GB856932A - Improvements in or relating to colour-selective optical systems corrected for astigmatism - Google Patents

Abstract

856,932. Optical systems. PHILIPS ELECTRICAL INDUSTRIES Ltd. Feb. 21, 1957 [Feb. 24, 1956], No. 5889/57. Class 97(1) A colour beam-splitter corrected for astigmatism comprises a system of dichroic plane mirrors positioned inclined to one another so that considered from the direction of incident light, the first colour-selective layer is provided on the front side of a transparent plane-parallel plate having a thickness d1 and refractive index n1 and making an angle a1 with the optical axis, whilst the second colour selective layer is provided on the rear side of a second transparent plane-parallel plate of thickness d2 and refractive index n2 and making an angle a2 with the axis, and a third transparent plane-parallel plate of thickness d3 and refractive index n3 and making an angle a3 with the axis, the incident planes of the second and third plates each being displaced about the axis through an angle of approximately 90 degrees with respect to the incident plane of the first plate and As shown a plate 1 at an angle a1 to the axis xx carries a dichroic layer reflecting the red rays R and transmitting the blue and green (B+G) to a second plate framed by two plates 2, 3 each of half the thickness of the plate 1, arranged with the plane of incidence of an axis beam perpendicular to that of the plate 1 and having between them a dichroic layer 2<1> reflecting the blue ray and transmitting the green. The plates 2 and 3 may be separated, the layer 21 being on the rear face of the plate 2. The planes of incidence on the plates 2 and 3 may be relatively displaced through 180 degrees.