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Angle
from
the
Normal
Proportion of Light Reflected
(Assuming 100% from Beaded at
Normal)
Beaded
Silver
White
o°
20 • 5o°
100% 38% 16%
84,% 42%
7%
35% 32% 20%
Chart reproduced by courtesy of Neville Brown & Co., Ltd., makers of "Cinepro" Screens.
Choice of screen will depend on the operator's particular needs, but care should be taken to get one which is sufficiently strong and with a clean and even surface. Beaded screens should be examined under exhibiting conditions, and with the light from a projector focussed full upon the surface. Directional screens cannot be examined properly in daylight.
The size of the screen required will depend on the projector lamp's wattage, the length of the throw, and the focal length of the projection lens.
It should be noted that the brightness of the picture depends on the amount of reflection from the screen, and as this varies according to the type of surface, we may judge a screen by the direction and strength of the reflections.
Screens which reflect the light evenly are known as nondirectional, and in this category the matt-white and translucent screens are placed respectively. The perforated screen is also non-directional, though it should be mentioned that quite a few of these screens are of poor quality, and like the translucent types, may be directional when they should be otherwise.
On the other hand the beaded and silver screens are definitely directional, and with them there is a marked falling-off in brightness as the angle of viewing becomes more acute, and in some cases the picture is even seen distorted.
In choosing a screen, therefore, you must take into consideration the area of good visibility, the area of poor visibility, and the angle of distortion, though the latter need not worry you if your hall is long and narrow.
SO