Patent ID: 8004585

Claim:
A zoom lens system comprising a plurality of lens units and an aperture diaphragm arranged in the lens units, wherein the plurality of lens units include: a positive lens unit that is arranged on an object side relative to the aperture diaphragm and that has positive optical power; a negative lens unit that is arranged on an image side relative to the positive lens unit and on an object side relative to the aperture diaphragm and provided with negative optical power having an absolute value greatest in the entire system and that moves in a direction along an optical axis at the time of zooming; and a focusing lens unit that is arranged in an optical path between the negative lens unit and the aperture diaphragm and that moves in a direction along the optical axis at the time of focusing such that an interval relative to the negative lens unit should vary, and wherein the following condition is satisfied: 1.20<β NT /β NW <4.50 (4) (here, f T /f W >3.0) where, β NT is a composite focal length of the focusing lens unit and the negative lens unit in an infinity in-focus condition at a telephoto limit when the focusing lens unit has negative optical power, or a lateral magnification of the negative lens unit at a telephoto limit in an infinity in-focus condition when the focusing lens unit has positive optical power, β NW is a composite focal length of the focusing lens unit and the negative lens unit in an infinity in-focus condition at a wide-angle limit when the focusing lens unit has negative optical power, or a lateral magnification of the negative lens unit at a wide-angle limit in an infinity in-focus condition when the focusing lens unit has positive optical power, f T is a focal length of the entire system at a telephoto limit, and f W is a focal length of the entire system at a wide-angle limit.