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 having negative refractive power. 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 fourth 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 having negative refractive power,
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 third lens has a concave surface facing the image plane side at a paraxial region thereof,
said fifth lens has a concave surface facing the image plane side at a paraxial region thereof, and
said fourth lens has an Abbe's number vd4 so that the following conditional expression is satisfied:
15<vd4<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<f1/f2<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<F1/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<f2/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<f1/f3<−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<F2/F1<−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<D34/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<f5/f4<−5.
9. The imaging lens according to claim 1 , wherein said fifth lens and said sixth lens have a composite focal length f56 so that the following conditional expression is satisfied:
−3<f56/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<f6/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 having negative refractive power,
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 at a paraxial region thereof, and
said fourth lens has an Abbe's number vd4 so that the following conditional expression is satisfied:
15<vd4<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<f1/f2<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<F1/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<f2/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<f1/f3<−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<F2/F1<−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<D34/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<f5/f4<−5.
19. The imaging lens according to claim 11 , wherein said fifth lens and said sixth lens have a composite focal length f56 so that the following conditional expression is satisfied:
−3<f56/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<f6/f<−0.5,
where f is a focal length of a whole lens system.