Patent GB-448264-A (GB)
Title: Improvements in or relating to colour photography
IPC: G03C7/04
Filed: 1934-12-04
Abstract: 448,264. Colour photography; multicolour-screen processes. CHAPMAN, W., 71, Grovelands Road, Palmer's Green, and DUFAYCOLOR, Ltd., 19, New Bridge Street, both in London. Dec. 4, 1934, No. 34872. [Class 98 (ii)] In apparatus for printing by contact from a regular pattern screen master photograph on to similar sensitive material, the master and copy are passed preferably continuously through a gate with a narrow slit aperture extending transversely to the films across the full width of the photograph and illuminated by a system comprising a light source and a condenser forming an image of the source in front of the gate at the principal focus of a cylindrical lens arranged with its axis parallel to the slit. This image is large compared with the width of the slit in order to provide for diffusion of the screen elements in copying. The cylindrical lens should illuminate the whole length of the slit ; and if a lens is used which is wider than the slit, two facets are formed on it in order to concentrate the light upon the slit. The invention also includes a grid diaphragm for reducing the intensity of the printing beam in accordance with the printing density of the negative without reducing the overall size of the condenser image of the light source ; a colour filter with strips parallel to the slit for eliminating undesired light from the printing beam ; and a central masking disc for obtaining uniform light distribution.. As shown, the films 9, 10 slightly separated, are passed across a slit aperture 2 illuminated by a source 1 of which a broad image 3 is formed by a condenser 4 at the principal focus of a cylindrical lens 6 whose axis is parallel to the slit 2. Facets 7 are provided on the lens to concentrate the light on the slit. The inclination of the rays between the films indicates how diffusion of the screen elements is produced. A colour screen is disposed at 8, comprising, for example, strips of blue 13, red 14, and green 15, Fig. 8, each colour being sharp-cut so that those colours which would be transmitted bv two or more colours of the screens of the films 9, 10 are eliminated from the printing beam. The grid diaphragm comprises a pair of slidable grid plates 16, Fig. 5, having slots parallel to the slit 2, and arranged behind a fixed masking aperture 5. When the grids are moved together to close the gap between them, the light passes through the slots only ; in other positions of the grids the light passes partly through the slots and partly through the gap between the grids. The positions of the grids are controlled automatically, in accordance with the printing density of the master film, from notches or staples on the film acting through electromagnets on scissors-linkages which serve to displace in relation to a fixed stepped stopbar, a bar connected by bell-crank levers to the slidable grids. The central masking disc for rendering the light uniform may be placed on the axis either between the lens 6 or filter 8 or between the components of the condenser 4. Specification 322,432, [Class 98 (ii)], is referred to. The Provisional Specification describes also an alternative to the above described grid diaphragm, comprising a pair of overlapping neutral-tint wedges, and means for adjusting the degree of overlap of the wedges.