Wide-angle lens
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In photography and cinematography, a wide-angle lens is a lens whose focal length is shorter than the focal length of a normal lens. For a 35 mm camera with a 36 mm by 24 mm format, the normal lens is 50 mm. A lens of focal length 35 mm or less is considered wide-angle.
In addition to giving a wider angle of view, the resulting image can also have perspective distortion.
Construction
There are two different varieties of wide-angle lens: short-focus lenses and retrofocus lenses.Short focus lenses are generally made up of multiple glass elements that are symmetrical in front of and behind the diaphragm. As the focal length decreases, the distance of the rear element of the lens from the film plane or digital sensor also decreases. This makes short focus wide-angle lenses undesirable for single-lens reflex cameras unless they are used with the reflex mirrors locked up. Short focus lenses are widely used on large format view cameras.
The retrofocus lens solves this proximity problem through an asymmetrical design that allows the rear element to be further away from the film plane than its effective focal length would suggest. (See Angenieux retrofocus.) For example, it is not uncommon for the rear element of a retrofocus lens of 18mm to be more than 25 mm from the film plane. This makes it possible to design really wide angle lenses for single-lens reflex cameras.
Common wide-angle lenses for a 35 mm camera are 35, 28, 24, 20, 17 and 14 mm. These lenses will produce a more or less rectilinear image at the film plane (though some degree of barrel distortion is not uncommon here).
Those extreme wide-angle lenses that do not produce a rectilinear image are called fisheye lenses. Common focal lengths for these in a 35 mm camera are 6 to 8 mm (which produce a circular image). Lenses with focal lengths of 15 or 16 mm can produce either curvilinear fisheye-like (high barrel distortion) full-frame images or rectilinear full frame images, depending on the design.
See also
- angle of view for an example of an image taken by a wide-angle lens
- film format
- normal lens
- anamorphic lens
- scioptric ball
- stitching images
- panorama camera
External links
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