Topogon is a wide field (originally 100 degrees

field of view The field of view (FoV) is the extent of the observable world that is seen at any given moment. In the case of optical instruments or sensors it is a solid angle through which a detector is sensitive to electromagnetic radiation. Humans a ...

), symmetrical

photographic Photography is the art, application, and practice of creating durable images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. It is employed i ...

lens A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements''), ...

Metrogon Metrogon is a high resolution, low-distortion, extra-wide field (90 degree field of view) photographic lens design, popularized by Bausch and Lomb. Variations of this design are said to have been used extensively by the US military for use in aerial ...

also cite the US patent of the Topogon design. The initial design patented by Richter was for a f=66mm 6.3 lens, although the patent also contains two other refinements to the basic design, including one that used parallel elements to minimize vignetting. Topogon lenses have been produced with maximum apertures ranging from f/3.5 to f/15 in various

focal length The focal length of an optical system is a measure of how strongly the system converges or diverges light; it is the inverse of the system's optical power. A positive focal length indicates that a system converges light, while a negative foca ...

s. According to Richter, the Topogon was developed from the earlier Hypergon. Although the Hypergon covered a wide

angle of view The angle of view is the decisive variable for the visual perception of the size or projection of the size of an object. Angle of view and perception of size The perceived size of an object depends on the size of the image projected onto the ...

(140°) and had good flatness of field and

distortion In signal processing, distortion is the alteration of the original shape (or other characteristic) of a signal. In communications and electronics it means the alteration of the waveform of an information-bearing signal, such as an audio signal ...

characteristics, the maximum aperture was limited to 22 to control longitudinal

spherical aberration In optics, spherical aberration (SA) is a type of optical aberration, aberration found in optical systems that have elements with spherical surfaces. Lens (optics), Lenses and curved mirrors are prime examples, because this shape is easier to man ...

and

chromatic aberration In optics, chromatic aberration (CA), also called chromatic distortion and spherochromatism, is a failure of a lens to focus all colors to the same point. It is caused by dispersion: the refractive index of the lens elements varies with the wave ...

. A new computation of a "fast" Hypergon was made by limiting the angle of view to 90°, increasing maximum aperture to 6.3. The Topogon was then derived from the "fast" Hypergon by adding a second set of strongly curved meniscus elements inboard of the larger spherical elements to correct longitudinal spherical aberration. The Topogon was later developed into the Pleogon lens by Richter and Friedrich Koch in 1956. The Pleogon, used for

photogrammetry Photogrammetry is the science and technology of obtaining reliable information about physical objects and the environment through the process of recording, measuring and interpreting photographic images and patterns of electromagnetic radiant ima ...

, used a cemented achromatic lens just ahead of the central stop and added two meniscus groups on either side to maintain lens symmetry.

References

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External links

HYPERGON - TOPOGON - RUSSAR - BIOGON - AVIOGON - HOLOGON: LA STORIA DEFINITIVA DEI SUPER-GRANDANGOLARI SIMMETRICI
Photographic lenses Zeiss lenses