Angénieux retrofocus

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Template:Short description Script error: No such module "Unsubst". Template:Infobox lens design 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]Template:Rp

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]Template:Rp 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]Template:Rp

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]Template:Rp[3] Horace Lee patented an inverted telephoto lens design in 1930 with an angle of view of 50° and maximum aperture of <templatestyles src="F//styles.css" />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]Template:Rp

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]Template:Rp

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]

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.[8]

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 <templatestyles src="F//styles.css" />f/2.5, while the second example had a maximum aperture of <templatestyles src="F//styles.css" />f/2.2.[9] 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]Template:Rp

File:NIKKOR-H 2.8cm f-3.5 lens (4202223258).jpg
Nikon Nikkor-H f=2.8cm <templatestyles src="F//styles.css" />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[24] for almost every 35mm SLR, helping to make it the definitive camera type of the late 20th century.Script error: No such module "Unsubst".

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.[11] 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.[15][16]

File:Flektogon 4 20 lens -4636.jpg
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 <templatestyles src="F//styles.css" />f/2.5 with the original Retrofocus R-1 (1950) to 28 mm <templatestyles src="F//styles.css" />f/3.5 with the Retrofocus R-11 (1952) and R-61 (24 mm <templatestyles src="F//styles.css" />f/3.5, 1958).[25][26] These used multiple negative meniscus elements in the front group, a trend that would continue with the Zeiss (Jena) Flektogon 20 mm <templatestyles src="F//styles.css" />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).[23]

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]Template:Rp[27]

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.[28]Template:Rp 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.[28]Template:Rp

References

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  1. ↑ Template:Kingslake-lens-history
  2. ↑ a b c d e f g Template:Kingslake-lens-history
  3. ↑ a b Template:Cite report
  4. ↑ a b <templatestyles src="Citation/styles.css"/>Template:Citation/make link, Horace William Lee, "Improvements in lenses for photography and the like", assigned to Kapella Ltd. Script error: No such module "Check for unknown parameters".
  5. ↑ a b <templatestyles src="Citation/styles.css"/>Template:Citation/make link, Horace William Lee, "Lens", issued Script error: No such module "auto date formatter"., assigned to Kapella Ltd. Script error: No such module "Check for unknown parameters".
  6. ↑ <templatestyles src="Citation/styles.css"/>Template:Citation/make link, Joseph A Ball, "Optical apparatus", issued Script error: No such module "auto date formatter"., assigned to Technicolor Motion Picture Corp. Script error: No such module "Check for unknown parameters".
  7. ↑ a b <templatestyles src="Citation/styles.css"/>Template:Citation/make link, Rudolf Kingslake & Paul W. Stevens, "Wide-angle lenses", published Script error: No such module "auto date formatter"., assigned to Eastman Kodak Co. Script error: No such module "Check for unknown parameters".
  8. ↑ Script error: No such module "citation/CS1".
  9. ↑ <templatestyles src="Citation/styles.css"/>Template:Citation/make link, Pierre Angénieux, "Wide-angle photographic objective lens assembly", issued Script error: No such module "auto date formatter"., assigned to Pierre Angénieux Script error: No such module "Check for unknown parameters".
  10. ↑ <templatestyles src="Citation/styles.css"/>Template:Citation/make link, Pierre Angénieux, "Wide-angle photographic objective lens assembly", published Script error: No such module "auto date formatter". Script error: No such module "Check for unknown parameters".
  11. ↑ a b <templatestyles src="Citation/styles.css"/>Template:Citation/make link, Albrecht Wilhelm Tronnier, "Photographic objective of the modified triplet type and a meniscus shaped negative member axially separated therefrom", published Script error: No such module "auto date formatter"., assigned to Voigtländer & Sohn AG Script error: No such module "Check for unknown parameters".
  12. ↑ <templatestyles src="Citation/styles.css"/>Template:Citation/make link, Pierre Angénieux, "Wide-angle photographic objective", published Script error: No such module "auto date formatter". Script error: No such module "Check for unknown parameters".
  13. ↑ <templatestyles src="Citation/styles.css"/>Template:Citation/make link, Johann Lautenbacher, "High-speed wide-angle photographic objective", published Script error: No such module "auto date formatter"., assigned to Enna Werk Optik Apelt Script error: No such module "Check for unknown parameters".
  14. ↑ <templatestyles src="Citation/styles.css"/>Template:Citation/make link, Ludwig Bertele, "Wide angle photographic objective comprising three air spaced components", published Script error: No such module "auto date formatter". Script error: No such module "Check for unknown parameters".
  15. ↑ a b <templatestyles src="Citation/styles.css"/>Template:Citation/make link, Harry Zollner & Rudolf Solisch, "Photographisches Objektiv mit einem sammelnden Systemteil und einem in verhaeltnismaessig grossem Abstand davor liegenden zerstreuenden Meniskus", issued Script error: No such module "auto date formatter"., assigned to Jenoptik AG Script error: No such module "Check for unknown parameters".
  16. ↑ a b <templatestyles src="Citation/styles.css"/>Template:Citation/make link, Harry Zöllner & Rudolf Solisch, "Photographic objective comprising a rear collective part and front dispersive meniscus part", published Script error: No such module "auto date formatter"., assigned to Jenoptik AG Script error: No such module "Check for unknown parameters".
  17. ↑ <templatestyles src="Citation/styles.css"/>Template:Citation/make link, Gunter Klemt, "Wide-angle photographic and cinematographic objective", published Script error: No such module "auto date formatter"., assigned to Scheider Co. Optische Werke Script error: No such module "Check for unknown parameters".
  18. ↑ <templatestyles src="Citation/styles.css"/>Template:Citation/make link, Franz Schlegel, "Fotografisches Objektiv", published Script error: No such module "auto date formatter"., assigned to Rodenstock Optik G Script error: No such module "Check for unknown parameters".
  19. ↑ <templatestyles src="Citation/styles.css"/>Template:Citation/make link, Fritz Determann, "Photographic objective", published Script error: No such module "auto date formatter"., assigned to Voigtländer & Sohn AG Script error: No such module "Check for unknown parameters".
  20. ↑ <templatestyles src="Citation/styles.css"/>Template:Citation/make link, Rudolf Solisch, "Asymmetrical photographic or cinematographic objective with large angle of view", published Script error: No such module "auto date formatter"., assigned to ISCO Optische Werke GmbH Script error: No such module "Check for unknown parameters".
  21. ↑ <templatestyles src="Citation/styles.css"/>Template:Citation/make link, Helmut Eismann & Gunther Lange, "Asymmetrical photographic objective", published Script error: No such module "auto date formatter"., assigned to Carl Zeiss AG Script error: No such module "Check for unknown parameters".
  22. ↑ <templatestyles src="Citation/styles.css"/>Template:Citation/make link, Pierre Angénieux, "Objectif photographique du type grand-angulaire", published Script error: No such module "auto date formatter". Script error: No such module "Check for unknown parameters".
  23. ↑ a b <templatestyles src="Citation/styles.css"/>Template:Citation/make link, Wolf Dannberg & Eberhard Dietzsch, "Improvements in or relating to wide-angle lenses", published Script error: No such module "auto date formatter"., assigned to Carl Zeiss Jena VEB Script error: No such module "Check for unknown parameters".
  24. ↑ Script error: No such module "citation/CS1".
  25. ↑ Script error: No such module "citation/CS1".
  26. ↑ Script error: No such module "citation/CS1".
  27. ↑ <templatestyles src="Citation/styles.css"/>Template:Citation/make link, Michael Michaelovitch Roosinov, "Wide angle orthoscopic anastigmatic photographic objective", issued Script error: No such module "auto date formatter". Script error: No such module "Check for unknown parameters".
  28. ↑ a b Script error: No such module "Citation/CS1".

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Bibliography

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