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Is FOV linked to brightness?

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Old Wednesday 6th May 2015, 14:40   #1
tpcollins
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Is FOV linked to brightness?

Forgive me for asking on a binocular sub forum but I can always count on getting the correct answer here on optics questions.

I understand exit pupil and lens coatings that allow light transfer, but let's take two variable power rifle scopes for example. Scope A is a 2.5-10x40 and on 5x has an 8mm exit pupil and a FOV of 35' at 100 yards. Scope B is a 2-7x32 and on 4x has the same 8mm exit pupil but a narrower FOV of only 30' at 100 yards.

With all coatings being the same, would the 2.5-10 scope actually be brighter because of a larger FOV or would it be an illusion tricking the mind into just thinking it was brighter? Thanks.
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Old Wednesday 6th May 2015, 15:00   #2
Binastro
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I don't think that the field of view is linked to brightness, except for perhaps wide fields of view where there may be vignetting towards the edges.
It is common for zoom eyepieces to have variable fields of view. Normally the apparent field of view is greater at the higher magnifications and smallest at the lowest magnification. I don't actually mind good quality zoom eyepieces, even with some binoculars, although the great majority of zoom eyepiece binoculars are poor, there are exceptions. I haven't looked through a zoom eyepiece rifle scope, although and I have used many zoom eyepiece telescopes. When I used to shoot it was at Bisley using Lee Enfield .303 rifles without optical aid. It used to bruise my shoulder unless I put a handkerchief under my shirt.

With the two examples given, not only are the apertures different, but the magnifications vary, so brightness is not a simple matter here and also depends on the size of your eye pupil, and also the ambient light conditions.

Last edited by Binastro : Wednesday 6th May 2015 at 15:04.
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Old Wednesday 6th May 2015, 15:03   #3
mayoayo
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No...Field of View (FOV) doesnt affect brightness as a conditionant, though they can run parallel in certain cases...In a variable power eyepiece,the Real field of view and the exit pupil BOTH will diminish with the increase of magnification..so the scope Wouldn't be brighter BECAUSE of the larger field of view, But the lower the magnification(x) ,the brighter the image (exit pupil in mm) AND the larger the REAL field of view ( number of feet seen at a given distance).

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Old Wednesday 6th May 2015, 15:42   #4
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This is a perennial question that receives the same perennial responses, however, I've found that, as in other aspects of viewing through binoculars, perception plays a role that doesn't show up on the chalk board.

Case in point is the Nikon 8x SE vs. Nikon 8x EII. Even if you had samples with the latest AR coatings (550xxx SE and black body EII), the SE would still be brighter 'on paper" because it has 2mm larger objectives. Under the most dismal conditions that extra aperture delivers more light to the eye that might be noticeable as your pupils open wider, but under sunny skies or partly sunny skies, the EII looks brighter to me, because of its larger FOV.

When I'm looking at a scene, there's more background around the bird with the EII. Unless I'm looking into a dark area, that background is sunlit, so there's more light reflecting off objects, and that makes the scene appear brighter.

So there are two answers to this question, the Physics answer- No, and the perceptual answer- Maybe, depending on how your brain perceives "brightness."

bp
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Old Wednesday 6th May 2015, 17:09   #5
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Brock said: " . . . perception plays a role that doesn't show up on the chalk board."

Carve that in stone . . . especially since these posts deal as much with "perceptions" as realities.

Hey Brock, see how short I made my "perennial response," this time. Yeah, Yeah, I know; don't count on it holding!

Bill
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Old Wednesday 6th May 2015, 17:41   #6
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tpcollins,

This matter is discussed in an earlier thread, there you can find some interesting stuff: http://www.birdforum.net/showthread.php?t=297760
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Old Wednesday 6th May 2015, 19:47   #7
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Quote:
Originally Posted by brocknroller View Post
So there are two answers to this question, the Physics answer- No, and the perceptual answer- Maybe, depending on how your brain perceives "brightness."
Thanks Brock, makes sense. I knew I'd get the right answer here.
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Old Wednesday 6th May 2015, 21:30   #8
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Old Wednesday 6th May 2015, 23:54   #9
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Quote:
Originally Posted by brocknroller View Post
This is a perennial question that receives the same perennial responses, however, I've found that, as in other aspects of viewing through binoculars, perception plays a role that doesn't show up on the chalk board.

Case in point is the Nikon 8x SE vs. Nikon 8x EII. Even if you had samples with the latest AR coatings (550xxx SE and black body EII), the SE would still be brighter 'on paper" because it has 2mm larger objectives. Under the most dismal conditions that extra aperture delivers more light to the eye that might be noticeable as your pupils open wider, but under sunny skies or partly sunny skies, the EII looks brighter to me, because of its larger FOV.

When I'm looking at a scene, there's more background around the bird with the EII. Unless I'm looking into a dark area, that background is sunlit, so there's more light reflecting off objects, and that makes the scene appear brighter.

So there are two answers to this question, the Physics answer- No, and the perceptual answer- Maybe, depending on how your brain perceives "brightness."

bp
Brock:

This question was posed about these 2 binoculars some time ago, as to
which one had higher transmission, or appeared brighter, the Nikon SE
8x32 or the 8x30 EII. It may be on the Nikon subforum, not sure.

I remember my careful observation was that the EII, appeared to have
a bit brighter image at last light. These were both newer models with
recent coatings. The SE may have a bit more complicated eyepiece since
it offers a flat field. One more lens would do that.

That post had some differing opinions but the size of the FOV may have something to do with it.

Jerry
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Old Thursday 7th May 2015, 14:49   #10
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In the days before AR coatings and to a lesser degree with single layer coatings, the opposite was the case i.e. vintage wide field binoculars tended to have dimmer fields of view because their 3 lens Erfle type eyepieces had 6 air to glass surfaces which reflected more light with consequent lower levels of light transmission than did conventional 2 lens/4 air to glass surfaces eyepieces of non-wide angle binos.

Last edited by LPT : Thursday 7th May 2015 at 14:52.
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Old Sunday 10th May 2015, 22:05   #11
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Quote:
Originally Posted by Pileatus View Post

That was a darn good read . . . !
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