Telephoto zoom lens system having four lens groups

Claim 1

A telephoto zoom lens system comprising: four lens groups comprising, in order from the object side, of a first group having a positive refractive power and comprising a first sub-part I-1 having a positive refractive power, a second sub-group I-2 having a negative refractive power, and a third sub-group I-3 having a positive refractive power, a second group having a negative refractive power, a third group having a positive refractive power, and a fourth group having a positive refractive power, said lens system achieving zooming by moving the second lens group, which is chiefly responsible for varying magnification, and the third lens group, which has an image position correcting capability, along the optical axis of said lens system, said system achieving focusing when photographing an object at a finite distance by moving only the sub-group I-3 toward the object side, and said lens system further satisfying the following conditions: (1) 0.08<d.sub.(I-1, I-2) /f L <0.16; (2) 0.5<h I-2 /h I-1 <0.8; and (3) 0.3<f L /f.sub.(I-1, I-2) <1.0 where f L : focal length of the overall system at the narrow-angle end; d.sub.(I-1, I-2) : distance between said sub-part I-1 and sub-group I-2; h I-1 : height of paraxial rays from an object at infinity to said sub-part I-1 paraxially at an incident angle of 0°; h I-2 : height of the paraxial rays from an object at infinity to said sub-group I-2 paraxially; and f.sub.(I-1, I-2) : composite focal length of said sub-part I-1 and sub-group I-2.