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 first lens having a convex object-side surface near an optical axis; a second lens having a convex object-side surface near the optical axis; a third lens having at least one aspheric surface; a fourth lens having at least one aspheric surface; a fifth lens as a double-sided aspheric lens; a sixth lens as a double-sided aspheric lens having a concave image-side surface near the optical axis; and a 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, in which the lenses are arranged in order from an object side to an image side, comprising:
a first lens having a convex surface on the object side near an optical axis;
a second lens having a convex surface on the object side near the optical axis;
a third lens having at least one aspheric surface;
a fourth lens having at least one aspheric surface;
a fifth lens as a double-sided aspheric lens;
a sixth lens as a double-sided aspheric lens having a concave surface on the image side near the optical axis; and
a seventh lens as a double-sided aspheric lens having a concave surface on the image side near the optical axis,
wherein the lenses are not joined to each other.
2. The imaging lens according to claim 1 , wherein the first lens and the second lens each have positive refractive power, and the third lens has negative refractive power with a concave surface on the image side near the optical axis.
3. The imaging lens according to claim 1 , wherein the fourth lens has a biconvex shape near the optical axis, and the image-side surface thereof has an aspheric shape with a concave surface in a peripheral portion thereof.
4. The imaging lens according to claim 1 , wherein the fifth lens has a meniscus shape with a concave surface on the object side near the optical axis.
5. The imaging lens according to claim 1 , wherein the sixth lens has a meniscus shape with a convex surface on the object side near the optical axis, and the aspheric object-side and image-side surfaces thereof each have a pole-change point.
6. The imaging lens according to claim 1 , wherein the seventh lens has negative refractive power, and the image-side surface thereof has an aspheric shape with a pole-change point.
7. The imaging lens according to claim 1 , wherein the first lens has a meniscus shape near the optical axis, and both surfaces thereof have aspheric shapes with peripheral portions thereof curved toward the object side.
8. 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, and
νd3: Abbe number of the third lens at d-ray.
9. The imaging lens according to claim 1 , 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, and
νd5: Abbe number of the fifth lens at d-ray.
10. 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: focal length of the overall optical system of the imaging lens,
f12: composite focal length of the first lens and the second lens, and
f3: focal length of the third lens.
11. A fixed-focus imaging lens composed of seven lenses to form an image of an object on a solid-state image sensor, in which the lenses are arranged in order from an object side to an image side, comprising:
a first lens with positive refractive power;
a second lens with positive refractive power;
a third lens having at least one aspheric surface;
a fourth lens having at least one aspheric surface;
a fifth lens having a concave surface on the object side near an optical axis;
a sixth lens as a double-sided aspheric lens; and
a seventh lens as a double-sided aspheric lens having a concave surface on the image side near the optical axis,
wherein the lenses are not joined to each other.
12. The imaging lens according to claim 11 , wherein the first lens and the second lens have convex surfaces on the object side near the optical axis, and the third lens has negative refractive power with a concave surface on the image side near the optical axis.
13. The imaging lens according to claim 11 , wherein the fourth lens has a biconvex shape near the optical axis, and the image-side surface thereof has an aspheric shape with a concave surface in a peripheral portion thereof.
14. The imaging lens according to claim 11 , wherein the sixth lens has a meniscus shape with a convex surface on the object side near the optical axis, and the aspheric object-side and image-side surfaces thereof each have a pole-change point.
15. The imaging lens according to claim 11 , wherein the seventh lens has negative refractive power, and the image-side surface thereof has an aspheric shape with a pole-change point.
16. The imaging lens according to claim 11 , wherein the first lens has a meniscus shape near the optical axis, and both surfaces thereof have aspheric shapes with peripheral portions thereof curved toward the object side.
17. The imaging lens according to claim 11 , 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, and
νd3: Abbe number of the third lens at d-ray.
18. The imaging lens according to claim 11 , 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, and
νd5: Abbe number of the fifth lens at d-ray.
19. The imaging lens according to claim 11 , 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: focal length of the overall optical system of the imaging lens,
f12: composite focal length of the first lens and the second lens, and
f3: focal length of the third lens.