Patent ID: 7394599

Claim:
A zoom lens comprising: a first lens group having a positive or negative refractive power as a whole, a second lens group having a negative refractive power as a whole, a third lens group having a positive refractive power as a whole, and a fourth lens group having a positive refractive power, wherein a variable power as a whole lens system of the zoom lens is established by configuring such that the first lens group and the fourth lens group are left fixed while a variable power is effected, the second lens group is made to move on an optical axis in such a manner as to move in a direction from a magnifying side to a contracting side over a range from a wide angle end to an intermediate area and in a direction from the contracting side to the magnifying side over a range from the intermediate area to a telephoto end, and the third lens group is made to move on the optical axis in such a manner as to move in a direction from the contracting side to the magnifying side over a range from the wide angle end to the telephoto end, and wherein the following conditional expression (1) is satisfied with respect to a power set at the second lens group, the following conditional expression (2) is satisfied with respect to a power set at the third lens group, and the following conditional expression (3) is satisfied with respect to a positional relationship between the third lens group and the fourth lens group at the wide angle end: −1.1 <f w /f II <−0.5 (1) 0.35 <f w /f III <0.55 (2) 1.7 <d wIII /f w (3) where f w : composite focal length of the whole lens system at the wide angle end (focused at a magnifying side object distance of 1700 mm from a lens surface of the first lens group which is situated closest to the magnifying side); f II : composite focal length of the second lens group; f III : composite focal length of the third lens group; d wIII : airspace between the third lens group and the fourth lens group at the wide angle end.