Topogon

[1] As there are four meniscus elements in four groups, deployed symmetrically around the central aperture, it is considered a double Gauss lens variant.

[7] 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 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.

Lenses using similar designs also were produced by Canon (25mm f/3.5, 1956),[13][14] KMZ (Oриoн-15/Orion-15 28mm f/6, 1964),[15] and Nikon (W-NIKKOR·C 2.5cm f/4, 1954)[16] for their rangefinder systems after World War II.

[5][17][18] 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.

Topogon -design lens and auxiliary viewfinder for the Mamiya Press line of cameras