PURPOSE: To obtain a small size zoom lens system of zooming ratio 3W6 by changing magnification by changing distance between the first and second groups and distance between the second and third groups and moving the first group in manual focussing and moving rear lens groups in case of automatic focussing in a zoom lens system that starts with the first group of positive refraction and the second group of negative refraction.

CONSTITUTION: The system starts with the first groupIof positive refraction and the second group II of negative refraction from the subject side successively. Magnification is varied by changing air distance between the first and second groups and air distance between the second and third groups. In manual focussing, the first groupIis moved in the direction of optical axis independently, and in case of automatic focussing, a lens group LF provided in the rear of the lens system is moved. Accordingly, no mechanical interference takes place between manual focussing and automaic focussing. Deterioration of aberration and enlargement of the lens system are prevented by making the focal length f1 of the first group and the focal length fF the lens group LF 0.3<fW/f1<0.6, 0.07< fW/fF<0.4 (fW: shortest focal length of the whole system).