A reflector uses a mirror as the primary light-gathering element. A refractor uses a set of specially designed lenses. A catadioptric system is usually a folded 'cassegrain' reflecting telescope with a large aperture field lens that is used to correct the distortions in the field of view such as 'coma'. These are caused by the non-parabolic shape of the primary mirror. Refractors are very expensive for each square inch of aperture.
Newtonian reflectors are the least expensive, and catadioptrics are in between.
The 'cats' look spiffy, but as a beginner you want to get the most light gathering 'power' per dollar and should consider Newtonian reflectors first. Those on 'Dobsonian' mountings are the best value, but you cannot do much astrophotography with them because they cannot be tract to follow the stars. Copyright 1997 Dr. Sten Odenwald Return to Ask the Astronomer .