the front to those in the rear, there should not be any
obstructions.
In most situations, particularly in rooms where the
floor does not slope and there is no platform, the bottom
edge of the screen should be at least 4 1/2 feet from the
floor. With the screen at this height, most people will
have an unobstructed view. On the other hand, the screen
should not be too high for viewing comfort.
The screen should be tilted as necessary to eliminate
“keystoning” (a distortion of the image in which the top
of the picture is enlarged out of proportion). The
principle involved is that the plane of the screen should
be at a right angle to the center line of projection;
otherwise, the image will be distorted as shown in
figure 6-8.
Wide horizontal angles of vision should also be
avoided. Preferably, in an oblong room, the screen
should be parallel to the shorter dimension. If the screen
is set parallel to the longer dimension, the angle of vision
at either side becomes too great for easy viewing.
Types of Screens
In general, there are five types of screens used in
presentations today:
high-gain aluminum, matte,
lenticular, beaded and rear-projection.
HIGH-GAIN ALUMINUM SCREENS.– High-
gain aluminum screens have thin sheets of specially
grained aluminum foil laminated to a slightly concave,
noncollapsible lightweight frame. The screen reflects
the projected light onto an area approximately
60 degrees wide by 30 degrees high. The reflected
image is about six times brighter than that of other
screens. Because of the special surface characteristics,
this type of screen can be used in a normally lighted
room. When properly positioned, the screen rejects
room light by reflecting it away from the viewers,
Figure 6-8.-Proper screen positioning.
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