chs@loral.UUCP (07/16/84)
After posting a collection of articles on buying binoculars last week, I
received an article saying that there was an error in one of the comments.
Here is the text of that message:
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Date: Fri, 13 Jul 84 09:01:53 pdt
Re: binoculars
One of the comments you posted is incorrect. The second number in
the spec -- the 36 in 7x36 -- does not determine how wide a field of
view you get, except very indirectly. Rather, the field of view
is often quoted separately (as: 385' @ 1000 yds). The size of the
objective lens does, however, determine the "exit pupil" of the binoculars,
a number that can be determined by dividing the second number by the
first. Thus 7x36 binoculars have exit pupils of 5.14 mm. The larger
the exit pupil, the brighter the image will be, until the exit pupil
exceeds the size of the pupil of your eye at that brightness. I think
that most people's eyes won't open more than about 7mm, so you won't
gain anything more beyond 7x50, 10x70, 12x85, and so on. On the small
side, exit pupils less than about 3mm make the binoculars very difficult
to line up with your eyes in bright conditions, because the exit pupil
has to match your own eyes exactly and both are very small. Thus,
expect trouble with 8x20 (which I have seen).
I own a pair of Nikon 7x26 roof prism binoculars and love them.
They can be obtained in the large NY discounters for about $160/pair.
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I haven't bought any binoculars yet, but I think that these articles will
help me. Thanks again for the replies to my original posting.
--
Craig Schamp
Loral Instrumentation, San Diego
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