Wide-angle lens system
View Patent ↗A wide-angle lens system includes a positive front lens group, a diaphragm, and a positive rear lens group. The front lens group includes a negative first-sub-lens group and a positive second-sub-lens group. The negative first-sub-lens group includes a negative lens element, a positive lens element, and a negative lens element. The front lens group satisfies the following conditions: 0.5< f/|f 1a |<0.75 (1) 0.5<| f 1a |/f 1b <1.0 (2) 0.35< f/f 1bi <0.6 (3) wherein f: the focal length of the entire lens system; f 1a : the focal length of the negative first-sub-lens group; f 1b : the focal length of the positive second-sub-lens group; f 1bi : the focal length of the most image-side surface of the positive second-sub-lens group; r 1bi : the radius of curvature of the most image-side surface of the positive second-sub-lens group; and N 1bi : a refractive index of the most image-side lens element of the positive second-sub-lens group.
1. A wide-angle lens system comprises a positive front lens group, a diaphragm, and a positive rear lens group, in this order from an object,
wherein said front lens group comprises a negative first-sub-lens group and a positive second-sub-lens group, in this order from the object;
wherein said negative first-sub-lens group comprises a negative lens element, a positive lens element, and a negative lens element, in this order from the object; and
wherein said front lens group satisfies the following conditions:
0.5< f/|f 1a |<0.75
0.5 <| f 1a |/f 1b <1.0
0.35 < f/f 1bi <0.6
wherein
f designates the focal length of the entire lens system;
f 1a designates the focal length of said negative first-sub-lens group (f 1a <0);
f 1b designates the focal length of said positive second-sub-lens group (f 1b >0);
f 1bi designates the focal length of the most image-side surface of said positive second-sub-lens group (f 1bi =r 1bi /(1−N 1bi ));
r 1bi designates the radius of curvature of the most image-side surface of said positive second-sub-lens group (r 1bi <0); and
N 1bi designates a refractive index of the most image-side lens element of said positive second-sub-lens group.
2. The wide-angle lens system according to claim 1 , further satisfying the following condition:
1.7 <d 1a-1b /f< 3.0
wherein
d 1a-1b designates the distance from the most object-side surface of said negative first-sub-lens group to the most object-side surface of said positive second-sub-lens group; and
f designates the focal length of the entire lens system.
3. The wide-angle lens system according to claim 1 , wherein said positive second-sub-lens group comprises a positive lens element and a negative lens element, or, a negative lens element and a positive lens element, which are cemented to each other, in this order from the object; and
wherein said positive second-sub-lens group satisfies the following conditions:
0.25 <f 1bp /|f 1bn |<0.5
10 <ν 1bp −ν 1bn <30
wherein
f 1bp designates the focal length of said positive lens element in said positive second-sub-lens group;
f 1bn designates the focal length of said negative lens element in said positive second-sub-lens group;
ν 1bp designates the Abbe number of said positive lens element in said positive second-sub-lens group; and
ν 1bn designates the Abbe number of said negative lens element in said positive second-sub-lens group.
4. The wide-angle lens system according to claim 1 , wherein focusing is performed by advancing the entire lens system.