Wide-angle zoom lens system
View Patent ↗A wide-angle zoom lens system includes a negative first lens group, a positive second lens group, a negative third lens group and a positive fourth lens group, in this order from the object. Upon zooming from the short focal length extremity to the long focal length extremity, a distance between the negative first lens group and the positive second lens group decreases, a distance between the positive second lens group and the negative third lens group increases, and a distance between the negative third lens group and the positive fourth lens group decreases. The wide-angle zoom lens system satisfies the following conditions: 0.9< f 2 /ft <1.2 (1) 2.9< f 4 /fw <3.4 (2) wherein f2: the focal length of the positive second lens group; f4: the focal length of the positive fourth lens group; ft: the focal length of the entire wide-angle zoom lens system at the long focal length extremity; and fw: the focal length of the entire wide-angle zoom lens system at the short focal length extremity.
1. A wide-angle zoom lens system comprises a negative first lens group, a positive second lens group, a negative third lens group and a positive fourth lens group, in this order from an object;
wherein upon zooming from the short focal length extremity to the long focal length extremity, a distance between said negative first lens group and said positive second lens group decreases, a distance between said positive second lens group and said negative third lens group increases, and a distance between said negative third lens group and said positive fourth lens group decreases;
wherein said wide-angle zoom lens system satisfies the following conditions:
0.9< f 2 /ft< 1.2
2.9< f 4 /fw< 3.4
wherein
f 2 designates the focal length of said positive second lens group;
f 4 designates the focal length of said positive fourth lens group;
ft designates the focal length of the entire wide-angle zoom lens system at the long focal length extremity; and
fw designates the focal length of the entire wide-angle zoom lens system at the short focal length extremity.
2. The wide-angle zoom lens system according to claim 1 , further satisfying the following condition:
1.3<| f 1|/ fw< 1.5( f 1<0)
wherein
f 1 designates the focal length of said negative first lens group; and
fw designates the focal length of the entire wide-angle zoom lens system at the short focal length extremity.
3. The wide-angle zoom lens system according to claim 1 , further satisfying the following condition:
1.0<| f 3| /ft< 1.5( f 3<0)
wherein
f 3 designates the focal length of said negative third lens group; and
ft designates the focal length of the entire wide-angle zoom lens system at the long focal length extremity.
4. The wide-angle zoom lens system according to claim 1 , wherein said negative first lens group comprises, at least, a negative meniscus lens element having the convex surface facing toward the object, another negative meniscus lens element having the convex surface facing toward the object, a negative lens element having a concave surface facing toward the image, and a positive lens element, in this order from the object.
5. The wide-angle zoom lens system according to claim 1 , wherein said negative first lens group comprises a positive lens element, a negative meniscus lens element having the convex surface facing toward the object, another negative meniscus lens element having the convex surface facing toward the object, a negative lens element having a concave surface facing toward the image, and a positive lens element, in this order from the object.
6. The wide-angle zoom lens system according to claim 1 , wherein said positive second lens group comprises positive cemented lens elements and a positive lens element.
7. The wide-angle zoom lens system according to claim 1 , wherein said negative third lens group comprises two sets of negative cemented lens elements.
8. The wide-angle zoom lens system according to claim 1 , wherein said positive fourth lens group comprises cemented lens elements and two positive lens elements, or two sets of cemented lens elements and a positive lens element.