Patent ID: 8390935

Claim:
A projection zoom lens comprising: a first lens group having a negative refractive power, the first lens group being fixed and performing focusing when a power of the projection zoom lens varies; a second lens group having a positive refractive power, the second lens group moving when the power varies; a third lens group having a positive refractive power, the third lens group moving when the power varies; a fourth lens group having a negative refractive power, the fourth lens group moving when the power varies; a fifth lens group having a positive refractive power, the fifth lens group moving when the power varies; and a sixth lens group having a positive refractive power, the sixth lens group being fixed when the power varies, and the sixth lens group including a stop arranged closest to a magnification side, wherein the first to sixth lens groups are arranged in this order from the magnification side, a numerical aperture is constant in an entire power variation range, all lenses are single lenses, a reduction side is telecentric, and the projection zoom lens satisfies the following conditional expression: 2.5< Bf/f where Bf is an air-converted back focal length of the entire system, and f is a focal length of the entire system at a wide angle end.