GB324394A - Improvements in or relating to photography in natural colours - Google Patents

Abstract

324,394. Baker, T. T., and Colour Photographs (British & Foreign), Ltd. Oct. 25, 1928. Colour photography; plates and films; emulsions preparing. - A tri-pack for colour photography of the kind in which the front, intermediate, and rear sensitive layers record respectively the blue, green, and red sensations, and in which a blue-absorbing filter is interposed between the front and intermediate layers, is characterized mainly in that the front layer comprises an ordinary emulsion of coarser grain than the Lippmann emulsion, which has been rendered highly transparent either by dilution, as with gelatin, or by coating it thinly on its support, and the intermediate layer is less transparent than the front layer, but more transparent than the emulsion layers used in ordinary photography. The front layer recording blue may be an ordinary silver bromide emulsion yielding good density, so diluted or coated that it transmits about 65 per cent of the incident light. The intermediate layer may be a similar or similarly-coated emulsion transmitting about 55 per cent of the incident light, and sensitized for green as with erythrosin to such an extent that the green and blue maxima are equal when the light of a vacuum incandescent lamp is used. The rear layer may be a panchromatic emulsion, or an emulsion sensitized for red as with pinacyanol, coated at normal coating weight. The speeds in daylight of the three layers may be approximately in the ratio 5 : 12: 10, the front layer having a speed of about 250 H. and D. The layers may be coated on celluloid &c. films. The support of the front layer is tinted, or coated on the back, with a yellow filter layer as of acid yellow; and, if the rear layer is panchromatic, the support of the intermediate layer is tinted, or coated on the back, with a pink filter layer as of erythrosin or a dye which is removed or destroyed during development. The emulsions should be such that on development the characteristic curves are substantially straight up to a density of at least 1.2; and their development times for images of equal contrast should not be very different, for example, with equal exposures, they may give development factors of 1.7, 1.5 and 1.25 respectively, with full development. The pack may be exposed in the light of a gas-filled incandescent lamp without a compensating filter; or in daylight with a compensating filter comprising naphthol yellow, filter yellow K, or aesculin.