10X50 vs. 7X50

The following flash photograph method was the easiest, simplest, and
most accurate method for me. This was suggested in a post in this
usenet group by someone else a few months ago:

Take a nap with the house darkened. Pre-position an ordinary
disposable flash camera in front of the bathroom mirror and practice
holding it next to your face and taking a flash picture. You will need
to be proficient enough in operating the camera to take a flash picture
in total darkness. When you wake up in the darkened room, go to the
mirror and take the picture. Your exit pupil does not react fast
enough to the flash bulb to alter the measurement.

Measure the developed photo using measure calibers, or if digital, the
pixels coordinates displayed in picture editing software. Measure the
physical dimensions of your eyebrows, nose, eye "whites", or iris. A
little proportional math is then used to find the size of the your exit
pupil in the photograph.

One drawback of this method is that there is some uncertainty in
measuring the fuzzy border of exit pupil in a small photo, this seems
to be the most accurate of various alternative methods. Study of the
relative size of your dark adapted exit pupil, using a
very-low-intensity red light and a small hand mirror, when you
dark-adapted at a dark sky site, was also helpful.

One advantage of this method is that it can be performed reliably with
truly dark adapted eyes.

The photographic method seemed the be the simplest and most effective,
out of a variety of options, e.g. - the triangular S&T pupil gauge,
allen wrenches, drill bits, having a friend measure the exit pupil with
measuring calipers when dark adapted at a dark sky site, using the
measuring calipers at a dark sky site in a small hand mirror, etc.

- Canopus56

Exit_pupil_dia_physical =
( Exit_pupil_dia_photo * Eyebrow_ln_physical ) / (Eyebrow_ln_photo)

canopus56 wrote:
The following flash photograph method was the easiest, simplest, and
most accurate method for me. This was suggested in a post in this
usenet group by someone else a few months ago:

Take a nap with the house darkened. Pre-position an ordinary
disposable flash camera in front of the bathroom mirror and practice
holding it next to your face and taking a flash picture. You will need
to be proficient enough in operating the camera to take a flash picture
in total darkness. When you wake up in the darkened room, go to the
mirror and take the picture. Your exit pupil does not react fast
enough to the flash bulb to alter the measurement.

Measure the developed photo using measure calibers, or if digital, the
pixels coordinates displayed in picture editing software. Measure the
physical dimensions of your eyebrows, nose, eye "whites", or iris. A
little proportional math is then used to find the size of the your exit
pupil in the photograph.

One drawback of this method is that there is some uncertainty in
measuring the fuzzy border of exit pupil in a small photo, this seems
to be the most accurate of various alternative methods. Study of the
relative size of your dark adapted exit pupil, using a
very-low-intensity red light and a small hand mirror, when you
dark-adapted at a dark sky site, was also helpful.

One advantage of this method is that it can be performed reliably with
truly dark adapted eyes.

The photographic method seemed the be the simplest and most effective,
out of a variety of options, e.g. - the triangular S&T pupil gauge,
allen wrenches, drill bits, having a friend measure the exit pupil with
measuring calipers when dark adapted at a dark sky site, using the
measuring calipers at a dark sky site in a small hand mirror, etc.

- Canopus56

Exit_pupil_dia_physical =
( Exit_pupil_dia_photo * Eyebrow_ln_physical ) / (Eyebrow_ln_photo)


Turn the "red eye reduction" feature off on your camera, or else you'll
be seeing spots for no reason. :-)

Shawn

On Mon, 24 Jan 2005 16:54:35 -0600, wrote
(in article .com):

I thought a minimum of twenty minutes was the average for full dark
adapatation in very dark conditions? Perhaps it's less with moonlight
because the eye simply doesn't adapt fully? Presumably distant light
pollution and lying snow would have similar effects?

Chris.B


The pupil fully expands in a matter of minutes. The rest of dark adaptation
is a chemical process that does take 30 minutes or more. It is the first
part that you are interested in.

ROM SPACE KNIGHT NURSE wrote:

I'm going to buy binocs. I've read the ten power require a tripod due to
the natural shakiness of hands, but the 7 power not. Is that extra
3-power worth the extra $$ for a tripod and adaptor?

If you have steady hands get the 10x, otherwise 7x. The higher power can
make a difference for some objects, particularly planets. Get the widest
field you can find in either power but don't expect the focus to be good
at the edge of the field unless they have very good optics. Have you
considered a zoom binocular, like a 7x-15x/50mm?

Florian wrote:

This is my method for measuring pupil size...

I use a set of metric Allen wrenches. Go out at night and wait
a minute or two for your pupils to fully open. Hold an Allen wrench
one at a time close to your eye and look at a medium bright star. I rest
the wrench on my cheek. With small sizes you will see two stars, one on
each side of the wrench. Work up until you only see one star, on one
side of the wrench or the other. I've heard some people can see two
stars when using a regular wooden pencil. That's about 7mm. To me a
pencil looks like a board! I can just see two stars with a 3mm wrench
and only see one with a 4mm thus my pupil is 4mm or less. Sky &
Telescope magazine sells a little gauge for measuring nighttime pupils
as well. It's a piece of mylar with paired holes from 1mm to 9mm apart.
It works on the same principal as my Allen wrench method. You can also
use drill bits or strips of black paper cut to various widths.

-Florian

Would that work for wearers of glasses? You couldn't get the allen
wrench so close to the pupil for the test.

thanks to all posters for the info...Rom

MY HALLIBURTON BOARD OF DIRECTORS RIGHT OR WRONG!

Would that work for wearers of glasses? You couldn't get the allen
wrench so close to the pupil for the test.


Yes, will work if you wear glasses. The wrench doesn't have to be
right at your eye. A few inches away should give similar readings.

-Florian

Zoom binoculars have historically been optically inferior to fixed
power bioculars.
So the fixed power binos have always been recommended over zoom types.
The same has usually held true with fixed versus zoom telescope
eyepieces.
Perhaps the high-end zoom eyepieces have broken the rule?

Regarding allen wrenches (UK allen keys) I supopose you have noticed
they are hexagonal?
It seems too obvious to point out that they must be larger across the
"points" than they are across the flats.
Presumably deliberately laying the "handle" flat on one's cheek largely
eliminates this error? ;-)

Chris.B

On Tue, 25 Jan 2005 01:19:29 -0500, starman wrote:

Would that work for wearers of glasses? You couldn't get the allen
wrench so close to the pupil for the test.

Stars are so distant that the rays of light are parallel; therefore,
the distance from the eye to the allen wrench doesn't matter. The
effect of spectacles is that the rays of light diverge or converge
after they pass through the lens, depending on your prescription,
which affects the apparent size of your pupil.

You can take off your glasses and still get your pupil diameter,
assuming you can still see the star.

I brought the tripod first and then the 8X56's.