Imaging lens
An imaging lens includes an object-side lens group having positive refractive power; an aperture stop; and an image plane-side lens group having positive refractive power, arranged in this order from an object side to an image plane side. The object-side lens group includes a first lens having positive refractive power; a second lens having negative refractive power; and a third lens having positive refractive power. The image plane-side lens group includes a fourth lens having positive refractive power; and a fifth lens having negative refractive power. The first lens has an aspheric shape to have negative refractive power increasing toward a lens periphery from an optical axis, and has a surface on the object side having a positive curvature radius. The first to third lenses have specific focal lengths to satisfy specific conditions. The first to fifth lenses have specific Abbe's numbers to satisfy specific conditions.
1. An imaging lens comprising:
an object-side lens group having positive refractive power;
an aperture stop; and
an image plane-side lens group having positive refractive power, arranged in this order from an object side to an image plane side,
wherein said object-side lens group includes a first lens having positive refractive power; a second lens having negative refractive power; and a third lens having positive refractive power,
said image plane-side lens group includes a fourth lens having positive refractive power; and a fifth lens having negative refractive power,
said first lens is formed in an aspheric shape so as to have negative refractive power increasing toward a lens periphery thereof from an optical axis thereof, and has a surface on the object side having a positive curvature radius, and
said first lens has a focal length f1, said second lens has a focal length f2, said third lens has a focal length f3, said first lens has an Abbe's number νd1, said second lens has an Abbe's number νd2, said third lens has an Abbe's number νd3, said fourth lens has an Abbe's number νd4, and said fifth lens has an Abbe's number νd5 so that the following conditional expressions are satisfied:
| f 2|< f 1 and | f 2|< f 3
40<ν d 1<70
40<ν d 2<70
40<ν d 3<70
40<ν d 4<70
20<ν d 5<35.
2. The imaging lens according to claim 1 , wherein said second lens is formed in an aspheric shape having refractive power increasing toward a lens periphery thereof from an optical axis thereof,
said second lens has a surface on the image plane side having a positive curvature radius, and
said third lens has a surface on the object side and a surface on the image plane side having negative curvature radii.
3. The imaging lens according to claim 1 , wherein said fourth lens has a surface on the object side having a positive curvature radius and a surface on the image plane side having a negative curvature radius, and
said fifth lens has a surface on the object side and a surface on the image plane side having negative curvature radii.
4. The imaging lens according to claim 1 , wherein said first lens has the focal length f1 so that the following conditional expression is satisfied:
1.5< f 1/ f< 7
where f is a focal length of a whole lens system.
5. The imaging lens according to claim 1 , wherein said first lens has the focal length f1 and said second lens has the focal length f2 so that the following conditional expression is satisfied:
2< f 1/| f 2|<8.
6. The imaging lens according to claim 1 , wherein said object-side lens group has a focal length Ff so that the following conditional expression is satisfied:
5< Ff/f< 12
where f is a focal length of a whole lens system.
7. The imaging lens according to claim 1 , wherein said image plane-side lens group has a focal length Fr so that the following conditional expression is satisfied:
0.5< Fr/f< 2.5
where f is a focal length of a whole lens system.
8. An imaging lens comprising:
an object-side lens group having positive refractive power;
an aperture stop; and
an image plane-side lens group having positive refractive power, arranged in this order from an object side to an image plane side,
wherein said object-side lens group includes a first lens having positive refractive power, a second lens, and a third lens, and
said first lens has a focal length f1, said second lens has a focal length f2, said third lens has a focal length f3 and an angle of view 2ω so that the following conditional expressions are satisfied:
| f 2|< f 1 and | f 2|< f 3
130°≦2ω.
9. The imaging lens according to claim 8 , wherein said image plane-side lens group includes a fourth lens having positive refractive power and a fifth lens having negative refractive power.
10. The imaging lens according to claim 9 , wherein said first lens has an Abbe's number νd1, said second lens has an Abbe's number νd2, said third lens has an Abbe's number νd3, said fourth lens has an Abbe's number νd4, and said fifth lens has an Abbe's number νd5 so that the following conditional expressions are satisfied:
40<ν d 1<70
40<ν d 2<70
40<ν d 3<70
40<ν d 4<70
20<ν d 5<35.
11. The imaging lens according to claim 8 , wherein said second lens is formed in an aspheric shape so as to have refractive power increasing toward a lens periphery thereof from an optical axis thereof, and has a surface on the image plane side having a positive curvature radius, and
said third lens has a surface on the object side and a surface on the image plane side having negative curvature radii.
12. The imaging lens according to claim 8 , wherein said fourth lens has a surface on the object side having a positive curvature radius and a surface on the image plane side having a negative curvature radius, and
said fifth lens has a surface on the object side and a surface on the image plane side having negative curvature radii.
13. The imaging lens according to claim 8 , wherein said first lens has the focal length f1 so that the following conditional expression is satisfied:
1.5< f 1/ f< 7
where f is a focal length of a whole lens system.
14. The imaging lens according to claim 8 , wherein said first lens has the focal length f1 and said second lens has the focal length f2 so that the following conditional expression is satisfied:
2< f 1/| f 2|<8.
15. The imaging lens according to claim 8 , wherein said object-side lens group has a focal length Ff so that the following conditional expression is satisfied:
5< Ff/f< 12
where f is a focal length of a whole lens system.
16. The imaging lens according to claim 8 , wherein said image plane-side lens group has a focal length Fr so that the following conditional expression is satisfied:
0.5< Fr/f< 2.5
where f is a focal length of a whole lens system.