Patent ID: 7564632

Claim:
A projection zoom lens comprising, in order from a screen side to an image source side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a positive refractive power, a fourth lens group having a negative refractive power and a fifth lens group having a positive refractive power; wherein, during zooming from a wide-angle end to a telephoto end, the second, third and fourth lens groups move toward the screen side, while the first and fifth lens groups are kept stationary, and wherein the following conditions are satisfied:  fw ⁢ ⁢ 23 fw  -  ft ⁢ ⁢ 23 fw  > 0.06743 ; and  fw ⁢ ⁢ 23 ft  -  ft ⁢ ⁢ 23 ft  > 0.05621 where fw23 represents combined refractive power of the second and third lens groups at the wide-angle end; ft23 represents combined refractive power of the second and third lens groups at the telephoto end; fw represents focal length of the projection zoom lens at the wide-angle end; and ft represents the focal length of the projection zoom lens at the telephoto end.