Patent ID: 8976455
Filing Date: 2015-03-10
Classification: G02B

Abstract:
1. A variable-magnification projection optical system substantially consisting of: a first lens group that has a negative refractive power, is disposed at a most enlargement-side position and is fixed during magnification change; a last lens group that has a positive refractive power, is disposed at a most reduction-side position and is fixed during magnification change; and a plurality of lens groups that are disposed between the first lens group and the last lens group and are moved during magnification change, wherein a most enlargement-side lens group of the lens groups that are moved during magnification change has a negative refractive power, the variable-magnification projection optical system is configured to be telecentric on a reduction side, and conditional expressions (1-1), (2) and (5) below are satisfied: where Bf is a back focus, which is an equivalent air distance, on the reduction side of the entire system at a wide-angle end, fw is a focal length of the entire system at the wide-angle end, f2 is a focal length of the most enlargement-side lens group of the lens groups that are moved during magnification change, and fe is a focal length of the last lens group.