Imaging lens
A compact high-resolution imaging lens which provides a wide field of view of 80 degrees or more and corrects various aberrations properly. Designed for a solid-state image sensor, the imaging lens includes constituent lenses arranged in the following order from an object side to an image side: a first positive (refractive power) lens having a convex object-side surface; a second negative lens having a concave image-side surface; a third positive lens as a double-sided aspheric lens having a convex object-side surface; a fourth positive lens having a convex image-side surface; a fifth lens as a double-sided aspheric lens having a concave image-side surface; and a sixth negative lens having a concave image-side surface. The image-side surface of the sixth lens has an aspheric shape with a pole-change point in a position off an optical axis.
1. An imaging lens, comprising, in order from an object side to an image side of the imaging lens:
a first lens having positive refractive power and a convex surface facing the object side;
a second lens having negative refractive power, a convex surface facing the object side, and a concave surface facing the image side;
a third lens that is a double-sided aspheric lens having positive refractive power and convex surfaces facing the object side and the image side;
a fourth lens that is a double-sided aspheric lens having a concave surface facing the object side and a convex surface facing the image side;
a fifth lens that is a double-sided aspheric lens having a convex surface facing the object side;
a sixth lens that is a double-sided aspheric lens having a convex surface facing the object side and a concave surface facing the image side, an image-side surface of the sixth lens having an aspheric shape with a pole-change point separated from an optical axis of the imaging lens; and
when f 2 is a focal length of the second lens, f 3 is a focal length of the third lens, and f is an overall focal length of the imaging lens, expressions (2′) and (12′) below are satisfied:
−1.57≦ f 2 /f<− 0.8 (2′)
1.62≦ f 3 /f< 7.0 (12′).
2. The imaging lens according to claim 1 , wherein when ih is a maximum image height, an expression (11) below is satisfied:
0.8< ih/f< 1.2 (11).
3. The imaging lens according to claim 1 , wherein when TTL is a distance along the optical axis from an image plane of the imaging lens to an object-side surface of an optical element located nearest an imaged object, and Σd is a distance along the optical axis from an object-side surface of the first lens to the image-side surface of the sixth lens, an expression (9) below is satisfied:
0.65< Σd /TTL<0.90 (9).
4. The imaging lens according to claim 3 , wherein an expression (10) below is satisfied:
TTL/ f< 1.6 (10).
5. The imaging lens according to claim 1 , wherein:
the fifth lens is a meniscus lens having negative refractive power and each of an object-side surface and an image-side surface of the fifth lens has an aspheric shape with a pole-change point separated from the optical axis, and
an object-side surface of the sixth lens has an aspheric shape with a pole-change point separated from the optical axis.
6. The imaging lens according to claim 1 , wherein when f 1 is a focal length of the first lens, an expression (1) below is satisfied:
0.55< f 1 /f< 1.7 (1).
7. The imaging lens according to claim 1 , wherein, when vdl is an Abbe number of the first lens at d-ray, and vd2 is an Abbe number of the second lens at d-ray, expressions (3) and (4) below are satisfied:
45<vd1<80 (3)
20<vd2<40 (4).
8. The imaging lens according to claim 1 , wherein, when vd 3 is an Abbe number of the third lens at d-ray, vd 4 is an Abbe number of the fourth lens at d-ray, vd 5 is an Abbe number of the fifth lens at d-ray, and vd 6 is an Abbe number of the sixth lens at d-ray, expressions (5) to (8) below are satisfied:
50<vd3<75 (5)
50<vd4<75 (6)
20<vd5<40 (7)
50<vd6<75 (8).
9. The imaging lens according to claim 7 , wherein, when vd 3 is an Abbe number of the third lens at d-ray, vd 4 is an Abbe number of the fourth lens at d-ray, vd 5 is an Abbe number of the fifth lens at d-ray, and vd 6 is an Abbe number of the sixth lens at d-ray, expressions (5) to (8) below are satisfied:
50<vd3<75 (5)
50<vd4<75 (6)
20<vd5<40 (7)
50<vd6<75 (8).
10. An imaging lens, comprising, in order from an object side to an image side of the imaging lens:
a first lens having positive refractive power and convex surfaces facing the object side and the image side;
a second lens having negative refractive power, a convex surface facing the object side, and a concave surface facing the image side;
a third lens that is a double-sided aspheric lens having positive refractive power and a convex surface facing the object side;
a fourth lens that is a double-sided aspheric lens having a concave surface facing the object side and a convex surface facing the image side;
a fifth lens that is a double-sided aspheric lens;
a sixth lens that is a double-sided aspheric lens having a convex surface facing the object side and a concave surface facing the image side, an image-side surface of the sixth lens having an aspheric shape with a pole-change point separated from an optical axis of the imaging lens; and
when f 56 is a composite focal length of the fifth lens and the sixth lens, and f is an overall focal length of the imaging lens, an expression (14) below is satisfied:
−1.2< f 56 /f<− 0.5 (14).
11. The imaging lens according to claim 10 , wherein when ih is a maximum image height, an expression (11) below is satisfied:
0.8< ih/f< 1.2 (11).
12. The imaging lens according to claim 10 , wherein when TTL is a distance along the optical axis from an image plane of the imaging lens to an object-side surface of an optical element located nearest an imaged object, and Σd is a distance along the optical axis from an object-side surface of the first lens to the image-side surface of the sixth lens, an expression (9) below is satisfied:
0.65< Σd /TTL<0.90 (9).
13. The imaging lens according to claim 12 , wherein an expression (10) below is satisfied:
TTL/ f< 1.6 (10).
14. The imaging lens according to claim 10 , wherein:
the fifth lens is a meniscus lens having negative refractive power and each of an object-side surface and an image-side surface of the fifth lens has an aspheric shape with a pole-change point separated from the optical axis, and
an object-side surface of the sixth lens has an aspheric shape with a pole-change point separated from the optical axis.
15. The imaging lens according to claim 10 , wherein when fl is a focal length of the first lens, an expression (1) below is satisfied:
0.55< f 1 /f< 1.7 (1).
16. The imaging lens according to claim 10 , wherein when f 2 is a focal length of the second lens, an expression (2) below is satisfied:
−2.3< f 2 /f<− 0.8 (2).
17. The imaging lens according to claim 16 , wherein when f 3 is a focal length of the third lens, an expression (12) below is satisfied:
1.3< f 3 /f< 7.0 (12).
18. The imaging lens according to claim 10 , wherein when vd 1 is an Abbe number of the first lens at d-ray, and vd 2 is an Abbe number of the second lens at d-ray, expressions (3) and (4) below are satisfied:
45<vd1<80 (3)
20<vd2<40 (4).
19. The imaging lens according to claim 10 , wherein when vd 3 is an Abbe number of the third lens at d-ray, vd 4 is an Abbe number of the fourth lens at d-ray, vd 5 is an Abbe number of the fifth lens at d-ray, and vd 6 is an Abbe number of the sixth lens at d-ray, expressions (5) to (8) below are satisfied:
50<vd3<75 (5)
50<vd4<75 (6)
20<vd5<40 (7)
50<vd6<75 (8).
20. The imaging lens according to claim 18 , wherein when vd 3 is an Abbe number of the third lens at d-ray, vd 4 is an Abbe number of the fourth lens at d-ray, vd 5 is an Abbe number of the fifth lens at d-ray, and vd 6 is an Abbe number of the sixth lens at d-ray, expressions (5) to (8) below are satisfied:
50<vd3<75 (5)
50<vd4<75 (6)
20<vd5<40 (7)
50<vd6<75 (8).