An optical system includes a first focusing unit and a second focusing unit that move in different loci during focusing. In a first arrangement state, the first focusing unit and the second focusing unit are so arranged to generate a first aberration while maintaining an in-focus state at a predetermined object distance, and in a second arrangement state, the first focusing unit and the second focusing unit are so arranged to generate a second aberration different from the first aberration while maintaining the in-focus state at the predetermined object distance.