British Kinematography (1950)

December, 1950 189 PRECISION METHODS IN PRODUCING 16mm. COLOUR FILMS Denis Ward, Ph.D., M.B.K.S., F.R.P.S* Read to the B.K.S. Sub-standard Film Division on November 8, 1950. IT is proposed to confine this talk mainly to production of films in 16 mm. Kodachrome. This is done for two reasons : first because I have had more practical experience of this medium than other colour processes, and secondly because 16 mm. Kodachrome is one of the few processes which can be used for direct 16 mm. production in this country. The target to be arrived at in producing .a 16 mm. colour film must be the results in projection : for the picture, a bright picture of high definition ; for the sound, quality, with particular reference to intelligibility under average 16 mm. projection conditions. Let us consider these. Colour Photography. It is not proposed to discuss picture definition except to say that fully corrected lenses and good equipment are required, and that contributory factors to apparent good definition are depth of focus and careful lighting. Neither is it felt necessary to go into the theory of colour photography ; this has been dealt with fully many times before by those more competent to do so than myself. It is sufficient to mention that Kodachrome is a subtractive colour process, and consists of an integral tripack film made up of a base with three emulsion layers. The top layer is sensitive to blue light, the middle layer is sensitive to blue and green light, and the bottom layer is sensitive to blue and red light ; a yellow filter coating beneath the top layer prevents any blue light reaching the other layers, so that the result is that the layers working from the top are sensitive to blue, green and red light respectively.1-2. After exposure in the camera, the film is reversal processed. In the course of the processing, dyestuffs are developed in the layers, the silver removed, and the result is a colour positive comprising the base and three dyestuff images, one in each layer, complementary in colour to the colour which the layer recorded, that is working from the top, yellow, magenta and cyan. The same fundamental principle is true for other integral tri-pack reversal colour films, such as Agfa1 and Ansco Colour,1-3 though the methods of developing the dyestuffs differ, whilst for negative-positive colour processes, again, the same principles apply, except that the colour positive is obtained by printing. Colour photography makes use of the fact that if the visible spectrum be divided into three approximately equal parts, the radiations in each third will give rise to the sensations of red, green and blue respectively. There are unfortunately no dyestuffs yet known of which the spectral transmission curves are perfect for three-colour reproduction. Therefore accurate colour reproduction cannot be expected. The best that can be hoped for is a compromise and an approximation to truth in the picture. Printing Limitations. A further degradation inevitably occurs in making prints.4 The spectral characteristics of the printing light are rarely the same as those of the light illuminating the original scene, also in any photographic copying process contrast is increased ; attempts to combat this tend to result in loss of colour saturation in the print. In professional film production we are, of course, concerned with print quality. The master original film must be regarded and treated in the same * Managing Director, Technical & Scientific Films, Ltd.