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 positive first lens, a second lens, and a third lens. The second lens group includes a fourth lens, a negative fifth lens, and a positive sixth lens. The first lens is formed in a shape so that surfaces thereof on the object and image plane sides have positive curvature radii. The second lens is formed in a shape so that a surface thereof on the image plane side has a negative curvature radius. The fifth lens is formed in a shape so that a surface thereof on the image plane side has a positive curvature radius. The sixth lens is formed in a shape so that surfaces thereof on the object and image plane sides are aspheric.
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 having positive refractive power, a second lens, and a third lens,
said second lens group includes a fourth lens, a fifth lens having negative refractive power, and a sixth lens having positive refractive power,
said first lens is formed in a shape so that a surface thereof on the object side and a surface thereof on the image plane side have positive curvature radii,
said second lens is formed in a shape so that a surface thereof on the image plane side has a negative curvature radius,
said fifth 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 is formed in a shape so that a surface thereof on the object side and a surface thereof on the image plane side are aspheric.
2. The imaging lens according to claim 1 , wherein said first lens has an Abbe's number vd1, said second lens has an Abbe's number vd2, and said third lens has an Abbe's number vd3 so that the following conditional expressions are satisfied:
40<vd1<75,
40<vd2<75,
15<vd3<35.
3. The imaging lens according to claim 1 , wherein said first lens group has a focal length F 1 so that the following conditional expression is satisfied:
0.6 <F 1 /f <1.4,
where f is a focal length of a whole lens system.
4. 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:
0.5 <f 1 /f 2<5.0.
5. The imaging lens according to claim 1 , wherein said first lens group has a focal length F1 and said third lens has a focal length f3 so that the following conditional expression is satisfied:
−3.5 <f 3 /F 1<−0.5.
6. The imaging lens according to claim 1 , wherein said first lens is disposed away from the second lens by a distance D12 on an optical axis and said second lens is disposed away from the third lens by a distance D23 on the optical axis so that the following conditional expression is satisfied:
3 <D 12 /D 23<8.
7. The imaging lens according to claim 1 , wherein said fourth lens and said fifth lens have a composite focal length f45 so that the following conditional expression is satisfied:
−7.0 <f 45 /f< −0.5,
where f is a focal length of a whole lens system.
8. The imaging lens according to claim 1 , wherein said sixth lens has a focal length f6 so that the following conditional expression is satisfied:
2 <f 6 /f <10,
where f is a focal length of a whole lens system.
9. 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 has a focal length f6 so that the following conditional expression is satisfied:
−0.8 <f 45 /f 6<−0.1.
10. The imaging lens according to claim 1 , wherein said sixth lens is formed in the shape so that the surface thereof on the image plane side has a curvature radius R6r so that the following conditional expression is satisfied:
0.3 <R 6 r/f <1.2,
where f is a focal length of a whole lens system.
11. The imaging lens according to claim 1 , wherein said sixth lens has an Abbe's number vd 6 so that the following conditional expression is satisfied:
15<vd6<35.
12. 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 having positive refractive power, a second lens, and a third lens having negative refractive power,
said second lens group includes a fourth lens, a fifth lens, and a sixth lens,
said first lens is formed in a shape so that a surface thereof on the object side and a surface thereof on the image plane side have positive curvature radii,
said fifth lens is formed in a shape so that a surface thereof on the object side has a positive curvature radius,
said sixth lens is formed in a shape so that a surface thereof on the object side and a surface thereof on the image plane side have positive curvature radii and are aspheric, and
said first lens has a focal length f1, said second lens has a focal length f2, said first lens group has a focal length F1, said first lens is disposed away from the second lens by a distance D12 on an optical axis, and said second lens is disposed away from the third lens by a distance D23 on the optical axis so that the following conditional expressions are satisfied:
0.5 <f 1 /f 2<5.0,
0.6 <F 1 /f <1.4,
3 <D 12 /D 23<8,
where f is a focal length of a whole lens system.
13. The imaging lens according to claim 12 , wherein said first lens has an Abbe's number vd1, said second lens has an Abbe's number vd2, and said third lens has an Abbe's number vd3 so that the following conditional expressions are satisfied:
40<vd1<75,
40<vd2<75,
15<vd3<35.
14. The imaging lens according to claim 12 , wherein said first lens group has the focal length F1 and said third lens has a focal length f3 so that the following conditional expression is satisfied:
−3.5 <f 3 /F 1<−0.5.
15. The imaging lens according to claim 12 , wherein said fourth lens and said fifth lens have a composite focal length f45 so that the following conditional expression is satisfied:
−7.0 <f 45 /f <−0.5.
16. The imaging lens according to claim 12 , wherein said sixth lens has a focal length f6 so that the following conditional expression is satisfied:
2 <f 6 /f <10.
17. The imaging lens according to claim 12 , wherein said fourth lens and said fifth lens have a composite focal length f45, and said sixth lens has a focal length f6 so that the following conditional expression is satisfied:
−0.8< f 45 /f 6<−0.1.
18. The imaging lens according to claim 12 , wherein said sixth lens is formed in the shape so that the surface thereof on the image plane side has a curvature radius R6r so that the following conditional expression is satisfied:
0.3 <R 6 r/f <1.2.
19. The imaging lens according to claim 12 , wherein said sixth lens has an Abbe's number vd6 so that the following conditional expression is satisfied:
15<vd6<35.