Forced Perspective

Forced perspective is a technique that employs optical illusion to make an object appear farther away, closer, larger or smaller than it actually is. It manipulates human visual perception through the use of scaled objects and the correlation between them and the vantage point of the spectator or camera. It has uses in photography, filmmaking and architecture.

In filmmaking

An example of forced perspective is a scene in an action movie in which dinosaurs are threatening the heroes. By placing a miniature model of a dinosaur close to the camera, the director may make the dinosaur look monstrously tall to the viewer, even though it is just closer to the camera.

Forced perspective had been a feature of German silent films and ''Citizen Kane'' revived the practice. Movies, especially B-movies in the 1950s and 1960s, were produced on limited budgets and often featured forced perspective shots.

Forced perspective can be made more believable when environmental conditions obscure the difference in perspective. For example, the final scene of the famous movie ''Casablanca'' takes place at an airport in the middle of a storm, although the entire scene was shot in a studio. This was accomplished by using a painted backdrop of an aircraft, which was "serviced" by dwarfs standing next to the backdrop. A downpour (created in the studio) draws much of the viewer's attention away from the backdrop and extras, making the simulated perspective less noticeable.

Role of light

Early instances of forced perspective used in low-budget motion pictures showed objects that were clearly different from their surroundings: often blurred or at a different light level. The principal cause of this was geometric. Light from a point source travels in a spherical wave, decreasing in intensity (or ''illuminance'') as the inverse square of the distance travelled. This means that a light source must be four times as bright to produce the same illuminance at an object twice as far away. Thus to create the illusion of a distant object being at the same distance as a near object and scaled accordingly, much more light is required. When shooting with forced perspective, it's important to have the aperture stopped down sufficiently to achieve proper DOF (depth of field), so that the foreground object and background are both sharp. Since miniature models would need to be subjected to far greater lighting than the main focus of the camera, the area of action, it is important to ensure that these can withstand the significant amount of heat generated by the incandescent light sources typically used in film and TV production.

In motion

Peter Jackson's film adaptations of ''The Lord of the Rings'' make extended use of forced perspective. Characters apparently standing next to each other would be displaced by several feet in depth from the camera. This, in a still shot, makes some characters ( dwarves and Hobbits) appear much smaller than others. If the camera's point of view were moved, then parallax would reveal the true relative positions of the characters in space. Even if the camera is just rotated, its point of view may move accidentally if the camera is not rotated about the correct point. This point of view is called the 'zero-parallax-point' (or front nodal point), and is approximated in practice as the centre of the entrance pupil.

An extensively used technique in '' The Lord of the Rings: The Fellowship of the Ring'' was an enhancement of this principle, which could be used in moving shots. Portions of sets were mounted on movable platforms which would move precisely according to the movement of the camera, so that the optical illusion would be preserved at all times for the duration of the shot. The same techniques were used in the Harry Potter movies to make the character Hagrid look like a giant. Props around Harry and his friends are of normal size, while seemingly identical props placed around Hagrid are in fact smaller.

Comic effects

As with many film genres and effects, forced perspective can be used to visual-comedy effect. Typically, when an object or character is portrayed in a scene, its size is defined by its surroundings. A character then interacts with the object or character, in the process showing that the viewer has been fooled and there is forced perspective in use.

The 1930 Laurel and Hardy movie '' Brats'' used forced perspective to depict Stan and Ollie simultaneously as adults and as their own sons. An example used for comic effect can be found in the slapstick comedy ''Top Secret!'' in a scene which appears to begin as a close-up of a ringing phone with the characters in the distance. However, when the character walks up to the phone (towards the camera) and picks it up, it becomes apparent that the phone is extremely oversized instead of being close to the camera. Another scene in the same movie begins with a close-up of a wristwatch. The next cut shows that the character actually has a gargantuan wristwatch.

The same technique is also used in the Dennis Waterman sketch in the British BBC
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