Patent GB-547062-A (GB)
Title: Improvements in or relating to the production of sound tracks on motion picture film
IPC: G11B7/00
Filed: 1940-06-18
Abstract: 547,062. Kinematograph picture and sound films. MITCHELL, J. June 18, 1940, No. 10553. [Class 98 (ii)] In the production of kinematograph films bearing picture and sound records, a film is used which has a light-sensitive silver halide coating which is capable of yielding images of widely different contrast under the same development conditions according to the colour composition of the light used in forming the images; the colour composition of the light used in forming the picture record is selected to yield a developed image of the desired contrast under predetermined development conditions, the colour composition of the light used in forming the sound record is similarly selected, and the two records are developed together under the predetermined conditions. White light may be used in forming the picture record (modified if desired by the usual taking filters), and the light for forming the sound record is selected to give the desired difference of contrast. In the original recording of a negative picture record and a negative variable density sound record, the material employed may comprise a mixture of two silver halide emulsions, one panchromatically sensitized and of normal contrast characteristics for negative material, and the other infra-red sensitized and of low contrast characteristics. Variation in the contrast of the sound record may be effected by the use of filters which pass in addition to the infra-red more or less of the visible light. Where a variable-area sound record is employed, the infrared sensitized emulsion should have high contrast characteristics. The independent control of the picture and sound records may also be applied to a film to be processed to a positive by reversal. In printing from sound and picture records carried on separate films or on the same film, light of different colour may be used in printing the two records. The material may comprise a support carrying a mixture of a highcontrast green-sensitized silver chloride emulsion with a low-contrast non-optically sensitized silver bromide emulsion. The contrast of any section or sections of one print, sound or picture, may be controlled to compensate for inequalities of contrast in the original record, the requisite relative contrast of the picture and sound prints being maintained. In an example, kinematograph film base is coated with a light-sensitive emulsion consisting of a mixture of 1 litre of normal-gradation panchromatic emulsion containing 2.2 per cent of silver and 25 mgms. of 2:21- diethyl-8-methylthiacarbocyanine bromide with 1 litre of a very high-contrast emulsion of the same silver content to which has been added 12 ccs. of a 0.005 per cent solution of 2:21-diethyl- 5:6:51:61-dibenzthiadicarbocyanine iodide. Under the same development conditions, exposure to unscreened daylight results in a gamma of 1.2 whereas exposure through a filter transmitting only freely above 7,000 A results in a gamma of 3.05. The material is used in the original recording of a negative picture record and a negative variable-area sound record, infra-red light being used in the recording of the latter. In a second example, kinematograph film base is coated with an emulsion consisting of a mixture of 2 litres of a panchromatic emulsion of the kind used in the first example and litre of a normal-gradation emulsion of the same silver content to which has been added 12 ccs. of a 0.005 per cent solution of 2:21-diethyl-5:6:51:61- dibenzthiadicarbocyanine iodide. Under the same development conditions, a gamma of 1.5 is obtained on exposure with unscreened daylight, whereas a gamma of 0.65 is obtained using a filter of the kind referred to in example 1. The material is used in the original recording of a negative picture record and a negative variabledensity sound record. In a third example, the base is coated with an emulsion consisting of a mixture of 8 parts by weight of a high-contrast silver chloride emulsion containing 2.7 per cent of silver and 0.0025 per cent of 2:21-diethyl-5:51- dimethoxyoxacarbocyanine iodide and 5 parts by weight of a normal-contrast non-colour sensitized silver bromide emulsion containing 5.3 per cent of silver. Various mixtures of blue and yellow light are used in printing pictures and sound records on to this material, curves being given for the results obtained. Specifications 494,088 and 547,060 are referred to.