Imaging lens
An imaging lens includes a first lens having negative refractive power; an aperture stop; a second lens; a third lens; a fourth lens; a fifth lens; and a sixth lens having negative refractive power, arranged in this order from an object side to an image plane side. The fourth lens is formed in a shape so that a surface thereof on the image plane side is convex at a paraxial region thereof and has an aspheric shape having an inflection point. The fifth lens is formed in a shape so that a surface thereof on the image plane side is concave at a paraxial region thereof.
1. An imaging lens comprising:
a first lens having negative refractive power;
an aperture stop;
a second lens;
a third lens;
a fourth lens;
a fifth lens; and
a sixth lens having negative refractive power, arranged in this order from an object side to an image plane side,
wherein said fourth lens is formed in a shape so that a surface thereof on the image plane side is convex at a paraxial region thereof,
said fourth lens is formed in the shape so that the surface thereof on the image plane side has an aspheric shape having an inflection point, and
said fifth lens is formed in a shape so that a surface thereof on the image plane side is concave at a paraxial region thereof, wherein said second lens has a focal length f2 and said third lens have a focal length f3 so that the following conditional expression is satisfied:
0.5 <f 2/ f 3<3.
2. 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 thereof so that the following conditional expression is satisfied:
0.05< D 12/ f< 0.8,
where f is a focal length of a whole lens system.
3. The imaging lens according to claim 1 , wherein said second lens and said third lens have a composite focal length f23 so that the following conditional expression is satisfied:
0.3 <f 23/ f< 1.2,
where f is a focal length of a whole lens system.
4. The imaging lens according to claim 1 , wherein said fourth lens has a focal length f4 so that the following conditional expression is satisfied:
−4< f 4/ f<− 0.4,
where f is a focal length of a whole lens system.
5. The imaging lens according to claim 1 , wherein said fifth lens has a focal length f5 and said sixth lens has a focal length f6 so that the following conditional expression is satisfied:
0.3<| f 5|/| f 6|<1.5.
6. The imaging lens according to claim 1 , wherein said sixth lens has a focal length f6 so that the following conditional expression is satisfied:
−5< f 6/ f<− 0.5,
where f is a focal length of a whole lens system.
7. 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 thereof and said fifth lens is disposed away from the sixth lens by a distance D56 on an optical axis thereof so that the following conditional expression is satisfied:
D 56< D 12.
8. The imaging lens according to claim 1 , wherein said fifth lens is disposed away from the sixth lens by a distance D56 on an optical axis thereof so that the following conditional expression is satisfied:
0.05 <D 56 /f< 0.35,
where f is a focal length of a whole lens system.
9. The imaging lens according to claim 1 , wherein said first lens is arranged so that a surface thereof on the object side is away from an image plane by a distance La on an optical axis thereof so that the following conditional expression is satisfied:
0.2< La/H max<1.5,
where Hmax is a maximum image height of the image plane.
10. An imaging lens comprising:
a first lens having negative refractive power;
an aperture stop;
a second lens;
a third lens;
a fourth lens;
a fifth lens; and
a sixth lens, arranged in this order from an object side to an image plane side,
wherein said fourth lens is formed in a shape so that a surface thereof on the image plane side is convex at a paraxial region thereof,
said fourth lens is formed in the shape so that the surface thereof on the image plane side has an aspheric shape having an inflection point,
said fifth lens is formed in a shape so that a surface thereof on the image plane side is concave at a paraxial region thereof, and
said first lens is disposed away from the second lens by a distance D12 on an optical axis thereof and said fifth lens is disposed away from the sixth lens by a distance D56 on an optical axis thereof, and said second lens has a focal length f2 and said third lens has a focal length f3 so that the following conditional expressions are satisfied:
D 56< D 12,
0.5 <f 2/ f 3<3.
11. The imaging lens according to claim 10 , wherein said first lens is disposed away from the second lens by the distance D12 on the optical axis thereof so that the following conditional expression is satisfied:
0.05< D 12/ f< 0.8,
where f is a focal length of a whole lens system.
12. The imaging lens according to claim 10 , wherein said second lens and said third lens have a composite focal length f23 so that the following conditional expression is satisfied:
0.3 <f 23/ f< 1.2,
where f is a focal length of a whole lens system.
13. The imaging lens according to claim 10 , wherein said fourth lens has a focal length f4 so that the following conditional expression is satisfied:
−4< f 4/ f<− 0.4,
where f is a focal length of a whole lens system.
14. The imaging lens according to claim 10 , wherein said fifth lens has a focal length f5 and said sixth lens has a focal length f6 so that the following conditional expression is satisfied:
0.3<| f 5|/| f 6|<1.5.
15. The imaging lens according to claim 10 , wherein said sixth lens has a focal length f6 so that the following conditional expression is satisfied:
−5< f 6/ f<− 0.5,
where f is a focal length of a whole lens system.
16. The imaging lens according to claim 10 , wherein said fifth lens is disposed away from the sixth lens by the distance D56 on the optical axis thereof so that the following conditional expression is satisfied:
0.05 <D 56 /f< 0.35,
where f is a focal length of a whole lens system.
17. The imaging lens according to claim 10 , wherein said first lens is arranged so that a surface thereof on the object side is away from an image plane by a distance La on an optical axis thereof so that the following conditional expression is satisfied:
0.2< La/H max<1.5,
where Hmax is a maximum image height of the image plane.