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 second lens is formed in a meniscus shape. The fourth lens is formed in a shape so that a surface thereof on the image plane side is convex toward the image plane side. The fifth lens is formed in a shape so that a surface thereof on the object side is convex toward the object side, and a surface thereof on the image plane side is convex toward the image plane side. 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.
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 imaging lens has a total of six lenses,
said first 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,
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 the optical axis,
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 a surface thereof on the image plane side is convex toward the image plane side near the optical axis thereof, and
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.
2. The imaging lens according to claim 1 , wherein each of said first lens, said second lens, said third lens, and said fourth lens has refractive power weaker than that of each of the fifth lens and the sixth lens.
3. 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<f1/f2<−0.4.
4. The imaging lens according to claim 1 , wherein said third lens has a focal length f3 so that the following conditional expression is satisfied:
0.5<f3/f<2.0
where f is a focal length of a whole lens system.
5. The imaging lens according to claim 1 , wherein said second lens is formed in the 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<R2r/R2f<0.8.
6. The imaging lens according to claim 1 , wherein said fourth lens has a focal length f 4 so that the following conditional expression is satisfied:
−5.0<f4/f<−1.0
where f is a focal length of a whole lens system.
7. 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<f5/f6 <−0.5.
8. An imaging lens comprising:
a first lens having positive refractive power;
a second lens;
a third lens;
a fourth lens having negative refractive power;
a fifth lens having positive refractive power; and
a sixth lens, 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 the optical axis,
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<f4/f<−1.0
where f is a focal length of a whole lens system.
9. The imaging lens according to claim 8 , wherein each of said first lens, said second lens, said third lens, and said fourth lens has refractive power weaker than that of each of the fifth lens and the sixth lens.
10. The imaging lens according to claim 8 , 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<f1/f2<−0.4.
11. The imaging lens according to claim 8 , wherein said third lens has a focal length f3 so that the following conditional expression is satisfied:
0.5<f3/f<2.0.
12. The imaging lens according to claim 8 , wherein said second lens is formed in the 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<R2r/R2f<0.8.
13. The imaging lens according to claim 8 , 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<f5/f6<−0.5.
14. An imaging lens comprising:
a first lens having positive refractive power;
a second lens;
a third lens;
a fourth lens having negative refractive power;
a fifth lens; and
a sixth lens having at least one aspheric surface, 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 object side is concave toward the object side near an optical axis thereof, and a surface thereof on the image plane side is convex on the optical axis,
said third lens has a focal length f 3 so that the following conditional expression is satisfied:
0.5<f3/f<2.0
where f is a focal length of a whole lens system, and
said fourth lens has an Abbe's number vd4 and said fifth lens has an Abbe's number vd5 so that the following conditional expressions are satisfied:
20<vd4<40,
45<vd5<75.
15. The imaging lens according to claim 14 , wherein each of said first lens, said second lens, said third lens, and said fourth lens has refractive power weaker than that of each of the fifth lens and the sixth lens.
16. The imaging lens according to claim 14 , 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<f1/f2<−0.4.
17. The imaging lens according to claim 14 , wherein said second lens is formed in the 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<R2r/R2f<0.8.
18. The imaging lens according to claim 14 , wherein said fourth lens has a focal length f4 so that the following conditional expression is satisfied:
−5.0<f4/f<−1.0.
19. The imaging lens according to claim 14 , 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<f5/f6<−0.5.
20. An imaging lens comprising:
a first lens having positive refractive power;
a second lens having negative refractive power;
a third lens;
a fourth lens;
a fifth lens having positive refractive power; and
a sixth lens having negative 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 surface thereof on the object side is convex toward the object side near an optical axis thereof,
said second 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 a surface thereof on the image plane side is concave toward the image plane side near the optical axis thereof,
said fourth lens is formed in a shape so that a surface thereof on the object side is concave toward the object side near an optical axis thereof, and a surface thereof on the image plane side is convex on the optical axis,
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,
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 a focal length f5 and said sixth lens has a focal length f6 so that the following conditional expression is satisfied:
−2.0<f5/f6<−0.5.
21. The imaging lens according to claim 20 , wherein each of said first lens, said second lens, said third lens, and said fourth lens has refractive power weaker than that of each of the fifth lens and the sixth lens.
22. The imaging lens according to claim 20 , 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<f1/f2<−0.4.
23. The imaging lens according to claim 20 , wherein said third lens has a focal length f3 so that the following conditional expression is satisfied:
0.5<f3/f<2.0
where f is a focal length of a whole lens system.
24. The imaging lens according to claim 20 , wherein said second lens is formed in the 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<R2r/R2f <0.8.
25. The imaging lens according to claim 20 , wherein said fourth lens has a focal length f4 so that the following conditional expression is satisfied:
−5.0<f4/f<−1.0
where f is a focal length of a whole lens system.