Zoom lens system

A zoom lens system with a vibration reduction mechanism comprising, in order from an object:

• a first lens group having positive refractive power;
• a second lens group having negative refractive power;
• and
• a third lens group having positive refractive power,
• when a state of lens group positions varies from a wide-angle end state to a telephoto end state, a distance between the first lens group and the second lens group increasing, and a distance between the second lens group and the third lens group decreasing,
• the third lens group being composed of, in order from the object, a 31 lens group having positive refractive power, a 32 lens group having negative refractive power, and a 33 lens group, and
• image blur on an image plane caused by a camera shake being reduced by moving only the 32 lens group perpendicular to the optical axis.

A method for forming an image of an object and varying a focal length, comprising:

• providing a zoom lens system that includes, in order from the object, a first lens group having positive refractive power, a second lens group having negative refractive power, and a third lens group having positive refractive power, the third lens group, including in order from the object, a 31 lens group having positive refractive power, a 32 lens group having negative refractive power, and a 33 lens group;
• varying the focal length by increasing a distance between the first lens group and the second lens group, and decreasing a distance between the second lens group and the third lens group, when the state of the zoom lens system varies from a wide-angle end state to a telephoto end state;
• and
• moving only the 32 lens group perpendicularly to the optical axis to reduce image blur on an image plane caused by a camera shake.