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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. They are often used by photographers shooting broad landscapes to suggest the curve of the Earth.

All ultra-wide angle lenses suffer from some amount of distortion. While this can easily be corrected for moderately wide ) 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. The widest lens ever produced was a 6 mm circular fisheye made by Nikon . 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 still manufactured by Nikon upon special order, and is used nowadays to produce interactive virtual-reality images such as QuickTime VR and IPIX .


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.

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.


OTHER USES

  • 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 Omnimax motion-picture format involves photography through a circular fisheye lens, and projection through the same onto a hemispherical screen.



MAPPING FUNCTION


The mapping of a sideways object leads to a picture position displacement from the (film) picture-center. The manner of this conversion is the mapping function. "f" is the focal length of the optical system.

Normal (non-fisheye) lens:

  • gnomonical: r = f --- tan(a), works like the pinhole camera. Straight lines remain straight (distortion free). "a" has to be smaller than 90°. The aperture angle is gaged symmetrically to the optical axis and have to be smaller than 180°. Large aperture angles demand extreme effort and lead to very high prices.


Fisheyes can have many different mapping functions:

  • linear scaled (equidistant): r = f --- (Pi / 180) --- a (a in ° {Link without Title} ), practical for angle measurement (star maps). PanoTool assumes to that.


  • orthographic: r = f --- sin(a), acts like an orb with the surroundings lying on it; max. 180° aperture angle.


  • equal area (equisolid angle): r = 2 --- f --- sin(a / 2), acts like a mirror image on a ball, best spacial effect (unsophisticated distances), suitable for area comparing (clouds grade detemination). This type won the recognition and also the photographers have to put up with it - because it compresses the marginal objects. The price of this lens are high, but not extreme.


  • stereographic (conform): r = 2 --- f --- tan(a / 2), would be perfect for photographers - because it doesn't compress marginal objects. No lens has been developed for this type by now, but this mapping is easy implemented by software.


All types of fisheye bend straight lines. Aperture angles of 180° and more are possible only by Barrel Distortion .

{Link without Title} is deploying with this mapping (German language).