Patent ID: 7649693

Claim:
A zoom lens consisting of plural groups and serving to change group spacing or spacings to thereby perform magnification changing or adjusting operation, the zoom lens comprising a first lens group GR 1 having positive refractive power, a second lens group GR 2 having negative refractive power and a third lens group GR 3 having positive refractive power which are arranged in order from the object side, and a last lens group GRR arranged at the side closest to image surface and having negative refractive power, wherein the first lens group GR 1 is constituted by single positive lens, and satisfies the following conditional formulas (1), (2) 0.5< Y max/ FW< 1.3 (1) VdG1>40 (2) wherein in the above formulas, Ymax: maximum image height on an image pick-up surface; FW: focal length at the wide-angle end state of the entire lens system; and VdG1: Abbe number at d line of the first lens group GR 1 , wherein the first lens group GR 1 satisfies the following conditional formula (3) 2< F 1/√ FW·FT< 15 (3) wherein in the above formula, F1: focal length of the first lens group GR 1 ; FT: focal length at the telescopic end state of the entire lens system; and √FW·FT: square root of product of FW and FT and wherein the last lens group GRR includes a negative lens GRn at the side closest to the object, and a positive lens GRp at the side closest to the image surface, and satisfies the following conditional formulas (4), (5) and (6) 1.2<βGRRT<1.8 (4) 0.2< Twbf/FW< 1.2 (5) VdGRRn>VdGRRp (6) wherein in the above formulas, βGRRT: magnification at the telescopic end state of the last lens group GRR; Twbf: back focus (air conversion length) at the wide-angle end state; VdGRRn: Abbe number at a d line of the negative lens GRn; and VdGRRp: Abbe number at a d line of the positive lens GRp.