chs@loral.UUCP (07/11/84)
Here is a summary of the responses I got to my request for information
on buying binoculars. Thanks to all who responded; the information will
be very helpful to me.
--Craig Schamp
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In a binocular spec expressed as nXm, n is the magnification, m is
the diameter of the lens nearest the object under view in millimeters.
Thus, 10X35 binoculars magnify everything 10X and have 35 millimeter
diameter lenses.
The usual tradeoff is magnification versus field of view. A higher
magnification covers a smaller piece of the world at a given distance.
The spec is usually given as the width of the field of view at 1000
yards, e.g., 450 feet. Larger lenses offer a wider field of view for
a given magnification. 10X50 will cover a bigger area than 10X35.
Other considerations are lens material, glass (heavy) or plastic
(scratches easily). Cheap binoculars will show distortion,
particularly at the edges of the lens. Look at a grid pattern, such
as a brick wall to see the problem. Also look for chromatic aberration.
This is a condition where the lens refracts different colors by different
amounts, creating rainbow effects at sharp lines.
A higher magnification binocular is harder to keep steady on the target,
especially if it is moving (e.g., aircraft).
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10x is kind of high to hold steady. 7x is usually about the
highest power one can hold steady enough to not get a constantly
jumpy image.
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Tip on buying binoculars: They are highly individual items.
Do NOT buy without trying them out first, i.e. do not buy by mail
unless you don't mind sending things back.
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I would definitely recommend 'roof prism' binoculars. My wife and I have
the Bushnell 7x25 model. The roof prism means they look like two small
parallel tubes rather than like the big double jointed World War II type.
They are light and compact. They are also made by Nikon, Minolta and other
makers of quality products. We picked Bushnell because they worked best
with glasses and were easiest for my wife to get accustomed to. She has
a problem with many binoculars in trying to see the same image with both
eyes. The zoom models are a waste since they sacrifice quality and have
virtually no benefits. The highest power you can hand hold is usually
7x. Try this to be sure. Higher powers are empty since hand shake takes
away anything you might gain. Less than 5x and you might-as-well not
use any unless you really need glasses. 5x is probably best for football
games. Make sure you try anything you buy since some people trouble using
some models.
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--
Craig Schamp
Loral Instrumentation, San Diego
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