Topogon

''Topogon'' is a wide field (originally 100 degrees field of view), symmetrical photographic lens patented by Robert Richter in 1933 for Carl Zeiss AG. As there are four meniscus elements in four groups, deployed symmetrically around the central aperture, it is considered a double Gauss lens variant.

Design

According to Richter, the ''Topogon'' was developed from the Goerz '' Hypergon'' (1900), one of the first super-wide-angle lenses. Richter credits the mathematician Emil von Höegh, who had designed the ''Dagor'' anastigmat (1892), with designing the ''Hypergon'' for Goerz. Although the ''Hypergon'' covered a wide angle of view (140°) and had good flatness of field and distortion characteristics, the maximum aperture was limited to 22 to control longitudinal spherical aberration and chromatic aberration. A new computation of a "fast" ''Hypergon'' was made by limiting the angle of view to 90°, which allowed an increased maximum aperture of 6.3.

The ''Topogon'' was derived from the "fast" ''Hypergon'' by adding a second, symmetric set of strongly curved meniscus elements inside the larger spherical elements to correct longitudinal spherical aberration. The initial design patented by Richter was for a f=66mm 6.3 lens covering 100°, although the patent also contains two other refinements to the basic design, including one that used parallel elements to minimize vignetting. As the name suggests, the ''Topogon'' was intended to be used for topographical surveys and photogrammetry.

The Topogon was later developed into the ''Pleon'' fisheye lens (1938) and ''Pleogon'' lens by Richter and Friedrich Koch in 1956. The ''Pleon'' was used for aerial surveillance during World War II, and was equipped with a large negative meniscus cemented group ahead of the ''Topogon'' core as an early example of an inverted telephoto design; a special projector was required to display an undistorted image. The Pleogon, used for photogrammetry, used a cemented achromatic lens just ahead of the central stop and added two meniscus groups on either side to maintain lens symmetry.

Topogon lenses have been produced with maximum apertures ranging from f/3.5 to f/15 in various focal lengths.

File:Goerz Hypergon (1900).svg, Goerz ''Hypergon'' by von Höegh (1900), from US 706,650
File:Richter-Zeiss Topogon (1933).svg, Zeiss ''Topogon'' by Richter (1933), from US 2,031,792
File:Richter-Zeiss Pleon (1938).svg, Zeiss ''Pleon'' by Richter (1938), from US 2,247,068
File:Richter & Koch - Zeiss Pleogon (1956).svg, Zeiss ''Pleogon'' by Richter & Koch (1956), from DE 1,097,710

Influence

Goerz was merged into the Zeiss Ikon company in 1926. An independent branch of Goerz in America, which had been established in 1895, licensed the ''Topogon'' design to Bausch & Lomb, who produced it as the ''Metrogon'' for the United States, citing the same US patent as the ''Topogon''. The ''Metrogon'' was introduced in the early 1940s at the same cost "as a light automobile", limiting its market to aerial surveillance cameras for the United States Army Air Corps. A later patent by Wilbur B. Rayton, assigned to Bausch & Lomb in 1943, separated one of the outer positive meniscus lenses into two air-spaced positive menisci, similar to an earlier patent issued in 1938 to Hasselkus & Richmond.

Although the main market for the ''Topogon'' similarly was aerial photography and mapping for military and government applications, a consumer version was produced for the pre-war Zeiss Ikon Contax 35mm rangefinder cameras and produced in small numbers as the ''Topogon'' 2.5 cm . Lenses using similar designs also were produced by Canon (25mm , 1956), KMZ (''Oриoн-15''/''Orion-15'' 28mm , 1964), and Nikon (''W-NIKKOR·C'' 2.5cm , 1954) for their rangefinder systems after World War II. In addition, Mamiya released a lens with a similar design for the Mamiya Press camera system, the ''Mamiya–Sekor'' 65mm .

Hybrid designs

The front meniscus elements of the ''Topogon'' were paired with the rear half of a double Gauss by Albrecht Tronnier and released as the Voigtlander ''Ultragon'', a wide angle lens for large format cameras.

As the opposite hybrid asymmetric design, the rear meniscus elements of the ''Topogon'', forming a Gauss lens, have been paired with the front elements from a ''Planar''-type double Gauss lens, resulting in the designs shared by the Schneider Kreuznach ''Xenotar'' (1952) and Zeiss ''Planar'' (1953) & ''Biometar'' (1959). The ''Xenotar'' and ''Planar'' were fitted to Rolleiflex TLR cameras as an upgrade over ''Tessar''/''Xenar'' types, and the ''Biometar'' was the standard lens for the Pentacon Six (aka Praktisix / Exakta 66) SLRs, with a ''Xenotar'' available for the same camera.

File:Hasselkus & Richmond US2116264A (Topogon-5, 1936).svg, ''Topogon'' derivative by Hasselkus & Richmond (1936), from US 2,116,264
File:Rayton US2325275A (Metrogon, 1942).svg, Bausch & Lomb ''Metrogon'' by Rayton (1942), from US 2,325,275
File:Tronnier US2670659A (Ultragon, 1951).svg, Voigtländer ''Ultragon'' by Tronnier (1951), from US 2,670,659
File:Klemt & Macher US2683398A (Xenotar, 1952).svg, Schneider ''Xenotar'' by Klemt & Macher (1952), from US 2,683,398
File:Lange US2724994A (Planar, 1953).svg, Zeiss ''Planar'' by Lange (1953), from US 2,724,994
File:Zöllner US2968221A (Biometar, 1959).svg, Zeiss ''Biometar'' by Zöllner (1959), from US 2,968,221

References

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External links

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

Photographic lenses
Zeiss lenses