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The Schmidt camera was designed by Bernhard Schmidt (1879-1935). Its optical components are an easy to make spherical primary mirror, and an aspherical correcting lens, known as a corrector plate , located at the radius of curvature of the primary mirror. The film or other detector is placed inside the camera, at the prime focus. The design is noted for allowing very fast focal ratio s, while controlling coma and astigmatism.
Schmidt cameras have very strongly curved focal plane s, thus requiring that the film, plate, or other detector be correspondingly curved. In some cases the detector is made curved; in others flat media is mechanically conformed to the shape of the focal plane through the use of retaining clips or bolts, or by the application of a vacuum.
The Schmidt camera is typically used as a survey instrument, for research programs in which a large amount of sky must be covered. These include astronomical survey s, comet and asteroid searches, and nova patrols.
In addition, Schmidt cameras and derivative designs are frequently used for tracking artificial earth satellites.
Arguably the most famous and productive Schmidt camera is the Oschin Schmidt Telescope at Palomar Observatory. It was used for the National Geographic Society - Palomar Observatory Sky Survey (POSS), the POSS-II survey, the Palomar-Leiden (asteroid) Surveys, and and other projects. The telescope used in the Lowell Observatory Near-Earth-Object SearchLowell Observatory Near-Earth-Object Search LONEOS is a program run by NASA and Lowell Observatory to discover near-Earth objects. The LONEOS system began observations in December 1997. The principal investigator is Ted Bowell. In addition to discovering (LONEOS) is also a Schmidt camera.
In 1940, James Baker of Harvard UniversityHarvard University is a private university in Cambridge, Massachusetts, USA and a member of the Ivy League. It was founded on September 8, 1636 by a vote of the Great and General Court of the Massachusetts Bay Colony, making it the oldest post-secondary s modified the Schmidt camera design to include a convex secondary mirror, which reflected light back toward the primary. The photographic plate was then installed near the primary, facing the sky. This variant is called the Baker-Schmidt camera.
The Baker-Nunn design replaces the Baker-Schmidt camera's corrector plate with a small triplet corrector lens closer to the focus of the camera.
The Mersenne-Schmidt camera consists of a concave paraboloidal primary mirror, a convex spherical secondary mirror, and a concave spherical tertiary mirror, with the focal plane again in the center of the telescope.
The addition of a flat secondary mirrorA secondary mirror (or secondary is a second light gathering and focusing surface in a reflector telescope. Light gathered by the primary mirror is directed towards a focal point typically past the location of the secondary. The secondary directs the ligh at 45° to the optical axis of a Schmidt camera creates a Schmidt-Newtonian telescope . This design is popular amongst amateur astronomers.
The addition of a convex secondary mirror directing light through a hole in the primary mirror creates a Schmidt-Cassegrain Telescope .