Re: Dark adaptation on exit pupil size

From: Bill Ferris (billferris_at_aol.comic)
Date: 09/07/04 

Date: 07 Sep 2004 14:47:34 GMT

canopus wrote:
>One would expect to find a reduction in the ability to see faint stars
>with the naked eye with age, since a reduction from 6.9mm (15 year
>olds) to a 6.2mm (50 year olds) in average dark adapted eye pupil size
>corresponds to about a 20% reduction in the eye's light grasp.

However, dark adaptation is primarily a chemical process within the eye. The
additional light grasp of the fully dilated eye pupil accounts for just a
fraction of the total improved light sensitivity of the dark adapted eye. I'm
not aware of research showing a correlation between pupil size and naked eye
limiting magnitude among experienced observers. All the research I've seen
points to the chemical process as the key to dark environment light
sensitivity. So, while there may be age-related degradations of scotopic
vision, I wouldn't assume constriction of the eye pupil to have a measurable
impact.

Regards,

Bill Ferris
"Cosmic Voyage: The Online Resource for Amateur Astronomers"
URL: http://www.cosmic-voyage.net
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