Schmidt cameras have very strongly curved focal planes, 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. A field flattener, -in its simplest form, a planoconvex lens in direct contact with the film- is sometimes used. Systems with such lens are called Schmidt-Väisälä camera.
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 surveys, comet and asteroid searches, and nova patrols.
In addition, Schmidt cameras and derivative designs are frequently used for tracking artificial earth satellites.
Starting in the early 1970s, Celestron marketed an 8-inch Schmidt Camera. The camera was focused in the factory and was made of materials with low expansion coefficients so it would never need to be focused in the field. Early models required the photographer to cut and develop individual frames of 35mm film as the film holder could only hold one frame of film. About 300 Celestron Schmidt Cameras were produced.
The Schmidt system was popular, used in reverse, for television projection systems. Large Schmidt projectors were used in theaters but systems as small as 8-inches were made for home use and other small venues.
A Schmidt telescope was at the heart of the Hipparcos satellite from the European Space Agency(1989–1993). This was used in the Hipparcos Survey which mapped the distances of more than a million stars with unprecedented accuracy - this included 99% of all stars up to magnitude 11. The spherical mirror used in this telescope was extremely accurate; if scaled up to the size of the Atlantic Ocean, bumps on its surface would be about 10 cm high.
Another famous and productive Schmidt camera is the Oschin Schmidt Telescope at Palomar Observatory, which was used in the National Geographic Society - Palomar Observatory Sky Survey (POSS, 1958), the POSS-II survey, the Palomar-Leiden (asteroid) Surveys, and other projects. The telescope used in the Lowell Observatory Near-Earth-Object Search (LONEOS) is also a Schmidt camera. The Schmidt telescope of the Karl Schwarzschild Observatory is the largest Schmidt camera of the world.
The last two designs are popular with telescope manufacturers because they are compact and use simple spherical optics.
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