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52
Transactions of S.M.P.E., Nov. 1924
to fulfill the conditions. We have analyzed the magnification of the projected image with relation to the observer in the following manner: (Fig.l.)
Viewing a strip of standard film at a distance of 12 inches, or reading distance we have adopted this ratio of one inch (the diameter of the film image) to one foot (the viewing distance) as a unit of one, their being no magnification of the image. If we increased the diameter of the film image by projection to ten inches and viewed it at ten feet we have maintained the same ratio and there is still no effective magnification apparent. But if we will magnify by projection the one inch image on the film to five feet or 60 inches on the screen
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and still view it at the same distance, we have obtained an effective magnification of six diameters. We find that the graininess of the film image can be examined quite as satisfactorily on the film itself \>y examining the image with a magnifjdng glass that gives a relative magnification to the film of six diameters, as though we viewed the projected image five feet in diameter at a distance of ten feet. The majority of spectators in a theatre are not as close as this to the screen. The same angle of vision 28° would give us six diameters for a twenty foot picture viewed 40 feet from the screen. (Fig. 2)
In connection with the work undertaken in the Warner Research Laboratory a camera is in use which carries a strip of negative film 1-7/8 inches in width which is Y2 an inch wider than the standard film. The film passes through the camera horizontally, the height of the image being nearly an inch and a half, and the film being moved 2 inches at each exposure giving us a picture four times the area of the positive. An optical printer with the negative and positive film running at ,^ight angles gives us by reduction the standard positive.