Proceedings of the British Kinematograph Society (1931)

colour matrix has, therefore, to be separated from the emulsion, and this is done by first coating it with an excessively thin layer of gelatine about 3 ee in thickness, and on top of this is coated a second layer of celluloid about the same thickness. E ti The finished roll then passes to the emulsioning department, whereitis coated with a panchromatic emulsion which we : have worked out specially for the process. Fig. 4 The spectogram (lig. 4), shows the colour sensitiveness to half-watt light of this emulsion, which has a speed according to our estimation of 3,000 to 4,000 H. and D. I do not wish to enter into the controversial field of speed determination, but I think we can justly claim that our emulsion, to light of the average talking picture studio, is considerably faster than any other make. The Autochrome and Agfa plates are too well known to make it necessary to describe what happens in the processing of the film. The film is self-screening ; it is used in any Kinecamera without any alteration, except that it is threaded with the film-side facing the lens, so that the emulsion is exposed through the colour matrix. The pictures are exposed at the usual rate of 16 or 24 per second, as the case may be, and using an aperture of F/2 or F/2.5 our experience is that no extra light is necessary in the studio The many artists we have engaged in our experimental studio at Sawston seem united on this point. We have, of course, photometric data of the light intensity used, which can readily be translated into terms of larger studios. The exposed film is developed in one of the well-known baths containing a solvent of silver bromide for three minutes at 65° F., and is then put through an acid bichromate bath in order to dissolve out the original image. After reversal the film is re-developed with a simple metol-hydroquinone bath, and is then ready for printing. It may, perhaps, be an advantage that the original negative is developed actually as a positive, and, as it only takes eight or ten minutes for the whole procedure, the producer can, if desired, see his various shots on the screen almost as fast as they are taken. We now come to the second stage of the process—the making of duplicates. Those who have devoted any time in endeavours to copy or duplicate Autochrome or Agfa screen plates will, I am sure, realise the nature of the problem we have had to deal with in this matter. Indeed, it has been said on more than one occasion that to copy a screen image with a geometrical pattern is an impossibility. No process of this kind is of any commercial value unless the duplication is both commercial and good. The technique we have worked out for duplicates is briefly as follows :— A standard type of projection printer (a Debrie in our case), is used with the three following slight modifications :— (1) A special lens working at F/2 has been designed, which gives us extremely critical definition of the silver image, while slightly diffusing the image of the matrix, which, as you will remember, is separated from the silver image by a distance of 6u. (2) Between the lens and the copying film is a piece of special shaped glass, which we call the diffuser. This further throws out the image of the reseau, and makes moiré pattern practically an impossibility. (3) In order to control the brightness of the light as the density of the original varies, we employ a rotating drum containing a number of neutral grey filters. We cannot alter the strength of the lamp in the ordinary way, because the introduction of resistance into its circuit would alter the spectral distribution. The various neutral grey filters are swung into position quite easily and automatically, and in this way long lengths of films can be printed, with perfect results. The standard rate of printing obtains, viz., 800 pictures per minute, In the pictures which I shall show presently, the originals, termed by us Master Positives, and duplicates are mixed indiscriminately, and, although the duplicates are not quite as perfect as the originals, it must be remembered that the public will only see the copies, and, having no standard of comparison,will be perfectly satisfied. There is one point I should like to add in connection with duplicates, and that is, that quite unexpected progress during the last month or two on certain new lines of investigation leads us to feel certain thatin the very near future it will be impossible to tellthe copy from the original. Before showing the pictures there are one or two points of interest in connection with the sensitometry of the high speed colour screen emulsions which it may be of interest to touch upon. 5