Sweet-spot assessment. (1 Viewer)

Cluster · Sep 3, 2014

Perhaps a naive question, but how does one assess the scope of a sweet-spot?

My expectation is that, if I were to finely focus on a detailed object in the centre of my view, sharpness and detail would remain as I panned the binocular to the point that I detected a loss in detail/sharpness. That would be the limit of my sweet-spot. I suspect that for some, it is allowed to refocus, so that the point at which good focus cannot be achieved is the limit of their sweet-spot.
For most of the binoculars I have tried, critical sharpness is lost pretty quickly as the original centre is panned across the field. Most seem to loose detail to the effects of CA first.

Is there an accepted standard for this?

Dave

WJC · Sep 4, 2014

Cluster said:
Perhaps a naive question, but how does one assess the scope of a sweet-spot?

My expectation is that, if I were to finely focus on a detailed object in the centre of my view, sharpness and detail would remain as I panned the binocular to the point that I detected a loss in detail/sharpness. That would be the limit of my sweet-spot. I suspect that for some, it is allowed to refocus, so that the point at which good focus cannot be achieved is the limit of their sweet-spot.
For most of the binoculars I have tried, critical sharpness is lost pretty quickly as the original centre is panned across the field. Most seem to loose detail to the effects of CA first.

Is there an accepted standard for this?

Dave

I posted a how to do that pseudo-scientifically within the last week. I don't remember which post but it's out there.

Bill

elkcub · Sep 4, 2014

Hello Cluster,

With regard to assessing "sweet spots" one could do no better than to read THIS OLD THREAD. (Sorry Bill, I didn't see you there.)

Several of us contributed to it, and I'm reminded that there was a time when I was actually polite, if not verbose. It's worth reading. Note that Stephen Ingraham discusses how they did it at Zeiss (post #19), and I'll bet do so today.

Feel free to ask about anything that's unclear.

Ed

james holdsworth · Sep 4, 2014

Seems a very personal thing - with every bin I have ever tried, I can detect a visible [but slight] falloff in sharpness just outside of the ''super-sweetspot'' [a tiny central area of perfect [or best] sharpness].

In some models, this sharpness returns as you move outward - not usually at the edge but somewhere near maybe 70% out. Many others see nothing like this at all.

ceasar · Sep 4, 2014

I shall not today attempt further to define that kind of view in a binocular which I understand to be embraced within that shorthand description ["Sweet Spot"]; and perhaps I could never succeed in intelligibly doing so. But I know it when I see it!

Hope this helps! :king:

P. Stewart

ronh · Sep 4, 2014

"Perhaps a naive question, but how does one assess the scope of a sweet-spot?"

Perhaps a naive answer, but you look through and determine if the sweet spot looks large or small.

It is impossible to quantify in a meaningful way however, because most binoculars have a good bit of field curvature among other things, and field curvature is well tolerated by young and accommodative eyes but not by old and unfocusable ones like mine.

I have a 7x50 Fujinon FMT-SX whose field aberration is almost purely curvature, and a healthy dollop at that, about 3 diopters from center to edge. Young observers describe this model as sharp to the edge. To me who at age 63 must strain to accommodate my eyes even one diopter, it's about a 50 percenter.

Ron

typo · Sep 4, 2014

Dave,

I think you've already got some sense of the difficulties involved. Keeping it simple there are two things that contribute to fuzzy edges of the view.

The first is field curvature, as mentioned, where the periphery simply focusses at a closer point than the middle. How much of the view is sharp will depend partly on the focal accommodation of your eyes, which gets worse as we get older, so the sweet spot at a given distance gets smaller. It also changes with light level. As the pupil of you eye constricts and dilates the depth of focus changes. The sweet spot is bigger in bright conditions. So age and light levels can easily contribute to totally different judgements. Unless someone specifies their near sight correction and light levels at the time it probably doesn't mean much.

The second type is the various aberrations that normally increase towards the edges and produce a blur that cannot be focused out. Quite where you precisely draw the line as the edge of sharp focus will be affected a little by acuity accommodation, light levels and relative distance from the centre.

Field curvature is a deliberate design feature of some very high quality binoculars and may be favoured by users for various uses. For me it's where the aberration blur kicks in that's more important.

Having said all that it's never easy to come up with a satisfactory description, particularly when looking at a bino in isolation. I usually resort to high, low or flat to describe field curvature and some vague judgement on distance from the centre where the unfocusable blur kicks in. I'd welcome a better suggestion.

David

Cluster · Sep 4, 2014

Thank you all for your responses...

elkcub said:
Hello Cluster,

With regard to assessing "sweet spots" one could do no better than to read THIS OLD THREAD. (Sorry Bill, I didn't see you there.)

Several of us contributed to it, and I'm reminded that there was a time when I was actually polite, if not verbose. It's worth reading. Note that Stephen Ingraham discusses how they did it at Zeiss (post #19), and I'll bet do so today.

Feel free to ask about anything that's unclear.

Ed

It's all in here......Thanks for the link. I guess that my interpretation is as per the Zeiss way..... but, I hadn't even thought about how my eyes might allow more or less accommodation of a curved field.

Dave

typo · Sep 4, 2014

Cluster said:
Thank you all for your responses...

It's all in here......Thanks for the link. I guess that my interpretation is as per the Zeiss way..... but, I hadn't even thought about how my eyes might allow more or less accommodation of a curved field.

Dave

Dave I didn't wade though the whole thread but I suspect the Zeiss way is very small apertures and large DOF. Fiddle about with f-number and you would get a totally different answer.

David

SteveTS · Sep 4, 2014

Cluster said:
I hadn't even thought about how my eyes might allow more or less accommodation of a curved field.

I hadn't thought about this either until I looked at a budget 8x56 bino for a friend.

My view was that it had a small sweet spot with a very high degree of peripheral field curvature ; younger eyes saw it differently !

Kammerdiner · Sep 4, 2014

ceasar said:
I shall not today attempt further to define that kind of view in a binocular which I understand to be embraced within that shorthand description ["Sweet Spot"]; and perhaps I could never succeed in intelligibly doing so. But I know it when I see it!

Hope this helps! :king:

P. Stewart

:-O

Having just perused the thread Ed mentioned above, I think I'm in your camp on this one. Yikes what a thread that was! :eek!:

I've concluded my accommodation is just about zero, which may partially explain why I gravitate to flat field binoculars.

And how, in the other thread, Ingraham (Zeiss) could argue that something like the 8x32 FL does not have a small sweet spot is quite beyond me, that's for sure.

Mark

OPTIC_NUT · Sep 4, 2014

james holdsworth said:
Seems a very personal thing - with every bin I have ever tried, I can detect a visible [but slight] falloff in sharpness just outside of the ''super-sweetspot'' [a tiny central area of perfect [or best] sharpness].

In some models, this sharpness returns as you move outward - not usually at the edge but somewhere near maybe 70% out. Many others see nothing like this at all.

For me, the 'super-sweetspot' seems to have an uncanny depth/3D effect.
Then there is 'sharp', and then 'usable detail'.
I'd call the edge of 'sharp' (but not super) the edge of the sweet spot.
Many fast-focusing binoculars make it hard to attain the 'super' point,
since it takes a while to see it snap into best focus. You might miss it
and strain the eyes so it fades after a while.

The edge of 'sharp' might vary person-to-person, but since good binocs
peak out well past human acuity, by the time you see things lose sharpness,
someone else is probably not far behind. There is already momentum to the
defocusing.

I prefer a field that smoothly loses focus to the tweaked 'fuzzy donut'
or 'sharp donut' (same thing a tiny focus away) design. If someone is
always searching they would pferer the extra usable field..

The biggest problem in figuring 'sweet spot' is 'staring':
that is, flexible eyes will end up focusing themselves to a spot
in the field if you concentrate on it, and that's not the same
as seeing the whole scene clearly. So...as folks go from single
to double vision to trifocal.... the 'apparent' sweet spot would shrink.

brocknroller · Sep 4, 2014

elkcub said:
Hello Cluster,

With regard to assessing "sweet spots" one could do no better than to read THIS OLD THREAD. (Sorry Bill, I didn't see you there.)

Several of us contributed to it, and I'm reminded that there was a time when I was actually polite, if not verbose. It's worth reading. Note that Stephen Ingraham discusses how they did it at Zeiss (post #19), and I'll bet do so today.

Feel free to ask about anything that's unclear.

Ed

Well, I'm glad you didn't say it was another "rhetorical question."

Ah, yes, I remember Ingraham's "zone of critical sharpness." He used that term on his now defunct website, zbirding. The selling point being that despite the FLs getting criticized for being fuzzy at the edges, that in a bench test using a "collimating lens" showed that the FL's "zone of critical sharpness" was actually bigger than the competitors, which just looked wider because they had a wider "zone of unacceptable sharpness."

The problem with this is that other than a few so called "static birders" among us (whom I avoid in the field for fear of being zapped by static electricity), most birders pan with their bins, and when they pan, their eyes dart ahead toward the edge and into the "zone of unkowningness"* where you can't tell what you're looking at because the image at edges are so blurry. *© 2014 by brocknroller productions, LLC

I like Ingraham, he was my mentor when it came to learning about birding bins and purchasing birding bins early on when he had BVD, but to me, this is Kennebunk. If I can still a bird at the edge of the field well enough to tell that it's a bird even if I can't ID the species clearly, I'd still rather have that than a steep fall off in sharpness like the FL's alleged have (depending on who you talk to) and that other bins I've owned have had. What really makes it bunk is that he goes on to say that stretching the image farther than Zeiss stretches the "ZOCS" means that the resolution in the centerfield will be compromised.

Ingraham, who once touted the 8x32 SE as "best in class" and as the overall reference standard, should know better. When I read this, I realized that he had become a "company man," and that I could no longer rely on him for non-biased advice about optics. (to be fair, I would sell out in a heartbeat, myself, and tout whatever optical philosophy Nikon wanted me to spout if they hired me, paid me well, and flew me around the world to birding hot spots!).

Robert / Seattle is spooky looking. He reminds me of Edgar Allan Poe

e.e. lemmings

Pileatus · Sep 4, 2014

Cluster said:
Perhaps a naive question, but how does one assess the scope of a sweet-spot?

My expectation is that, if I were to finely focus on a detailed object in the centre of my view, sharpness and detail would remain as I panned the binocular to the point that I detected a loss in detail/sharpness. That would be the limit of my sweet-spot. I suspect that for some, it is allowed to refocus, so that the point at which good focus cannot be achieved is the limit of their sweet-spot.
For most of the binoculars I have tried, critical sharpness is lost pretty quickly as the original centre is panned across the field. Most seem to loose detail to the effects of CA first.

Is there an accepted standard for this?

Dave

The only valid assessment is to judge for yourself...by looking through the instrument. The list of visual variables external to the bin is extensive. Individual eyes vary considerably, eyeglasses distort, lighting enhances/intrudes, IPD's and diopters are poorly adjusted and the aging process inhibits accommodation. Last, but not least, is familiarity. Use something long enough and you may learn to ignore its deficiencies. Conversely, the great view you saw in the store may not last as soft edges begin to intrude on your landscape. Thankfully, there is a way out of the maze.

When enough people tell you they see a flat field, a sharp field, a soft edge or any other interesting quality you can bet they're on to something. I've been using my 8.5X42 & 8X32 Swarovisions, 8X32 SE, and ED82 scope (30X and 50X DS eyepieces) on the stars and I can attest that, to my aging eyes, the Swarovisions are flat field, the ED82 is flat AND my beloved SE has the most amount of edge distortion of the lot. There are hundreds of SE posts claiming edge-to-edge blah blah blah but it's not true, something Henry stated long ago. When I see pinpoint stars in the entire FOV of my ED82 or Swarovision I know I'm on to something and truly thankful I don't have to "focus out the soft edges" or adjust position just so I can "look around" the field. The ED82 focus is far too sensitive and a real pain to readjust! Thankfully, I don't have to.

Believe it or not, when it comes to optics, I trust the majority of reviews to be honest, personal revelations. The FL did have soft(er) edges...when compared against its magnificent centerfield. I mentioned this early on and was accused of working for...Nikon. Several reviews later others saw and reported the same thing. Zeiss commented and is now preparing to release a flat field SF binocular. Happy FL owners probably wonder why.

As Steve Ingraham so eloquently stated in his 8X32 SE review, "Finally, I just like these binoculars. Liking goes beyond rational comparison, or an assessment of the various features, strengths and weakness, of any binoculars. Some glasses you just like better than others." Thanks again, Steve, for recommending the SE. It's truly an old friend.
http://betterviewdesired.com/Stephen-Ingraham.php
http://betterviewdesired.com/Nikon-Superior-E-8x32.php

elkcub · Sep 5, 2014

Pileatus said:
The only valid assessment is to judge for yourself...by looking through the instrument. The list of visual variables external to the bin is extensive. Individual eyes vary considerably, eyeglasses distort, lighting enhances/intrudes, IPD's and diopters are poorly adjusted and the aging process inhibits accommodation. Last, but not least, is familiarity. Use something long enough and you may learn to ignore its deficiencies. Conversely, the great view you saw in the store may not last as soft edges begin to intrude on your landscape. Thankfully, there is a way out of the maze.

When enough people tell you they see a flat field, a sharp field, a soft edge or any other interesting quality you can bet they're on to something. I've been using my 8.5X42 & 8X32 Swarovisions, 8X32 SE, and ED82 scope (30X and 50X DS eyepieces) on the stars and I can attest that, to my aging eyes, the Swarovisions are flat field, the ED82 is flat AND my beloved SE has the most amount of edge distortion of the lot. There are hundreds of SE posts claiming edge-to-edge blah blah blah but it's not true, something Henry stated long ago. When I see pinpoint stars in the entire FOV of my ED82 or Swarovision I know I'm on to something and truly thankful I don't have to "focus out the soft edges" or adjust position just so I can "look around" the field. The ED82 focus is far too sensitive and a real pain to readjust! Thankfully, I don't have to.

Believe it or not, when it comes to optics, I trust the majority of reviews to be honest, personal revelations. The FL did have soft(er) edges...when compared against its magnificent centerfield. I mentioned this early on and was accused of working for...Nikon. Several reviews later others saw and reported the same thing. Zeiss commented and is now preparing to release a flat field SF binocular. Happy FL owners probably wonder why.

As Steve Ingraham so eloquently stated in his 8X32 SE review, "Finally, I just like these binoculars. Liking goes beyond rational comparison, or an assessment of the various features, strengths and weakness, of any binoculars. Some glasses you just like better than others." Thanks again, Steve, for recommending the SE. It's truly an old friend.
http://betterviewdesired.com/Stephen-Ingraham.php
http://betterviewdesired.com/Nikon-Superior-E-8x32.php

Although I try not to take issue with someone's preferences, I would point out that your primary justification for the SV's flat field is based on night sky observation. The is no question that under those conditions the human eye operates in an entirely different way than under photopic birding conditions, and, moreover, the viewing field at infinity is essentially flat. Birding tasks occur in a much more three dimensional and dynamic environment where relative distance judgments are essential for size estimation. As I see it, flat field optics distort those perceptions in an uncomfortable way.

Fortunately, my own preferences are less expensive to satisfy.

Ed

peatmoss · Sep 5, 2014

ronh said:
"Perhaps a naive question, but how does one assess the scope of a sweet-spot?"

Perhaps a naive answer, but you look through and determine if the sweet spot looks large or small.

It is impossible to quantify in a meaningful way however, because most binoculars have a good bit of field curvature among other things, and field curvature is well tolerated by young and accommodative eyes but not by old and unfocusable ones like mine.

I have a 7x50 Fujinon FMT-SX whose field aberration is almost purely curvature, and a healthy dollop at that, about 3 diopters from center to edge. Young observers describe this model as sharp to the edge. To me who at age 63 must strain to accommodate my eyes even one diopter, it's about a 50 percenter.

Ron

I know what you mean. As far as my middle-aged eyes are concerned, most binoculars' sweet spots are around 50%, give or take. Anytime I come across one thats 60% or more, I'm like "whoa, this is a big sweet spot".

Pileatus · Sep 5, 2014

elkcub said:
Although I try not to take issue with someone's preferences, I would point out that your primary justification for the SV's flat field is based on night sky observation. The is no question that under those conditions the human eye operates in an entirely different way than under photopic birding conditions, and, moreover, the viewing field at infinity is essentially flat. Birding tasks occur in a much more three dimensional and dynamic environment where relative distance judgments are essential for size estimation. As I see it, flat field optics distort those perceptions in an uncomfortable way.

Fortunately, my own preferences are less expensive to satisfy.

Ed

Night skies are absolutely unique when evaluating optics. However, extensive daytime use clearly demonstrates, to me, that the SV's are so-called "flat field" optics. To me they are far more pleasing than others I've considered, including the superb 8X42 SLC. I've adapted to whatever optical and mechanical limitations the SV's present and I'm quite happy as a result. I'll bet Swarovski had us both in mind when they developed these two excellent product lines!

PS
Plenty of blurry edges show up in night sky viewing, especially with binoculars. The SV's presentation is, to my eyes, superbly uniform across the entire FOV. In fact, the whole FOV is sweet.

brocknroller · Sep 5, 2014

peatmoss said:
I know what you mean. As far as my middle-aged eyes are concerned, most binoculars' sweet spots are around 50%, give or take. Anytime I come across one thats 60% or more, I'm like "whoa, this is a big sweet spot".

Peatmoss,

I "dig" we're your coming from.

I find field curvature more distracting than it used to be since I could accommodate it better when had a younger man's eyes.

I also noticed that I couldn't "set and forget" with low power IF EP bins any longer, but had to keep adjusting the diopters for different distances.

My focus accommodation gets worse in low light, so the "sweet spot" on a bin with field curvature shrinks in portion to decreasing light. In bright light, I have to move a bird to the edge to get it to blur with my EII. In dim light, I can see the blur off axis.

So now I use the EII on sunny days and the SE on cloudy days.

Brock

Sweet-spot assessment. (1 Viewer)

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Cluster

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WJC

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james holdsworth

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