{{short description|Wide-angle lens for photographic camera}} {{no footnotes|date=March 2013}} {{Infobox lens design |scheme = Angenieux35f25Retrofocus-t.svg |year = 1950 (stills) |author = Pierre Angénieux (1950) |elements = 6 |groups = 5 |aperture = {{f/|2.5}} }} The '''Angénieux retrofocus''' photographic lens is a wide-angle lens design that uses an '''inverted telephoto''' configuration. The popularity of this lens design made the name '''retrofocus''' synonymous with this type of lens. The Angénieux retrofocus for still cameras was introduced in France in 1950 by Pierre Angénieux.
==Inverted telephoto concept== The telephoto lens configuration combines positive and negative lens groups with the negative at the rear, serving to magnify the image, which reduces the back focal distance of the lens (the distance between the back of the lens and the image plane) to a figure shorter than the focal length. This is for practical, not optical reasons, because it allows telephoto lenses to be made shorter and less cumbersome. The first practical telephoto lens was developed by Peter Barlow in the early 1800s, with the eponymous Barlow lens referring to the negative achromat inserted between the eye and a telescope.<ref name=Kingslake-9>{{Kingslake-lens-history |chapter=9}}</ref>{{rp|131–132}}
The inverted telephoto configuration does the reverse, employing one or more negative lens groups at the front to increase the back focal distance of the lens – possibly to a figure greater than the focal length – in order to allow for additional optical or mechanical parts to fit behind the lens.<ref name=Kingslake-10>{{Kingslake-lens-history |chapter=10}}</ref>{{rp|141–142}} The negative front group also serves to increase peripheral illumination; some symmetric wide-angle lenses require a radially-graduated filter or other means to make the exposure even across the frame.<ref name=Kingslake-10/>{{rp|144}}
The inverted telephoto design was first employed in the 1930s by Taylor-Hobson for the early Technicolor "3-strip" cameras since the beam splitter unit behind the lens required significant space, so that a long back focal distance was essential.<ref name=Kingslake-10/>{{rp|142}}<ref name=Names /> Horace Lee patented an inverted telephoto lens design in 1930 with an angle of view of 50° and maximum aperture of {{f/}}2 which afforded a distance between the rear element and the film plane approximately 10% greater than the focal length.<ref name=GB355452>{{cite patent |url=https://patents.google.com/patent/GB355452/ |title=Improvements in lenses for photography and the like |inventor=Horace William Lee |country=GB |number=355452 |pridate=12 July 1930 |fdate=27 August 1931 |status=Application |assign=Kapella Ltd.}}</ref><ref name=US1955590>{{cite patent |url=https://patents.google.com/patent/US1955590/ |title=Lens |inventor=Horace William Lee |country=US |number=1955590 |pridate=12 July 1930 |gdate=17 April 1934 |status=Grant |assign=Kapella Ltd.}}</ref> Joseph Ball showed how a beam-splitting apparatus could be fitted in the space gained.<ref>{{cite patent |url=https://patents.google.com/patent/US1862950A/ |title=Optical apparatus |inventor=Joseph A Ball |country=US |number=1862950 |pridate=17 June 1929 |gdate=14 June 1932 |status=Grant |assign=Technicolor Motion Picture Corp.}}</ref> Also, wide-angle lenses for narrow-gauge movie cameras had to be of this type because of the shutter mechanism that had to fit in between.<ref name=Kingslake-10/>{{rp|142–143}}
In still photography, a single-lens reflex camera requires a space for the reflex mirror, imposing a limit on the use of wide-angle lenses of symmetric designs. The retrofocus lens addressed this situation by increasing the distance between the rear element and the focal plane, thus making wider-angle lenses usable while retaining normal viewing and focusing. Unless the reflex mirror were locked in the "up" position, blacking out the viewfinder, the rearmost element(s) of a non-retrofocus (symmetric wide-angle) lens would interfere with the movement of the mirror as it flipped up and down during exposure.<ref name=Kingslake-10/>{{rp|143}}
==Implementation== Rudolf Kingslake and Paul Stevens filed for a patent in 1941 for the ''WA Ektanar'', which featured a negative meniscus element facing the object, followed by a ''Tessar''-derived four-element/three-group lens. However, the spacing between the first element and the following lens was relatively small and so the back focus was approximately equal to the focal length.<ref name=US2341385/>
On 13 August 1949 Harry Zöllner and Rudolf Solisch completed the computation of the first version of the Zeiss Jena Flektogon 35 mm f/2.8. This lens was presented at the Leipzig Spring Fair from 5 to 12 March 1950 and serial production started in July 1950.<ref>{{Cite web |last=Kröger |first=Marco |date=2024 |title=Flektogon 2,8/35 |url=https://zeissikonveb.de/start/objektive/wechselobjektive1950er/carl-zeiss-jena/flektogon-2-8-35.html |website=Zeissikonveb}}</ref>
Pierre Angénieux applied for a patent in 1950. In the original patent, he presented two lenses with an angle of view of 65°, approximately equal to the view of a f=35 mm lens on the 35mm format for still cameras; the first example had a maximum aperture of {{f/}}2.5, while the second example had a maximum aperture of {{f/}}2.2.<ref>{{cite patent |url=https://patents.google.com/patent/US2649022A/ |title=Wide-angle photographic objective lens assembly |country=US |number=2649022 |status=Grant |pridate=17 February 1950 |fdate=29 July 1950 |gdate=18 August 1953 |inventor=Pierre Angénieux |assign=Pierre Angénieux}}</ref> The Angénieux corporation coined the name ''Retrofocus'' for its line of inverted telephoto wide-angles, and the name has become synonymous as a generic trademark for similar lens designs.<ref name=Kingslake-10/>{{rp|143}}
<gallery heights=150px widths=200px caption="Inverted telephoto wide-angle lens development"> File:Lee - Inverted telephoto (1930).svg|Taylor-Hobson 'inverted telephoto' lens by H.W. Lee (1930), GB 355,452<ref name=GB355452 /> and US 1,955,590<ref name=US1955590 /> File:Kingslake & Stevens US2341385A (WA Ektanar, 1941).svg|Kodak ''WA Ektanar'' (35 mm {{f/|3.5}}, 1941) by Kingslake & Stevens, from US Patent 2,341,385<ref name=US2341385>{{cite patent |country=US |status=Patent |number=2746351A |title=Wide-angle lenses |pridate=November 6, 1941 |fdate=November 6, 1941 |pubdate=February 8, 1944 |inventor=Rudolf Kingslake |invent2=Paul W. Stevens |assign=Eastman Kodak Co.}}</ref> File:Angénieux - Retrofocus (1950).svg|Angénieux ''Retrofocus R-1'' (35 mm {{f/|2.5}}, 1950), from US Patent 2,649,022<ref>{{cite patent |country=US |status=Patent |number=2649022A |title=Wide-angle photographic objective lens assembly |pridate=February 17, 1950 |fdate=July 29, 1950 |pubdate=August 18, 1953 |inventor=Pierre Angénieux}}</ref> File:Tronnier US2746351A (Skoparon, 1952).svg|Voigtländer ''Skoparon'' (35 mm {{f/|3.5}}, 1952) by Tronnier, from US Patent 2,746,351<ref name=US2746351>{{cite patent |country=US |status=Patent |number=2746351A |title=Photographic objective of the modified triplet type and a meniscus shaped negative member axially separated therefrom |pridate=March 5, 1952 |fdate=March 3, 1953 |pubdate=May 22, 1956 |inventor=Albrecht Wilhelm Tronnier |assign=Voigtländer & Sohn AG}}</ref> File:Angénieux US2696758A (Retrofocus R-11, 1952).svg|Angénieux ''Retrofocus R-11'' (28 mm {{f/|3.5}}, 1952), from US Patent 2,696,758<ref>{{cite patent |country=US |status=Patent |number=2696758A |title=Wide-angle photographic objective |pridate=May 29, 1952 |fdate=March 23, 1953 |pubdate=December 14, 1954 |inventor=Pierre Angénieux}}</ref> File:Lautenbacher US2983191A (Lithagon, 1953).svg|Enna ''Lithagon'' (35 mm {{f/|2.5}}, 1953) by Lautenbacher, from US Patent 2,983,191<ref name=US2983191>{{cite patent |country=US |status=Patent |number=2983191A |title=High-speed wide-angle photographic objective |pridate=February 19, 1955 |fdate=February 15, 1956 |pubdate=May 9, 1961 |inventor=Johann Lautenbacher |assign=Enna Werk Optik Apelt}}</ref> File:Bertele US2772601A (Travegon, 1954).svg|Schacht ''Travegon'' (35 mm {{f/|2.5}}, 1954) by Bertele, from US Patent 2,772,601<ref name=US2772601>{{cite patent |country=US |status=Patent |number=2772601A |title=Wide angle photographic objective comprising three air spaced components |pridate=June 18, 1954 |fdate=June 13, 1955 |pubdate=December 4, 1956 |inventor=Ludwig Bertele}}</ref> File:Zöllner-Solisch US2793565A (Flektogon), 1955.svg|Zeiss Jena ''Flektogon'' by Zöllner & Solisch (1955), from US Patent 2,793,565<ref name=DE953471/><ref name=US2793565A>{{cite patent |country=US |status=Patent |number=2793565A |title=Photographic objective comprising a rear collective part and front dispersive meniscus part |pridate=April 26, 1955 |fdate=April 26, 1955 |pubdate=May 28, 1957 |inventor=Harry Zöllner |invent2=Rudolf Solisch |assign=Jenoptik AG}}</ref> File:Klemt US2824495A (Curtagon, 1955).svg|Schneider ''Curtagon'' (28 mm {{f/|4}}, 1955) by Klemt, from US Patent 2,824,495<ref name=US2824495A>{{cite patent |country=US |status=Patent |number=2824495A |title=Wide-angle photographic and cinematographic objective |pridate=July 5, 1955 |fdate=July 3, 1956 |pubdate=February 25, 1958 |inventor=Gunter Klemt |assign=Scheider Co. Optische Werke}}</ref> File:Schlegel DE1017382B (Eurygon, 1955).svg|Rodenstock ''Eurygon'' (35 mm {{f/|4}}, 1955) by Schlegel, from DE Patent 1,017,382<ref name=DE1017382>{{cite patent |country=DE |status=Patent |number=1017382B |title=Fotografisches Objektiv |pridate=October 22, 1955 |fdate=October 22, 1955 |pubdate=October 10, 1957 |inventor=Franz Schlegel |assign=Rodenstock Optik G}}</ref> File:Determann US2927506A (Skoparet, 1956).svg|Voigtländer ''Skoparet'' (35 mm {{f/|3.4}}, 1956) by Determann, from US Patent 2,927,506<ref name=US2927506A>{{cite patent |country=US |status=Patent |number=2927506A |title=Photographic objective |pridate=September 12, 1956 |fdate=September 9, 1957 |pubdate=March 3, 1960 |inventor=Fritz Determann |assign=Voigtländer & Sohn AG}}</ref> File:Solisch US2878724A (Westrogon, 1956).svg|ISCO ''Westrogon'' (24 mm {{f/|4}}, 1956) by Solisch, from US Patent 2,878,724<ref name=US2878724>{{cite patent |country=US |status=Patent |number=2878724A |title=Asymmetrical photographic or cinematographic objective with large angle of view |pridate=November 10, 1956 |fdate=October 29, 1957 |pubdate=March 24, 1959 |inventor=Rudolf Solisch |assign=ISCO Optische Werke GmbH}}</ref> File:Eismann & Lange US3038380A (Distagon, 1958).svg|Carl Zeiss (Oberkochen) ''Distagon'' (35 mm {{f/|4}}, 1958) by Eismann & Lange, from US Patent 3,038,380<ref name=US3038380A>{{cite patent |country=US |status=Patent |number=3038380A |title=Asymmetrical photographic objective |pridate=February 27, 1958 |fdate=February 19, 1959 |pubdate=June 12, 1962 |inventor=Helmut Eismann |invent2=Gunther Lange |assign=Carl Zeiss AG}}</ref> File:Angénieux FR1214945A (Retrofocus R-61, 1958).svg|Angénieux ''Retrofocus R-61'' (24 mm {{f/|3.5}}, 1958), from French Patent 1,214,945<ref>{{cite patent |country=FR |status=Patent |number=1214945A |title=Objectif photographique du type grand-angulaire |inventor=Pierre Angénieux |pridate=October 9, 1958 |fdate=October 9, 1958 |pubdate=April 12, 1960}}</ref> File:Dannberg & Dietzsch GB978797A (Flektogon, 1963).svg|Carl Zeiss (Jena) ''Flektogon'' (20 mm {{f/|4}}, 1963) by Dannberg & Dietzsch, from GB Patent 978797A<ref name=GB978797A>{{cite patent |country=GB |status=Patent |number=978797A |title=Improvements in or relating to wide-angle lenses |pridate=June 11, 1963 |fdate=June 11, 1963 |pubdate=December 23, 1964 |inventor=Wolf Dannberg |invent2=Eberhard Dietzsch |assign=Carl Zeiss Jena VEB}}</ref> </gallery> [[File:NIKKOR-H 2.8cm f-3.5 lens (4202223258).jpg|thumb|right|Nikon ''Nikkor-H'' f=2.8cm {{f/|3.5}} lens (early 1960s); note large front element, characteristic of inverted telephoto designs]] The Angénieux ''Retrofocus'' lens line inspired other manufacturers to produce similar wide-angle lenses of this type<ref name="Nikkor-28/3.5">{{cite web |url=https://imaging.nikon.com/history/story/0012/index.htm |title=NIKKOR - The Thousand and One Nights No. 12: NIKKOR-H Auto 2.8cm F3.5 (March 1960) |author=Ohshita, Kouichi |website=Nikon Imaging – History |access-date=15 March 2023 |quote=At [the time the Nikon F was released, in 1959], various companies had been competing to develop wide-angle lenses having a reversed telephoto type (a large diameter concave (negative) lens is arranged in front of an ordinary lens) for SLR cameras with the release of a ''Retrofocus''™ 35mm by Angenieux (France) as the start. However, satisfactory optical performance could not seem to be obtained without changing the lens construction of known reversed telephoto type including the ''Retrofocus'' when the focal length was shortened to 28mm. Thus, Mr. WAKIMOTO, Zenji found a new reversed telephoto type as a result of trial and error. This is the NIKKOR-H Auto 2.8cm f/3.5}}</ref> for almost every 35mm SLR, helping to make it the definitive camera type of the late 20th century.{{Citation needed|date=March 2011}}
Similar lenses with prominent object-facing meniscus lenses were patented a few years after the original ''Retrofocus'' patent. For example, Albrecht Tronnier used the ''Tessar''-derived ''Skopar'' lens with a single negative meniscus for the Voigtländer ''Skoparon'' of 1952.<ref name=US2746351/> Carl Zeiss Oberkochen also created an inverted telephoto design branded ''Distagon'' (5.6/60 mm) for the Hasselblad 1000F in 1952.<ref name=Names>{{cite report |url=https://lenspire.zeiss.com/photo/app/uploads/2018/02/en_CLB41_Nasse_LensNames_Distagon.pdf |title=From the series of articles on lens names: Distagon, Biogon and Hologon |author=Nasse, Dr. Hubert H. |date=December 2011 |publisher=Carl Zeiss AG |website=Lenspire [blog] |accessdate=15 November 2018}}</ref> In 1955, Harry Zöllner and Rudolf Solisch applied for a similar patent on an inverted telephoto lens design, branded ''Flektogon'', for Carl Zeiss Jena, which uses a single negative meniscus element ahead of a Double-Gauss lens.<ref name=DE953471>{{cite patent |url=https://patents.google.com/patent/DE953471/ |title=Photographisches Objektiv mit einem sammelnden Systemteil und einem in verhaeltnismaessig grossem Abstand davor liegenden zerstreuenden Meniskus |country=DE |number=953471 |status=Grant |pridate=20 December 1953 |gdate=29 November 1956 |inventor=Harry Zollner |invent2=Rudolf Solisch |assign=Jenoptik AG}}</ref><ref name=US2793565A/>
thumb|left|Zeiss (Jena) ''Flektogon'' 4/20 Angénieux were not content to rest on their laurels, continuing to develop the inverted telephoto scheme by shortening the focal length from 35 mm {{f/|2.5}} with the original ''Retrofocus R-1'' (1950) to 28 mm {{f/|3.5}} with the ''Retrofocus R-11'' (1952) and ''R-61'' (24 mm {{f/|3.5}}, 1958).<ref>{{cite web |url=https://www.pacificrimcamera.com/rl/01286/01286.pdf |title=P. Angénieux lenses for 35mm cameras |date= |publisher=P.Angénieux |website=Pacific Rim Camera, Reference Library |access-date=15 March 2023}}</ref><ref>{{cite web |url=https://www.cameramuseum.ch/en/discover/permanent-exhibition/the-century-of-the-film/retrofocus-and-zoom/ |title=Retrofocus and zoom |website=Swiss Camera Museum |access-date=29 March 2023}}</ref> These used multiple negative meniscus elements in the front group, a trend that would continue with the Zeiss (Jena) ''Flektogon'' 20 mm {{f/|4}} design of 1963, with three negative meniscus elements and an angle of view expanded to 94° from 62° (with the original ''Retrofocus R-1'').<ref name=GB978797A/>
===Further development=== The highly symmetric super-wide angle lenses developed in the late 1940s and early 1950s, including the ''Biogon'', are sometimes described as a mirrored pair of inverted telephoto objectives, as first presented by Roosinov in 1946.<ref name=Kingslake-10/>{{rp|150}}<ref name=US2516724>{{cite patent |country=US |number=2516724 |inventor=Michael Michaelovitch Roosinov |pridate=August 23, 1946 |fdate=August 23, 1946 |gdate=July 25, 1950 |status=patent |title=Wide angle orthoscopic anastigmatic photographic objective}}</ref>
Pincushion distortion is common with inverted telephoto designs because they are so highly asymmetric. Lee suggested using an air space in the negative group to control this distortion.<ref name=Kingslake66>{{cite journal |url=https://archive.org/details/sim_smpte-motion-imaging-journal_1966-03_75_3_0046_202205/sim_smpte-motion-imaging-journal_1966-03_75_3_0046.jpg |title=The Reversed Telephoto Objective: A Tutorial Paper |author=Kingslake, Rudolf |author-link=Rudolf Kingslake |date=March 1966 |journal=Journal of the SMPTE |volume=75 |pages=203–207}}</ref>{{rp|204}} By removing the constraint for rectilinear projection and deliberately introducing barrel distortion, the illumination of the field can be made more even; the resulting fisheye lenses can be considered a subset of the inverted telephoto lens design, with strong negative front elements.<ref name=Kingslake66/>{{rp|205–206}}
==References== {{reflist}}
===Bibliography=== * {{cite journal |url=https://archive.org/details/sim_smpte-motion-imaging-journal_1966-03_75_3_0046_202205/sim_smpte-motion-imaging-journal_1966-03_75_3_0046.jpg |title=The Reversed Telephoto Objective: A Tutorial Paper |author=Kingslake, Rudolf |author-link=Rudolf Kingslake |date=March 1966 |journal=Journal of the SMPTE |volume=75 |pages=203–207}} * {{cite web|url=http://www.mwclassic.com/articles/agenieux/ageniuex.htm |title=An introduction to Angenieux lenses |author=Paul Gates |url-status=dead |archiveurl=https://web.archive.org/web/20150212023138/http://www.mwclassic.com/articles/agenieux/ageniuex.htm |archivedate=2015-02-12 }} * {{cite web|url=http://www.camerarepair.com/Retrofocus-Design-Problems-A-Synopsis-T37.html|archive-url=https://archive.today/20130103050721/http://www.camerarepair.com/Retrofocus-Design-Problems-A-Synopsis-T37.html|url-status=dead|archive-date=2013-01-03|title=Retrofocus Design Problems: A Synopsis|author=Bruce Sirovich}}
{{DEFAULTSORT:Angenieux retrofocus}} Category:Photographic lens designs