Patent ID: 9541743
Date: 2017-01-10
CPC Classifications: G02B,G03B

Claim:
1. A projection zoom lens, consisting of: a first lens group, which is provided most toward the magnification side, has a negative refractive power, and is fixed while changing magnification; a second lens group, which is positioned at the reduction side after the first lens group, has a positive refractive power, and moves while changing magnification; a third lens group, which is positioned at the reduction side after the second lens group, has a positive refractive power, and moves while changing magnification; a final lens group, which is provided most toward the reduction side, has a positive refractive power, and is fixed while changing magnification; at least one lens group positioned between the final lens group and the third lens group; and an aperture stop provided between adjacent moving lens groups or provided within one of the moving lens groups; the aperture stop being a variable stop, of which the aperture diameter changes such that the numerical aperture of the zoom lens becomes constant through the entire magnification range; the projection zoom lens being configured such that the reduction side is telecentric; and the projection zoom lens satisfying Conditional Formulae (1′) and (2) below: wherein Bf is an air converted distance of the back focus of the entire system at the reduction side at the wide angle end, Imφ is the maximum effective image circle diameter at the reduction side, and L is the distance along the optical axis from the lens surface most toward the magnification side to the lens surface most toward the reduction side when the projection distance is infinity.