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A type of wide-field astronomical telescope, designed purely for photographic use.
It was invented by Bernhard Schmidt in 1930. The light collector is a spherical mirror
(see illustration). Correction for spherical aberration is achieved by means of a thin
glass corrector plate with a complex profile, placed at the end of the telescope tube,
beyond the focal point. The photographic plate is placed at the prime focus, where the
focal plane is curved. A special plate holder is used to bend the photographic plate
into the focal plane. By this means, sharp undistorted images can be obtained over very
wide fields of view - up to tens of degrees across.
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