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1954-55 Theatre Catalog, 12th Edition, Page 291 (255)

1954-55 Theatre Catalog, 12th Edition
1954-55 Theatre Catalog
1954-55 Theatre Catalog, 12th Edition, Page 291
Page 291

1954-55 Theatre Catalog, 12th Edition, Page 291

Scope projection, if a directional screen can be obtained with twice the reflection factor of a normal matte screen, the two-fold increase in screen area produced by the anamorphic lens would be approximately compensated for and the existing screen brightness with the same projection lamp would be essentially thesame. '

Requirements of 3-D

The stereoscopic motion pictures of the type being shown in this country employ separate lamps, projectors and 35mm films for the projection of rightand left-eye pictures each polarized at right angles to the other; a metallictype screen is used and polarizing viewers are worn by the audience. The light losses will depend upon the transmission factors of these various stereoscopic components, which vary with the particular design and with technical characteristics.

Typical transmission values must be discussed here, realizing that these may be altered by future design changes during the evolution of stereoscopic motion picture projection.

Present-day polarizing materials are reported to have a typical light transmission value of 40 per cent, The viewing spectacles, likewise, are reported to have a transmission of 80 per cent. At the present time the screen redection factor of suitable metallic-type screens is more uncertain and subject to Variation depending upon the particular type employed. A general characteristic of the metallic-type screen is an inverse relation between maximum screen refiection factor and uniformity of screen brightness over all angles of view in the theatre.

Directional Screens

Consequently, a compromise is chosen between high screen reflection factor with undesirable directional variation on the one hand, and lower screen reflection factor with better directional characteristics on the other. A redection factor of 125 per cent is typical for a number of screens, meaning that the redected screen brightness measured in foot-1am berts is 125 per cent times the light intensity in foot-candles incident on the screen.

The combination of this screen redection factor with the transmission values of the polarizer and the viewer results in an overall light transmission of 40 per cent (1.25 x .40 x .80 = 0.40) compared with the 75 per cent refiection factor assumed for the matte screen used for conventional projection.

The stereoscopic projection components therefore reduce the final screen brightness to a value equal to 53 per cent (40 divided by 75 = 0.53) of that with the same projection system with a matte screen without stereoscopic accessories. In other words, the screen brightness requirement is approximately

double that for conventional 35-min projection. FIGURE 3 is screen illumination with carbon urc 35mm film-0.600 by 0.825 inch aperture.


The fact that separate projectors are employed for the right- and left-eye pictures does not alter the basic facts of this analysis, for each projector is subjected to this approximately 50 per cent loss in brightness and contributes only to the brightness and picture observed .by one eye, and the composite picture brightness visible to both eyes is still equal to that furnished by the individual projectors to each of the observers eyes.

Should efforts to produce screens with higher reflection factor and with adequate uniformity of brightness over the theatre viewing angles be successful, then the final screen brightness figure will be increased with a corresponding

decrease in the required amount of projection light. CONCLUSION

The foregoing discussion emphasizes the need for more projection light. The

revolutionary techniques are still new, and since it is not practical to develop and control everything all at once, immediate perfection cannot be expected. The new carbons which have been developed will produce considerably more screen light; their successful utilization, however, will require suitable lamps and other projection equipment.

For the present, however, acceptable levels of screen brightness for these new systems are within reach, provided the equipment necessary to operate the higher capacity carbons is installed; and provided the entire projection system. including lenses, mirrors, condensers, and port glasses, is in exact adjustment and in good clean optical condition.

'l'"Srreen Illuminalion Wit/7 Carbon Ant Motion Pirlme Projection Synem,H by R. I. Zaraky, C. I. Gertixcr, and W. W. Lozier; Journal of SMPE, 48: 73-81, January, 1947.

*Tbe Iermi "Hiilex," "lUllrex" and "Supra" an trade-mark; of Umon Carbide and Carbon Corp.


CARBONS Approxp I clrbon Positive Negalive An 80% dm' M'x' I'd"; $2.5m); Lamp own-I Screen % Scrcen % Type Type amp rolls sys. lumensl dial.2 Iumens' dist. Poi. Neg. Non-Rotating, Refleclnr-Type Lamps-"One Kilowau" d-c Trim 7-mm X 12 or 11 in. 6-mm X 9 in. Orolip C 40 27.5 11% in. (lief/2.5 5.900 80 6.500 65 5.8 3.4 Suprcx mirror Non-Routihg High-lniensily Trims 7-mm X 12 or 14 in. 6-mm X 9 in. Orolip C 42 36 14 in. dia [/23 7,250 80 8,650 60 7.6 3.8 New Suprex mirror 7-mm X 12 or 14 in. 6omm X 9 in. Orolip C 46 38 14 in. dis f/2.3 8,150 80 10.000 60 9.3 4.0 New Suprcx mirror 7-mm X 12 or 14 in. 6-mm X 9 in. Orolip C 50 40 14 in. dia [/23 9,200 80 11.700 60 11.6 4.3 New Suprex mirror 8-mm X 12 or 14 in. 7-mm X 9 in. Orolip C 60 36 14 in. dis [/23 10,300 80 11,000 65 9.0 3.8 Suprex mirror 8

NOTE: Values in nsnnlhcsea Ire EnllmIled or obtained from limited


I Screen lumen figure is [or syslcms willl no shuuur. Elm or fillers of my kind: measured with 5-in. ELF. //2.0 and [/13 projcelion lenses.

2 % distribution rrfen up nnio oi liglu inlenuity n side of screen to Ilul u the cenler.

' 5 Muimum light is vnlue willl sy'alem adju-Ied Io produce maximum light

intensity .1 the corner a! [he screen.

i Experimental carbons burned with shun prulrusion in experimcnlll water-cooled silver jaws.

1954-55 Theatre Catalog, 12th Edition, Page 291