There are two major types of telescopes.
1. Reflective (Uses lenses and mirrors to reflect light on to the eye peace) - Generally smaller in size.
2. Refractive(Uses lenses only) - Generally larger in size.
There is a third type called the Catadioptric telescope. It uses both the properties of Reflective and Refractive telescopes. Generally not used by ametures.
If you are planning to buy a telescope don't get too confused with what kind of telescope to buy. First things first.. try to understand how telescopes work. You would need to know a few terms before you understand its functioning.
1. Aperture: A telescope's most important attribute is its aperture, which determines the brightness and sharpness of everything you see through your scope. Inreal simple terms this is the diameter of the main lense(or the Objective lense). Here is what most of the ameture astronomers tend to believe... "getting a bigger objective lense or a larger aperture would mean a better telescope". That would be a mistake! The size of objective lense that you want also depends on what you want to observe in space? If you just want to observe the moon and some nearby planets like Mars and Jupiter - a 3" Objective is good enough, however, if you wanted to observe galaxies you would need a much larger telescope that can accommodate a large Objective(at least 6" and above).
2. Power of Magnification: This is a critical factor since it decides how close a view you can get of the space and planets. You can make any telescope magnify at effectively any power you want by using different eyepieces. An eyepiece is the small removable lens assembly you look into.
Few myths that need clarification:
Don't buy a "department store" telescope: While the price may seem right, and the pictures on the box look compelling, small telescopes found in retail stores are of consistently poor quality.So, dont buy them.
It's not about magnification: It is actually one of the least important aspects, and is something you control based on your choice of eyepieces.
Computer pointing is not necessary: These systems increase the cost of the telescope significantly, and don't add much value for beginners. In fact, my personal suggestion is to begin with a manual telescope. When you struggle hard to focus on an object of your interest... you learn the most. So, dont go the easy way... there is less learning.
