Motion picture handbook; a guide for managers and operators of motion picture theatres ([c1916])

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122 MOTION PICTURE HANDBOOK the light on the paper. If the lens measures 2 inches in diameter and the light measures 2 inches across, all is well. If the light measures more than 2 inches across, but only 2 inches up and down, the lens still will do fairly well, though there will be some loss. If, however, the lens measures greater than the light, stop the lens down to the diameter of the light at both ends, by means of rings of metal in which you have made a circular opening of proper size. I do not pretend to say that this advice is perfect. It is, however, the best I can offer at this time, and is, I am sure, based on the right idea. A Digression. Let me pause here, for T-; want of a more fitting place, and digress ^J for a moment to show you an interesting £ light ray picture. .£? In Plate 10 we see a condenser with a ^ metal plate having a number of holes, each £f about one-quarter inch in diameter. This o picture has no considerable value, except to £ allow the operator or student to trace the ^ light ray action on both sides of the objective. It will be noted that the screen illumination is not complete, especially at the outer edges where there were but few holes in the metal plate. Another interesting point in this picture is the circle of light on the back side of the aperture plate, showing the loss of light through reflection from the polished surface of the lens. In fact, there are a number of things in this photograph that will interest the studentoperator. Spherical Aberration. — An examination into the effect of spherical aberration points to the fact that it operates mainly to cause impurity of the light, by reason of the fact that those rays which draw in toward the center earliest must naturally reach somewhat into the center of the spot, and coming, as they do, from the outer edge of the lens, they carry with them considerable color.