Imaging lens
A low-cost imaging lens which corrects aberrations properly with a small F-value, ensures high performance with a larger number of constituent lenses and has a more low-profile design than before. The constituent lenses are arranged in the following order from an object side to an image side: a positive (refractive power) first lens having a convex object-side surface near an optical axis; a positive second lens having convex object-side and image-side surfaces near the optical axis; a negative third lens having a concave image-side surface near the optical axis; a fourth lens having at least one aspheric surface; a meniscus fifth lens having a concave object-side surface near the optical axis; a sixth lens as a double-sided aspheric lens; and a negative seventh lens as a double-sided aspheric lens having a concave image-side surface near the optical axis. These constituent lenses are not joined to each other.
1. A fixed-focus imaging lens composed of seven lenses to form an image of an object on a solid-state image sensor, comprising, in order from an object side to an image side of the imaging lens:
a first lens having a convex surface facing the object side near an optical axis of the imaging lens;
a second lens having an aspheric surface;
a third lens having an aspheric surface;
a fourth lens having an aspheric surface;
a fifth lens having an aspheric surface;
a sixth lens that is a double-sided aspheric lens having a concave surface facing the image side near the optical axis; and
a seventh lens that is a double-sided aspheric lens having a concave surface facing the image side near the optical axis,
wherein none of the lenses has a lens surface that contacts an adjacent lens.
2. The imaging lens according to claim 1 , wherein the first lens has positive refractive power and a meniscus shape near the optical axis.
3. The imaging lens according to claim 1 , wherein the second lens has positive refractive power and convex surfaces facing the object side and the image side near the optical axis.
4. The imaging lens according to claim 1 , wherein the third lens has negative refractive power and a concave surface facing the image side near the optical axis.
5. The imaging lens according to claim 1 , wherein the fourth lens has a biconvex shape near the optical axis.
6. The imaging lens according to claim 1 , wherein the fifth lens has a meniscus shape with a convex surface facing the object side near the optical axis.
7. The imaging lens according to claim 1 , wherein the sixth lens has a meniscus shape with a convex surface facing the object side near the optical axis, and each of an object-side surface and an image-side surface of the sixth lens has a pole-change point.
8. The imaging lens according to claim 1 , wherein the seventh lens has negative refractive power and a meniscus shape near the optical axis, and an image-side surface of the seventh lens has a pole-change point.
9. The imaging lens according to claim 1 , wherein conditional expressions (1), (2), and (3) below are satisfied:
50<ν d 1<60 (1)
50<ν d 2<60 (2)
20<ν d 3<30 (3)
where
νd1: Abbe number of the first lens at d-ray
νd2: Abbe number of the second lens at d-ray
νd3: Abbe number of the third lens at d-ray.
10. The imaging lens according to claim 9 , wherein conditional expressions (4) and (5) below are satisfied:
50<ν d 4<60 (4)
20<ν d 5<30 (5)
where
νd4: Abbe number of the fourth lens at d-ray
νd5: Abbe number of the fifth lens at d-ray.
11. The imaging lens according to claim 1 , wherein conditional expressions (6) and (7) below are satisfied:
0.55< f 12/ f< 0.88 (6)
−1.2< f 3/ f<− 0.7 (7)
where
f: overall focal length of the imaging lens
f12: composite focal length of the first lens and the second lens
f3: focal length of the third lens.
12. A fixed-focus imaging lens composed of seven lenses to form an image of an object on a solid-state image sensor, 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 near an optical axis of the imaging lens;
a second lens having a convex surface facing the image side near the optical axis;
a third lens having an aspheric surface;
a fourth lens having an aspheric surface;
a fifth lens having a meniscus shape near the optical axis and an aspheric surface;
a sixth lens that is a double-sided aspheric lens; and
a seventh lens that is a double-sided aspheric lens having a concave surface facing the image side near the optical axis,
wherein none of the lenses has a lens surface that contacts an adjacent lens.
13. The imaging lens according to claim 12 , wherein the first lens has a meniscus shape near the optical axis.
14. The imaging lens according to claim 12 , wherein the second lens has positive refractive power and a convex surface facing the object side near the optical axis.
15. The imaging lens according to claim 12 , wherein the third lens has negative refractive power and a concave surface facing the image side near the optical axis.
16. The imaging lens according to claim 12 , wherein the fourth lens has a biconvex shape near the optical axis.
17. The imaging lens according to claim 12 , wherein the fifth lens has a meniscus shape with a convex surface facing the object side near the optical axis.
18. The imaging lens according to claim 12 , wherein the sixth lens has a meniscus shape with a convex surface facing the object side near the optical axis, and each of an object-side surface and an image-side surface of the sixth lens has a pole-change point.
19. The imaging lens according to claim 12 , wherein the seventh lens has negative refractive power and a meniscus shape near the optical axis, and an image-side surface of the seventh lens has a pole-change point.
20. The imaging lens according to claim 12 , wherein conditional expressions (1), (2), and (3) below are satisfied:
50<ν d 1<60 (1)
50<ν d 2<60 (2)
20<ν d 3<30 (3)
where
νd1: Abbe number of the first lens at d-ray
νd2: Abbe number of the second lens at d-ray
νd3: Abbe number of the third lens at d-ray.
21. The imaging lens according to claim 20 , wherein conditional expressions (4) and (5) below are satisfied:
50<ν d 4<60 (4)
20<ν d 5<30 (5)
where
νd4: Abbe number of the fourth lens at d-ray
νd5: Abbe number of the fifth lens at d-ray.
22. The imaging lens according to claim 12 , wherein conditional expressions (6) and (7) below are satisfied:
0.55< f 12/ f< 0.88 (6)
−1.2< f 3/ f<− 0.7 (7)
where
f: overall focal length of the imaging lens
f12: composite focal length of the first lens and the second lens
f3: focal length of the third lens.