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. 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 while the 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 35 mm film format, typical focal lengths of fisheye lenses are between 8 mm and 10 mm for circular images, and 15–16 mm for full-frame images. For digital cameras using smaller electronic imagers such as " and " format CCD or CMOS sensors, the focal length of "miniature" fisheye lenses can be as short as 1 to 2 mm.
These types of lenses also have other applications such as re-projecting images that were originally filmed through a fisheye lens, or created via computer generated graphics, onto hemispherical screens. Fisheye lenses are also used for scientific photography such as recording of aurora and meteors, and to study plant canopy geometry and to calculate near-ground solar radiation. They are perhaps most commonly encountered as peephole door viewers to give the user a wide field of view.

History and development

Panoramas with fisheye distortion predate 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 50; 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 8. 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 Dr Hans Schulz with the design of the Weitwinkelobjektiv. The basic patented design was produced for cloud recording as a 17 mm 6.3 lens, and the artist known as 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 Fish-eye-Nikkor 16 mm 8 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. After the war, the 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. A photograph of pole vaulter Bob Gutowski taken by the Fisheye Camera was published in Life in 1957.
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, reminiscent of the 4-element Topogon design, also 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 8 and used a plano-concave front element in diameter; the image on the negative was approximately in diameter.

35mm 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 8, but later examples were computed half a stop faster, to 6.8. 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.
The Nikon Fisheye Camera was discontinued in September 1961, and Nikon subsequently introduced the first regular production fisheye lens for miniature cameras in 1962, the Fish-eye-Nikkor 8 mm 8, 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 135 format increased its popular use. The Nikkor 8 mm 8 has a field of view of 180° and uses 9 elements in 5 groups; it is fixed focus and has built-in filters mainly intended for black-and-white photography. Research indicates that fewer than 1,400 lenses were built.
Nikon subsequently released several more milestone circular fisheye lenses in Nikon F mount through the 1960s and 70s:
Meanwhile, 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 11, released by Pentax in 1962, followed by the slightly faster UW Rokkor-PG 18 mm 9.5 from Minolta in 1966. Both of these were reflex viewing and fixed-focus, and 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 and then converted to autofocus for the Alpha system., the same basic optical design is still sold as the Sony SAL16F28.

Design

In a circular fisheye lens, the image circle is inscribed in the film or sensor area; in a full-frame fisheye lens the image circle is circumscribed around the film or sensor area.
Further, different fisheye lenses distort images differently, and the manner of distortion is referred to as their [|mapping function]. A common type for consumer use is equisolid angle.
Although there are digital fisheye effects available both in-camera and as computer software they can't extend the angle of view of the original images to the very large one of a true fisheye lens.

Focal length

The focal length is determined by the angular coverage, the specific mapping function used, and the required dimensions of the final image. Focal lengths for popular amateur camera sizes are computed as:
;Notes

Circular fisheye

The first types of fisheye lenses to be developed were "circular fisheye"—lenses which took in a 180° hemisphere and projected this as a circle within the film frame. Some circular fisheyes were available in orthographic projection models for scientific applications. These have a 180° vertical angle of view, and the horizontal and diagonal angle of view are also 180°. By design, most circular fisheye lenses cover a smaller image circle than rectilinear lenses, so the corners of the frame will be completely dark.
Sigma currently makes a 4.5mm fisheye lens that captures a 180-degree field of view on a crop body. Sunex also makes a 5.6mm fisheye lens that captures a circular 185-degree field of view on a 1.5x Nikon and 1.6x Canon DSLR cameras.
in the Nikon Museum.
Nikon produced a 6 mm circular fisheye lens that was initially designed for an expedition to Antarctica. It featured a 220-degree field of view, designed to capture the entire sky and surrounding ground when pointed straight up. This lens is no longer manufactured by Nikon, and is used nowadays to produce interactive virtual-reality images such as QuickTime VR and IPIX. Because of its very wide field of view, it is very large and cumbersome—weighing, having a diameter of, a length of and an angle of view of 220 degrees. It dwarfs a regular 35 mm SLR camera and has its own tripod mounting point, a feature normally seen in large long-focus or telephoto lenses to reduce strain on the lens mount because the lens is heavier than the camera. The lens is extremely rare.
However, there are new developments by the Japanese manufacturer Entaniya for the Micro Four Thirds standard, which offer an angle of view of 250 degrees with lenses that have a focal length of to, an aperture of f/2.8 to f/4.0, a weight of, a diameter of and a length below. In 2018 Venus Optics introduced a 210° fisheye lens for the Micro Four Thirds system.
An 8 mm fisheye lens, also made by Nikon, has proven useful for scientific purposes because of its equidistant projection, in which distance along the radius of the circular image is proportional to zenith angle.

Full-frame fisheye

As fisheye lenses gained popularity in general photography, camera companies began manufacturing fisheye lenses that enlarged the image circle to cover the entire rectangular frame, called a "full-frame fisheye".
The picture angle produced by these lenses only measures 180 degrees when measured from corner to corner: these have a 180° diagonal angle of view, while the horizontal and vertical angles of view will be smaller; for an equisolid angle-type 15 mm full-frame fisheye, the horizontal AOV will be 147°, and the vertical AOV will be 94°.
One of the first full-frame fisheye lens to be mass-produced was the Fisheye-Nikkor 16mm 3.5, made by Nikon in the early 1970s. Digital cameras with APS-C sized sensors require a 10.5 mm lens to get the same effect as a 16 mm lens on a camera with full-frame sensor.

Miniature fisheye lenses

s, especially when used as security cameras, often tend to have fisheye lenses to maximize coverage. Miniature fisheye lenses are designed for small-format CCD/CMOS imagers commonly used in consumer and security cameras. Popular image sensor format sizes used include ", ", and ". Depending on the active area of the image sensor, the same lens can form a circular image on a larger image sensor, and a full frame on a smaller one.

Examples and specific models

Fisheye lenses for APS-C cameras

The APS-C image sensor used in Canon cameras is or on the diagonal, which is slightly smaller than the sensor size used by other popular manufacturers of cameras with APS-C sensors, such as Fuji, Minolta, Nikon, Pentax, and Sony. The other common APS-C sensors range from on the long dimension and on the shorter side, for a diagonal measurement between.

Circular APS-C fisheye lenses

Circular fisheye

Other applications

The subject is placed in the image by the lens according to the mapping function of the lens. The mapping function gives, the position of the object from the center of the image, as a function of, the focal length, and, the angle from the optical axis. is measured in radians.
;Details
Other mapping functions are also possible for enhancing the off-axis resolution of fisheye lenses.
With appropriate software, the curvilinear images produced by a fisheye lens can be remapped to a conventional rectilinear projection. Although this entails some loss of detail at the edges of the frame, the technique can produce an image with a field of view greater than that of a conventional rectilinear lens. This is particularly useful for creating panoramic images.
All types of fisheye lenses bend straight lines. Aperture angles of 180° or more are possible only with large amounts of barrel distortion.