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

From: Chris L Peterson (clp_at_alumni.caltech.edu)
Date: 08/25/04 

Date: Wed, 25 Aug 2004 22:11:46 GMT

On 25 Aug 2004 14:31:51 -0700, dkelvey@hotmail.com (dwight elvey) wrote:

> 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...

Another thing to consider is that even in the case where the exit pupil of the
telescope is larger than the eye's pupil, you may be better off. That's because
the eye exhibits a large amount of spherical aberration, primarily from the
cornea (the eye's primary refractive surface). A smaller pupil blocks the more
steeply curved outer part of the cornea, and provides a higher resolution image
at the retina. So you trade some brightness for quality. This probably wouldn't
be obvious for dim objects (where visual acuity is poor anyway), but for bright
objects like M42 it might be.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

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