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264 HANDBOOK OF PROJECTION FOR
tive and high diffusive power) fall off very rapidly, none of them standing much above 50 per cent, at 50 degrees angle. We may therefore conclude that for all the high reflective surfaces tested the range of efficiency lies well within the 50 degree angle, and it must be considered that beyond 30 degrees the difference between screen brilliancy in different sections of the house is such that it is apt to be noted by patrons, though this may be to some extent balanced by the preference some patrons have for a more or less brilliant picture.
Applying Fig. 76 let us suppose the exhibitor to have a house 40 feet wide by 70 feet deep. We have indicated a 16-foot wide picture by the thick black line. Following the 20 degree angle lines through the auditorium we see that considering a single point at the center of the screen at 20 feet from the screen, a space considerably less than 20 feet wide, or less than half the width of the house, falls within that angle, and even the 40 degree angle does not take in the entire width at 20 feet from the screen. At 30 feet from the screen the 30 degree angle does not take in the entire width of the house, whereas the 20 degree angle only includes a little more than 20 feet of its width.
But we consider only a point at the center of the screen, whereas the screen is 16 feet wide, so that the angle will include 8 feet more space on one side, but the patron seated on that side will be just that much worse off insofar as has to do with the other half of the screen.
Our purpose, however, is to indicate how Fig. 76 should be applied in practice, rather than to draw conclusions, since we shall, later, give you the conclusions arrived at by those making the tests. We give you Fig. 76 and we give yon the tables showing the characteristics of the various surfaces. The rest is up to you, insofar as application of the data to your own local condition be concerned.
Remember that each one of the horizontal lines in Fig. 76 represents 10 feet of front to back depth, while each perpendicular line represents 10 feet of auditorium width.
The makers of the test drew their own conclusions, which same we shall present verbatim, and with no more comment than may be necessary to make the meaning clear.
CONCLUSIONS ARRIVED AT.— In order to facilitate the examination of the data, it will be well to separate them into their respective classes. After careful consideration of the characteristics of the screens and of the requirements of