Patent ID: 7193787

Claim:
A zoom lens system, in an order from an object side to an image side, comprising: a first lens unit having a positive optical power; a second lens unit having a negative optical power; a third lens unit having a positive optical power; and a fourth lens unit having a positive optical power, wherein intervals of the lens units are changed during zooming; and wherein letting N 21 be a refractive index of a material constituting a negative lens element disposed on the most object side in the second lens unit, a following condition is satisfied: 1.90<N21 <2.50, wherein at least a part of the fourth lens unit is moved during focusing; and wherein letting BF be a smaller one of air conversion quantities from the fourth lens unit to an image plane in a state focused on an infinite object at a wide-angle end and at a telephoto end, and fw be a focal length of the whole system at the wide-angle end, a following condition is satisfied: 4.5 <BF/fw< 8.0.