Imaging lens
An imaging lens includes a first lens; a second lens; a third lens; a fourth lens; and a fifth lens, arranged from an object side to an image plane side. The first lens is formed such that a curvature radius of a surface on the object side is positive. The third lens is formed such that a curvature radius of a surface on the object side is positive. The fourth lens is formed such that a surface on the object side and a surface on the image plane side are aspheric. The fifth lens is formed such that a surface on the object side and a surface on the image plane side are aspheric, and a curvature radius of the surface thereof on the image plane side is positive near an optical axis thereof. The first lens and the third lens have specific focal lengths.
1. An imaging lens comprising:
a first lens having positive refractive power;
a second lens having negative refractive power;
a third lens having positive refractive power;
a fourth lens having negative refractive power; and
a fifth lens having refractive power, arranged in this order from an object side to an image plane side,
wherein said first lens is formed in a shape so that a curvature radius of a surface thereof on the object side is positive,
said third lens is formed in a shape so that a curvature radius of a surface thereof on the object side is positive,
said fourth 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,
said fifth 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,
said fifth lens is formed in the shape so that a curvature radius of the surface thereof on the image plane side is positive near an optical axis thereof, and
said first lens has a focal length f 1 and said third lens has a focal length f 3 so that the following conditional expression is satisfied:
f1<f3.
2. The imaging lens according to claim 1 , wherein said fifth lens has negative refractive power.
3. The imaging lens according to claim 1 , wherein said second lens is formed in a shape so that a curvature radius of a surface thereof on the object side and a curvature radius of a surface thereof on the image plane side are positive.
4. The imaging lens according to claim 1 , wherein said third lens is formed in the shape so that a curvature radius of a surface thereof on the image plane side is positive.
5. The imaging lens according to claim 1 , wherein said fourth lens is formed in the shape so that a curvature radius of the surface thereof on the object side and a curvature radius of the surface thereof on the image plane side are negative.
6. The imaging lens according to claim 1 , wherein said fifth lens is formed in the shape so that a curvature radius of a surface thereof on the object side is positive.
7. The imaging lens according to claim 1 , wherein said second lens has a focal length f 2 , said third lens has a focal length f 3 , said fourth lens has a focal length f 4 , and said fifth lens has a focal length f 5 so that the following conditional expressions are satisfied:
|f2|<f3
f3<|f4|
|f2|<|f5|.
8. The imaging lens according to claim 1 , wherein said first lens has an Abbe's number vd 1 , said second lens has an Abbe's number vd 2 , said third lens has an Abbe's number vd 3 , said fourth lens has an Abbe's number vd 4 , and said fifth lens has an Abbe's number vd 5 so that the following conditional expressions are satisfied:
45<vd1<85
vd2<35
45<vd3<85
vd4<35
45<vd5<85.
9. The imaging lens according to claim 1 , wherein said second lens has a focal length f 2 so that the following conditional expression is satisfied:
−1.5< f 2/ f<− 0.4
where f is a focal length of a whole lens system.
10. The imaging lens according to claim 1 , wherein said first lens has a focal length f 1 and said second lens has a focal length f 2 so that the following conditional expression is satisfied:
−1.0< f 1/ f 2<−0.5.
11. The imaging lens according to claim 1 , wherein said second lens is formed in a shape so that a surface thereof on the object side has a curvature radius R 2 f and a surface thereof on the image plane side has a curvature radius R 2 r so that the following conditional expression is satisfied:
3.0< R 2 f/R 2 r< 6.0.
12. The imaging lens according to claim 1 , wherein said third lens has a focal length f 3 so that the following conditional expression is satisfied:
3.0< f 3/ f< 7.0
where f is a focal length of a whole lens system.
13. The imaging lens according to claim 1 , wherein said third lens is formed in the shape so that the surface thereof on the object side has a maximum effective diameter φ 3A and a surface thereof on the image plane side has a maximum effective diameter φ 3B , and
said fourth lens is formed in the shape so that the surface thereof on the object side has a maximum effective diameter φ 4A and the surface thereof on the image plane side has a maximum effective diameter φ 4B so that the following conditional expression is satisfied:
Z 0.7 /f< 0.1
where Z 0.7 is an absolute value of a maximum sag up to 70% of the maximum effective diameters φ 3A to φ 4B , and f is a focal length of a whole lens system.
14. The imaging lens according to claim 1 , wherein said third lens and said fourth lens have a composite focal length f 34 so that the following conditional expression is satisfied:
2.0< f 34/ f< 10.0
where f is a focal length of a whole lens system.
15. The imaging lens according to claim 1 , wherein said second lens, said third lens, and said fourth lens are arranged so that the following conditional expression is satisfied:
0.3< dA/dB< 2.0
where dA is a distance on the optical axis from a surface of the second lens on the image plane side to the surface of the third lens on the object side, and dB is a distance on the optical axis from a surface of the third lens on the image plane side to the surface of the fourth lens on the object side.