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404 RICHARDSON'S BLUEBOOK OF PROJECTION
is an indication of what happens when the filament is off center.
Filament out of center up or down 1/16 inch, loss 96.0%; 1/8 inch, loss 95.3%; 3/16 inch, loss 66.6%
Filament out of center sidewise 1/16 inch, loss 92.8%; 1/8 inch, loss 76.2%; 3/16 inch, loss 57.7%
In the above tabulation we see that if all other optical train elements are in correct alignment, but the lamp filament is, for example, 1/8 inch too high or too low, almost 15 per cent of the light is lost; if it is 3/16 inch too far to one side, almost 43 per cent of the light is wasted which emphasizes the importance of centering the lamp filament exactly on the axis of the optical train.
(188) The majority of the high wattage projection lamps show a certain amount of coil distortion (sagging) towards the end of life. If allowed to continue it may result in a short circuit in the coils. Filament sag cuts down the illumination on the screen or it may cause the lamp to burn out immediately. It is best to replace such lamps to avoid trouble during a performance.
(189) Throwing the full operating load directly on these high wattage, heavy current projection lamp filaments often causes some distortion of the filament. (190) To offset this most lamps have an arrangement that permits them to be burned at reduced current until the filament warms up. In 10 to 15 seconds the various parts of the filament warm up to the same temperature and then it is safe to give it the full current load.
• Properties of the Component Elements
Since the standard professional projector aperture and projection lens present openings of considerable size, a light source of generous area can be used. (191) The maximum size of the light source which can be employed effectively with a given optical system is dependent upon (a) the diameter of converging element of the condenser and its distance from the aperture; (b) the size of the aperture opening; (c) the diameter of the projection lens