BEAM-COMBINING DEVICE AND COLOUR IMAGE PROJECTION APPARATUS PROVIDED WITH SUCH A DEVICE

摘要

An optical device for combining three sub-beams of different colors to one color beam is disclosed having a first and a second color-selective reflector arranged on transparent plate-shaped substrates, the first reflector reflecting a first of said sub-beams, the second reflector reflecting the first sub-beam and a second of said sub-beams and a third of said sub-beams passing through the second reflector and its substrate. A transparent plate is arranged in the path of the first sub-beam and in front of the first reflector, the transparent plate having a product of refractive index and thickness equal to that of the substrates of the first and second reflectors. An astigmatism correcting element is positioned in the path of the color beam.