GB319195A - Improvements in or relating to the taking of colour photographs for use in cinematography - Google Patents

Abstract

319,195. Chapman, W. March 17, 1928. Grant of Patent opposed. C o l o u r kinematography. - Colour - record images are produced in pairs by means of one lens and light dividing means, each pair of images being formed on one film, being contained in the area normally occupied by a monochrome image, and being arranged so that the film carries two rows of spaced images, the spaces in each row being alongside the images in the other row. Figs. 1 and 2 show a lens 8 and a system comprising a rhomboidal prism 1 with a semi-silvered or other transmitting- reflecting surface 5, a second rhomboidal prism 3 having its plane of deflection at right angles to that of the prism 1, a connecting-prism 2, and a parallel plane glass plate 4. The prisms 1, 3 may be identical, but, as shown, the prism 3 produces a smaller deflection of the axis of the beam than does the prism 1, and the images produced are equal in dimensions, are in contact at the corners, and occupy diagonally opposite quarters of the normal image area of a standard film. The optical lengths of the light paths may be made equal, so that the images 9, 10 lie in the same plane, by adjusting the thickness of the plate 4, or by varying the refractive indices of the prism 3 and plate 4, the emergent faces being in the same or different planes. A modification is described in which the angles of the prisms 1, 3 are respectively increased and decreased to equalise the lengths of the light paths. To increase the light transmission from the lens 8 through the prism 3, the prisms 2, 3 are extended so that the prism 2 has an entrance face covering the aperture of the back lens element; a parallel plate 7 may be cemented over the entrance faces of the prisms 1, 2, The colour filters may be placed between the units 1, 4 and 2, 3 respectively, or they may be between the prisms and the film; in the latter position their thickness, or the thickness of their cover glasses, may be varied to effect a fine adjustment of the image planes. Reflections and stray images may be prevented by the provision of grey portions 5<b> on the surfaces, and by making the units of greater width than is otherwise necessary and chamfering off the surplus polished areas as at C. The prisms &c. may be assembled on a plate 1, Fig. 9, carrying a lens L and rotatable by a tangent screw 2, the units U<1> U<2> being secured to the plate 1. The units U<3> U<4> may be carried by a mount 3 so as to be rotatable with respect to the other units about the lens axis. The parts may be assembled with colour filters F<1> F<2> between them, the meeting surfaces being coated with soft Canada balsam, and may be adjusted to the position which they are to occupy permanently, while the Canada. balsam is still soft. The blades of the shutter may have stepped edges, as shown in Fig. 7, so that the pictures P<1> P<2> may be covered and exposed approximately simultaneously.