The term retrofocus (also: retro-focus) refers to an approach to designing wide-angle lenses for SLR cameras. The name ‘retrofocus’ was popularized by Angenieux in the naming of their 1950 35 mm focal length wide-angle.

Design-wise the retrofocus lens is akin to a reversed telephoto lens, in that it uses one or several negative lenses or lens groups at the front of a lens to increase the back focal distance of the lens.

Schematic of the Meyer-Optik Görlitz Primagon 35 mm f/4.5
(Another early representative of the retrofocus design)

Initially the retrofocus lenses were designed in the 1930s for color cinema cameras which needed to make room for a 3-way beam splitter between lens and film(s). While neither Angenieux (Retrofocus R1; 35 mm f/2.5; 1950) nor Carl Zeiss Jena (Flektogon; 35 mm f/2.8, 1949) actually developed the first retrofocus lens for still cameras (that honour should go to Kingslake and Stevens at Kodak for the WA Ektanar 35 mm f/3.5; 1941), they did play a central role in the wide availability of retrofocus lenses.

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