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

stage.* The Black Swan was to be presented for 22 weeks on a screen only 10 ft 4 in. in width (M = 150), and this suggested shooting it for a 1 5-ft screen (M = 218), since it was known that results on even a 20-ft screen would then be entirely acceptable. Accordingly, the Stereo measure was permanently set at M = 218, this being analogous to the choice of a film emulsion for a production, which gives rise to a fixed speed setting on the exposure meter. While the movement of the camera on its crane was being rehearsed, distance measurements were taken from it to the dancer and to different parts of the set. These measurements were made with the special Stereotape graduated in p on one side and linear units (for focusing) on the other. For the first shot, the entry in the stereotechnician's log begins as follows: Slate 35: LS Prince (John Field), who dances his Variation. Rear of set at 10p. During the dance, camera tracks in, and the Prince finishes in MLS at 33p. At end of dance, as Prince kneels, banners rise in front of him, covering whole frame, at 65p from camera. For continuity with following shot (already taken), banners should be at or around #2.75. It should first be determined whether this shot can be made with B = 0, i.e. with linear transmission, placing DQ at Op. Since the banners are to appear at -#2.75, the depth range is A2.75. The cameraman having selected a 35mm lens (fc = 1.38 in.), it can readily be determined by Eq. (8), or from the Stereomeasure, that tc = 2.1 in. However, * The excessive positive zs resulting from projection with too large a value of M. can be corrected by supplying a negative correction of suitable size which will alter B and increase the N value of the nearest planes. This can be done by projecting with ZCL negative, but better by optical correction. Note that N factors will be increased both by the larger M and by the extra negative screen parallax. this value of tc is not obtainable on our camera with the 35mm lens, and the shot must therefore be recalculated for B-\-. The simplest procedure is as follows. Taking the minimum setting of tc (i.e. 2.5 in.), we then have M, fc and /c, and therefore the C factor. The most distant plane in the set, 10p (i.e. 50 ft), is set at infinity, DQ. The Stereomeasure, solving Eq. (8) directly, gives 30p as the value of Z>i, and shows that the banners will in fact appear at A^.ya. Hence the stereotechnician's entry concludes, Treat shot as B+, with fc = 35mm, tc — 2.5 in., and cot ^ = 160. Dl to be at 30p. Nearness factor of raised banners works out at JV2.75, as desired. These measurements and calculator readings occupy only a couple of minutes, and in a few moments more the camera is set to tc = 2.5 in. and cot p = 160, the latter value having been obtained from scales on the Stereomeasure which relate tc and D\, as in Eq. (9). Two further points deserve comment. Firstly, what could have been done if the proposed settings had placed the banners in the wrong plane in theater space? Had they proved too far away, it would have been possible (a) to reduce the distance in the studio between camera and banners, (b) to increase /c, or (c) to increase te. Both (a) and (b) alter the composition of the shot, and so (c) is usually the preferable alternative. Had the banners proved to have too great a nearness factor, it would have been necessary to resort to the inverse procedure of (a) or (b), since the tc setting was already a minimum; This points to the need of incorporating the lowest practicable minimum tc in the design of the camera. Secondly, it may be asked what effect on the appearance of the shot is likely to result from changing B = 0 to B-\-. Setting the rearmost plane at Do should of course place it at infinity, and clever set design will in fact produce a very 268 October 1952 Journal of the SMPTE Vol. 59