Imaging lens
An imaging lens includes a first lens group and a second lens group, arranged in this order from an object side to an image plane side. The first lens group includes a first lens, a second lens, and a third lens. The second lens group includes a fourth lens, a fifth lens having negative refractive power, and a sixth lens having positive refractive power. The first lens is formed in a shape so that a surface thereof on the object side and a surface thereof on the image plane side have positive curvature radii. The sixth lens is formed in a shape so that a surface thereof on the object side and a surface thereof on the image plane side are aspheric. The sixth lens has a specific Abbe's number.
1. An imaging lens comprising:
a first lens group; and
a second lens group, arranged in this order from an object side to an image plane side,
wherein said first lens group includes a first lens, a second lens, and a third lens,
said second lens group includes a fourth lens, a fifth lens having negative refractive power, and a sixth lens having positive refractive power,
said first lens is formed in a shape so that a surface thereof on the object side and a surface thereof on the image plane side have positive curvature radii,
said sixth lens is formed in a shape so that a surface thereof on the object side and a surface thereof on the image plane side are aspheric, and
said sixth lens has an Abbe's number νd6 so that the following conditional expression is satisfied:
15<ν d 6<35.
2. The imaging lens according to claim 1 , wherein said first lens has an Abbe's number νd1, said second lens has an Abbe's number νd2, and said third lens has an Abbe's number νd3 so that the following conditional expressions are satisfied:
40<ν d 1<75,
40<ν d 2<75,
15<ν d 3<35.
3. The imaging lens according to claim 1 , wherein said first lens group has a focal length F1 so that the following conditional expression is satisfied:
0.6< F 1/ f< 1.4,
where f is a focal length of a whole lens system.
4. The imaging lens according to claim 1 , wherein said first lens has a focal length f1 and said second lens has a focal length f2 so that the following conditional expression is satisfied:
0.5< f 1/ f 2<5.0.
5. The imaging lens according to claim 1 , wherein said first lens group has a focal length F1 and said third lens has a focal length f3 so that the following conditional expression is satisfied:
−3.5< f 3/ F 1<−0.5.
6. The imaging lens according to claim 1 , wherein said first lens is disposed away from the second lens by a distance D 12 on an optical axis and said second lens is disposed away from the third lens by a distance D 23 on the optical axis so that the following conditional expression is satisfied:
3< D 12/ D 23<8.
7. The imaging lens according to claim 1 , wherein said fourth lens and said fifth lens have a composite focal length f45 so that the following conditional expression is satisfied:
−7.0< f 45/ f<− 0.5,
where f is a focal length of a whole lens system.
8. The imaging lens according to claim 1 , wherein said sixth lens has a focal length f6 so that the following conditional expression is satisfied:
2< f 6/ f< 10,
where f is a focal length of a whole lens system.
9. The imaging lens according to claim 1 , wherein said fourth lens and said fifth lens have a composite focal length f45, and said sixth lens has a focal length f6 so that the following conditional expression is satisfied:
−0.8< f 45/ f 6<−0.1.
10. The imaging lens according to claim 1 , wherein said sixth lens is formed in the shape so that the surface thereof on the image plane side has a curvature radius R6r so that the following conditional expression is satisfied:
0.3< R 6 r/f< 1.2,
where f is a focal length of a whole lens system.
11. An imaging lens comprising:
a first lens group; and
a second lens group, arranged in this order from an object side to an image plane side,
wherein said first lens group includes a first lens, a second lens, and a third lens having negative refractive power,
said second lens group includes a fourth lens, a fifth lens having negative refractive power, and a sixth lens having positive refractive power,
said first lens is formed in a shape so that a surface thereof on the image plane side has a positive curvature radius,
said fifth lens is formed in a shape so that a surface thereof on the image plane side has a positive curvature radius,
said sixth lens is formed in a shape so that a surface thereof on the object side and a surface thereof on the image plane side are aspheric, and
said sixth lens has a focal length f6, and said fourth lens and said fifth lens have a composite focal length f45 so that the following conditional expressions are satisfied:
2< f 6/ f< 10,
−7.0< f 45/ f<− 0.5,
where f is a focal length of a whole lens system.
12. The imaging lens according to claim 11 , wherein said first lens has an Abbe's number νd1, said second lens has an Abbe's number νd2, and said third lens has an Abbe's number νd3 so that the following conditional expressions are satisfied:
40<ν d 1<75,
40<ν d 2<75,
15<ν d 3<35.
13. The imaging lens according to claim 11 , wherein said first lens group has a focal length F1 so that the following conditional expression is satisfied:
0.6< F 1/ f< 1.4.
14. The imaging lens according to claim 11 , wherein said first lens has a focal length f1 and said second lens has a focal length f2 so that the following conditional expression is satisfied:
0.5< f 1/ f 2<5.0.
15. The imaging lens according to claim 11 , wherein said first lens group has a focal length F1 and said third lens has a focal length f3 so that the following conditional expression is satisfied:
−3.5< f 3/ F 1<−0.5.
16. The imaging lens according to claim 11 , wherein said first lens is disposed away from the second lens by a distance D 12 on an optical axis, and said second lens is disposed away from the third lens by a distance D 23 on the optical axis so that the following conditional expression is satisfied:
3< D 12/ D 23<8.
17. The imaging lens according to claim 11 , wherein said fourth lens and said fifth lens have a composite focal length f45, and said sixth lens has a focal length f6 so that the following conditional expression is satisfied:
−0.8< f 45/ f 6<−0.1.
18. The imaging lens according to claim 11 , wherein said sixth lens is formed in the shape so that the surface thereof on the image plane side has a curvature radius R6r so that the following conditional expression is satisfied:
0.3< R 6 r/f< 1.2.
19. The imaging lens according to claim 11 , wherein said sixth lens has an Abbe's number νd6 so that the following conditional expression is satisfied:
15<ν d 6<35.