Patent GB-763966-A (GB)
Title: Improvements in and relating to the production of stereoscopic pictures
IPC: G03B35/00
Filed: 1953-02-17
Abstract: 763,966. Stereoscopic cameras. SPOTTISWOODE, N. L. Feb. 17, 1954 [Feb. 17, 1953], No. 4440/53. Classes 97(1) and 98(2) Apparatus for producing stereoscopic images comprises a camera system with two objectives, means for adjusting the convergence and interaxial separation of the objectives, range finding means which can be set simultaneously upon two points of different distances, and couplings operating the adjusting means in accordance with computing mechanism coupled between the rangefinder and the camera. so as to produce a pair of related images which when projected on a screen are fusible as a stereoscopic picture. The computing mechanism solves the equations R = t/ZM NDo/DN-DO and t o  = Nt/M#c(DN - DO h being the convergence-varying displacement of each lens axis relative to the centre line of each light-sensitive recording area beyond that required for ZM the " ortho-infinite " condition in which objects at infinity in the original scene appear at infinity on projection if the projectors are disposed so that their axes intersect at the screen, and tc being the inter-axial separation of the camera objectives, where t is the interocular distance, fc is the focal length of each camera lens, M is the projection magnification, N is the nearness factor for the spectator screen distance space image distance, DN is the reciprocal of the camera object distance which will appear on projection with a nearness factor N and DN - DO is the depth range in the projected scene. The camera system may be for still or kinematographic pictures or for television. As shown, the rangefinding means is of the short home base coincidence type having one reference and two adjusting ranging fields and comprises two fixed coplanar mirrors 26, 28 at 45 degrees to the line of sight of the eye, a fixed mirror 27 also at 45 degrees to the line of sight but at right angles to the mirrors 26, 28, a fixed mirror 29 parallel to the mirror 28 filling a top reference field, and two mirrors 31, 30 rotatable inwardly from zero positions parallel to the mirrors 27, 26 filling the middle and lower ranging fields. The mirror 31 is rotated to bring into coincidence in the top and middle fields the object which on projection is to appear at infinity (No), thereby producing a rotation of the shaft of the knob 35 proportional to Do, while the mirror 30 is rotated to bring into coincidence in the two lower fields the the object which is to appear to the audience at a chosen nearness N, thus producing a rotation of the shaft of the knob 40 proportional to DN - DO. Rotations of the knobs 35 and 40 alter rheostats 36 and 38. 39 in bridge circuits 52 (Fig. 6) and 53 (Fig. 7) while are balanced by adjusting rheostats 43 and 46 respectively controlling the h (convergence) and tc (camera lens separation) controls on the camera 50. Instead of manual balancing the galvanometers in the detector arms may be replaced by polarized relays controlling driving motors for the rheostats 43, 46. The Provisional Specification describes also an arrangement in which the mirror 31 is fixed and the mirror 29 is movable but this has the disadvantage that if in order to accommodate the depth range it is necessary to move the projected scene bodily away from the audience, both the movable mirror controls must be rotated equal amounts so that the depth range indications are not altered.