GB675357A - Multiple beam optical system - Google Patents

Abstract

675,357. Optical systems. AMERICAN CYANAMID CO. Dec. 11, 1950 [March 31, 1950], No. 30243/50. Class 97 (i). A system for producing a multiple beam from a single beam or vice versa, particularly for use in colour photography or colour television comprises in optical alignment a double prism splitting an incident beam into two diverging beams plane polarized at right angles to each other, means, such as a retardation plate, for depolarizing the divergent beams without changing their relative intensities, a second double prism splitting each depolarized beam into two beams plane polarized at right angles to each other, and a lens for focusing the beams to form images. Fig. 4 shows the system as applied to a three-colour television camera. Light from the objective 13 after passing a stop 24 is divided by a Wollaston prism 1 into two beams which are depolarized by a retardation plate 2, for example of calcite, and again divided by a second Wollaston prism 3 oriented at right-angles to the first. The beams pass through a lens 5, a decentred lens 15 and colour filters R, G, B to reach the camera tubes 16, the fourth beam being absorbed by a filter 17. The elements 1, 2 and 3 may be slidably mounted on rails to permit of adjustment of the images relative to the tubes 16. A similar system is described for three- or fourcolour photography or kinematography. Fig. 5 shows the system applied to the projection in superposition of four colour separation records 4, four collimated beams from which after passing through the appropriate colour filters R, G, B and neutral filter N are converged by a lens 5. Each beam is passed through a filter 20 rendering the beams plane polarized, the members of the upper and lower pairs being plane polarized at right-angles to correspond with the polarization states of the beams diverging from the system shown in Fig. 4. After passing the Wollaston prism 3 and depolarizer 2, the beams, now recombined as two beams, are rendered plane polarized at right angles by polarizers 21, are combined by the Wollaston prism 1 and focused on the screen by a suitable objective. For use in television the images 4 are replaced by three television receivers, or the filters R, G, B, N are dispensed with, the receiver tubes having suitable phosphors producing appropriately coloured beams. Instead of using the polarizers 20 and 21 the unwanted beams may be removed by a suitable diaphragm located at the position of the stop 24 shown in Fig. 4. For television projection the decentred lenses 15 of Fig. 4 may be used to allow the television receivers to be spaced apart on a pyramid reflector provided for this purpose. If desired, a further depolarizer and Wollaston prism may be provided beyond the prism 3 shown in Fig. 4, to produce further images.