FOUNDATION FOR EFFECTIVE AUDIOVISUAL PROJECTION

• Document Type: CREST
• Collection: NGA Records (Formerly NIMA)
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78B04770A000800010012-1
• Release Decision: RIFPUB
• Original Classification: K
• Document Page Count: 20
• Document Creation Date: December 28, 2016
• Document Release Date: September 27, 2004
• Sequence Number: 12
• Content Type: REPORT

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FOUNDATION
EFFECTIVE AUDIOVISUAL
PROJECTION
0 MOTION PICTURES ? SLIDES ? FILMSTRIPS
LARGE TRANSPARENCIES ? OPAQUE MATERIALS
Declass Review by NGA.
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TABLE OF CONTENTS
Section Page
Room Facilities ................................................................................................. 4
Seating Plan and Screen Type ................................................................... 5
Screen Size ............................................................................................................. 8
Loud-Speaker
Location .................................................................................... 11
Image Brightness Required .......................................................................... 11
The Projector-Lens-Lamp Combination .................................................. 16
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Motion Pictures ? Slides. Filmstrips ? Large Transparencies ? Opaque Materials
U Successful projection transfers ideas and images from film to people's
minds. Good projection clears away physical and mental hurdles along the
film-to-mind path.
As good projection makes the communication path easier, it increases
the chances of conveying ideas and impressions successfullyand of chang-
ing attitudes and behavior.
"Check-list" jobs, such as scheduling the material to be shown and
U notifying people of the meeting, are usually no great problem. But this
routine often neglects the matter of selecting appropriate apparatus and
arranging it in the room to insure the most effective projection. This must
. be done well to make sure that the message reaches the audience, without
interference by the projection process.
For Good Projection, Follow These Steps
a (clarified in the following pages)
1. Choose a room with adequate facilities.
2. Select a seating plan and screen type.
. 3. Determine the screen size and location.
4. Choose loud-speaker location.
5. Select the projector location and lens focal length.
6. Determine the image brightness required.
. 7. Select a projector-lens-lamp combination to meet the need.
Although these steps are in logical order, in practice it is often neces-
sary to compensate for available equipment and facilities which may be
less than ideal by backtracking and modifying early decisions.
This leaflet takes up these steps in order. The suggestions and data will
help you prepare for an effective audiovisual presentation in almost any
type of room. The information is not intended for application to commercial
theater projection. Nor is it intended to detail the operation of a projector
or "showmanship" techniques.
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1. ROOM FACILITIES
Where the "ideal" room is not available, modifying existing conditions will
improve a "possible" room.
The room should:
a. Be large enough for the greatest number of viewers expected. Large
auditoriums or meeting rooms with folding chairs need 5 to 6 square feet
of floor space per person within the good viewing area. Conference rooms
or classrooms with fixed seating require about twice that area - 10 to 12
square feet per viewer within the good viewing area.
b. Permit suitable light control. For daytime projection in rooms with
outside windows, ordinary window shades are usually suitable for Class C
materials (page 13) opaque shades, two thicknesses of ordinary shades,
ordinary venetian blinds, or drapes, for Class B. Almost complete darken-
ing is usually needed for Class A materials.
Temporary opaque drapes, portable blackboards, or other makeshift
devices to shield light from the screen may be used if darkening is inade-
quate. Light shields may be placed either at the screen or to block general
room lighting coming in a window. For some specific purposes, a perma-
nent shadow box around a screen may be desirable.
c. Provide needed illumination. Light sources which provide some illumi-
nation during projection, but not directly on the screen, help maintain a so-
cial atmosphere and permit note-taking. During projection the screen image
highlights should be brighter than any other surface within the viewers' field
of view. "Hot spots," caused by the glare from bare bulbs, reflections from
shiny surfaces, or gaps in window covering, should be eliminated.
d. Provide adequate electrical control. Preferably, room lights should
be controllable from a point near either the projector or the speaker's
stand. Or, arrangements may be made for someone to turn lights off as
soon as an image appears on the screen. The electrical outlet for the
projector must remain "live" when room lights are turned off. .
e. Provide good ventilation. The ventilation should be independent of the
room-darkening devices. If smoking is permitted, a generous supply of
fresh air will be needed.
f. Be acoustically good. Most rooms are satisfactory. Check rever-
beration by a smart clap of the hands. A sharp, ringing echo indicates too
much reverberation for good intelligibility. A "live" room (with objection-
able echoes) is improved acoustically when well filled with people. Any
high-volume noises or clearly intelligible speech at anylevel coming from
outside the room should be controlled or eliminated. Low-level background
noise does little or no harm.
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2. SEATING PLAN AND SCREEN TYPE
All screen and image dimensions in this leaflet apply to picture aspect
ratios commonly used in audiovisual materials. These range from squares
to rectangles with the longer dimension no more than 1 1/2 times the shorter.
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Figure 1 - In a long, narrow room (more than 1Y2 times as long as wide), the best
arrangement is usually that shown. A beaded screen or other narrow-angle screen is
suitable.
Figure 2 - In 'squarish" rooms, more Figure 3 - In "squarish" rooms, more
people will be able to see a satisfactory people can often sit in the good viewing
image if a matte or lenticular screen is area if projection is diagonal. A slightly
chosen, because of the wider viewingan- larger screen may be needed because of
gle it permits. the greater maximum viewing distance.
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In the use of two or three screen images, the adequacy of each image or
image area should be considered individually, whether the images are on
the same or different screens. That is, image size, as well as brightness
and legibility requirements, is the same for each image as if it were the
only image.
The screen is often the weakest link in a projection chain. A projection
screen interrupts the light falling on it from the projector (or other sources)
and diverts it to the viewers' eyes. The efficiency with which it does this
affects image brightness, evenness of image brightness, color saturation,
and contrast of the image. Following are brief discussions of some screen
types and their qualities.
Matte screens diffuse light evenly in all directions. Images on matte
screens appear almost equally bright at any viewing angle. To avoid dis-
tortion because of viewing angle, however, viewers should be no more than
about 30 degrees to the side of the projection axis, and not closer than two
image widths to the screen.
Most matte screens are about 85 percent efficient. That is, an illumina-
tion level of 10foot-candles on the screenprovides a screen surface bright-
ness of 8.5foot-lamberts, regardless of viewing angle or the angle at which
light strikes the screen.
Lenticular screens have a regular pattern of stripes, ribs, rectangles
or diamond-shaped areas. The pattern is too small to see at viewing dis-
tances for which the screen is designed. The screen surface may appear
to be enameled, pearlescent, granular metal, or smooth metal; and it may
or may not have a coating over the reflective surface.
By control of the shape of the reflecting surfaces, the screen can reflect
nearly all the light from the projector evenly over a fan-shaped area 70
degrees wide and 20 degrees deep. People seated farther to the sides of the
screen than the 70-degree angle or above or below the 20-degree angle
would see no image - no image-forming light would be wasted outside the
viewing area. It is also possible to produce a surface which will reject light
from outside the viewing area that might otherwise reduce the contrast of
the projected image. Many lenticular screens provide an image three or
four times as bright as a matte screen would.
Other lenticular screens may provide wider viewing angles with less
"gain" or narrower viewing angles with more gain.
Because the characteristics of lenticular screens do vary, it may be
difficult to select the best screen for a particular use. But often the im-
proved results make it well worth while.
Beaded screens are useful in long narrow rooms or other locations
where most viewers are near the projector beam. They are white surfaces
with imbedded or attached small clear glass beads. Most of the light reach-
ing the beads is reflected back toward its source. Thus, a beaded screen
provides a very bright image for viewers seated near the projector beam.
a
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As a viewer moves away from the beam, the image brightness decreases.
At about 22 degrees from the projector beam, the image brightness on a
. beaded screen will be about the same as that on a matte screen. Beyond
this angle it will be less bright than on the matte screen.
Since non-image or stray light is also reflected back in the general
. direction from which it comes, stray light falling on a beaded screen from
a viewer's position at the side of a room can be a major problem.
Rear-projection images have the same requirements for image bright-
ness, size, and contrast as front-projected images. Rear projection has
. advantages in some situations, disadvantages in others.
A person or object in front (on the viewer side) of a rear-projected
image does not interfere with the projection beam. This makes rear pro-
jection useful for situations in which the mechanism of projection must be
. unobtrusive or hidden as in displays. It permits close examination of the
screen image.
Rear projection may provide advantages in image contrast and color
. saturation in a lighted room. A dark rear-projection screen will reduce
image brightness, but it will reduce the amount of room light reflected back
toward viewers by a greater factor. Thus a dark rear-projection screen
can provide better contrast and color saturation when used in a lighted area,
S provided that stray light does not fall on the back of the screen.
Rear projection may also have disadvantages. With conventional projec-
tion, the space over the heads of viewers is usually used for the projector
beam. With rear projection, the projection beam is wholly or partially on
. the opposite side of the screen from the viewers. Consequently, space for
the beam must be provided outside the normal room space (behind the screen).
To reduce space requirements in rear projection, short-focal-length
. lenses are sometimes used. More commonly, one or more mirrors are used
to fold the projection beam. Either is likely to reduce image brightness and
quality.
Makeshift rear-projection screens, such as ground glass, are seldom
. satisfactory. Just as the satisfactory viewing angle of lenticular screens
can be controlled, so the dispersion (viewing) angle of rear-projection
screens can be controlled. A narrow-angle screen will give a bright image
. for viewers almost directly in front of the screen, but a dim image for
people at the sides of the viewing area. As the angle is increased, and with-
in limits, the image will become less bright for the viewer squarely in
front of the screen, and brighter for viewers toward the sides.
. Another important consideration in rear-projection screens is the dark-
ness of the screen as seen by reflected light. A dark screen can improve
image contrast and color saturation in a lighted room. But this is an advan-
tage only if the projector-screen combination can provide a bright enough
image for good viewing. As with front projection, the highlight brightness
of the image should be as bright, or brighter than, other areas within the
viewers' peripheral vision.
If the image is to be viewed in a well-darkened room, there is no advan-
tage in a dark screen. If the image is to be large, a light screen is usually
preferable since it will absorb less image light than a dark screen.
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With most tungsten projectors, images as wide as 42 or 48 inches will
be satisfactory on a dark rear-projection screen in moderately lighted
rooms. For larger images a light screen in a darkened room is usually
needed. In very brightly lighted rooms, images should usually be no more
than 24 or 30 inches wide, and the screen material dark.
The commonest form of rear projection involves a rear-projection
cabinet or console. Many of these are on the market. You can, however,
build your own. For plans, write to Sales Service Division, Eastman Kodak
Company for Rear-Projection Cabinets, KODAK Pamphlet No. T-47.
For an authoritative discussion of rear-projection screens, see "Selection
and Specification of Rear-Projection Screens," by Petro Vlahos, in the
February, 1961, journal of the Society of Motion Picture and Television
Engineers (Volume 70, No. 2).
3. SCREEN SIZE
Screen size should be such that the back row of viewers is no more than
6 times the image width (W)from the screen, with the following exceptions:
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a. Certain materials, including many teaching films, are designed with
titles and important picture elements bold enough to permit satisfactory
viewing at distances of 8 to 10 times the image width. If this is true for the
materials to be projected, the projector maybe moved closer to the screen
to give a smaller and brighter image. Moving the projector enough closer
to change the back row from 6W to 8W will approximately double the image
brightness and allow the front row to be moved a little nearer the screen.
b. In some situations, materials which limit maximum viewing distance
to less than 6W are commonly used. Typewritten material projected with
an opaque projector is an example. For showing the full area of an 8 1/2
by 11-inch page, pica type calls for a maximum viewing distance of 3W. A
compromise minimum viewing distance of 1 1/2W may be necessary to
give adequate audience capacity.
The graph onpage 9 is based onfloor space within the area of good view-
ing, not the area of the entire room. For an auditorium or other meeting
room, the allowance is 5 to 6 square feet per viewer; it is 10 to 12 square
feet for a conference room or classroom with fixed seating. The table in-
cludes an allowance for aisles within the seating area and assumes the entire
trapezoidal area of good viewing is available for seating. It may be used
in determining either the screen size needed for a given number of people
or the number of people accommodated by an image of a given size.
For example, a 5-foot image in an auditorium or other meeting room
can be expected to provide good viewing for 50 people if a beaded screen
is used or for 80 people if a matte or lenticular screen is used. Other
factors of course must also be satisfactory Conversely if 50 people are
8
expected, a 5-foot image will be required if a beaded screen is used; a .
4-foot image, if a matte or lenticular screen is used.
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500
450
400
350
300
FOR THIS MULTIPLY VIEWER
W VALUE FIGURE BY
8W 2
low 3
12W 4.5
250
225
200
175
150
125
m
100
12 11 10 9 8 7 6 5 4 3 2
WIDTH (IN FEET) OF PROJECTED IMAGE
'ptn
For a conference room or classroom with fixed seating, the number of
viewers is shown at the right of the chart. Thus, a 5-foot image will pro-
vide good viewing for 25 people if a beaded screen is used, for 40 people
if a matte screen is used. Or, if 25 people are expected for a conference
or classroom presentation, a 5-foot beaded or 4-foot matte screen will
be needed.
If the character of the projected materials is such that 8W (rather than
6W) viewing is satisfactory, the number of people accommodated may be
multiplied by a factor of 2, as shown in the table in the upper-right corner.
Thus, a 5-foot image on a beaded screen would provide adequate viewing
for 100 people in an auditorium or other meeting room; or a 5-foot image
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on a matte screen would be adequate for about 170 people. Conversely, if
50 people were expected and 8W projection were satisfactory, either a
3 1/2-foot beaded screen or a matte screen a little less than 3 feet wide
would be adequate.
These image-size considerations are based on legibility. For a more
complete discussion, see KODAK Pamphlet No. S-4, "Legibility Standards
for Projected Materials," available on request from the Sales Service
Division, Eastman Kodak Company, Rochester 4, New York. There is often
a psychological advantage in having a large image, even though it may not
be required for legibility.
Typical seating measurements are shown in the following diagrams:
1-4' _* 4'--~
0 I 3- j
CLASSROOM WITH
FIXED SEATING
~-- 7'~e-T
T Fi
UUU
000 i 000
CONFERENCE OR SEMINAR
42"
IF
36
[- 21"
28'
AUDITORIUM OR OTHER MEETING ROOM
If vertical or square pictures are to be shown, a square screen is pref-
erable. If only horizontal pictures are to be shown, either a horizontal
screen with proportions of about 3:4 or a square screen masked or opened
part way is usually preferred.
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4. LOUD-SPEAKER LOCATION
Sound quality is usually most satisfactory if the loud-speaker is near the
screen and high enough to be seen by everyone. Low placement causes loss
of intelligibility for all except those in the front row.
Where acoustics are poor, a corner location or extra speakers placed
part way back in the room may help. Extra speakers should ordinarily be
aimed toward the back of the room to avoid interference between separate
units.
Proper tone-control adjustment can help greatly in any room. In an
acoustically poor room, best intelligibility is usually achieved with the tone
or balance control near maximum treble. These settings do not give the most
pleasing reproduction of music, but they do improve crispness of speech
and reduce reverberation.
5. PROJECTOR LOCATION
For an undistorted image, the projector lens should be on a line extended
at right angles, vertically and horizontally, from the center of the screen
surface. For overhead and opaque projectors, this usually requires that
the top of the screen be tilted toward the viewers. Projectors should be
high enough so that their beams will "clear" obstructions, such as the heads
(and hats) of viewers.
Strongly upward or downward projection angles will cause "keystoning"
of the image unless the screen is tilted. That is, if the screen is vertical
and the projector is tilted upward, an image which should be rectangular
will be wider at the top than at the bottom. With beaded screens, such pro-
jection angles reduce image brilliance and increase unevenness of image
brightness.
The distance from projector to screen is determined by the size of the
area being projected, the focal length of the projection lens, and the image
size needed.
6. IMAGE BRIGHTNESS REQUIRED
Brightness (the amount of light the viewer sees) depends on viewing angle;
screen type; projector design; wattage, life rating, and age of lamp; char-
acter of material being projected; image size; line voltage; and design and
cleanliness of optics. Lamp wattage alone gives little indication of image
brightness; using it as a measure of image brightness is like rating an
engine by the fuel consumed rather than the work done.
The work done by a projector, in terms of image brightness, is lumen
output. Lumen output divided by image area (in square feet) gives the foot-
candles falling on the screen from the projector. Foot-candles of illumi-
nation multiplied by the reflectance of the screen (about 0.85 for a good
matte screen) give foot-lamberts - the measure of brightness of the image
seen by the viewer.
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Projection Distance for Desired Image Width (W)
Desired Image Width
For other
Lens
40"
50"
60"
70"
widths,
lti
l
Type of
Focal
mu
p
y
Material
Length
Projection
Distance
desired
*
(inches)
(Feet-to ne
arest Y2 foot)
width by
16mm Motion
1Y2
13
1612
20
23
3.9
Pictures
1-5/8
14
17)4
21
2412
4.2
(0.284" x 0.38'
2
1712
22
2612
31
5.3
protector mask)
212
22
2712
33
3812
6.6
3
2614
33
40
46 Y2
7.9
4
3512
44
53
61 1/2
10.5
8mm Motion Pictures
3
1414
18
21
26
4.4
(0.1294 x 0.172"
7/8 (22mm)
17
21
25
29
5.0
projector mask) zoom(15-25mm)
1112-19
1412-24
17-29
20-33
3.4-5.7
Filmstrip
3
11
14
17
1912
3.3
(17.2 x 23.Omm
4
15
19
2212
26
4.4
protected area)
5
19
2314
28
3212
5.5
7
2612
33
39
4512
7.7
2x2"Slides
3
8
912
1112
1312
2.3
(23 x 34mm
4
1012
13
15
18
3.0
horizontal mask)
5
13
16
19
2212
3.7
7
18
2212
2612
31
5.2
9
23
29
3412
40
6.7
11
28
35
42
49
8.2
zoom
31/4-61/4
912-16
12-20
14Y2-24
1612-29
2.8-4.7
2x2" Slides
3
7
812
1012
12
2.0
(38mm square
4
9
1112
1312
16
2.7
or 26.2 x 38mm
5
1112
141/2
17
20
3.3
horizontal mask)
7
16
20
24
28
4.7
9
21
26
31
36
6.0
11
2512
3112
3712
4312
7.4
zoom
33/-6y
812-1414
1012-18
13-2112
15-25
2.5-4.2
2x2" Slides
3
9
11
13
1512
2.6
(30mm square mask)
4
1112
1412
17
20
3.4
5
1414
18
2112
25
4.2
7
20Y2
25
30
35
5.9
9
26
3212
39
45
7.6
11
32
3912
4712
5512
9.3
zoom
33/-6'%
11-18
1312-2212
16-2612
19-31 Y2
3.2-5.3
Lantern Slides
612
8
912
11 Y2
13
2.2
(Mask opening
12
141/2
18
21
2412
4.0
3" wide)
16
19
23%
28
3212
5.3
26
31
3812
4512
5212
8.7
Overhead and Opaque 1212
"
7
812
10
11 Y2
1.8
Material 7
wide
Material 10" wide
14 or 1412
6
7
814
912
1.4
18
714
9
1012
12
1.8
22
9
11
13
1412
2.2
*After multiplying, add lens focal length for greater accuracy.
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Thus, a projector with a 120-lumen output provides 10 foot-candles of
illumination for a 3 by 4-foot (12 square-foot) screen image; that is, 8.5
foot-lamberts of image brightness for the viewer of a good matte screen.
Light output of a projector is measured with no film in the projector
but with the standard aperture in place and, for motion-picture projectors,
with the shutter running. Image brightness needed is not an absolute value,
with one exception, which is discussed later. It depends primarily on the
brightness needed to overrride the non-image brightness of the screen in
order to give satisfactory image quality.
Non-image brightness of a screen is the result of all the light falling on
the screen other than that actually forming the image. High non-image
brightness makes it difficult to obtain good blacks or dark areas in the
projected image. The principal sources of non-image brightness are ceiling
and exit lights in the room or incompletely darkened windows, doors, and
skylights.
Light escaping from within the projector itself, as well as from im-
properly designed or dirty projection optics, also contributes to non-image
brightness. These projector sources of non-image light are usually of little
consequence in well-designed audiovisual equipment in good condition.
The amount of image brightness needed to override non-image brightness
depends on the kind of audiovisual material being projected:
Class of Material Brightness Ratio
Non-Image Image
CLASS A
Full-scale continuous-tone black-
and-white or color pictures where
pictorial values are important and
color or tone differences must be
discriminated ...................... I to 100 or more
Color diagrams and continuous-tone
black-and-white pictures in high key........ 1 to 25
CLASS C
Simple line material, such as text,
tables, diagrams, and graphs -
either positive or negative (reverse)........ 1
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On the next page are three ways of determining lumen output needed. All
depend on measuring or estimating non-image brightness of the screen -
not on measuring projector output. The first is best, since it depends on
actual brightness measurement. The second will serve almost as well if a
matte screen is used or if the primary source of stray light on a beaded
screen is in the same general direction as the projector. The third, based
on estimating non-image brightness, is subject to considerable errors;
nevertheless, it is better than trusting to luck.
Method I - For determining the light output required of the projector.
1. With the room lighted as it will be during projection, measure non-
image screen brightness with a brightness meter. For greatest accuracy
in small rooms, the projector should be operating (with the lens capped).
However, the projector usually contributes little stray light in large rooms.
Changing the projector lamp to meet brightness requirements usually
makes no important difference in stray-light levels. A single measurement
taken at 10 to 30 degrees from the projection axis is usually enough for a
matte screen. For other screens, the reading should usually be made at the
greatest viewing angle (where image brightness will be lowest). Brightness
meters give reading in foot-lamberts. They are often available in physics
or optics departments of colleges and universities. Commercially available
meters include the Spectra, Brightness Spot Meter (Photo Research Corp.,
127 W. Alameda Avenue, Burbank, California), the Luckiesh-Taylor Bright-
ness Meter (General Electric Co., Instrument Division, 40 Federal Street,
West Lynn, Massachusetts), and the Macbeth Illuminometer (Macbeth
Instrument Corp., P.O. Box 950, Newburgh, New York).
2. Multiply the non-image brightness reading by 1.2 (to allow for screen-
reflectance factor).
3. Multiply by the brightness-ratio factor (5, 25, or 100 - see table,
page 13) for the class of material being projected.
4. Multiply by square feet of image area.
Method II - For determining the light output required of the projector.
1. Under the projection conditions listed in Method I (projector capped),
measure the non-image light falling on the screen. For use in making
measurements of this type, foot-candle meters can be borrowed from most
electric power companies: also, some photoelectric exposure meters are
suitable.
2. Multiply by the factor for the class of material being projected (5,
25, or 100).
3. To obtain the light output required of the projector, multiply by the
square feet of image area. (No allowance is made for screen reflectance.
This method assumes similar reflectance for image and non-image light.
The error resulting from this assumption may be great with highly direc-
tional screens.)
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Method III - For making a rough estimate of the lumen output required.
1. Estimate non-image brightness according to these categories:
0.1 foot-lambert:
In a well-darkened room, with exit and aisle lights turned on and the
projector running but capped, people at the screen location are visible
primarily as silhouettes. At the screen surface, newspaper headlines set
in type one inch high are readable with difficulty from a normal reading
distance.
5.0 foot-lamberts:
On a sunny day, in a classroom with two layers of tan shades or tightly
closed "regular" venetian blinds; the text of a newspaper at the screen
surface is readable with some eyestrain.
10 foot-lamberts:
In a classroom with unshaded windows lighted by light from the sky or
by direct sun on single-thickness tan shades, reading is fairly easy for
newspaper-text type. These estimates assume that there is good screen
placement in the room; that, if a beaded screen is used, it does not face a
light source; and that, if a matte screen is used, no light from nearby
sources is allowed to fall directly on it.
2. Multiply the estimate by the brightness factor for the class of ma-
terial being projected (5, 25, or 100).
3. Multiply by the image area (in square feet).
(This method is not accurate enough to justify an allowance for screen
reflectance.)
A special case of this brightness-ratio concept is encountered in rooms
where the non-image brightness of the screen falls below 0.1 foot-lambert
and the brightness of other surfaces within the field of view is appreciably
lower. The minimum acceptable image brightness then depends on the a-
mount of light needed for good seeing rather than on the ratio of image to
non-image brightness. Its minimum value is about 5 foot-lamberts, although,
in some instances, such as outdoor projection on large screens, levels of
2 or 3 foot-lamberts are tolerated. In general, it is better to show a slightly
smaller image and bring the level up to 8 or 10 foot-lamberts.
It must be clearly understood that levels below 5 foot-lamberts are
marginal and are not to be recommended where a screen image is being
viewed for informative purposes. At low stray-light levels, it is usually
possible to avoid excessive contrast for Class B and C materials by in-
creasing the light in the room. If this is done in such a way that little extra
light falls on the screen surface, but instead illuminates the wall against
which the screen image is viewed, eye comfort is generally improved. The
position and intensity of the supplementary light should be such that none
of the surfaces it illuminates approaches the brightness of image highlights.
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Supplementary light is especially important with Class C materials. A
bright screen image of Class C material in a completely darkened room
results in a dazzle which reduces legibility.
7. THE PROJECTOR-LENS-LAMP COMBINATION
When the required lumen output of the projector and focal length of the lens
are determined, the equipment most nearly meeting those requirements
should be selected.
The table on page 19 gives
projectors.
Adapting to Requirements
Obviously, the projection equipment available for a given situation will not
always meet the exact lumen-output requirements for good projection.
In order to have adequate image brightness, lumen output should be at
least as great as specified.
A reasonable excess in lumen output is permissible. Because of the
variable image brightness (depending on the viewing angle) of beaded
screens, a greater excess can be tolerated when a matte or lenticular
screen is used than when a beaded screen is used.
An "overage" of 50 percent in lumen output should be the maximum for
a beaded screen. This will give an image approximately 4 1/2 times as
bright, near the projection axis, as the desired brightness 20 degrees from
the projection axis.
For a matte or lenticular screen, the light output may be 4 times that
desirable, giving an image brightness from all viewing angles about 4 times
as bright as specified.
Image Not Bright Enough
The difficulty most often recognized is insufficient light output. As sug-
gested on page 8, one possibility for producing brighterand smaller images
is to move the projector closer to the screen. Halving the distance will
increase image brightness 4 times. However, this solution is satisfactory
only when the material being projected is so designed that the information
it contains can be discriminated satisfactorily in the smaller size (see
page 8).
If the lamp in the projector has a life rating of more than 10 hours or is
smaller than the maximum wattage recommended for the projector, light
output can be increased by using a 10-hour lamp of maximum permissible
wattage. Often 10-hour lamps smaller than 1000 watts are not regularly
stocked by dealers. A lamp which is either larger than recommended or
rated at substantially lower voltage than the existing line voltage will in-
crease the light output, but it is also very likely to damage film and may
cause the condenser lenses or heat-absorbing glass to crack. Heat-
absorbing glass should not be removed to increase illumination, because
its removal will cause film and equipment damage.
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Screen characteristics can be utilized to obtain a brighter image. If it
is possible to confine all viewers to an area no more than 10 degrees off
the projection axis, the least bright image seen on a beaded screen will be
approximately twice as bright as that seen either on a beaded screen from
20 degrees off the projection axis or on a matte screen from any angle.
When stray-light levels are high, locating the screen in the room so that
it is seen against the darkest part of the room will help. If a beaded screen
is used, stray light from the audience direction may be an especially
serious problem.
a It may also be possible to increase image brightness and obtain better
rejection of stray light by using a metallic screen - either a flat one or
one with ribs or lenticules. Most portable metallic screens are highly
directional. The projector and screen must be placed and aimed very care-
fully to take advantage of their special characteristics and to obtain good
images with even brightness.
If a visual test of the equipment specified does not demonstrate satis-
factory brightness, check these common causes for reduced brightness:
1. When the equipment is operating, the line voltage at the projector
plug should be within 5 volts of the rated lamp voltage. A lamp rated at
115 volts produces 15 percent less light when the voltage drops from 115
to 110. At 104 volts, the loss is 30 percent. A light-weight extension cord
can easily cause such a voltage drop.
2. All equipment and materials in the optical system should be clean.
The optical system includes reflectors or mirrors, lamp envelope, con-
densing lenses, heat-absorbing glass, cover glasses or glass pressure
plates, the material being projected, the projection lens (all surfaces), and
the screen itself.
3. Old and darkened projection lamps produce less light. A lamp im-
properly centered or not locked in position may reduce brightness and
cause uneven illumination.
4. Unusually dense (dark) transparencies, of course, give less bright
images. Some photographers consistently and intentionally produce dense
transparencies, often because they project them regularly on a small
screen with a powerful projector. In such a situation, properly exposed
transparencies may look "washed out." Thus, the photographer may under-
expose reversal film to obtain denser-than-normal transparencies which
look well with his own equipment, but are too dense for standard projection.
5. Even though they are clean, old projection screens may have become
yellowed or darkened so that they do not perform well.
Image too Bright
While the need for greater light output is usually recognized, the need for
reducing light output can be as great and may be neglected. Over-bright
images may cause a dazzling effect and make flicker more apparent in
motion pictures. The problem of too much brightness is encountered most
often with Class C materials.
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A good means of reducing light output is the substitution of lower-wattage
lamps. It is usually possible to use a 300- or 500-watt lamp in a projector
designed for a 750- or 1000-watt lamp.
Reducing lamp voltage or using a lamp intended for a higher line voltage
is a satisfactory way of reducing light output, up to a point. Reducing the
lamp voltage 10 or 15 percent will reduce light output 30 or 40 percent, and
prolong lamp life 4 or 5 times. Reducing the lamp voltage more than about
15 percent may cause an objectionable shift in color quality toward yellow
and red. Only the voltage on the lamp should be reduced; reducing the volt-
age to a projector motor or amplifier below its minimum design voltage
may cause overheating, unsatisfactory operation, and consequent damage.
Raising the general room illumination will often serve the same purpose
rather than
htness ratio
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as reducing
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absolute image brightness, which is pertinent. This is especially useful in
reducing the dazzle effect of excess brightness in showing negative, or
"reverse"-text, slides.
The light output of a KODAK PAGEANT Sound Projector with a KODAK
SUPER-40 Shutter can be reduced about 30percentat sound speed by lock-
ing the shutter in the 3-blade position.
Lumen Output of Projectors Manufactured by the Eastman Kodak Co.
(See table on facing page.)
These figures are averages for projectors and lamps randomly selected.
Measurements were based on recommendations of the American Standards
Association, Inc., for determining projector light output. Each figure rep-
resents a number of projector-lens-lamp combinations and measurements for
each combination measured. Any individual measurement, of course, may be
expected to vary from the average. All figures are for lamps operated at
their rated voltages. All arefor lamps with a 25-hour life rating, except that
1000 and 1200-watt lamps hove a 10-hour rating. The lenses are all KODAK
projection lenses. Some projectors no longer manufactured are included be-
cause many are still in use.
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2x2 Slide Projectors
Projector
Mask Size
Lens
(in mm)
3" f/3.5
4" f/3.5
5" f/3.5
5" f/2.8
7" f/3.5
CAROUSEL with
23x34
465
610
640
750
710
DFW lamp*
38 x 38
-
1100
1200
1390
1280
KODAK 500, READY-
MATIC or SUPER-
23x34
440
575
550
750
500
MATIC, with CZA
38x38
-
950
900
1390
825
or DBJ lamps
CAVALCADE with
DFR lamps*
Universal condenser
23x34
325
425
415
525
500
38x38
-
-
705
750
840
135 condenser
23 x 34
465
605
590
750
710
SIGNET 500
23x34
-
-
585
650
600
with CZX lamp*
38x38
-
-
1030
1145
1040
17.5x23
-
-
270
300
275
*Use 60% of figures given for "Lo" switch position on CAROUSEL and CAVALCADE
projectors; 55% of figures given for SIGNET projectors with 300-watt lamps.
16mm Motion-Picture Projectors
2" f/1.6 with KODAK
Bifocal Converter
KODAK Pageant*
1Y2" f/2.0
2" f/1.6
3" f/2.0
4" f/2.5
1-5/8 2)4
750-w lamps
115-165
220-310
180-255
120-170
195-275
135-190
1000-w lamps
150-215
290-410
230-320
150-210
260-365
180-250
1200-w lamps
170-240
350-490
250-350
165-230
290-405
195-275
2-blade position. Use 1200-w lamps only in models designed for them.
EASTMAN 16mm, 2", 2%", 2-5/8", 3', or 4" f/1.5 Ions (With matching condensers,
lumen output is approximately the same for all lenses.)
Model 25
Mode125B
1000-w tungsten lamp
450
595
1200-w tungsten lamp
515
680
Strong arc, 46 amperes
with filter (for B&W films)
2000
2400
without filter (for color films)
2500
3000
ANALYST 11 Projector, 2" f/1.6 lens -750-w lamp, 130lumens; 100-w lamp, 190 lumens
. 8mm Motion-Picture Projectors
Current and recent KODAK 8mm Movie Projectors have light outputs ranging from
about 80 to 160 lumens, depending on the projector, lamp, Ions, and the switch set-
tings on some models. With a projector light-output of 80to 100 lumens and a matte
screen in a well-darkened room, a satisfactory image can be 3 or 4 feet wide; with
130 to 160 lumens and a lenticular screen, 6 to 9 feet wide. For further considera-
tions, see KODAK Pamphlet S-14, What Can You Do with 100 Lumens?
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Sales Service Division
EASTMAN KODAK COMPANY ? ROCHESTER 4, N.Y.
Foundation for Effective
Audiovisual Projection
7-62 Minor Revision ^
238-L-GLP-AX
Printed in the United States of America
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