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Fig. 3. Schematic of system — top view.
port, so that the projectionist can see the screen and the meter at the same time. Figure 2 shows the three basic units of the second model — the optical flat and brass attenuator mounting, the metal-encased photocell, and the microammeter. The optical flat occupies the space normally used by the thread-up lamp when it is lowered for threading up. The lamp was repositioned so that it missed the optical flat when lowered. The perforated brass attenuator slides into a slot cut just ahead of the photocell housing. The edge of the attenuator is visible in the figure. There is a ground glass immediately behind the attenuator to break up the light through the pin holes, and thereby avoid any local "hot spots" on the surface of the photocell. Figure 3 is a schematic drawing of an arc projector with the unit installed. In operation, the system requires only
a 5-min warm-up period in the morning, after which it will remain constant all day. The warm-up is necessary because the photocell has greater sensitivity when cold, and temperature equilibrium must be reached before the system stabilizes. During projection, the operator needs only to keep the needle at a constant standard value by appropriately trimming the arc. The use of this system has resulted in a great improvement in projection quality, both at Cinecolor and M-G-M.
Thanks are expressed by the author to James Phillips, Chief Projectionist at Cinecolor, for initiating and doing most of the original work in this project, and at M-G-M to Merle Chamberlain, Chief Projectionist, and Clayton C. Troxel, Jr., Projection Engineer, for their modification which contributed to the success of the final model.
Harry P. Brueggemann: Continuous Arc Projector Meter
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