Imaging lens
There is provided an imaging lens with high resolution which effectively achieves low-profileness while maintaining the wide field of view, and favorably corrects aberrations. The imaging lens comprising a first lens having negative refractive power, a second lens having positive refractive power, a third lens, a fourth lens having positive refractive power, a fifth lens having negative refractive power as a double-sided aspheric lens, and a sixth lens as a double-sided aspheric lens, wherein the first lens has a concave surface facing the image side, and the aspheric surface on the image side of the sixth lens is formed as a concave surface near the optical axis and has at least one pole point at an off-axial point, and a below conditional expression (1) is satisfied: ω≥45° (1) where ω: a half field of view.
1. An imaging lens forming an image of an object on a solid-state image sensor, comprising in order from an object side to an image side,
a first lens having negative refractive power,
a second lens,
a third lens,
a fourth lens,
a fifth lens having negative refractive power and is a double-sided aspheric lens, and
a sixth lens having negative refractive power and is a double-sided aspheric lens,
wherein the third lens has a meniscus shape near an optical axis, and
the sixth lens has at least one pole point at an off-axial point on the image-side surface, and below conditional expressions (10b) and (12) are satisfied:
−2.1< f 6/ f<− 1.2. (10b)
0.2< t 1/ f< 0.6 (12)
where
f6: a focal length of the sixth lens,
f: a focal length of the overall optical system, and
t1: a distance along the optical axis between the first lens and the second lens.
2. The imaging lens according to claim 1 ,
wherein the first lens has a concave surface facing the image side near the optical axis.
3. The imaging lens according to claim 1 ,
wherein the second lens having positive refractive power, the third lens having negative refractive power, and the fourth lens having positive refractive power.
4. The imaging lens according to claim 1 ,
wherein a conditional expression below is satisfied:
ω≥45° (1)
where
ω: a half field of view.
5. The imaging lens according to claim 1 ,
wherein a conditional expression below is satisfied:
0.1<SAG L 1 R/r 2<0.6 (2)
where
SAG L1R: an amount of sag at the peripheral area of the effective diameter of the image-side surface of the first lens,
r2: a curvature radius of the image-side surface of the first lens.
6. The imaging lens according to claim 1 ,
wherein a conditional expression below is satisfied:
0.5< r 2/ f< 1.5 (3)
where
r2: a curvature radius of an image-side surface of the first lens.
7. The imaging lens according to claim 1 ,
wherein the second lens has a convex surface facing the object side near the optical axis.
8. The imaging lens according to claim 1 ,
wherein the third lens has a concave surface facing the image side near the optical axis.
9. The imaging lens according to claim 1 ,
wherein the fourth lens has a convex surface facing the image side near the optical axis.
10. The imaging lens according to claim 1 ,
wherein the sixth lens has a convex surface facing the object side near the optical axis and a concave surface facing the image side near the optical axis.
11. The imaging lens according to claim 1 ,
wherein a conditional expression below is satisfied:
f 2− f 4>0 (4)
where
f2: a focal length of the second lens, and
f4: a focal length of the fourth lens.
12. The imaging lens according to claim 1 ,
wherein conditional expressions below are satisfied:
−2.5< f 1/ f<− 1.0 (5)
0.5< f 2/ f< 1.5 (6)
−6.0< f 3/ f<− 1.5 (7)
0.5< f 4/ f< 1.5 (8)
−6.0< f 5/ f<− 1.5 (9)
where
f1: a focal length of the first lens,
f2: a focal length of the second lens,
f3: a focal length of the third lens,
f4: a focal length of the fourth lens, and
f5: a focal length of the fifth lens.
13. The imaging lens according to claim 1 ,
wherein a conditional expression below is satisfied:
1.0< f 456/ f< 2.5 (11)
where
f456: a composite focal length of the fourth lens, the fifth lens and the sixth lens.
14. The imaging lens according to claim 1 ,
wherein a conditional expression below is satisfied:
0.5< CA 1 /ih< 2.0 (13)
where
CA1: an effective diameter of an object-side surface of the first lens, and
ih: a maximum image height.
15. The imaging lens according to claim 1 ,
wherein conditional expressions below are satisfied:
0.05<SAG L 1 F/CA 1<0.50 (14)
0.05<SAG L 1 R/CA 2<0.50 (15)
where
SAG L1F: an amount of sag at the peripheral area of the effective diameter of the object-side surface of the first lens,
SAG L1R: an amount of sag at the peripheral area of the effective diameter of the image-side surface of the first lens,
CA1: an effective diameter of the object-side surface of the first lens, and
CA2: an effective diameter of the image-side surface of the first lens.