Patent ID: 7764438

Claim:
A zoom lens system comprising, in order from an object side: a first lens unit having a positive refractive power; a second lens unit having a negative refractive power; a third lens unit having a positive refractive power; and a fourth lens unit having a positive refractive power, wherein the first lens unit comprises a negative lens element and a positive lens element in order from the object side; the second lens unit comprises a negative lens element and a positive lens element in order from the object side; the third lens unit comprises a positive lens element, a positive lens element and a negative lens element in order from the object side; the fourth lens unit comprises a positive lens element; the total number of the lens elements of the first to fourth lens units is eight; during magnification change from a wide-angle end to a telephoto end, an interval between the first lens unit and the second lens unit, an interval between the second lens unit and the third lens unit and an interval between the third lens unit and the fourth lens unit change, and the first lens unit moves, the positive lens element in the first lens unit is a double convex lens, and the negative lens element in the second lens unit is double concave lens having an aspherical surface.