Imaging lens
An imaging lens includes a first lens group; a second lens group; and a third 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 and a fifth lens. The third lens group includes a sixth lens having negative refractive power and a seventh lens having negative refractive power. The first lens is formed in a shape so that a surface thereof on the image plane side has a positive curvature radius. The sixth lens has a specific focal length. The seventh lens has a specific focal length and a specific Abbe's number.
1. An imaging lens comprising:
a first lens group;
a second lens group; and
a third 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 and a fifth lens,
said third lens group includes a sixth lens having negative refractive power and a seventh lens having negative 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, and
said sixth lens has a focal length f6, said seventh lens has a focal length f7, and said seventh lens has an Abbe's number νd7 so that the following conditional expressions are satisfied:
0.02< f 7/ f 6<0.3,
40<ν d 7<75.
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,
20<ν d 3<35.
3. 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:
2.5< f 1/ f 2<30.
4. The imaging lens according to claim 1 , wherein said first lens and said second lens have a composite focal length f12 so that the following conditional expression is satisfied:
0.5< f 12/ f< 1.1,
where f is a focal length of a whole lens system.
5. The imaging lens according to claim 1 , wherein said second lens has a focal length f2 and said third lens has a focal length f3 so that the following conditional expression is satisfied:
−1.0< f 2/ f 3<−0.2.
6. The imaging lens according to claim 1 , wherein said first lens and said second lens have a composite focal length f12 and said third lens has a focal length f3 so that the following conditional expression is satisfied:
−1.0< f 12/ f 3<−0.1.
7. The imaging lens according to claim 1 , wherein said sixth lens and said seventh lens have a composite focal length f67 so that the following conditional expression is satisfied:
−1.5< f 67/ f<− 0.5,
where f is a focal length of a whole lens system.
8. 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 and said seventh lens have a composite focal length f67 so that the following conditional expression is satisfied:
−3< f 45/ f 67<−0.8.
9. The imaging lens according to claim 1 , wherein said third lens is arranged to be away from the fourth lens by a distance D34 on an optical axis thereof so that the following conditional expression is satisfied:
0.03< D 34/ f< 0.2
where f is a focal length of a whole lens system.
10. An imaging lens comprising:
a first lens group;
a second lens group; and
a third 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 and a fifth lens having negative refractive power,
said third lens group includes a sixth lens having negative refractive power and a seventh lens,
said first lens, said second lens, said third lens, said fourth lens, said fifth lens, said sixth lens, and said seventh lens are arranged with a space between each of the lenses,
said first lens is formed in a shape so that a surface thereof on the object side has a positive curvature radius, and
said third lens is arranged to be away from the fourth lens by a distance D34 on an optical axis thereof so that the following conditional expression is satisfied:
0.03< D 34/ f< 0.2
where f is a focal length of a whole lens system.
11. The imaging lens according to claim 10 , 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,
20<ν d 3<35.
12. The imaging lens according to claim 10 , wherein said seventh lens has an Abbe's number νd7 so that the following conditional expression is satisfied:
40<ν d 7<75.
13. The imaging lens according to claim 10 , 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:
2.5< f 1/ f 2<30.
14. The imaging lens according to claim 10 , wherein said first lens and said second lens have a composite focal length f12 so that the following conditional expression is satisfied:
0.5< f 12/ f< 1.1.
15. The imaging lens according to claim 10 , wherein said second lens has a focal length f2 and said third lens has a focal length f3 so that the following conditional expression is satisfied:
−1.0< f 2/ f 3<−0.2.
16. The imaging lens according to claim 10 , wherein said first lens and said second lens have a composite focal length f12 and said third lens has a focal length f3 so that the following conditional expression is satisfied:
−1.0< f 12/ f 3<−0.1.
17. The imaging lens according to claim 10 , wherein said sixth lens and said seventh lens have a composite focal length f67 so that the following conditional expression is satisfied:
−1.5< f 67/ f<− 0.5.
18. The imaging lens according to claim 10 , wherein said fourth lens and said fifth lens have a composite focal length f45 and said sixth lens and said seventh lens have a composite focal length f67 so that the following conditional expression is satisfied:
−3< f 45/ f 67<−0.8.
19. The imaging lens according to claim 10 , wherein said sixth lens has a focal length f6 and said seventh lens has a focal length f7 so that the following conditional expression is satisfied:
0.02< f 7/ f 6<0.3.