Mark Wagner wrote:
>
> Is there such thing as a pupilometer, so I can measure the
> size of my exit pupil?
I use a caliper. Point the scope & eyepiece at the daytime sky or
lighted ceiling. Stand behind the eyepiece with both eyes open, about a
foot or two back, and you'll see a tiny light disk, floating just above
the eye lens. With a bit of practice, you'll find that you can hold the
caliper at just the right distance. Adjust it in steps of 0.1 mm or so,
and you'll find that you can measure the image.
OTOH -- if you know the actual focal lengths of primary and eyepiece,
divide the eyepiece focal length by the f/ratio of the primary. Or
divide the diameter of the primary by the magnification.
OR -- did you mean to measure the pupil of your eyeball?? I'd call
that your eye pupil, or entrance pupil, maybe.
Cut a strip of paper about 300 mm long, tapered from about 12 mm wide
to about 3 or 4 mm wide. Set up a small point source a few meters away.
Put on your eye patch. Darken the room. Wait a while. Hold the paper
strip vertically before your observing eye, and move it up and down
until you *just* lose the point of light. It'll take some practice; as
you move your head side to side, you'll see the light past each edge of
the paper. What you want is to lose the light for the smallest instant;
if the paper is too wide, you'll have a range over which the light is
lost; too narrow and you won't lose it at all. When you believe you
have the correct position, CAREFULLY mark the paper with a pencil, at
your eye's pupil. Do it over a few times. At last, turn on your red
light and see if the pencil marks are consistent. If so, measure the
width at that spot.
One of the secrets of a well-known SJAA comet hunter is that his
dark-adapted eye has a 10 (ten) mm pupil!
-- Jim Van Nuland, San Jose (California) Astronomical Association <a href="http://www.svpal.org/~jvn/ ">JVN's home page</a>Received on Tue Jul 27 14:08:40 2004