History
Beginnings
Despite common belief, the ''Tessar'' was not developed from the 1893 Cooke triplet design, although it appears the ''Tessar'' replaces the single rear element of the Cooke triplet with a cemented achromatic doublet. Instead, the ''Tessar'' underwent a parallel evolution from Paul Rudolph's 1890 ''Anastigmat'' lens, which had four elements in two cemented groups. Hugh L. Aldis patented the ''Stigmatic'' lens line for Dallmeyer in 1895; in one implementation, the front group from the ''Anastigmat'' design was modified by adding a narrow air gap, which acted as a positive element and improved zonal correction. Later, Rudolph adopted the same device to modify the ''Anastigmat'' design, resulting in the ''Unar'' of 1899. In addition, this allowed the photographers to have greater freedom when choosing the lenses. In one implementation, the ''Unar'' has four air-spaced elements in four groups, which replaced the two cemented interfaces of the earlier ''Anastigmat'' design. In 1902, Rudolph realized the two cemented interfaces had many virtues, so he reinserted them in the back of his ''Anastigmat'', maintaining the "air gap" of the previous part of the ''Unar'', thus creating the ''Tessar'' design (from the Greek word τέσσερα (''téssera'', four) to indicate a design of four elements) of 1902. The frontal element of the ''Tessar'', like that of the ''Anastigmat'', had little power since its only function was to correct the few aberrations produced by the powerful posterior element. The set of interfaces cemented in the posterior element had 3 functions: to reduce the spherical aberration; reduce the overcorrected spherical-oblique aberration; and reduce the gap found between astigmatic foci.Improvements and evolutions
The first ''Tessar'' appeared with a maximum aperture of , but by 1917, the maximum aperture had been increased to . In 1930, Ernst Wandersleb and Willy Merté from Zeiss developed ''Tessar'' lenses with apertures of and . In 1925, E. Wandersleb and W. Merté of Zeiss created the ''Biotessar'' consisting of two elements cemented in the front, a single negative element in the center, and three cemented in the rear. After World War II and the partitioning of Germany, the Zeiss factory at Eisfeld ended up in East Germany; Zeiss Jena developed a popular camera line named the 'Werra', after the''Tessar''-derived lenses
Zeiss had strong control over the ''Tessar'' design, because Rudolph's patent was very general. In the corresponding U.S. Patent, he claimed:''"A spherically, chromatically and astigmatically corrected objective, consisting of four lenses separated by the diaphragm into two groups each of two lenses, of which groups one includes a pair of facing surfaces and the other a cemented surface, the power of the pair of facing surfaces being negative and that of the cemented surface positive."''The ''Tessar'' design patent was held by Zeiss for two decades, and licensed to Ross in the United Kingdom, Bausch & Lomb in the United States, and to Krauss in France. Only licensed manufacturers were allowed to use the brand name ''Tessar''. Many other manufacturers tried to copy the design of the ''Tessar'' lenses but due to the breadth of the patent, they could not. The simplest way was to use a cemented triplet for the rear group instead of a doublet. In 1913, many designs of this type appeared, including the Ross ''Xpress'' by J. Stuart and J.W. Hasselkus, Gundlach ''Radar'', and Berthiot ''Olor'' by Florian. After the patent expired, ''Tessar''-derived lenses were widely made by many manufacturers under different trade names. For example, the ''Minoxar'' 35/2.8 lens on the Minox M.D.C and GT-E is the fastest and widest ''Tessar''-type lens achieved so far by using lanthanum glass elements. The picture quality was outstanding. Other ''Tessar''-type lenses include: *
— Paul Rudolph, US Pat. 721,240
Leitz ''Elmar''
It is sometimes believed the Leitz ''Elmar'' 50 mm , designed by Max Berek in 1920, was derived from the ''Tessar'', as they share the same general layout. The ''Elmar'' lenses were used in the first Leica cameras. Although the ''Tessar'' and ''Elmar'' lenses appear similar in layout, there is a lot more to the design and performance of a lens than simply the layout of the glass elements. The position of the stop, the optical characteristics of the glasses used for each element, the curvature of each lens surface, and the negative format that the lens is designed to cover, are all vital to the performance of the lens, and in the Leica lens these were all different from the ''Tessar''. When the Leica was being developed,Pro Tessar
The front element of the Tessar can be replaced to make a long-focus or wide-angle lens. In 1957 Carl Zeiss offered the long-focus Pro Tessar 115 mm ''f''/4 and 85 mm ''f''/4, and the wide-angle Pro Tessar 35 mm ''f''/3,2 for use on the central-shutter SLR Zeiss Ikon Contaflex Super B cameras.Licensed ''Tessar'' lenses / ''Vario-Tessar''
Other ''Tessar'' lenses, for example those equipped on certainDesign
Common uses
''Tessar'' lenses are frequently found in mid-range cameras, as they can provide a very good optical performance at a reasonable price, and are often quite compact. They are also frequently used in photographic enlargers, as they provide more contrast than many competing lens designs due to the limited number of air-to-glass surfaces.Focusing methods
All lenses can be focused by moving the lens assembly towards or away from the film ("unit focusing"), and the ''Tessar'' is no exception. Unit-focusing Tessars were used on higher-end cameras such as the Contaflex Super B, Rolleiflex TLR, and larger-format plate cameras such as the Maximar. Some lenses, including ''Tessars'', can be focused by moving lens elements relative to each other; this usually worsens optical performance to some extent, but is cheaper to implement. As the front element of the ''Tessar'' has three times the power of the whole lens, it must be moved one-third of the distance that the whole lens would need to move to focus at the same point. The large airspace between the first and second elements allows focusing by moving the front element only; as the displacement is small compared with the airspace, the adverse effect on image performance is not severe. The front-element-focusing ''Tessar'', cheaper than a unit-focusing lens, was widely used in many midrange Zeiss Ikon cameras.See also
* Pancake lens * * Planar * Sonnar * Biogon * * * Hologon * Elmar (lens)Further reading
*References
{{Reflist Photographic lens designs Zeiss lenses