GB829874A - Improvements in or relating to the production of a negative photogravure screen and camera apparatus therefor - Google Patents

Abstract

829,874. Photogravure procedure and camera apparatus therefor. GARDNER, R. M. Nov. 26, 1956 [Dec. 29, 1955], No. 37316/55. Classes 98(1) and 98(2) A photographic representation in photogravure formation for use in preparation of a printing plate or cylinder is made by exposing a negative through a lens, a halftone screen and a negative photogravure screen having splayed openings relative to the openings of the halftone screen, so that light rays diverging from the lens and passing through the centres of the openings of the half-tone screen will pass also through the centres of the openings of the photogravure screen to give normal halftone formation up to the joining of the dots and thereafter photogravure formation with provision for support of the doctor blade. The screen assembly is made first, as with the apparatus of Fig. 1, which is an exploded view showing from left to right a halftone screen holder 12, screen 15 (rulings, which are normal, not shown), rectangular frame 3, screen supporting frame 7 front view, then rear view thereof; photographic plate 18 and holder therefor 34; all of this being assembled so that the' screen 15 is at its correct working distance from the plate 18, and exposure is effected in a camera to give a same-size image of a light source through lens 40 of Fig. 5 and stop 36 having apertures 37 of Fig: 7 to give openings 44 with latent screen lines 43 of the negative photogravure screen in splayed positions relative to openings 41 of the half-tone screen 15 as shown in Fig. 6. Plate 18 is removed after this exposure, processed, and returned to its original position at the rear of support frame 7 and a sensitive plate is placed in contact therewith; a negative from which the photogravure positive is to be made is positioned in front of the camera lens and with the same extension but with an iris diaphragm adjusted to the aperture for the working distance of the half-tone screen replacing the square stop of Fig. 7 exposure is effected through the two screens in register and the plate so exposed is removed from the camera and processed to show full tone range of the negative but with doctor blade provision of greater area than that formed by other methods. The invention includes the method of producing the splayed negative photogravure screen, and camera apparatus fitted with a square line stop as of Fig. 7 and the necessary features as of Fig. 1 to produce this screen.