Patent ID: 7450316

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; a third lens unit having a positive refractive power; and a fourth lens unit having a positive refractive power, during zooming from a wide-angle end to a telephoto end, at least the first lens unit and the third lens unit being moved toward the object side so as to increase a space between the first lens unit and the second lens unit and decrease a space between the second lens unit and the third lens unit, the following conditions being satisfied: 35°<tan −1 ( I/f w ) (1); 5<( f t /f w ) (2); 0.5 <f g1 /f t <1.35 (3); 0.4 <|f g2 /f g3 |<1 (4); and 0.5<( M 2gt /M 2gw )/( M 3gt /M 3gw )<1.3 (5), in which f w is a focal length of the zoom lens system in the wide-angle end, f t is a focal length of the zoom lens system in the telephoto end, I is a maximum image height of a formed image, f g1 is a focal length of the first lens unit, f g2 is a focal length of the second lens unit, f g3 is a focal length of the third lens unit, M 2gw is a lateral magnification of the second lens unit in the wide-angle end, M 2gt is a lateral magnification of the second lens unit in the telephoto end, M 3gw is a lateral magnification of the third lens unit in the wide-angle end, and M 3gt is a lateral magnification of the third lens unit in the telephoto end.