A distinctive type of lens design that uses a large, curved front element resembling the eye of a fish. A very large angle of view is given, up to 180 or even 220 degrees. This is made possible by abandoning optical correction for curvilinear distortion in the lens, so that the image is characterized by lines that are strongly curved instead of straight. The imagery has a novelty value, as well as scientific applications such as cloud studies of the whole sky.
In photography, a fisheye lens is a wide-angle lens that takes in an extremely wide, hemispherical image. Originally developed for use in astronomy and called "whole-sky lenses", fisheye lenses quickly became popular in general photography for their unique, distorted appearance.
All ultra-wide angle lenses suffer from some amount of distortion. While this can easily be corrected for moderately wide angles of view, rectilinear ultra-wide angle lenses with angles of view greater than 90 degrees are difficult to design. Fisheye lenses achieve extremely wide angles of view by foregoing a rectilinear image, opting instead for a special mapping (for example: equisolid angle), which gives images a characteristic convex appearance. A panorama by rotating lens or stitching images (cylindrical perspective) is not a fisheye photo.
Types of fisheye lenses
Circular
The first types of fisheye lenses to be developed were "circular fisheyes" - lenses which took in a 180-degree hemisphere and projected this as a circle within the film frame. Some circular fisheyes were available in orthographic projection models for scientific applications.
Full-frame
As fisheye lenses gained popularity in general photography, camera companies began manufacturing fisheye lenses that enlarged the image circle to cover the entire 35 mm film frame. Because of this, the picture angle produced by these lenses only measures 180 degrees when measured from corner to corner. The first full-frame fisheye lens to be mass-produced was a 16 mm lens made by Nikon in the late 1960s. This is the fisheye most commonly used by photographers.
Focal length
The focal lengths of fisheye lenses depend on the film format. For the popular 35 mm film format, typical focal lengths of fisheye lenses are between 8 mm and 10 mm for circular lenses, and 15-16 mm for full-frame lenses.
The widest lens ever produced was a 6 mm circular fisheye made by Nikon. It dwarfs a regular 35mm 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.
Other uses
Skateboarding videos use fisheye lenses so the the photographer can get the camera as close as possible to the board and still retain an image of the skater. The peepholes in most doors contain a fisheye lens. Most planetariums use a form of fisheye lens to project a two-dimensional film image of the night sky onto the interior of a dome. Similarly, the IMAX Dome (previously 'OMNIMAX') motion-picture format involves photography through a circular fisheye lens, and projection through the same onto a hemispherical screen. The distance of a point from the image centre 'r' is dependent on the focal length of the optical system 'f', and the angle from the optical axis 'θ'.Fisheyes can have many different mapping functions:
Linear scaled (equidistant): , where θ is in radians.All types of fisheye lens bend straight lines.
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