Catadioptrik

Catadioptrik is a term used to describe optical systems that use both mirrors and lenses to form an image. This combination allows for the correction of optical aberrations that might be present in purely reflective or purely refractive systems. Catadioptric designs are often found in telescopes, cameras, and other optical instruments where high image quality and compact design are important.

The primary advantage of a catadioptric system is its ability to correct for chromatic aberration, which is a color fringing effect that occurs in lenses. By using mirrors, which do not suffer from chromatic aberration, along with lenses, designers can create systems with excellent color fidelity. Another benefit is the ability to achieve long focal lengths in a relatively short physical tube, making these instruments more portable.

Common catadioptric designs include the Schmidt-Cassegrain telescope and the Maksutov-Cassegrain telescope. In a Schmidt-Cassegrain, a spherical primary mirror is combined with a corrector plate at the front of the tube and a secondary mirror. The corrector plate, which is aspheric, corrects for spherical aberration introduced by the primary mirror. The Maksutov-Cassegrain uses a deeply curved meniscus lens as its corrector, which also effectively corrects for spherical aberration and is generally easier to manufacture than the Schmidt corrector plate. These designs are popular for both amateur and professional astronomical observation.