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126 The Audio-Visual Handbook
the brightest picture for all angles up to 12 degrees; the silver screen is satisfactory at angles up to 30 degrees; and the mat-white surface should be used where there will be angles greater than 30 degrees. In most cases the angle of reflection will not be greater than 30 degrees so either the silver screen or the matwhite will prove to be satisfactory. The chief claim for superiority on the part of the beaded screen is its brilliance of reflection through a rather narrow angle.
Silver Screens. Silver screens, as mentioned above, have a metallic coating. These screens are flexible and will permit rolling without damage to the surface. The angle of reflection from the silver screen is greater than the angle of reflection from the glass-beaded screen, but has certain limitations. First, unless the screen hangs perfectly straight without the slightest wave on its surface, it distorts projected pictures, which does not occur with either white or beaded screens. Second, silver screens are commonly referred to as being color selective, since some of the finer coloring is lost when projected upon them. Silver screens are, therefore, becoming less popular since colored film is gaining in popularity.
Polaroid Screens. These screens are similar in appearance to silver screens, but the surface has been designed so as not to depolarize the projected light. This is essential in the projection of Polaroid three-dimensional pictures, recently developed by the Polaroid Research Laboratory in conjunction with the Society for Visual Education, Inc. Three-dimensional pictures are described briefly on page 97.
White Screens. It has been found that a screen which has a white surface does not provide the brilliant reflection one would secure from either the beaded screen or the silver screen, but the reflection at an angle of from 30 to 60 degrees is brighter than from the beaded screen, making this type of screen unusually satisfactory for the classroom which is approximately square in shape. Many who project glass slides and filmslides prefer this type of screen and base this preference upon their feeling that the surface which is not so highly reflective is less tiring to the eyes of pupils. Furthermore, the projection of colored film is more accurate in reproduction when the white-surfaced screen is used. Some of these screens are made with a rubberized surface and may be washed with ordinary soap and water.
When choosing a screen it should be remembered that while its reflective properties are paramount, there are other important considerations, such as quality, cost, and probable life, which should receive careful attention.