Motion-Picture Screen

a flat or curved surface for dispersing toward the viewer the light from each section of the film image projected on it. If the light dispersion is the same in all directions, the brightness of the screen is perceived as the same at any point of the theater. The brightness of the picture is determined by the technical characteristics of the screen and by the effective light flux of the projector. One of the main technical characteristics of the screen is the luminance coefficient, which is the ratio of the brightness of the screen surface to the brightness of an absolutely white surface with equal illumination. Another characteristic that determines the light dispersion of the screen is the angle of diffusion (the angular zone within which the luminance coefficient is not less than 0.5).

According to the projection method, a distinction is made between light-reflecting and light-transmitting screens. The surface of a reflecting screen is nontransparent, and the image is viewed from the side from which the film is projected. The surface of a transmitting or translucent screen is semitransparent, and the film is projected onto it from the back. Light-reflecting screens are the most common. In terms of their ability to diffuse light, they are divided into diffusely scattering (matte white) and semireflecting. The former have a luminance coefficient of 0.7–0.9 within the limits of a scattering angle of ±90°. They are made from a fabric with a white pigmented coating or from a plasticized resin (for example, polyvinyl chloride film), whose surface is given a particular shape by impressing. The luminance coefficient of semireflecting screens is 1.5–6.0, and the diffusion angle is 30°-60°. The material for such screens is a smooth plasticized resin with a metallized (aluminized) surface or varnished (“pearly”) coating or a specially treated bead-covered backing (a “beaded” screen). A lenticular screen is used for stereoscopic projection.

The main material for large screens is sheet plastic joined into screen panels by welding. The light-passing screens are used mainly in daylight motion-picture units or in rooms with artificial lighting, as well as for rear projection in motion-picture filming. The material for these screens is matted glass, semitransparent sheet plastic, and film coatings. Their coefficient of light reflection is low (0.3–0.4), their light transmission coefficient is about 0.5, and their luminance coefficient reaches 5–7, with a diffusion angle of 30°-40°. The main disadvantages of translucent screens are sharp directivity and the coincidence of the maximum brightness with the direction of incident light flux. As a result, a bright spot is created that obstructs the viewing of the picture; as the viewing angle increases, the brightness declines sharply.

Screens also differ in terms of the types of motion picture--conventional, wide-screen, wide-gauge, and special-purpose (stereoscopic, varioscopic, and so on). The width of the effective field of the screen (along a chord) is determined by the standards and rules for motion-picture theaters depending on the length of the theater: 0.25 of the theater’s length for an ordinary film, 0.43 for a wide-screen film, and 0.6 for a wide-gauge film. For showing wide-gauge and wide-screen films, the effective field of the screen may be changed by changing the width of the curtain in front of the screen; for wide-screen films, it may be changed by changing the height of the cropping device. The width of a screen in a large theater may be as great as 30 m; for amateur purposes, 0.8 m and more.