Patent ID: 7433130

Claim:
A zoom lens telecentric on a reduction side, comprising, in the mentioned order from enlargement side to reduction side: a first negative lens; a second negative lens; and a first positive lens, wherein at least one negative lens among the first negative lens and the second negative lens has an aspherical surface, and the zoom lens satisfies the following conditions: − f 12 /fw< 1.4, − f 12/( Hwpn−f 12)<0.6, and | dn/dt|< 1.0×10 −5 , where f12 is the focal length of the combined optical system composed of the first negative lens and the second negative lens, Hwpn is the distance from the rear principal point of the combined optical system composed of the first negative lens and the second negative lens to the front principal point of the first positive lens, dn/dt is a change in the refractive index of the material of said one negative lens relative to a change in its temperature from 25° C., and fw is the focal length of the entire lens system at the wide angle end.