Big fan of Porro prism . (1 Viewer)

Surveyor said:

Hi Bill, I thought I would take a whack at this while David gets his thoughts together since I used to do more of it in the past than anyone else on the forum.

The key to taking the eyes out of the equation is magnification. My visual acuity is pretty poor, about 90”, or about twice as bad as Kimmo and Henry. For instance if I expect a 7x bino to have about a 4” lp/mm I would need to use an auxiliary scope (booster) with at least 3.5x magnification to get to 24.5x total. This would allow, with my 90” acuity, to see about 3.7” of limiting resolution. I would choose a “booster” of higher magnification, ISO allows up to 45x, see attached excerpt from the ISO 14490-7 resolution specification.

Also note the picture of a test I did on a Zen Ray 7x36ED2 posted on the forum several years back. I think I reported at the time a resolution of 4”. Best I can remember now I was able to see group 7 element 1 very well but could not hardly see the vertical bars of element 2. I tried to take a picture of the result but have never been able to get a camera to focus well enough to get to the same point as I do with my eyes.

This is used to insure the bino meets the technical requirements and for comparing hardware to hardware. Optics metrics need to meet a certain level even if the average human may not be able to make full use of them. A bad resolution test usually indicates other aberrations in the system. The same reasoning for having standards for collimation, etc.

I think ISO 14133 sets out the limit of resolution. This protects consumers with no optics knowledge from buying a pair of Coke bottles joined together that would not make out a car at 50 meters. David (typo) has informed me there is a newer ISO standard out, but I do not have a copy of it.

An additional observation, with my acuity of about 90" a 10x bino would have to have a limiting resolution less than 9" to keep from limiting me. A person like Henry Link with an acuity of about 50" would need a limiting resolution of less than 5", very hard to do with objective in the 20-25 mm range.

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Hi Surveyor:

It seems there are TWO things afoot, here. First, is that MAGNIFICATION can dramatically aid in stating resolution. I will give anyone that. Still, I see this is splitting hairs with an ax. To me it is on the same level as those who say they have “collimated” their binocular when, in fact, they have only “conditionally” aligned it. It may serve a single user—or others with nearly the same IPD—EXCEPTIONALLY WELL—based on their range of spatial accommodation. But, is it clinically collimated? Without the use of a couple of very big IFs, it is not! From my standpoint, although human involvement is at a minimum it has not been eliminated. For PRACTICAL purposes it has been. But bino forums often seem to be places where non-existent or inconsequential problems are milked for all they are worth. Am I wrong?

Secondly, take my original statement in light of its intended audience, those who want or need to quantify EVERYTHING in terms of opto-mechanics with ZERO concerns for physiological considerations, which can’t be removed from the equation. Am I wrong? :cat:

On another topic: what part of Tennessee are you from?

Bill

WJC said:

Hi David:

As this is a very important point for me (in that I will be sharing with others), I would like you to explain how this can be done. I don't see how the "human factor" can be removed except through totally relying on computers and digital imaging. I guess what I'm asking is: What do you consider "a properly executed resolution test"? In addition, how can this be of consequence since ultimately the binocular is going to be used by a REAL human with REAL eyes. I’m not trying to be difficult but this seems to be another treatise on “BB stacking.”
:cat:

Bill

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Bill,

Not long after I joined the forum I posted a comment that I thought one binocular had a higher resolution than another. I was politely told that was mistaken as binocular resolution always exceeded the visual acuity of the eye. It was clear as daylight to me that with one I could read a line of newsprint at the other end of the garden, yet it was blurred and illegible with the other. So who was right? Be clear about one thing, I am a REAL human with REAL eyes and that binocular and many others besides were genuinely limiting. It just took a bit longer to figure out why others (including the big manufacturers) had got it ‘wrong’. Turns out we were talking about two totally different parameters. (Something you might recall I explained to you in PMs some years ago.) Essentially it’s the resolution of the diameter of the objective corresponding to the pupil diameter at optimum acuity that is important. It actually means that for those with better than average eyesight some models or samples may well be optically limiting, but for the majority, it’s their eyesight that will be limiting.

A variety of binoculars parameters do vary significantly, but the bottom line is, the observation opinion of someone with 20/20 will be quite irrelevant to someone with 20/10, and to some extent at least, vice versa. That is a resolving difference. How do you bridge that gap? All you need is to know your own acuity and the effective resolution of the binocular. The simplified list is as follows. Obviously, the first step is removing acuity as a variable factor in the evaluation by boosting the magnification. You need a calibrated target to ensure the results are transferable. You need to mask the objective to correspond to the optimum pupil diameter and standardise the illuminance of the target and surround to eliminate sensitivity issues and glare. These simple steps are enough to remove the major human variables and at this point it makes little difference to the resolution endpoint if you use the eye or remove the human entirely and use a camera read the results, (though the latter is much more challenging to implement). A chart, a plastic cutout, a couple of tripods and a light meter are all you need to find out if a binocular is any good or not. A professional setup is obviously rather more sophisticated and will furnish additional information.

Unfortunately when I changed my specs last summer my own acuity dropped a little to 20/12. I now find it more difficult to spot the variability in limiting effective resolution I once could. However, I still seem to have no difficulty picking out samples that turn out have an effective resolution that match the Dawes limit by their sharpness at lower spatial frequencies. I tried them on others that swore they couldn’t tell the difference. Henry also appears to be able to spot similar quality differences . I suspect it’s because we have systematically compared view characteristics with resolution results over several years. REAL humans and REAL eyes may still have a useful purpose in evaluating binocular performance, but perhaps they require appropriate training.

To me the “BB stackers” are the industry professional who perpetually denied that users could tell the difference in resolution, devised pathetic ISO standards and produced c**p binoculars at premium prices. Yes I include Zeiss, Swarovski and Leica. Fortunately I’ve seen clear signs in the last couple of years that some of them at least have woken up to the problem and are giving us decent products. If a the Fuji 8x32 version of the Sightron BSII can give me 5.8” stopped down to 20mm, I think we should expect that a $2000 model should at least match it.

David

WJC said:

Hi Surveyor:

On another topic: what part of Tennessee are you from?

Bill

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Hi Bill, I added the last paragraph as an edit you may not have noticed. Not everyone can get full resolution with their eyes if the hardware does not match up.

As to location, you may remember some of our email discussions in the past about Cleveland, Ooltewah and Indian mounds near your old school.

adhoc said:

David, In your experience, what is the max. variation in center resolution, in arc seconds, within the same model of an "alpha" binocular (among different individual instruments of the model)? Within models of lesser optical quality? Thanks. Adhoc

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Adhoc,

It would be nice if manufacturers would send me a dozen of each of their models so I could give you an accurate answer to your question. Unfortunately they don't. However I have become pretty good at guessing the stopped down effective resolution result using just my eyes. For an 8x binocular and my eyes that would be for the centre 20mm of the objective which would have a Dawes limit of 5.8".

My guesstimates from trying multiple sampes at BirdFair and other places is that untill a year or two ago most of the premium alphas were in the range of 6" to 7" with perhaps 6.5" being the norm. However rogue models like the Zeiss HT were looked around 8.5 to9". In my opinion, the Swarovski CL 8x30 was probably over 10". The mid range Japanese and the better Chinese were typically in the 6.5 -7" range. Cheaper Chinese models were generally in the 7.5 to 10" range.

Looking through something more than a thousand binoculars over a five year period there were a some samples, scattered across the different brands that looked exceptionally good. Almost certainly better than 6", but in some cases these were obviously not representative of the model in general.

If your eyesight is an average 20/15 then a binoclar need to be better than 12.5" to avoid being limiting. For 20/10 that would be 7.5".

To my mind several manufacturers have moved up a gear in optical performance in the last year or two. The Noctivid would be my headline model, but the revised SF was looked good as well and the Meostar HD 12x50 I picked up on the stand and later reviewed was clearly in the very top league, for effective resolution at least that was 5.8" seconds measured. Something matched by the sample of the Fujinon version of Philippines made Sightron BSII clone I reviewed! Obviously that did not match the big boys by other metrics.

Hope that helps,

David

Ron,

Can you check your arcecond acuities for yourself and Henry? I'm pretty sure Henry has never claimed to be better than 20/9.

David

Hi David, my acuity for my right eye is routinely checked by USAF target at various known distances, example, group -2 element 5 at 6 meters or group 0 element 3 at 2 meters. I am not sure what my vision is in 20/20 terms since it has never been measured by that definition although I assume 20/20 refers to single line of 60” or line pairs of 120”.

It seems to me that in the past both Henry and Kimmo related to me they were in the 45” second range using the resolution target method. If 20/9 means 2.22x better than average then that would be about 54” for line pairs.

I never use the 20/20 metrics, all I know from the optometrist is that my right eye requires between 0 and 0.25 diopter correction.

On average days I can see 90”. When my sugar level is up or very shortly after taking my required meds these days, I have seen it as high as 150”. I assume that means about 20/25 on bad days and closer to 20/20 on average days.

As a general rule if I hold a USAF target at arms length (about 1 meter for my height) I can see anywhere from group 1 element 3 to 5 depending on my physical condition and mood.

Ron,

I think you might have mixed up line with line pairs or frequency acuities. Your results are 86" and 82" respectively putting you around 20/14 as line pairs. I don't believe an acuity of 45" per line pair has ever been reported. I seem to recall Kimmo and Henry them mentioning acuities of 20/14 to 20/16 or 84" to 96" in the past. That would be around double the 45" value.

Cheers,

David

Surveyor said:

Hi Bill, I added the last paragraph as an edit you may not have noticed. Not everyone can get full resolution with their eyes if the hardware does not match up.

As to location, you may remember some of our email discussions in the past about Cleveland, Ooltewah and Indian mounds near your old school.

Click to expand...

Apparently one of the memories wiped out by the stroke.

Bill

Hi all:

I asked two “yes or no” questions. If someone would answer those with “yes or no” answers, I would have a starting point to enrich my understanding.

Also, I seem forced to be over my head; so here goes:

For most of my time in optics, two arcminutes was the best resolution a human could appreciate—scientifically PROVEN. However, according to posts on an optical engineering forum I frequent that has been upgraded to ONE (scientifically PROVEN)—the result of new studies related to cell phones and flat screen TVs.

This has been reinforced by conversations showing that some things can be SEEN (like high-tension power lines in the distance) that clinically can’t be RESOLVED—diffraction at work. I realize that sounds like academic double talk. However, that’s often what you get when a “screw-turner” visits engineering sites.

But, right now I’m caught up in a conundrum wondering why Brits don’t type with a Brit accent. So much to ponder ... so little time. :cat:

Bill

Resolution varies from about 0.5 arcseconds, or less for the best observers, for wires against the sky to several arcminutes.
There are so many different resolutions.
White dots on black.
Black dots on white.
Multiple dots.
Double stars, equal and unequal.
Lines. Black on white. White on black.
Line pairs.
Grey markings.
Opticians charts.
Number plates.
Dawes limit, which is continually misused here.
It goes on and on.

With astro scopes, particularly refractors and Maksutovs up to 6 or 8inch aperture, high magnification tests on planets and double stars separates the good, the bad and the ugly.

Any good such scope can take 50x per inch of aperture with ease for testing and actual use on the best nights.
A very good scope 75x per inch.
A superb scope 100x per inch.
I stopped there but some testers of Televue scopes have gone up to 150x per inch without the optics themselves breaking down.

Nowadays I can only go down to 0.3mm exit pupil in one eye and 0.5mm with the other. But not long ago I was still able to use 0.25mm.

Not long ago Sky and Telescope published some of Rev Dawes observations of Mars, and Jupiter and his moons.
He used 65x to 70x per inch on refractors up to about 6.5 inch aperture.

Star tests are important, but not tough enough.
The real test of a fine astro scope is detection of faint planetary detail.

Also here, known test charts are being used for tripod mounted binoculars where observations are continuous and then being applied to glimpsed observations using hand held binoculars.
This is not on and not valid.
It definitely doesn't apply to hidden unknown detail being detected by hand held binoculars.

There's more to this than meets the eye.

Ed

elkcub said:

There's more to this than meets the eye.

Ed

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:-O :t:

David, thanks for your reply (post #64), thorough and more as usual.

That then, as I understand, is the core of it. Then come other factors of which some may be yet unknown, despite all the excellent research done to date.

I would still maintain that most of the disagreement on this forum, not in this thread though, on the clarity of some binocular model in question, is due to variability in eyesight among users. (I have expanded on that elsewhere.)

The visibility of single lines and point sources is very different topic from what we generally understand as resolution. I don't kwow anything about astronomy but I've read some of the brightest stars in the sky only have an angular diameter of 0.005". I know I've glimpsed spiders balooning on single gossamer threads at 30 or 40m with my naked eye which would be about 0.02", yet I can't see the web in the corner of this room in the shaded morning light. Every strand is visible with a 10x binocular, and as soon as the afternoon light floods the room it drives my wife mad. The difference is contrast. It the target is bright enough and the background is dark enough, seeing objects over 10000 times smaller than the smallest resolvable angle is childs play. (Well they are much better at it than most of us.) The lower the contrast the bigger the angle we need to be able to see it.

It doesn't matter if you uses double stars, letters or line patterns it's generally acknowled that we need at least a 5% dip in contrast between the features to resolve them. For the optically imperfect eye the best reported visual acuity I've found is 48" (but that is extremenly rare). In optimal light conditions the maximum useful magnification using diffracted optics would then be 11 times per inch. With 'normal' 20/20 eyesight that would be 25x per inch. Nocternal vision is very obviously much worse. If 150x per inch was required to resolve a target that would be 20/120 or 720" vision.

David

P.S. with a 0.25mm exit pupil the theoretical best the eye could resolve is 420".

Bill,

It's well documented that guys in the 1800s knew visual acuity got a lot better than 2 arcminutes and I supect guys like Galileo or even Pythagarous knew it too. Two arcminutes is actually below average but I think it was Snellen in the 1860s who first decided it should be the arbitrary threshold for 'normal' vision. More recent population studies and now more sophisticated scientific techniques have pushed the limit below one minute.

David

If your eyesight is an average 20/15 then a binoclar need to be better than 12.5" to avoid being limiting. For 20/10 that would be 7.5".

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David:

Can you please explain how you have arrived at the above figures? (they don't seem to be consistent, as 7.5x1.5=11.25). Would these figures be independent of magnification, and are they in arcsec for l or lp?

Cheers,
Peter.

Peter,

I used 8x binocular magnification as an illustration. For 20/10 that would be 60"/8 or 7.5" and 20/15 90"/8 = 11.25". 20/15 acuity is 1.5 times worse than 20/10. Hope that's clearer.

David

The use of very high magnifications to test the finest refractors is not to do with resolution.
It is trying to see if there are any imperfections in the figure and construction of the objective.
By examining the star images and planetary detail one can see if the image actually breaks down.

One cannot say that because of the use of high magnification the observer's eyes are poor.

Also to discuss what skilled astro users are observing without having used astro telescopes extensively is not valid.
So called theory will not work. It isn't theory. It is all empirical data that is then used to make a plausible theory.
To discuss everything in terms of resolution is not correct.
Also to talk of the magic phrase and mantra "Dawes limit" where the Dawes limit is not being judged is incorrect.

For Rev Dawes and many other planetary observers to use 65x or 70x per inch is because that has teased out the most information, often starting with a lower power for the general observation.

In my opinion typo David is correct. Binocular quality, surface accuracies, optical design and implimentation can be judged by eye in normal use. And that even high quality binoculars are lacking and less good than they should be.
It is a great pity that David was not able to keep the very high quality high performance Meopta 12x50.

Surveyor is correct that examining the images with boosted high magnification does reveal the optical quality of the binocular.

Also the stated "resolution" given by different observers is correct for them. Each observer will have his understanding of what "resolution" means to him or her. They may well be different for each observer's methods and testing procedure.

I accept Rathaus observations of spider threads, but not the statement that another very skilled tester"s binocular is a lemon.

I accept Dennis's observation of flare in a Habicht looking at mountain goats.

I accept David's observation of the planet Uranus near Venus.

Some observations are incorrect.

When I was a comet section Director two amateurs said they had definitely found a new comet near the Andromeda nebula. I got people up in the middle of the night to photograph the area to make these amateurs famous.
Not a chance. They had seen the small nebula near M31. They did not even have the grace to apologise for their ineptitude and time wasting.

An Italian rang me from Italy and asked me to hand over all my data on a topic so that he could get a degree. I told him to get st....d.
A British student told me with delight that he had copied my work and got a degree.
I recently tried to contact someone who asked for information that I was willing to give. A senior scientist. He seemed fearful to reply to me because he had copyrighted material that was likely lifted from me.

I am old, I did not care and was willing to help him anyway.

I really don't rate modern degrees, seeing how some are obtained.

typo said:

Bill,

It's well documented that guys in the 1800s knew visual acuity got a lot better than 2 arcminutes and I supect guys like Galileo or even Pythagarous knew it too. Two arcminutes is actually below average but I think it was Snellen in the 1860s who first decided it should be the arbitrary threshold for 'normal' vision. More recent population studies and now more sophisticated scientific techniques have pushed the limit below one minute.

David

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David;

Yes, BUT!

Columbus wanted to “prove” the earth was spherical, but that had been proven by Pythagoras in the 6th century BC—2,000 years earlier. There is a difference between KNOWING and REMEMBERING you knew. When data is more obscure it is often swept aside for that which is more popular—accurate or not. Those who taught me were doing the best they knew.:cat:

Bill

typo said:

My guesstimates from trying multiple sampes at BirdFair and other places is that untill a year or two ago most of the premium alphas were in the range of 6" to 7" with perhaps 6.5" being the norm. However rogue models like the Zeiss HT were looked around 8.5 to 9". In my opinion, the Swarovski CL 8x30 was probably over 10". The mid range Japanese and the better Chinese were typically in the 6.5 -7" range. Cheaper Chinese models were generally in the 7.5 to 10" range. <snip>

To my mind several manufacturers have moved up a gear in optical performance in the last year or two. The Noctivid would be my headline model, but the revised SF was looked good as well and the Meostar HD 12x50 I picked up on the stand and later reviewed was clearly in the very top league, for effective resolution at least that was 5.8" seconds measured. Something matched by the sample of the Fujinon version of Philippines made Sightron BSII clone I reviewed! Obviously that did not match the big boys by other metrics.

Click to expand...

Very interesting stuff. I've had the feeling for some time that some modern alpha roofs weren't quite as good on resolution as some of the older models, and your observations confirm that impression.

Hermann