Buying a Telescope
Observing >
We are fast approaching the most hyper-commercialized
gift-giving season of the year. Perhaps you are considering giving (or
receiving!) a telescope.
If so, the last thing you want to do is buy a bad scope with shoddy mirrors
or eyepieces and which leaves you seeing nothing but red. The last thing
we amateur astronomers want is for you or your gift-receiver to be turned
off to a beautiful and aesthetically satisfying pastime because of that
cheap scope.
Here are some things to be aware of:
There are basically two types of telescope. “Refractors” are
those which use lenses to collect light from a distant object and focus
it into an image. They are sturdy and can provide excellent images. A
refractor is shown below.
“Reflectors” use mirrors rather than lenses
to gather and focus the light. They are usually less expensive, but occasionally
the mirrors need to be realigned. A reflector is shown below.
The most important characteristic of a telescope is its
aperture, i.e. how wide across the refractor’s main lens or a reflector’s
primary (big) mirror is.
A larger aperture allows in more light. In fact, astronomers often refer
to scopes as “light buckets” because their main purpose is to
collect as much light from those distant objects as they can to make an
image that our weak eyes could not otherwise detect.
The bigger the bucket the better. Department store lenses (or mirrors)
a couple of inches across can’t gather enough light to be of much
use.
Look for a good, steady mount. A wimpy camera tripod is way too wobbly
for an instrument whose slightest movement means you’ve just lost
what you were looking at. Make sure your scope is on a solid tripod or
on a “Dobsonian”-type mount which is a sturdy wooden base riding
on Teflon pads.
LEFT
An 8" reflector on an equatorial mount. RIGHT A 10" Dobsonian
relector. (Notice the small finderscopes on each scope.)
Each telescope has an eyepiece and focuser. Opt for a
1.25-inch diameter focuser. The 0.965-inch focuser and eyepieces on department
store scopes are... let’s say, cruddy. And look for “Kellner”
or “Plössl” printed on the eyepiece. These types are the
best reasonably priced eyepieces.
Notice I haven’t mentioned magnification? That’s because it’s
a bogus selling point made by manufacturers selling a cheap product. Stay
away from those little department store refractors boasting about magnifying
“more than 500 times.” It’s a gimmick!
In brief, keep an eye open for a scope with a large aperture, a rugged
mount, a 1.25-inch focuser, and good eyepieces.
Your tastes will vary, of course, but I would suggest as a good starter
scope a 6” Dobsonian reflector. It has a decent aperture, is light-weight,
can be easily transported, and has the 1.25-inch focuser. A 6” Dob
can set up in less than a minute and is very user-friendly and low-tech.
They are usually in the $300-$400 range.
If that’s too much money, seriously consider a good pair of binoculars
as a "starter," instead. They won’t pick out the deep-sky
objects, but they are superb for scanning the heavens for a plethora of
other interesting objects.
There is no way I can cover in this space all the helpful advice available
for telescope buying so I’ve posted images and links to telescope
websites at http://firstlightastro.com/icolumn.html.
You might also want to contact your local astronomy club. They can help
you see the different telescopes “in action.” Be careful, though,
this hobby can become a wonder-full addiction!
Until next time, clear skies!
Mark Ritter is the proud owner of an old 10” Dob and can be reached
here.
Posted by Administrator at 2000.10.29 09:03 AM | Comments (0)
