ZOOM OPTICAL SYSTEM, ALIGNER HAVING THE ZOOM OPTICAL SYSTEM, AND ALIGNING METHOD

摘要

A zoom optical system capable of ensuring a required magnification without substantially changing positions of an object plane and an image plane and positions of an entrance pupil and an exit pupil when a focal length is changed. When the focal length is changed between a maximum focal length state and a minimum focal length state, at least two lens groups are moved along a predetermined track, and the predetermined track is specified so as not to substantially change the positions of the object plane and the image plane and positions of the entrance pupil and the exit pupil. When the focal length is changed to the minimum focal length state, the lens group (G2) having a negative refractive power is moved toward the object. When the focal length is changed to the maximum focal length state, the lens group (G2) having a negative refractive power is moved toward the image.