| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical system that easily offers good optical performance over an entire range of projection distance.SOLUTION: An optical system comprises, in order from the magnification conjugate side to the reduction conjugate side, a first lens group having negative refractive power and a rear group comprising one or more lens groups, the first lens group including, in order from the magnification conjugate side to the reduction conjugate side, a subgroup B1a having negative refractive power, a subgroup B1b having negative refractive power, and a subgroup B1c having positive refractive power, where the subgroup B1a has a negative lens located on the most magnification conjugate side and one or more positive lenses. When shifting focus from infinity to a very short distance, the subgroup B1b and the subgroup B1c move toward the reduction conjugate side while increasing the distance therebetween. |
