Imaging lens
An imaging lens includes a first lens having positive refractive power; 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. The fourth lens is formed in a shape so that a surface thereof on the image plane side is convex on an optical axis thereof. The sixth lens is formed in a shape so that a surface thereof on the image plane side is concave toward the image plane side near an optical axis thereof. The fifth lens has a specific Abbe's number and the third lens has a specific focal length.
1. An imaging lens comprising:
a first lens having positive refractive power;
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 on an optical axis thereof,
said sixth lens is formed in a shape so that a surface thereof on the image plane side is concave toward the image plane side near an optical axis thereof, and
said fifth lens has an Abbe's number νd5 and said third lens has a focal length f3 so that the following conditional expressions are satisfied:
45<ν d 5<75,
0.5< f 3/ f< 2.0,
where f is a focal length of a whole lens system.
2. 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:
−1.5< f 1/ f 2<−0.4.
3. 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 R2f and a surface thereof on the image plane side has a curvature radius R2r so that the following conditional expression is satisfied:
0.4< R 2 r/R 2 f< 0.8.
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:
−5.0< f 4/ f<− 1.0.
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:
−2.0< f 5/ f 6<−0.5.
6. An imaging lens comprising:
a first lens having positive refractive power;
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 second lens is formed in a meniscus shape near an optical axis thereof,
said fourth lens is formed in a shape so that a surface thereof on the image plane side is convex on an optical axis thereof,
said sixth lens is formed in a shape so that a surface thereof on the image plane side is concave toward the image plane side near an optical axis thereof, and
said fourth lens has a focal length f4 so that the following conditional expression is satisfied:
−5.0< f 4/ f<− 1.0,
where f is a focal length of a whole lens system.
7. The imaging lens according to claim 6 , 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:
−1.5< f 1/ f 2<−0.4.
8. The imaging lens according to claim 6 , wherein said third lens has a focal length f3 so that the following conditional expression is satisfied:
0.5< f 3/ f< 2.0.
9. The imaging lens according to claim 6 , wherein said second lens is formed in a shape so that a surface thereof on the object side has a curvature radius R2f and a surface thereof on the image plane side has a curvature radius R2r so that the following conditional expression is satisfied:
0.4< R 2 r/R 2 f< 0.8.
10. The imaging lens according to claim 6 , 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:
−2.0< f 5/ f 6<−0.5.
11. An imaging lens comprising:
a first lens having positive refractive power;
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 on an optical axis thereof,
said fifth lens is formed in a shape so that a surface thereof on the object side is convex toward the object side near an optical axis thereof, and
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:
20<ν d 4<40,
45<ν d 5<75.
12. The imaging lens according to claim 11 , 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:
−1.5< f 1/ f 2<−0.4.
13. The imaging lens according to claim 11 , wherein said third lens has a focal length f3 so that the following conditional expression is satisfied:
0.5< f 3/ f< 2.0,
where f is a focal length of a whole lens system.
14. The imaging lens according to claim 11 , wherein said second lens is formed in a shape so that a surface thereof on the object side has a curvature radius R2f and a surface thereof on the image plane side has a curvature radius R2r so that the following conditional expression is satisfied:
0.4< R 2 r/R 2 f< 0.8.
15. The imaging lens according to claim 11 , wherein said fourth lens has a focal length f4 so that the following conditional expression is satisfied:
−5.0< f 4/ f<− 1.0,
where f is a focal length of a whole lens system.
16. The imaging lens according to claim 11 , 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:
−2.0< f 5/ f 6<−0.5.