Motion-Picture Projector

a device for projecting motion-picture films onto a screen. The main elements of a motion-picture projector are the feed mechanism, which moves the film; the feed and take-up reels (if the process of showing the film is automated, nonrewinding devices may be used in place of the spools); a system for illuminating the screen and projecting the image; and equipment for sound reproduction, electric power supply, and control.

The film in the projector is moved intermittently by a Geneva or claw feed mechanism. During the time that the frame is stopped in the film gate, the image is projected onto the screen. During movement from one frame to the next, the light flux is broken by a special baffle, the shutter. The shutter operates in synchronization with the intermittently moving mechanism, and as a consequence the movement of the frame at a set frequency is unnoticed by the viewer. The projector objective, which forms an enlarged image on the screen, has a focal length that is selected depending on the length of the viewing area and the size of the screen. In certain projectors, objectives with a variable focal length are used for showing 16-mm and 8-mm films.

The most important characteristic of a projector is the light flux, which determines the brightness of the image on the screen. The light flux of a professional projector is 350 to 50,000 lumens; that of a home projector, not less than 50 lumens. The greatest light flux is created by an electric carbon arc lamp (50,000 lumens); smaller fluxes are formed by a gas-discharge (xenon) lamp (15,000 lumens) and an incandescent lamp (90 lumens). Therefore, projectors with carbon arc or xenon lamps are used for large theaters with large-area screens. In small theaters, and also in projection units for school, home, and other purposes, projectors with an incandescent lamp are used.

All motion-picture projectors for professional use are designed for showing sound films; only projectors for home use show silent 8-mm films or sound films using a tape recorder and a synchronizer. Projectors are also made for showing 8-mm sound films.

In terms of operating conditions, a distinction is made between stationary and mobile motion-picture projectors. Stationary projectors are located in special projection or screening rooms, and mobile projectors, which are usually portable, are used in mobile units for showing narrow-gauge 16-mm and 8-mm films.

Depending on the film size, motion-picture projectors may be designed for showing 35-mm films with a standard image (an aspect ratio of 1:1.37), anamorphized films (wide-screen, with ratios of 1:1.65, 1:1.85, and 1:2.35), and 70-mm (wide-frame) films (with a ratio of 1:2.2), as well as 16 and 8-mm narrow-gauge films. Universal projectors, as well as special projectors for large-frame and stereoscopic films, are also manufactured. The universal projector is used in theaters with large auditoriums (up to 6,000 spectators) and is designed for showing standard 35-mm films, cropped films (with reduced height of the usual frame), and anamorphized films, as well as 70-mm wide-gauge films. When changing from one film size to another, only a simple resetting of the feed device and a change of objective are necessary. The illuminating system consists of an elliptical mirror 600 mm in diameter with an interferential surface that reflects about 95 percent of the visible light into the film gate. The source of light is an air-cooled carbon arc lamp. The effective light flux is about 25,000 lumens for ordinary 35-mm films, 30,000 lumens for wide-screen 35-mm films, and 50,000 lumens for wide-gauge 70-mm films. The capacity of the feed and take-up reels reaches 1,500 m.

Mobile projection units of the Ukraina type are widely used for showing 16-mm films. The housing of the device is made of aluminum alloy. All the elements of the feed mechanism, the objective, and the sound reproduction system for optical and magnetic sound tracks are located in the front part; the parts of the drive mechanism are located inside the housing. An incandescent projection lamp (30 volts, 400 watts), a three-lens condenser, and an electric motor are located in the lamphouse adjacent to the rear wall of the housing. A fan is attached to the motor shaft for cooling the lamp. The effective light flux of the projector is 350 lumens. The feed and take-up spools have a capacity of 600 m each, which corresponds to five reels.