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504 NEW AMERICAN STANDARDS April
American Standard
Location and Size of Picture Aperture of 8-Millimeter Motion Picture Projectors
ASA
Rrf. V. S. Pal. Og.
Z22.20-1950
Revision of Z 22. 201941
•UDC 778.55
Page 2 of 2 Pages
The angle between the vertical edges of the aperture and the edges of normally positioned film shall be 0 degrees, ' Vz degree.
The angle between the horizontal edges of the aperture and the edges of normally positioned film shall be 90 degrees, ' V? 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 1 -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: In 8-mm. projectors the edge guide should bear on the edge of the film adjacent to the perforations. The other edge of the film usually is slit after processing and so is more likely to weave laterally with respect to the pictures.
The value of dimension C has been chosen so that film having a slight shrinkage when it is projected will be properly centered. This is the normal condition.
Note 4: The K dimensions are measured along the path of the film from the horizontal centerline of the aperture to the stopping position of the registration device. It is customary to provide a framing movement of approximately 0.025 inch above and below this nominal position. For any given projector, use the value of K corresponding to the location of the registration device.
If the film does not stop exactly where the film registration device leaves it, because of coasting or some other cause, a slight adjustment of the value of K will be necessary.
Note 5: "Optical axis of projector" is defined as the mechanical axis or centerline of the sleeve for holding the projection lens/ Except for manufacturing tolerances, it coincides with the lens axis.