Darrell Heath
Astronomy Columnist
Selecting a telescope is
just like buying any other
kind of precision tool or
high-end gadget in the sense
that you really need to be
informed about what it is
you are buying before making
a final selection. In
other words: DO YOUR
HOMEWORK!
Here are things you need
to bear in mind before you
buy a telescope:
1) Telescopes are not
toys and if you go into this
thinking that they are then
chances are that whatever
you buy is going to be a
big disappointment to you
or the person you are buying
for. In fact, steer well
clear of department store
telescopes because they
generally are toys and will
not deliver the goods when
it comes to stargazing.
2) Do not expect to see
Hubble Space Telescope
images like you see in books,
magazines, or on TV. No
telescope can deliver that
simply because the human
eye does not have the same
kind of light and color sensitivity
that a camera does.
3) Never buy a telescope
based upon its advertised
magnification. The main
purpose of a telescope is
to gather light from objects
very far away so the most
important factor is going to
be the aperture of the main
light-collecting element
(lenses or mirrors depending
upon the type of telescope),
not magnification.
So, diameter and not power
is the thing to remember
here.
4) Do not succumb to
“aperture fever” and buy
a telescope that is too big.
Portability is something
you will certainly want to
consider.
5) Set a budget. As a general
rule any telescope that
costs under $100 is likely
to be of very poor quality.
You can find good beginner
telescopes for about $200
to $300 and prices, as well
as quality, go up from there.
6) Telescopes can be very
simple to use or very complicated
depending upon the
kind you buy. If you are not
a techie then simple is the
route to go.
7) If possible try and look
through a variety of telescopes
at your local amateur
astronomy club. Amateurs
often host star parties
for the public and they are
more than willing to tell you
about their telescopes (in
fact, you may have a hard
time getting away from them
once you get them going!).
Failing that you can always
email a club and ask questions
or make arrangements
to come visit. The Central
Arkansas Astronomical Society
will gladly field your
questions by dropping us
a line at info@caasastro.org
There are three basic
kinds of telescopes used by
amateurs today: reflectors,
refractors, and hybrids.
Refractors are the kind
that most people think of
when they think of telescopes.
They use a set of
glass lenses to collect light
from one end and then focus
it into an image at the other
end. A quality refractor is
great for providing sharp
images of the moon and
planets and some deep sky
objects. They are also easy
to maintain and use but
unfortunately they tend
to be expensive because
quality glass lenses are not
cheap. Also, above a certain
size refractors are prone to
what is known as “chromatic
aberration” where not all of
the colors in the light being
gathered are focused at the
same point. The result is
images that have an annoying
halo around them. Very
special lenses (known as
“apochromatic” lenses) can
correct for this but they too
are very expensive. Don’t
expect to buy a good apochromatic
for under $500
(the best quality ones will be
over $1,000). If all you want
to do is look at the moon
and a few planets then you
can find a refractor without
the apochromatic lenses
for around $200. Chances
are though that you will tire
of looking at just the moon
and you will want something
capable of going after bigger
“game”.
A reflector telescope
uses a system of mirrors to
collect and direct starlight
rather than glass lenses. Mirrors
are cheaper than lenses
and consequently you can
build bigger telescopes at
a fraction of the cost of a
refractor. Let’s just cut to
the chase here: this is my
personal recommendation
for a first time telescope;
you simply get more bang
for your buck. The trade
offs are that reflectors require
more maintenance and
are a bit more bulky to carry
around. A good aperture
for a beginner is 6 inches,
4 inches for a kid, and the
cost is generally about $300
for the 6” and about $250 or
the 4”. My personal suggestion
is to start out with an 8”
aperture (about $400).
Hybrid scopes (ie. Catadioptrics
and Cassegrains)
are very popular but also
complicated. They use a
combination of lenses and
mirrors to collect light and
form images. Their optical
pathway design makes
them very compact but
image quality is poor: great
for astrophotography, not
so much for casual viewing.
If you are not a techie then
this is not the first telescope
you should buy. Otherwise,
these scopes are great
choices but just be aware
that they are bit expensive
and are more technology
driven.
Next week we will look at
the different types of mounts
for telescopes.
