projector

Apparatus that projects a picture on to a screen. In a slide projector, a lamp shines a light through the photographic slide or transparency, and a projection lens throws an enlarged image of the slide onto the screen. A film projector has similar optics, but incorporates a mechanism that advances the film and then holds it still while light is transmitted through each frame (picture). A shutter covers the film when it moves between frames. A television projector, often used at sports events, produces an enlarged image of the television screen. It shines an intense light through a small LCD (liquid crystal display) throwing the television picture onto a large screen. A digital projector is used for computer-aided presentations. The oldest types use cathode-ray tube technology. One newer type has LCD screens like those used in calculators and flat-screen televisions, through which light shines onto the screen. A third type has a million or more tiny mirrors mounted on a microchip. Each mirror can be deflected or vibrated to control the light going to a single pixel (picture element) in the image.