Patent ID: 7540671

Claim:
A zoom optical system comprising, in order from an object side thereof, a first lens group having positive refracting power, a second lens group having negative refracting power, a third lens group having positive refracting power and a fourth lens group having positive refracting power, wherein: at least one lens is formed by molding of a first lens blank that provides a surface including at least an optical function surface after molding, and a second lens blank that provides a surface other than said surface including at least an optical function surface after molding, and comprises a one-piece lens wherein said first lens blank and said second blank are integrated together, said second lens group or said fourth lens group comprises at least one said one-piece lens, and at least one positive lens is positioned in said second lens group, and satisfies the following condition: 0.1 <HH 2/φ2<15 (3G) where HH2 is a principal point spacing (mm) of the positive lens in the second lens group and φ2 is a refracting power of the positive lens in the second lens group.