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Table I. Screen Areas and Light Fluxes in Some Cinemas on the Continent
Cinema
Seats
Screen size (picture width) Screen area, in ft sq m
Projection distance, m
Projection angle, deg
Light flux (ASA), 1m
Kapitol in Bern
720
19
4.2 X 5.6
= 23.5
34
17
3161
Urban in Zurich
1150
22
5 X 6.7
= 33.5
31.5
12
4506
Rex in Paris
3200
33
7.5 X 10
= 75
45
21
10087
Marignan in Paris
1800
40
9 X 12
= 108
33.5
23
14526
Le Regent in Neuilly
sur-Seine
1400
19
4.2 X 5.6
= 23.5
26
15
3161
Cineac des Ternes in
Paris
600
19
4.2 X 5.6
= 23.5
22
18
3161
Cineac in Strasbourg
500
16
3.5 X 4.7
= 16.5
21
23
2219
Royal in Rabat
1500
20
4.5 X 6
= 27
39
20
3631
Palazzo del Cinema in
Venice
1400
33
7.5 X 10
= 75
34
12
10087
Palladium in Copen
hagen
1400
27
6X8
= 48
35
5
6466
Asta at The Hague
1200
22
5 X 6.7
= 33.5
27
3
4506
Capitol at The Hague
1000
20
4.5 X 6
= 27
23.5
17
3631
enable us to produce very powerful light fluxes which are sufficient even for the screens of the largest theatres. A further advantage lies in the possibility of adapting the optical layout of the system to the architectural necessities of the various theatres and to install the projector in the existing booth, as it is commonly done with ordinary cinema equipments.
The brightness Bs of the screen required in good cinema projection amounts to about 10 ft-L. For a given screen area A' the required light flux can be computed as follows
• 078 A>B>
(1)
The factor 0.8 is the coefficient of remission of the screen, as for an ordinary medium quality cinema screen with diffuse reflexion.
Table I states the screen areas used in some well-known cinemas on the Continent. The light flux necessary for these screens according to Eq. 1 is given as well. The table shows that 0, = 10,000 1m are necessary for the largest theatres.
This means an enormous light-flux in television, and we have now to consider how it can be produced.
We shall assume, without going into details now, that the projection of our picture follows exactly the same principles as cinematographic projection. Only we have the Eidophor surface instead of the film and we shall therefore speak of the Eidophor picture. In Fig. 1 the Eidophor picture of the area A lies in the plane S, the projection screen of the area A' in the plane Sr. The total light flux that falls on the screen is equal to the light flux passing the lens. From every point of the Eidophor picture a light-pencil of half the opening angle, 2 0, hits the lens; thus the light flux can be computed to be
(2)
B being the brightness of the Eidophor picture, and sin 6 being ~ D/2f,
(3)
(D/f)~l is called the /-number of the lens.
346
April 1953 Journal of the SMPTE Vol.60