RE: ATM Exit Pupil Question

["Bill T." <twentiethwave@hotmail.com>]

>There was an idea that you could flash photo your dark adapted pupil with a
>metric ruler near you eye to determine your maximum actual pupil

It is much less painful to try out several eyepieces of different focal 
length, and note whether or not the shadow of your iris is detectable 
against a slightly out of focus star.

eyepiece_exit_pupil = eyepiece_focal_length / telescope_f-ratio

I tried taking eye diameter measurements with the infrared feature of a 
video camera.  What I usually saw at first was the iris closing down in 
response to the dim red component of the infrared LED's in the camera.

I wonder if consideration of the dark-adapted iris diameter is really 
relevant to telescope design.  Since most images seen through a scope 
consist of "lights" and subjects brighter-seeming and sharper than the dark 
observing environment, the iris must close down at least a little at the 
eyepiece.

I had brief talk with an vision specialist.  He contended that to dialate 
fully, the iris required both darkness AND a lack of perceivable shapes.

Bill T.




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