Color separation/synthetic optical system including two dichroic mirrors angled for correction of astigmatism

Claim 1

A color separation/synthetic optical system in which a plurality of dichroic mirrors for allowing an incident light to be transmitted therethrough or to be reflected thereon every different ray of color light are provided in succession on a center axis of the transmitted bundle of light to separate a white light into respective rays of color light of red, green and blue by the plurality of dichroic mirrors, and to synthesize respective rays of color light of red, green and blue into a predetermined color light, wherein the system has at least two first and second dichroic mirrors which are disposed adjacent to each other, said first dichroic mirror comprising a substrate and a mirror layer disposed on a light incident side of said substrate and being arranged within a plane including a first axis vertical to the optical center axis and inclined by a predetermined angle with respect to the optical center axis, said second dichroic mirror comprising a pair of substrates and a mirror layer interposed between said pair of substrates, the thickness and refraction index of one of said pair of substrates at the light incident side being prescribed to give a light, which is reflected by said second dichroic mirror, an astigmatism to compensate an astigmatism given by said first dichroic mirror, the thicknesses and refraction indexes of said pair of substrates being prescribed to give a light, which is transmitted through said second dichroic mirror, an astigmatism to compensate the astigmatism given by said first dichroic mirror, said second dichroic mirror being arranged within a plane including a second axis vertical to both of the optical center axis and the first axis and inclined by a predetermined angle with respect to the optical center axis.