Imaging lens
An imaging lens includes a first lens group; a second lens group having positive refractive power; 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 having positive refractive power, a second lens, and a third lens. The second lens group includes a fourth lens and a fifth lens. The third lens group includes a sixth lens having negative refractive power and a seventh lens having negative refractive power. Each of the first lens and the second lens is formed in a shape so that a surface thereof on the object side has a positive curvature radius. The seventh lens is formed in a shape so that a surface thereof on the object side has a negative curvature radius, and has a specific Abbe's number.
1. An imaging lens comprising:
a first lens group;
a second lens group having positive refractive power; 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 having positive refractive power, a second lens, and a third lens,
said second lens group includes a fourth lens 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 object side has a positive curvature radius,
said second lens is formed in a shape so that a surface thereof on the object side has a positive curvature radius,
said fifth lens is formed in a shape so that a surface thereof on the object side has a negative curvature radius,
said seventh lens is formed in a shape so that a surface thereof on the object side has a negative curvature radius, and
said seventh lens has an Abbe's number νd7 so that the following conditional expression is satisfied:
40<νd7<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<νd1<75,
40<νd2<75,
20<νd3<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 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.
10. The imaging lens according to claim 1 , wherein said third lens is arranged to be away from the fourth lens by a distance D 34 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. 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 having positive refractive power, a second lens, and a third lens, arranged respectively with a space in between,
said second lens group includes a fourth lens and a fifth lens having positive refractive power, arranged respectively with a space in between,
said third lens group includes a sixth lens having negative refractive power and a seventh lens having negative refractive power, arranged respectively with a space in between,
said second lens is formed in a shape so that a surface thereof on the object side has a positive curvature radius,
said third 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 image plane side has a positive curvature radius, and
said seventh lens has an Abbe's number νd7 so that the following conditional expression is satisfied:
40<νd7<75.
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<νd1<75,
40<νd2<75,
20<νd3<35.
13. 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:
2.5 <f 1 / f 2<30.
14. The imaging lens according to claim 11 , 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.
15. The imaging lens according to claim 11 , 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 11 , 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 11 , 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.
18. 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 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 11 , 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.
20. The imaging lens according to claim 11 , wherein said third lens is arranged to be away from the fourth lens by a distance D 34 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.