Forced perspective
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Forced perspective is a filmmaking technique employed to make larger objects appear smaller to the viewer or vice versa, depending on their relationship to the camera and each other. Forced perspective creates an optical illusion, used primarily to make objects appear far away when set space is limited.
Basic Examples
Examples of forced perspective:
- Imagine a scene in an action/adventure movie in which dinosaurs are threatening the heroes. By placing a miniature model of a dinosaur close to the camera, the dinosaur may look monstrously tall to the viewer, even though it is just closer to the camera.
- Imagine another scene in which two characters are supposed to be interacting in the foreground of a vast cathedral. Instead of actually filming in a cathedral, the director mounts a large painting of a cathedral's interior in a studio and films the actors talking in front of the painting. This gives the effect on film that the characters are in the foreground of a large room, when in reality they are standing next to a flat surface.
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 little people standing next to the backdrop. A downpour (created in-studio) draws much of the viewer's attention away from the backdrop and extras, making the simulated perspective less noticeable.
The example below, taken from Andrei Tarkovsky's Nostalghia, is one notable instance.
The Role of Light
Early instances of forced perspective use in low-budget motion pictures showed objects that were clearly different from their surroundings, sometimes blurred or at a different light level.
The principal cause of this was mathemetical, since light from a point source travels in a spherical wave, decreasing in strength at a square root of the distance travelled, eg. the light hitting a 1m square from a source will be x, the light hitting the same 1m square moved double the distance from the point source will be x/4. Thus to create the illusion of the distant object being at the same depth of field, scaled accordingly, 4x the light would be required to light the far object than the near object.
Opening the iris to allow more light into the camera, allowing both near and far objects to be seen at a more similar light level, has the secondary effect of decreasing depth of field. By increasing the volume of light hitting the closer objects, the iris opening can be restricted and depth of field is increased, thus portraying both near and far objects as in focus, and if well scaled, existing in a similar lateral plane.
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 / TV production, as they may be prone to combustion.
The Nodal Point - Forced perspective in motion
Peter Jackson's film adaptations of The Lord of the Rings employ an almost constant 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 appear unnaturally small (for the Dwarves and Hobbits) in relation to others.
A new technique developed for 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. Note that props around Harry and his friends are of normal size, while identical props placed around Hagrid are smaller.
The techniques developed centred around a nodal point axis, so the camera's panning axis was at the point between the lens and aperture ring where the light travelling through the camera met its axis. By comparison, the normal panning axis would be at the point at which light would strike the film (or CCD in a TV camera).
Peter Jackson enhanced this known effect by adding moving jigs to extend the pan to be effective outside the camera during motion - which is not possible to show in a still photograph.
The position of this nodal point can be different for every lens. However, on wide angle lenses it is often found between the midpoint of the lens and the aperture ring.
Digital effects
Another method is to film the actions of the "smaller" character on a set with normal-sized props, film the matching actions of the "large" character on an identical but smaller set, then combine the footage digitally. This is the most straightforward modern technique, and is most likely to be used with blue screen filming in TV production due to its lower cost and quality requirements.
Comedic effects
As with many film genre and effects, forced perspective can be used to visual comedy effect. Typically, an object or character is portrayed in a scene, its size 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.
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 close to the perspective of the camera.
See also
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