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Is it me, my eyes, or what? (1 Viewer)

Tringa45

Well-known member
Europe
Sorry, but you are mistaken. Some individuals definitely can, and do so easily hand held.

David,
As someone who tests binoculars using scientific methods, you and Henry are the last people from whom I would have expected this statement.
Joachim did qualify his statement with good or better quality bins of 7x to 10x magnification.
Would you care to elaborate?

John
 

Troubador

Moderator
Staff member
Supporter
I discussed this subject in some detail with Milos a couple of years ago. He did argue that twilight performance was particularly important for their hunting and military customers. In fact they run MTF profiles at multiple wavelengths and optimise the contrast at lower spatial frequencies to aid target detection in low light. Given the relatively poor acuity of users in low light, the resolution is not the most critical factor. He did acknowledge that the situation was very different in bright conditions where magnified visual acuity can approach or even exceed the resolution of the instrument. That Meostar 12x50HD I reviewed, was one of the sharpest binoculars I've tested. It was diffraction limited when stopped down which shows they don't overlook this aspect. Unfortunately there were details of there methods and standards that Milos wouldn't disclose. Trade secrets I guess!

David


And Milos did say that stopped-down testing does give useful additional information.

Lee
 

typo

Well-known member
Tringa,

This argument goes back to my the early days of the forum and beyond, and is one I'd hoped we'd put to bed many years ago.

If you follow the different threads you will be aware that the sharpness of certain binoculars are fairly regularly criticised by some contributors. Perhaps the original Swarovski CL was the highest profile, where dozens on the forum described the view as soft, and was widely ridiculed in the trade. Smaller numbers have complained about the Conquest HD, the Nikon MHG and the Ultravid HD. You might have noticed it tends to be the same group of people? You need to ask yourself, what was the difference that made a higher proportion complain about the CL and a smaller proportion the others. The debate within the forum was pretty heated, but eventually sense prevailed.

It all depends on the comparison between the effective resolution of the binoculars and the visual acuity of the user at specific pupil diameters. Although I would normally report the stopped down resolution of binoculars equating to a pupil diameter of 2.5mm, I think it's clearer if I illustrate it at 2.2mm which would occur at slightly higher light levels.

When the light levels are bright enough to shrink the pupil of the eye to 2.2mm the effective objective diameter of the binocular will be 8x2mm or 17.6mm. If you recall, the Dawes limit for 17.6mm is 116/17.6 or 6.6 arcsecond resolution. There are other slightly varying definitions but is pretty much the same as 5% contrast by MTF analysis and the limit using line charts.

Obviously visual acuity does vary between individuals. The threshold for normal vision is 20/20 ( or 6/6) in metric. This is the average acuity for 65 year old. That is better than 120 arcseconds to the naked eye, or 8 times better at 15 arcseconds with an 8x binocular. 15" is over 2x worse than the Dawes limit for an effective objective diameter of 16mm. I don't know that anyone would test a binocular for sharpness with one eye, so for home testing I would normally do a two eye test. The best result I've measured was 20/9 acuity or 54 arcseconds. With 8x magnification that would be 6.75 arcseconds.

We now have a situation where an individual's magnified resolving power is virtually at the Dawes limit; 6.6" vs. 6.75". I asked that person to compare two binoculars. One was the amongst the best I've tested and at the Dawes limit stopped down, the other was just half an arcsecond worse. Whick would be about tyipical for an alpha. Having tried the worse one first, hand held, it then took him no more than 5 seconds to pronounce the better one sharper. No charts, tripods or boosting, just a look down the garden.

No it wasn't me, it was my son who doesn't own a binocular and might only pick up mine once a year. I had 20/9 eyesight when I joined the forum. It's now 20/11. It still only took me recently a few seconds to realise the new Trinovid HD was poor. These days, the Conquest HD, Nikon MHG and even the new Swaro CL take me a little longer to spot the difference between those and their top of the range bretheren, but then, very few of those are diffraction limited either. I'm sure it wont be long before I need a tripod, a suitable target and have to rely on boosting to spot these differences. But don't forget, there are others on the forum, that have never seen a USAF 1951 chart or attempted a boosted test that see differences even more clearly than I do... or did. :-C

David
 

giosblue

Well-known member
Can someone explain what they mean by "stopped down" I get it with a camera lens with a variable aperture.

How does it work with binoculars? They are open aperture all the time aren't they?
 
Last edited:

Binastro

Well-known member
I use Mizar an unequal double star 14.4 arcsecond separation.

I bought 6 new 12x45 Russian binoculars at a low price.
All are quite good, but I picked the best, and used it for ten years as my main binocular. It is beautifully balanced and easily outresolves the excellent Nikon 10x35 EII.
However, the Russian binoculars star images are bloated.

So although I could routinely separate Mizar braced against the double glazing with the Russian 12x45, the original Canon 10x30 IS was better, even with the stabilizer off. I could separate Mizar at 10x. I could also separate Mizar in several other good 10x binoculars.
This is of course for night use with expanded pupils.

I definitely test binoculars with one eye also.
My vision was 20/15 then. Now when rested it is 20/16 one eye, 20/20 the other. I am old.

My cousin who unfortunately died long ago had at least 20/8 vision. He could read car number plates at twice my best distance when I was probably in my late 30s.

I can still see whether many binoculars are good or not, but I usually brace them against the double glazing.

The VisionKing 5x25 is potentially very useful but one barrel is very soft. If I hadn't got the excellent Foton 5x25 I would have thought the problem was my eyes.

The Fujinon 14x40 also troubles me as the stabilizer motion is very obvious and disturbing to me in most lighting, although probably not at night.

I would think that someone with 20/8 eyes could separate Mizar with my 5x25 Foton.
 

Troubador

Moderator
Staff member
Supporter
Can someone explain what they mean by "stopped down" I get it with a camera lens with a variable aperture.

How does it work with binoculars? They are open aperture all the time aren't they?

It means applying a mask to the objective lens to reduce its effective diameter. On a bright day with your pupils 'stopped down' due to the strong light, you are only receiving light from a central portion of the lens, so testing the lens 'stopped-down' means replicating this situation.

Lee
 

Binastro

Well-known member
The pupils of ones eyes stops down binoculars in bright light, or one can put masks in front of the objectives.

One can also stop down camera lenses or telescopes by masking the objectives.
 

WJC

Well-known member
Tringa,

This argument goes back to my the early days of the forum and beyond, and is one I'd hoped we'd put to bed many years ago.

If you follow the different threads you will be aware that the sharpness of certain binoculars are fairly regularly criticised by some contributors. Perhaps the original Swarovski CL was the highest profile, where dozens on the forum described the view as soft, and was widely ridiculed in the trade. Smaller numbers have complained about the Conquest HD, the Nikon MHG and the Ultravid HD. You might have noticed it tends to be the same group of people? You need to ask yourself, what was the difference that made a higher proportion complain about the CL and a smaller proportion the others. The debate within the forum was pretty heated, but eventually sense prevailed.

It all depends on the comparison between the effective resolution of the binoculars and the visual acuity of the user at specific pupil diameters. Although I would normally report the stopped down resolution of binoculars equating to a pupil diameter of 2.5mm, I think it's clearer if I illustrate it at 2.2mm which would occur at slightly higher light levels.

When the light levels are bright enough to shrink the pupil of the eye to 2.2mm the effective objective diameter of the binocular will be 8x2mm or 17.6mm. If you recall, the Dawes limit for 17.6mm is 116/17.6 or 6.6 arcsecond resolution. There are other slightly varying definitions but is pretty much the same as 5% contrast by MTF analysis and the limit using line charts.

Obviously visual acuity does vary between individuals. The threshold for normal vision is 20/20 ( or 6/6) in metric. This is the average acuity for 65 year old. That is better than 120 arcseconds to the naked eye, or 8 times better at 15 arcseconds with an 8x binocular. 15" is over 2x worse than the Dawes limit for an effective objective diameter of 16mm. I don't know that anyone would test a binocular for sharpness with one eye, so for home testing I would normally do a two eye test. The best result I've measured was 20/9 acuity or 54 arcseconds. With 8x magnification that would be 6.75 arcseconds.

We now have a situation where an individual's magnified resolving power is virtually at the Dawes limit; 6.6" vs. 6.75". I asked that person to compare two binoculars. One was the amongst the best I've tested and at the Dawes limit stopped down, the other was just half an arcsecond worse. Whick would be about tyipical for an alpha. Having tried the worse one first, hand held, it then took him no more than 5 seconds to pronounce the better one sharper. No charts, tripods or boosting, just a look down the garden.

No it wasn't me, it was my son who doesn't own a binocular and might only pick up mine once a year. I had 20/9 eyesight when I joined the forum. It's now 20/11. It still only took me recently a few seconds to realise the new Trinovid HD was poor. These days, the Conquest HD, Nikon MHG and even the new Swaro CL take me a little longer to spot the difference between those and their top of the range bretheren, but then, very few of those are diffraction limited either. I'm sure it wont be long before I need a tripod, a suitable target and have to rely on boosting to spot these differences. But don't forget, there are others on the forum, that have never seen a USAF 1951 chart or attempted a boosted test that see differences even more clearly than I do... or did. :-C

David

DIFFERENT tests performed at DIFFERENT times with DIFFERENT subjects having DIFFERENT ranges of accommodation for DIFFERENT visual acuities under DIFFERENT conditions will produce DIFFERENT results which will always be open to DIFFERENT interpretations.

I am surprised that often the more scientific among us fail to take the above—our different physiologies—into consideration. For getting to root causes they must be. I know I overuse my BB stacking analogy, but does it not apply, here?

My version of logic:

Within a group of binocular enthusiasts some of whom change their binoculars more frequently that their socks, why do they spend time on myriad and ever-fallible tests? If the binocular is not performing as you would like, just spend $50, 43 €, or 39 £ more and get the instrument that will satisfy your desire?

Finally, putting anything "to bed" on a binocular forum is like putting a 5-year old to bed at 3:30 and expecting him to stay there. :cat:

Back in my hole, now.

Bill
 

Binastro

Well-known member
Most of my observations including research papers have been done with imperfect optics.

There is a difference between being an optics enthusiast and a long time observer recording observations that actually appear in papers in Journals eight years later.

The same applies to my fellow observers.
 

typo

Well-known member
Finally, putting anything "to bed" on a binocular forum is like putting a 5-year old to bed at 3:30 and expecting him to stay there. :cat:

Back in my hole, now.

Bill

Bill we can agree on that at least. ;)

That diffraction limited binocular I referred to costs less than $200 in the US, but at that price I don't imagine the next sample would be as good. I was irritated that it cost more than twice as much here, but I really should have bought it.

David
 

giosblue

Well-known member
So, in my case the optics must have better resolution than my eyes, otherwise I too would be able to see the difference in sharpness, No?

Stopping down the lens with a mask means you are only using the centre, which is the sharpest part of the lens anyway. Does this mean if your eyes are stopped down because the light is bright you are only using the centre of the lens? , so bright light = sharper image?
 

WJC

Well-known member
Bill we can agree on that at least. ;)

That diffraction limited binocular I referred to costs less than $200 in the US, but at that price I don't imagine the next sample would be as good. I was irritated that it cost more than twice as much here, but I really should have bought it.

David


Hi David:

I wasn’t referring to any particular post, but the thread as a whole. Also, a diffraction limited bino ... can I smell your breath? Optics importers often play to the crowd. When Meade came out with the ETX telescope, people who wanted to do things on the cheap kept making themselves feel good by saying, “It’s as good as a Questar.” Well, according to what I heard, the first 100 optics sets came from Cumberland, the same company that makes the optics for Questar. All that glitters is not gold. :cat:

Bill
 

typo

Well-known member
So, in my case the optics must have better resolution than my eyes, otherwise I too would be able to see the difference in sharpness, No?

Stopping down the lens with a mask means you are only using the centre, which is the sharpest part of the lens anyway. Does this mean if your eyes are stopped down because the light is bright you are only using the centre of the lens? , so bright light = sharper image?

A step at a time.

Yes, if both optics have better effective resolution than you magnified acuity then the level of detail you see through both will be equally eyesight limited. I've worded that carefully because the contrast and colour can affect sharpness perception, so may be different.

The pupil of the eye when contracted block the light from the perimeter of the objective, so that only the centre of the objective forms the image on your retina.

On average peak acuity occurs when the pupil is approximately 2.5mm in diameter at a luminance level around 300 to 500cd/m2. I find I am more likely to spot a binocular's deficiencies when the light is a little brighter and my pupil a bit smaller.

A good mid range binocular will have an effective resolution around 6.5 arcseconds stopped down to 20mm, but would typically be around 4.5 arcseconds at 42mm. Effective resolution usually improves as the objective diameter increases, but your eyesight gets progressively worse as your pupils correspondingly dilate, so even a very modest binoculars will always beat your eyesight by a good margin in low light. There are other consideration like the transmission profile, which can also affect perceived sharpness.

Hope that's clearer.

David
 

paddy7

Well-known member
Kind of thinking aloud, i can see how twilight testing would have some merit.
The exit pupil of the binocular is a property of the physical characteristics, and unchanging. The eye, however, is constantly adapting to available light, with dilation and contraction occurring without the knowledge of the owner.

At a time when the eye has dilated to approximately the size of the exit pupil, thus using all the available light provided from that particular set may provide the basis for a comparative test of two binoculars of the same dimensions - almost like a stress test.... so, same test, same user, same light etc. Stopping down mimics this condition, but working on reducing the light at the objective.
It would work for THAT user at THAT time however, but may be sufficient for an individual to make his or her own conclusions if trying to make a choice.
I find that effective resolution is harder to achieve earlier in the twilight with an 8x32 than an 8x42 (obviously), but in my book, that's time to go and get a beer.
 

b3rd

Reg1stered User
I agree James and when I was interviewing Milos Slany from Meopta and we were discussing the usefulness or otherwise of testing binoculars with them stopped-down, his closing remark was that testing at full aperture especially in twilight conditions is very revealing of binocular performance.

Lee

How do you stop down a binocular? I would think your f/D would be constant for a given design. I've actually wondered what a typical f/D would be for a set of bins. Someone on the internet seems to have said f/4 is typical. heh.
 

Troubador

Moderator
Staff member
Supporter
How do you stop down a binocular? I would think your f/D would be constant for a given design. I've actually wondered what a typical f/D would be for a set of bins. Someone on the internet seems to have said f/4 is typical. heh.



You stick an appropriately sized annulus-shaped mask over the objective lens of one tube, thus reducing effective size of the objective lens.

Lee
 

typo

Well-known member
I think i've been posting about stopped down testing for 6 or 7 years but it looks like it might be worth explaining things again.

Firstly some background. The pupil of the eye responds to light levels through a photo sensitive cell in the peripheral vision which are most sensitive in the blue region of the spectrum. The range in diameter is from close to 1mm to over 9mm, but the maximum reduces with age, but with significant individual variation. Apart from regulating the light levels reaching the retina, the iris will also progressively block out stray light as the pupil contracts, and improve contrast. The lens of the eye is far from perfect, as those of us that where glasses will know, and generally visual acuity will decrease as the pupil diameter increases. It also decreases at the smallest diameters as the optical resolution becomes increasingly diffraction limited. it seems many individuals are unaware of these changes. Optimum acuity occurs at a specific pupil diameter (and luminance) and varies a little with individuals, but the average is about 2.5mm. Ultimately it is actually the receptor density in the retina that limits acuity. The maximum achievable acuity, even in an optically perfect eye, is 20/8 and is incredibly rare. Of couse, individal acuity varies considerably, even in youngsters, and unfortunately, generally deteriorates with age.:-C

When you use a binocular or telescope the diameter of the objective that forms an image on your retinal will be the diameter of your pupil multiplied by the magnification. So for the average user they will see the most detail when their pupils are 2.5mm in diameter and with an 8x binocular the view they see will be formed by 2.5x8 =20mm of the objective. I've long argued that the best measure of a binocular's optical performance is to determin the optical resolution of that 20mm, or corresponding value for other magnifications. I simply cover the objective with a mask with a 20mm diameter aperture in the centre, and with a test chart and extra magnification estimate the optical resolution. What we refer to as stopped down testing. I have found these results correspond exactly with my visual assessment of a binocular's sharpness. However, that will very much depend on the user's acuity. Those with an average visual acuity, and particularly worse, are very unlikely to see these kind of differences for the reasons i described in #23 of this thread. It frequently leads to disagreements on the forum. Traditionally optics manufacturers only measured resolution for the full diameter objective. There are signs that at least some are now aware of the shortcomings of this method and may be including some reduced aperture profiling as part of their quality control.

Binoscoper mentions another thread where some have noted other benefits wom stopping down the objective were discussed. There can be various points in a binocular design where stray light can intrude in the optical path and reduce contrast or produce patterns of glare. Quite often an unpainted or poorly blacked internal surface might be to blame. Much of this scattered light travels along the perimeter of the ligh path and degrades the view. An external mask, stopping down the effective objective will often improve contrast.

As i mentioned earlier, visual acuity is related to pupil diameter. Although I probably wouldn't recommend it for general use there are occasions where stopping down an objective will improve apparent resolution. Of course it is a trade off between brighness and sharpness, but as the light decreases, there is at least a small range of light levels at which limiting an exit pupil to around 2.5mm will improve the level of observable detail. This might be more obvious using a scope. I have seen a few accounts of astronomers using this technique with binoculars or low magnification telescopes.

David
 

paddy7

Well-known member
Thanks David - very clear explanation, which in the development of this thread, probably needed reiteration.
I suppose that the only grit in the vaseline is the fact that the stray light issues (which the stopping-down is intended to prevent) will re-present themselves when the binocular is in general use in the field (i.e. not stopped-down).
Thus these manufacturing issues may prevent the high-performing, resolution-tested set from duplicating this in the birding environment.
Perhaps one with a better build quality and more care taken to QC issues, but performing slightly less well on the stopping down test, may thus be 'better' (if that is the word....)
Anyway, very appreciative of the concise revision of this issue.
thanks
 

Binastro

Well-known member
Prof. Taylor.
Studies of Aboriginal Australians in armed forces.

6/2 and 6/3 common. 6/1.4 best visual acuity.
I.e. down to 20/4.7
Also they are able to see very faint stars.

I haven't read the study, but may try to find it.

Also maybe Namibian nomads.

Some astronomers have been shown to see fainter than mag 8.0 stars within a dark observatory with a small opening and to read fine newspaper print across a room.
These were U.S. astronomers.
 
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