Imaging lens
A compact low-cost imaging lens which provides brightness with an F-value of 2.5 or less and a wide field of view and corrects aberrations properly, meeting the demand for low-profileness. The imaging lens elements are arranged in the following order from an object side to an image side: a first lens with positive refractive power having a convex surface on the object side; a second lens with negative refractive power; a third lens with positive or negative refractive power having at least one aspheric surface; a fourth lens with positive refractive power; a fifth lens as a meniscus double-sided aspheric lens having a concave surface near an optical axis on the image side; and a sixth lens as a meniscus lens having a concave surface near the optical axis on the object side. The both surfaces of the fifth lens have pole-change points off the optical axis.
1. An imaging lens which forms 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;
a second lens having negative refractive power;
a third lens that is a meniscus lens having positive or negative refractive power, a convex surface facing the object side, and at least one aspheric surface;
a fourth lens having positive refractive power;
a fifth lens that is a double-sided aspheric lens having an image-side surface that is concave near an optical axis of the imaging lens; and
a sixth lens having an object-side surface that is concave near the optical axis,
wherein a conditional expression (8′) below is satisfied:
50<ν d 3<80 (8′)
where
νd3: Abbe number of the third lens at d-ray.
2. The imaging lens according to claim 1 , wherein conditional expressions (1) and (2) below are satisfied:
0.5< f 1/ f< 1.5 (1)
−2.0< f 2/ f<− 0.5 (2)
where
f: overall focal length of the imaging lens,
f1: focal length of the first lens, and
f2: focal length of the second lens.
3. The imaging lens according to claim 1 , wherein conditional expressions (3), (4), and (5) below are satisfied:
0.3< f 4/ f< 1.0 (3)
−1.5< f 5/ f<− 0.3 (4)
−3.0< f 6/ f<− 0.8 (5)
where
f: overall focal length of the imaging lens,
f4: focal length of the fourth lens,
f5: focal length of the fifth lens, and
f6: focal length of the sixth lens.
4. The imaging lens according to claim 1 , wherein a conditional expression (6) below is satisfied:
0.3< r 4/ f< 1.0 (6)
where
f: overall focal length of the imaging lens, and
r4: curvature radius of an image-side surface of the second lens.
5. The imaging lens according to claim 1 , wherein a conditional expression (7) below is satisfied:
20<ν d 1−ν d 2<50 (7)
where
νd1: Abbe number of the first lens at d-ray, and
νd2: Abbe number of the second lens at d-ray.
6. The imaging lens according to claim 1 , wherein conditional expressions (9) and (10) below are satisfied:
1.0<( r 9+ r 10)/( r 9− r 10)<2.7 (9)
−1.5<( r 11+ r 12)/( r 11− r 12)<−0.5 (10)
where
r9: curvature radius of an object-side surface of the fifth lens,
r10: curvature radius of the image-side surface of the fifth lens,
r11: curvature radius of the object-side surface of the sixth lens, and
r12: curvature radius of an image-side surface of the sixth lens.
7. The imaging lens according to claim 1 , wherein a conditional expression (11) below is satisfied:
0.3< f 4/ f 1<1.5 (11)
where
f1: focal length of the first lens, and
f4: focal length of the fourth lens.
8. The imaging lens according to claim 1 , wherein conditional expressions (7) and (8′) below are satisfied:
20<ν d 1−ν d 2<50 (7)
50<ν d 3<80 (8′)
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. An imaging lens which forms 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;
a second lens that is a meniscus lens having negative refractive power and a concave surface facing the image side;
a third lens that is a meniscus lens having positive refractive power, a convex surface facing the object side, and at least one aspheric surface;
a fourth lens having positive refractive power;
a fifth lens that is a double-sided aspheric lens; and
a sixth lens having an object-side surface that is concave near an optical axis of the imaging lens,
wherein a conditional expression (8″) below is satisfied:
50<ν d 5<80 (8″)
where
νd5: Abbe number of the fifth lens at d-ray.
10. The imaging lens according to claim 9 , wherein conditional expressions (1) and (2) below are satisfied:
0.5< f 1/ f< 1.5 (1)
−2.0< f 2/ f<− 0.5 (2)
where
f: overall focal length of the imaging lens,
f1: focal length of the first lens, and
f2: focal length of the second lens.
11. The imaging lens according to claim 9 , wherein conditional expressions (3), (4), and (5) below are satisfied:
0.3< f 4/ f< 1.0 (3)
−1.5< f 5/ f<− 0.3 (4)
−3.0< f 6/ f<− 0.8 (5)
where
f: overall focal length of the imaging lens,
f4: focal length of the fourth lens,
f5: focal length of the fifth lens, and
f6: focal length of the sixth lens.
12. The imaging lens according to claim 9 , wherein a conditional expression (6) below is satisfied:
0.3< r 4/ f< 1.0 (6)
where
f: overall focal length of the imaging lens, and
r4: curvature radius of an image-side surface of the second lens.
13. The imaging lens according to claim 9 , wherein a conditional expression (7) below is satisfied:
20<ν d 1−ν d 2<50 (7)
where
νd1: Abbe number of the first lens at d-ray, and
νd2: Abbe number of the second lens at d-ray.
14. The imaging lens according to claim 9 , wherein conditional expressions (9) and (10) below are satisfied:
1.0<( r 9+ r 10)/( r 9− r 10)<2.7 (9)
−1.5<( r 11+ r 12)/( r 11− r 12)<−0.5 (10)
where
r9: curvature radius of an object-side surface of the fifth lens,
r10: curvature radius of an image-side surface of the fifth lens,
r11: curvature radius of the object-side surface of the sixth lens, and
r12: curvature radius of an image-side surface of the sixth lens.
15. The imaging lens according to claim 9 , wherein a conditional expression (11) below is satisfied:
0.3< f 4/ f 1<1.5 (11)
where
f1: focal length of the first lens, and
f4: focal length of the fourth lens.
16. An imaging lens which forms 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;
a second lens that is a meniscus lens having a concave surface facing the image side;
a third lens that is a meniscus lens near an optical axis of the imaging lens and having positive refractive power and at least one aspheric surface;
a fourth lens having positive refractive power;
a fifth lens that is a double-sided aspheric lens having negative refractive power and an image-side surface that is concave near the optical axis; and
a sixth lens having negative refractive power and an object-side surface that is concave near the optical axis.
17. The imaging lens according to claim 16 , wherein conditional expressions (1) and (2) below are satisfied:
0.5< f 1/ f< 1.5 (1)
−2.0< f 2/ f<− 0.5 (2)
where
f: overall focal length of the imaging lens,
f1: focal length of the first lens, and
f2: focal length of the second lens.
18. The imaging lens according to claim 16 , wherein conditional expressions (3), (4), and (5) below are satisfied:
0.3< f 4/ f< 1.0 (3)
−1.5< f 5/ f<− 0.3 (4)
−3.0< f 6/ f<− 0.8 (5)
where
f: overall focal length of the imaging lens,
f4: focal length of the fourth lens,
f5: focal length of the fifth lens, and
f6: focal length of the sixth lens.
19. The imaging lens according to claim 16 , wherein the third lens has a meniscus shape and an object-side surface that is convex near the optical axis.
20. The imaging lens according to claim 16 , wherein a conditional expression (6) below is satisfied:
0.3< r 4/ f< 1.0 (6)
where
f: overall focal length of the imaging lens, and
r4: curvature radius of an image-side surface of the second lens.