Tessar

Introduced in	1902
Author	Paul Rudolph
Construction	4 elements in 3 groups
Aperture	f/6.3 (1902) f/4.5 (1907) f/2.8 (1930, by Willy Merté)

TheTessar is aphotographic lens design conceived by the German physicist Dr.Paul Rudolph in 1902 while he worked at theZeiss optical company and patented by Zeiss in Germany; the lens type is usually known as theZeissTessar. Since its introduction, millions ofTessar andTessar-derived lenses have been manufactured by Zeiss and other manufacturers, and are still produced as excellent intermediate aperture lenses.

TheTessar design uses four spherical lens elements in three groups, one positivecrown glass element at the front, one negativeflint glass element at the center and a negative concave flint glass elementcemented with a positive convex crown glass element at the rear.

• Tessar and design antecedents
• 
  ZeissProtar (akaAnastigmat;Rudolph, 1890)^[1]
• 
  CookeTriplet (Taylor, 1893)^[2]
• 
  DallmeyerStigmatic (Aldis, 1895)^[3]
• 
  ZeissUnar (Rudolph, 1899)^[4]
• 
  ZeissTessar (Rudolph, 1902)^[5]

Despite common belief, theTessar was not developed from the 1893Cooke triplet design, although it appears theTessar replaces the single rear element of the Cooke triplet with a cementedachromatic doublet. Instead, theTessar underwent a parallel evolution from Paul Rudolph's 1890Anastigmat lens, which had four elements in two cemented groups.^{[1][6]: 82–83} Hugh L. Aldis patented theStigmatic lens line forDallmeyer in 1895;^[3] in one implementation, the front group from theAnastigmat design was modified by adding a narrow air gap, which acted as a positive element and improved zonal correction.^[6]: 84 Later, Rudolph adopted the same device to modify theAnastigmat design, resulting in theUnar of 1899.^[4] In addition, this allowed the photographers to have greater freedom when choosing the lenses. In one implementation, theUnar has four air-spaced elements in four groups, which replaced the two cemented interfaces of the earlierAnastigmat design.^[6]: 86

In 1902, Rudolph realized the two cemented interfaces had many virtues, so he reinserted them in the back of hisAnastigmat, maintaining the "air gap" of the previous part of theUnar, thus creating theTessar design (from the Greek wordτέσσερα (téssera, four) to indicate a design of four elements) of 1902.^[5][6]: 87 The frontal element of theTessar, like that of theAnastigmat, 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 thespherical aberration; reduce the overcorrected spherical-oblique aberration; and reduce the gap found between astigmatic foci.^[6]: 87

The firstTessar appeared with a maximum aperture off/6.3, but by 1917, the maximum aperture had been increased tof/4.5. In 1930, Ernst Wandersleb and Willy Merté from Zeiss developedTessar lenses with apertures off/3.5 andf/2.8.^{[6]: 87 [7]}

In 1925, E. Wandersleb and W. Merté of Zeiss created theBiotessar consisting of two elements cemented in the front, a single negative element in the center, and three cemented in the rear.^[8]

After World War II and the partitioning of Germany, the Zeiss factory atEisfeld ended up in East Germany; Zeiss Jena developed a popular camera line named the 'Werra', after theWerra river which runs through the town.^[9] Many models were equipped withTessar 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".

• Tessar improvements and derived lens designs
• 
  RossXpres (Stuart & Hasselkus, 1913)^[10]
• 
  BerthiotOlor (Florian, 1913)^[11]
• 
  LeitzElmar (Berek, 1920)^[12]
• 
  Biotessar (Merté & Wandersleb, 1925)^[8]
• 
  ImprovedTessar (Merté & Wandersleb, 1930)^[7]
• 
  SchneiderXenar (Tronnier, 1935)^[13]
• 
  VoigtländerSkopar (Tronnier, 1949)^[14]

Zeiss had strong control over theTessar design, because Rudolph's patent was very general.^[6]: 87 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."

 —Paul Rudolph, US Pat. 721,240^[15]

TheTessar design patent was held by Zeiss for two decades, and licensed toRoss in the United Kingdom,Bausch & Lomb in the United States, and to Krauss in France. Only licensed manufacturers were allowed to use the brand nameTessar. Many other manufacturers tried to copy the design of theTessar 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 RossXpress by J. Stuart and J.W. Hasselkus,^[10] GundlachRadar, and BerthiotOlor by Florian.^{[6]: 89 [11]}

After the patent expired,Tessar-derived lenses were widely made by many manufacturers under different trade names. For example, theMinoxar 35/2.8 lens on theMinox M.D.C and GT-E is the fastest and widestTessar-type lens achieved so far by usinglanthanum glass elements. The picture quality was outstanding.^[16] OtherTessar-type lenses include:^[6]: 88

It is sometimes believed the LeitzElmar 50 mmf/3.5, designed by Max Berek in 1920, was derived from theTessar,^[6]: 87 as they share the same general layout.^[5][12] TheElmar lenses were used in the first Leica cameras.

Although theTessar andElmar 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 theTessar.

When the Leica was being developed,Oskar Barnack tried a 50 mmTessar, but because it had been designed to cover only the 18×24 mm field of a cine frame, he found it inadequate for coverage of the Leica 24×36 mm format. The lens designed byMax Berek [de] for theLeicarangefinder camera was a modifiedCooke 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 theElmax, gave good coverage of the 24×36 mm format and was used until improved optical glass allowed the third group to be simplified to a cemented pair when it was renamedElmar. It was not until Zeiss Ikon was developing the Contax camera to compete with the Leica that theTessar was redesigned to cover a 24×36 mm negative.^[17]

The front element of the Tessar can be replaced to make a long-focus orwide-angle lens. In 1957 Carl Zeiss offered the long-focus Pro Tessar 115 mmf/4 and 85 mmf/4, and the wide-angle Pro Tessar 35 mmf/3,2 for use on the central-shutter SLR Zeiss Ikon Contaflex Super B cameras.

OtherTessar lenses, for example those equipped on certainNokia mobile phones, have only the nameTessar in common with the originalTessar, not the four-element, three-group design. They are for example a 5-elements-in-1-group, aperture-less all-aspherical lens, as in theNokia 808 Pureview andNokia Lumia 800 camera.

Vario-Tessar lenses also only have the nameTessar in common with the originalTessar. TheVario-Tessar name has been used by Zeiss for various zoom lenses fitted to Sony cameras, including that of the digital still camerasSony Cyber-shot DSC-P100,^[18] DSC-P200, and DSC-W330 as well as theE-mount lenses such as Sony Alpha Carl ZeissVario-Tessar T* E 4/16-70mm ZA OSS (Sony SEL-1670Z) and Sony Alpha Carl ZeissVario-Tessar T* FE 4/16-35mm ZA OSS. Sony also usesVario-Tessar lens branding for their consumer camcorders such as the HDR-CX405 extending the wide angle view with 1.9mm to 57mm zoom range.

• Tessar lenses
• 
  2 historical lenses Carl Zeiss, Jena, Nr. 145077 and Nr. 145078, Tessar 1:4,5 F=5,5cm DRP 142294 (produced before 1910)
• 
  Carl Zeiss Tessar 50/2.8 lens onZeiss Ikon Contessa camera.
• 
  Tessar 40/3.5 lens made byRollei.
• 
  Minox MDC Minoxar 35mm/2.8 lens, a wide angle Tessar type lens.
• 
  Unit focusing Tessar 50/2.8 of Zeiss Ikon Contaflex Super B. The front element of this Tessar can be replaced with Tele Pro Tessar or Wide angle Pro Tessar.

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 photographicenlargers, as they provide more contrast than many competing lens designs due to the limited number of air-to-glass surfaces.

All lenses can be focused by moving the lens assembly towards or away from the film ("unit focusing"), and theTessar 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, includingTessars, 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 theTessar 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-focusingTessar, cheaper than a unit-focusing lens, was widely used in many midrange Zeiss Ikon cameras.

• Pancake lens
• Biotar [de]
• Planar
• Sonnar
• Biogon
• Distagon [de]
• Flektogon [de]
• Hologon
• Elmar (lens)

• Nasse, H. Hubert (March 2011)."From the series of articles on lens names: Tessar"(PDF).Camera Lens News (CLN) (39th ed.). Carl Zeiss AG, Camera Lens Division. Archived fromthe original(PDF) on 2013-02-17. Retrieved2013-06-08.(NB. English:[1]; German:[2],[3]){{cite web}}:External link in|quote= (help)

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