GB1251482A - - Google Patents

Abstract

1,251,482. Colour television. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. 20 March, 1970 [25 March, 1969], No. 13481/70. Heading H4F. [Also in Division G2] A colour separating prism system comprises a plurality of dichroic layers 44, 46, each on a prism surface, each layer being reflective for a different part of the optical spectrum, and at least one partially reflective, partially transmissive layer, on a further prism surface, disposed in an air gap 45 adjoining a dichroic layer. The blue component of incident light 57 is reflected by the dichroic layer 44 on a prism 41, and after total internal reflection at face 48 of the prism impinges on a 'blue' camera tube 54. Red and green light passes through the layer 44, crosses an air gap 45 and strikes a partially reflective partially transmissive layer on face 49 of a second prism 42, and that part which is reflected also reaches the " blue " tube 54, so that if the incident light 57 is white the light received by the tube 54 is white-blue. Light passing through the layer on face 49 strikes the second dichroic layer 46 on the prism 42, where the red component is reflected and reaches a " red " tube 55 after further reflection at face 49. The green component crosses an air gap 47 where some is reflected at a second partially reflective partially transmissive layer on face 50 of a third prism 43 and reaches the " red " tube, while most passes directly through the prism 43 to a " green " tube 56. The layers on the faces 49 and 50 may comprise small reflecting domains, and their reflection coefficients may or may not be frequency-dependent. Each partially reflective layer gives rise to a second image at the corresponding camera tube, and the air gap must be so narrow that the system is incapable of resolving the two images.