Patent ID: 7495842

Claim:
A zoom lens comprising, in order from a magnifying side, 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 cover glass, wherein: changing the magnification of a whole lens system thereof is attained by configuring such that while a magnification varying operation is in effect, the first lens group is left fixed, 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 to move 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 an airspace set on a contracting side of the third lens group at the wide angle end; −1.1< f w /f II <−0.45 (1) 0.4< f w /f III <0.6 (2) 1.7< d wIII /f w (3) where f w : composite focal length of the whole lens system at the wide angle end in which it is 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 said cover glass at the wide angle end.