Re: Dark adaption and pupil size - an experiment (longish)

From: dwight elvey (dkelvey_at_hotmail.com)
Date: 08/25/04 

Date: 25 Aug 2004 14:31:51 -0700

boo@fractalfreak.com (eric bazan) wrote in message news:<ca17eb03.0408231339.689f4579@posting.google.com>...
> (background)
>
---snip---
>
> When I got home I looked at my pupils in the mirror. They were
> *huge* - freakish in fact. My right pupil had dilated to well
> over 9mm, and the room didn't have to be very dark to achieve
> this - the effects of the atropine.
>
> This surprised me. I had thought the chemical changes in the
> retina during dark adaption (buildup of 'visual purple', etc.) would
> far outweigh any slight changes in pupil size. However, because the
> area of a circle varies with the square of the radius, going from
> (as an example) a 7mm to a 9mm pupil nearly doubles the amount
> of light the eye can gather. My experiment seems to bear this out.
>
>

Hi
 One thing to consider here is that for use with a telescope,
once your eye's pupil exceeds the exit pupil of the telescope,
opening the eye more has little effect other than it is
easier to center the eye on the exit pupil. In fact, increasing
the pupil size can increase the amount of stray light, causing
loss of contrast.
 Increasing your pupil size can make a difference on vary low power
but in general, the image will already be so bright that there
is a lot of scatter in the telescope and your eye. More light
might not improve the appearance of the image.
 Increasing your pupil size can also decrease yours eyes dark
adaption when not actually looking into the telescope. This
is because the trail you are on doesn't have an exit pupil,
all of the light gets in. This can decrease the effectiveness
of the dark adaption when going back to look through the
telescope.
Just some thoughts.
Dwight

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