Quote:
Originally Posted by Satchmo
It would be interesting to find a simple test by which people could survey their pupil diameters. I always err on the side smaller side, as I doubt most observers have the ambient conditions to achieve a maximum pupil. The eye is pretty poor quality at maximum aperture : contrast and sharpness are well down, so I rarely use those mags despite th efield of view.
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Hi Mark,
You can do this yourself without any fancy equipment and get a very close estimate of your pupil's maximum dilation. You need a set of allen keys or twist drills of known diameter.
Go to a dark observing site, and give your eyes about 30 minutes to fully dilate. When dark adapted and ready to test, try to block the light from a star by putting increasingly large sizes of allen keys or drills a couple of inches in front of your eye. Start a couple of millimetres less than what you expect your pupil dilation to be. When the allen key or drill is smaller than your pupil, you will see the star as double. When the wrench matches your pupil, the star will wink in and out as you move the wrench in front of your eye. Only after you find the right size allen key or drill should you turn on your red torch and find out its size. I am 48 yrs old and mine is about 6.2 mm under really dark skies. Many things affect your pupil dillation including age, general health, smoker or non smoker, heavy drinker, high blood pressure, blood sugar levels etc etc etc. As you correctly point out, it is better to err on the side of conservatism and go with an undersized exit pupil. In other words, stay around 6mm to 6.5mm maximum, if high contrast views with black sky background, are your goal. Thus, a 31mm Nagler or 30mm Pentax XW in an F5 scope is ideal IMO.
CS-John B