"Alan French" wrote in message . ..
You can measure your exit pupil when you are dark adapted. Make a long
strip of light cardboard (a manila folder works well) that tapers from 2mm
wide to 8mm wide. While looking at a star, place the narrow end of the stip
in front of your eye, as close to your pupil as possible. .... [big snip]

Great tip Alan. I'm going to try this since everyone's vision is
unique. Using a general relationship, Mike, at 47 years of age, may
have aways to go to get down under a 5mm pupil size:

D_exit_pupil = 7 mm exp(-0.5[A/100]^2])

Age D_ep
10 7.0
20 6.9
30 6.7
40 6.5
50 6.2
60 5.8
70 5.5
80 5.1
90 4.7
100 4.2

Schaefer, B.E., Telescopic Limiting Magnitudes, Pub. Astron. Soc. Pac.
102:212-229 (Feb. 1990)
citing prior work of:
Kadlecova, V., Peleska, M., and Vasko, A. Nature 182:1520 (1958)
Kumnick, L.S., J. Opt. Soc. Am. 34:319 (1954)

- Kurt