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Visual Examination of 16mm Photographic Sound Tracks
By O. L. GOBLE
V,
ISUAL INSPECTION of the sound track on 16mm film can yield much valuable information, particularly with regard to the presence of processing faults. To enable large quantities of film to be inspected, a simple type of projection microscope has been specially constructed.
A magnified image of the sound track (X36 diameters) on a ground-glass screen can be viewed without eyestrain while the film moves through the gate. A graticule in contact with the screen enables rapid dimensional checks to be made, if necessary while the film is in motion.
The instrument has been in service for a considerable time, and it has been found that after a little experience an operator can examine considerable footage without fatigue.
Description of Instrument
The instrument is built on a wooden case, approximately 3 ft 6 in. high, which stands on the floor (Fig. 1). The film is
Communication No. 1560A from the Kodak Research Laboratories, Rochester 4, N.Y., by O. L. Goble, Research Laboratories, Kodak Australasia (Pty.) Ltd., Abbotsford 9, Melbourne, Victoria, Australia.
(This paper was received on April 24j 1953.)
fed manually through a gate which is located on top of the case. An image of the sound track, about 4 in. wide, is thrown onto the inclined ground-glass screen.
Figure 2 is a schematic diagram showing the layout of the optics, and is largely self-explanatory. The light source is a standard 10-v, 7.5-amp, exciter lamp. The projection lens is an //3.5 photographic objective, having a focal length of 2 in.
The enclosed mirror at the base is mounted so that it can be adjusted for final alignment.
Figure 3 is a photograph of the groundglass screen, showing the image of the sound track and the graticule. Distances from the film edge are shown in thousandths of an inch, while horizontal lines indicate the dimensional limits according to accepted standards. The film gate is adjustable so that the edge of the film can be lined up with the graticule, and it is important in the design of the gate that the sound-track edge of the film should not weave as the film moves.
This instrument was built only as an experimental model from readily available components; a new instrument based on the same principle, with many improvements, is at present being designed.
688
June 1953 Journal of the SMPTE Vol. 60