Cassegrain Reflector
From Freepedia
Image:Cassegrain telescope.png First developed in 1672 by Laurent Cassegrain, a Cassegrain Telescope this type of reflector is a combination of a prime concave and a secondary convex mirror, both aligned axially. The prime mirror is usually featuring a hole in the centre thus permitting the light to reach an eyepiece, a camera, or a light detector.
- Concave Mirror: Paraboloid type
- Convex Mirror: Hyperboloid type
A Cassegrain reflecting telescope consists of primary and secondary reflecting mirrors. In a traditional Newtonian reflector, light from the primary mirror is deflected by a flat mirror to the eye-piece, placed on the side of the telescope body. In a Cassegrain telescope, there is a hole in the primary mirror; light from the primary mirror is reflected by the secondary mirror through the hole in the primary to reach the eyepiece, placed behind the telescope.
There are three basic types of telescopes: refractors, reflectors and combined lens-mirror systems or catadioptric sensors. Catadioptrics are a combination of a refractor and reflector telescope, using both mirrors and lens to focus the incoming light. There are two popular catadioptrics designs: the Schmidt-Cassegrain and the Maksutov-Cassegrain; both are similarly designed.
Another descendent of the Cassegrain design is the Ritchey-Chrétien telescope, which uses a hyperbloid primary and secondary mirror, eliminating the corrector plate needed for the catadioptic telescopes. Most modern telescopes, including the Hubble Space Telescope, uses the Ritchey-Chrétien design.
