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1952 Theatre Catalog, 10th Edition, Page 304 (268)

1952 Theatre Catalog, 10th Edition
1952 Theatre Catalog
1952 Theatre Catalog, 10th Edition, Page 304
Page 304

1952 Theatre Catalog, 10th Edition, Page 304

detrimental effect on the screen image quality.

Proiecfion for Increased Screen Brightness

In recent years much interest has been shown in the problem Of obtaining higher screen illumination, particularly for use in drive-in theatres and for indoor theatres using very large screens. Increased illumination has been made possible by developments in high speed optical sys tems and new types of carbon arcs. With the increase in the screen illumination, there has been a corresponding increase in the temperature of the film at the aperture. The film performance places a limitation on the maximum light available for screen illumination, since as the film is heated to higher temperatures a point is reached beyond which satisfactory projection becomes difficult.

One of the first effects noted in the film as projection intensity is increased is an embossing of the frames and of the image within each frame. When examined by reflected light, at an angle nearly coincident with the plane of the film, each frame can be seen to stand out like a small cushion and frequently the image itself appears as though it were carved into a small plaque, as shown in Figure 33-F. Most film, after having been projected, shows some embossing and the extent of this embossing increases with the light source intensity. This embossing, however, even when severe, does not impair the screen image quality, although when embossed film is spliced to unembossed film it may be necessary to refocus slightly at the splice.

As the light source intensity is increased still further, the film may, in many cases, show a discoloration of the image. This discoloration is not noticeable when the picture is projected upon the screen but when the film itself is examined against a piece of white paper, the frame areas show a distinct sepia tint. NO real danger to the print exists, however, as a consequence of this effect, since it is still capable of giving a top quality screen image.

However, if the intensity is increased still further, an in-and-out-of-focus effect may be produced on the screen and the film may even become blistered from the intense heat. The in-and-out-of-focus effect usually begins during the second or third projection under conditions where the intensity is excessive. When this effect occurs, the focus shifts so rapidly from frame to frame, that it becomes impossible for the projectionist to keep the picture on the screen sharply focused at all times. At theSe dangerously high intensities it is possible to blister the print so severely that it is no longer usable. Two examples of blistered film are shown in Figure 34. At the early stages of blistering small bubbles occur between the emulsion and the base of the film and these areas have a dirty, grainy appearance. At later stages the bubbles break through the emulsion surface and appear as white spots with burnt edges. Blisters can be detected by examining the film by reflected light, at an angle close to the plane of the film, in which case they

appear as tiny bubbles in the emulsion surface. More severe blisters can be seen from the base side of the film and have a whitish appearance. Heavy blis l tering, such as that shown in the lower

illustration of Figure 34, can be seen from any angle. Blistered prints cannot be repaired or restored in any manner for further use in projection.

Several methods have recently been proposed for extending the safe limit for increased screen illumination. One method utilizes heat absorbing glass between the arc and the film. This filters out some of the infra-red portion of the arc spectrum, since this only increases the temperature of the film and does not contribute to higher screen illumination. Many theatres employing higher amperages use a blower system for directing a current of air to the surfaCe of the heat absorbing glass in order to keep the glass itself at a lower temperature. Air cooling has also been applied directly to the film in the aperture by means of high velocity air jets. These jets actually cool the film and permit it to perform satisfactorily in a hotter beam than could normally be tolerated. For the projector itself, Water cooling has in some instances been applied tO the gate in order to reduce the temperature of the metal in contact with the film and to make projector threading more convenient.

For further information regarding the problems associated with high intensity projection and the methods employed for obtaining higher screen illumination, the following references should be consulted:

CARVER, E. K., TALBOT, R. H., and LOOMIS, H. A., "Effect of High Intensity Arcs Upon 35mm Film Projection," J. Soc. Mot. Pict. Eng., 41: 69-87, July, 1943.

CARVER, E. K., TALBOT, R. H., and LOOMIS, H. A., uFilm Distortions and Their Effect Upon Projection Quality), J. Soc. Mot. Pict. Eng., 41: 88-93, July, 1943.

JONES, M. T., ZAVESKY, R. J., and LOZIER, W. W., ffA New Carbon Arc for Increased Light in Studio and Theatre Projection," J. Soc. Mot. Pic. Eng., 45: 449-458, December, 1945.

TALBOT, R. H., "Some Relationships Between the Physical Properties and the Behavior of Motion Picture Film," J. Soc. Mot. Pict. Eng., 45: 209-217, September, 1945.

ZAVESKY, R. J., GER'I'ISER, C. J., and LOZIER, W. W., "Screen Illumination with Carbon Arc Motion Picture Projection Systems," J. Soc. Mot. Pict. Eng., 48: 73-81, January, 1947.

ZAVESKY, R. J., NULL, M. R., and LOZIER, W. W., ttStudy of Radiant Energy At Motion Picture Film Aperture," J. Soc. Mot. Pict. Eng., 45: 102-108, August, 1945.

KOLB, F. J., JR., "Air Cooling of Motion Picture Film for Higher Screen Illumination," J. Soc. .Mot. Pict. Eng., 53: 635-664, December, 1949. *1 ' 4,

When maximum light output is desired from,jprojection equipment, it is necessary to make certain that all optical elements of the projector are clean and adjusted [properly and that the lamp is Operating at its highest efficiency.

The are current should never be increaSed arbitrarily without first ascertaining by test whether such procedure is liable to cause film damage.

Final testing of any installation of projection equipment should include the projection of test film to insure that the. equipment is operating properly and that misadjustments will not cause damage to prints furnished to the exhibitor. The following test procedure is recommended for film testing of projection equipment:

Film: Eastman Fine Grain Release Positive Safety Film, Type 5302.

Processing: Normal. The image should contain dark areas distributed about the frame and especially near the center.

Age: Film can be used for only one test. Previous projection makes the film test less critical, and the results difficult to interpret. '

Storage: Film must be used within six months of the processing date. The processed test film should be kept in a closed metal film container.

Test Loop: Nine-foot loops are recommended. Splice a fresh 9-foot piece into a loop, and thread into the projector. Magazine doors will probably have to remain Open, and the loop may have to be guided by hand to prevent its twisting off the sprockets.

Test: Strike the arc and burn-in at least one minute. In general, set to the maximum operating current, condenser setting, screen light, etc. available to the projectionist. Start projector, Open dowser and change-over. If possible watch the projected picture on the screen, refocusing frequently as needed. Count 30 to 50 revolutions of the loop (three to five minutes projection). Stop the projector and remove the film for examination.

Examination: Look first for any bliso tering of the film. Examine the emulsion side by reflected light at an angle nearly coincident with the plane of the film for any small raised blisters. A hand magnifier is helpful but not essential. Severe blisters will show on the screen and on the film as white pinholes in the image. Any sign of blisters indicates that the arc intensity is too high or that failure of the film protective devices has occurred. The exhibitorsi prints are in danger of damage under any conditions which will produce blisters on the test loop.

Look also for excessive scratching, perforation damage, or other evidence of faulty mechanical adjustments in the projector.

-If the, test loop is undamaged, then the projection equipment will handle normal films safely (when operated at the arc current, condenser settings, etc. at which the test was made).


It is a well established fact that film damage does occur and that it may be caused in a variety of ways and in any one of the various places where film is handled. This survey has been presented however, with the sole purpose of helping to reduce unwarranted film damage and in no way is it intended as a condemnation or criticism of any single individual or group of individuals.


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1952 Theatre Catalog, 10th Edition, Page 304