Imaging lens
There is provided an imaging lens with high-resolution which satisfies demand of the wide field of view, the low-profileness and the low F-number, and excellently corrects aberrations. An imaging lens comprises in order from an object side to an image side, a first lens having a convex surface facing the object side near an optical axis, a second lens, a third lens having negative refractive power near the optical axis, a fourth lens, a fifth lens, a sixth lens, a seventh lens, and an eighth lens having a concave surface facing the image side and the negative refractive power near the optical axis, wherein an image-side surface of said eighth lens is formed as an aspheric surface having at least one pole point in a position off the optical axis, said sixth lens has positive refractive power near the optical axis, an object-side surface of said seventh lens is a convex surface facing the object side near the optical axis, and a below conditional expression (1) is satisfied: 0.15< vd 7/ vd 8<0.55 (1) where vd7: an abbe number at d-ray of the seventh lens, vd8: an abbe number at d-ray of the eighth lens.
1. An imaging lens comprising, in order from an object side to an image side,
a first lens having a convex surface facing the object side near an optical axis,
a second lens having positive refractive power near the optical axis,
a third lens having negative refractive power near the optical axis,
a fourth lens,
a fifth lens having positive refractive power near the optical axis,
a sixth lens having positive refractive power near the optical axis,
a seventh lens, and
an eighth lens having a concave surface facing the image side and the negative refractive power near the optical axis, wherein
an image-side surface of said eighth lens is formed as an aspheric surface having at least one pole point in a position off the optical axis,
an object-side surface of said seventh lens is a convex surface facing the object side near the optical axis, and
conditional expressions (1), (3) and (13a) are satisfied:
0.15 <vd 7/ vd 8<0.55 (1)
3.00<( D 7 /TTL )×100<8.70 (3)
5.00<| f 4|/ f (13a)
Where
vd7: an abbe number at d-ray of the seventh lens,
vd8: an abbe number at d-ray of the eighth lens,
D7: a thickness along the optical axis of the seventh lens,
TTL: a total track length,
f4: a focal length of the fourth lens, and
f: the focal length of the overall optical system of the imaging lens.
2. The imaging lens according to claim 1 , wherein an image-side surface of said sixth lens is a convex surface facing the image side near the optical axis.
3. The imaging lens according to claim 1 , wherein an image-side surface of said seventh lens is a concave surface facing the image side near the optical axis.
4. The imaging lens according to claim 1 , wherein a below conditional expression (2) is satisfied:
0.50<( D 1 /|f 1|)×100<13.00 (2)
where
D1: a thickness along the optical axis of the first lens, and
f1: a focal length of the first lens.
5. The imaging lens according to claim 1 , wherein a below conditional expression (4) is satisfied:
0.30 <D 4 /D 8<1.20 (4)
where
D4: a thickness along the optical axis of the fourth lens, and
D8: a thickness along the optical axis of the eighth lens.
6. The imaging lens according to claim 1 , wherein a below conditional expression (5) is satisfied:
0.40 <D 7 /D 8<1.40 (5)
where
D7: the thickness along the optical axis of the seventh lens, and
D8: the thickness along the optical axis of the eighth lens.
7. The imaging lens according to claim 1 , wherein a below conditional expression (6) is satisfied:
0.30 <f 6 /f< 4.50 (6)
where
f6: a focal length of the sixth lens, and
f: a focal length of the overall optical system of the imaging lens.
8. The imaging lens according to claim 1 , wherein a below conditional expression (8) is satisfied:
−1.80 <f 8 /f<− 0.60 (8)
where
f8: a focal length of the eighth lens, and
f: the focal length of the overall optical system of the imaging lens.
9. The imaging lens according to claim 1 , wherein a below conditional expression (10) is satisfied:
−3.00< r 12 /f<− 0.20 (10)
where
r12: paraxial curvature radius of the image-side surface of the sixth lens, and
f: the focal length of the overall optical system of the imaging lens.
10. An imaging lens comprising, in order from an object side to an image side,
a first lens having a convex surface facing the object side near an optical axis,
a second lens having positive refractive power near the optical axis,
a third lens having negative refractive power near the optical axis,
a fourth lens,
a fifth lens having positive refractive power near the optical axis,
a sixth lens having positive refractive power near the optical axis,
a seventh lens, and an eighth lens having a concave surface facing the image side and the negative refractive power near the optical axis,
wherein an image-side surface of said eighth lens is formed as an aspheric surface having at least one pole point in a position off the optical axis, an object-side surface of said seventh lens is a convex surface facing the object side near the optical axis, and conditional expressions (1), (9) and (13a) are satisfied:
0.15< vd 7 /vd 8<0.55 (1)
0.70< r 4 /f< 2.70 (9)
5.00<| f 4|/ f (13a)
where vd7: an abbe number at d-ray of the seventh lens,
vd8: an abbe number at d-ray of the eighth lens,
r4: paraxial curvature radius of the image-side surface of the second lens,
f: the focal length of the overall optical system of the imaging lens, and
f4: a focal length of the fourth lens.