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126 MOTION PICTURE PROJECTION
surface of lens, as though it may not show when looking through the lens it will undoubtedly affect the definition of picture on screen.
Condenser lenses should be cleaned every day, and the objective lens once or twice a week. It will not be found necessary to take the lens apart to do this, as it will only be the exposed glass surfaces that will need attention. Use a clean soft handkerchief for this purpose. The lens can be taken apart every three or four months and all surfaces thoroughly cleaned, great care should be taken when taking the lens apart so that you get the lenses back in the same position and order.
Successful results in projection depend largely upon the correct adjustment of the lamp, which must throw a brilliantly illuminated clear circle on the screen. After the objective is focused as will be evidenced by a sharp, clear image on the creen, examine the illuminated circle. If the light be centered and the lamp correctly adjusted, the circle will be entirely free from coloration or shadows. In Figures 1 and 2 the crater of arc needs to be properly adjusted laterally, it being as shown too far to the right or left. Figures 3 and 4 show the crater too high or too low. In Figures 5, 6 and 7 the crater is too near or too far away from condensers. Figure 8 shows it in right position, the screen being free from all shadows or ghosts.
Fig. 9 shows the various lenses: (a) double convex; (6) piano convex; (c) concavo convex; (d) double concave; (e) piano concave; (/) convexo concave.