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Can a small bino really deliver? (1 Viewer)

Wow, you guys are speaking Binoese. Could someone please provide a short translation for the simple minded?
Thanks,
Dave

If it´s any consolation to you Dave, I´ve no idea what they´re talking about either, they lost me a few pages ago. But they´re the experts - a bit like my mechanic, when my "Timing Chain" broke a few weeks ago. He spoke to me a lot about the chain, the bearings, head gaskets, cam-shafts and the like, all of which is Double Dutch to me. But because he´s the expert, he was able to locate a 2nd-hand engine and pop it into my car at a good price. I don´t understand what he says, but I trust him, if that makes sense. Kind of a blind faith thing. As an end-user of binos, I like to read all the above by Henry, Surveyour, Kabsetz etc., and see if any of it filters through, then try to combine it in a very half-digested form with what I experience through usage (a bit like my old car).
 
Henry, here is a quick and dirty stab at it. Still need to do a lot of checking and proofing to make sure data is being handled properly, much beta testing to do.

One thing I’ve noticed right off, if the stab is close to correct, is that it appears larger objectives are going to have a contrast advantage over the smaller objectives even at the lesser resolutions. Note the contrast % of the 20 mm Promaster; this needs to be checked thoroughly. It may answer a lot of my questions.


EDIT: The curves shown for the Alpha 20's are old and need to be redone. Same as posted to RonH.

Excellent work, Ron. That's just what I had in mind.

Two anomalies stand out to me. One is the overachieving Trinovid and the other is a worse result than I would have expected from the 1/4 wave optics of the stopped down Promaster (perhaps some of that is explained by its slightly undersized exit pupil compared to the others?).

I agree with Ronh about extending the low spacial frequencies to allow the contrast curves to reach 100%, although for the 20mm apertures that looks like it will be a few hundred arcseconds. Anybody else have suggestions for modifications or a completely different approach?

Henry
 
Good point Henry, just low enough to get 98 or 99% contrast would be plenty. Angle units are desirable because they relate to the eye's acuity in an easy way, but a linear angle scale would have to be pretty long to reach down to zero frequency!
Ron
 
Henry, I have run into problems (questions actually) and here at the office, busier than a cat in a sand box.

I will look into it over the weekend, but when I change the x values to reverse order, or change the values, for some reason that I do not fathom yet, the hump in the line goes above the straight line.

There is going to be a problem with wave error and diffraction estimates since I have not figured out how to do the diffraction calculation, based on a normalized sequence and lp/mm at the optic level, not the eye reference.

I will let you know when things slow down and I can think a little bit. Going to go hide for awhile right now.

I have noticed several errors that need attention.
 

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Wow, you guys are speaking Binoese. Could someone please provide a short translation for the simple minded?
Thanks,
Dave

They are testing to see if larger binoculars have a resolution advantage and surprisingly enough it looks like they might have a contrast advantage also. It's nice to see verification of what you see through the binoculars. Nice job Surveyor and Henry your technical expertise at testing lends credence and scientific validity to these forums, as well as, making them extremely interesting.
 
Dennis

I certainly don't agree with your analysis of the 7x26 Customs, as I have two of them and think they are outstanding little binos. I will however have to agree that I too see more resolution and possibly contrast with my larger binos as compared side by side with the compact roofs. I spent several days testing an older pair of Bushnell Legend 9x25's against a new pair of Zeiss Victory 10x25's. The net result was that I found the Vicory's only about 5% better than my Legends and got rid of the Victorys as being entirely cost ineffective. The entire time I was testing the little roofs, I was also comparing the view thru a pair of 10x50 Nikon Action porros and a pair of 10x42 Zen ZRS HD. At almost every step of the test phase I felt like I had better resolution and contrast with the larger binos at longer distances. It just seemed like there was more apparent detail and a much easier view.

Following this thread has certainly piqued my interest in doing a little web research, and I am curious how the airy disc and diffraction principles factor into all this.
 
Dennis

I certainly don't agree with your analysis of the 7x26 Customs, as I have two of them and think they are outstanding little binos. I will however have to agree that I too see more resolution and possibly contrast with my larger binos as compared side by side with the compact roofs. I spent several days testing an older pair of Bushnell Legend 9x25's against a new pair of Zeiss Victory 10x25's. The net result was that I found the Vicory's only about 5% better than my Legends and got rid of the Victorys as being entirely cost ineffective. The entire time I was testing the little roofs, I was also comparing the view thru a pair of 10x50 Nikon Action porros and a pair of 10x42 Zen ZRS HD. At almost every step of the test phase I felt like I had better resolution and contrast with the larger binos at longer distances. It just seemed like there was more apparent detail and a much easier view.

Following this thread has certainly piqued my interest in doing a little web research, and I am curious how the airy disc and diffraction principles factor into all this.

I am glad you agree. When you put those big apertures up to your eyes it is just like relief and I go AAAgh that's nice and relaxing! I feel the 7x26 Customs are pretty nice binoculars but I just don't like the view. I like a flat field and with the Customs I get an artificial view in my eyes. It's almost like the curvature you get when you look in a fisbowl. It is just not natural. I really can't put my finger on what I don't like about them but I don't. The minute I tried them I didn't like them. I guess it is a personal thing. I am positive I get a clearer more detailed view with my bigger binoculars especially at a distance. Some disagree but I will not sway from what I see. Compacts are alright out to a hundred feet or so but give me big aperture after that. Compacts are totally worthless when it starts getting dark also. Leica 8x32 BN's aren't my favorite binoculars but they are almost as small as the compacts and will totally kill them in performance.
 
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With the way Henry and RonE are investigating this, I have to say I was expecting the stopped down aperture to give the sharper results. MTF I barely understand, but as most photographers will know stopping down a camera lens to about f8 will usually produce optimal sharpness. Of course you need to increase the exposure or iso or illumination to compensate.
There is a nice set of 6 plots about half way down this article that show that the lens perform better whan stopped down, but the plots have been normalised for each aperture.
http://photo.net/learn/optics/mtf/

We all understand that bigger objectives are brighter. When comparing the different apertures should you compensate with illumination, or by RonE's method would a proportional increase in camera exposure enough to 'normalize' the results or would a simple math adjustment for the diffraction limited LPM be the best basis for comparison?

Apologies if this is a bit ignorant irrelevance.

David
 
I don't have time now for a real post, but I want to caution folks not to jump in too quickly with interpretations of the experimental MTF's presented so far. For instance, they shouldn't be used to advocate for a particular opinion about aperture.
 
We all understand that bigger objectives are brighter.

We do?

A bigger aperture is brighter only if all the light through that bigger aperture makes it into the entrance pupil of the detector (the eye in this case). If the exit pupil associated with the bigger aperture is bigger than entrance pupil of the eye the "extra" light is never seen. So bigger objectives aren't always "brighter". Magnification has a bigger impact on brightness given a fully illuminated entrance pupil.

The MTF is a plot of contrast (from 0% to 100% or 0 to 1) versus spatial frequency. The total illumination is always normalized out.
 
Even if a compact produces all the theoretical light the entrance pupil of the eye can handle because of vignetting a bigger aperture will appear brighter because of more even illumination across the field. It's kind of what Henry said about his 8x56 Zeiss. You are using the center of the objective to illuminate your pupil in the bigger binocular. Not all of the light gathered by say a compact 10x25 reaches the eye. Light from the outer portions of the objective are reduced by vignetting. The central 50% of an objective lens provides 100% illumination of the exit pupil.The light delivered from the area outside the central 50% doesn't not reach the exit pupil. Here is a further explanation of this principal.

http://www.cloudynights.com/documents/binoexit.pdf







We do?


A bigger aperture is brighter only if all the light through that bigger aperture makes it into the entrance pupil of the detector (the eye in this case). If the exit pupil associated with the bigger aperture is bigger than entrance pupil of the eye the "extra" light is never seen. So bigger objectives aren't always "brighter". Magnification has a bigger impact on brightness given a fully illuminated entrance pupil.

The MTF is a plot of contrast (from 0% to 100% or 0 to 1) versus spatial frequency. The total illumination is always normalized out.
 
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Dennis,

The paragraphs in your link that deal with vignetting are based on a misconception. I think Ed is aware of his mistake now, but his old writing on the subject has not been revised.

The only "exit pupils" that are vignetted are those that form from off-axis rays and the effect is only pronounced near the edge of the field where the off-axis exit pupil of a typical binocular at full aperture is reduced to a cat's eye shape that passes 50% or less of the light of the axial exit pupil. The dimming of the off-axis image is so gradual that it mostly goes unnoticed. Your current favorite binoculars do this. Have you noticed it?

The reason large exit pupils (by which I mean 6-7mm) show less dimming at the field edge in bright light is because the minor axis of the cat's eye shape of such a large exit pupil may still be pretty large, perhaps 3-5mm. If the minor axis of the exit pupil is larger than the pupil diameter of the eye there is no visible dimming.

Henry
 
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Dennis,

The paragraphs in your link that deal with vignetting are based on a misconception. I think Ed is aware of his mistake now, but his old writing on the subject has not been revised.

The only "exit pupils" that are vignetted are those that form from off-axis rays and the effect is only pronounced near the edge of the field where the off-axis exit pupil of a typical binocular at full aperture is reduced to a cat's eye shape that passes 50% or less of the light of the axial exit pupil. The dimming of the off-axis image is so gradual that it mostly goes unnoticed. Your current favorite binoculars do this. Have you noticed it?

The reason large exit pupils (by which I mean 6-7mm) show less dimming at the field edge in bright light is because the minor axis of the cat's eye shape of such a large exit pupil may still be pretty large, perhaps 3-5mm. If the minor axis of the exit pupil is larger than the pupil diameter of the eye there is no visible dimming.

Henry

Henry, in the concurrent thread "Pocket Binocular - Advice" I wrote about an experiment I did yesterday looking at a scene through an 80mm f/7.5 ED refractor. Using a 35mm eyepiece I observed at full aperture at 80mm and at a stopped down aperture of 42.5mm. If the 80, the 7.5, and the 35 are accurate figures, the resulting exit pupils were 4.7mm and 2.5mm. There was a very noticeable difference in the brightness of the scene.

Is this a scenario different from what you've been describing, and from what all others have said about a large light cone not fitting into a small pupil, effecting a "waste" of light?

Howard
 
Although I agree with Henry that we should not jump to conclusions about aperture, I'm still tempted to suggest something on the basis of what Ron's curves as well as calculated MTF curves for diff.-lim. optics show. Along the lines of what Ron says in the following quote from post #78:

"One thing I’ve noticed right off, if the stab is close to correct, is that it appears larger objectives are going to have a contrast advantage over the smaller objectives even at the lesser resolutions."

The point I wish to make is that much of what we view in daylight involves trying to make out detail that is not of particularly high contrast to begin with - much different from a black-and-white bar-target or a double-star against dark sky background. So, supposing my eye is dilated to anything bigger than the 2.5mm an 8x20 binocular offers, there perhaps is a meaningful difference brought by increased aperture in my ability to extract detail from all sorts of lower-contrast objects where the spatial frequency/contrast ratio of the target was around the detection threshold of my eyes.

The personal reason why I keep coming back to this is that in addition to the limited testing I have done, I have now for some three years owned and used a very good sample (very low aberrations, excellent measured resolution for the aperture) of the Leica Ultravid 8x20, and am consistently surprised by how seldom I find the view fully satisfying despite knowing full-well there is very little room for improvement in it within its size and design parameters.

Kimmo

Kimmo
 
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Dennis,

The paragraphs in your link that deal with vignetting are based on a misconception. I think Ed is aware of his mistake now, but his old writing on the subject has not been revised.

The only "exit pupils" that are vignetted are those that form from off-axis rays and the effect is only pronounced near the edge of the field where the off-axis exit pupil of a typical binocular at full aperture is reduced to a cat's eye shape that passes 50% or less of the light of the axial exit pupil. The dimming of the off-axis image is so gradual that it mostly goes unnoticed. Your current favorite binoculars do this. Have you noticed it?

The reason large exit pupils (by which I mean 6-7mm) show less dimming at the field edge in bright light is because the minor axis of the cat's eye shape of such a large exit pupil may still be pretty large, perhaps 3-5mm. If the minor axis of the exit pupil is larger than the pupil diameter of the eye there is no visible dimming.

Henry

Hi Henry,

While I agree with your vignetting comments, I'm afraid that EdZ and others pay scant attention to the visual system side, usually being satisfied with convenient oversimplifications, which to my mind are beginning to sound like fairy tales.

I would agree that much of this is arcane and complicated, and I don't profess to be an expert, but when it comes to understanding what the observer actually "sees" with binoculars, it really should be considered. As one example, in the course of his discussion EdZ ranges from photopic (daylight birding) to scotopic (night astronomy) vision. What goes unstated and unrecognized is that retinal sensitivity also changes by 9 orders of magnitude between these two extremes, — i.e., a billion to one!

What most folks don't really connect with is that pupil diameter itself is only an observable correlate of the unseen biological process of light/dark adaptation; perhaps giving us some clue as to the observer's momentary state of retinal sensitivity, but not really being of overriding importance. The adaptation process is occurring constantly, not just as we go from bright daylight conditions to dawn. So, given the fact that the pupil contracts quickly but opens slowly, it would also appear that pupil response has more to do with protecting the eye from overload than modulating light for optimum visibility. But even if it were of greater import, we must also consider the fact that the 'effective' pupil size of the eye is always smaller than its measured diameter due to the Styles-Crawford effect: i.e., the foveal receptor cells act as light tubes, which accept less input from rays arriving from the edges of the eye's lens. This is not a minor consideration and under photopic viewing conditions, the S-C effect probably has important implications for how color information is processed.

I hope this doesn't sound like a rant, but when I get that fairy tale feeling it always leads me to being concerned about how the capitalist enterprise will be taking advantage of it. Think holiday season. ;) Next, someone will say that my trusty 10x25 SLCs can't or shouldn't be used beyond 100 ft., or don't have a large enough entry/exit pupil, or that my old eyes need to wander around a bit more than they already do. Oh, oh, ... they already have ...

Regards,
Ed
 
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Interesting theory but this thread from Cloudy Nights seems to disagree that objective size can increase contrast ratio. I am not totally convinced because I feel contrast is better in bigger binoculars and scopes. Here is the discussion:
An excellent exploration of the eye pupil vs. exit pupil issue. That said, I would like to comment on the following paragraph from your article:

[Begin Quote]
What consideration should be given to exit pupil for use in brightly lit light polluted skies?
In this case you might consider even smaller exit pupil than your maximum dilated eye pupil. You can vary the values in the relationship of aperture/magnification (which gives exit pupil) by either decreasing aperture or increasing magnification. Either choice will decrease exit pupil and therefore increase the apparent contrast in the image by decreasing the brightness of the background sky. This should help bring out the images of target objects.
[End Quote]

Unfortunately, contrast ratio (see below note) is always at its maximum to the naked eye. You can't improve the contrast ratio using any optical aid at any magnification.

Put simply, Contrast ratio is the ratio of object surface brightness to sky surface brightness. This ratio of surface brightnesses determines the contrast between the object and background sky. Surface brightness is defined as a brightness per unit area, and is typically expressed by astronomers in units of magnitude per square arcminute or magnitude per square arcsecond.

Surface brightness is determined by dividing the total brightness of the object into its area. For the sake of discussion, let's say an observer is using his 60-mm refractor to look at some distant galaxy. To the naked eye, the galaxy has a surface brightness, SBgal, and the sky has a surface brightness, SBsky. If the observer has 6-mm eye pupils, let's find out how the telescope affects the contrast ratio of the galaxy vs. background sky.

The telescope has an aperture (60-mm) 10x that of the observer. As a result, the telescope theoretically collects 100x as much light. But to take full advantage of that aperture, the observer needs to use at least 10x magnification in the telescope. 10x produces a (60/10=6) 6-mm exit pupil in that aperture, which just happens to match the observer's eye pupil size.

So, the telescope collects 100x as much light as the observer. But the telescope also must spread that light over (10x^2) 100x the surface area in producing the largest exit pupil that preserves the full aperture of the instrument. In short, the surface brightness of the galaxy (SBgal) remains unchanged. And since the background sky behaves just as any extended DSO, its surface brightness (SBsky) also remains unchanged. The net result is that contrast ratio also remains unchanged by the application of larger aperture.

What happens if we use higher magnifications to lower the surface brightness of the sky? The extended galaxy's surface brightness is reduced by an equal amount. And again, we find that the ratio of their respective surface brightnesses (SBgal/SBsky) remains unchanged.

What happens if we use even lower magnifictations that produce exit pupils larger than the eye pupil? Well, the apparent surface area of the object is decreased. On the surface, this may seem a good way to increase object surface brightness. However, as you clearly demonstrate in your article, the larger exit pupil effectively reduces the aperture of the instrument. The net result is that object surface brightness is lowered due to the reduced effective aperture. And contrast ratio is, again, unchanged.

But by reducing the effective aperture, we've also raised the contrast threshold at which objects become visible to the eye. (For a discussion of aperture, sky brightness and contrast threshold, please see the following: ODM Matrixes) So, even though contrast ratio is unchanged, we've actually made it harder to detect the object. Some objects that were visible at the threshold are now invisible in that reduced aperture.

The inescapable conclusion is that you cannot improve contrast ratio by the application of increased aperture, or by changing magnifications and, by extension, exit pupil. To illustrate, let's look at the scenario you discussed in the above quoted paragraph; the observer in a light-polluted environment choosing smaller binoculars.

I own a pair of 10x50s. If I brought those and a friend's 10x25s into the field, what could I expect in terms of performance? The 10x50s produce a 5-mm exit pupil. The 10x25s produce a 2.5-mm exit pupil. Both magnify the target by 10x, so the target has the same apparent surface area in both binocs. For the sake of discussion, I'll assume my eye pupil dilates to 5-mm under these conditions. Since the 50-mm binoculars have twice the aperture, they collect 4x as much light. Therefore the surface brightness of the target object will be 4x greater in the 10x50s than in the 10x25s.

Clearly, there is no advantage to using the 10x25s in this situation. It's been shown that the contrast ratio is the same in both instruments. Object apparent size is the same. The only binocular with an advantage is the 10x50, which presents objects as having 4x the surface brightness vs. their appearance in the 25-mm aperture binocs.

Suppose that, instead of bringing my friend's 10x25s, I bring his 20x50s into the field. How would these stack up against the 10x50s? Well, the 20x50s collect the same amount of light but produce a 2.5-mm exit pupil. Object surface brightnesses would be reduced but that wouldn't impact the contrast ratio. I'd need to use the higher mag binocs on a tripod or some sort of stabilizing device to address the shakes. And if we're talking about a very bright observing location, my eye pupils may not open wider than about 2.5-mm. The 20x magnification would, in that scenario, allow me to make full use of the aperture. The 10x50s would not.

If my eye pupils are just 2.5-mm in size, then the 10x25 binocs should--all other factors being equal--perform just as well as the 10x50s. That's because, as you've shown, my eye pupil shuts down the 10x50s to a 25-mm effective aperture. Theoretically, both instruments perform as 10x25s.
But the smaller binocs wouldn't have any optical advantage.

In conclusion, I'd recommend you consider editing your article to reflect the fact that contrast ratio (object surface brightness vs. sky surface brightness) is not affected by changes in aperture or magnification. Two ways to improve contrast ratio, are to observe under a darker sky or to use line filters that reduce sky brightness more than object brightness. Increasing aperture has the effect of lowering contrast threshold, which produces the perception of improved contrast ratio.










Although I agree with Henry that we should not jump to conclusions about aperture, I'm still tempted to suggest something on the basis of what Ron's curves as well as calculated MTF curves for diff.-lim. optics show. Along the lines of what Ron says in the following quote from post #78:

"One thing I’ve noticed right off, if the stab is close to correct, is that it appears larger objectives are going to have a contrast advantage over the smaller objectives even at the lesser resolutions."

The point I wish to make is that much of what we view in daylight involves trying to make out detail that is not of particularly high contrast to begin with - much different from a black-and-white bar-target or a double-star against dark sky background. So, supposing my eye is dilated to anything bigger than the 2.5mm an 8x20 binocular offers, there perhaps is a meaningful difference brought by increased aperture in my ability to extract detail from all sorts of lower-contrast objects where the spatial frequency/contrast ratio of the target was around the detection threshold of my eyes.

The personal reason why I keep coming back to this is that in addition to the limited testing I have done, I have now for some three years owned and used a very good sample (very low aberrations, excellent measured resolution for the aperture) of the Leica Ultravid 8x20, and am consistently surprised by how seldom I find the view fully satisfying despite knowing full-well there is very little room for improvement in it within its size and design parameters.

Kimmo

Kimmo
 
Sounds a like a more concise explanation of the more evenly lit field of a bigger aperture binocular. Another advantage of aperture. Good explanation.







Dennis,


The paragraphs in your link that deal with vignetting are based on a misconception. I think Ed is aware of his mistake now, but his old writing on the subject has not been revised.

The only "exit pupils" that are vignetted are those that form from off-axis rays and the effect is only pronounced near the edge of the field where the off-axis exit pupil of a typical binocular at full aperture is reduced to a cat's eye shape that passes 50% or less of the light of the axial exit pupil. The dimming of the off-axis image is so gradual that it mostly goes unnoticed. Your current favorite binoculars do this. Have you noticed it?

The reason large exit pupils (by which I mean 6-7mm) show less dimming at the field edge in bright light is because the minor axis of the cat's eye shape of such a large exit pupil may still be pretty large, perhaps 3-5mm. If the minor axis of the exit pupil is larger than the pupil diameter of the eye there is no visible dimming.

Henry
 
...

The personal reason why I keep coming back to this is that in addition to the limited testing I have done, I have now for some three years owned and used a very good sample (very low aberrations, excellent measured resolution for the aperture) of the Leica Ultravid 8x20, and am consistently surprised by how seldom I find the view fully satisfying despite knowing full-well there is very little room for improvement in it within its size and design parameters.

Kimmo

Kimmo

Hi Kimmo, Kimmo,

I have a similar feeling about my Swaro compacts not providing a completely satisfying view by comparison with larger optics. Otherwise, I guess, I really wouldn't have a need for larger optics. Rightly or wrongly, however, I rationalize this by other design variables, in particular, the narrower field of view that is typical of even the best compacts.

Several years ago I reported on BF an (incomplete) factorial experiment that convinced me at least (holding power and objective size constant, and controlling for retinal offset) that FOV alone has an important impact on stereo perception. Since stereo acuity is one of the primary visual processes that a birder relies upon, that aspect may be an unavoidable limitation for all compacts. I would certainly not put up with a similar FOV limitation in larger instruments, particularly those with roof designs that sacrifice retinal offset to boot.

Just a thought.

Best regards,
Ed
===================================

Dennis,

My understanding is that neutral density and other color filters may be used to enhance visual contrast. I know that aviator glasses aid target identification under open field viewing conditions, primarily due to target contrast enhancement. Shooters use yellow filters to enhance black/white contrast and score better.

How does this jibe with what you're saying?

Best regards,
Ed
 
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The personal reason why I keep coming back to this is that in addition to the limited testing I have done, I have now for some three years owned and used a very good sample (very low aberrations, excellent measured resolution for the aperture) of the Leica Ultravid 8x20, and am consistently surprised by how seldom I find the view fully satisfying despite knowing full-well there is very little room for improvement in it within its size and design parameters.

I've got a feeling that part of this "uneasiness" when using small binoculars may be due to the fact that it is somewhat difficult to keep the entrance pupil of the eye within the exit pupil of the binocular, making it harder to actually concentrate on what you're observing. I've still got pretty steady hands, but even in bright daylight I find I can't really "relax" when using small binoculars, "small" here meaning binoculars with an exit pupil of ~2.5mm.

Some anecdotal evidence: Last weekend I visited someone in hopital. She's an avid birder, so she's got a pair of alpha compacts at her bedside. There was a large flock of thrushes in treetops some 200 meters away, and we checked them in bright sunlight to see if there was something "interesting". I had got my old Zeiss 10x40 dating back to the late 1970's - no phase-coating, only single layer coatings. Optically her compacts were clearly superior, with better colour rendition, better sharpness and so on. And yet we both very much preferred my old Zeiss. It was so much easier to use and made for much more relaxed viewing, I think because of it's larger exit pupil.

Hermann
 
Same difference with the filters. Astronomers use filters to increase contrast on telescopes so binoculars could do the same thing. I think some binoculars used to have screw on filters that you could change and we discussed it on a thread here on Bird Forum. Could be a nifty idea really. Change your filter depending on what kind of a view you want or what kind of conditions you are viewing under.

Hi Kimmo, Kimmo,

I have a similar feeling about my Swaro compacts not providing a completely satisfying view by comparison with larger optics. Otherwise, I guess, I really wouldn't have a need for larger optics. Rightly or wrongly, however, I rationalize this by other design variables, in particular, the narrower field of view that is typical of even the best compacts.

Several years ago I reported on BF an (incomplete) factorial experiment that convinced me at least (holding power and objective size constant, and controlling for retinal offset) that FOV alone has an important impact on stereo perception. Since stereo acuity is one of the primary visual processes that a birder relies upon, that aspect may be an unavoidable limitation for all compacts. I would certainly not put up with a similar FOV limitation in larger instruments, particularly those with roof designs that sacrifice retinal offset to boot.

Just a thought.

Best regards,
Ed
===================================

Dennis,

My understanding is that neutral density and other color filters may be used to enhance visual contrast. I know that aviator glasses aid target identification under open field viewing conditions, primarily due to target contrast enhancement. Shooters use yellow filters to enhance black/white contrast and score better.

How does this jibe with what you're saying?

Best regards,
Ed
 
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