Motion control photography

Motion control photography is a technique used in still and motion photography that enables precise control of, and optionally also allows repetition of, camera movements. It can be used to facilitate special effects photography. The process can involve filming several elements using the same camera motion, and then compositing the elements into a single image. Other effects are often used along with motion control, such as chroma key to aid the compositing. Motion control camera rigs are also used in still photography with or without compositing; for example in long exposures of moving vehicles. Today's computer technology allows the programmed camera movement to be processed, such as having the move scaled up or down for different sized elements. Common applications of this process include shooting with miniatures, either to composite several miniatures or to composite miniatures with full-scale elements.

The process is also commonly used when duplication of an element which cannot be physically duplicated is required; motion control is the primary method of featuring multiple instances of the same actor in a shot that involves camera movement. For this technique, the camera typically films exactly the same motion in exactly the same location while the actor performs different parts. A blank take (with no actor in the shot) is sometimes also taken to give compositors a reference of what parts of the shot are different in each take. This, in common film-making language, is also known as shooting a "plate".

In today's film, the reference take is also useful for digital manipulation of the shots, or for adding digital elements. A simple duplication shot confines each "copy" of an element to one part of the screen. It is far more difficult to composite the shots when the duplicate elements cross paths, though digital technology has made this easier to achieve. Several basic camera tricks are sometimes utilized with this technique, such as having the hand of a body double enter a shot to interact with the actor while the duplicate's arm is to be off-screen. For the sake of compositing, the background elements of the scene must remain identical between takes, requiring anything movable to be locked down; the blank reference take can aid in resolving any discrepancies between the other shots.

Similar technology in modern film allows for a camera to record its exact motion during a shot so that the motion can be duplicated by a computer in the creation of computer generated elements for the same shot.

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