Patent ID: 7359126

Claim:
A projection zoom lens having an enlarging side and a reducing side opposite the enlarging side and comprising at least two lens groups arranged from the enlarging side along an optical axis; wherein at least two lens groups move along the optical axis during zooming; of the lens groups that move during zooming, the lens group nearest the reducing side moves to a position closest to the enlarging side at an intermediate position of zooming between the wide-angle end and the telephoto end; a lens group that does not move during zooming may be located on the reducing side of the lens group nearest the reducing side that moves during zooming; and the following conditions are satisfied 2.2 ≦bf/fw≦ 5.0 1.5 ≦ft/fw 55≦νdA 10 <|fr/dd| where bf is the air-equivalent distance along the optical axis between the lens surface on the reducing side of the projection zoom lens and the image plane of the projection zoom lens; fw is the focal length of the projection zoom lens at the wide-angle end; ft is the focal length of the projection zoom lens at the telephoto end; νdA is determined as follows: (a) if a lens group that does not move during zooming is located on the reducing side of the lens group nearest the reducing side that moves during zooming, then vdA is the average value of the Abbe number(s) of the lens element(s) having positive refractive power, among the lens groups that move during zooming, of the lens group that is nearest the reducing side, and the Abbe number(s) of the lens element(s) having positive refractive power of the lens group that does not move during zooming that is located on the reducing side of the lens group that moves during zooming that is nearest the reducing side; or (b) if a lens group that does not move during zooming is not located on the reducing side of the lens group nearest the reducing side that moves during zooming, then vdA is the average value of the Abbe number(s) of the lens element(s) having positive refractive power, among the lens groups that move during zooming, of the lens group that is nearest the reducing side; fr is the focal length of the lens group that moves during zooming that is nearest the reducing side; and dd is the distance along the optical axis between the positions at the wide-angle end and at the telephoto end of the lens group that moves during zooming that is nearest the reducing side.