GB739276A - Improvements in and relating to the production of screened photographic images - Google Patents

Abstract

739,276. Half-tone photographic images. CONRAD, R.M. P. Dec. 4, 1952 [Dec. 12, 1951], No. 30827/52. Classes 98 (1) and 98 (2). A method of producing a screened photographic image suitable for use in manufacturing a photogravure printing plate of the type in which the screen cells are of different lateral dimensions and different depths in dependence on the variations in light and shade in the image to be printed by the plate comprises the steps of producing a continuous tone positive transparency by contact printing from a continuous tone photographic negative, placing the transparency in a first plane, placing a photosensitive emulsion in a second plane on the opposite side of a lens from the first plane, projecting an image of the transparency through a half-tone screen on to the emulsion in the second plane with the aid of a light source and the.lens, removing and processing the emulsion to produce a screened negative of the continuous tone positive transparency, removing the transparency from the first plane and placing the continuous tone negative into the first plane placing the screened negative in the second plane, placing a further photographic emulsion in contact with the image on the screened negative on the side thereof remote from the lens, removing the half-tone screen and with the aid of the light source and the lens projecting an image of the continuous tone negative on to the screened negative to expose the further emulsion. As shown, Fig. 1, the continuous tone positive 10 is printed by light 12 through lens 13, compensating glass 16 and screen 17 onto plate 14. In the second operation, Fig. 2, the screen 17 is removed, the negative 18 from which the positive 10 was made takes the place of the positive 10 and this is printed through a second compensating glass 19 and the developed plate 14 on to a further plate 20. Emulsions of the several plates are shown in thick black lines, plate 14 in Fig. 2 being laterally reversed. Compensating glasses 16, 19 have the thicknesses of the support 14 and the half-tone screen 17 respectively. In printing transparencies and sensitive emulsions are located accurately in the planes 11, 15 respectively, as by the apparatus of Specification 693,703.