Patent ID: 7605987

Claim:
A zoom optical system comprising, in order from its object side, a positive first lens group, a negative second lens group, a positive third lens group and a positive fourth lens group wherein upon zooming from a wide-angle end to a telephoto end, the second lens group moves in such a way as to lie more on an image plane side at the telephoto end than at the wide-angle end and the third lens group moves, characterized in that a lens component L 21 having negative refracting power is located in, and nearest to the object side of, the second lens group, and satisfies the following conditions: −1.0<( R 21f +R 21r )/( R 21f −R 21r )<0.1 (1) 1.5 <FL 21 /F 2 <6.0 (2) where R 21f is a paraxial radius of curvature on an object side of the lens component L 21 having negative refracting power, R 21r is a paraxial radius of curvature on an imaging plane side of the lens component L 21 having negative refracting power, F 2 is a focal length of the whole second lens group, and FL 21 is a focal length of the lens component L 21 having negative refracting power.