Patent ID: 7298560

Claim:
A zoom optical system comprising, in order from reduction conjugate side to magnification conjugate side: a first lens unit having a positive optical power; a second lens unit having a negative optical power; a third lens unit having a positive optical power; and a fourth lens unit having a negative optical power, wherein in an entire zoom range, a magnification-side conjugate position relative to a reduction-side conjugate position, and the position of a magnification conjugate side exit pupil of the zoom optical system relative to the reduction-side conjugate position are each substantially fixed, the interval between the first lens unit and the second lens unit at a telephoto end is larger than the interval between the first lens unit and the second lens unit at a wide-angle end, the interval between the second lens unit and the third lens unit at the telephoto end is larger than the interval between the second lens unit and the third lens unit at the wide-angle end, and the interval between the third lens unit and the fourth lens unit at the telephoto end is smaller than the interval between the third lens unit and the fourth lens unit at the wide-angle end.