Catadioptrics

Catadioptic telescopes are long focal length telescope in a short body. This is achieved by folding the optics internally in the tube.

These scopes were popularized by the Space Agencies to put large telescopes into small spaceships.  The scopes make excellent scopes for computerized mounts that use special drives to move the scope.

Schmidt-Cassegrain

The Schmidt-Cassegrain telescopes (SCT) are the most popular of the large aperture catadioptric systems.  Typically these scopes have a focal ratio of f10 and are extremely versatile platforms.  SCTs are characterized by a thin plate corrector plate (the front lens)

Maksutov-Cassegrain

The Maksutov-Cassegrain telescopes (Mak) are usually more popular in the smaller apertures (3”-7”).  They have a longer focal ratio than the SCT (typically around f15) and give a more “refractor like” view with a narrower field than a SCT.  Maks have thick, spherical corrector plates and the secondary mirror is part of the corrector plates curve, hence Maks do not need to be collimated.

Ritchey-Chretian

Richey-Cretian telescopes (RC) are the latest entries on the catadiotric telescope market. These are a relatively faster optical system (around f8) than the other catadiotric scopes. Rc telescope are excellent astrophotography systems giving clean starlike images.

The Hubble Space Telescope is an example of a Richey-Chretian system.