Zoom lens system
View Patent ↗A zoom lens system includes a positive first lens group, a negative second lens group, and a rear lens group which is provided on the image side of the negative second lens group, and has a combined positive refractive power, in this order from the object; and the zoom lens system satisfies the following conditions: 5.0< f 1 /fw <6.5 (1) 0.4< fRt/ft <0.55 (2) wherein f 1 designates a focal length of the positive first lens group; fw designates a focal length of the entire the zoom lens system at the short focal length extremity; fRt designates a combined focal length of the positive rear lens group at the long focal length extremity; and ft designates a focal length of the entire zoom lens system at the long focal length extremity.
1. A zoom lens system comprises a positive first lens group, a negative second lens group, and a rear lens group that is provided on the image side of said negative second lens group, and that has a combined positive refractive power, in this order from an object,
wherein said zoom lens system satisfies the following conditions:
5.0 <f 1 /fw< 6.5
0.4 <fRt/ft< 0.55
wherein
f 1 designates a focal length of said positive first lens group;
fw designates a focal length of the entire zoom lens system at the short focal length extremity;
fRt designates a combined focal length of the positive rear lens group at the long focal length extremity; and
ft designates a focal length of the entire zoom lens system at the long focal length extremity,
wherein said positive rear lens group comprises a positive third lens group, a negative fourth lens group, and a positive fifth lens group, in this order from the object.
2. The zoom lens system according to claim 1 , satisfying the following condition:
2.7 <f 4 /f 2<4.5
wherein
f 4 designate a focal lengths of said negative fourth lens group; and
f 2 designate a focal lengths of said negative second lens group.
3. The zoom lens system according to claim 1 , satisfying the following condition:
2.0 <fBw/|f 12 w|< 2.5
wherein
fBw designates a back focal distance of said zoom lens system at the short focal length extremity; and
fl 2 w designates a combined focal length of said positive first lens group and said negative second lens group at the short focal length extremity, and f 12 w<0.
4. The zoom lens system according to claim 1 , wherein said negative second lens group comprises a negative lens element, a negative lens element, a negative lens element, a positive lens element, a negative lens element, and a positive lens element, in this order from the object.
5. The zoom lens system according to claim 1 , wherein
said positive fifth lens group comprises at least one lens element having an aspherical surface.
6. The zoom lens system according to claim 1 , wherein
said positive third lens group and said positive fifth lens group are arranged to integrally move along the optical axis direction upon zooming.