Patent ID: 6215599
Filing Date: 2001-04-10
Classification: G02B

Abstract:
A zoom lens capable of forming an image of an object and zooming between a maximum wide-angle state and a maximum telephoto state, the zoom lens comprising objectwise to imagewise:a) a first lens group having overall positive refractive power;b) a second lens group having overall negative refractive power and separated from said first lens group by a first air space;c) a third lens group having overall negative refractive power and separated from said second lens group by a second air space, said third lens group being axially moveable for focusing;d) a fourth lens group having overall positive refractive power and separated from said third lens group by a third air space;e) wherein the zoom lens is designed such that when zooming from the maximum wide-angle state to the maximum telephoto state, at least one lens group among said first lens group and said fourth lens group moves axially and said second lens group moves axially imagewise so as to increase said first and second air spaces, and decrease said third air space; andf) the following conditions are satisfied:-0.5<.phi.12.sub.t.multidot.f.sub.t <0.30.8<.vertline.f.sub.3.vertline./(f.sub.w.multidot.f.sub.t).sup.1/2 <1.2wherein f.sub.3 is the focal length of said third lens group .phi.12.sub.t is the composite refractive power of said first lens group and said second lens group in the maximum telephoto state, f.sub.w is the focal length of the zoom lens in the maximum wide-angle state, and f.sub.t is the focal length of the zoom lens in the maximum telephoto state.