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6pO MOTION PICTURE HANDBOOK
known as "stage cable," a heavily insulated twin wire. These wires should be not less than No. 8.
Fig. 288 illustrates the optical system of a spotlight. The main difference in handling a spot with A. C. is that it is almost impossible to avoid a blue ghost at the top of the spot, or a double spot, the latter being due to the double crater.
It is possible to make a fairly satisfactory home-made spotlight by using an old projection machine lamphouse. You can fit up the standard the same as the one shown in Fig. 289, using any convenient floor base, and arranging to attach the lamphouse to the standard in such way that you can tilt it and swing it from side to side. The standard is made by having a hollow stem below, with a small one inside it which can be raised or lowered and clamped in place by means oi a collar and set screw. Two pieces of different size gaspipe make an excellent standard. One must fit inside the other.
The Stereopticon
THE Stereopticon consists of a lamphouse and lamp, a condenser, a slide carrier and an objective lens. The slides used in America measure 3% inches by 4 inches overall, with a mat opening 2% by 3 inches. In foreign countries the slides are for the most part square, though I do not remember the exact dimensions.
With moving pictures electric light forms the only satisfactory illuminant. With the Stereopticon excellent results may be had by the use of ozo-carbi light, lime-light, or even with acetylene gas; this by reason of the fact that whereas in projecting moving pictures, using a modern mechanism, fully 50 per cent of the light is cut by the revolving shutter, and, moreover, there is a large loss of light at the spot, which must of necessity overlap the aperture by considerable, with the Stereopticon practically all the light passing through the mat opening of the slide finds its way to the screen, and the only light loss by overlapping is a slight loss at the outer edge of the condensers where the light is weakest.
In moving picture projection the picture (film) is from one to two feet away from the condensing lens, whereas with the Stereopticon the picture is right up as close as it can be got to the frbnt surface of the condenser. With moving picture projection the objective is comparatively near the film, where