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Projector Speed
Speed is correctly maintained in modern projectors by means of an electrically-controlled automatic speed-governor, which is actuated by using a sound /silent switch. Sound-speed is at the rate of 24 frames per second and silent-speed 16 f .p.s.
In some projectors the speed may be regulated by the voltage supply, and in cases of sudden lamp failure, the extra voltage (released by the lamp failure) may surge to the motor and cause it to speed up at an alarming rate. In such cases the motor must be stopped at once.
Many silent projectors have their speed controlled by the use of a slide resistance, and with these the quickest method to find the correct speed will be to watch the screen — there must be no flicker, and the pictured movements must appear as normal.
The rate of projector-speed for the various gauges is as follows: —
8 mm.: 100' reel at silent speed: 8 minutes = 12' per minute
9.5 mm.: 300' reel at silent speed: 12 ,, =24/
300' reel at sound speed: 8 J ,, =36'
300" reel at mute speed: 8 J ,, =36'
16 mm.: 400' reel at silent speed: 16 J ,, =24'
400' reel at sound speed: n ,, =36'
400' reel at mute speed: n ,, =36'
Note that mute films are silent versions of sound films, and are to be projected at sound speed.
The Pilot Light
The chief function of this small light is to enable you to see when lacing up the film and also to provide sufficient light for you to keep the film under observation during projection. But should you find that sufficient incidental light escapes from the gate area, the pilot light should be switched off as being unnecessary. The lamp itself is of small wattage and usually lasts for many months, which is probably the reason why it is so often omitted from the list of spares.
The Controls
The controls on a silent projector may be as follows: — Lamp switch; motor switch; a framing knob (or racking lever);
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