DG 1110-3-106
D 30 Degrees
Figure 3-11
Projection Screen Location Related to the
Cone of Vision
operation. These characteristics should be carefully
d. The bottom of the screen must be 48 inches from
investigated prior to programing a projected television
the floor; the top may extend to within 6 inches of the
system.
ceiling.
e. Reflected screens are not limited in size.
(1) Tube Screen Viewing Characteristics:
(Figure 3-12).
(3) Comparison of Front and Rear Projection Systems.
a. The maximum viewing area extends 45 degrees each
With a front projection system, images are projected
side of center, forming a "visual cone" of 90 degrees.
onto an opaque screen from a location in front of the
screen. Rear projection systems project an image onto
b. The minimum viewing distance (that is, the closest
a translucent screen from a position behind the screen.
The following is a comparison of the two systems in
the spectators may sit to the screen) is 5W (five times
the width of the screen). The preferred minimum
terms of their spatial impact on classroom design:
viewing distance, however, is 8W.
a. Shadows on Image.
c. The maximum viewing distance is 14W; the
Rear projection systems permit lecturing and
preferred maximum is 10W.
demonstrating concurrent with medial projection, with
no obstruction of the image by shadows. With front
d. The bottom of the screen must be 48 inches from
projection systems this is more difficult to accomplish.
the floor to permit unobstructed viewing by all
spectators.
b. Location of Projector.
Front projection equipment is located at the end of the
e. "W" for tube screen is practically limited to a
room opposite the lecturer. This necessitates either
25-inch screen unit (actual visual "W" approximately
remote operation, an attendant, or automatic delivery.
22 inches). However, tube screen equipment is
Rear projection equipment located in a separate
improving, and larger, more economical screens may
projection room presents the same problem. However,
be developed. The availability of such screens must be
it may also be located beside the lecturer, with the
investigated when audio-visual systems are programed.
image being projected onto the rear of the screen by a
series of mirrors. This system permits manual control
of the projector by the lecturer, and facilitates the
(2) Reflected Screen Viewing Characteristics:
handling of projector malfunctions.
(Figure 3-13).
c. Audience Size.
a. The maximum viewing area extends 50 degrees
Given equally sized screens of equal brightness, a front
either side of the screen. The preferred area, however,
projection system permits more persons to be seated
extends 40 degrees.
within the favorable viewing area because the projector
is farther from the screen. As Figure 3-14 shows,
b. The minimum viewing distance from the screen is
theoretically it would be possible to locate a rear
2W, but 4W is the preferred minimum.
projector at a distance from the screen of 6W, thereby
c. The maximum viewing distance is 8W, 6W the
preferred.
3-10
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