American cinematographer (Jan-Dec 1941)
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Projecting
Sound and Silent rums
By James A. Sherlock
WHEN threading film into a projector it should be remembered that as the film passes the gate it should be upside down and wrong way round, as from left to right. Thus when facing the screen, the top of the picture should face the floor and the titles read from right to left. Below is a table showing which side should face the screen when various types of film are being projected:
Reversal original . . Emulsion or dull side Reversal duplicate . Base or shiny side Positive print from
negative Base or shiny side
Dupe from a rever J sal made by taking a negative and making a print Emulsion or dull side
Kodachrome and
Agfacolor original . . Emulsion or dull side
Dufaycolor Base or shiny side
Kodachrome duplicate Base or shiny side
Reversal dupe from
positive print Emulsion or dull side
Reversal dupe from
reversal dupe Emulsion or dull side
Projection-lenses
Standard cine projection-lenses supplied by manufacturers are usually twice the focal length of standard cine
camera-lenses; thus a 1-inch lens is provided with 8mm. projectors, and a 2inch lens with IK mm. projectors. These lenses will be found suitable for home use, but other focal length lenses are available for most popular projectors.
The accompanying table indicates the sizes of pictures obtained with various lenses at given distances. It should be noted that, under given conditions, as the distance between the screen and projector increases, the brilliancy of the picture decreases.
Projection lenses should be kept scru' pulously clean and free from oil and dirt in a manner similar to that recommended for camera lenses.
Placing Projector and Screen
The projection lens should be placed above the heads of the audience to permit an unobstructed view to those seated in the rear. The projector should be seated on a very firm base and cushioned on a piece of sponge-rubber or felt which has the effect of absorbing noise. The bottom of the screen should be about 4 ft., 6 in. from the floor.
If the projector is moved or jolted when the lamp is burning its filament is liable to collapse, therefore the machine should be placed on a firm stand before it is used, and the lamp turned off before the projector is moved.
Screen Types
There are three types of screens commonly used for home projection:
Type (1) is the popular glass-beaded screen, composed of minute glass beads covering a white cloth. This screen is easily damaged and therefore should be handled with great care. It is most suitable for audiences seated in a narrow room because pictures viewed from an angle of more than 15 degrees from the projecting angle are affected by refraction. The advantage to be gained by using glass-beaded screens is that they do not require a screen illumination of more than 8 foot-candles.
Type (2) has aluminum sprayed on a smooth surface. These screens require only 4 foot-candles for their illumination, but like the glass-beaded screen, the audience should be seated within a viewing angle of 15 degrees from the screen, because they reflect light more strongly within this angle, outside of which the screen-brightness falls off rapidly.
Type (3) when sufficient projection light is available the best type of screen to use is a dull white-surfaced screen made of opaque cloth or possibly some other solid material such as wood, surfaced with a matte white pigment. This type is suitable for use in square rooms where some of the audience might be seated at a wide angle from the screen. Unfortunately these screens require a
Projected Picture Sizes obtained villi Filmo Projection Lenses
Lens
Tocal Sth
Distance in Feet From Screen
Len
8'
10'
12'
16'
20'
.
32'
36'
40'
50'
64'
75'
100'
125' 150'
16 mm. Projector
On 8 mm. Projector
Width of Picture
H"
■no"
6'0"
7'2*
9' 7"
12'0"
W
1 ii
5'0"
6'0"
8'0"
lO'O"
12'6"
1"
:;n
3'9"
4'6"
6'0'
7'6'
9'4"
ll'll"
13'5'
14'11'
%
w
2'0*
2'6"
3'0"
4'0"
o'O'
6'3'
8'0'
9'0'
10'0'
12 6
r
2"
1'6*
1'10'
2'3"
3'0'
3'9"
4'8'
6'0'
6'9'
7'5*
9'4'
ll'll'
14'0'
a
2' 2
1'2'
1'6'
1'9"
2'4"
3'0"
3'9'
4'9'
5'4"
6'0"
7'6'
9'7'
11'3'
15'0'
19'8'
\Vi
y
IT
1'6'
2'0'
2'6'
3T
4'0'
4'6'
5'0'
6'3'
8'0'
9'4'
12'6'
V /
l'O"
1'3"
1'8"
2'8'
3'5"
3' 10"
4'3'
5'4'
6'11*
8'0'
10'S'
13'4'
16'0'
t
IT
1'6'
no'
2'4"
3'0'
3'3'
3'9'
4'8'
6'0'
7'0'
9'4'
11 '8'
M'O'
122
March, 1941
American Cinematographer