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The Metrogon is an extra-wide field photographic lens used extensively by the US military for use in aerial photography. The design is by Bausch & Lomb based on the Topogon design by Zeiss. It is composed of a double-Gauss design with an extremely curved meniscus to provide a 90° field of view. The lens is symmetrical front to back. The two outer positive elements are of high index crown glass while the two inner negative elements are of a high index flint glass.[1] The lens was used in Fairchild K17C, KA3, K-22, T-11, KC-1, KC-1B, and KC-9A aerial cameras.

The lens rim cites the U.S. Patent number (US 2031792) which is in fact the Carl Zeiss Jena Patent for the Topogon (design by Robert Richter in 1933).[2]