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.