The forced perspective is, with the Cinéma or the Théâtre, a visual proceeded intended to give an impression of depth artificially, or to simulate differences in size between objects or characters intervening in the same scene.

Appeared with the cinema since 1910, the forced prospect was largely used in the years 1950 and 1960, in particular in films with small budget. One still finds it in the current productions, because it is a technique rather inexpensive and very effective, for little that it is well controlled.

• In studio, to amplify the depth of a scene, one prolongs the first elements of the decoration by objects with reduced size, models. If the camera is well placed, an illusion of distance of the background is obtained. It is also possible to exaggerate the size of the first elements of decoration.

• to reveal larger characters the ones than the others, a similar technique applies, but with the opposite effect: the character whom one wishes to reduce will be simply far away from the camera. So that the system functions, it is necessary naturally that the other visual references coincide. Thus, the elements of decoration surrounding the distant character will have to be proportionally larger, in order to give the illusion. He will have to be also connected harmoniously with those of the foreground.

These various constraints make that the forced prospect is more easily used out of fixed camera. Indeed, during displacements, it is difficult simultaneously to adjust the visual reference marks which form the prospect. Nevertheless this technique exists, one can then speak about perspective forced animated , of which here a recent example, drawn from the turning of the film the Lord of the Rings: The Community of the Ring :

One wishes to film two characters behind a table, one having to appear taller than the other, while making evolve/move the visual angle. One uses a side Travelling for the displacement of the camera, and simultaneously, the seat on which sat the character in background slides in the opposed direction, on another track of dolly. It is not possible to synchronize these movements manually, also two displacements they are managed by computer with servomotors.