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

the film velocity, Vmiu, in the corresponding v-scale, or Vmin in the V-scale. Lower w-scale: This scale is for the width of field, w, measured in feet, with a range from 0.1 to 2.5 ft, to be used together with the upper w-scale for conversion of inches into feet and vice versa. The transparent indicator has a hairline, perpendicular to the direction of the log scales, for alignment of the corresponding values in various scales. Use of Slide Rule for Evaluation Tasks 1. Correct Slide Position With Reading of Frame Time and Film Velocity To find the frame time, ti, and the film velocity, v or V, in a given part of the film record, the procedure outlined below should be followed. A part of the film strip, short enough so that the film velocity during film run in the camera can be assumed constant for evaluation purposes, should be considered. Then any time interval within this film part, t, will have a constant proportion to the corresponding number of frames, N, where this proportion is identical with the frame time, ti, defined previously. For example, when iiooo = 5 timing units or 5 ms correspond to 8 frames, 10 ms will correspond to 16 frames, and the frame time is 0.625 ms. The following, therefore, applies to the slide rule : When any time, t, on the t-scale of the slide is aligned with the corresponding number of frames, N, on the N-scale of the slide rule body, all time values, t, will be aligned with the corresponding number of frames, N. Especially, index "1" on the N-scale, indicated by arrow (ti), will be aligned with the frame time, ti, on the t-scale. This slide position with the proper alignment of t-scale and N-scale may be called "correct slide position" for the given part of film with constant velocity. For another part of film with a different velocity, another positioning of the slide within the slide rule body will be the correct one. The procedure for determining the correct slide position, therefore, includes readings on the film as well as on the slide rule. In the given part of film, select a small number of timing units, iiooo or ieo, and count the corresponding number of frames, N, by visual approximation or by means of the frame counter. For example, it will be found when iiooo = 5 timing units, N = 8 frames. Reading fractions of frames increases the accuracy of computation, especially for a smaller number of frames. The procedure for the slide rule is comprised of the following steps : Move the indicator to the value 8 on the N-scale, i.e., the hairline of the indicator must coincide with value 8 (see Fig. 5). Move the slide so that the corresponding number of timing units, iiooo = 5, of the iiooo-scale converges with the hairline on the indicator, that is, with N = 8. (When the corresponding time is given in terms of ieo timing units, then that value of the ieo-scale has to be aligned with N = 8 of the N-scale.) This is now the "correct slide position" for all evaluations of time and velocity within the given part of film assumed to have constant velocity. Corresponding numbers of frames of the N-scale, and times of the t-scale, are in alignment as illustrated in Fig. 5. For different evaluations in this part of film, only the indicator is moved. Move the indicator to arrow (ti) (index "1") on the N-scale and read the frame time, ti = 0.625 ms, in the tscale. (When arrow (ti) on N-scale falls outside of t-scale, read time, t, at N = 10 and the frame time will be ti = t/10.) Move the indicator to arrow (v) inside ieo-scale and read the film velocity v and V in the corresponding v-scale and Vscale, respectively. For 16-mm film, v = 40 ft/sec and V = 1600 frames/ sec. For 8-mm film, the result is v = 20 ft/sec and V = 1600 frames/sec. The frame time, ti, and film velocity, v, which are related, can be considered 630 June 1951 Journal of the SMPTE Vol. 56