Wide-angle lens system
View Patent ↗A wide-angle lens system includes a negative front lens group and a positive rear lens group, in this order from the object. The negative front lens group includes a negative first sub-lens group and a positive second sub-lens group, in this order from the object. The positive rear lens group includes cemented lens elements having a positive R1 lens element and a negative R2 lens element, a positive R3 lens element having a convex surface facing toward the image, and a positive R4 lens element, in this order from the object. The wide-angle lens system satisfies the following conditions: −0.8< f 1 a/f 1 b <−0.1 (1) 0.6< f/fR <1.1 (2) wherein f1a designates the focal length of the negative first sub-lens group; f1b designates the focal length of the positive second sub-lens group; f designates the focal length of the entire wide-angle lens system; and fR designates the focal length of the positive rear lens group.
1. A wide-angle lens system comprises a negative front lens group and a positive rear lens group, in this order from an object,
wherein said negative 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 positive rear lens group comprises cemented lens elements having a positive R1 lens element and a negative R2 lens element, a positive R3 lens element having a convex surface facing toward the image, and a positive R4 lens element, in this order from the object; and
wherein said wide-angle lens system satisfies the following conditions:
−0.8 <f 1 a/f 1 b<− 0.1
0.6 <f/fR< 1.1
wherein
f1a designates the focal length of said negative first sub-lens group;
f1b designates the focal length of said positive second sub-lens group;
f designates the focal length of the entire wide-angle lens system; and
fR designates the focal length of said positive rear lens group.
2. The wide-angle lens system according to claim 1 , further satisfying the following condition:
−0.7 <fR/fF<− 0.1
wherein
fF designates the focal length of said negative front lens group; and
fR designates the focal length of said positive rear lens group.
3. The wide-angle lens system according to claim 1 , wherein said negative first sub-lens group comprises one positive lens element and one negative lens element; and
wherein said positive second sub-lens group comprises one positive lens element and one negative lens element.
4. The wide-angle lens system according to claim 3 , wherein in said negative first sub-lens group, said positive lens element and said negative lens element are arranged in this order from the object; and
wherein in said positive second sub-lens group, said negative lens element and said positive lens element are arranged in this order from the object.
5. The wide-angle lens system according to claim 1 , wherein said negative first sub-lens group comprises a positive F1 lens element having a convex surface facing toward the object and a negative F2 lens element, in this order from the object; and
wherein said positive second sub-lens comprises a negative F3 lens element having a convex surface facing toward the object and a positive F4 lens element, in this order from the object.
6. The wide-angle lens system according to claim 1 , further satisfying the following condition:
νd1-7>70
wherein
νd1-7 designates the Abbe number of said positive R3 lens elements having a convex surface facing toward the image.
7. The wide-angle lens system according to claim 1 , further satisfying the following condition:
0.1 <d/f< 0.35
wherein
d designates the axial distance between said negative front lens group and said positive rear lens group.
8. The wide-angle lens system according to claim 1 , wherein a diaphragm is provided between said negative front lens group and said positive rear lens group.