Patent ID: 9645483
Date: 2017-05-09
CPC Classifications: G02B,G03B

Claim:
1. A projection optical system comprising: in order from a reduction side, a first optical group which is formed of a plurality of lenses and has positive power; and a second optical group which has one reflective surface having a concave aspherical shape, wherein the first optical group is formed to include a 1-1st lens group having positive power, on the reduction side, and a 1-2nd lens group having weaker positive or negative power, compared to the power of the 1-1st lens group, on the enlargement side, with the widest air interval as a boundary, and wherein the 1-2nd lens group has an reduction-side fixed lens group which is disposed on the outermost reduction side, is fixed when focusing is performed in response to the magnification change, and has positive power, an enlargement-side fixed lens group which is disposed on the outermost enlargement side, is fixed when focusing is performed in response to the magnification change, and has negative power, and at least one moving lens group which is disposed between the reduction-side fixed lens group and the enlargement-side fixed lens group, and moves in the optical axis direction when focusing is performed in response to the magnification change.