Catadioptric Magnifier

A single spherical mirror, with an aperture stop placed at its center of curvature, forms an image that suffers only from spherical aberration and field curvature. To correct spherical aberration for all field points, an aspheric plate can be placed at the stop. This combination of a spherical mirror and aspheric corrector plate defines the classic Schmidt camera, invented by Bernard Schmidt in the early 1930s.1 If either the aperture or focal length of a Schmidt camera is sufficiently small, then it is possible to eliminate the aspheric corrector plate and still achieve high quality imagery. This system is commonly known as a lensless Schmidt camera.

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