As pointed out, "Exit Pupil" is the term used to define the spot size of the
light leaving the telescope.
A number of people have described methods for measuring the diameter of the
fully dilated pupil. However, you don't have to wait 30 minutes before
measuring. The pupil dilates essentially immediately once you enter a
darkened room. Waiting a minute is fine. The chemical processes to acquire
true dark adaptation is what takes longer and is irrelevant to measuring
your pupil size. The size of someone's fully dilated pupil is an interesting
number, but also isn't relevant to how well you see dim objects through a
telescope. It is a number for selecting eyepieces.
I've used the following simple method to measure the diameter of fully
dilated pupils. You can make the tool and measure your pupil size in about
15 minutes.
On a sheet of aluminum foil, use a pin to make a series of holes with
various spacings. Use a fine metric ruler and make very small pinholes
spaced 5, 5.5, 6, 6.5, 7, etc apart.
Go to a closet (or a darkened room) and crack the door so that you are
looking out at a dim light. The light should be bright enough so you can
detect the pinholes while holding the aluminum foil up to your eye. Hold the
aluminum foil so a pair of pinholes is between your pupil and the light.
With closer-spaced holes, you should see two overlapping circles of light.
If the two pinholes are too far apart, you won't be able to see both
simultaneously. One will overlap your pupil, one won't. Your pupil size
corresponds to the hole spacing where you see two circles of light that just
touch one another. I've done this test on a number of people and it worked
very well. Adult pupil sizes ranged from 5mm to 6.5mm.
Albert
Received on Wed Jul 28 10:26:08 2004