vxg@panda.UUCP (Vincent Gonzalez) (12/19/85)
WARNING - Long summary follows - Of interest to individuals interested in
the purchase of a pair binoculars. Experts need not read further.
I would like to thank all of the people who replied to my need for
help in selecting a pair of binoculars. The general consensus was that
the 7X50 binocular was the better choice for beginners as will as experienced
viewers. The following is an editted summary of their replies.
SUMMARY
---------
For night viewing, the most important thing is to make full use of your
eyes. The diameter of typical dilated pupils is 7mm; the size of the
effective aperture is the aperture size (the second number) divided by
the magnification (the first number). Thus 7x50's are just about perfect
for night use; any larger magnification without an increase in aperture
is useless. The point is not to have high magnification, but to maximize
the number of photons coming in. Larger binoculars than 7x50 exist, but
are too large to be held easily. I would go with the 7x50's.
Courtenay Footman
----------
I would recommend the 7x50s. The "exit pupil" (the pencil of light
emerging from the eyepiece) of these binoculars is 7mm, which pretty
exactly matches the fully opened iris of your eye. This means that
you will see the brightest possible image of extended objects (such as
galaxies, nebulae, and comets). Larger aperture telescopes will only
be able to show such things bigger, not brighter.
Higher magnification binoculars have the following disadvantages:
1) Objects such as comets will appear dimmer (though larger)
due to the smaller exit pupil (exit pupil = aperture (50mm)
divided by magnification (7x), so 7x50 yields 7mm (approx.))
2) They will be harder to hand-hold, since any shakiness will
be magnified.
3) They will view a smaller area of sky (all else being equal -
the field of view is a partially independent variable, and one
that you might want to check) and thus things will be harder
to find.
If you have access to a library, Sky and Telescope had a very good article
in the October '83 issue (I'm pretty sure that's right) on choosing binoculars.
Dean Krafft
----------
One of the most important consideration I have found for purchasing
binoculars is comfort. A 20x80 may be wonderful for looking at the
sky, but who is going to want to hold on to such monsters for more
than a few minutes. 7x50 and 8x50 seem to be good all-around choices.
One other piece of equipment that should be purchased is a comfortable
outdoor adjustable lounge chair. This can make the viewing even more
comfortable. Take it from someone who is still suffering a sore neck
after trying to look straight up at Halley's.
Dick Pierce
--------
As you probably know, a binocular specification such as
7X50 means "seven power magnification, 50mm-diameter
front lenses". For astronomy, light grasp is of the
essence, so that the larger the second number is, the
better! On the other hand, binoculars that are in
some combination too heavy, or magnify too much, cannot
be held sufficiently steady without a tripod. Most
people have no trouble with a 7X50, but an 11X80 is
more difficult to use. I recommend a 7X50 as an
excellent instrument for a beginner. There are several
good ones available in the $100 range (a bit less on
sale, rather more at list price).
Jay Reynolds Freeman
---------
1) 70, 80mm lens and larger are some trouble to
use, so you should only get them if you are
really serious.
2) 20x and higher magnifications are also more than
someone just starting out would want.
That leaves the most common: 7x, 10x, 35mm, 50mm.
You would want 50mm if most of your viewing is at
night (to gather more light). If most viewing will
be in the daytime, 35mm is fine.
7x and 10 x I think is just a matter of how much
magnification you would like to pay for. For
astronomy, I would get 10x50, although sometimes
you can get a good deal on 7x50.
Optics still seem to response to price. You can
get a 7x35 for $30 to $90, and the $90 pair IS far better
than the $30 pair. Avoid "Western Field". Tasco
is mediocre. Bushnell is a little better, particularly
because of their "Insta-Focus" lever. I hear that
Nikon is suppose to be fantastic. Macy's has them
on sale.
Finally, the last issue of Astronomy had an article
on buying binoculars. It talked about how to look
for chromatism and aberrations; and how different
binoculars are constructed.
- Chris Salander