GB582773A - Improvements in or relating to the projection of stereoscopic cinematograph images - Google Patents

Abstract

582,773. Stereoscopic kinematography. WRIGHT, E. H. May 3, 1944, Nos. 8377/44 and 12922/45. [Class 97 (i)] Left and right eye pictures arranged alternately on a single width film are projected simultaneously by plane or circularly polarised light of differing polarisations in respect of each picture, the film being fed forward a single frame for each projection and means being provided to change the polarisation of the projection beams during each picture shift so that each eye-view picture is always projected by light polarised in the same plane or circularly polarised in the same direction. For plane polarised light the beam from a source 10 falls on a polariser 12 of the type described with reference to Fig. 1 of Specification 580,869 and the emergent plane polarised beam falls on the film 13 in a gate 14 accommodating two picture frames. A half-wave plate 15 covers one of the pictures in the gate and rotates the plane of polarisation of part of the beam through a right angle. The two beams pass through the projection lens 17 and are superimposed on screen 19 by the mirror system 20, 21, 22, the mirrors 21, 22 being slightly inclined to one another. When the film is fed by one frame, the picture previously covered by the plate 15, for example a left-eye film, is replaced by a right-eye view and to ensure that it is projected by light polarised in the same plane as for the previous projection an alternator 18 of the type described in Specification. 555,670 is employed. Alternatively, this may comprise a disc rotated in synchromism with the picture fed and including two arcuate apertures, one of ordinary glass and the other comprising a halfwave plate. For circularly polarised light, the polariser 12 is substituted by a polariser of the type described with reference to Fig. 2 of Specification 580,869, which produces two plane polarised beams of different planes of polarisation. A quarter-wave plate placed in front of or behind the lens 17 converts the plane polarised beams into clockwise and anticlockwise rotating circularly polarised beams which may be superimposed on the screen by the mirror system shown or by a biprism. The direction of rotation of the polarisation of each beam is reversed during picture shift by a similar alternator 18. The audience is equipped with suitable spectacles and a half-wave plate 16 may be inserted in the beam to ensure appropriate polarisation when projection begins. Specifications 570,878 and 580,870 also are referred to.