GB729004A - A colour filter and apparatus for the determination of printing filters in colour photography - Google Patents

Abstract

729,004. Colour photography. AGFA AKT.- GES. FUR PHOTOFABRIKATION. June 10, 1953 [June 14, 1952], No. 16044/53. Classes 97 (1) and 98 (2). To determine the filter to be used to avoid colour degradation in printing by contact or in an enlarger, a compound filter plate has three filters of different colours as of yellow, magenta and cyan along the sides of a triangle, usually arranged to overlap in pairs at the corners and with each colour comprising adjacent stripes of different densities, one of the strips being of zero density. As shown, Fig. 1, the filter has pairs of parallel stripes of arbitrary densities 40 and 20 with pure colour K in the middle of the stripes, compound colours at the corners, and outer colourless areas marked G, P and Bg to identify the colour stripes. In use different parts of a light-sensitive printing material are successively exposed through a chosen part of the colour negative, each through a different partial section of the filter plate, and the filter corresponding to the section of the processed printing material with the best colour rendering is selected as the desired correction filter. An apparatus for the purpose comprises, Fig. 8, a cover-plate a fitted to swivel on a holding plate d and provided with a trapeziumshaped opening b beneath which is an exchangeable disc c pivoted at i and constituting at the same time a carrier for the above described filter plate, a sensitive printing material holder, and a switching element. The underside of the holding plate d, and also a foot beneath the top right-hand corner of the cover-plate a are provided with a porous rubber layer so that the apparatus may adhere as to the printing area of an enlarger and exposures through each corner of the triangular filter may be effected by revolving the disc c with its filter plate and sensitive material through 120 degrees to the stop n. Other Figures show the triangular filter mounted centrally in a circular disc similar to c for operation in a similar manner.