Angénieux retrofocus
Introduced in1950 (stills)
AuthorPierre Angénieux (1950)
Construction6 elements in 5 groups
Aperturef/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.[1]: 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.[2]: 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.[2]: 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.[2]: 142 [3] 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.[4][5] Joseph Ball showed how a beam-splitting apparatus could be fitted in the space gained.[6] 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.[2]: 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.[2]: 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.[7]

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.[8] 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.[2]: 143 

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[23] for almost every 35mm SLR, helping to make it the definitive camera type of the late 20th century.

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.[10] Carl Zeiss Oberkochen also created an inverted telephoto design branded Distagon (5.6/60 mm) for the Hasselblad 1000F in 1952.[3] 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.[14][15]

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).[24][25] 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).[22]

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.[2]: 150 [26]

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.[27]: 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.[27]: 205–206 

References

  1. ↑ Kingslake, Rudolf (1989). "9. Telephoto Lenses". A History of the Photographic Lens. San Diego: Academic Press. pp. 131–140. ISBN 0-12-408640-3. Retrieved 15 December 2023.
  2. 1 2 3 4 5 6 7 Kingslake, Rudolf (1989). "10. Reversed Telephoto Lenses". A History of the Photographic Lens. San Diego: Academic Press. pp. 141–152. ISBN 0-12-408640-3. Retrieved 15 December 2023.
  3. 1 2 Nasse, Dr. Hubert H. (December 2011). From the series of articles on lens names: Distagon, Biogon and Hologon (PDF). Lenspire [blog] (Report). Carl Zeiss AG. Retrieved 15 November 2018.
  4. 1 2 GB Application 355452, Horace William Lee, "Improvements in lenses for photography and the like", assigned to Kapella Ltd.
  5. 1 2 US Grant 1955590, Horace William Lee, "Lens", issued 17 April 1934, assigned to Kapella Ltd.
  6. ↑ US Grant 1862950, Joseph A Ball, "Optical apparatus", issued 14 June 1932, assigned to Technicolor Motion Picture Corp.
  7. 1 2 US Patent 2746351A, Rudolf Kingslake & Paul W. Stevens, "Wide-angle lenses", published February 8, 1944, assigned to Eastman Kodak Co.
  8. ↑ US Grant 2649022, Pierre Angénieux, "Wide-angle photographic objective lens assembly", issued 18 August 1953, assigned to Pierre Angénieux
  9. ↑ US Patent 2649022A, Pierre Angénieux, "Wide-angle photographic objective lens assembly", published August 18, 1953
  10. 1 2 US Patent 2746351A, Albrecht Wilhelm Tronnier, "Photographic objective of the modified triplet type and a meniscus shaped negative member axially separated therefrom", published May 22, 1956, assigned to Voigtländer & Sohn AG
  11. ↑ US Patent 2696758A, Pierre Angénieux, "Wide-angle photographic objective", published December 14, 1954
  12. ↑ US Patent 2983191A, Johann Lautenbacher, "High-speed wide-angle photographic objective", published May 9, 1961, assigned to Enna Werk Optik Apelt
  13. ↑ US Patent 2772601A, Ludwig Bertele, "Wide angle photographic objective comprising three air spaced components", published December 4, 1956
  14. 1 2 DE Grant 953471, Harry Zollner & Rudolf Solisch, "Photographisches Objektiv mit einem sammelnden Systemteil und einem in verhaeltnismaessig grossem Abstand davor liegenden zerstreuenden Meniskus", issued 29 November 1956, assigned to Jenoptik AG
  15. 1 2 US Patent 2793565A, Harry Zöllner & Rudolf Solisch, "Photographic objective comprising a rear collective part and front dispersive meniscus part", published May 28, 1957, assigned to Jenoptik AG
  16. ↑ US Patent 2824495A, Gunter Klemt, "Wide-angle photographic and cinematographic objective", published February 25, 1958, assigned to Scheider Co. Optische Werke
  17. ↑ DE Patent 1017382B, Franz Schlegel, "Fotografisches Objektiv", published October 10, 1957, assigned to Rodenstock Optik G
  18. ↑ US Patent 2927506A, Fritz Determann, "Photographic objective", published March 3, 1960, assigned to Voigtländer & Sohn AG
  19. ↑ US Patent 2878724A, Rudolf Solisch, "Asymmetrical photographic or cinematographic objective with large angle of view", published March 24, 1959, assigned to ISCO Optische Werke GmbH
  20. ↑ US Patent 3038380A, Helmut Eismann & Gunther Lange, "Asymmetrical photographic objective", published June 12, 1962, assigned to Carl Zeiss AG
  21. ↑ FR Patent 1214945A, Pierre Angénieux, "Objectif photographique du type grand-angulaire", published April 12, 1960
  22. 1 2 GB Patent 978797A, Wolf Dannberg & Eberhard Dietzsch, "Improvements in or relating to wide-angle lenses", published December 23, 1964, assigned to Carl Zeiss Jena VEB
  23. ↑ Ohshita, Kouichi. "NIKKOR - The Thousand and One Nights No. 12: NIKKOR-H Auto 2.8cm F3.5 (March 1960)". Nikon Imaging – History. Retrieved 15 March 2023. 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
  24. ↑ "P. Angénieux lenses for 35mm cameras" (PDF). Pacific Rim Camera, Reference Library. P.Angénieux. Retrieved 15 March 2023.
  25. ↑ "Retrofocus and zoom". Swiss Camera Museum. Retrieved 29 March 2023.
  26. ↑ US patent 2516724, Michael Michaelovitch Roosinov, "Wide angle orthoscopic anastigmatic photographic objective", issued July 25, 1950
  27. 1 2 Kingslake, Rudolf (March 1966). "The Reversed Telephoto Objective: A Tutorial Paper". Journal of the SMPTE. 75: 203–207.

Bibliography

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