Pasachoff, Jay M. Hopkins Observatory, Williams College, Williamstown, Massachusetts.
Pickles, Andrew J. Las Cumbres Observatory Global Telescope Network, Goleta, California.
Last reviewed:January 2020
- Sky surveys
- Related systems
- Schmidt-Cassegrain design and amateur use
- Related Primary Literature
- Additional Reading
A fast, compact, wide-field optical system that uses a thin aspheric front lens at the center of curvature of a larger concave spherical mirror. The image is focused onto a curved focal plane between the two elements (Fig. 1). Schmidt cameras are sometimes used in microscopes, astronomical spectrographs, and projection televisions. The largest such devices can image several degrees of the sky and are known as Schmidt telescopes. The Estonian optician Bernhard Schmidt devised the scheme in 1930. The field of best focus is located midway between the lens and the mirror and is curved toward the mirror, with a radius of curvature equal to the focal length. Historically, film or photographic plates were bent to match this curved focus, and used to make the first all-sky survey pictures. Field-flattening lenses permit the use of charge-coupled devices (CCDs) in newer applications. Large mosaics of CCDs have replaced photographic emulsions in some applications, and large numbers of optical fibers have also been used in multiobject spectrograph configurations. See also: Astronomical imaging; Charge-coupled devices; Geometrical optics; Lens (optics); Mirror optics
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