Fisheye lens


A fisheye lens is an ultra wide-angle lens that produces strong visual distortion intended to create a wide panoramic or hemispherical image. Fisheye lenses achieve extremely wide angles of view, well beyond any rectilinear lens. Instead of producing images with straight lines of perspective, fisheye lenses use a special mapping, which gives images a characteristic convex non-rectilinear appearance.
The term fisheye was coined in 1906 by American physicist and inventor Robert W. Wood based on how a fish would see an ultrawide hemispherical view from beneath the water. Their first practical use was in the 1920s for use in meteorology to study cloud formation giving them the name whole-sky lenses. The angle of view of a fisheye lens is usually between 100 and 180 degrees, although lenses covering up to 280 degrees exist. Their focal lengths depend on the film format they are designed for.
Mass-produced fisheye lenses for photography first appeared in the early 1960s and are generally used for their unique, distorted appearance. For the popular 35mm film format, typical focal lengths of fisheye lenses are for circular images, and for diagonal images filling the entire frame. For digital cameras using smaller imagers such as and format CCD or CMOS sensors, the focal length of "miniature" fisheye lenses can be as short as.
Fisheye lenses also have other applications, such as re-projecting images originally filmed through a fisheye lens, or created via computer-generated graphics, onto hemispherical screens. They are also used for scientific photography, such as recordings of aurora and meteors, and to study plant canopy geometry, and to calculate near-ground solar radiation. In everyday life, they are perhaps most commonly encountered as peephole door viewers to give a wide field of view.

History and development

Panoramas with fisheye distortion predate photography and the fisheye lens. In 1779, Horace Bénédict de Saussure published his downward-facing fisheye view of the Alps: "All the objects are drawn in perspective from the centre".
In 1906, Wood published a paper detailing an experiment in which he built a camera in a water-filled pail starting with a photographic plate at the bottom, a short focus lens with a pinhole diaphragm located approximately halfway up the pail, and a sheet of glass at the rim to suppress ripples in the water. The experiment was Wood's attempt "to ascertain how the external world appears to the fish" and hence the title of the paper was "Fish-Eye Views, and Vision under Water". Wood subsequently built an improved "horizontal" version of the camera omitting the lens, instead using a pinhole pierced in the side of a tank, which was filled with water and a photographic plate. In the text, he described a third "Fish-Eye" camera built using sheet brass, the primary advantages being that this one was more portable than the other two cameras, and was "absolutely leaktight". In his conclusion, Wood thought that "the device will photograph the entire sky a sunshine recorder could be made on this principle, which would require no adjustment for latitude or month" but also wryly noted "the views used for the illustration of this paper savour somewhat of the 'freak' pictures of the magazines."
W.N. Bond described an improvement to Wood's apparatus in 1922 which replaced the tank of water with a simple hemispheric glass lens, making the camera significantly more portable. The focal length depended on the refractive index and radius of the hemispherical lens, and the maximum aperture was approximately ; it was not corrected for chromatic aberration and projected a curved field onto a flat plate. Bond noted the new lens could be used to record cloud cover or lightning strikes at a given location. Bond's hemispheric lens also reduced the need for a pinhole aperture to ensure sharp focus, so exposure times were also reduced.

Hill Sky Lens

In 1924, Robin Hill first described a lens with 180° coverage that had been used for a cloud survey in September 1923 The lens, designed by Hill and R. & J. Beck, Ltd., was patented in December 1923. The Hill Sky Lens is now credited as the first fisheye lens. Hill also described three different mapping functions of a lens designed to capture an entire hemisphere. Distortion is unavoidable in a lens that encompasses an angle of view exceeding 125°, but Hill and Beck claimed in the patent that stereographic or equidistant projection were the preferred mapping functions. The three-element, three-group lens design uses a highly divergent meniscus lens as the first element to bring in light over a wide view followed by a converging lens system to project the view onto a flat photographic plate.
The Hill Sky Lens was fitted to a whole sky camera, typically used in a pair separated by for stereo imaging, and equipped with a red filter for contrast; in its original form, the lens had a focal length of and cast an image in diameter at. Conrad Beck described the camera system in an article published in 1925. At least one has been reconstructed.

German and Japanese development

In 1932, the German firm Allgemeine Elektricitäts-Gesellschaft AG filed for a patent on the Weitwinkelobjektiv, a 5-element, 4-group development of the Hill Sky Lens. Compared to the 1923 Hill Sky Lens, the 1932 Weitwinkelobjektiv featured two diverging meniscus elements ahead of the stop and used a cemented achromatic group in the converging section. Miyamoto credits Hans Schulz with the design of the Weitwinkelobjektiv. The basic patented design was produced for cloud recording as a 17 mm lens, and Umbo used the AEG lens for artistic purposes, with photographs published in a 1937 issue of Volk und Welt.
The AEG Weitwinkelobjektiv formed the basis of the later Nippon Kogaku Fisheye-Nikkor 16 mm lens of 1938, which was used for military and scientific purposes. Nikon, which had a contract to supply optics to the Imperial Japanese Navy, possibly gained access to the AEG design under the Pact of Steel.
Also in 1938, Robert Richter of Carl Zeiss AG patented the 6-element, 5-group Pleon lens, which was used for aerial surveillance during World War II. The converging rear group of the Pleon was symmetrical, derived from the 4-element Topogon lens designed by Richter for Zeiss in 1933. Testing on a captured lens after the war showed the Pleon provided an equidistant projection to cover a field of approximately 130°, and negatives were printed using a special rectifying enlarger to eliminate distortion. The Pleon had a focal length of approximately 72.5 mm with a maximum aperture of and used a plano-concave front element in diameter; the image on the negative was approximately in diameter.

35 mm development

At approximately the same time that Schulz was developing the Weitwinkelobjektiv at AEG, at Zeiss was developing the Sphaerogon, which was also designed to encompass a 180° field of view. Unlike the Weitwinkelobjektiv, Merté's Sphaerogon was not limited to medium format cameras; prototype versions of the Sphaerogon were constructed for the Contax I miniature format camera. The first prototype Sphaerogon lenses constructed had a maximum aperture of, but later examples were computed half a stop faster, to. Several prototype examples of Sphaerogon lenses were recovered as part of the Zeiss Lens Collection seized by the Army Signal Corps as war reparations in 1945; the collection, which the Zeiss firm had retained as a record of their designs, was later documented by Merté, the former head of optical computation for CZJ, working under Signal Corps officer Edward Kaprelian.
After the war, the Fisheye-Nikkor lens was mated to a medium format camera and was produced in slightly modified form as the "Sky-image Recording Camera" in March 1957 for the Japanese government, followed by a commercial release as the Nikon Fisheye Camera in September 1960, which had a retail price of. The revised lens created a circular image in diameter and covered a complete hemispherical field of 180°. Only 30 examples of the Nikon Fisheye Camera were manufactured, and of those, 18 were sold to customers, mainly in the United States; Nikon likely destroyed the remaining stock to avoid tax penalties. Photographs taken with the Fisheye Camera that were published in Life in 1957 marked the first wide exposure of the public to fisheye distortion; including a photograph of the United States Senate caucus room, taken by Ed Clark and published in an April 1957 issue, and a photograph of pole vaulter Bob Gutowski taken by Ralph Crane, published in July 1957.
File:Are You Experienced - US cover-edit.jpg|thumb|left|Album cover of Are You Experienced by The Jimi Hendrix Experience, featuring the trio photographed using a fisheye lens
The Nikon Fisheye Camera was discontinued in September 1961, and Nikon subsequently introduced the first regular production fisheye lens for 35 mm cameras in 1962, the Fisheye-Nikkor 8 mm, which required the reflex mirror on its Nikon F and Nikkormat cameras to be locked up prior to mounting the lens. Prior to the early 1960s, fisheye lenses were used primarily by professional and scientific photographers, but the advent of the fisheye for the 35 mm format increased its popular use. The Fisheye-Nikkor 8 mm has a field of view of 180° and uses 9 elements in 5 groups; it has a fixed focus and built-in filters intended for black-and-white photography. Research indicates that fewer than 1,400 lenses were built. As fisheye lenses became more widely available, the distinctive distortion grew in popularity, especially for album covers. For example, British fashion photographer Tim Walker used a fisheye lens to capture the cover of Harry Styles' 2019 pop/rock album, Fine Line. Other genres that have taken advantage of the fisheye lens look include punk rock, hip-hop, and skateboarding videos. In particular, the fisheye lens became a signature style of music video director Hype Williams, especially in the mid-to-late 1990s when he directed videos for artists such as Busta Rhymes, Missy Elliott, and Puff Daddy.
Nikon subsequently released several more milestone circular fisheye lenses in Nikon F mount through the 1960s and 70s:
  • 10 mm OP, the first fisheye to feature orthographic projection, which was also the first lens to feature an aspherical element
  • 6 mm , the first fisheye to feature a 220° field of view; the patent accompanying this lens includes a design for a lens with a 270° field of view. A 6.2 mm SAP fisheye was later produced in limited numbers with an aspherical surface, encompassing a 230° field of view.
  • 8 mm , the first circular fisheye with variable focus, automatic aperture, and reflex viewing.
Contemporaneously, other Japanese manufacturers were developing the so-called "full-frame" or diagonal fisheyes, which captured approximately a 180° field of view across the diagonal of the film frame. The first such diagonal fisheye was the Fish-eye Takumar 18 mm, released by Pentax in 1962, followed by the slightly faster UW Rokkor-PG 18 mm from Minolta in 1966. Both of these were reflex-viewing and fixed-focus. Both Pentax and Minolta followed up with faster lenses with variable focus in 1967 and 1969, respectively. The 16 mm Rokkor was later adopted by Leica as the Fisheye-Elmarit-R for its SLRs and then converted to autofocus for the Alpha system., the same basic optical design is still sold as the Sony SAL16F28.