Patent ID: 7113346

Claim:
A variable magnification optical system for forming an optical image of an object on a light-receiving surface of an image sensor with variable magnification, the variable magnification optical system consisting of: from an object side, 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, a fourth lens unit having a positive optical power, and a fifth lens unit, wherein, in magnification variation from a wide-angle end to a telephoto end, the first lens unit, the third lens unit, and the fifth lens unit are kept in fixed positions whereas the second lens unit and the fourth lens unit move, wherein the third lens unit includes, from the object side, a positive lens element having a biconvex form, and a negative lens element having a form concave to an image side, the negative lens element having an aspherical surface; and wherein conditional formula (1) below is satisfied: 1 <f 3 /fw <2.6 (1) where f3 represents a focal length of the third lens unit, and fw represents a focal length of an entire system at the wide angle end.