Patent ID: 7889431

Claim:
A projection zoom lens comprising, in order from a magnification side: a first lens group having negative refractive power adapted to perform focusing with being fixed during power-varying; a second lens group having positive refractive power adapted to move during power-varying; a third lens group having negative refractive power adapted to move during power-varying; a fourth lens group having positive refractive power adapted to move during power-varying; a fifth lens group having positive refractive power adapted to move during power-varying; and a sixth lens group having positive refractive power adapted to be fixed during power-varying and to include a first stop nearest to the magnification side, wherein a numerical aperture is set constant over the whole region of power-varying, each lens included in the first to sixth groups is a single lens, a reduction side is made telecentric, and the following conditional expression (1) is satisfied: 2.5 <Bf/f (1) where Bf denotes an air-converted back focal length of the entire system, and f denotes a focal length at a wide-angle end of the entire system.