Patent ID: 7643222

Claim:
A zoom optical system comprising, in order from an object side: a first lens unit having a negative refractive power; a second lens unit having a positive refractive power; a third lens unit having a positive refractive power; and a fourth lens unit, the zoom optical system changing a space between the lens units to thereby perform zooming and focusing, the fourth lens unit being fixed to an image surface, the first lens unit comprising a biconcave negative lens, the zoom optical system satisfying the following condition: −3.0<( r 1GF +r 1GR )/( r 1GF −r 1GR )<0.3 wherein r 1GF denotes a paraxial radius of curvature of an object-side surface of the negative lens of the first lens unit, and r 1GR denotes a paraxial radius of curvature of an image-side surface of the negative lens of the first lens unit, and wherein the total number of lenses included in the zoom optical system is six.