Patent ID: 8331033

Claim:
A zoom optical system comprising, in order from an object side: a first lens unit with a negative power; a second lens unit with a positive power; a third lens unit with a positive power; and a fourth lens unit; wherein a position of the first lens unit and a position of the fourth lens unit are fixed in reference to an image surface, while the second lens unit and the third lens unit are moved along an optical axis for magnification change, to change distances between the respective lens units of the zoom optical system, wherein the third lens unit comprises an aperture stop and at least three lens elements that include at least one lens element with a positive power and at least one lens element with a negative power, and a most image-side lens element of the third lens unit is a meniscus lens element with a concave surface facing the image side, and wherein the third lens unit comprises, in order from the object side, the aperture stop, a lens element with a positive power, a lens element with a negative power and the meniscus lens element with a concave surface facing the image side, and the following condition (1) is satisfied: −1.0 <HF 3 g/fw<− 0.55 (1) where HF3g is a position of a front principal point of the third lens unit, and fw is a focal length of the entire zoom optical system at a wide-angle end position.