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682 MOTION PICTURE HANDBOOK
lens, which would mean heavy loss of light. This is, however, only my impression. I have not actually tried it out. I should think a 5l/2 lens next the arc would be better under those conditions.
Objective Lens. — Never use an objective lens of small diameter for limelight projection. Be certain the lens diameter is large enough to receive the entire light ray (see Page 110). You have a comparatively weak illuminant at best, and cannot afford to waste any of it. Three and one-half, 4 and 4^inch E. F. objectives are. popular with gas users. An eightfoot picture at 40 feet seems to be the one best liked. A 3l/2inch will give close to an eight-foot picture at 30 feet, and a 4^-inch will give a little more than an eight-foot picture at 40 feet.
Clean Lenses. — Clean lenses are extremely important when using limelight. A dirty lens wastes much light by reflection, and you cannot afford to waste any of your light when using limelight. See "Cleaning Lenses," Page 108.
Fitting the Limelight Burner into a motion picture projection lamphouse will in the newer models of) projectors call for a new lamppost, since, while the lamppost used for some of the old style, small arc lamps will serve also as a support for the limelight burner, the lamppost of the newer, heavier arc lamps cannot be used for the purpose. The method of anchoring the new post into place will vary with different makes of projector, and must be left to the ingenuity of the operator. Be sure, however, and get it located so that the backward and forward adjustment of the arc lamp base will still answer its purpose in the forward and back adjustment of the light with relation to the lens.
Machine Shutter. — It is never wise to use a three-wing revolving shutter with limelight. It cuts too much light, and with such a weak illuminant the flicker is not sufficient to require the three wings. Use a two-winger, with the blades reduced in width as much as is possible and avoid travel ghost. (See "The Shutter," Page 469.) It is even claimed by some operators that, when using oxygen and hydrogen with a lime pencil, they get excellent results with a onewing shutter. I cannot vouch for this. In fact I am just a little bit skeptical, but it is nevertheless worth trying. Remove your regular shutter blade from its hub, cut a single block from stiff but thin cardboard, using the main shutter blade for a pattern, and substitute for the regular shutter blade. If you find it works satisfactorily insert a metal blade in place of the pasteboard. This cannot be recommended