A movie projector is a mechanical device used for showing motion pictures. The projectors transfer movie images from a roll of film onto a nearby screen or other viewing surface. Movie projectors can range from simple models used in the home to more complex units found in theaters and other commercial establishments.
There are four basic parts that make up the average movie projector. They include the spooling system, the lamp, the lens and the audio system. While each of these systems consists of multiple parts and processes, almost any motion picture can be shown using only these four systems.
Once a roll of film is placed on the spool of the movie projector, the spool is turned using an electric motor. As the spool turns, it transfers the film on the roll to a second spool. In between the two spools, each frame of film is paused for a fraction of a second. This pause is timed so that the image freezes as it is centered in front of a bright lamp, which projects light through the image and transfers it to the screen. Before the image leaves the projector, it passes through a lens, which magnifies the image to multiple times its original size.
Most projectors also include a built-in audio system that transfer sound from the film to nearby speakers. The sound portion of a movie scene often reaches the projector a few frames ahead of the visual portion of the scene. This causes the audio to reach the ears at the same time that the matching image reaches the eyes. The audio must be introduced early because of the relative difference in speed between sound waves and light.
A movie projector is available in different sizes based on the type of film it can accommodate. An 8 mm movie projector is the standard model used for old home movies, while a “Super 8” is a slightly higher quality version of the original 8 mm. The 16 mm movie projector is found in many educational facilities, and produces a slightly improved picture over the 8mm model. Most motion pictures are shown using 35 mm projectors, which produce some of the highest quality images available.
Most movie projectors are used in combination with projection screens. These screens often have a light-colored reflective surface to present the best possible image quality. They may also be coated with aluminum or other minerals to increase reflectance and contrast.