View source for Engineering:Tessar

{{Short description|Photographic lens design}}
{{Infobox lens design
|scheme = Tessar.png
|year = 1902
|author = [[Biography:Paul Rudolph (physicist)|Paul Rudolph]]
|elements = 4
|groups = 3
|aperture = {{f/}}6.3 (1902)<br/>{{f/}}4.5 (1907)<br/>{{f/}}2.8 (1930, by Willy Merté)
}}

The '''''Tessar''''' is a photographic lens design conceived by the German physicist Dr. [[Biography:Paul Rudolph (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'''''. Since its introduction, millions of ''Tessar'' and ''Tessar''-derived lenses have been manufactured by Zeiss and other manufacturers, and are still produced as excellent intermediate aperture lenses.

The ''Tessar'' design uses four spherical lens elements in three groups, one positive [[Engineering:Crown glass (optics)|crown glass]] element at the front, one negative [[Physics:Flint glass|flint glass]] element at the center and a negative concave flint glass element [[Doublet (lens)#Cement|cemented]] with a positive convex crown glass element at the rear.

== History ==
<gallery widths=200px heights=150px caption="''Tessar'' and design antecedents>
File:Rudolph US444714A (Protar, 1890).svg|Zeiss ''Protar'' (aka ''Anastigmat''; [[Biography:Paul Rudolph (physicist)|Rudolph]], 1890)<ref name=DE56109C>{{cite patent |country=DE |status=Patent |number=56109C |title=Photographisches Doppelobjectiv |inventor=Paul Rudolph |pridate=April 3, 1890 |fdate=April 3, 1890 |pubdate=May 20, 1891 |assign=Carl Zeiss AG}}</ref>
File:Taylor US568052A (Cooke Triplet, 1893 Fig 11).svg|Cooke ''Triplet'' (Taylor, 1893)<ref>{{cite patent |country=GB |status=Patent |number=189322607A |title=A Simplified Form and Improved Type of Photographic Lens |inventor=H. Dennis Taylor |pridate=November 25, 1893 |fdate=November 25, 1893 |pubdate=October 6, 1894 |assign=Taylor, Taylor & Hobson}}</ref>
File:Aldis GB16640-95 (Stigmatic, 1895).svg|Dallmeyer ''Stigmatic'' (Aldis, 1895)<ref name=GB16640A-95/>
File:Rudolph US660202A (Unar, 1899).svg|Zeiss ''Unar'' ([[Biography:Paul Rudolph (physicist)|Rudolph]], 1899)<ref name=DE134408C>{{cite patent |country=DE |status=Patent |number=134408C |title=Sphärisch und chromatisch korrigirtes Objektiv mit anastigmatischer Bildebenung |inventor=Paul Rudolph |assign=Carl Zeiss Jena |fdate=November 3, 1899 |pubdate=October 10, 1902}}</ref>
File:Rudolph US721240A (Tessar, 1902).svg|Zeiss ''Tessar'' ([[Biography:Paul Rudolph (physicist)|Rudolph]], 1902)<ref name=DE142294C>{{cite patent |country=DE |status=Patent |number=142294C |title=Sphärisch, chromatisch und astigmatisch korrigiertes Objectiv aus vier, durch die Blende in zwei Gruppen geteilten Linsen |inventor=Paul Rudolph |assign=Carl Zeiss Jena |fdate=April 25, 1902 |pubdate=July 4, 1903}}</ref>
</gallery>
=== Beginnings ===
Despite common belief, the ''Tessar'' was not developed from the 1893 [[Engineering:Cooke triplet|Cooke triplet]] design, although it appears the ''Tessar'' replaces the single rear element of the Cooke triplet with a cemented [[Physics:Achromatic lens|achromatic]] doublet. Instead, the ''Tessar'' underwent a parallel evolution from Paul Rudolph's 1890 ''Anastigmat'' lens, which had four elements in two cemented groups.<ref name=DE56109C/><ref name=":0"/>{{rp|82–83}} Hugh L. Aldis patented the ''Stigmatic'' lens line for Dallmeyer in 1895;<ref name=GB16640A-95>{{cite patent |country=GB |status=Patent |number=189516640A |title=Improvements in Photographic Lenses |inventor=Hugh Lancelot Aldis |pridate=September 5, 1895 |fdate=September 5, 1895 |pubdate=July 4, 1896 |assign=J.H. Dallmeyer, Ltd.}}</ref> 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.<ref name=":0"/>{{rp|84}} Later, Rudolph adopted the same device to modify the ''Anastigmat'' design, resulting in the ''Unar'' of 1899.<ref name=DE134408C/> 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.<ref name=":0"/>{{rp|86}}

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.<ref name=DE142294C/><ref name=":0"/>{{rp|87}} 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.<ref name=":0">{{Kingslake-lens-history |chapter=6}}</ref>{{rp|87}}

===Improvements and evolutions===
The first ''Tessar'' appeared with a maximum aperture of {{f/|6.3}}, but by 1917, the maximum aperture had been increased to {{f/|4.5}}. In 1930, Ernst Wandersleb and Willy Merté from Zeiss developed ''Tessar'' lenses with apertures of {{f/|3.5}} and {{f/|2.8}}.<ref name=":0"/>{{rp|87}}<ref name=DE603325C>{{cite patent |country=DE |status=Patent |number=603325C |title=Dreiteiliges photographisches Objektiv |inventor=Ernst Wandersleb |invent2=Willy Merté |assign=Carl Zeiss Jena |fdate=July 18, 1930 |pubdate=September 29, 1934}}</ref>

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.<ref name=DE451194C>{{cite patent |country=DE |status=Patent |number=451194C |inventor=Wandersleb |invent2=Merté |title=Sphaerisch, komatisch, chromatisch und astigmatisch korrigierte Lichtbildlinse |pridate=August 7, 1925 |fdate=August 7, 1925 |pubdate=October 22, 1927}}</ref>

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 Werra river which runs through the town.<ref>{{cite web |url=http://www.cjs-classic-cameras.co.uk/zeiss/werra.html |title=Werra |website=CJ's Classic Camera Collection |access-date=18 May 2023}}</ref> Many models were equipped with ''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".
<gallery widths=200px heights=150px caption="''Tessar'' improvements and derived lens designs>
File:Stuart & Hasselkus GB29637-13 (Xpress, 1913).svg|[[Company:Ross (optics)|Ross]] ''Xpress'' (Stuart & Hasselkus, 1913)<ref name=GB29637-13/>
File:Florian US1122895A (Olor, 1913).svg|Berthiot ''Olor'' (Florian, 1913)<ref name=US1122895A/>
File:Berek DE343086C (Elmar, 1920).svg|Leitz ''Elmar'' (Berek, 1920)<ref name=DE343086C/>
File:Merte & Wandersleb US1697670 (Biotessar, 1925).svg|''Biotessar'' (Merté & Wandersleb, 1925)<ref name=DE451194C/>
File:Merte & Wandersleb US1849681A (Tessar B, 1930).svg|Improved ''Tessar'' (Merté & Wandersleb, 1930)<ref name=DE603325C/>
File:Tronnier US2084714A (Xenar, 1935).svg|[[Company:Schneider Kreuznach|Schneider]] ''Xenar'' (Tronnier, 1935)<ref>{{cite patent |country=US |status=Patent |number=2084714A |inventor=Albrecht Tronnier |title=Unsymmetrical photographic objective |pridate=August 26, 1935 |fdate=October 25, 1935 |pubdate=June 22, 1937 |assign=Jos. Schenider & Co.}}</ref>
File:Tronnier US2573511A (Color-Skopar, 1949).svg|[[Company:Voigtländer|Voigtländer]] ''Skopar'' (Tronnier, 1949)<ref>{{cite patent |country=US |status=Patent |number=2573511A |inventor=Albrecht Tronnier |title=Four-lens photographic objective |pridate=April 30, 1949 |fdate=November 17, 1949 |pubdate=October 30, 1951 |assign=Voigtländer & Sohn AG}}</ref>
</gallery>

===''Tessar''-derived lenses===
Zeiss had strong control over the ''Tessar'' design, because Rudolph's patent was very general.<ref name=":0" />{{rp|87}} In the corresponding U.S. Patent, he claimed:<blockquote>''"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."''<br/><br />{{pad|0.5em}}—[[Biography:Paul Rudolph (physicist)|Paul Rudolph]], US Pat. 721,240<ref name=US721240A>{{cite patent |country=US |status=Patent |number=721240A |title=Photographic Objective |inventor=Paul Rudolph |assign=Carl Zeiss Jena |pridate=July 15, 1902 |fdate=July 15, 1902 |pubdate=February 24, 1903}}</ref></blockquote>

The ''Tessar'' design patent was held by Zeiss for two decades, and licensed to [[Company:Ross (optics)|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,<ref name=GB29637-13>{{cite patent |country=GB |status=Patent |number=191329637A |title=Improvements in Lenses for use in Photography and Projection, or the like. |inventor=John Stuart |invent2=John W. Hasselkus |pridate=December 23, 1913 |fdate=December 23, 1913 |pubdate=October 22, 1914}}</ref> Gundlach ''Radar'', and Berthiot ''Olor'' by Florian.<ref name=":0"/>{{rp|89}}<ref name=US1122895A>{{cite patent |country=US |status=Patent |number=1122895A |title=Objective |inventor=Charles Henri Florian |assign=Berthiot |pridate=June 4, 1913 |fdate=June 4, 1913 |pubdate=December 29, 1914}}</ref>

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.<ref>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</ref> Other ''Tessar''-type lenses include:<ref name=":0"/>{{rp|88}}
{{div col |colwidth=15em}}
* Agfa ''Solinar''
* [[Company:Kodak|Kodak]] ''Ektar'' (some, but not all)
* [[Company:Krasnogorsky Zavod|KMZ]] ''Industar''
* [[Company:Minolta|Minolta]] ''Rokkor'' 75mm (twin-lens-reflex design)
* Rodenstock ''Ysar''
* [[Company:Schneider Kreuznach|Schneider]] ''Xenar''
* [[Company:Voigtländer|Voigtländer]] ''Skopar''
* Yashica ''Yashinon'' 80mm (twin-lens-reflex design)
{{div col end}}

==== Leitz ''Elmar''====
{{main|Engineering:Elmar (lens)}}
It is sometimes believed the Leitz ''Elmar'' 50&nbsp;mm {{f/|3.5}}, designed by Max Berek in 1920, was derived from the ''Tessar'',<ref name=":0" />{{rp|87}} as they share the same general layout.<ref name=DE142294C/><ref name=DE343086C>{{cite patent |country=DE |status=Patent |number=343086C |inventor= |assign=E. Leitz |title=Unsymmetrisches Objektiv |pridate=October 9, 1920 |fdate=October 9, 1920 |pubdate=October 28, 1921}}</ref> 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, Oskar Barnack tried a 50&nbsp;mm ''Tessar'', but because it had been designed to cover only the 18×24&nbsp;mm field of a cine frame, he found it inadequate for coverage of the Leica 24×36&nbsp;mm format.  The lens designed by {{ill|Max Berek|de}} for the [[Company:Leica Camera|Leica]] [[Engineering:Rangefinder camera|rangefinder camera]] was a modified [[Engineering:Cooke triplet|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 24×36&nbsp;mm format and was used until improved optical glass allowed the third group to be simplified to a cemented pair when it was renamed ''Elmar''.  It was not until Zeiss Ikon was developing the Contax camera to compete with the Leica that the ''Tessar'' was redesigned to cover a 24×36&nbsp;mm negative.<ref>"Die Leica" 1933, No. 6. Was ist eigentlich "Elmar"?</ref>

===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&nbsp;mm ''f''/4 and 85&nbsp;mm ''f''/4, and the wide-angle Pro Tessar 35&nbsp;mm ''f''/3,2 for use on the central-shutter SLR Zeiss Ikon Contaflex Super B cameras.

===Licensed ''Tessar'' lenses / ''Vario-Tessar''{{anchor|Vario-Tessar}}===
Other ''Tessar'' lenses, for example those equipped on certain [[Company:Nokia|Nokia]] mobile phones, have only the name ''Tessar'' in common with the original ''Tessar'', not the four-element, three-group design. They are for example a 5-elements-in-1-group, aperture-less all-aspherical lens, as in the Nokia 808 Pureview and [[Engineering:Nokia Lumia 800|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 fitted to Sony cameras, including that of the digital still cameras Sony Cyber-shot DSC-P100,<ref name=dscp100>[http://www.steves-digicams.com/2004_reviews/p100.html Sony Cyber-shot DSC-P100 review]</ref> 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. Sony also uses ''Vario-Tessar'' lens branding for their consumer camcorders such as the HDR-CX405 extending the wide angle view with 1.9mm to 57mm zoom range.

==Design==
<gallery mode=packed heights=150px widths=200px caption="''Tessar''  lenses">
Image:Objektive Carl Zeiss, Jena, Nr. 145077 und Nr. 145078, Tessar 4,5 F 5,5cm DRP 142294 (Baujahr vor 1910) 1.jpg|2 historical lenses Carl Zeiss, Jena, Nr. 145077 and Nr. 145078, Tessar 1:4,5 F=5,5cm DRP 142294 (produced before 1910)
Image:Zeiss Ikon Contessa1.jpg|Carl Zeiss Tessar 50/2.8 lens on Zeiss Ikon Contessa camera.
Image:Rollei 35.JPG|Tessar 40/3.5 lens made by Rollei.
Image:Minox MDC.jpg|Minox MDC Minoxar 35mm/2.8 lens, a wide angle Tessar type lens.
Image:Contaflex1.jpg|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.
</gallery>
===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 [[Engineering:Enlarger|enlarger]]s, 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==
*[[Engineering:Pancake lens|Pancake lens]]
*{{Interlanguage link multi|Biotar|de}}
*[[Engineering:Zeiss Planar|Planar]]
*Sonnar
*Biogon
*{{Interlanguage link multi|Distagon|de}}
*{{Interlanguage link multi|Flektogon|de}}
*[[Engineering:Hologon|Hologon]]
*[[Engineering:Elmar (lens)|Elmar (lens)]]

==Further reading==
*{{cite web
 |title=From the series of articles on lens names: Tessar
 |first=H. Hubert
 |last=Nasse
 |work=Camera Lens News (CLN)
 |edition=39th
 |date=March 2011
 |publisher=Carl Zeiss AG, Camera Lens Division
 |url=http://www.zeiss.com/C12567A8003B8B6F/EmbedTitelIntern/CLN_39_en_Tessar/$File/CLN39_en_tessar.pdf
 |quote=(NB. English: [http://www.zeiss.com/C12567A8003B8B6F/EmbedTitelIntern/CLN_39_en/$File/CLN39_en_web.pdf]; German: [http://www.zeiss.com/C12578B8004E8E1D/0/0AEA4868222570AFC12578CE003B51A1/$file/cln-special_objektivname-tessar_ger.pdf], [http://www.zeiss.de/C12567A8003B8B6F/EmbedTitelIntern/CLN_39_de/$File/CLN39_dt_web.pdf])
 |accessdate=2013-06-08
 |archive-date=2013-02-17
 |archive-url=https://web.archive.org/web/20130217050241/http://www.zeiss.com/C12567A8003B8B6F/EmbedTitelIntern/CLN_39_en_Tessar/$File/CLN39_en_tessar.pdf
 |url-status=dead
 }}

==References==
{{Reflist}}

[[Category:Photographic lens designs]]

{{Sourceattribution|Tessar}}