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June, 1930]
THE APERTURE EFFECT
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does not depend upon the primary aperture at all and may be decreased by increasing U, the object distance, since this decreases image distance, V.
This is most easily seen from the first form for Wm given in equation (20). In this expression, the variables, r, D, n\ and w2, are to be considered fixed for any given primary aperture, W, lens, and exciter lamp conditions. Although the magnification ratio, V/U, for the image of W will be reduced if U is increased, the additional image width, APF0 due to chromatic aberration alone will also be reduced. It will be observed from the second form of equation (20) that this effect is also decreased if a lens of large focal length is used or if the lens aperture, D, is made small. Of course, if monochromatic light is used,
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FIG. 9. Recording and reproducing aperture effect on fundamental response. Recording and reproducing effective apertures (0.001) inches and film speed 90 ft./min.
the effect is eliminated altogether. Fig. 8 shows the effect of increasing U on the total additional aperture width, A Wh due to the combined effects of chromatic and spherical aberration in an experimental lens. The effects of spherical aberration must be treated at another time. The above analytical work was performed to estimate the possible limiting amounts of the aperture effect on the fidelity in film recording and reproduction. It will be evident from the text that by proper design, these effects can, and should be, minimized. For example, if the loud speaker is incapable of adequately reproducing frequencies above 5000 cycles, the introduction of harmonics due to the recording aperture effect can be reduced to a negligible amount by the use of the proper recording aperture, since the frequencies introduced will then be made higher than the cut-off frequency of the loud speaker or at least placed in a range where faithfulness