Aplanat

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Related to aplanatic: aplanatic Gregorian, aplanatic lens
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Aplanat

 

a photographic objective with an optical system consisting of two achromatic lenses placed symmetrically about the diaphragm. The aplanat is free from spherical aberration, chromatic aberration, and distortion; but astigmatism, though severely attenuated, remains present. Because of its simplicity of design and loose mounting requirements, the aplanat lends itself readily to use as a universal lens with a relative aperture from f/8—rarely f/5 (for portrait work and group photographs)—to f/16 (as a wide-angle lens). With the appearance of anastigmats, aplanats lost their significance and are now produced in small quantities.

REFERENCE

Lapauri, A. A. Fotograficheskaia optika. Moscow, 1955.
The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
During the 1930s Maksutov's opticians found time to produce a wide variety of extremely challenging optical systems, including fast apochromatic objectives, aspheric projection lenses, two 14-inch f/2 Schmidt cameras, a 16-inch aplanatic reflector for Byurakan Observatory in Armenia, and a 20-inch horizontal solar telescope for Pulkovo.
Wilson, designer of the 3.5-m New Technology Telescope, wrote: "The RC aplanatic form of the Cassegrain telescope is, and will always remain, the ultimate optical design for a 2-mirror telescope."
Thus an "aplanatic patch" arises, meaning that in the visible spectrum, the correction works perfectly only over a small field around one star.
A high-school mathematics teacher by profession, ED TURCO also built the 4-inch f/4.2 aplanatic telescope and crutch tripod featured in this magazine in November 1979, page 473, and January 1996, page 31, respectively.
As a young scientist in the 1920s Maksutov explored the general properties of two-mirror optical systems and found a number of aplanatic combinations - those free of both spherical aberration and coma.
In his 1932 book, Aberration-free Reflecting Surfaces and Systems and New Methods for Testing Them, he discussed the pros and cons of aplanatic systems.