Patent ID: 8049970

Claim:
A zoom lens system comprising, in order from an object side: a first lens unit having a positive refractive power; a second lens unit having a negative refractive power; an aperture stop; a third lens unit having a positive refractive power; and a fourth lens unit having a positive refractive power, during magnification change, the first lens unit, the second lens unit, the third lens unit, the fourth lens unit and the aperture stop being configured to move along an optical axis of the zoom lens system, the first lens unit including two lenses of a negative lens and a positive lens in order from the object side, the second lens unit including two lenses of a negative lens and a positive lens in order from the object side, the third lens unit including three or less lenses including one positive lens and one negative lens, the fourth lens unit including one positive lens, a total number of lens elements included in the first lens unit is two, a total number of lens elements included in the second lens unit is two, a total number of lens elements included in the third lens unit is three or less, and a total number of lens elements included in the fourth lens unit is one, wherein the negative lens and the positive lens of the first lens unit are consisting of single lenses, respectively, and are not cemented to each other, an air lens is formed between the negative lens and the positive lens of the first lens unit, and the following condition is satisfied: −105.0 <SF 1air <0 (9), in which SF 1air is defined as SF 1air =(R 1nr +R 1pf )/(R 1nr −R 1pf ), R 1nr is a radius of curvature of an image-side surface of the negative lens of the first lens unit, and R 1pf is a radius of curvature of an object-side surface of the positive lens of the first lens unit.