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J. A. MAURER
[J. S. M. P. E.
contrasts greater than 10 it is fairly satisfactory; above a contrast of 20 the improvement in resolution is not noticeable except by very precise measurements.
The contrast of the image impressed on the film in a variable area recorder is usually at least 10. The contrast of a negative of density 1.3 is about 18. Thus if we work for densities of 1.3 in both negative and print, we will have satisfied practically all requirements for obtaining the highest resolving power of the film in both negative and positive. Since a resolving power of 60 lines per millimeter would theoretically allow us to record a frequency of 27,000 cycles per second on film running 90 feet per minute, while the highest frequencies in which we are interested in practice are not above 6000, we should ex
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3. Loss of high frequency output due to slit widths, including hot recording and reproducing.
pect to find that the photographic loss of high frequencies is not ordinarily a serious matter. The experimental results about to be given will show that this is indeed the case.
These results were obtained from the same series of measurements which gave the two dotted curves of Fig. 4. The differences in general level which were shown in Fig. 4 have been eliminated by replotting all the results in terms of the output obtained at 500 cycles on each film. This frequency is so low that the losses due to imperfect resolving power and the width of the slits used in recording and reproducing are all negligible. Thus the results can be compared strictly on the basis of high frequency response.