GB716332A - Optical beam splitting or combining systems - Google Patents

Abstract

716,332. Optical systems. TECHNICOLOR MOTION PICTURE CORPORATION. Nov. 13, 1951 [July 21, 1951], No. 26548/51. Class 97(1) An optical image-forming system is combined with a transparent body carrying a wedge-shaped interference coating disposed at a predetermined distance from the exit pupil of the system. The thickness gradient of the coating is so related to this distance from the exit pupil that for chief rays the shift of the reflection and transmission bands in one sense due to change in angle of incidence across the coating is substantially equal to the shift of such bands in the opposite sense due to change in thickness of the coating, whereby there is substantially no variation across the coating of the peak reflected and transmitted wavelengths. The transparent body may be an optical flat or cube 'and there may be more than one interference coating. In one form, Fig. 9, the optical system comprises a lens 04 and the transparent body is composed of four prisms P5 to P8 supporting crossed wedge-shaped interference coatings, the thickness gradients of which are related to the distance of the coatings from the exit pupil of the system. The coatings transmit green light while one coating Cw3 reflects blue light and coating Cw4 reflects red light. In another form, Fig. 11, light from three cathode ray tubes 41, 42. 43 passes through a Schmidt system and is combined by crossed coatings Cw8, Cw9 on a screen 51. In Fig. 10, light from a cathode ray tube 21 is modulated by a colour film 25 and split by coatings Cw6 and Cw7 so that blue, green and red light falls on phototubes 30b, 30g and 30r respectively. The wedgeshaped coatings are obtained by vaporization on a surface tilted at the required angle which is determined from known calibration data. The optical principles underlying the invention are fully explained in the Specification and Specifications 398,339, 666,160 and 711,814 are referred to.