Patent ID: 7595936

Claim:
A zoom lens system, in that 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, the third lens unit including a first lens subunit having a negative optical power, and a second lens subunit having a positive optical power, in that order from the object side to the image side; and a fourth lens unit having a positive optical power, the fourth lens unit including at least a positive lens element, wherein the second and fourth lens units move along an optical axis during zooming, wherein the first lens subunit has no more than a positive lens element and a negative lens element, wherein the second lens subunit has no more than a positive lens element and a negative lens element, and wherein the following conditional expressions are satisfied: 0.21<3aNn−3bPn 0.07<4Pn−3bPn where 3aNn is a refractive index of a material of the negative lens element in the first lens subunit, 3bPn is a refractive index of a material of the positive lens element in the second lens subunit, and 4Pn is a refractive index of a material having the highest refractive index in a material of the positive lens element included in the fourth lens unit.