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post #29 of Old 07-03-2013
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Re: Binocular Conundrum: Field of View?

Originally Posted by hellosailor View Post
pappy, I understand what you are saying but I think you are missing something.

The binoc makers all claim that a larger exit pupil size is crucial, because the size of the exit pupil (or the iris, whichever is smaller) will "crop" the size of the image on the retina.

So, given that the image is being cropped by the same size exit pupil, which in theory means the same size image is falling on the retina, if the smaller FOV already produces an image that fills the retina, how can the larger FOV be presented onto the same retinal area? Unless the image size is reduced, which would mean a smaller magnification.

You see where I'm finding a contradiction in their logic? If you can fit a camel through the eye of a needle...don't you need smaller camels if you want to fit them through two at a time? (Do I get an award for most mangled analogy on that one?)
Its a good question Hellosailor
One fundamental mistake you are making is with the understanding of the pupil. The pupil does not effect the field of view.

All the feild of view passes through each point of the pupil.

As our pupil gets larger and smaller our field of view does not change.

This is true when viewing without binoculars (your field of view is not smaller in bright sunshine when your pupil is smaller) or with binoculars (once again the FOV with the binoculars is not worse in bright sunshine)

Another way of understanding the problem is to think of camera. As we stop the lens down we don't take a picture with a narrow FOV. We take the same FOV but some of the light captured by the camera lens does not get thought to the film. Despite blocking of some of the light we still get the whole FOV. We can make the iris bigger, smaller round or a funny shape and we get the same photograph just brighter or duller.

I hope this helps at least part of the puzzle.

Last edited by noelex77; 07-03-2013 at 02:41 PM.
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