Imaging lens
An imaging lens includes a first lens having negative refractive power; a second lens having positive refractive power; a third lens having positive refractive power; a fourth lens having negative refractive power; 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 near an optical axis thereof.
1. An imaging lens comprising:
a first lens having negative refractive power;
a second lens having positive refractive power;
a third lens having positive refractive power;
a fourth lens having negative refractive power;
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 near an optical axis thereof,
said fourth lens is formed in the shape so that the surface thereof on the image plane side has an aspherical shape having at least one inflection point,
said fifth lens is formed in a shape so that a surface thereof on the image plane side is concave near an optical axis thereof,
said fifth lens is formed in the shape so that the surface thereof on the image plane side has an aspherical shape having at least one inflection point, and
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.
2. The imaging lens according to claim 1 , wherein said fourth lens has refractive power increasing from the optical axis thereof toward a peripheral portion thereof.
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.
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.
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 61|<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.
7. An imaging lens comprising:
a first lens having negative refractive power;
a second lens having positive refractive power;
a third lens having positive refractive power;
a fourth lens having negative refractive power;
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 near an optical axis thereof,
said fourth lens is formed in the shape so that the surface thereof on the image plane side has an aspherical shape having at least one inflection point,
said fifth lens is formed in a shape so that a surface thereof on the image plane side is concave near an optical axis thereof,
said fifth lens is formed in the shape so that the surface thereof on the image plane side has an aspherical shape having at least one inflection point, and
said sixth lens has an Abbe's number v6 so that the following conditional expression is satisfied:
10<ν6<40.
8. The imaging lens according to claim 7 , wherein said fourth lens has refractive power increasing from the optical axis thereof toward a peripheral portion thereof.
9. The imaging lens according to claim 7 , 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.
10. The imaging lens according to claim 7 , 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.
11. The imaging lens according to claim 7 , 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.
12. The imaging lens according to claim 7 , 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.
13. An imaging lens comprising:
a first lens having negative refractive power;
a second lens having positive refractive power;
a third lens having positive refractive power;
a fourth lens having negative refractive power;
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 near an optical axis thereof,
said fourth lens is formed in the shape so that the surface thereof on the image plane side has an aspherical shape having at least one inflection point,
said fifth lens is formed in a shape so that a surface thereof on the image plane side is concave near an optical axis thereof,
said fifth lens is formed in the shape so that the surface thereof on the image plane side has an aspherical shape having at least one inflection point, 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 so that the following conditional expression is satisfied:
D 56< D 12.
14. The imaging lens according to claim 13 , wherein said fourth lens has refractive power increasing from the optical axis thereof toward a peripheral portion thereof.
15. The imaging lens according to claim 13 , 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.
16. The imaging lens according to claim 13 , 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.
17. The imaging lens according to claim 13 , 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.
18. The imaging lens according to claim 13 , 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.