Patent ID: 7554744

Claim:
A zoom lens system comprising: a first lens unit having positive refractive power; a second lens unit having negative refractive power; a third lens unit having positive refractive power; a fourth lens unit having positive refractive power; and a fifth lens unit, wherein, the lens units are disposed in this order from an object, when the lens positions change from the wide-angle end to the telephoto end, at least the first to fourth lens units are movable in an optical axis direction, the second lens unit moves toward an image and the third lens unit moves toward the object so that the distance between the first lens unit and the second lens unit increases and the distance between the second lens unit and the third lens unit decreases, and the fourth lens moves in the optical axis direction to compensate for a displacement of an image plane due to the movement of the lens units, the fifth lens unit includes a negative subunit having negative refractive power and a positive subunit having positive refractive power and being disposed on the image side of the negative subunit with an air gap provided between the negative subunit and the positive subunit, the fifth lens unit being capable of shifting the image by shifting the positive subunit relative to the negative subunit in a direction substantially orthogonal to the optical axis, a movable aperture stop is provided closer to the object than the fifth lens unit, wherein the following expression is satisfied: 0.03<Δ S/ft< 0.15 where ΔS represents the movement of the aperture stop from the wide-angle end to the telephoto end, in which the movement toward the object is positive, and ft represents the focal length at the telephoto end, and wherein the fifth lens unit is fixed in the optical axis direction.