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116 AMATEUR MOVIE MAKING
above ten amperes. Such lamps may be safely operated on any ordinary house current.
A simple arc will gradually increase the current consumption as the carbons are consumed and the path of the arc becomes longer and longer. In the older type of lamp screw controls were arranged so that the operator could manually move the carbons closer together as they burned away, but this required almost constant attention which would greatly decrease their value to the photographer. Moreover the old time arc spluttered and spit and had a constantly varying light intensity. This was not of so much moment in still photography, but it is fatal in motion photography with its 1/32 second maximum exposure.
The next improvement was a magnetic arrangement whereby the arc constantly renewed itself. When the arc grew to a certain length the upper carbon would drop upon the lower and be jerked away again instantly, renewing the arc. This arrangement is still used in some lamps, but not in the most modern forms.
The modern photographic arc lamp has special carbons which give an intensely white light, with extreme photographic power. They are so arranged that the arc is started manually, after which the arc will burn for a predetermined time and then go out, unless renewed manually before the automatic extinction takes place. Four or five minutes, the usual length of time for these lamps to burn, is ample for making an exposure of a single scene, with time for focussing and final checkup on the setup before the actual exposure. In case the lamp is left burning it will be extinguished automatically, which is in itself a valuable feature. Moreover these lamps burn with very little noise and without flickering, or spluttering.
Cameralite. — One of the most outstanding lamps for amateur use is the Cameralite made by the widely known firm of M. J. Wolil. This lamp is made of sheet metal, and shaped like a rollfilm camera. It measures 314 x 6 x 11 inches and weighs six pounds. While it is rated at 8,000 candlepower for use over an area not to exceed fourteen square feet, the lamp will deliver about 12,000 candlepower. The writer has used it very successfully with an