Imaging lens
An imaging lens includes a first lens group having positive refractive power 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 having positive refractive power, a fifth lens, and a sixth lens. The third lens has a concave surface facing the image plane side near an optical axis thereof. The fifth 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 second lens has a specific Abbe's number.
1. An imaging lens comprising:
a first lens group having positive refractive power; 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 having positive refractive power, a fifth lens, and a sixth lens,
said third lens has a concave surface facing the image plane side near an optical axis thereof,
said fifth 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 second lens has an Abbe's number νd2 so that the following conditional expression is satisfied:
40<ν d 2<75.
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 having positive refractive power; 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, and a sixth lens,
said third lens has a concave surface facing the image plane side near an optical axis thereof,
said fifth 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 second lens has an Abbe's number νd2 and said fifth lens has an Abbe's number νd5 so that the following conditional expressions are satisfied:
40<ν d 2<75,
40<ν d 5<75.
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.