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1954-55 Theatre Catalog, 12th Edition, Page 312 (276)

1954-55 Theatre Catalog, 12th Edition
1954-55 Theatre Catalog
1954-55 Theatre Catalog, 12th Edition, Page 312
Page 312

1954-55 Theatre Catalog, 12th Edition, Page 312

the difference between these limits, the better will be the conditions for obtaining good quality on the projection screen. Whenever these limits are less than 300:1, picture quality for normal density prints will begin to change. A decrease in these limits to less than 3021 results in almost total degradation of the screen image. For these last conditions, you may rightly question the visual value of any motion picture for telling a story or educating a group of people.

Data in Figure 1 show how 16 observers judged the picture quality of several light, normal, and dark 35mm motion picture scenes as they were viewed at various percentage levels of stray-light brightness. Judging was done by numbers which represented the various quality classifications noted on the left side of the graph.

5-4 represents excellent to good quality

4-3 " good to fair F 3-2 " fair to poor " 2-1 " poor to useless "

The classification of light, normal, and dark scenes is the result of analyzing data from many motion picture prints, both black and white and color, which Were selected at random over the last five years. The majority 'of the scenes examined were obtained from actual 35mm theatre release prints, representing films from many differnt studios. Measurements were made on all these prints to obtain data concerning the maximum density, minimum density, face density, and average density which was used as a further guide in classifying the special scenes selected for the stray-light judgings. The results of these measurements were later compared with those reported by C. M. Tuttle in his 1935 paper, ffDensity Measurements of Release Prints."a These recent results indicate that the average projection density of both black-and-White and color prints have increased somewhat

FIGURE 1 shows audience reaction to stray light. Quality rating of projected pictures at various levels of stray light by 16 viewers twice.

over that reported by Tuttle. The most noticeable change observed was that the average maximum density of theatre release prints is now approximately 3.0 as compared to the 1935 results of 2.4. It should be noted that during the viewing of the various scenes at different stray-light levels, the darker scenes were found to suffer the greatest loss in quality for any given stray-light level compared to the scenes classified as light or normal. This result is common knowledge to the drive-in theatre owners where the screen quality of dark murder-mystery scenes is sometimes quite objectionable on a bright moonlit evening. A dotted line has also been added to the graph in order to represent the "average print." This line will serve as the standard for picture quality vs. the stray light in the illustrations to follow.

The range in stray-light conditions found in Figure 1 is known to exist at variolls times during the projection of motion pictures on outdoor theatre screens, as well as in poorly-darkened classrooms and auditoriums. It is hoped that this information will bring about a better understanding of how the screenbrightness and stray-light problems affect the picture quality of the projection screen.

Damage Picture Quality

The sources of stray-light damage to picture quality can usually be limited to one or more of the following:

1. Darkened room admitting unwanted light from outside the room or from unsuitable light fixtures in the room.

2. High reflectance of the projection room walls and ceiling which reflect the screen light falling upon them back upon

the screen. This effect from light-colored surfaces may be quite pronounced in narrow rooms and rooms with low ceilings, whenevef the screen occupies a relatively large area at one end of the room, or is so located that the picture area is very close to the walls or ceiling.

3. The light produced by lens flare. In the past few years, the effect of lens flare has been reduced considerably by coating projection lenses, and it is not as great a source of stray light on the screen as formerly. For some lenses, the effect of coating has been to reduce the flare light from the lens by more than two times. Even so, scratches, dust, and finger prints on projection lens surfaces may cause a large amount of flare light. For outdoor theatres, dust and dirt on projector lenses must be removed at frequent intervals. Great care should be taken in this operation, because the high grit content in the dust will easily damage the lens surfaces.

4. Where fairly long distances are involved between projector and screen, scattering of light from the projection beam by moisture and dust particles in the air gives rise to non-image-forming light which may set a minimum straylight level on {the screen below which further modification in theatre design and optical equipment cannot be effecc tive.

5. Moonlight, skylight, and other sources of illumination add additional stray-light problems for the outdoor or drive-in theatre screen.


The upper curve in Figure 2 represents the general tone reproduction for a reversal color print whenever it is projected on a screen free from all stray light. For this condition, a projected color picture matches very closely that

1954-55 Theatre Catalog, 12th Edition, Page 312