Types of Telescopes

1) The refractor is what most people think of when they hear the word "telescope". Refractors gather light with an objective lens at one end and focus the light at the eyepiece at the other end. Refractors were almost extinct at one point, but modern glass elements (including an exciting new artificially grown crystal known as fluorite) have brought the refractor back to prominence.

2) The Newtonian Reflector, invented by Sir Isaac Newton, uses a parabolic mirror at the end of a tube and focuses the light back at the front of the tube, where the eyepiece sits, after being deflected by a smaller secondary mirror in the light path.

3) The Schmidt-Cassegrain and its derivatives (Maksutov-Cassegrain, Classical Cassegrain, etc.) use BOTH mirrors and lenses to fold the optical path back onto itself, resulting in a compact tube. The technical term for these scopes is catadioptrics, but since nobody seems to use this term, I won't.