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June, 1930]
VARIABLE AREA SOUND FILMS
645
The loss of high frequencies as measured by running the films through the projector comes from two causes, the width of the slits referred to above and the spreading of the image on the film itself. At present we are interested only in the latter effect. I have, therefore, made a further correction in the curves by subtracting from the losses found in the experiment those losses known to be due to the slits.
These slit losses can be calculated mathematically. The result of such calculation for the widths of the slits now in use is given in Fig. 6. It will be understood, then, that in the figures which are to follow the zero level is, in effect, the curve of Fig. 6. When the photographic losses are isolated in this way it becomes much easier to observe how they vary with differences in handling.
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FREQUENCY CYCLES PER SECOND
FIG. 7. Photographic loss of high frequencies in making a sound negative (upper curve) and in printing from this negative. (Highest print curve for density 1.25, lowest for density 2.15.)
Fig. 7 shows the losses due to recording on Eastman positive film and then making from that negative a series of nine prints, the densities of the prints varying over the range from 0.5 to 2.15. The negative was made on a recorder which was in commercial operation, no special attempt being made to place it in perfect adjustment. Thus the result is representative of what is obtained in practice. Possibly a slight improvement could have been made by refocusing the lenses, but since the loss in the negative is only 2.4 db. at the highest frequency, it is evident that this improvement could be only slight, and of no practical importance.