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

摘要

A device for combining three sub-beams (bG, bR, bB) of different colours to one coulour beam (bC) is described, which device comprises two colour-selective reflectors (21, 23) which are arranged on transparent substrates (20, 22). By arranging a plate (27) whose product of refractive index and thickness is equal to that of the substrates (20, 22) in the path of only the beam (bG) which is reflected by both reflectors, it is possible to correct the astigmatism caused by the substrates (20, 22) by means of one correction element (28) in the path of the combined beam (bC).