Zeiss Sonnar

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The Sonnar is a photographic lens design originally patented by Carl Zeiss, notable for its relatively light weight, simple design and fast aperture. The name "Sonnar" is derived from the German word "Sonne", meaning sun. It was given this name because its large aperture (f/2.0) made it considerably brighter than many other lenses available at the time.

The first production Sonnar was a 50mm f/2.0 lens with six elements in three groups created for the Zeiss Ikon Contax rangefinder camera. In 1932, it was reformulated with seven elements in three groups allowing a maximum aperture of f/1.5.

Compared to Planar designs the Sonnars had more aberrations, but with fewer glass-to-air surfaces it had better contrast and less flare. Though compared to the earlier Tessar design, its faster aperture and lower chromatic aberration was a significant improvement.

The Sonnar has proven incompatible in shorter focal lengths with SLR cameras due to the space taken up by an SLR's mirror. For this reason it has been used most commonly with rangerfinders, though Sonnar lenses with longer focal lengths still appear on single-lens reflex cameras, most notably the 150mm and 250mm lenses for the Hasselblad V-system. Some portrait Sonnars were also made for large format cameras, presumably the press cameras - like Sonnar 250/5.6 for 9x12cm (4x5") format. Though these lenses were quite heavy (> 2 kg) and large, they were optimised for working on a full aperture with the same sharpness and contrast as on smaller apertures. The coverage of these lenses was also not too good for LF lenses, but the camera movements are not too important for portrait work.

The Sonnar design has been extensively copied by other lens manufacturers, due to its excellent sharpness, low production cost and fast speed. The Soviet factory KMZ produced several lenses that used the Sonnar formula: The KMZ Jupiter-3, Jupiter-8, and Jupiter-9 are direct copies of the Zeiss Sonnar 50mm/1.5, 50mm/2.0 and 85mm/2.0 respectively.

A zoom lens derivative of the Sonnar, the Vario-Sonnar also exists, in which a number of lens groups are replaced with floating pairs of lens groups.