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

FOR MANAGERS AND OPERATORS 125 would show as curves, and more closely resemble the true shape of the actual beam. Nevertheless, when a small screen is placed at different sections of the actual beam, the results show a very close agreement with the theories set forth. In photographing the beam, only the white and green zones are actinic and show in the photograph, and by observing Plate 11B, it is seen that the theoretical shape of the combined white and green zones agrees very closely with the photograph. But even to the eye the beam has a curved shape, which is probably due to the existence of infra red at the outer edge of the orange envelope. It is finally seen, as a further point in practical application, that one of the important functions of having the crater in true focus at the aperture is to purify the light and avoid color effects. The aperture may be placed a little forward of the focal plane, |^ but should never be behind it. Some of the practical effects of chromatic aberration are seen in Plate 11C. It will be observed that whereas the holes in the metal shield covering the condenser are of equal size the lower ray is much the stronger. This is partly due to its position, but also to a very considerable extent to color in the upper ray which reduces its actinic effect on the photographic plate. Another important point in connection with the condenser/is loss of light through poorly polished, unevenly finished surfaces, and through discoloration/ of the glass. Of late there have been those who have advocated the addition of yellow to the condenser lens glass, with the idea of mellowing light. With this I cannot agree. I think it is hardly necessary to enter into a discussion of the matter, and most emphatically advise operators to avoid the use of lenses containing discoloration of any kind. In selecting a condenser lens first examine its