The Tessar is a famous photographic lens design conceived by the German physicist Paul Rudolph in 1902 while he worked at the Zeiss optical company and patented by Zeiss in Germany; the lens type is usually known as the Zeiss Tessar.
 | |
| Introduced in | 1902 |
|---|---|
| Author | Paul Rudolph |
| Construction | 4 elements in 3 groups |
| Aperture | f/6.3 (1902) f/4.5 (1917) f/2.8 (1930, by Willy Merté) |
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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.
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 (téssera, four) to indicate a four-element design.
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 Zeiss developed Tessar lenses with apertures of f/3.5 and f/2.8.[1]
Common uses
Tessar 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.
Tessar type lenses
The Tessar design patent was held by Zeiss for two decades, and licensed to Ross (optics) 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". However, Tessar-type lenses were widely made by many manufacturers under different trade names. 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.[2] Other Tessar-type lenses include the Schneider Xenar, Agfa Solinar, Rodenstock Ysar, Kodak Ektar, KMZ Industar, Yashica Yashinon 80mm (twin-lens-reflex design), and Minolta Rokkor 75mm (twin-lens-reflex design).[3]
After WW2 the Zeiss factory at Jena ended up in East Germany behind the Iron Curtain, and developed a popular camera named the 'Werra' after the river which runs through the town. This used Tessar lenses, which were marked as 'Zeiss-Tessar', resulting in legal action from the Zeiss company in Western Germany. For a while the Werra Tessar lenses were marked simply as 'T', but eventually they were allowed to market the lenses as 'Carl Zeiss - Jena Tessar'.
Leitz Elmar
It is sometimes thought that The Leitz Elmar 50/3.5 was a Tessar copy or clone. This is not the case. Although the 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 which 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 Oskar Barnack tried a 50mm Tessar, but because it had been designed to cover only the 18x24mm field of a cine frame he found the coverage of the Leica 24x36mm format to be inadequate. The lens designed by Max Berek for the Leica rangefinder camera was a modified Cooke Triplet with five elements in three groups, the third group being three cemented elements, with the aperture stop in the first air space. This lens, called the Elmax, gave good coverage of the 24x36mm format and was used until improved optical glass allowed the third group to be simplified to a cemented pair and then lens was renamed the Elmar. It was not until Zeiss Ikon were developing the Contax camera to compete with the Leica that the Tessar was redesigned to cover a 24x36mm negative.[4]
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 115mm f/4 and 85mm f/4, and the wide-angle Pro Tessar 35mm f/3,2 for use on the central-shutter SLR Zeiss Ikon Contaflex Super B cameras.
Other Tessar lenses / Vario-Tessar
Other Tessar lenses, for example for Nokia mobile phones, have only the name "Tessar" in common with the original Tessar. They are for example a 5-elements-in-1-group, aperture-less all-aspherical lens, as in the Nokia 808 Pureview and Nokia Lumia 800 camera.
Vario-Tessar lenses also only have the name "Tessar" in common with the original Tessar. The Vario-Tessar name has been used by Zeiss for various zoom lenses including that of the digital still cameras Sony Cyber-shot DSC-P100,[5] DSC-P200 and DSC-W330 as well as the E-mount lenses such as Sony Alpha Carl Zeiss Vario-Tessar T* E 4/16-70mm ZA OSS (Sony SEL-1670Z) and Sony Alpha Carl Zeiss Vario-Tessar T* FE 4/16-35mm ZA OSS.
See also
Further reading
References
- ^ Rudolf Kingslake A History of The Photographic Lens, Chapter 6, section 4, "Unar and Tessar", Academy Press, 1989, ISBN 0-12-408640-3
- ^ 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
- ^ ^ Rudolf Kingslake A History of Photographic Lens, Chapter 6, section 4
- ^ "Die Leica" 1933, No. 6. Was ist eigentlich "Elmar"?
- ^ Sony Cyber-shot DSC-P100 review