are comparable due to the same amount of softness in a test? Or do you favour the instrument whose edge softness is purely due to field curvature, and hence many/most users will be able to adjust their eyes to correct for it?'

From what I have seen of field curvature in the many binoculars I have used, I would not expect anyone over the age of about twelve to have the necessary accomodation.
By "softness" (another ambiguous term), do you mean defocus or loss of image integrity due to aberration?

'Photography is an area where huge amount of work has been done to assess optics from various manufacturers. Although MTF plots are useful they do not tell you everything, and often do not tell you about the most important aspects of a lens. One of the most respected lens reviewers is B. Rorslett, and the following might be of interest to you:

http://www.naturfotograf.com/lens_surv.html

Note that although he does take test photographs, his lens reviews are essentially short informative descriptions, not masses of data.And they are very useful.'

Not sure what this demonstrates. This appears to be some guy who tests nothing but Nikon lenses. He even suggests in no uncertain terms that his test ratings are 'subjective'. The very thing I suggest is rarely useful when describing the performance and testing of geometrical optics.

andytyle

andytyle

Wednesday 2nd January 2008, 01:35

Quote: 'I have read reviews by Kimmo and liked them a lot, as well as other's using USAF charts etc. and would say I have never read any review of binocular or spotting scope using what Andy describes. Telescopes maybe. I would much sooner be able to read what others say as well as test, than nothing at all. Why doesn't Andy post some of his reviews?
Regards,Steve'
--------------------------------------------------------------------------------

Steve

To answer the first part of your point. In the birding consumer optics market, no-one has ever bothered (as far as I am aware) to use a proper test bench for assessing an instrument. You need to understand how to do it, and apart from professional opticians, I don't know anyone else who does. Even amongst all optical companies there are only a small handful of people who are the optical designers and testers, and even here, in a company that mass produces instruments, these people have very narrow areas of expertise. Very, very few people have the interest and experience to understand many areas of geometrical optics, and then you have to be very fortunate for those people to be also interested in subjects like astronomy and birding.......hobbies that require good quality optics.

The second part of your question. I have never been asked to review binoculars or spotting scopes using test bench methods. It can be done, but so far, testing has been accomplished using test charts. This is useful for comparing instruments (providing there are strict environmental conditions, and a level playing field), but what it doesn't do is highlight which particular aberrations are the most destructive.
I have carried out interferometry and testbench tests like this before on a variety of instruments, but am not at liberty to post the articles, as they legally belong to a company.

This topic has been covered a few weeks ago on another thread, and it might be that during 2008, a few members of the forum begin testing using non-conventional methods. We will have to see what occurs.

andytyle

elkcub

Wednesday 2nd January 2008, 06:35

The conversion of figures into something meaningful happens every time any optic is tested on an interferometer, thats what an interferometer does. It gives values to all the aberrations it tests for and then gives an RMS figure for the optic. The meaning is how the aberrations affect the image. That comes from a knowledge of what the aberrations are and what affect they have. Testbench testing and how the results correspond to performance is all very well known and practised in every professional optical shop virtually every day.

Andy,

I think you were responding to Leif in this quote, but the same basic theme comes through several posts (which I seriously enjoy reading). The theme seems to be that interferometer analysis potentially (if not actually) says everything one needs to know about the optics. Apparently, it can determine all the third-order aberrations (or higher), assembly errors, glare resistance, and so forth — to a gnat's eyelash or better.

A moment's reflection will show, however, that such results must constitute a multi-dimensional description of the optic under evaluation, the dimensions being the separate aberrations, assembly errors, environmental conditions, etc. We also know, however, that: (a) many of the dimensions are not physically/optically independent of one other, and (b) decisions were made by some designer or design team to stress or suppress certain dimensions in favor of others. We generally refer to these as "tradeoffs." Third order Seidel aberrations, for instance, can not all be eliminated simultaneously, so the question switches to the balance of aberrations as opposed to their presence.

It's generally understood that the design process involves contending with these tradeoff decisions, and the most important factors entering into the process ultimately involve the user population. The most salient of these is probably the acuity of the eye, but, even this must be put into context. Is it day or night, pod mounted or hand held, and exactly what is the observer expected to be doing, e.g., finding enemy troops on the battlefield or birds in the foliage? Each task condition defines its own optimum optics, and these optima (plural), in turn, relate back to the multi-dimensional response surface that is measurable with an interferometer, or related equipment, on a stark lab table.

What can't be determined on an optical bench, are these performance optima. They must be provided from the outside, specifically by the people who will use the equipment for various tasks or task combinations. But how will they do that? The easiest way is by expressing subjective opinions about how well a given optical design suits their needs. Function trumps form. These opinions can be validated (objectified) through expensive behavioral studies, but not on an equally expensive optical bench.

So, as I see it, the reason why subjective evaluations and descriptions are essential is that users who perform similar tasks, such as particular types of birding or astronomy, or hunting, can communicate efficiently without first understanding the myriad of pscho-physical functions relating the physics of their optics to the desired performance characteristics (that is, if anyone knew them). Steve Ingraham coined the phrase a "Better View Desired," I'm inclined to think, to emphasize that the ultimate criterion is the human one, i.e., the better "view," not the better optic.

I'm sure you realize these comments are only intended to enliven the discussion.

Blue skies, and HNY,

Elk

Leif

Wednesday 2nd January 2008, 17:57

Elkcub: Well expressed.

As you indicate a binocular is a compromise, in that there will be aberrations and faults, and the preferred balance between them is subjective.

Leif

Wednesday 2nd January 2008, 18:44

AndyTyle: "Or do you mean that the variety of ways to test an optic still leaves an objective description of that optic far from complete? If its the former, then yes, it may well be true with some manufacturers. If its the latter then I'm sorry but it simply isn't true. "

The number of degrees of freedom is too large to carry out complete and sufficient tests. In practice you do a sample of tests, to gain a reasonable assessment. And that choice of tests is subjective, based on experience and knowledge. And of course the interpretation of the results is subjective as someone has to decide what is acceptable and what isn't, given that the instrument is to be used by a human, and not just to carry out some well defined and routine task, such as creating an image of a mask on a silicon chip.

AndyTyle: "From what I have seen of field curvature in the many binoculars I have used, I would not expect anyone over the age of about twelve to have the necessary accomodation."

I am middle aged, and I can re-focus my eyes to counteract some of the field curvature present in various binoculars I have owned. I can also twiddle the focus knob and correct for the softness when it is due to field curvature. Not so for other aberrations.

AndyTyle: "Not sure what this demonstrates. This appears to be some guy who tests nothing but Nikon lenses. He even suggests in no uncertain terms that his test ratings are 'subjective'. The very thing I suggest is rarely useful when describing the performance and testing of geometrical optics."

Yes it is 'some guy' who tests mainly Nikon lenses. The point I was making is that subjective tests are useful, and Rorslett is an example of an experienced and respected photographer who presents subjective tests which are widely quoted by amateur and professional photographers alike. I find that his subjective tests are usually far more accurate than supposedly objective tests such as those on www.PhotoZone.de. The problem with many/all objective tests is that they give an incomplete picture.

I guess you propose performing a test of an optic not only with an 'infinite' target, but with an intermediate and near ones too? And then performing tests of the amount of scattered light (flare) under goodness knows how many different illuminations? It would require huge amounts of work, would take ages to do, and it would generate massive amounts of data. And then you would have to make subjective decisions when presenting the data e.g. how much CA is acceptable, how much field curvature is acceptable etc. Hence you are back to the fuzzy subjective domain rather than the cold precise and rational objective one.

Alternatively why not just pick up the instrument, and spend a few months using it, then tell us all what you think of it? Sure you might have older eyes than the average, and your acuity might be a bit low, and you might only use it in daylight, but your experience when combined with others would be valid.

Incidentally posts here on BF indicate that sample variation is a significant issue for both spotting scopes and binoculars. That objective test tells you about one sample of an instrument. A range of 'horribly subjective and worthless' user opinions gives an idea of how multiple samples perform.

andytyle

Wednesday 2nd January 2008, 18:44

Quote: 'I think you were responding to Leif in this quote, but the same basic theme comes through several posts (which I seriously enjoy reading). The theme seems to be that interferometer analysis potentially (if not actually) says everything one needs to know about the optics. Apparently, it can determine all the third-order aberrations (or higher), assembly errors, glare resistance, and so forth — to a gnat's eyelash or better.'

Elk

HNY

The interferometer does not tell you everything you want to know about an optic, it can tell you most things about the state of the surface of an optic or the maximum error on the wavefront. This allows an understanding of fabrication error of that optic (not other areas of an instrument that may contribute to the final image). I include interferometry under a blanket term of "testbench". An optical testbench can include many tests, one or more of which can demonstrate any aspect of the instrument that can affect the image. The benefit of an optical testbench is that it is essentially a lab environment. So conditions can be controlled. This means we can see what occurs when the instrument is in a state of equilibrium where we can see the designed state of the instrument.
An interferometer looks at the entire surface or surfaces as an "entire", and compares "interference fringes" formed by errors on the optic to reference fringes. From here we can see the contribution of errors from Seidel aberrations, and described as a fraction of a wave. More importantly (in terms of the instrument's performance) it gives a figure in RMS (Root Mean Square), which is an account of errors over the entire tested area of the optic, rather than a "worst case" wavefront error.
A Foucault test can see everything an interferometer can (it is as sensitive), but does not have a software programme that immediately converts errors into quanitities of errors. Other tests such as Ronchi can show basic geometrical errors and is better at showing directional errors such as coma.

Not sure I know exactly what you mean by trade-offs. Do you mean it is OK to have certain aberrations but not others - in terms of what manufacturers choose to have? If so, I understand what is meant by this because we are dealing with short focal ratio refracting instruments. However, there is no excuse for on-axis coma, on-axis astigmatism or lower order spherical aberration. Chromatic aberration is something that can largely be supressed if the designer uses low dispersion elements in the design. Field curvature is common, and should only affect off-axis field edge areas. Distortion is very common, and can be placed to one side, "so to speak" as it is not an aberration that affects image sharpness as it is a variation of magnification across the field. If we accept that distortion and field curvature are going to be there to some respect then we only need to concentrate on how common the other aberrations are.

Veiling glare whether diffuse light covering the whole field, or a sharp internal reflection, does not alter the "sweet spot" in terms of destroying image sharpness, but rather masking it making it less detectable.

It must also be stated that "trade-offs" are only acceptable in the context of economy. It is possible to improve on what we see in modern high quality binoculars, but at a price. I'm not sure the public would understand or accept the high prices involved in these improvements. The "trade-offs" should not be thought of as "just the way it is", but rather "what you get for your money".

A testbench can show the presence of coma (on-axis and off-axis), astigmatism (on-axis and off-axis) LSA and HSA, the various chromatic aberrations, surface roughness (micro ripple), Veiling glare, field curvature (defocus) and distortion (a simple grid chart will do that). We can see the effect of these aberrations on the image when we use the instrument in the field, but we can't quantify them. By quantifying them we can accurately predict their effect on the image in field use, and what damage to the image the observer will see. The correlation between what is measured and what is seen really is that close. Quantifying errors also helps to show inconsistency, and also user error (perception).

'It's generally understood that the design process involves contending with these tradeoff decisions, and the most important factors entering into the process ultimately involve the user population. The most salient of these is probably the acuity of the eye, but, even this must be put into context. Is it day or night, pod mounted or hand held, and exactly what is the observer expected to be doing, e.g., finding enemy troops on the battlefield or birds in the foliage? Each task condition defines its own optimum optics, and these optima (plural), in turn, relate back to the multi-dimensional response surface that is measurable with an interferometer, or related equipment, on a stark lab table.

What can't be determined on an optical bench, are these performance optima.'

Yes they can, simply by knowledge of the optic determining what effect on the image will have. We can't forsee the individual user acuity or the environment the instrument is used in, and we shouldn't accept that as a genuine reason for muddying the waters when designing an instrument for optical quality. There is nothing subjective about geometrical optics at all, because it is all mathematical.
The quality of an instrument should always be a constant, individual visual acuity and environments (darkness, bright reflecting water, Snow Buntings on snow, Green finches on the lawn, a tiny distant raptor in the bright blue sky, hand tremor) will always be different and changeable, the highest quality optic with the minimum aberrations is still always the best choice. We should never compromise on quality simply because the perfect image is rarely if ever realised in field use. Once we do, that's when we start getting excuses about the varying individual uses being the main cause of uncertainty and the differences between qualities of models and within models. Its a good escape route for the marketing people.
Subjective opinions are fine for a personal "take" on something, but thats all they are - an opinion, and an opinion requires no knowledge or understanding in order to form it.

'Steve Ingraham coined the phrase a "Better View Desired," I'm inclined to think, to emphasize that the ultimate criterion is the human one, i.e., the better "view," not the better optic.'

I'm not sure I agree with this. Geometrical optics is mathematics. The better optic provides the best views. Whether or not we take advantage of this, or are in a position to is quite another point. The so called "personal equation" is real but in my view should not affect the quality requirement, or infect any part of the chain of design, fabrication and consistency of quality. All this may sound like a fairly obvious thing to say, but in my experience, because of the complicated mathematical nature of optics, marketing ideas are more often than not replacing fundamental truths about optics, and after all, a marketing idea is much easier to swallow than equations.

Bright but overcast sky (for even light) and minimum heat distortion.

May I wish you zero astigmatism for the coming year.

andytyle

Leif

Wednesday 2nd January 2008, 19:01

It must also be stated that "trade-offs" are only acceptable in the context of economy. It is possible to improve on what we see in modern high quality binoculars, but at a price. I'm not sure the public would understand or accept the high prices involved in these improvements. The "trade-offs" should not be thought of as "just the way it is", but rather "what you get for your money".

Exactly. Even top end binoculars are very much a compromise imposed by the constraints of price, size and weight. Though economy is maybe not the best term when referring to instruments that cost ~£1,000. |=)|

"the highest quality optic with the minimum aberrations is still always the best choice"

Sadly even top end binoculars show obvious optical flaws. I see excessive CA through most roof prism binoculars, apart from the Zeiss FL, and some people consider the edge softness of the Zeiss FL range unacceptable.

andytyle

Wednesday 2nd January 2008, 20:01

Quote: 'The number of degrees of freedom is too large to carry out complete and sufficient tests. In practice you do a sample of tests, to gain a reasonable assessment. And that choice of tests is subjective, based on experience and knowledge. And of course the interpretation of the results is subjective as someone has to decide what is acceptable and what isn't, given that the instrument is to be used by a human, and not just to carry out some well defined and routine task, such as creating an image of a mask on a silicon chip.'

None of this correct because definitive tests in a scientific testbench environment are mathematical in nature and hence not subjective. If we measure something and we get a definitive result, and the test is repeatable, and we get the same result, then we have an objective answer. Where is the subjectivity? The whole basis of scientific testing is based upon repeatable tests being executable. Why does any measuring tool exist if results are subjective? If the results of an objective test are entirely subjective then what sort of test is it? If you understand what aberrations are, and can measure them, and you understand how they affect the image, then there is no subjectivity. The subjectivity is "introduced" by human perception or human misunderstanding, it is not there in the measured scientific results. Simply because test methods are not understood or because there is little awareness of what they mean is no basis for assuming they are somehow inferior to nothing more than an opinion.

'Yes it is 'some guy' who tests mainly Nikon lenses. The point I was making is that subjective tests are useful, and Rorslett is an example of an experienced and respected photographer who presents subjective tests which are widely quoted by amateur and professional photographers alike. I find that his subjective tests are usually far more accurate than supposedly objective tests such as those on www.PhotoZone.de. The problem with many/all objective tests is that they give an incomplete picture.'

Yes, subjective tests are useful if you want someone's opinion, and yes, you may or may not respect someone's opinion....but that does not mean that the opinion is definitive or objective. There are as many opinions as there are individuals, there is only one truth, if that truth can be measured. With optics it can......and...the results do have meaning in an abstract sense. So, contrary to your preference for subjectivity, the complete picture is to be had from many if not all objective tests.

'I guess you propose performing a test of an optic not only with an 'infinite' target, but with an intermediate and near ones too? And then performing tests of the amount of scattered light (flare) under goodness knows how many different illuminations? It would require huge amounts of work, would take ages to do, and it would generate massive amounts of data. And then you would have to make subjective decisions when presenting the data e.g. how much CA is acceptable, how much field curvature is acceptable etc. Hence you are back to the fuzzy subjective domain rather than the cold precise and rational objective one.'

I think I have answered this or a similar point before. Binoculars and scopes are corrected for infinity. If they show LSA at infinity and slightly less at closer focus, then this is a fabrication error not a design feature. Testing using collimated light tells you everything you need to know regarding coma, astigmatism, chromatic errors and LSA. Contrary to your suggestion, the more information and data you have the more certain you are about objectivity, and the less room for subjectivity.

'Alternatively why not just pick up the instrument, and spend a few months using it, then tell us all what you think of it? Sure you might have older eyes than the average, and your acuity might be a bit low, and you might only use it in daylight, but your experience when combined with others would be valid.'

Sure, why not? Give an opinion....................

'Incidentally posts here on BF indicate that sample variation is a significant issue for both spotting scopes and binoculars. That objective test tells you about one sample of an instrument. A range of 'horribly subjective and worthless' user opinions gives an idea of how multiple samples perform.'

If you had been reading the other threads regarding consistency, you would have seen that multiple objective testing is proposed, and further, that it would involve an agreed objective test procedure that those chosen would be able to carry out. This is yet to occur and a trial is required initially. But, it can easily be done. The guys in Scandinavia and Henry in the US, and perhaps Ron the surveyor seem, initially, set up and appropriate people to take part, if they want to.

I think the message here should end with - Subjective opinions are fine as long as they are understood to be subjective and hence not necessarily representative of reality. Objective lab condition tests are repeatable and provide coherent results which are re-testable. Anyone who has faith in science and scientific methods should understand the importance of objectivity, but also the meaning of subjectivity, and not confuse their importance.

andytyle

elkcub

Wednesday 2nd January 2008, 22:05

What can't be determined on an optical bench, are these performance optima.

Yes they can, simply by knowledge of the optic determining what effect on the image will have. We can't forsee the individual user acuity or the environment the instrument is used in, and we shouldn't accept that as a genuine reason for muddying the waters when designing an instrument for optical quality. There is nothing subjective about geometrical optics at all, because it is all mathematical.

andytyle

Finally, there is the tiresome issue of image quality metrics. It would be nothing short of a miracle if there were universal agreement on an image quality metric, especially one applicable to visual systems with all the additional complications introduced by the instrument-eye coupling. P. Mouroulis, 1999, Visual Instrumentation: Optical Design and Engineering Principles, pg. xx.

Andy,

You guys need to get your house in order before preaching to the rest of us. ;)

A big part of the problem, I think, is that although one can idealize optical performance in terms of image quality, that is much different from optimizing man-machine performance. The elephant in the room is that there are limits to human performance, e.g., visual, manual, etc, which (fortunately) constrain optical requirements.

Incidentally, although I appreciate the mathematical beauty of optical theory (some of it, anyway), the use of RMS as a practical measure of image quality is simply an engineering heuristic to simplify a complex response. One might also use some other combination of statistical moments, RMS only involving the first two. The topic became "subjective" when that metric was chosen, and, as a mathematical purist, I must say it's incomplete and aesthetically unpleasing. |:(|

Your friend,
Elk

Leif

Wednesday 2nd January 2008, 22:56

There is a danger I will repeat myself. Oh well. If you can repeat your errors, then so can I. (Humour intended.)

AndyTyle: "I think the message here should end with - Subjective opinions are fine as long as they are understood to be subjective and hence not necessarily representative of reality.

That is reasonable. Of course opinions such as "Wow, this bin sure is sharp" are to be taken with plenty of salt.

Personally I find subjective opinions helpful and informative assuming a trusted observer and more so than any objective tests that I have seen. I am referring to binoculars and photographic lenses. Most if not all so-called objective tests of photographic optics consist of MTF plots which are not a complete description, and in my experience the tests of trusted observers such as Rorslett are far more reliable than any so-called objective tests I have seen. I have never seen 'objective tests' which can compete with subjective evaluations.

AndyTyle: "The problem with just describing "what you see" as another has suggested, is that the results can not be trusted. "

There are people whose opinion I trust. Not as fact, but as educated opinion.

AndyTyle: "For me, a proper testbench method is the only meaningful method for assessing any real optical aspect of an instrument. Other than that, point sources in darkness at least allow the condition where the exit pupil is the defining pupil."

Then we disagree completely.

AndyTyle: "Objective lab condition tests are repeatable and provide coherent results which are re-testable. Anyone who has faith in science and scientific methods should understand the importance of objectivity, but also the meaning of subjectivity, and not confuse their importance."

Anyone who understands the scientific method should realise the limitations of what they are doing. They should not confuse experiment with reality. You are trying to build a model of reality from a limited set of measurements. If you measure on-axis resolution - using double stars or whatever - that is an objective test subject to experimental error. But it tells you only one quantity for one instrument. To get information which would be believable, you would have to test a random selection of samples of each instrument. You would then have to perform a battery of tests on each. You would have to test resolution as a function of angle from the axis. And you would have to measure field curvature, and aberrations. Then we have flare and stray light, which requires multiple light sources from various angles. And I have not yet mentioned eye relief and blacking out that some experience. Designing those tests would not be easy. And then - and here is a point you keep avoiding - you would have to convert the data from raw meaningless information to something that meant something. In other words you would have to interpret that data.

Of course if you can do this, for a range of instruments, then I will be in the queue to pat you on the back, and ask you how you developed such stamina. Seriously, please do it. |=)|

In practice all of the binocular tests that I have seen consist of a combination of subjective assessments, sometimes from a range of observers, and limited testing in a more formal context e.g. resolution testing. The reason for this is no doubt pragmatism, and realism. Few people have high end test equipment, and even fewer have the inclination to use it to test consumer optics.

Tests of high end telescopes - such as apochromatic refractors - usually consist of resolution tests, such as resolving double stars, or even performing a Foucault test or similar. That is fine for an astronomical(ly priced) telescope which focuses on point objects at infinity with no side lighting and which has little in the way of aberrations due to high optical quality.

If some people here do tests on a range of optics, such as yourself, then that's to our benefit as it will add to our knowledge. But to think that tests are the same as reality, and superior to subjective evaluations is mistaken IMO. They can support a subjective assessment, by providing evidence, but no more.

Anyway, sorry about not being brief. Oh well. At least you will sleep well tonight, assuming you got this far, and are still awake.

andytyle

Thursday 3rd January 2008, 02:15

Quote: 'Quote:
Finally, there is the tiresome issue of image quality metrics. It would be nothing short of a miracle if there were universal agreement on an image quality metric, especially one applicable to visual systems with all the additional complications introduced by the instrument-eye coupling. Mouroulis, Visual Instrumentation: Optical Design and Engineering Principles, pg. xx.'

Elk

Yes, not quite sure why this is said the way it is. Of course, no-one can cater for lots of individual requirements of the eye. The eye is also an optical instrument whose parameters are known but because of individuality.....are unknown in this context, this is essentially why I favour controlled lab measuring techniques. We use the eye to read the results, not to play a part in forming them.
If we construct the perfect sphere, and most people give an opinion that to their eyes it is not quite spherical, so we change it so it meets the approval of most people, but when we measure it, we find it is no longer spherical, who is right? When is it a sphere?
All that can be done is to understand how geometrical optics work, understand what the aberrations are and what damage they do to diffraction limited images. If the user is imperfect, surely this doesn't mean it's OK for the tools that he uses to be imperfect. We do understand how to measure the accuracy of optical surfaces, either in isolation or in combination. We can use maths to make optics and optical instruments to the best standard we can. Its us and our perceptions that are the faulty units. By that I don't mean we are incapable of detection, but rather our interpretation. To act on individual grounds to solve an issue like this is to blame the messenger for the message.

I wouldn't say that 'RMS as a practical measure of image quality', it is a measure of geometrical error totality. From this it is possible to accurately predict the formation of the image the instrument is capable of. There is a clear correlation between geometrical optical error and image error. All we need to do is accurately measure the error....and then add our own abstract meaning, if thats what we want to do.
For years, purchasers of some high performance astronomical instruments have trusted maths to tell them of the quality of the instruments optics prior to purchase, either from derived figures from Foucault testing or from direct interferometry. If the tests are done correctly, and the tester is honest (a lot of dishonesty in the astro industry), the performance of the instrument can be accurately predicted. So consistent is this correlation, that some will only trust these figures and purchase only high rated test result instruments (Strehl peddling).
It is just as possible with smaller instruments used for birding, all it takes is someone with the know-how and the facilities,.........and.....the will and desire for honest results.

andytyle

Mike Penfold

Thursday 3rd January 2008, 03:13

IMO someone who offered a testing service in North America for sports optics, with a two week turnaround, at reasonable cost, could make a decent living.

Mike

elkcub

Thursday 3rd January 2008, 03:33

Well, hell, if you can't figure out why "... universal agreement on an image quality metric would be a miracle ..." don't look to me for the answer. ;) I'm only a behavioral scientist trying to understand optical requirements within the limits of human perception. I admit to being completely baffled about the need for much more. I do know, however, at the risk of being repetitive, |=o|, that perceptual gestalten are more than the sum of measurable aspects of the image on an optical bench. So my sense of Mouroulis' dilemma is that someone is saying that the image not only includes the optics of the eye, which requires effective modeling, but also that the view includes processing by the brain. Do we judge the quality of the image by the optic(s) that produced it, or the brain that interprets it? Agreeing on that would be a miracle!

Elk

iporali

Thursday 3rd January 2008, 10:35

... the "sweet spot" is not really definable - in a true sense, except to say that the area at and around the centre of the field of view is likely to be the sharpest.....that's all you can say really.

And yet many BF members (including me) find it very useful. Just like you try to hit the tennis ball with the subjective "sweet spot" of a tennis racquet, you try to place the bird in the binocular's "sweet spot" (you don't need to know what it is, you feel/see it). In some binoculars and for some users the "sweetness" and size of this spot varies, but you may find some informative consistency when you read several forum posts critically.

The Nikon 8x32SEs are said to have a very good sharpness across the relatively wide FOV and many BF members consider them as one of the best binoculars ever made. At one time the SEs were almost universally praised on the BF - but suddenly some users started to mention blackouts, which prevented them from actually using the wide "sweet spot" that so many especially enjoyed. This is what I experienced in practice as well. If I had been equipped with information that exists now in BF, I might have bought the less expensive Nikon 8x30EII, which isn't as sharp to the edges (hasn't as flat field), but has an "easier" sweet spot for me. I don't think I would have been able to read this from Ronchi patterns or interferometer data - these instruments don't get eyestrain nor do they have to accept suboptimal binocular placement at milliseconds of time that a birder often does.

I am all for objective/scientific testing of binoculars, but I can easily accept many subjective descriptions that can be helpful when people choose birding optics. ...but if you'll ever open a thread "Scientific binocular testing for dummies", I will be ready and willing to participate. :t:

Best regards,

Ilkka

lightshedder

Thursday 3rd January 2008, 14:46

Just for the record, since my name has come up several times in the resurrection of this thread...

Based on my personal experience (your mileage may vary), objective testing can often confirm and, indeed, explain the performance I perceive in use...whether we are talking optics and the view, hifi and the sound, digital camera sensor performance and image quality...or any other set of technical/objective factors and the corresponding "real world/real use" experience of performance...but I have yet to see any instance where objective testing, no matter how extensive, can predict my experience of performance.

No matter how you measure, the overall perceived performance is based on a complex interaction of the factors we can measure, acting on each other, and then that whole complex acting on our sensory systems, and then their input being interpreted by our internal processing software...part of which is self-written, or at least heavily revised, based on individual experience (which is why your mileage will vary).

In optics all that matters is what you see. In hifi all that matters is what you hear. etc.

To one degree or another it is useful to us humans to have a more or less trusted fellow human describe his or her perception of performance. If we listen to enough such voices 1) we can form a somewhat intelligent, still tentative, conclusion about how we might perceive the performance, and 2) looking for or listening for what others claim they see or hear often rewrites our processing software so that we too can see or hear what they claim. (This is, truth to be told, more often negative than positive. It is much easier to describe the flaws in performance than it is the strengths...since strength is transparent...just things as they ought to be...while flaws are opaque...they get in the way and diminish our enjoyment of the experience. Therefore we are more likely to learn to see and hear the flaws than we are to appreciate the strengths. Bummer.)

There is a place for lab testing. If we are going to improve performance, then we must be able to confirm and explain the factors that contribute to it. We have to know why people are perceiving the flaws and not the strengths.

Which is the reason I turned this sweet spot thread to a more serious discussion, low these many months ago. People perceive something in the performance of binoculars where I have vested interest in the design which I do not...I need to understand what they are seeing, so that we can develop the lab tests to identify the causes, so that, someday, we can do better...or at least produce a product in which fewer folks perceive the flaws...and more people appreciate the strengths.

Wouldn't it be wonderful, won't it be wonderful, when a binocular hits the market and no one can find anything wrong with the perceived performance? Don't hold your breath, and begin saving right now...since they will cost the proverbial arm and a leg...unless, of course, new and unexpected technologies and solutions are developed. We can hope. We can even work on that.

In the meantime, it is simply amazing that you can buy the kind of perceived performance that today's binoculars provide, at any price, let alone at under $2500. You pay that for a high end laptop and don't think twice. Hunters invest 2 to 3 times that in a rifle...and don't get me started on shotguns. HDTV anyone? State of the art home theater system? Set of golf clubs? Piano? And let's not mention a violin or cello at that performance level.

Of course, that doesn't mean that those of us involved in the optics industry won't continue to try to get you more performance at that price...

That's what I am here for...your mileage may vary.

andytyle

Thursday 3rd January 2008, 16:07

Quote: 'There is a danger I will repeat myself. Oh well. If you can repeat your errors, then so can I. (Humour intended.) '
Which errors specifically?

'Personally I find subjective opinions helpful and informative assuming a trusted observer and more so than any objective tests that I have seen.'

I have found the opposite to be true. Test bench methods in any industry would simply not be respected and completely ignored if what you are saying is more universally true.

'I am referring to binoculars and photographic lenses. Most if not all so-called objective tests of photographic optics consist of MTF plots which are not a complete description, and in my experience the tests of trusted observers such as Rorslett are far more reliable than any so-called objective tests I have seen. I have never seen 'objective tests' which can compete with subjective evaluations.'

Ah, that is a more honest approach. You have never seen them doesn't mean there aren't any. MTF tests are useful in giving certain performance results based on a type of - looking through an instrument and seeing what it can do, perhaps compared to another instrument, but importantly against a reference measure. MTF is a godsend to the QA beurocrats (spelling?) that simply wish to push a button to get an answer. It requires little understanding of geometrical optical aberrations in order to be able to do it, some testers acquire a little knowledge as they go along.....if they can be bothered or are interested, but it is not essential in order to do the test. You just need to be able to set up the test and read the results. MTF is not very diagnostic, and therein lies the problem, in the context of this debate. In order to quantify errors for the purpose of deciding which instrument has the best and most useful "sweet spot", or for providing evidence of aberrations that keep cropping up, to get manufacturers to improve QC, we need more diagnostic tests, and that is what Foucault and interferometry provide.
With optical testbench testing, you are identifying and (in some cases) measuring errors on the surfaces of the optics or on the wavefront. You become acquainted with the "warts an' all" state of the lens or mirror, because you can see it and measure what you see. Without an understanding of aberration theory, this cannot be done properly. It requires discipline. From this, opticians can predict MTF results to a good level of accuracy, and importantly, understand what it is about the optic that creates the result. (It is even possible to predict an MTF from nothing more than a prescription of a lens, and modern interferometers can, as a sideshow, provide accurate MTF for a tested optic simply by.....pressing a button).
This is how opticians work when they design and build an optic. They test using testbench methods, and they know when they have got it to the correct standard, that it will give a particular MTF result when tested properly. Opticians are that confident......from many many decades of repeat experience in correlation.

'Anyone who understands the scientific method should realise the limitations of what they are doing. They should not confuse experiment with reality. You are trying to build a model of reality from a limited set of measurements. If you measure on-axis resolution - using double stars or whatever - that is an objective test subject to experimental error. But it tells you only one quantity for one instrument. To get information which would be believable, you would have to test a random selection of samples of each instrument. You would then have to perform a battery of tests on each. You would have to test resolution as a function of angle from the axis. And you would have to measure field curvature, and aberrations. Then we have flare and stray light, which requires multiple light sources from various angles. And I have not yet mentioned eye relief and blacking out that some experience. Designing those tests would not be easy. And then - and here is a point you keep avoiding - you would have to convert the data from raw meaningless information to something that meant something. In other words you would have to interpret that data.'

??????????????????????? Who is talking about experimentation? Experiments are things that you do to find out whether some process works or not. Once it is known that it does it becomes a measure, a standard, or even a constant. I don't need to keep adding 5 to 5 to find out whether 10 results every time. The experiment was done thousands of years ago. Today I can add 5 to 5 to make 10 without feeling doubt about whether the answer is going to be subjective.

The above paragraph is obviously made from a position of not being aware of or understanding how optical testbenches work and what they can reveal. Believe me, opticians do not measure or test their optics under construction using charts or handing them to people with a cheerful request of "See what you think of these then". They use, for example, Ronchi and Foucault tests often in auto-collimation, most of the big optical houses have Zygo or at least Twyman Green interferometers. Data conversion is practised daily and is well understood. I have done it myself, why would I want to avoid it? There is nothing mysterious or untrustworthy about it, just as a solar eclipse is simply a big rock passing in front of the sun, and not a god showing displeasure.
Eye relief and 'blacking out' do not affect the area of the field that is diffraction limited or nearly diffraction limited.

'Of course if you can do this, for a range of instruments, then I will be in the queue to pat you on the back, and ask you how you developed such stamina. Seriously, please do it.'

Of course optical testing that cover areas of your concern can be done, and are done....daily. It's common practise. In modern optical design you just switch on the computer, plug in your optical design software, set parameters, and sit back. Much easier these days, no need for slide rules or log tables, even ray tracing using pencil and paper is a thing of the past. 'Getting it right' by design is a lot easier these days, testing is still difficult in comparison, it requires effort, but is doable.

'In practice all of the binocular tests that I have seen consist of a combination of subjective assessments, sometimes from a range of observers, and limited testing in a more formal context e.g. resolution testing. The reason for this is no doubt pragmatism, and realism. Few people have high end test equipment, and even fewer have the inclination to use it to test consumer optics'

There is no argument to this. It depends on who is testing, marketeers, end users....then yes. Opticians do have the right equipment for testing correctly, otherwise it would not be possible to make high standard optical surfaces.

'Tests of high end telescopes - such as apochromatic refractors - usually consist of resolution tests, such as resolving double stars, or even performing a Foucault test or similar. That is fine for an astronomical(ly priced) telescope which focuses on point objects at infinity with no side lighting and which has little in the way of aberrations due to high optical quality.'

It makes no difference what you test, the procedures are known and data interpretation is known. You can introduce whatever environmental influence you like on a test.

'But to think that tests are the same as reality, and superior to subjective evaluations is mistaken IMO. They can support a subjective assessment, by providing evidence, but no more.'

Of course tests are not reality (in the context of this debate) subjective ones even less so. An objective test (in this context) uses results that are repeatable if the test is carried out correctly. The results can then be used to predict with accuracy the optical performance. This happens all the time. It happens during the manufacture of binoculars and spotting scopes, astronomical telescopes, microscopes and other optical instruments. It is the very basis of a tolerance standard of manufacturing.....and yes, with geometrical optics they are vastly superior to subjective analysis because the answers are coherent, mathematical and thus trustworthy.

andytyle

andytyle

Thursday 3rd January 2008, 16:10

Quote: 'Well, hell, if you can't figure out why "... universal agreement on an image quality metric would be a miracle ..." don't look to me for the answer. I'm only a behavioral scientist trying to understand optical requirements within the limits of human perception. I admit to being completely baffled about the need for much more. I do know, however, at the risk of falling into Leif's endless repetition syndrome, that perceptual gestalten are more than the sum of measurable aspects of the image on an optical bench. So my sense of Mouroulis' dilemma is that someone is saying that the image includes the optics of the eye, but the view includes processing by the brain. Do we judge the quality of the image by the optic that produced it, or the brain that interprets it? Agreeing on that would be a miracle!.'

Absolutely. Quite agree.

We can't manufacture for individual interpretation (eye/brain) because there are so many variables. The optical industry relies on mathematical (machinery or pen and paper) test methods because geometrical optics is mathematical. We judge the optic by a reference standard we know is as near perfect as can be achieved, and we know that it will perform within the limits set by diffraction. That's all you can do. You can mess around with lenses and prisms, but if they make no improvement over what is already diffraction limited, is there a point? We can mess around with baffles to eliminate stray light, we can mess around with coatings so that a maximum transmission is achieved with a peak transmission matching the peak sensitivity of the photopic eye. But all of this is measurable, and still we are left with nothing but a hope that the end user will/can appreciate what we know to be correct. We can't act because of subjectivity, we construct by measuring and leave interpretation to the beholder. Otherwise we will find ourselves witness to Jeff Goldblums line in Jurrassic Park - "The essence of chaos".

andytyle

andytyle

Thursday 3rd January 2008, 16:55

Quote: 'Based on my personal experience (your mileage may vary), objective testing can often confirm and, indeed, explain the performance I perceive in use...whether we are talking optics and the view, hifi and the sound, digital camera sensor performance and image quality...or any other set of technical/objective factors and the corresponding "real world/real use" experience of performance...but I have yet to see any instance where objective testing, no matter how extensive, can predict my experience of performance.'

Of course not, I think we are all agreed on that one. All we can do is get the optics right via measurement. Experience is then personal. Can't really do anything about that. Not until some genius comes up with a directly responsive two-way neuro-optic monitor. Then it will be like turning the colour or contrast up or down on the TV. That would be great. We could all view a rose-coloured world. :hippy:

etudiant

Friday 4th January 2008, 18:03

Leif

Friday 4th January 2008, 18:29

'Personally I find subjective opinions helpful and informative assuming a trusted observer and more so than any objective tests that I have seen.'

I have found the opposite to be true. Test bench methods in any industry would simply not be respected and completely ignored if what you are saying is more universally true.

A manufacturer has to use objective measurements and calculations to assess expected and actual performance. But, with a few exceptions, they do not thoroughly test every optical instrument they make.

I feel that you are ignoring the human element, especially perception, and the fact that binoculars are a compromise and are not on a par with a diffraction limited telescope. But since I do not want to repeat myself, it is better to accept that we disagree.

It would be quite interesting to know the process that the big names in the binocular world go about designing a product, the weight they place on field testing a range of prototypes, assuming they do, and the critieria they use for reaching a compromise. My guess is that there is much art as well as science. However, I suspect that it would be hard to obtain an accurate account, given commercial secrecy.

Leif

Friday 4th January 2008, 18:45

In another thread,
http://www.birdforum.net/showthread.php?t=104496 ,
Surveyor notes that the current ISO standard allows plus or minus 5% performance leeway between the two barrels of a binocular. Given that low a manufacturing uniformity standard, it suggests that much of the above discussion is derived from normal sample variations, rather than from fundamental product design differences. Perhaps it might be good marketing for one of the better manufacturers to emphasize the superior uniformity of their products, if that is justifiable. It would at least represent an improvement on the current hyperbole rich advertising. Also it might appeal to the average customer, who is generally seeking a reliably satisfactory product, rather than hoping to find a superior "cherry" binocular in a mass of more or less adequate exemplars.

The whole question of consistency, and standards, is a thorny one IMO. I recently purchased a quite decent microscope for mycology. The objectives were described as 'Plan' which means flat field in the microscope world. However, the 10x field is flat to about 50% from the axis, and then image softness from field curvature sets in, and is poor at the edge. The 100x objective is better but not by much. That said, the overall IQ is good. And of course some binocular manufacturers refer to 'colour fringe free' images, whereas I can see 'em clear as day. I wonder how manufacturers can get away with misleading descriptions? I suspect that they point to measurements and say that they are within perceptual tolerances. What lies within perceptual tolerances is highly subjective.

However, many people will simply not be aware of even moderately severe aberrations until they are pointed out to them. (It's best not to enlighten them though.)

Someone on this forum some while back suggested that optics such as high end binoculars should be supplied with a test certificate, to assure us that they at least conform to certain standards. Or at least they did when tested in the factory. I have no idea if the idea has legs.

elkcub

Friday 4th January 2008, 21:22

[Leif]... It would be quite interesting to know the process that the big names in the binocular world go about designing a product, the weight they place on field testing a range of prototypes, assuming they do, and the critieria they use for reaching a compromise. My guess is that there is much art as well as science. However, I suspect that it would be hard to obtain an accurate account, given commercial secrecy...

The Mouroulis book I mentioned in #84 includes an excellent 68 page chapter written by T.L. Williams, UK, entitled "Testing of Visual Instrumentation." Summarizing it here is out of the question, but he does make a general statement worth quoting:

... The purpose of testing optical instruments is, in principle, to ensure that they can perform the task for which they are intended. This task may be translated into a set of specifications giving values and tolerances of the parameters described [later] in this section. Testing can be an expensive process, and it is important for the customer and the manufacturer to reduce testing requirements to a minimum and of course not to impose unnecessarily close tolerances or high values on test parameters. Although on a prototype instrument it may be desirable to confirm that most, if not all, of the values and tolerances originally specified have been met, testing in production should be selective and limited to parameters that are critical to the performance of the instrument and/or that have a significant likelihood of being outside tolerance. It should also be noted that some of the constructional tolerances required to meet some of the most critical test parameters automatically ensure that tolerances on other parameters will be met, and that if the former meet specification so will the later.

This, of course, doesn't tell us what specific manufacturers actually do, but it does suggest that testing is, at best, more judicious than what might be done by an independent tester, and, at worst, insufficient to prevent lemons.

The chapter also discusses several measures of image quality, based on different approaches, but this goes well beyond my interest in the subject. |=o| References to what humans can perceive in the image is implied here and there, so it's safe to assume that "the better view" is still left up the customer to decide. (Whew!)

Elk

Leif

Friday 4th January 2008, 22:09

T
This, of course, doesn't tell us what specific manufacturers actually do, but it does suggest that testing is, at best, more judicious than what might be done by an independent tester, and, at worst, insufficient to prevent lemons.

I have a Nikon 12-24mm F4 AFS lens which is unusable between 12mm and 14mm at any aperture as the image is smeared in the corners. You might consider this a rare aberrant sample, but one or two other owners have reported the same defect, and many others have reported lesser defects. Some samples of course are superb. And Canon are no better by all accounts.

As you indicate in the quote, testing is expensive, especially since if it is to have any valid purpose, items which fail the tests must be rejected, or rectified. Anecdotal accounts suggest that Zeiss and Leica lenses - the expensive high end ones only - have a better quality control than Nikon and Canon. I suppose they have to at least given the cost of the Leica's.

Kimmo Absetz has some interesting comments on sample variation in spotting scopes in his Alula online magazine reviews.

APSmith

Saturday 5th January 2008, 04:14

Back on topic:

If an effort were made to quantify in a comprehensive technical fashion all of the complex factors related to the Sweet Spots of various models, the results (or summary of the results) would only be useful to the common consumer IF they agreed with the consensus impressions, and would likely be disputed to the extent that no layperson could decipher the truth. Therefore, is it really worth the effort to do such a thing?

But, knowing that the Sweet Spot IS a very real and noticeable characteristic, and arguably one of the most significant factors in defining the quality of the view, why can't we simply accept the technique (that has been described) of measuring the acceptably sharp angle of field for the units under comparison? This can be done with a simple measuring tape at a given distance. Most interested people can relate to (and possibly duplicate) such a real-world analysis.

APS

andytyle

Saturday 5th January 2008, 19:19

Quote: 'In another thread,
http://www.birdforum.net/showthread.php?t=104496 ,
Surveyor notes that the current ISO standard allows plus or minus 5% performance leeway between the two barrels of a binocular. Given that low a manufacturing uniformity standard, it suggests that much of the above discussion is derived from normal sample variations, rather than from fundamental product design differences. Perhaps it might be good marketing for one of the better manufacturers to emphasize the superior uniformity of their products, if that is justifiable. It would at least represent an improvement on the current hyperbole rich advertising. Also it might appeal to the average customer, who is generally seeking a reliably satisfactory product, rather than hoping to find a superior "cherry" binocular in a mass of more or less adequate exemplars.'

Tried this angle with Kowa Europe, but they don't appear to want to rock the boat by being different. I get the feeling they are motivated more by fear of losing sales rather than an opportunity to make sales.

andytyle

andytyle

Saturday 5th January 2008, 22:24

Quote: 'I feel that you are ignoring the human element, especially perception, and the fact that binoculars are a compromise and are not on a par with a diffraction limited telescope. But since I do not want to repeat myself, it is better to accept that we disagree.'

I am fully aware of the human element, as the human is the end user. What I am saying, again and again, is that if we take into consideration the many thousands of opinions and perceptions that exist within the end user masses, then we must accept that there are potentially, and actually, many subtley and radically different percepter views. Manufacturers can not cater for individuality with mass produced optical products...........even more so with instruments having quality less than diffraction limited. All that manufacturers can do and should do is manufacture the optics as close to diffraction limited as possible. I believe that in many cases they try, but because of the cost of doing so including expensive QC, the results are as we find them.........less than optimum performance, and inconsistency. Further, it is and has been my belief for at least two decades that this inconsistency is a prime cause of the belief by a large proportion of the consumer market as a whole, that geometrical optical performance is inherently personal. It is not. Perception is.

andytyle

elkcub

Sunday 6th January 2008, 02:49

Andy,

With all due respect, somehow I don't think you are quite "fully aware of the human element," or at least not willing to acknowledge certain aspects that most of us take for granted — including opticians. Namely, human sensory capabilities have measurable limits, and there are known relationships between optical variables and what can be detected, discriminated, or perceived. I doubt that a large proportion of the consumer market really believes "...geometrical optical performance is inherently personal..." A large portion of the market may be primarily concerned with higher-order perceptions, like the overall "view," which transcends optical particulars considered trivial in the larger scheme of things.

But, I think you need to address the following general question: Why should a manufacturer meet optical requirements that exceed our best understanding of what the most capable humans can perceive on a sensory basis? These are generally called psycho-physical limits. If your answer is that by meeting a pure diffraction limited (or other physical) criterion the manufacturer can escape the murky waters of human psycho-physics, then your claim should not be that you are fully aware of the human element, but that the human element is simply irrelevant to the design and manufacture of visual systems. Otherwise, why have you never made reference to human sensory limitations (as far as I know) in the evaluation of optics?

Again, this is just my take on what you are saying, and I look forward to it being affirmed or corrected.

Best regards,
Elk

andytyle

Monday 7th January 2008, 17:59

Elk

Sorry for late reply. saw that a post had been made last night, but not had time or opportunity to answer till this afternoon.

Quote: 'With all due respect, somehow I don't think you are quite "fully aware of the human element," or at least not willing to acknowledge certain aspects that most of us take for granted — including opticians. Namely, human sensory capabilities have measurable limits, and there are known relationships between optical variables and what can be detected, discriminated, or perceived. I doubt that a large proportion of the consumer market really believes "...geometrical optical performance is inherently personal..." A large portion of the market may be primarily concerned with higher-order perceptions, like the overall "view," which transcends optical particulars considered trivial in the larger scheme of things.'

Of course. The eye places limits on what is potentially visible in terms of resolution and contrast, because of neural modifiers such as foveal cone diameter and spacing, the various refractive indices of the crystalline lens, maybe even obstruction of ganglion and bipolar cells, colour sensitivity etc. We can debate whether 3.2mm or 2.4mm is the ideal diameter of the pupil depending on whether or not we want to find out where diffraction takes over from aberrations in the eye, in placing limitations. If you meant this aspect, then no, this is not what I meant.

By human element, I am referring to the many opinions that accompany the many perceptions that end users have when using instruments like binoculars and spotting scopes. If most end users do not understand the technical aspects of the image they are seeing, i.e. what aspect of optical image formation is creating the image they are experiencing, it does not stop them from enjoying an image, or making assumptions and forming opinions about what they like or dislike.
A great many birders choose or prefer one instrument over another because to them, the image seems better, or they like the view for one or more reasons. They can form their own opinions about why they think the image is better, and to them the image is preferable - better - in a certain instrument. To someone else, another instrument may provide an image which they think is superior - for their own reasons. I have seen this first hand, many times. Saying that 'geometrical optical performance is inherently personal', means that to them, what they experience is personal. I can assure you, having dealt with a great many users of binoculars and telescopes, most are indeed under the impression that optical performance is personal. Some don't really think about it at all, they just choose the instrument they "like". Others are told by the media and other birders that choosing a binocular is personal, and to pick the pair they think is the best. Others rely on the views of others because they may think they are incapable of making the right choice, and magazine reviewers must know what they are talking about mustn't they? (I have lost count of the number of times I have seen people walk into a dealer armed with a magazine group review). Others sort out in their mind a routine for assessment, based on what they may have heard, or what makes sense to them. The pair that pushes all the right buttons is the winner. It is the best. They have made a personal choice. What is it that is personal? The experience or the 'real' image formed by the optics? They make their own minds up what creates the experience. The various aspects of the optics good or bad that create the image are experienced without necessarily being understood. The experience is what it is. What we can do is understand the "cold hard" maths and optical physics that construct the image. Without an understanding of these laws, none of the binoculars we use would exist. We can understand these laws and apply them to the optics we manufacture.

'But, I think you need to address the following general question: Why should a manufacturer meet optical requirements that exceed our best understanding of what the most capable humans can perceive on a sensory basis? These are generally called psycho-physical limits. If your answer is that by meeting a pure diffraction limited (or other physical) criterion the manufacturer can escape the murky waters of human psycho-physics, then your claim should not be that your are fully aware of the human element, but that the human element is simply irrelevant to the design and manufacture of visual systems. Otherwise, why have you never made reference to human sensory limitations (as far as I know) in the evaluation of optics?'

I am not saying that that the human element is irrelevant when designing binoculars and telescopes, and have not said so. In the consumer optics market, the end user is human, it would be stupid to say the human element is irrelevant. What I am saying is that because optics are made using methods controlled by precise mathematical standards, and when the precise mathematical standards are met, the optics work as they should. When they are tested, they should be evaluated by precise mathematical standards, to see if those standards have been met. There is nothing wrong in picking up a pair of binoculars and saying that you prefer them to another, but that is preference, nothing more. You may happen to pick the pair that a lab test suggests is the best corrected, and agree that in use it is the best, but then again, you may not.

'Why should a manufacturer meet optical requirements that exceed our best understanding of what the most capable humans can perceive on a sensory basis?'

Why are some telescopes diffraction limited? How often do we use high quality astronomical telescopes in conditions where the image is limited only by diffraction? Very rarely. The observing conditions rarely allow it. Why make them diffraction limited then? Because it is still possible to use them on occasion at the limit. It is desirable for the separation of double stars at the limit of separation for that aperture, for example. This is just one specific example.
When we use a diffraction limited astronomical telescope at low or medium powers, can we see the maximum resolved detail? Not usually, no. Why? Because the image scale needs to be at the magnified level where the eye can resolve it too. This is similar to the "Why make a diffraction limited binocular when it is only a 10X40"? We can't see the maximum resolving limit at 10X so what's the point? The answer is two-fold. 1. It is possible to see the difference between a diffraction limited binocular (within the design of the binocular) and an identical instrument that is not diffraction limited, even if we can't see that maximum resolvable detail and even with magnifications we use commonly for birding. This is a pretty generalised answer because some instruments may be diffraction limited by design but not after assembly. 2. It is always a good idea to design an instrument to be either diffraction limited or as near as can be, because otherwise, manufacturing and assembly errors simply worsen the image. Make the instrument to the highest standard your economy allows.
When we talk about size of "sweet spot", we are surely talking about the area of field which is either diffraction limited or nearest to being....what others may simply describe as the sharpest area, within the accommodation of the eye's pupil within the exit pupil (allowing for those that describe sweet spot "personally" as simple accommodation). By reducing aberrations we increase the area of the sweet spot. By decreasing certain primary aberrations more than others, we can also increase the area of the sweet spot. For example, if a manufacturer designs an instrument for terrestrial use, they may decide on a simple statement of "Our optics are carefully designed and fabricated to a tolerance of maximum of 1/2 wavefront error". So what? What do they mean? If its 1/2 wave of lower order spherical aberration, we may pass that as OK. If the 1/2 wave error is coma, we may also agree that that is just acceptable (the manufacturer's may look away at this point with a little embarrassment as coma error is usually an allowance for assembly error, not designed). If the error is 1/2 wave of astigmatism, then it is not acceptable as the image is notably worse. With the chromatic aberrations, we might measure the longitudinal error between the focus for green, and that for red/blue by focusing on the halfway point and seeing whether one colour position is more than 1/2 wave from focus. If it is, we have secondary spectrum which some may find objectionable and some may not. Quite often this will be because it exists in the presence of other errors, compounding the errors and destroying the image particularly in the presence of spherical aberration. Some notice this and "home in" on chromatic aberration being some indicator of poor quality. In a perfect world, we really ought to say 1/4 wave front error being maximum (astigmatism is acceptable at 1/4 wave). Trouble is that this doubles the price on most binoculars and most consumers would not accept this. If we put aside the chromatic aberrations for a minute and concentrate on monochromatic aberrations, then it should really be possible to categorise (loosely) primary aberrations (we are not considering higher order errors here) in order of importance in their destructive properties within a given tolerance limit. We are talking about widening the sweet spot here by increasing the diffraction limited area (within the design of the instrument - short focal length achromatic doublet or long focal length triplet, for example). Within the bounds set by the economics of mass production, we can put up with 1/4 wave of astigmatism, 1/2 wave of coma and one wave of lower order spherical aberration. I would like to see much better than this but economics prevents it. All of this is measurable and the quality level of the image is thus predictable. We don't need to introduce personal interpretation or physiological complications here, we use maths (objective design/testing) to understand how the image is composed, and how it can be improved. We then experience what we experience and this experience is personal.

andytyle

Leif

Monday 7th January 2008, 19:08

Elk
I am not saying that that the human element is irrelevant when designing binoculars and telescopes, and have not said so. In the consumer optics market, the end user is human, it would be stupid to say the human element is irrelevant. What I am saying is that because optics are made using methods controlled by precise mathematical standards, and when the precise mathematical standards are met, the optics work as they should. When they are tested, they should be evaluated by precise mathematical standards, to see if those standards have been met. There is nothing wrong in picking up a pair of binoculars and saying that you prefer them to another, but that is preference, nothing more. You may happen to pick the pair that a lab test suggests is the best corrected, and agree that in use it is the best, but then again, you may not.

Firstly, you make many very valid points, and I agree with much of what you say in your post (not just the snipped bit above). But at the risk of repetition, I think you miss an important point.

Out of curiosity, have you ever used top end roof prism binoculars such as Leica Trinovids? If so, do they seem 'perfect' to you? To me they do not.

If the optics were perfect, then I would pretty much agree with the entire content of your post. However, due to cost constraints, they are not perfect BY DESIGN. We as a consumer need some way to assess the overall impression of the image - i.e. subjective image quality- created by the balance of compromises chosen by the optics designers.

You seem to think that only equations and/or 'objective' measurements are completely sufficient. But IMO they are not. Even if the measurements/calculations are complete (which I doubt), we still need some way to get from the calculated/measured result to the perceived image quality, since numbers alone are of little meaning. In other words, what do the numbers mean. We could make choices of what we consider acceptable and enter that into the equations/results, but that choice is somewhat subjective, based on an 'average observer', or our expectations/assumptions. In fact I think this is only really useful as a guideline. For example, saying that "binocular X is sharp within 10 degrees of the optical axis" as determined by measurement, with an objective cut-off for sharpness is useful, probably very useful. But it is not complete.

IMO the only way to assess the subjective impression of image quality is by using it.

Now you contend that user reports/reviews are of little value because a) they are subjective and b) they are subject to huge variation due to physiological and psychological reasons. In other words, the human observer is not a reliable consistent witness.

Well, we have little choice about them being subjective. It is after all an assessment of perceived IQ. I and others find that of considerable value. And many of these observers take care to present a balanced assessment within the limitations of their own physiognomy e.g. the Alula and Better View Desired reviews. Some writers also present a some semi-objective measurements.

Secondly my experience of reading reviews is that some observers are capable of presenting coherent consistent opinions, and there is considerable agreement between these observers. In fact there is sufficient consistency that I consider the opinions of considerable value.

In other words, careful observers can reach relatively consistent opinions on a particular instrument.

And in the absence of access to sophisticated measuring equipment, and an accepted model to map the results to perceived IQ, it is all we have got. IMO this is even more useful for cheaper instruments, where the compromises imposed by cost constraints lead to even more image defects. Of course much is subjective, but there is little we can do about that.

andytyle

Tuesday 8th January 2008, 02:34

Quote: 'Out of curiosity, have you ever used top end roof prism binoculars such as Leica Trinovids? If so, do they seem 'perfect' to you? To me they do not.'

Of course, I own a couple of pairs of Leicas, have used a great many and sold large numbers. Do they seem perfect? No.

'However, due to cost constraints, they are not perfect BY DESIGN.'

Are you saying that manufacturers, because of costs, simply OK a certain amount of aberration errors? If so then yes, that's exactly the point I made in my last post. Or are you saying that manufacturer's deliberately introduce coma, astigmatism and spherical aberration??? If not what aberrations do they introduce?

'You seem to think that only equations and/or 'objective' measurements are completely sufficient.'

To establish the geometry of a lens, or prism or eyepiece, that directly predicts its performance....then yes.

'Even if the measurements/calculations are complete (which I doubt), we still need some way to get from the calculated/measured result to the perceived image quality, since numbers alone are of little meaning. In other words, what do the numbers mean. We could make choices of what we consider acceptable and enter that into the equations/results, but that choice is somewhat subjective, based on an 'average observer', or our expectations/assumptions. In fact I think this is only really useful as a guideline. For example, saying that "binocular X is sharp within 10 degrees of the optical axis" as determined by measurement, with an objective cut-off for sharpness is useful, probably very useful. But it is not complete.'

I really cannot make sense of what you are saying. It seems that you are not "getting it". I have, and it appears am doomed to keep answering the same questions.

'IMO the only way to assess the subjective impression of image quality is by using it.

Now you contend that user reports/reviews are of little value because a) they are subjective and b) they are subject to huge variation due to physiological and psychological reasons.'

One last time. Scientific analysis of image quality using measurement is not that concerned with assessing the subjective impression of image quality. One is an opinion (amongst many........the essence of subjectivity, which one do you choose)? The other is a measurement, an objective test that can be repeated.

'In other words, the human observer is not a reliable consistent witness.'

Do I really need to answer that?

I don't think we are going to agree. So, let's just leave it with your faith in the opinion of others, and I'll stick to science.

andytyle

elkcub

Tuesday 8th January 2008, 02:53

Andy,

Thanks for the comprehensive response, but I'm not sure we have a meeting of the minds. Our paths are crossing. ;)

...What I am saying is that because optics are made using methods controlled by precise mathematical standards, and when the precise mathematical standards are met, the optics work as they should. When they are tested, they should be evaluated by precise mathematical standards, to see if those standards have been met. There is nothing wrong in picking up a pair of binoculars and saying that you prefer them to another, but that is preference, nothing more. You may happen to pick the pair that a lab test suggests is the best corrected, and agree that in use it is the best, but then again, you may not.

It seems to me this statement is basically in defense of selecting an instrument by way of bench testing it. I don't see where it address my point that "...human sensory capabilities have measurable limits, and there are known relationships between optical variables and what can be detected, discriminated, or perceived. " If you were to say that the "precise mathematical standards," which I assume mean objectively measured acceptance criteria, were set by human sensory/perceptual thresholds, then we might be getting somewhere. If not, then it seems like a quest for diffraction-limited perfection or bust. (One need be aware that "diffraction-limited" is also subject to several interpretations.)

... We can't see the maximum resolving limit at 10X so what's the point? The answer is two-fold. 1. It is possible to see the difference between a diffraction limited binocular (within the design of the binocular) and an identical instrument that is not diffraction limited, even if we can't see that maximum resolvable detail and even with magnifications we use commonly for birding. This is a pretty generalised answer because some instruments may be diffraction limited by design but not after assembly. 2. It is always a good idea to design an instrument to be either diffraction limited or as near as can be,because otherwise, manufacturing and assembly errors simply worsen the image. Make the instrument to the highest standard your economy allows.

See what I mean? Point (1) is that humans can see a difference beyond their sensory limits, (some of which you allude to at the start of the paragraph). Point (2) appears to seek optical perfection as a practical matter, just in case there is assembly imperfection. Let's face it, it really is a quest for diffraction-limited perfection or bust. Don't get me wrong, you are entitled to this position. I respect it, but I don't share it.

That aside, I greatly appreciate your entry onto the BF scene, because single-handedly you've gotten me to pay attention to wave optics. In the course of it I've reread one or two chapters that I hadn't really connected with, and also discovered important articles that address the perceptual limits of refractive errors. The relationships, in general, relate RMS to JND (Just-Noticeable Differences), — the hard measurements of perceptual psychophysics. How this information is incorporated into current optical product designs I'm not quite sure, but I have no doubt that it is.

Regards,
Elk

andytyle

Tuesday 8th January 2008, 03:51

Elk

Quote: 'If not, then it seems like a quest for diffraction-limited perfection or bust.'

In a nutshell......yes. Although 'bust' is a bit tough. I would say diffraction limited, or as near to diffraction limited as costs allow.

'Point (1) is that humans can see a difference beyond their sensory limits, (some of which you allude to at the start of the paragraph).'

No, if humans can see something that is there, i.e. the image has an objective counterpart, then it's within their sensory limits, or they can't see it. There is a danger here of going off on a tangent quest into Descart and Bertrand Russel's quest for reality and universality.
The 'some of which you allude to' bit, simply means that the angular magnification of the instrument is insufficiently high to allow the eye to resolve it as well as the instrument. That doesn't mean that errors at this low power, contributing to image degredation, cannot be seen by the eye, they can. Errors on-axis, like coma and astigmatism modify the shape of every Airy disc and diffraction pattern making up the image. Spherical aberration modifies the size of every Airy disc whilst spreading light out into the diffraction rings from the bright maxima, where it should be. Chromatic aberration is defocus of particular wavelengths with respect to others, and Distortion is a variance in magnification across the field, even in the centre.

'Point (2) appears to seek optical perfection as a practical matter, just in case there is assembly imperfection.'

Yes, what's wrong with that? If we find (as Kimmo has found in his tests), that the main cause of error in binoculars is misalignment due to assembly, and we can put up with a small error of coma (say 1/2 wave), and that 1/2 wave is likely to occur because of assembly error, then we absolutely need to have zero wedge, otherwise we get greater than 1/2 wave error in the area we wish to be sharp - the centre. If we have 1/4 wave of astigmatism due to surface or surfaces not having rotational symmetry, then we have 1/4 wave of astigmatism plus the 1/2 wave coma from wedge, plus coma in another direction from misalignment, then we have an image that is not as sharp as we could have. So, taking assembly errors into account, (as manufacturers do....they have to because it occurs) leaves little or no room for manufacturing errors, because errors generally compound.

So yes, a quest for diffraction limited performance is what I want to see, or at least a good attempt at it.

'One need be aware that "diffraction-limited" is also subject to several interpretations.)'

Which interpretations had you in mind?

andytyle

elkcub

Tuesday 8th January 2008, 04:16

One last time. Scientific analysis of image quality using measurement is not that concerned with assessing the subjective impression of image quality. One is an opinion (amongst many........the essence of subjectivity, which one do you choose)? The other is a measurement, an objective test that can be repeated.

andytyle

Oops, so sorry, Andy, but scientific measurement of image quality can be based on subjective impressions. Not all such impressions are elicited or analyzed to meet scientific standards, but there are acceptable tools. A careful study can also be replicated and is useful for predicting what people do on a statistical basis (like buying binoculars, telescopes, tooth brushes. etc. ;)). This is the essence of MARKET CAPITALISM!, and conforms to Steve Ingraham's earlier statement about using optical measurements to better understand consumer preferences (or something like that), assuming one believes there is something inherently scientific about preference measurement in the first place.

I'm sure we all know the story of the blind men describing an elephant ... you get the tail, Leif gets the trunk, and I'll take the head. o:D

Elk

elkcub

Tuesday 8th January 2008, 04:23

Andy,

Very good. Your position is understood. As I mentioned in #106 "... Don't get me wrong, you are entitled to this position. I respect it, but I don't share it."

Regards,
Elk

PS. On further thought, I didn't mean to be curt.

...
That doesn't mean that errors at this low power, contributing to image degredation, cannot be seen by the eye, they can. Errors on-axis, like coma and astigmatism modify the shape of every Airy disc and diffraction pattern making up the image. Spherical aberration modifies the size of every Airy disc whilst spreading light out into the diffraction rings from the bright maxima, where it should be. Chromatic aberration is defocus of particular wavelengths with respect to others, and Distortion is a variance in magnification across the field, even in the centre...
andytyle

Yes, wavefront errors may be seen by the eye, as you hypothesize. In fact, I've taken that position several times to the consternation of others on BF. One might not actually have to see CA to be influenced by it, for example. The problem is that the mere presence of any error does not, in itself, prove that the eye can see it, or its manifestations. What is needed, I maintain, is scientific evidence that humans can make such discriminations in the image. The studies I mentioned above attempt to do just that. Some of this is reviewed in Mouroulis' (1999) book, and I have also found more recent studies relating JNDs for controlled refractive errors and spherical aberration using sophisticated psychophysical methods. Much of this work is done by optometry and other visual scientists. All of it speaks to setting optical standards based on the actual capabilities and limitations of the user, and image quality is intimately related to these standards. I would be reticent to complain about errors that have not been shown scientifically to be perceptible.

Incidentally, I have real trouble believing that many assembly errors can be offset by diffraction-limited design. Pinching, collimation, and misalignment, I would think, care little about what's being pinched, and so forth.

Elk

kabsetz

Tuesday 8th January 2008, 10:06

[Incidentally, I have real trouble believing that many assembly errors can be offset by diffraction-limited design. Pinching, collimation, and misalignment, I would think, care little about what's being pinched, and so forth.]

Elk,

Just to pitch in and defend Andy a little (and let me say right up front that I'm enjoying your discussion greatly and finding much to agree with both in your and Andy's positions).

I think Andy is differentiating between a) optical design (how the optics have been calculated: configuration, figures of individual lenses, glass types, coating types etc.) which he wishes to be as close to allowing diffraction-limited performance in a perfectly manufactured and assembled unit, b) manufacture (by which is meant the tolerances to which the individual components, optical or mechanical, are produced, selected and rejected, and c) assembly (the care and precision with which the product is put together and the rigorousness or lack thereof of the QC procedures). Now, since optical problems compound, less than diffraction limited design is going have measurably and perceptibly worse performance when compounded by the same flaws in areas b) and c) than a design that would be diffraction-limited if perfectly executed.

So, I do not read Andy as saying that a diffraction-limited design would offset assembly errors or manufacturing errors, but that it would tolerate more of such errors before the image quality would become visibly compromised.

Incidentally, this reminds me of how heat haze (thermal instability in the air), which is generally considered one of the worst problems preventing us from enjoying diffraction-limited optics, actually affects the image produced by perfect or near-perfect optics much less than optics that have a stack of aberrations present to begin with. In my view, this is one of the chief reasons why even in binoculars it is always better to have flawless optics, even if in perfectly stable air you would need two-to-three times the magnification to see the smallest detail they can resolve.

Keep up the good work,

Kimmo

Leif

Tuesday 8th January 2008, 13:13

So, let's just leave it with your faith in the opinion of others, and I'll stick to science.

andytyle

That does not merit any further comment.

Leif

Tuesday 8th January 2008, 13:18

I'm sure we all know the story of the blind men describing an elephant ... you get the tail, Leif gets the trunk, and I'll take the head. o:D

He might do well to carry an umbrella ... |=)|

andytyle

Tuesday 8th January 2008, 15:11

Quote: 'I think Andy is differentiating between a) optical design (how the optics have been calculated: configuration, figures of individual lenses, glass types, coating types etc.) which he wishes to be as close to allowing diffraction-limited performance in a perfectly manufactured and assembled unit, b) manufacture (by which is meant the tolerances to which the individual components, optical or mechanical, are produced, selected and rejected, and c) assembly (the care and precision with which the product is put together and the rigorousness or lack thereof of the QC procedures). Now, since optical problems compound, less than diffraction limited design is going have measurably and perceptibly worse performance when compounded by the same flaws in areas b) and c) than a design that would be diffraction-limited if perfectly executed.

So, I do not read Andy as saying that a diffraction-limited design would offset assembly errors or manufacturing errors, but that it would tolerate more of such errors before the image quality would become visibly compromised.

Incidentally, this reminds me of how heat haze (thermal instability in the air), which is generally considered one of the worst problems preventing us from enjoying diffraction-limited optics, actually affects the image produced by perfect or near-perfect optics much less than optics that have a stack of aberrations present to begin with. In my view, this is one of the chief reasons why even in binoculars it is always better to have flawless optics, even if in perfectly stable air you would need two-to-three times the magnification to see the smallest detail they can resolve.'

As usual, Kimmo has summed up well and understood my meaning.

andytyle

andytyle

Tuesday 8th January 2008, 15:17

Quote: 'He might do well to carry an umbrella ...'

You're not kidding, what with some of the stuff coming my way :'D

andytyle

Tuesday 8th January 2008, 15:27

Quote: 'Oops, so sorry, Andy, but scientific measurement of image quality can be based on subjective impressions. Not all such impressions are elicited or analyzed to meet scientific standards, but there are acceptable tools. A careful study can also be replicated and is useful for predicting what people do on a statistical basis (like buying binoculars, telescopes, tooth brushes. etc. ). This is the essence of MARKET CAPITALISM!, and conforms to Steve Ingraham's earlier statement about using optical measurements to better understand consumer preferences (or something like that), assuming one believes there is something inherently scientific about preference measurement in the first place.'

You want to use statistics to measure optical quality? Why don't we just read tea leaves?
Perhaps the Queen of Cups, followed by The Fool, followed by a man with a goat's head means too much secondary spectrum? |=)|

andytyle

APSmith

Tuesday 8th January 2008, 15:36

Leif

Tuesday 8th January 2008, 17:29

But ... aren't the manufacturers trying?

Surely, they know the compromises better than anyone. If they could accomplish these goals consistently, without blowing their budgets, wouldn't they? Didn't someone (possibly Steve I.) say on a different thread that the manufacturers could indeed produce a nearly perfect binocular, but that it would have to sell for around $5000? Meanwhile, the market seems to often demand gimmicks and style, rather than optical perfection.

APS

Several people with inside knowledge including one in this thread have said that the cost of a 'perfect' roof prism binocular would be a lot more than we currently pay. Personally I think the Nikon 8x32 SE is as close to perfect as I need.

andytyle

Tuesday 8th January 2008, 17:38

Quote: 'Yes, wavefront errors may be seen by the eye, as you hypothesize.'

This is not a hypothesis, this is a fact used and practised every day by opticians, and observed every day by users of optical instruments. The very point of discussions about quality is that wavefront errors are noticed by users.

'One might not actually have to see CA to be influenced by it, for example.'

Can you explain further?

'The problem is that the mere presence of any error does not, in itself, prove that the eye can see it, or its manifestations.'

If the error is greater than the diffraction limit....then yes, it can.

'The studies I mentioned above attempt to do just that. Some of this is reviewed in Mouroulis' (1999) book, and I have also found more recent studies relating JNDs for controlled refractive errors and spherical aberration using sophisticated psychophysical methods. Much of this work is done by optometry and other visual scientists. All of it speaks to setting optical standards based on the actual capabilities and limitations of the user, and image quality is intimately related to these standards.'

Fine, a user may not be able to resolve detail in an image that another can. This shows variance in individual perception.....and...this also applies to whether an instrument is diffraction limited or not, because in this case it is dependant on the eye/observer.

Image quality formed by an optic though is independant of observer. Further, that quality is measurable and as such, a much better method for setting a tolerance standard.

Compound errors over the diffraction limit are observable. The perfect eye, if such a thing exists, can not see a diffraction limited image if the image is not diffraction limited.
Now....it is possible (you may be overjoyed to hear) that a condition may exist where an imperfect eye can purely by chance, compensate for aberrations in a non-diffraction limited instrument. This is where all errors in one are compensated by all opposite errors in the other. This is extremely rare and in order to deliberately provide this condition requires measured knowledge of both an individual and the optic. The main problem with this is that the variance of quality in the eyes of individuals is so large that it would be impossible to cater for this from the position of a manufacturer. The best way is simply to attempt optical perfection, you can't get better than this. We can control this, we can't control the thousands if not millions of individual perceptions.
I'm afraid what you are suggesting is essentially a case of the tail wagging the dog. Take your personal prescription to your favourite binocular manufacturer and ask a.) Will they be able to make a binocular that has compensatory aberrations within a price that does not require a major 25-year bank loan, and b.) If you inform the world's birders that they too can have this service individually, that the security guards will not throw you too heavily through the doors and into the carpark. |=)|

andytyle

andytyle

Tuesday 8th January 2008, 17:59

Quote: 'But ... aren't the manufacturers trying?

Surely, they know the compromises better than anyone. If they could accomplish these goals consistently, without blowing their budgets, wouldn't they? Didn't someone (possibly Steve I.) say on a different thread that the manufacturers could indeed produce a nearly perfect binocular, but that it would have to sell for around $5000? Meanwhile, the market seems to often demand gimmicks and style, rather than optical perfection.'

Yes they are trying (those that are genuinely interested in the market as a prime source of business), but only if it is profitable. If it isn't profitable, then they avoid the issue by highlighting other less important areas....as you suggest, gimmicks and style.

andytyle

elkcub

Tuesday 8th January 2008, 20:16

Kimmo, I wish what you summarized earlier really was what Andy has been saying, but I think not. First of all, I agree with it. ;)

At one point in Mouroulis' book he anticipates that amateur astronomers might take issue with some of his findings and says, tongue in cheek, that ultimately the issue will be between psychology [i.e., of the astronomers] and psycho-physics. Prophetic.

Thanks for your insights, Andy.

Elk

Leif

Tuesday 8th January 2008, 22:56

So, let's just leave it with your faith in the opinion of others, and I'll stick to science.

I wasn't sure what to say in response to the above condescending remark, which is offensive.

Anyway, your characteristic seems to be that you write huge amounts, liberally sprinkled with buzz words designed to make yourself sound 'scientific' but reading through it, you actually say very very ittle. Or at least very little that could not be summarised in a few words, and which is far from profound. But I must admit that it is a clever way to obfuscate, and talk down to others.

BTW Chris (that is your real name isn't it?), I seem to recall that you had a go at me for not using my name in the forum. Well, I do use my name. Why don't you use yours? Why are you hiding behind a false name?

andytyle

Wednesday 9th January 2008, 01:43

Quote: 'I wasn't sure what to say in response to the above condescending remark, which is offensive.

Anyway, your characteristic seems to be that you write huge amounts, liberally sprinkled with buzz words designed to make yourself sound 'scientific' but reading through it, you actually say very very ittle. Or at least very little that could not be summarised in a few words, and which is far from profound. But I must admit that it is a clever way to obfuscate, and talk down to others.

BTW Chris (that is your real name isn't it?), I seem to recall that you had a go at me for not using my name in the forum. Well, I do use my name. Why don't you use yours? Why are you hiding behind a false name?'

Well, it does appear that you are extremely threatened by what I have said. After your wail above, I started thinking and checked you out. I wasn't sure which forum it was, but it looks like it was this one. Turns out you are the same idiot that complained and shouted at what I said last time...remember...a few years ago when I suggested that consumer instruments were inconsistent. Now it is a commonly held belief. You obviously have insecurities and panic easily. This time you are throwing your toys out of the pram because I won't agree with your subjective nonsense. Am I to expect abusive private emails from you this time as well? I thought it pathetically childish behaviour then, and since have heard from another who no longer takes part on this forum because of your abusive squealings.

Anyone who really has studied optics will know whether my words are 'buzz words' or not. If Kimmo, Surveyor, Henry and the others wish to accept your ramblings, then there is no room on this forum for me, as I will be simply swimming against the tide. I thought there had been some progress since last time, but if people like you hold sway, then I guess not. There are a few on this forum who have shown intelligence, I am afraid you are not one of them.

Sure andytyle is not my name it is my forum avatar or whatever the word is. Common practise on the internet. So what? There's no hiding, I am a contributor to a public forum, what difference does it make whether I use an avatar or my name. If it is your rather desperate wish to discredit me, then do so by proving me wrong about what I say about optics. Attempting to paint me as untrustworthy because I use an avatar makes you look a bit of an idiot.

It would appear that you would like me gone and probably would like others to agree. If others agree and feel somehow threatened then I will leave this forum, I don't want be part of something where I am not welcome.

andytyle

Leif

Wednesday 9th January 2008, 09:02

"Sure andytyle is not my name it is my forum avatar or whatever the word is. Common practise on the internet. So what? There's no hiding,"

So you are Chris Garvey, hiding behind a pseudonym. And yet you attacked me, quite aggressively some years ago, for using what you thought was not a real name as my userid. Sigh. It took me a long while to realise who you were, and it had to be pointed out to me by someone else.

I have never discounted the fact that sample variation exists. 30 years ago, a friend of the family, a professional photographer, used to take home a collection of lenses from his local dealer, and return the best. That way he could cherry pick the best. He, like my father, was trained as an optical technician by a precision optics manufacturer. You like to mis-represent my views.

I have made some simple straight forward points, in what I believe to be a polite manner, and you have responded by trying to ridicule me, attributing to me absurd ideas, such as believing that classical optics is no more than perception, or that I do not accept 'science' . You could simply have said that you disagree, rather than respond in such a condescending manner, trying to turn me into a straw-man. Sigh. Yes, your condescension does wind me up.

And now you make a threat, whereby if I respond to your condescension and misrepresentation (as far as I can see I was polite before you insulted me), you will run away. Sigh.

As I have said, it really would be interesting if you could present a complete description of a binocular based on objective measurements.

I found the following on your Bray web site: "Russian optics have long been acclaimed to be amongst the finest in the world." Interesting.

kabsetz

Wednesday 9th January 2008, 09:44

[Kimmo, I wish what you summarized earlier really was what Andy has been saying, but I think not. First of all, I agree with it.
Elk,]

As you know, I always try to read what people mean as well as what they write ;)

Now I'll get back to topic and by-pass the flaming emotions in the few posts above (Leif and Andy, please calm down and give one another some grudging respect. For what it is worth, I have found plenty to agree with in Leif's posts as well, and don't think Andy always gives them a fair and balanced reading).

One of the problems when discussing sweet spots in binoculars is that due to simple physiology as well as viewing habits and tasks in birding, what happens in the eye-optics interplay is different from what happens when viewing with a telescope. The latter is on a stand, and since only one eye is used, the viewer has relative ease and freedom with aligning his/her eye to the exit pupil/s being used. So, without even thinking about it, we move our head as well as our eye relative to the eyepiece a little when we look off axis. When we use binoculars, we need to keep both eyes aligned on their respective exit pupils, with two eyepiece barrels to fit against our facial features while hand-holding the whole apparatus with our sadly shaky hands. An additional variable comes from the objects being viewed. In astronomy and surveying, the objects are stationary or move predictably and slowly. In birding, the objects can be stationary, move predictably and slowly, move predictably and quickly, move unpredictably and quickly; there can be many of them at the same time, some of them stationary and some moving etc. Situations differ, and so do people's ways of optimizing their own actions to the situation at hand. When (and how successfully) do we re-center the object in the field, how far off-center do we allow it to go before we re-center, how far off-axis do we let our eyes follow the object in the field? And how is all of this influenced by the way our optics have trained us, and how easy is it to re-learn perhaps different optimization habits that may suit our new binocular better?

I have no doubt that test bench methods are necessary and, further, I have no doubt that they are better and more reliable for determining the performance of optics than the human eye. Furthermore, I trust that (when sufficiently comprehensive) they can accurately predict how the eye will resolve the axial image. I would buy an astronomical telescope simply on the basis of its specs, at least if these included a trustworthy lab report of its total wavefront error. I'm less sure that test bench methods can (yet) accurately predict how the eye will resolve off-axis images in situations where the eye is allowed optimum positioning with respect to the off-axis exit pupil in question. Thus, I might not buy an eyepiece based on specs alone, without trying it out first. And finally, I seriously doubt (although I would be happy to be proven wrong) that anybody has yet been able to device a test-bench procedure which accurately models what happens -- even just on the mathematical optical terms -- with the two optical barrels-two eyes-two hands system when trying to i.d. multiple moving targets simultaneously. So, even if the quality consistency issue were not there, I would not buy a pair of binoculars without trying them first. Not even if it came with a lab report that included photographic evidence of its off-axis image quality.

The kind of testing that binocular manufacturers would maybe need to do (and perhaps some have already done) is to use a technology similar to what has been utilized in Canon SLR's where a sensor detects where the user is looking in the viewfinder and determines the focus spot and exposure accordingly. Equipping a sufficiently large number of birders with binoculars that can record their eye-movements and tracking their viewing behavior in real birding situations or very well simulated test situations would shed light on the parameters needed for a truly satisfying view. If such a test would be carried out, I will volunteer as a subject.

Kimmo

iporali

Wednesday 9th January 2008, 12:02

Leif said: In other words, careful observers can reach relatively consistent opinions on a particular instrument.

Andy said: So, let's just leave it with your faith in the opinion of others, and I'll stick to science.

I refer to wikipedia: http://en.wikipedia.org/wiki/Descriptive_science and say that Kimmo's, Henry's, Leif's, Ed's, Alexis' etc. etc. descriptive "opinions" have been extremely valuable for me - and I believe for many others. However, I eagerly look forward to what additional information possibly upcoming scientific measurements will bring us.

Ilkka :t:

Leif

Wednesday 9th January 2008, 13:43

Firstly thanks to Kimmo and Ilkka for constructive comments.

Andy/Chris: I have an issue with being characterised as an anti-scientific Mystic Meg figure. Hence Post 121 which in which I present an unfair and insulting characterisation of you. You could simply have said "I disagree, I think measurement can give a complete description" and have left out the put down. But you have to make it personal.

I looked at the other thread on binocular magnification, and clearly you know a lot that is new to many of us here. I do not claim to understand details of that thread, as I did not have the time to read in depth the postings. But I do have some understanding of basic classical optics, as do many here, and the sort of tests that can be applied, such as a Foucault test. 25 years ago I did a Foucault test on a spherical primary mirror from a 5" Maksutov-Cassegrain scope I owned (made by a UK company, and used on a German equatorial mount that I machined using SKF roller bearings, duralumin housings etc) and discovered to my disappointment that it had a turned down edge. I doubt that observation would have told me the underlying reason for the crummy image quality. Such quantititative assessments of an optical instruments performance is nothing new to me, and clearly in many respects measurement far exceeds observation.

I won't go into details of my position as I have already done so. And I have no problem with you saying "I disagree" or "Well I think you are mistaken". You could even present measurements relating to a binocular which support your case, if you have some. But please leave out the personal stuff. Or was your intention to purposefully wind me up, given that you knew who I was, but I did not know who you were, and did not expect belittlement.

Anyway, I have said enough here, and will bow out of this discussion.

andytyle

Wednesday 9th January 2008, 17:22

Leif

Wednesday 9th January 2008, 19:43

Quote: 'So you are Chris Garvey, hiding behind a pseudonym. And yet you attacked me, quite aggressively some years ago, for using what you thought was not a real name as my userid. Sigh. It took me a long while to realise who you were, and it had to be pointed out to me by someone else.'

I have already said there is no hiding behind anything. My avatar name (as some already know) is a mark of respect for someone who is no longer with us, so it is immature and insulting to claim it is a hiding place.

I find it hard to know how to respond as you seem to have double standards.

'I have never discounted the fact that sample variation exists. 30 years ago, a friend of the family, a professional photographer, used to take home a collection of lenses from his local dealer, and return the best. That way he could cherry pick the best. He, like my father, was trained as an optical technician by a precision optics manufacturer. You like to mis-represent my views.'

Contrary to your point above, you were indeed vocal in your disbelief about inconsistency.

You misrepresent my views. You argued that sample variation within a given model of binocular was so great that there was no point in comparing different makes and models of binoculars. I disagreed with that, and I still do.

So annoyed were you that your narrow views were questioned that you even sent a private email to me telling to "go and f**k myself". That, to me was a clear indicator of your character, and hence I no longer wished to be part of a discussion or forum where such people held sway. Nothing worthwhile is ever gained from such places.

I had found your manner rather aggressive and hard to deal with, as you were continually responding with put downs, and eventually I just replied in what I thought at the time was an appropriate manner. I still find you hard to deal with.

No, I did not know who you were this time, but after a while your character shone through again and it became clear.

And yet I am posting under the same user name as before, whereas you are using a false one. I had no idea that you were Chris Garvey until very recently when someone else alerted me to the fact, after I responded to you in a rude manner. I was doubtful at first, but when I thought about it, it made sense given the same writing style.

You knew who I was from the start.

Please do not attempt to suggest that I will 'run away' because of any merit in your words. Sometimes, like leaving a noisy child in a room, you have to escape tantrums to find a place with some order and sense again. If I want to study a book I go to a library. If I find shouting teenagers there, then there is little point in being there. Flogging a dead horse is never worthwhile.
I have been asked privately by some on this forum to enter discussions via private email regarding optical topics. They too prefer not to post very often as they too tire of the sort of posts that I have experienced from you. Perhaps it is best this way, I can be free of this ridiculous bleating. I have no doubt it will occur again on future topics. I will leave Leif to his "sighing".

There is not much I can say in response to the above which I find rather offensive. I presume that was the intention.

But I am surprised that some people here do "prefer not to post very often as they too tire of the sort of posts that I have experienced from you" because I rarely post to the birding optics forums these days, apart from in the last week or two.

Still, if I do upset other forum users, as you say, then perhaps they should post to this thread an explanation of why I annoy them so much they prefer not to post. I have checked my recent posts to other threads, and they look rather innocuous to me.

andytyle

P.S. I have no control over what is written on Bray website. I left Bray in 2004 to begin my own business. Changes have been made since then, I do not know what or by whom, nor do I care. However, I do know, as I have been told, that they still use my name on their site, presumably to attract sales. I can't think of another reason why.

Probably because you wrote useful information while in their employment, and rather than waste time rewriting it, they simply retained it and kept your name by it for reasons of courtesy.

I do not know if you are familiar with the reviews of Holger Merlitz:

http://www.holgermerlitz.de/dialyt10x40.html

They are user reviews, done in a methodical manner, and contain a mix of opinion and simple measurements, and I consider them very useful. If you can do better, then fine, go ahead, and show me how it should be done. I look forward to reading your writing.

Leif

Wednesday 9th January 2008, 20:08

Surveyor

Wednesday 9th January 2008, 21:53

It occurred to me that people who "prefer not to post very often as they too tire of the sort of posts that I have experienced from you" might prefer to remain anonymous. In which case they could perhaps contact a moderator and explain why they find me so annoying. The moderator might then be kind enough to post the explanations to this thread, but without attribution. Hopefully moderators would not mind, though I have not asked them.

Hi Leif;
I am at least one of the people that emailed Andy in response to his question if his presence annoyed me. I did so by email because I do not think this is appropriate for forum discussion. My email was:

Hi Andy;
I just viewed the comments. For what it is worth, I actively seek out your posts, even in the portions I do not usually follow.

I really enjoyed the give and take between you and Elk, but will be the first to admit that some of the points bandied about were way over my head.

One of the reasons I joined the forum was to learn more objective ways to evaluate binoculars. I really do not care if it is a test bench procedure or more informal way of evaluation, as long as it is repeatable. I do not like to see 10 different descriptions of a color cast or some other metric. If there is some way 10 people can look at the same instrument and see the same thing then I consider that result acceptable. I always like industry standard lab testing when available or if I can afford it.

Just to give some idea of how compulsive I am. When in the Navy in the early 60's, I was on a Navy competition pistol team. I spend more hours than I care to remember polishing, burnishing and fitting barrels to my frame trying to get perfect, uniform consistency with no slop in the action. I also am very good with analog electronics, during the 70's and early 80's I had about a dozen commercial stations where I was chief engineer and my hobby was working ham radio contests. I bought the best radio available and the first thing I did was take it down and do a proof of performance to verify its suitability, then immediately started a competition tune up using spectrum analyzers, noise bridges and other advanced equipment to get the noise figure down as low as possible, set the IF frequencies for the best filter response curves, adjusted components and tweaked/padded trimmers for the best Inter Mod distortion figures I could get. Won or placed well in many contests with that Icom 781.

As a kid, messed with racing go carts and later sports cars, you know what kind of tuning you can do on a stock vehicle and the improved performance to be gained.

Helped a friend with a archery pro shop and shot competition archery for some years and was always trading limbs, adjusting tiller, adjusting stabilizer and wheel timing, experimenting with knock points etc. trying to find perfect performance.

I could go on and on. In short, anyone who uses any equipment seriously is always looking for the perfect performing equipment, if for no other reason than to help cover his own mistakes.

Lets face it, if someone made a car that would go 0-60 in 1 second, be stable at 250 mph and got 100 mpg with a lifetime warranty, they would sell some regardless of the price.

If I knew of a way to fine tune a binocular, I probably would have already tried it.

In short I am always looking for optimum, if not perfect, performance even if I can not physically use all of it. Any competitor will try to get whatever minor edge he can and even birding can be considered a competition. You are trying to ID or even find a bird in the shortest possible time frame.

You are experiencing one of the reasons I do not post more often than I do. It does not matter how simple a point you try to make, there is always some question and it just takes to much time and studying so you do not mislead others. I am getting to old to want to study for others when I really want to improve my understanding.

I hope you keep posting but if you decide against it for whatever reason, feel free to contact me at any time.

Leif

Wednesday 9th January 2008, 22:46

Surveyer

I have absolutely no idea who you are, and as far as I am aware I have never responded to one of your postings, but please give me some examples of postings where I have annoyed YOU, since that is the claim being made.

So are you really saying that in the past you have refrained from posting on this forum because of me?

I suggest that you check out my recent posts, in other threads, and explain which ones offend you. Most of my posts have been in the Fungi forum, as mycology and nature photography is my key interest.

You said to Chris Garvey:

"You are experiencing one of the reasons I do not post more often than I do. It does not matter how simple a point you try to make, there is always some question and it just takes to much time and studying so you do not mislead others. I am getting to old to want to study for others when I really want to improve my understanding."

I do not understand how that relates to my posts. I tried to make the point that IMO calculations and/or objective measurements are not sufficient to describe a binocular from the users point of view. That is nothing new. Nor is it profound. In fact numerous people in this thread, including someone who works for a major optics manufacturer, have expressed a similar idea, though not in exactly the same words. And yet Chris Garvey has repeatedly tried to ridicule me with put downs. I do not accept his argument as I think he is plain wrong. But he does not agree, and that is fine by me. But I do not like being patronised. The fact that he refers to me as preferring opinion to science is offensive to me given that I spent 8 years working in physics research in universities in this country and North America. I know full well what the scientific method is, and do not need talking down to by someone who probably has no research experience, and talks to me in a rather condescending manner, with black and white arguments.

Perhaps you should go back in this thread, and read posts from people other than Chris and me, and reach a conclusion as to whether or not I am talking nonsense. I am sure Chris does know a lot, but he is wrong on this issue, and he needs to learn how to disagree without resorting to insults. I spent much of today arguing with two colleague about a work issue, and the argument was very productive, and fruitful, with no insults, just disagreement, discussion, and a sharing of ideas. We each had different viewpoints which came together into one more powerful viewpoint. Not once was I ridiculed.

Sorry but if you and others think that this forum is for Chris Garvey to express himself, that he is 100% correct, and that I must not disagree with him, or that I must keep quiet when I am ridiculed by him, then I suggest that you think again.

Anyway, I appreciate your openness. :)

Leif

Surveyor

Wednesday 9th January 2008, 23:04

Hello Leif;

I was responding to Andy's question about what Kimmo, Henry and I thought, I think. Please re-read my email. Nowhere were you even mentioned.

Ron

I was responding that I think Andy's posts are beneficial and disrespecting no one.

APSmith

Thursday 10th January 2008, 00:54

One has to wonder: If/when fuss-fights like these occur at places like Zeiss, Swarovski, Leica, or Nikon, do they compromise product development? Could human pride be the main reason that alpha-bins don't have larger sweet-spots than they do?

On the other hand, pride likely drives alot of technological development.

Just a thought - hopefully to lighten things up ... I'd like to learn more about this topic, so that I'll know if there's ever a chance that a roof bin will ever be produced which can outperform the Nikon EII.

andytyle

Thursday 10th January 2008, 03:00

Leif

When faced with someone with such narrow views, someone who will twist and turn and distort what is said, and accuses others of doing the very thing he is guilty of then there is little point of continuing discussion with such people. Regardless of what answer I give to your rantings, I have no doubt you will answer again and again with more distortions. Anyone with any sense will read the postings in this thread and come to a conclusion of their own. I have and will continue to hold my views on geometrical optics, the truth is there in virtually any text book on geometrical optics.
I made an assertion in another thread about the nature of these public forums, and the type of characters they can attract. Unfortunately, those that join because they wish to learn or share in discussions to gain insight, are, unfortunately and unknowingly, doomed to listen to a fair amount of nonsense from one or two that haunt these forums.
I realise (from the number of postings made on this forum) that this activity is probably a major part of your life, and your loud and somewhat panicky defensive posture to myself and Ron is perhaps thus expected. That said, I cannot continue conversing with such as you. On the last occasion a few years ago, you were the instigator of personal abuse when my views did not suit you. This time the same. Saying I prefer science whilst you prefer opinion is not insulting.....it is what you have said repeatedly. You know exactly what I meant - I prefer measurement - the scientific method of repeatable and testable proceedings, you prefer the opinions of those you trust. That is what was meant, as well you know, and I repeat it here - you stick to what you prefer...the opinion of others, and I'll stick to what I trust - scientific measurement methods. Is this reason enough to begin the personal abuse aimed at me and all the pathetic digging around for mud to sling, when there isn't any? I am simply confirming your own preferences.
I don't really have anymore to add. Your post #131 is the same emotional ravings, not worth answering. I agree with Ron here, the 'sensible room' is to be found by emailing info privately. That is what I will do. Those that wish to join in may of course do so.

andytyle

P.S. On the subject of variation of models, my view is still the same. In order to confirm whether binocular X is better than binocular Y you first need to establish whether all examples of X are the same, and whether all examples of Y are the same. This is more important, because this needs to be done first. Because the top brands are close to each other in performance, there is often more meaningful variation in quality within a model than is meaningful to talk about between models. Not always but often. Having sold and demonstrated a great many binoculars, it is something that I know from experience, and even something that I know one or two dealers have used (unethically) to sell one product in place of another. It is a question of order, you need to walk before you can run. I'm sorry you didn't/don't agree, but not really worth personal abuse is it?

elkcub

Thursday 10th January 2008, 03:18

...

I refer to wikipedia: http://en.wikipedia.org/wiki/Descriptive_science and say that Kimmo's, Henry's, Leif's, Ed's, Alexis' etc. etc. descriptive "opinions" have been extremely valuable for me - and I believe for many others. However, I eagerly look forward to what additional information possibly upcoming scientific measurements will bring us.

Ilkka :t:

Hi Ilkka,

I'm glad you picked up on this, since more thought should be given to what is and what is not science. Having been a senior scientist for the 15 yrs. preceding my retirement (from NASA), I still feel inadequate knowing that I was not a real "rocket scientist." Still, I'd like to express some thoughts on the subject, hopefully, without boring everyone to tears.

Science is essentially the business of finding new facts and relationships. Engineering is the business of applying these facts and relationships. "Research" is the process of science; and "Development" is the process of engineering. "Re"-search is a pretty good descriptor of how things happen, since, as a rule, "searching" is never-ending. "Develop"-ment carries an implication for product growth and refinement.

It is extremely rare that science produces an immutable fact, since every finding can be improved upon through further research. Nonetheless, development engineers routinely take research findings to be immutable facts and build products based upon them. The distinction is easy to lose sight of, particularly for those trained in different technical fields. Assumed facts, after all, are the hand-holds for the development process.

In the earlier discussion Leif and I had with Andytyle, several assertions were made about "science" or "facts," which, trying to be delicate, were provocative. One aspect of my background is psychophysics, a scientific branch of sensory psychology (see below). When the question on the table is whether or not humans can perceive some level of refractive error in a visual stimulus, it is inherently a psychophysical question to be addressed by psychophysical methods. However, to the optical engineer it may be perfectly acceptable to assume, as a fact, that the human can perceive (or be behaviorally influenced by) any level of refractive error no matter how small. If the engineer convinces himself that this is truly the case, without scientific evidence to prove it, then the working assumption also becomes a strongly held opinion — and there is no such animal as a non-subjective opinion. I say this with no disrespect, but that circumstance does constrain the nature or extent of the discussion, as it did in this case.

As is all too common, I have found, there was not even a modicum of interest in 20 years or more of excellent psychophysics research done on this subject. Since I understand the methods but not the implications, I was hopeful at first that someone more familiar with wave optics might provide insights I don't have, and we could puzzle out the significance together. So, Ilkka, in response to your statement "... However, I eagerly look forward to what additional information possibly upcoming scientific measurements will bring ..." I would say the information would need to be extracted in a less argumentative, more cooperative, interdisciplinary atmosphere than BF or CN.

Scientific method is applied to understanding all aspects of human behavior, including opinions, communications, perceptions, decisions, and much more. An early sub-domain of psychophysics involves introspection, which comes very close to what is found on BF in several instances. Henry Link is one of the best natural introspectionist I've found, and his findings often correspond to what has been studied more systematically using other laboratory methods. (I dub him to be a closet behavioral scientist ;)) Kimmo and Holger Merlitz clearly use survey methods that correspond with good scientific practice, and Kimmo is also a worthy introspectionist in his own right.

An important point to note here is that science demands transparency and verification. It is a public process. Sharing of observations, therefore, although not scientific in and of itself, is consistent with its higher principles. I have no doubt that forum participants can abstract consistent and useful information from what is reviewed and discussed. Since such "information" generally reduces uncertainty within the user community, it clearly has its advantages. Leif, good fellow! You got it right, IMO. :t:

Well, I've yammered enough, but it's been agreeably cathartic under the circumstances. I hope to have offended no one — particularly Andytyle whose contributions have added a new dimension.

Elk/Ed/Elkcub (whatever)

http://en.wikipedia.org/wiki/Psychophysics

Pinewood

Thursday 10th January 2008, 03:24

... I'd like to learn more about this topic, so that I'll know if there's ever a chance that a roof bin will ever be produced which can outperform the Nikon EII.

Probably not. A comparable roof prism binocular would still lack a reasonable price and it would be oversized compared to most roof prism glasses. I think in the 8x32 class, Zeiss has the widest field which design compromises make practical.

Happy bird watching,
Arthur :brains:

Leif

Thursday 10th January 2008, 09:07

Elk/Ed/Elkcub

IMO your post contains some interesting thoughts, and some generous comments about both Chris/Andy and myself.

As I have said, Andy/Chris no doubt has significant experience of testing high end instruments which he can share on this forum to everyone's benefit. But my request to him is to disagree when he sees fit, but not to ridicule the other person, or categorise them as ignorant, or anti-science, or whatever. He might be right, or he might be wrong, or it might be two views of the same thing. Anyway, if I had known AndyTyle was Chris Garvey, I would have avoided responding to his posts, for everyones sakes.

I do object to being talked down to, and it is best if I do not respond to the most recent post from Chris/Andy.

Leif

Thursday 10th January 2008, 09:08

kabsetz

Thursday 10th January 2008, 10:32

Surveyor

Thursday 10th January 2008, 13:40

Elk/Ed/Elkcub,

Just to say that I greatly appreciate your post #135. Thanks for taking the time to express your thoughts so well. If all of this discussion were to take place through private e-mails rather than public forums, postings like this would reach all too few readers.

Kimmo

Good morning Kimmo;

I guess I should clarify somewhat. If I have a specific question of a specific individual, then I prefer to handle by email so the discussion stays on point.

Threads have a life of their own and can take many unforeseen directions.

If it is a general question or answer, then I agree with you completely.

Have a good day
Ron

henry link

Thursday 10th January 2008, 20:16

Henry Link...natural introspectionist...

Has a nice ring to it...I like it!!

Leif

Thursday 10th January 2008, 20:45

I also find Ed's post very interesting. I know little about his field of work, my experience being hard science (and more recently, engineering).

I worked for some years in physics research, doing what is sometimes termed 'hard science'. This involved quantum mechanical calculations of the properties of solid matter, such as silicon, or carbon. The answers were invariably extremely precise, though the systems modeled had to be very simple, and many assumptions were made in order to make the calculations tractable. Precision is often a characteristic of physics, some measurements being accurate to incredibly small fractions of a metre, or an electron volt, or whatever unit is in use.

Physics studies an idealised world, removing the unrepeatable, and the uncontrolled, in order to study the underlying order. Only then can we discover new laws, that were previously hidden by extraneous complications. Classical (and quantum) optics are no different. Not unsurprisingly many physicists have a degree of disdain for softer less precise subjects. After all, they spend their entire professional lives trying to eliminate the 'human' - or animate - from their work. They also spend their entire lives idealising the world, and reducing it to a simplified model. There is an old joke about physics, which I forget, but it involves a group of scientists who study a herd of cows, and the physicist begins his analysis with "Let's consider a field of perfectly spherical cows ...".

IMO it is not surprising that psychology and perception are ignored by most of the physics community. These subjects belong to quite different realms of knowledge and require quite different skills, and tools to study. The physicists aversion to dealing with such concerns can be seen as rational and sensible. They are hard to study using the physicists usual tools, and subjects such as psychology rarely render themselves to precise answers. Softer more human aspects, such as perception are usually left to others, in for example the biological sciences, as well as biophysics. That is not to say that they have less value, just that they are different fields of study.