Patent ID: 8157386

Claim:
A projection optical system comprising: a plurality of lens groups including at least a first lens group and a second lens group, and a curved mirror, wherein the projection optical system includes a two story structure having a first story located below a second story in a first downward direction, and includes a plurality of plane mirrors that bends at least two times the light incident from a color combining system disposed upstream of the light path of the projection optical system, the plurality of plane mirrors including a first plane mirror disposed between the first lens group and the second lens group, the first plane mirror reflecting the light from the first lens group in a second upward direction that is opposite the first downward direction, a second plane mirror disposed between the first plane mirror and the second lens group in such a way that a normal to a reflection plane of the second plane mirror is perpendicular to a normal to a reflection plane of the first plane mirror, and a third plane mirror disposed between the second plane mirror and the second lens group, the third plane mirror reflecting the light from the second plane mirror toward the second lens group.