Zoom lens and projector using zoom lens

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 or negative refractive power as a whole, a fourth lens group having a positive refractive power as a whole and a fifth lens group having a positive refractive power as a whole, wherein a variable power as a whole lens system thereof is established by configuring such that the first lens group and the fifth lens group are left fixed while a variable power is effected, the second lens group and the third lens group are 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 fourth 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 and the third lens group, the following conditional expression (2) is satisfied with respect to a power set at the fourth lens group, and the following conditional expression (3) is satisfied with respect to a positional relationship between the fourth lens group and the fifth lens group at the wide angle end:

• (1) −1.1<fw/fII-III<−0.4
• (2) 0.3<fw/fIV<0.55
• (3) 1.7<dwIV/fw
• where
• fw:
• 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;
• fII-III:
• composite focal length of the second lens group and the third lens group 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;
• fIV:
• composite focal length of the fourth lens group;
• dwIV:
• airspace between the fourth lens group and the fifth lens group at the wide angle end.