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Sept., 1939] TECHNICAL STATUS OF 16-MM. SOUND-FILM
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printing condemned direct 16-mm. recording as an inferior method. This, however, was on the basis of recording image widths in the range from 0.0005 inch (Batsel and Sachtleben) to 0.00025 inch (Kellogg). The results are very different when the recording image is reduced to a width of 0.00015 inch.
The method of measuring the width of the recording image is important if valid comparisons are to be made. A figure for image width arrived at by dividing the width of a physical slit by the ratio of reduction of the lens used to image it on the film is not correct unless allowance is made for the diffraction pattern and the aberrations of the lens. The image widths stated in this paper are arrived at by
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FIG. 2. Characteristics of white-light recording on 16-mm. positive film. (A) Response with constantamplitude negative, non-slip white-light print; (B) Equalization employed in practice; (C) Overall reproduced characteristic of non-slip print; (D) Response of optical white-light print from same negative as A; (E) Overall reproduced characteristic of optical white-light print.
looking directly at the aerial image formed by the recording optical system, using a 4-mm. apochromatic microscope objective of the type that is corrected to work without a cover glass. A micrometer ocular calibrated in combination with this objective reads with fair reproducibility to 0.00002 inch. The aberrations and diffraction pattern of this apochromat lens are small in comparison with those of the image being measured.
The results of white-light recording on 16-mm. positive film stock with an image width of 0.00015 inch are shown in Fig. 2. Curve A shows the measured losses of non-slip white-light prints from several