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Perspective distortion

In photography and cinematography, perspective distortion is a result of using lenses with a focal length that differs significantly from a that of a normal lens.

Perspective distortion is especially noticeable using wide-angle lenses near a subject that extends away from the camera. Wide lenses (e.g. 24 or 18 mm focal length for a 35 mm camera) magnify apparent distance, causing objects close to the camera to appear considerably larger than objects farther away, and causing parallel lines to appear to converge.

In comparison, longer lenses (85 mm and greater for a 35 mm camera) appear to shorten distance between objects, and compress the perspective.

For this reason, lens choice in film and photography can influence perception of a scene. The general assumption that "undoctored" photos can not distort a scene is thus incorrect. This is particularly noticeable in en face portraits. Taken with wide-angle lenses, they generally give an unpleasant impression; making the nose appear far too large, and distorting the facial expression. For good results, portraits should generally be taken using a moderate telephoto lens. Again, for a 35 mm camera, a lens of focal length 85 or 105 mm is considered to be a portrait objective.

Below, a series of four photos shows an object framed as nearly the same as possible while taken with four different lenses. As a result of the different angle of view of each lens, the photographer moved closer to the object with each photo. Note that the angle of view changes significantly (compare the background in each photo), and the distance between objects appears greater with each succeeding image. In the fourth lower right image, taken with the widest lens, the building behind the object appears much further away than in reality.

The process described above is similar to the in-camera special effect known as the Hitchcock zoom, where the zoom lens zoomes out at the same time as the camera moves towards the subject in such a way as to keep the subject the same size in the frame whilst the background "changes size" relative to the subject. The Hitchcock zoom is an unsettling visual illusion that appears to undermine normal visual perception by visibly stretching distance. It was first used in Alfred Hitchcock's film Vertigo (when looking down a stairway) and has since been used in Jaws (when the main character sees the shark) and Goodfellas (in the cafe towards the end, where Henry Hill gets the unsavory assignment), Lord of the Rings 1 (where Frodo first senses the ringwraiths and yells "get off the road!") and many other films.



Photos taken using a 35 mm camera with a 100 mm, a 70 mm, a 50 mm, and a 28 mm lens.