8.
HOW TO CHOOSE BINOCULARS AND TELESCOPES
by R. Tomlinson
I would like to devote this article to
binoculars and add a few words on telescopes
because a lot of would-be bird-watchers are
sometimes confused by the sheer variety of
these instruments offered for sale. This is
a subject rarely dealt with in Natural History
magazines. I have paid particular attention
to binoculars and telescopes in the twenty
years or so I have been birdwatching so I feel
competent enough to write upon the subject.
Some people think that the larger the
magnification, the better the glasses, but
this is not so. You just stand on the sea-
wall on a windy day and try to focus on that
raft of ducks out on the tide
with even a pair of 10 x 50
glasses and you will see what
I mean. As proof of this,
after severe and exhaustive
tests, 7 x 50 binoculars have
been chosen by the Admiralty
for general use in the British
Navy, and an overwhelming pro-
portion of binoculars used in
the Army are 6 x and 7 x ... Let me explain,
take the figures 8 x 30 for example. The
first figure, 8, means that the object being
viewed is magnified 8 times, the figure 30
means that the binoculars have a 30mm object
lens - these are the big lenses at the end of
the binoculars that face the object you are
viewing. Now hold these 8 x 30's about 12
inches away from your eyes and direct them
upwards. A small circle of light can be seen
in each eyepiece. This is called the exit