what's the difference between a cassegrain and a catadioptric telescope?
Actually catadioptric means a device that uses both lenses and mirrors. A Newtonian reflector is a catadioptric device.
I rarealy hear the term catadioptric used outside of photography. In photography a catadioptric or "Cat" lens is a folded telescopic lens that allows a "long" lens to be physically short.
A Schmidt-Cassegrain telescope is a specific type of catadioptric telescope that uses a spherical main mirror and a lens to correct for aberration (optical faults). Other designs might use a parabolic mirror or a small aperature (f/10 or higher) where there is little spherical aberation.
It appears, type of sensor: http://en.wikipedia.org/wiki/Catadioptric_sensor