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Aperture Stop versus Exit Pupil Stop



 
 
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Old October 17th 03, 12:53 AM
Alan French
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Default Aperture Stop versus Exit Pupil Stop

Although I think I understand this, I am getting beat up, accused of being
stubborn, and probably close to being verbally abused about this elsewhere.
Since I know this never happens here, and that there will uniform agreement
on the issue, I thought I'd ask s.a.a. to join the discussion g.

We all know that an aperture stop reduces light grasp and resolution. If
you use a telescope at a very low power, or low power binoculars with large
objectives, the exit pupil can be larger than the eye, so the eye's pupil
acts as a stop. Obviously, light is lost, but what about resolution? Now I
know that when the exit pupil fills the eye's pupil, the power is too low
for you to utilize the resolution of the lens, although you have as much
light and resolution as you can possibly get at that magnification. So
let's just say "is potential resolution lost?"

Perhaps there is a better way to ask this. If you have a telescope with a 2
mm exit pupil, and you put a 1 mm stop at the exit pupil, is the resolution
halved? It would certainly seem that additional diffraction occurs from the
outer edge of the pupil or "exit pupil stop" opening - but how to you figure
out the effect of this on top of the diffraction from the telescope entrance
pupil?

Clear skies, Alan

 




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