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1950 NEW AMERICAN STANDARDS 499
American Standard
Location and Size of Picture Aperture of 16-Millimeter Motion Picture Projectors
R.-t. V. S. Pal. Og
Z22.8-1950
Revision of Z22.8-1941
and Z22.14.mi
•UDC 778.55
Page 2 of 3 pages
The angle between the vertical edges of the aperture and the edges of normally positioned film shall be 0 degrees, ' Vi degree.
The angle between the horizontal edges of the aperture and the edges of normally positioned film shall be 90 degrees, -' Vi degree.
Note 1 : Dimensions A, B, and R apply to the portion of the image on the film that is to be projected; the actual opening in the aperture plate has to be slightly smaller. The exact amount of this difference depends on the lens used and on the separation (dimension G) of the emulsion and the physical aperture. To minimize the difference in size and make the image of the aperture as sharp as practicable on the screen, G should be no larger than is necessary to preclude scratching of the film. When the reduction in size from the image to the actual aperture is being computed, it is suggested a 2-inch f/1 .6 lens be assumed unless there is reason for doing otherwise.
Note 2: The limiting aperture is shown as being between the film and the light source so that it will give the maximum protection from heat. If other factors are more important, it may be on the other side of the film.
Note 3: The edge guide is shown on the sound-track edge. This location for it has the advantage that the rails bearing on the face of the film along this edge and also between the sound track and picture area can be of adequate width. Disadvantages of this location for the edge guide are that, because film shrinkage and tolerances affect the lateral position of the perforations, the pulldown tooth must be comparatively narrow and will not always be centered in the perforation. Also, in some prints the sound-track edge is slit after processing, in which case there is likely to be some lateral weave between this edge and the pictures.
The guide can be on the other edge, adjacent to the perforated edge of sound film. With the guide at this edge, the width of the pulldown tooth does not have to be decreased to allow for shrinkage. Also, slitting the sound-track edge after processing will not introduce lateral unsteadiness. However, because of variations introduced by shrinkage of film, this location for the edge guide has the important disadvantage that it makes extremely difficult the provision of rails of adequate width to support the