Imaging lens comprising five lenses of +-0+- refractive powers
There is provided an imaging lens with excellent optical characteristics which satisfies demand of the wide field of view, the low-profileness and the low F-number. 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 and positive refractive power near an optical axis, a second lens having negative refractive power near the optical axis, a third lens having aspheric surfaces on both sides, a fourth lens, and a fifth 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 fifth lens is formed as an aspheric surface having at least one pole point in a position off the optical axis, and predetermined conditional expressions are satisfied.
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 and positive refractive power near an optical axis,
a second lens having negative refractive power near the optical axis,
a third lens having aspheric surfaces on both sides,
a fourth lens, and
a fifth 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 fifth lens is formed as an aspheric surface having at least one pole point in a position off the optical axis, an image-side surface of said first lens is a concave surface facing the image side near the optical axis and below conditional expressions (4), (5) and (10) are satisfied:
0.55<( T 1/ f )×100<1.40 (4)
7.50< f 2/ f 5<19.50 (5)
0.40< r 3/ f< 1.15 (10)
where
r3: paraxial curvature radius of an object-side surface of the second lens,
T1: a distance along the optical axis from an image-side surface of the first lens to an object-side surface of the second lens,
f: a focal length of the overall optical system of the imaging lens,
f2: a focal length of the second lens, and
f5: a focal length of the fifth lens.
2. The imaging lens according to claim 1 , wherein an object-side surface of said fifth lens is a convex surface facing the object side near the optical axis.
3. The imaging lens according to claim 2 , wherein a below conditional expression (1) is satisfied:
0.70< vd 3/ vd 4<1.30 (1)
where
vd3: an abbe number at d-ray of the third lens, and
vd4: an abbe number at d-ray of the fourth lens.
4. The imaging lens according to claim 2 , wherein a below conditional expression (2) is satisfied:
0.40< r 2/ f< 1.20 (2)
where
r2: paraxial curvature radius of an image-side surface of the first lens, and
f: a focal length of the overall optical system of the imaging lens.
5. The imaging lens according to claim 2 , wherein a below conditional expression (3) is satisfied:
2.20< r 9/ f< 6.00 (3)
where
r9: paraxial curvature radius of an object-side surface of the fifth lens, and
f: a focal length of the overall optical system of the imaging lens.
6. The imaging lens according to claim 2 , wherein a below conditional expression (11) is satisfied:
0.50< r 3/ r 4<1.45 (11)
where
r3: paraxial curvature radius of an object-side surface of the second lens, and
r4: paraxial curvature radius of an image-side surface of the second lens.
7. The imaging lens according to claim 2 , wherein a below conditional expression (12) is satisfied:
f 2/ f<− 3.50 (12)
where
f2: a focal length of the second lens, and
f: a focal length of the overall optical system of the imaging lens.
8. The imaging lens according to claim 2 , wherein a below conditional expression (13) is satisfied:
TTL/EPd<2.30 (13)
where
EPd: an entrance pupil diameter, and
TTL: a total track length.