The Angénieux retrofocus
photographic lens
A camera lens, photographic lens or photographic objective is an optical lens (optics), lens or assembly of lenses (compound lens) used in conjunction with a camera body and mechanism to Imaging, make images of objects either on photographic film ...
is a
wide-angle lens
In photography and cinematography, a wide-angle lens is a Photographic lens, lens covering a large angle of view. Conversely, its focal length is substantially smaller than that of a normal lens for a given film plane. This type of lens allows mo ...
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
France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...
in 1950 by
Pierre Angénieux.
Inverted telephoto concept
The
telephoto
A telephoto lens, also known as telelens, is a specific type of a long-focus lens used in photography and cinematography, in which the physical length of the lens is shorter than the focal length. This is achieved by incorporating a special lens ...
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
The focal length of an optical system is a measure of how strongly the system converges or diverges light; it is the inverse of the system's optical power. A positive focal length indicates that a system converges light, while a negative foca ...
of the lens (the distance between the back of the lens and the
image plane
In 3D computer graphics, the image plane is that plane in the world which is identified with the plane of the display monitor used to view the image that is being rendered. It is also referred to as screen space. If one makes the analogy of taki ...
) to a figure shorter than the
focal length
The focal length of an Optics, optical system is a measure of how strongly the system converges or diverges light; it is the Multiplicative inverse, inverse of the system's optical power. A positive focal length indicates that a system Converge ...
. 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.
The inverted telephoto configuration does the reverse, employing one or more negative lens groups at the front to increase the
back focal distance
The focal length of an optical system is a measure of how strongly the system converges or diverges light; it is the inverse of the system's optical power. A positive focal length indicates that a system converges light, while a negative foca ...
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.
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.
[
The inverted telephoto design was first employed in the 1930s by Taylor-Hobson for the early ]Technicolor
Technicolor is a family of Color motion picture film, color motion picture processes. The first version, Process 1, was introduced in 1916, and improved versions followed over several decades.
Definitive Technicolor movies using three black-and ...
"3-strip" cameras since the beam splitter
A beam splitter or beamsplitter is an optical instrument, optical device that splits a beam of light into a transmitted and a reflected beam. It is a crucial part of many optical experimental and measurement systems, such as Interferometry, int ...
unit behind the lens required significant space, so that a long back focal distance was essential. Horace Lee patented an inverted telephoto lens design in 1930 with an angle of view
In photography, angle of view (AOV) describes the angular extent of a given scene that is imaged by a camera. It is used interchangeably with the more general term '' field of view''.
It is important to distinguish the angle of view from the ...
of 50° and maximum aperture of 2 which afforded a distance between the rear element and the film plane approximately 10% greater than the focal length. Joseph Ball showed how a beam-splitting apparatus could be fitted in the space gained. 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.[
In still photography, a ]single-lens reflex camera
In photography, a single-lens reflex camera (SLR) is a type of camera that uses a mirror and prism system to allow photographers to view through the lens and see exactly what will be captured. SLRs became the dominant design for professional a ...
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.[
]
Implementation
Rudolf Kingslake
Rudolf Kingslake (born Rudolf Klickmann; August 28, 1903 – February 28, 2003) was an English academic, lens designer, and engineer.
Early life and education
Kingslake was born in London, England in 1903 as Rudolf Klickmann. The latter is i ...
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
The ''Tessar'' is a photographic lens design conceived by the German physicist Dr. 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''. Sinc ...
''-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.[
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.
Pierre Angénieux applied for a patent in 1950. In the original patent, he presented two lenses with an ]angle of view
In photography, angle of view (AOV) describes the angular extent of a given scene that is imaged by a camera. It is used interchangeably with the more general term '' field of view''.
It is important to distinguish the angle of view from the ...
of 65°, approximately equal to the view of a f=35 mm lens on the 35mm format
file:135film.jpg, 135 film. The film is wide. Each image is 24×36 mm in the most common "small film" format (sometimes called "double-frame" for its relationship to the "single-frame" 35 mm movie format or full frame after the introduc ...
for still cameras; the first example had a maximum aperture of 2.5, while the second example had a maximum aperture of 2.2. 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
A generic trademark, also known as a genericized trademark or proprietary eponym, is a trademark or brand name that, because of its popularity or significance, has become the generic term for, or synonymous with, a general class of products or ...
for similar lens designs.[
File:Lee - Inverted telephoto (1930).svg, Taylor-Hobson 'inverted telephoto' lens by H.W. Lee (1930), GB 355,452] and US 1,955,590
File:Kingslake & Stevens US2341385A (WA Ektanar, 1941).svg, Kodak ''WA Ektanar'' (35 mm , 1941) by Kingslake & Stevens, from US Patent 2,341,385
File:Angénieux - Retrofocus (1950).svg, Angénieux ''Retrofocus R-1'' (35 mm , 1950), from US Patent 2,649,022
File:Tronnier US2746351A (Skoparon, 1952).svg, Voigtländer ''Skoparon'' (35 mm , 1952) by Tronnier, from US Patent 2,746,351
File:Angénieux US2696758A (Retrofocus R-11, 1952).svg, Angénieux ''Retrofocus R-11'' (28 mm , 1952), from US Patent 2,696,758
File:Lautenbacher US2983191A (Lithagon, 1953).svg, Enna ''Lithagon'' (35 mm , 1953) by Lautenbacher, from US Patent 2,983,191
File:Bertele US2772601A (Travegon, 1954).svg, Schacht ''Travegon'' (35 mm , 1954) by Bertele, from US Patent 2,772,601
File:Zöllner-Solisch US2793565A (Flektogon), 1955.svg, Zeiss Jena ''Flektogon'' by Zöllner & Solisch (1955), from US Patent 2,793,565
File:Klemt US2824495A (Curtagon, 1955).svg, Schneider ''Curtagon'' (28 mm , 1955) by Klemt, from US Patent 2,824,495
File:Schlegel DE1017382B (Eurygon, 1955).svg, Rodenstock ''Eurygon'' (35 mm , 1955) by Schlegel, from DE Patent 1,017,382
File:Determann US2927506A (Skoparet, 1956).svg, Voigtländer ''Skoparet'' (35 mm , 1956) by Determann, from US Patent 2,927,506
File:Solisch US2878724A (Westrogon, 1956).svg, ISCO ''Westrogon'' (24 mm , 1956) by Solisch, from US Patent 2,878,724
File:Eismann & Lange US3038380A (Distagon, 1958).svg, Carl Zeiss
Carl Zeiss (; 11 September 1816 – 3 December 1888) was a German scientific instrument maker, optician and businessman. In 1846 he founded his workshop, which is still in business as Zeiss (company), Zeiss. Zeiss gathered a group of gifted p ...
(Oberkochen) ''Distagon'' (35 mm , 1958) by Eismann & Lange, from US Patent 3,038,380
File:Angénieux FR1214945A (Retrofocus R-61, 1958).svg, Angénieux ''Retrofocus R-61'' (24 mm , 1958), from French Patent 1,214,945
File:Dannberg & Dietzsch GB978797A (Flektogon, 1963).svg, Carl Zeiss
Carl Zeiss (; 11 September 1816 – 3 December 1888) was a German scientific instrument maker, optician and businessman. In 1846 he founded his workshop, which is still in business as Zeiss (company), Zeiss. Zeiss gathered a group of gifted p ...
(Jena) ''Flektogon'' (20 mm , 1963) by Dannberg & Dietzsch, from GB Patent 978797A
The Angénieux ''Retrofocus'' lens line inspired other manufacturers to produce similar wide-angle lenses of this type 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.[ Carl Zeiss Oberkochen also created an inverted telephoto design branded ''Distagon'' (5.6/60 mm) for the Hasselblad 1000F in 1952.] 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.[
]
Angénieux were not content to rest on their laurels, continuing to develop the inverted telephoto scheme by shortening the focal length from 35 mm with the original ''Retrofocus R-1'' (1950) to 28 mm with the ''Retrofocus R-11'' (1952) and ''R-61'' (24 mm , 1958). These used multiple negative meniscus elements in the front group, a trend that would continue with the Zeiss (Jena) ''Flektogon'' 20 mm design of 1963, with three negative meniscus elements and an angle of view expanded to 94° from 62° (with the original ''Retrofocus R-1'').[
]
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.
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. 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 lens
A fisheye lens is an ultra wide angle lens, ultra wide-angle lens that produces strong Distortion (optics), visual distortion intended to create a wide panorama, panoramic or Sphere#Hemisphere, hemispherical image. Fisheye lenses achieve extremel ...
es can be considered a subset of the inverted telephoto lens design, with strong negative front elements.[
]
References
Bibliography
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{{DEFAULTSORT:Angenieux retrofocus
Photographic lens designs