Patent ID: 6867925

Claim:
A zoom lens to form an image of an object with variable magnification between a shortest focal length and a longest focal length, comprising: a first lens group having a positive refracting power; a second lens group positioned closer to the image than the first lens group and having a negative refracting power; and a third lens group positioned closer to the image than the second lens group and having a positive refracting power; wherein when the magnification is changed from the shortest focal length to the longest focal length, the third lens group is shifted toward the object and the first lens group and the second lens group are shifted in such a manner that a distance between the first lens group and the second lens group is increased and a distance between the second lens group and the third lens group is decreased, wherein the third lens group comprises at least a single positive lens and at least a single negative lens, wherein a variable magnification ratio of the zoom lens is four times or more, and wherein the zoom lens satisfies the following formula: 2.9<β 3T /β 3W <8 wherein B 3T is a paraxial lateral magnification of the third lens group on the condition that the zoom lens is structured to effect the longest length, and β 3W is a paraxial lateral magnification of the third lens group on the condition that the zoom lens is structured to effect the shortest focal length.