Imaging lens
An imaging lens includes a first lens group and a second lens group having negative refractive power, 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 having positive refractive power, a fifth lens, and a sixth lens. The second lens has a concave surface facing the object side near an optical axis thereof. The third lens has a concave surface facing the image plane side near an optical axis thereof. The sixth lens has a concave surface facing the object side near an optical axis thereof. The fourth lens has a specific Abbe's number.
1. An imaging lens comprising:
a first lens group; and
a second lens group having negative refractive power, 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 having positive refractive power, a fifth lens, and a sixth lens,
said imaging lens has a total of six single lenses,
said second lens has a concave surface facing the object side near an optical axis thereof,
said third lens has a concave surface facing the image plane side near an optical axis thereof,
said sixth lens has a concave surface facing the object side near an optical axis thereof, and
said fourth lens has an Abbe's number νd4 so that the following conditional expression is satisfied:
15<ν d 4<35.
2. 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:
0.3< f 1/ f 2<0.9.
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:
0.8< F 1/ f< 1.2,
where f is a focal length of a whole lens system.
4. The imaging lens according to claim 1 , wherein said second lens has a focal length f2 so that the following conditional expression is satisfied:
1.0< f 2/ f< 2.0,
where f is a focal length of a whole lens system.
5. The imaging lens according to claim 1 , wherein said first lens has a focal length f1 and said third lens has a focal length f3 so that the following conditional expression is satisfied:
−1.2< f 1/ f 3<−0.4.
6. The imaging lens according to claim 1 , wherein said first lens group has a focal length F1 and said second lens group has a focal length F2 so that the following conditional expression is satisfied:
−12< F 2/ F 1<−1.5.
7. The imaging lens according to claim 1 , wherein said third lens is arranged away from the fourth lens by a distance D34 on an optical axis thereof so that the following conditional expression is satisfied:
0.05< D 34/ f< 0.35,
where f is a focal length of a whole lens system.
8. The imaging lens according to claim 1 , wherein said fourth lens has a focal length f4 and said fifth lens has a focal length f5 so that the following conditional expression is satisfied:
−15< f 5/ f 4<−5.
9. The imaging lens according to claim 1 , wherein said fifth lens and said sixth lens has a composite focal length f56 so that the following conditional expression is satisfied:
−3< f 56/ f<− 0.8,
where f is a focal length of a whole lens system.
10. The imaging lens according to claim 1 , wherein said sixth lens has a focal length f6 so that the following conditional expression is satisfied:
−3.5< f 6/ f<− 0.5,
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 having negative refractive power, 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 having positive refractive power, a fifth lens, and a sixth lens,
said imaging lens has a total of six single lenses,
said fifth lens has a concave surface facing the image plane side near an optical axis thereof, and
said third lens has an Abbe's number νd3 and said fourth lens has an Abbe's number νd4 so that the following conditional expressions are satisfied:
15<ν d 3<35,
15<ν d 4<35.
12. 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:
0.3< f 1/ f 2<0.9.
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:
0.8< F 1/ f< 1.2,
where f is a focal length of a whole lens system.
14. The imaging lens according to claim 11 , wherein said second lens has a focal length f2 so that the following conditional expression is satisfied:
1.0< f 2/ f< 2.0,
where f is a focal length of a whole lens system.
15. The imaging lens according to claim 11 , wherein said first lens has a focal length f1 and said third lens has a focal length f3 so that the following conditional expression is satisfied:
−1.2< f 1/ f 3<−0.4.
16. The imaging lens according to claim 11 , wherein said first lens group has a focal length F1 and said second lens group has a focal length F2 so that the following conditional expression is satisfied:
−12< F 2/ F 1<−1.5.
17. The imaging lens according to claim 11 , wherein said third lens is arranged away from the fourth lens by a distance D34 on an optical axis thereof so that the following conditional expression is satisfied:
0.05< D 34/ f< 0.35,
where f is a focal length of a whole lens system.
18. The imaging lens according to claim 11 , wherein said fourth lens has a focal length f4 and said fifth lens has a focal length f5 so that the following conditional expression is satisfied:
−15< f 5/ f 4<−5.
19. The imaging lens according to claim 11 , wherein said fifth lens and said sixth lens has a composite focal length f56 so that the following conditional expression is satisfied:
−3< f 56/ f<− 0.8,
where f is a focal length of a whole lens system.
20. The imaging lens according to claim 11 , wherein said sixth lens has a focal length f6 so that the following conditional expression is satisfied:
−3.5< f 6/ f<− 0.5,
where f is a focal length of a whole lens system.