Schmidt–Cassegrain telescope

The Schmidt–Cassegrain is a catadioptric telescope that combines a Cassegrain reflector's optical path with a Schmidt corrector plate to make a compact astronomical instrument that uses simple spherical surfaces.

In the non-compact, the corrector plate remains at or near the center of curvature (twice the focal length) of the primary mirror.

Compact designs combine a fast primary mirror and a small, strongly curved secondary.

Their high f-ratio means they are not a wide-field telescope like their Schmidt camera predecessor, but they are good for more narrow-field deep sky and planetary viewing.

Consumer versions of this design typically achieve focus by adjusting the position of the primary mirror rather than a traditional eye-piece.