International projectionist (Jan-Dec 1939)

Flicker In Motion Pictures CONSTANT efforts have been directed in the technical branches of motion picture production and exhibition toward the removal of effects -which make the mechanical processes in pictures obvious to the observers and detract thereby from the realism and entertainment value. Aside from features such as camera angle, lighting, sets, backgrounds, sound, etc., two completely mechanical effects in pictures can cause serious loss of entertainment value. These two are flicker and registration. This paper does not propose to discuss registration; therefore it is necessary to differentiate this effect from that of flicker. Briefly, registration is an irregularity in the position of successive picture frames on the film or screen. Flicker is an irregularity between successive frames in the total amount of reflected light from the screen, other than that purposely created, from a given scene. • Many Sources of Flicker Flicker still is an important problem in the industry, although the serious defects are intermittent in nature. Flicker is due not only to the frame frequency (24 per second) but also is the result of other variations superimposed upon the frame frequency. This latter effect can be considered in the same light as flutter in sound recording and reproducing. This paper will lay the greatest stress on these harmful superimposed variations. Consider now the many sources of flicker, and group them as follows for later consideration : (A) Original Photography: (1) Set lighting (2) Negative film tj. Soc. Mot. Pict. Eng., XXXIII (Sept. 1939). LORIN D. GRIGNON PARAMOUNT PICTURES, INC. Flicker in motion pictures has been receiving attention ever since the beginning of the art, and most of the sources of this defect have been minimized, if not eliminated, by technical accomplishments. The paper constitutes a qualitative review of the now prevalent sources of flicker, presenting some new concepts, emphasizing the sources of major importance at the present time, and reporting on two investigations made on the problem. Flicker and "registration jump" are differentiated, and the latter, which is really a separate problem, is not considered. Some data are presented to indicate the magnitude and characteristics of the flicker effect. (3) Irregular camera motion, including motor system (4) Development. (B) Printing: (1) Lamp irregularity (2) Positive (3) Printer motion (4) Development. (C) Projection: (1) Arc flicker (2) Intermittent shutter (3) Projector mechanics. (D) Background Projection: (1) All of A (2) All of B (3) All of C. With so many possible sources of flicker it is very easy to understand how flicker may easily occur. Also, although each of the above might be small in absolute value, in instances when two or more occur at the proper frequencies and phase relationships the effect becomes pronounced. This likewise accounts for the difficulty in tracing, separating, and minimizing the major sources. Two analyses and invesigations made at the Paramount Studios disclosed four important facts: First, considerable change in reflected light can be tolerated by the observer pro vided this change occurs at random intervals which are not closely spaced or of excessive duration. The moment the light change become cyclic, the amount of tolerable difference decreases sharply to a surprisingly small value. Second, the rate at which the cyclic flicker occurs determines the amount of disturbance to the observer. No accurate determinations of this fact have been made. However, the rate of maximum disturbance appears to be between 6 and 8 cycles per second. Fig. 1 shows an approximate curve representing the apparent disturbing effect versus the rate of flicker. Third, the change in transmission for perceptible periodic flicker occurring at the greatest disturbing rate of 6 to 8 cycles is about 3 per cent. The greater the change in transmission the greater the effect. Fourth, the disturbing effect is related to the amount of light. The greater the intensity the more obvious the defect. We shall now discuss the various sources of flicker, some briefly and others in more detail. (A) Original Photography. — The first cause of flicker in this group occurs in the set lighting. The intensity changes of incandescent lamps are of a relatively slow and random nature, and cause changes in the average brilliance of the scene and are dependent upon the regulation and stability of the power supply. Arc lamp flicker is more likely to be cyclic and therefore of a more serious nature. Arc lamp flicker generally resolves into slow periodic changes such as line-voltage and carbon-rotation effects and very fast random fluctuations. The very rapid fluctuations cause the most trouble in background process work, while the slow variations can cause serious trouble on split-screen shots. This is acknowledged and must be solved by the lamp and carbon manufacturers. 1.0 .6 .5 .4 .2 a. c V < o 2 < r, 0 1 CD Q \ 4 6 8 10 RATE OF FLICKER PER SECOND 1.5 SECONDS FIGURE 1 FIGURE 2 Snowing the apparent disturbing effect of cyclic flicker as Chart of picture negative in which photographic flicker is compared with rate of flicker just perceptible, representing about 3% in transmission 18 INTERNATIONAL PROJECTIONIST