GB567046A - Masks for use in reproducing colour transparencies and methods of making and using them - Google Patents

Abstract

567,046. Colour photography. KODAK, Ltd. (Eastman Kodak Co., Evans, R. M., and Miller, N. D.). June 21, 1943, No. 9939. Drawings to Specification. [Class 98 (ii)] A colour-correction mask for use in the lenscopying of a colour transparency compensates not only for undesired light absorption of the colouring matters used in the transparency, or in the copy, or in both, but also for the .uneven illumination of the field when making the transparency, or the copy, or both, due to the lens defect which causes a falling-off in the illumination from the centre to the periphery of the field. The mask is made by exposing a light-sensitive film or plate to light passed through a lens system showing said unevenness, producing from the developed image a positive, exposing another light-sensitive film or plate to light passed through this positive and the colour transparency in register, and processing the layer to yield a negative of lower gamma. Light exhibiting uneven field must be avoided in exposures other than that first mentioned. The said positive may be made by first making a negative on a high-contrast sensitive layer, developing the layer to gamma 3, printing from it a positive on a medium-contrast sensitive layer, and developing it to gamma 1. The mask is printed by contact from this positive, in register with the colour transparency, on to a sensitive layer which may be that described in Specification 555,383, using light which may be white, but preferably consists of wavelengths longer than blue, e.g. yellow, green, red, or green and red occupying a narrow waveband, as described in Specification 551,614. The print may be processed to neutral grey (e.g. a silver image of gamma 0.45), or to a colour (e.g. yellow) by colour development as described in Specifications 553,196, 553,229 and 553,230. The process of making the mask is the same, whether or not the original colour transparency exhibits uneven density due to defect in the taking lens, the difference in correction in the two cases being achieved by adjusting the gammas to which the fieldevening positive and the mask are developed. In printing the mask, instead of superimposing the field-evening positive and colour transparency in register, they may be printed successively in either order upon the sensitive layer. As the field-evening correction required varies according to the angular field of the copying projector, separate masks must be made for the principal magnifications of said projector. The mask is used in combination with the colour transparency from which it was made to print copies by projection, preferably in the same projector as was used in making the fieldevefiing positive, which copies may be multicolour made on multilayer material, or colourseparation records, which may be processed as by reversal colour development. Specifications 512,608 and 537,864 also are referred'to.