Tessar

Infobox lens design
scheme = Zeiss Tessar.svg
year = 1902
author = Paul Rudolph
elements = 4
groups = 3
aperture = f/6.3 (1902) f/4.5 (1917) f/2.8 (1930)The Tessar is a famous photographic lens design conceived by physicist Paul Rudolph in 1902 while he worked at the Zeiss optical company and patented by Zeiss; the lens type is usually known as Zeiss Tessar.

Despite common belief, the Tessar was not developed from the 1893 Cooke triplet design by replacing the rear element with a cemented achromatic doublet. In fact, Paul Rudolph designed the Anastigmat with two cemented doublets in 1890. In 1899, he separated the doublets in the Anastigmat to produce the four-element, four-group Unar lens. In 1902, he realized that reversing the two rear elements of the Unar and returning to a cemented doublet would improve performance; he named the result "Tessar", from the Greek word τέσσερα ("tessera") to indicate a four-element design.

A Tessar comprises four elements in three groups, one positive crown glass element at the front, one negative flint glass element at the center and a negative plano-concave flint glass element cemented with a positive convex crown glass element at the rear.

Early Tessar designs by Paul Rudolph allowed a maximum aperture of f/6.3. Later development allowed an aperture of f/4.5 by 1917. In 1930, Ernst Wanderslab and Willy Merté of Carl Zeiss developed Tessar lenses with apertures of f/3.5 and f/2.8. [Rudolf Kingslake A History of Photographic Lens, Chapter 6, section 4, "Unar and Tessar", Academy Press, 1989, ISBN 0-12-408640-3]

Focusing methods

All lenses can be focussed 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 focussed 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.

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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 85mm f/4 and the wide-angle Pro Tessar 35mm f/4 for use on the central-shutter SLR Zeiss Ikon Contaflex Super B cameras.

Tessar type lenses

The Tessar design patent was held by Zeiss for two decades, and licensed to Rollei in Germany, Bausch & Lomb in the United States and to Krauss in France. Only licensed manufacturers were allowed to use the brand name "Tessar". However, Tessar-type lenses were widely made by many manufacturers under different trade names. The Leitz Elmar 50/3.5 is a famous Tessar designed by Max Berek for the Leica rangefinder camera. 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. [Bob Shell:"The 35mm f2.8 Minoxar MC lens of this little camera is a jewel, it is razor sharp at all apertures, producing images which could not be distinguished from ones taken with my usual SLR outfit. Color rendition is excellent, partially due to the built in skylight filter which also acts as a lens protector. I could detect no distortion in my images at all.", from "Minox GT-E Pocket Camera" Shutterbug, Sep 1991 ] Other Tessar-type lenses include the Schneider Xenar, Agfa Solinar, Rodenstock Ysar, Kodak Ektar, Yashica Yashinon 80mm (twin-lens-reflex design), and Minolta Rokkor 75mm (twin-lens-reflex design). [^ Rudolf Kingslake A History of Photographic Lens, Chapter 6, section 4]

Vario Tessar

The Vario Tessar name is used by Zeiss for various zoom lenses including the digital still camera Sony Sony Cyber-shot DSC-P100 released in 2004.fact|date=February 2008 Vario Tessar hasonly the name "Tessar" in common with the original Tessar.

References