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Reflection Characteristics of Projection Screens
By Lloyd A. Jones and Milton F. Fillius HEN it is considered that the enjoyment of the entertainment
VV offered in the motion picture theater depends ahiiost entirely upon the visual organs, it will be recognized that the importance of providing conditions which will result in the least possible visual fatigue to the audience cannot be overestimated. There are many factors which deserve the consideration of the motion picture engineer in order that the maximum of visual comfort may be obtained, among which may be mentioned the proper distribution of the interior illumination, the elimination of excessively bright surfaces in the field of vision, and the proper adjustment of the screen brightness. The fact that the attention of the audience must remain fixed for long periods of time upon the projected picture makes it of utmost importance that the projecting system be so adjusted that the screen brightness is neither so high as to cause visual fatigue due to glare, nor so low as to throw an undue burden upon the retinal accommodation.
The optical properties of the surface upon which the motion picture is projected determines to a great extent the ultimate efficiency of the entire installation, and hence should receive due consideration at the hands of the motion picture engineer. While there is no doubt that this is recognized, and that considerable improvement in the c[uality of projection screens has been made in recent vears, it seems that the subject has been approached largely from the' practical standpoint and that little quantitative data are available relative to the optical characteristics of the materials used so extensively at the present time.
In view of this deficiency, it seemed worth while to examine critically the reflection properties of the large number of commercial screens on the market. From the data obtained by such examination, it will be a relatively simple matter to choose the most efficient screen surface for a given installation. An examination of the commercial screens obtained showed a remarkable variation in reflection characteristics, ranging from surfaces which almost completely diffuse the incident light to screens of a very specular nature, having very high reflecting powers on the projection axis and very low values in directions departing by relatively small amounts from the normal. When the question of adapting the screen to the shape of the room in which it is to be used is considered, it will be seen that it is quite hopeless to obtain in all cases the max'inum efficiency with a screen of fixed characteristics.
For instance, if the length of the room is large relative to its width, a screen of the completely diffusing type is very wasteful of light, and the necessary screen brightness can be obtained over the required angle by the use of a screen which reflects a large proportion of the incident light within a comparatively narrow angle.
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