Patent ID: 6249389
Filing Date: 2001-06-19
Classification: G02B

Abstract:
A variable-focal-length lens system characterized in that it possesses, in order from the object side thereof, a first lens group having positive refracting power, a second lens group having negative refracting power, a third lens group having positive refracting power, a fourth lens group having positive refracting power, and a fifth lens group having negative refracting power, an aperture stop being arranged between the aforesaid second lens group and the aforesaid third lens group,in that all of the lens groups move toward the object side in such fashion as to cause the distance between the aforesaid first lens group and the aforesaid second lens group to increase, the distance between the aforesaid second lens group and the aforesaid third lens group to decrease, the distance between the aforesaid third lens group and the aforesaid fourth lens group to increase, and the distance between the aforesaid fourth lens group and the aforesaid fifth lens group to decrease, when the positional state of the lens changes from the extreme wide-angle state to the extreme telephoto state, and the aforesaid second lens group and the aforesaid fourth lens group move in integral fashion during a change in the positional state of the lens,in that the aforesaid third lens group moves during short-distance focusing,in that the following conditional expression (1) is satisfied:0.05<Dc/{Z.multidot.(ft.multidot.fw).sup.1/2 }<0.1, (1)where:Dc=Length along the optical axis from the lens surface at the object-most side of the second lens group to the lens surface at the image-most side of the fourth lens group,fw=Focal length when in the extreme wide-angle state,ft=Focal length when in the extreme telephoto state, andZ=Zooming ratio (=ft/fw), andin that at least one of the following conditional expressions (2) and (3) is satisfied:0.4<Da/.vertline.f2.vertline.<0.8, (2)and0.4<f4/f1<0.7, (3)where:Da=Distance along the optical axis from the lens surface at the object-most side of the second lens group to the aperture stop when in the extreme wide-angle state,f2=Focal length of the second lens group (f2<0),f1=Focal length of the first lens group (f1>0), andf4=Focal length of the fourth lens group (f4>0).