Richardson's handbook of projection (1927)

192 HANDBOOK OF PROJECTION FOR at position A, Fig. 51. You will observe that, with the face of the converging lens 18 inches from the aperture and the two-inch free diameter projection lens three inches from the aperture, the light would, to all intents and purposes, be all admitted to the projection lens, and the condition would be almost 100 per cent, perfect. If, however, the working distance of the projection lens (the distance of its rear surface from the film) were increased, light loss would immediately be set up unless (A) the condenser be pulled further back or (B) a larger diameter projection lens be substituted for the two-inch one. However, let us remark, in passing, that condenser distance, commonly called "Distance Y," cannot be altered at will without changing the arc distance — distance light source to face of converging lens — which usually is inadvisable if it alters the correct distance (usually the least distance, in the case of the arc, at which the arc can be operated without undue lens breakage), since if it shortens it there will be excessive lens breakage, and if it lengthens it, then the effect set forth in Fig. 36H is made operative, and sets up heavy light loss. LENS CHART. — In past editions we have published a lens chart. This we now think inadvisable, for the reason that a most excellent chart has been worked out by John Griffith. This chart is far in advance of anything heretofore published. It can be incorporated in this book only in very reduced size. It may be had size 14" x 20" from the Chalmers Pub. Co., 516 Fifth Avenue, New York City. Price $1.00. We earnestly advise every theatre manager to get one, have it put in a frame under glass, and place it either in the projection room or in the office, where it will be available for consultation at all times. It is worth far more than its price to any theatre