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1954-55 Theatre Catalog, 12th Edition, Page 290 (254)

1954-55 Theatre Catalog, 12th Edition
1954-55 Theatre Catalog
1954-55 Theatre Catalog, 12th Edition, Page 290
Page 290

1954-55 Theatre Catalog, 12th Edition, Page 290


7, 8 8. 9mm. "SUPREX" CARBONS





9, 10 & llmm. H.l. CARBONS




10 20 15 30

Possible Protective Means

In some cases, these lamps can project more light and heat onto the film than can be accommodated without some suitable cooling means, This article does not specify means of protecting the film from high levels of radiant energy flux; it points out, however, that the use of infra-red absorbing filters, infra-red retiecting filters, controlled air-blast and the use of a water-cooled film gate have all been asserted to provide some protection to the film. Such protective means may require the sacrifice of a small portion of the screen light and will correspondingly change the lumen values of Figure 1.

The light requirements of the new projection systems may be analyzed in correlation with these latest developments, beginning with a restatement of the American Standards Association indoor theatre standards, which recommends a screen brightness of 9 to 14 foot-lamberts with the projector running and no film in the gate.

Screen Widths. Light

The data of Figure 1 have been used to calculate the widths of screens which can be illuminated to the aforementioned ASA standards, with a projection shutter of 50 per cent transmission, a projection room port glass of 90 per cent transmission, and a projection screen of 75 per cent reflection factor,

The resultant screen widths are shown in Figure 2. The lower ends of the screen width ranges shown in Figure 2 belong to the smaller and lower power carbon trims and to the maxinmm recommendcd scxeen brightness; While the larger screen widths pertain to the larger and higher power combinations and to the minimum recommended screen brightness.

No allowance has been made for light losses that may occur with heat filters which may be needed under some cone ditions to prevent heat-on-film troubles,

13.6 mm.

30 40 45 60


FIGURE 2 shows the size of the screen capable of illumination to indicated screen brightness at the center of the motion picture screen.

The data of Figure 2 will need to be correspondingly altered in case there are any additional light losses beyond those assumed. For example, a 10 per cent loss in light will reduce the indicated screen widths about five per cent.

Outdoor Theatres Pose Problem

Reference to Figure 2 shows that Suprex carbon trims are capable of illuminating screens approximately 16 to 30 feet wide at maximum light. Rotating-type redector lamps increase these screen widths to 23 to 33, and 26 to 37 feet with standard carbons. Generally speaking, the rotating-type condenser lamps are capable of illumi> nating about the same width screens as the rotating-type redector lamps.

The foregoing discussion shows the present difficulty of lighting screens of 50 to 70 feet width, common in outdoor theatres, to the standard of 9 to 14 foot-lamberts applicable to indoor theatres. However, the screen brightness requirements of outdoor theatres are not as precisely known as are those for indoor theatres, because of the widely variable physical conditions. Just what level of screen illumination can be obtained on these large screens depends upon the maximum amount of light obtained from the projection system.

Increasing the indicated screen widths by 50 per cent, without changing the present standard ratio of height to width, corresponds to a screen area 2 25 times greater. Such a screen can be. iiluminated by the combinations of Figure 1 to a center brightness of 4 to 6.2 footlamberts. These screen brightness limits have been chosen not because of their ultimate desirability but rather because they are in the range being obtained by some outdoor theatres. The rotating-type reflector lamps and the rotating-type

AMPERES 40 - 75



lO 8. ll mm. "ULTREX" CARBONS




13.6 mm. "ULTREX" CARBON

I25 -180 265 - 290


condenser lamps can illuminate screens of 45 to 70 feet width to a screen brightness of four to six foot-lamberts.

Wide-Picture Requirements

Although the data contained in the tables are limited to projection from a standard 354nm motion picture film aperture of 0.600 inches by 0.825 inches and thus are not directly applicable to other film aperture sizes and picture aspect ratios, rough estimates can be made in some instances. For example, the outputs of the various 35mm film projection systems may be redistributed by optical means over various sizes and shapes of film apertures and projection screens, If this be accomplished with minor or known losses, the results expected can be closely approximated.

The requirements of CinemaScope, which employs a standard projection frame but a 2.66 to 1 picture aspect ratio, can be calculated once the information on the transmission and redection of the added accessories employed is known.

Except for the optical losses in the added anamorphic lens which functions to produce a two-fold expansion of picture width during projection, this expansion would produce a two-fold increase in picture area and reduce by onevhalf the available screen brightness obtainable with it normal unexpanded image. Therefore, the light requirements for the same screen brightness would be double those of conventional 35mm pictures on the same type screensthat is, if the CinemaScope aspect ratio of 2.66 to l is to be observed.

Screen Retiectivity Level

If suitable directional-type screens of higher reflection factor, with adequate uniformity over the audience area, can be obtained, the lumen output required to illuminate a given size screen to a specified brightness can be reduced proportionately. In the caSe of Cinema THEATRE CATALOG 1954-55
1954-55 Theatre Catalog, 12th Edition, Page 290