Patent ID: 7672062

Claim:
A zoom lens for projection comprising, in order from a magnification side of the zoom lens: a first lens group having a positive refractive power and adapted to perform focusing with being fixed during power-varying of the zoom lens; a second lens group having a negative refractive power and adapted to move during the power-varying; a third lens group having a negative refractive power and adapted to move during the power-varying; a fourth lens group having a positive refractive power and adapted to move during the power-varying; a stop adapted to be fixed during the power-varying; and a fifth lens group having a positive refractive power and adapted to be fixed during the power-varying, wherein a reduction side of the zoom lens is configured to be telecentric, Fno is constant in a whole region of the power-varying, and the zoom lens satisfy conditional expression (1): 1.7 <Bf/f< 3.0 (1) wherein f is a focal length of the zoom lens at a wide angle end, and Bf is a back focal length of the zoom lens in air converted distance.