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

FOR MANAGERS AND OPERATORS 145 as possible to the condensers — say between 3^ and 2*/z inches, according to the amperage used, and always have the greatest possible distance between the condensers and aperture. These two conditions in some cases conflict with present apparatus, therefore, it may be necessary to compromise between the two. But the compromise means loss in efficiency. For convenience in the use of these tables the decimal equivalents for fractions are given. I believe the foregoing is reasonably clear — at least sufficiently so that the table can be readily applied by the operator. Caution. — In measuring the back focus of your lens be very careful that the end of your rule is PERFECTLY CLEAN, because otherwise it might leave a faint mark on the lens which would injure the definition of the picture on the screen. These tables do not appear very imposing, but you may take it from me they represent a vast amount of labor. I would not presume to claim perfection for them. In fact I think it quite possible they may be subject to improvement, but I do think they are the first really intelligent step in advance, in this particular direction, since the projection optical system was first evolved. I believe a great many operators are now losing a large percentage of their light by reason of the fact that the diameter of their objective lens is too small for the condition under which it works. You will observe, too, that the smaller the diameter of the lens the farther away must the condenser be from the aperture, and Table 2 will show you that Plate 18, Figure 63A. under certain conditions the arc will be a great distance from the lens, thus involving excessive light loss. If you are obliged to locate the arc more than 3l/2 inches from the condenser in order to have a normal spot \l/2 inches in diam