Journal of the Society of Motion Picture Engineers (1930-1949)

Record Details:

Something wrong or inaccurate about this page? Let us Know!

Thanks for helping us continually improve the quality of the Lantern search engine for all of our users! We have millions of scanned pages, so user reports are incredibly helpful for us to identify places where we can improve and update the metadata.

Please describe the issue below, and click "Submit" to send your comments to our team! If you'd prefer, you can also send us an email to mhdl@commarts.wisc.edu with your comments.




We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.

Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.

THE APERTURE EFFECT ELLSWORTH D. COOK* The earlier workers who recorded on, and reproduced from film will no doubt recall the poor high frequency response obtained. It has never been particularly difficult to obtain fair reproduction between the frequencies of 1000 and 2500 cycles from phonograph records, but many of the early film reproducers suffered severe losses in even this restricted range. It was soon found that the width of the beam of light which fell on the film played an important part in the reproduction of the higher frequencies. It was obvious that if the thickness of this beam of light should happen to be an integral number of wave-lengths of the recorded signal, no sound corresponding to that wave-length could be reproduced. It was also recognized that this effect was present in recording as well as in reproducing. Moreover, it is evident that this effect is oftentimes made more serious by the lens system. In order to explain the aperture effect, it is desirable to examine the complete process of recording and reproduction by means of a rectangular beam of light whose thickness in the direction of film travel is small. A little consideration shows that the same reasoning applies to both systems of recording under certain assumptions. For simplicity, the variable amplitude system will be examined. It will be evident that the ideal aperture is supposed to measure only the amplitude of the wave. In so far as area is involved, distortion results. This is mentioned because sometimes this system is called variable area recording. It is more correctly called variable amplitude recording. It is assumed that the film is moving with constant velocity, V, and the rectangular beam of light is of uniform intensity. It is further assumed in this system of recording that wherever light falls on the film, it is fully exposed. The corresponding assumption for the variable density system would be that the exposing power of the light on the film varies linearly with the product of the intensity of the light and the time of exposure of any element of film. * United Research Corporation, Long Island, N. Y. (This paper was read before the New York Section, April 16, 1930.) 650