Patent ID: 7196852

Claim:
A zoom lens system, comprising, in order from an object side to an image side: a first lens unit having a negative optical power; a second lens unit having a positive optical power; a third lens unit having a negative optical power; and a fourth lens unit having a positive optical power, wherein during zooming, an interval between the first lens unit and the second lens unit at a telephoto end is smaller than that at a wide angle end, an interval between the second lens unit and the third lens unit at the telephoto end is larger than that at the wide angle end, and an interval between the third lens unit and the fourth lens unit at the telephoto end is smaller than that at the wide angle end, and wherein following conditions are satisfied, 2.5 <ft/fw< 4.0 and 2.2 <bfw/H< 3.0, where fw and ft represent a focal length of the entire system at the wide angle end and that at the telephoto end, respectively, bfw represents a back focus at the wide angle end, and H represents a maximum image height, and wherein the first lens unit is moved along a locus first toward the image side and then toward the object side which is convex to the image side.