page_title: Ultra wide angle lens
section_title: 'Fisheye' and rectilinear lenses
hierarchical_section_title: Ultra wide angle lens / Features / 'Fisheye' and rectilinear lenses
caption_attribution_description: Peleng 8/3.5 full sky with the Sun. Seagull is lightened by flash
context_page_description: An ultra wide-angle lens is a lens whose focal length is shorter than the short side of film or sensor.
  Thus the term denotes a different range of lenses, relative to the size of the sensor in the camera in question.
  For 1" any 9mm or shorter is considered ultra wide angle.
  For 4/3" any 10mm or shorter lens is considered ultra wide angle.
  For APS-C any lens shorter than 15 mm.
  For 35mm film or full-frame sensor any lens shorter than 24 mm
  For 6x4.5 cm any lens shorter than 41 mm
  For 6x6 cm and 6x7 cm any lens shorter than 56 mm
context_section_description: Ultra-wide angle lenses come in two varieties: Fisheye lenses with curvilinear barrel distortion, and rectilinear lenses which are designed so that straight lines in the scene will render straight (uncurved) in the photographic image and thus lack the extreme distortion that is characteristic of a fisheye lens. Neither denotes a particular range of focal lengths, the difference is only whether distortion is present or not. However, the shorter the focal length, the more difficult it is to implement rectilinear correction.
  In fisheye lenses, the visual angle is close to or more than 180 degrees in at least one direction. For example, a "diagonal fish eye" would have a viewing angle of at least 180 degrees within the diagonals of the frame. A "circular fisheye" would represent the image in the form of a circle.
  Rectilinear ultra-wide angle lenses are used in photography and cinematography sometimes to achieve three-dimensional perspective distortion instead of simply two-dimensional barrel distortion. A notable, signature employment for this purpose is frequently seen in the films of Terry Gilliam, for instance.
caption: Bearing 8/3.5 fisheye. A capture of an entire scene, including the sun is shown (180-degree circular fisheye). The underside of the seagull is illuminated by flash
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