GB446016A - Improvements in or relating to methods of, and apparatus for, determining colour values of illumination, more particularly in relation to colour photography - Google Patents

Abstract

446,016. Photometric apparatus. HARRISON, G. B., 23. Roden Street, and PURSLOW, E. T., Rodenside Laboratory, Roden Street, Ilford, Essex. Oct. 22, 1934, No. 30289. [Class 97 (i)] The colour values of illumination for colour photographic purposes are determined by measuring the relative proportions of predetermined colour components in a given light by testing the light for each predetermined colour separately by means of a photo-electric cell responsive, or rendered responsive, selectively to that component. In the form shown, the cells 17, 18, 19 are connected to galvanometers 23, 24, 25 which are shunted respectively by variable resistances 26, 27, 28. The resistances are capable of proportional variation by a single control comprising a toothed wheel 29 engaging wheels 30, 31, 32 connected, to the rotating arms of the resistances. The apparatus is primarily designed to enable the necessary filters for colour photography to be found for any illumination when those for a standard illumination are known. The standard filters 20, 21, 22 are placed in front of the cells and the standard illumination is allowed to fall on the cells. By means of the shunt resistances the reading of one galvanometer is adjusted to a predetermined value, e.g. 100, and the readings of the other two 'galvanometers noted. The light to be analyzed then illuminates the cells and again the reading of the same galvanometer is adjusted to 100, the composition of the light in relation to the standard being then deduced from the galvanometer readings. When rectifier cells are used the potentials developed by the cells may be balanced by the fall of potential across three resistances connected in series to the same potentiometer, thus making the potential falls proportionally adjustable.