GB349107A - Improvements in cameras for colour photography - Google Patents

Abstract

349,107. Colour photography. HILGER, Ltd., A., and DOWELL, J. H., 24, Rochester Place, Camden Road, London. Jan. 18, 1930, No. 1821. [Class 97 (i).] The combination of prisms, in an optical system for colour photography, by which the incident beam is divided so that several images of the object are formed is constructed of glasses of more than one refractive index the prisms being so dimensioned and located that the total lateral shift of rays of the same obliquity of initial incidence is the same for each of the selected colours. This ensures that the images for near objects are the same for different colours as well as the images for distant objects. The prisms are dimensioned so that the optical paths through the system are the same for each colour. The mathematical basis for the necessary calculations are set out at length in the Specification. In the form of optical system shown in Fig. 1, the surface J between the prisms A, B is silvered to reflect and transmit the desired proportions of light received for reflection from the surfaces of the prisms C, D to enable images to be formed by the lenses E, F on the film f. The path of the rays is shown in Fig. 3 in which the distance L1 is the total length of the paths in the prisms A, B and the distances L2, L3 are the lengths of the paths in the prisms C, D for the two colours. The refractive index for each of the prisms C, D is chosen so that the points N, P of emergence of the rays are in the same horizontal plane, so that no lateral shift exists for rays of the same initial obliquity. An example is also given embodying the application of the principle to a three-colour system.