Zoom lens system

A zoom lens system consisting of, in order from an object:

• a first lens group having positive refractive power;
• a second lens group having negative refractive power;
• a third lens group having positive refractive power;
• and
• a fourth lens group having positive refractive power;
• zooming being carried out by moving the second lens group and the third lens group along the optical axis;
• the first lens group consisting of, in order from the object,
• a front lens group of the first lens group having positive refractive power;
• a middle lens group of the first lens group having negative refractive power;
• and
• a rear lens group of the first lens group having positive refractive power;
• in the fourth lens group, there being three lens portions with refractive power that are, in order from the object;
• a front lens group of the fourth lens group having positive refractive power;
• a middle lens group of the fourth lens group having negative refractive power;
• and
• a rear lens group of the fourth lens group having positive refractive power;
• the front lens group of the first lens group comprising two positive lens elements and a negative lens element;
• the middle lens group of the first lens group comprising a positive element and a negative lens element;
• the rear lens group of the first lens group comprising a positive lens element;
• focusing to a close object being carried out by moving the middle lens group of the first lens group along the optical axis;
• the front lens group of the fourth lens group comprising a positive element and a negative lens element;
• the middle lens group of the fourth lens group comprising a positive element and two negative lens elements;
• the rear lens group of the fourth lens group comprising a positive lens element and a negative lens element;
• imaging position being varied by shifting the middle lens group of the fourth lens group perpendicularly to the optical axis;
• and
• the following conditional expression being satisfied:
• 2.5<|(F1f×F1r234t)/(F1m×Φ1)|<5.0
• where Φ1 denotes the maximum effective diameter of the first lens group, F1f denotes the focal length of the front lens group of the first lens group, F1m denotes the focal length of the middle lens group of the first lens group, F1r234t denotes the combined focal length of the rear lens group of the first lens group, the second lens group, the third lens group, and the fourth lens group in the telephoto end state.