Patent ID: 7826147

Claim:
A zoom lens comprising, in order from a magnification conjugate side to a reduction conjugate side: a negative lens unit having a negative refractive power; at least one positive lens unit having a positive refractive power; an intermediate lens unit including a stop; and at least one reduction side lens unit, wherein at least two magnification side movable lens units out of the negative lens unit and the at least one positive lens unit, and at least one reduction side movable lens unit out of the at least one reduction side lens unit are moved during zooming, and wherein the following conditions are satisfied: 0.9<( X T ·β Tb ·φ W )/( X W ·β Wb ·φ T )<1.1 0.9<φ W /φ T <1.1 0.8<(β TS ·β Tb )/(β WS ·β Wb )<1.2 1.4 <f T /f W where X W indicates an interval between a focal position at a wide angle end, of a front synthetic system constituted by lens elements arranged at the magnification conjugate side as compared with the stop, and the stop, β Wb indicates an imaging magnification at the wide angle end, of a rear synthetic system constituted by lens elements arranged at the reduction conjugate side as compared with the stop, β WS indicates an imaging magnification of the intermediate lens unit at the wide angle end, φ W indicates a diameter of the stop at the wide angle end, X T indicates an interval between a focal position at a telephoto end, of the front synthetic system, and the stop, β Tb indicates an imaging magnification at the telephoto end, of the rear synthetic system, β TS indicates an imaging magnification of the intermediate lens unit at the telephoto end, φ T indicates a diameter of the stop at the telephoto end, f W indicates a focal distance of a whole zoom lens system at the wide angle end, and f T indicates a focal distance of the whole zoom lens system at the telephoto end.