Patent ID: 7046453

Claim:
A stepwise variable zoom lens system adapted to create an image of a scene on an image sensor, in order from an object side, comprising: a first lens group of negative refracting power, the first lens group being constructed from a single block; a second lens group of positive refracting power, the second lens group including a first lens unit having a positive refracting power and a second lens unit having a negative refracting power, the second lens unit being constructed from a single block; and a third lens group of positive refracting power, the third lens groups being constructed from a single block; wherein said first and third lens groups are fixed relatively to the image sensor, said second lens group is movable so as to be selectively disposed in several discrete positions, and focal lengths of said lens groups satisfy the following relations: f 2 · ( 1 + z ) > - f 1 f 2 · ( 1 + 1 z ) > f 3 · f b f 3 - f b wherein f 1 denotes the focal length of the first lens group, f 2 denotes the focal length of the second lens group, f 3 denotes the focal length of the third lens group, f b denotes the back focal length of the stepwise variable zoom lens system, and z denotes the zoom ratio.