GB922923A - Colour projectors and cameras - Google Patents

Abstract

922,923. Prism systems. E. M. WELCH. April 17 1959, No. 13206/59. Class 97 (1). A prism for use in a camera or projector to enable coloured images to be produced from an ordinary black-and-white film comprises four prisms 66, 68, 70, 72 arranged as shown in Fig. 8, prisms 66 and 70 being identical and having angles of 90 degrees 60 degrees 30 degrees while prisms 68, 72 are equilateral. Surfaces 70b 66b are silvered and two corners are cut off and rendered opaque so that the light transmitted through the prism assembly 60 (Fig. 3a) must be reflected at three surfaces. In Fig. 3a light from an object passes through a dove prism 26 which (a) rotates the image through 90 degrees and (b) reverses the leftright orientation a lens system 24, then inverts the images. The light passes through one of two filters S4 green-blue and S6 red-orange and enters the prism assembly 60. The refractive index of the prism is such that the light rays are totally internally reflected at surfaces 72b, 70c or 68b, 66c. On emerging from the prism assembly they form two adjacent images which are inverted, half the size of the image which would have been formed by the lens alone. In order to produce a stereoscopic effect a barrier 98 (Fig. 3) may be placed in front of the lens system 24 and the two lens components thus produced form dissimilar images which by using a suitable projector i.e. one which makes the images overlap and polarizes them give a stereoscopic effect. In order to prevent any accidental overlapping a barrier may be used in the projector and camera in front of the filters and film.