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, in which the lenses are arranged in order from an object side to an image side, comprising:
a first lens with positive refractive power having a convex surface on the object side near an optical axis;
a second lens with positive refractive power having convex surfaces on the object side and the image side near the optical axis;
a third lens with negative refractive power having a concave surface on the image side near the optical axis;
a fourth lens having at least one aspheric surface;
a meniscus fifth lens having a concave surface on the object side near the optical axis;
a sixth lens as a double-sided aspheric lens; and
a seventh lens as a double-sided aspheric lens with negative refractive power 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 has a meniscus shape near the optical axis and both surfaces thereof have aspheric shapes with peripheral portions thereof curved toward the object side.
3. The imaging lens according to claim 2 , wherein conditional expressions (1), (2), and (3) below are satisfied:
50 <νd 1<60 (1)
50 <νd 2<60 (2)
20 <νd 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.
4. The imaging lens according to claim 3 , wherein conditional expressions (4) and (5) below are satisfied:
50 <νd 4<60 (4)
20 <νd 5<30 (5)
where
νd4: Abbe number of the fourth lens at d-ray
νd5: Abbe number of the fifth lens at d-ray.
5. The imaging lens according to claim 2 , 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.
6. The imaging lens according to claim 2 , 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.
7. The imaging lens according to claim 2 , wherein the image-side surface of the seventh lens is an aspheric surface with a pole-change point.
8. The imaging lens according to claim 2 , 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
f3: focal length of the third lens.
9. The imaging lens according to claim 1 , wherein conditional expressions (1), (2), and (3) below are satisfied:
50 <νd 1<60 (1)
50 <νd 2<60 (2)
20 <νd 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 <νd 4<60 (4)
20 <νd 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 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.
12. 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.
13. The imaging lens according to claim 1 , wherein the image-side surface of the seventh lens is an aspheric surface with a pole-change point.
14. 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
f3: focal length of the third lens.