International photographer (Jan-Dec 1941)

The seriousness of flicker is due to the duration of the exposure when observing motion pictures of television programs. It has been found that at a constant average brightness the percentage duration of the light stimulus during the cycle affects the critical frequency (Fig. 3). The same authority states that the fundamental component of the Fourier series expressing the stimulus for constant average brightness exerts a major control on the critical frequency except when the stimulus is off for only small percentages of the cycle, in which case the perception, as well as the further depression of the critical frequency, is due to the higher order components. The critical frequencies were found to be lower when the surroundings were dark than when they were made equal in brightness to the field of the test and that results for a reduction of the field of test to 1/5 with surroundings left equal to the previously employed field were than either. Differential sensitivity as measured by the inverse of the Weber Fechner fraction AB/B was found to be highest when the test field lay in surroundings of about its own brightness, the sensitivity being lower for darkened surroundings and considerably lower as the surroundings level was increased over that of the test field. These findings are said to be parallel to the relation between sensitivity to brightness difference and comparative brightness conditions of the test field and surroundings. Other investigators have reported similar findings and state that the sensitivity of the eye to flicker is increased when adapted to bright light as well as when the region around flickering area is illuminated. Maximum sensitivity occurs when the surrounding field is equal to the test field. The process of adaptation continues for as much as a half hour I see Fig. 4). It is reported that maximum sensitivity to flicker occurs at yellow in the spectrum, being less at either end. It has been found that the retina is not uniformly sensitive to flicker over its entire surface. The region within 10 degrees of the fovea demands the highest critical frequencies. Since this area is most commonly needed for viewing motion picture and television programs it is indicated that results for this area should be satisfied in both fields. Flicker tests with a cathode-ray tube screen having an exponential decay curve falling to approximately 2 per cent in 1/24 second have been reported in which the room lighting was about 1/10 footcandle. At a screen brightness corresponding to 1 foot-lambert, the flicker was said to have been just noticeable at 38 frames per second, noticeable at 35 frames per second, and disagreeable at 28 frames per second. It was concluded from the curves shown and data presented that a satisfactory solution for reduction of the frame Motion Picture Equipment Studio and Laboratory Tested Since 1929 AUTOMATIC DEVELOPING MACHINE COMPLETE IN EVERY DETAIL LABORATORY EQUIPMENT WILL BE ON DISPLAY AT THE NEW SHOW ROOM, IN CONNECTION WITH MY New Address: 1515 Cahuenga Blvd. Hollywood, California ART REEVES Cable address: ARTREEVES V o V z r o d » UJ 0! U u a. a j v> < UJ U -I t y U 16 /z 8 A ft o .5 1.0 Relative Duration of Illumination over Cycle. Fig. 3. Variation of critical frequency with relative duration of illumination for spectral blue light in range where critical frequency does not change with intensity (P. W. Cobb, J. Opt. Soc. Amer., April, 1934, p. 107). frequency under 30 per second would not be found in an exponential light-output decay curve. It is important that effects such as this be reduced to a minimum. Standards of ideal performance should not be dictated by those best equipped visually, but the average of those with "impaired vision" must be seriously considered. It is apparent that frame frequency is not the only source of flicker either in the theater or on the television screen but since the work of this committee was primarily related to the effects of frame frequency upon certain phases of the television viewing problem, of which flicker was one, no attention has been given to collateral causes and effects of flicker in this field. It is assumed that those effects not being fundamentally subject to Standards having the relationship of the "key and lock," could be considered in other ways. The Portrayal of Motion — This problem has been the least satisfactorily treated, the literature being meager to the extent of almost non-existence. Resort has been taken to correspondence with the producers of animated cartoons. Only a few re ^ A Sh o -2 -l.fc -.11 .8 LOG|0 B (FT. LAM&ERTS) Fig. 4. Wcber-Fechner fraction as a function of brightss (B. O'Brien and C. M. Tuttle, J. Soc. Mot. Pict. Eng., 1936, p. 577). plies have been received at this time. Answers to this correspondence are still ex 24 Intkhnationai. Photographer for January, 1941