Deformation of prospect related to the focal distance
In Photography and Cinema tography, the adjustment of the focal Distance of the objective causes an impression of deformation of the Perspective . This distorts impression is due to the fact that one seldom looks at an image with the orthoscopic Distance necessary to correctly restore the object photographed. One can in particular observe it with a wide-angle lens to photograph or film a close object (William Klein used this process much). Let us recall that a silver camera 24x36 or a camera of cinema 35mm uses the both same films of 35 Misters For this width, one considers that the use of objectives with a focal distance of 50 mm corresponds about to the vision of the human eye. It is besides the standard equipment of many silver cameras. The more one moves away from this standard, the more the distortion of prospect is felt.
the wide-angle lenses have focal distances from 24 or 18 Misters In this case the objects close to the apparatus will appear exaggeratedly widened compared to those of the background.
- the objectives with long focal distance (85 mm and more) give the impression to reduce the distances between the objects, by compressing the distance.
Let us take the example of the portraits of face. With a wide-angle lens, they generally give an unpleasant impression, with an impressed nose and deformed features. To obtain good performances, one often takes the portraits with teleobjectives of moderated focal distance, between 85 and 105 Misters.
The 4 photographs with the bottom of this article visually illustrate the importance of the focal distance in made photographic and cinematographic. The object in the foreground was tallied in the most similar possible way between each catch of sight. The photographer used 4 different objectives, going from 100 mm to 28 mm of focal distance. To compensate for the change of visual angle, it each time approached the subject. The subject in the foreground remains about stable, but the bottom of the image varies considerably. It is noticed besides that with the use of the shortest focal distance (last image), the structure of wood also starts it to be deformed from its point of view (cf notices on the portraits). The third photograph (taken with the objective 50 mm) corresponds about to the natural vision, the others move away or bring closer artificially the background.
What is true for the fixed catch of photograph applies naturally in the dynamic cinema of way. The system of increase continues of the zoom compensating for the distance of the camera (or vice versa), is known under the name of “zoom of Hitchcock” or Travelling compensated for. It is a effect destabilizing which was used for the first time by Alfred Hitchcock in Cold sweats , and included since in many of other films.
Jacques Tati recalled, in connection with its film Playtime, which it employed only one focal distance for his objectives: nearest to the human glance, which does not have any reason to change during the cinematographic narration.
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