Telescopes
If you
are like most people, you know little about purchasing a
telescope. You have walk through the discount stores and
saw boxes of telescopes with pictures on them of beautiful
nebulas and planets. Of course, you figure if you bought
one you could see the same images that are on the box. (No,
No, No) If that is your belief your telescope will probably
end up in the closet in a few months or out on the front
yard at your next garage sale.
It’s my hope with the following information you will become
more knowledgeable in purchasing the correct telescope for
you and avoid the mistakes myself and others have made in
the past.
There are 4 Major Types of
Telescopes
1.
Refractors
2.
Newtonian
Reflectors
3.
Schmidt-Cassegrains
4.
Maksutov-Cassegrains
Let’s
take a look at the Refractors...
When
someone thinks of a telescope this is probably the
type most people envision. For many years this was
primarily the type of scope sold. It's still very popular
and telescope makers have improved the over all quality
and made them more affordable to everyone. There is
some excellent high-end models with a price to match
but you usually get what you pay for. The same holds
true for the low end, don't buy from a discount store
because...
"you usually get what you pay for."
There
are two types of
Refractors. Let’s
take a look at the pros and cons of each.
Achromatic
1. Rugged
& Reliable
2. Maintenance-free.
Optics are sealed so as a rule internal dust or scratches
isn’t a problem.
3. Portable
in 3 inch and smaller. This is important if you will be
transporting from home to viewing
site.
4. Excellent
for moon, planets, star clusters, double stars.
5. Poor on
nebulas, faint clusters & galaxies - Aperature to small
(in other words low light gathering
power.)
6. Beware
of spindly tripods on less expensive models which discount
stores usually sell.
7. On some
objects such as the moon or bright stars there appears a
“halo” or “coma” around the edge.
This is an inherit problem on
achromatics especially on less expensive models. There are
filters available to help reduce
this problem to a degree.
Apochromatic
1. Requires
little care & maintenance
2. No
collimation required (or alignment of primary and secondary
mirrors you fine on reflectors)
3. Finest
optical systems available
4. Eliminates
the chromatic abberation ("coma") found with achromatics.
Also corrected for spherical
aberration at two wave lengths instead of one like
achromatics.
This quality comes with a price but
many refractor enthusiats say it’s worth it.
5. Excellent
for astrophotography.
6. Nebulas,
faint star cluster and galaxies is not its strong point.
Usually they have small aperatures.
(or less light gathering ability)
7. Prices
range from $1000 to $10,000 or more and that’s usually
without a tripod.
Newtonian
Reflectors
They come
with two types of mounts. We’ll look at the features of
each.
1. If made well they have excellent performance.
2. Yields good results for all backyard activities.
3. Good when away from light-fogged skies.
4. Has tracking ability depending on the mount.
5. Requires frequent collimation.
6. Cumbersome with sizes over 8 inches.
1. Very Simple set-up.
2. Excellent for deep sky objects. (Nebulas, Galaxies, Distant Star Clusters)
3. The most bang for the buck.
4. Recommended for beginners. (Especially in 6 inch size and smalller.)
5. Requires collimation at each set-up.
6. Needs to climatize especially in the larger sizes.
7. Cumbersome in sizes above 8 inches.
Schmidt-Cassigrain (SCT)
2. Optical systems are good.
3. Compact design make transportation & set-up easy in sizes
8 inches and smaller.
4. Erect Image (right side up) allows for terrestrial viewing.
5. Well suited for photography and CCD imaging.
6. Has ability to track objects with the proper mount.
7. Less expensive then equal-aperature refractors.
8. Requires occasional collimation.
9. More expensive then equal-aperature reflectors.
Maksutov-Cassegrain (Maks)
1. Compact design.
2. Excellent for frequent travelers.
3. Good for most applications.
4. Has ability to track objects.
5. Never has seemed to be as popular as the SCT's.