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pj67coll · #4 12-16-2010, 09:58 AM

I assume you are looking for a scope for astronomical purposes? In that case there are some rules of thumb you should be aware of.

Generally yes, the larger the prime optical surface the better. Usuallyl in Astronomy bigger is always better. Unless you are looking for very specialized instuments but if you are just looking for an uncomplicated scope to show you the objects in the night sky that is a rule that holds true.

The simplest and best bang for your buck will be a reflecting telescope on a Dobsonian mount. I have a small 4.5" one for Orion which is a good quality insturment optically and mechanically. It's disadvantage as with all dobsonians is it's lack of drive ability which means that it cannot track objects so as the earth rotates they zoom out of your field of view quite easily. Thus you have to move the scope continuously by hand.

This can be compensated for by buying an equatorial platform, which in fact is something I'm looking into right now myslef but it ads cost to the endeavour.

A telescope with a german equatorial mount with motor drives on the two axes or at least the RA axis will allow you to track objects once the mount is correctly set up and aligned but if you are buying such a scope, especially a used you must be sure that the motors work. Have this demonstrated to you at night tracking an object in the sky.

Generally the larger the mirror, the shorter the F Ratio which makes the quality of the optics of paramount importance as the shorter the F Ratio the more susceptible the image is to breaking down at higher power magnifications. Longer F ratios are not as subject to that problem but they typicaly have smaller fields of view than shorter F ratios and thus can be more suited to viewing objects like the moon and planets at higher magnification than wide field deep space objects such as start clusters, nebulae and galaxies which are usually viewed at lower power magnification in a much wider field of view.

Meade does make some good products, so does Orion.

A good Catadioptric telescope like a Celestron or Meade is a fine instrument but you need one on a german equatorial mount or with GOTO capability on an altazimuth mount and these mounts and electronic controls add to the cost of the scope at the cost of aperture.

With a scope the more you pay for in non-optical related stuff, such as the mount and computer control, the less you recieve in optics. Everyting's a trade off.

If you really are interested in getting a scope I'd urge you to look at Orion's cataloge and Meades as well. There are a multitude of good scopes available out there for decent prices. It really is a buyers market but you need to know what you want out of the scope and not have unrealistic expectations.

There's an old saying in the hobby. The best telescope is the one that get's used. It does you no good haveing spent 2000 plus dollars on a large scope that's too bulky to move around and set up and that consequently sits in a corner of the garage and is never used.

- Peter.