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Buying Binoculars

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Darrell Heath | Astronomy Columnist

I get nauseous for even
thinking about holiday gift
buying any sooner than two
weeks after the Thanksgiving
leftovers have run out.
But, I understand that some
gifts demand a little forethought
before purchasing
and such is the case when it
comes to buying a telescope
for the beginning stargazer.
I’m going to let you in on a
little secret when it comes to
buying that first telescope:
DON’T! That’s right, walk
right past that department
store telescope (in fact, run,
don’t walk past it) and head
straight for a pair of binoculars.
“Binoculars, aren’t they
only good for bird watching
(not that there’s anything
wrong with that)?” No, binoculars
are a versatile bit
of optical equipment that
you can use for a number
of activities and stargazing
is just one of them. In fact,
if and when you ever decide
to purchase a telescope, you
will find that a good pair of
binoculars is still an essential
bit of gear.
Why should you consider
binoculars before a
telescope? Because if you
are a beginner you need to
learn how to navigate the
sky before you spend all that
money on a telescope. Sure,
you can buy a computerized
telescope that will steer you
around the heavens but I
am a believer in first learning
how the sky works and
where a few things are on
your own without having to
resort to a computer driven
telescope. Another reason
is that binoculars are affordable,
easy to use, portable,
versatile, and will give you
a wider field of view than
a telescope. If you decide
that stargazing as a hobby
is not right for you then you
have an inexpensive bit of
optical equipment you or
your kids can use any time,
any where for things like
sporting events, concerts,
or wildlife viewing.
What can you see with
a pair of binoculars? The
Moon with its craters and
lava plains, star fields within
the Milky Way, star clusters,
nebulae, and even a few
galaxies are within reach
of most binoculars. In fact,
some objects look better
through binoculars than
a telescope all because of
that wider field of view. A
good example is the Andromeda
Galaxy, which has
an angular size of 3 degrees
across, the equivalent of
six full Moons! A telescope
view will only show you the
central most portions of the
galaxy’s core but binoculars
can reveal much more. Of
course there are limits as
to what binoculars can do;
planetary details, for example,
will be beyond their
capability, as will the finer
details of most nebulae.
Here are the essentials
you need to consider before
buying.
Numbers. There are
two important numbers to
think about when it comes
to binoculars: one of them
denotes how much magnification
is being offered and
the other is related to the
diameter of the objectives
(the end where all the light
comes in). For example:
10×50. The 10 tells you that
the binoculars are magnifying
objects 10 times their
normal size while the 50 tells
you that the objective lenses
are 50mm in diameter. My
personal preference for astronomy
binoculars is a pair
of 10×50’s, anything bigger
than that is difficult for me to
hold steady. A quality pair
of 10×50 binoculars is a good
all purpose size but you can
go bigger, just be aware that
as you increase the size that
steadiness becomes a central
issue. Bracing your binoculars
against something
while you view can help; or
just make sure you buy a
pair that can be mounted on
a sturdy tripod. If you have
lots of money you can even
buy binoculars with image
stabilization capability.
Prisms. Whenever light
passes from one medium to
another it becomes bent and
binoculars use prisms to
correct for this so that you
have an image oriented the
right way for viewing. Roof
prisms and Porro prisms
are two different design
styles used to correct for
this. Roof prisms are finicky
and very expensive so you
should probably avoid these
and go with the Porro prism
design.
Coatings. Whether or
not the lenses are coated
will play a role in how much
light is transmitted through
your objectives and to what
extent that light gets bent.
Opinions vary on whether
or not multicoatings are better
than a single coating but
the bottom-line is that you
will pay a bit more for the
former over the latter. Just
make sure that you don’t
buy a pair with UV coatings.
That’s the barebones basics
but I strongly urge you
to do more homework on
line or by talking to others
who are experienced with
binoculars for astronomy.
You can always write to me
or other Central Arkansas
Astronomical Society members
by simply dropping us
a line at info@caasastro.org
Next week we will look
at the variety of telescopes
being offered on the market
today.