Patent ID: 7307794

Claim:
A zoom lens system comprises a negative first lens group, a positive second lens group, a diaphragm, a negative third lens group, and a positive fourth lens group, in this order from an object, wherein said negative third lens group comprises cemented lens elements having a positive lens element and a negative lens element; wherein said positive fourth lens group comprises a positive single lens element, and cemented lens elements having a positive lens element and a negative lens element, in this order from the object; wherein said negative first lens group is a focusing lens group; and wherein said zoom lens system satisfies the following conditions: 0.4 <|fi ( i= 1)|/ fBw< 0.8 1.0 <fi ( i= 4)/ fi ( i= 2)/<1.8 wherein fi designates the focal length of the i th lens group(1≦i≦4); and fBw designates the back focal distance at the short focal length extremity.