Imaging lens
There is provided an imaging lens which is compact and corresponds to wide field of view, and achieves excellent optical performance. An imaging lens comprises in order from an object side to an image side, a first lens having a convex surface facing an image side and positive refractive power, a second lens having a concave surface facing the image side near an optical axis and negative refractive power, a third lens having the convex surface facing the image side and the positive refractive power, and a fourth lens being a meniscus lens having the convex surface facing an object side near the optical axis and having the negative refractive power, wherein said fourth lens is a double-sided aspheric lens and has a pole point at an off-axial position on the image-side surface, and a below conditional expression (1) is satisfied: 0.5<Σ d /TTL<0.9 (1) where Σd: distance along the optical axis from an object-side surface of the first lens to an image-side surface of the fourth lens, and TTL: total track length.
1. An imaging lens comprising, in order from an object side to an image side,
a first lens having concave surface facing the object side and a convex surface facing an image side, the first lens having positive refractive power,
a second lens having a concave surface facing the image side near an optical axis and negative refractive power,
a third lens having the convex surface facing the image side and the positive refractive power, and
a fourth lens being a meniscus lens having the convex surface facing an object side near the optical axis and having the negative refractive power, wherein said fourth lens is a double-sided aspheric lens and has a pole point at an off-axial position on the image-side surface, and below conditional expressions (1), (2) and (3) are satisfied:
0.5<Σ d/TTL< 0.9 (1)
0.7<| r 5|/ f< 3.5 (2)
1.0< f 1/ f (3)
where
Σd: distance along the optical axis from an object-side surface of the first lens to an image-side surface of the fourth lens,
TTL: total track length,
r5: curvature radius near the optical axis of the object-side surface of the third lens,
f1: focal length of the first lens, and
f: focal length of an overall optical system.
2. The imaging lens according to claim 1 , wherein a conditional expression (6) below is satisfied:
0.5<( T 3 /f )×100<2.0 (6)
where
T3: distance along the optical axis from the image-side surface of the third lens to the object-side surface of the fourth lens, and
f: focal length of the overall optical system.
3. The imaging lens according to claim 1 , wherein a conditional expression (7) below is satisfied:
1.0 <|r 3 /r 4|<4.2 (7)
where
r3: curvature radius near the optical axis of the object-side surface of the second lens, and
r4: curvature radius near the optical axis of the image-side surface of the second lens.
4. The imaging lens according to claim 1 , wherein a conditional expression (8) below is satisfied:
0.3 <D 3 /f< 0.9 (8)
where
D3: thickness on the optical axis of the third lens, and
f: focal length of the overall optical system.
5. The imaging lens according to claim 1 , wherein a conditional expression (9) below is satisfied:
f 4 /f< 0.8 (9)
where
f4: focal length of the fourth lens, and
f: focal length of the overall optical system.
6. The imaging lens according to claim 1 , wherein a conditional expression (5) below is satisfied:
20 <νd 4<32 (5)
where
νd4: abbe number at d-ray of the fourth lens.
7. The imaging lens according to claim 1 , wherein a conditional expression (10) below is satisfied:
−1.4 <r 2 /f<− 0.2 (10)
where
r2: curvature radius near the optical axis of the image-side surface of the first lens, and
f: focal length of the overall optical system.
8. The imaging lens according to claim 1 , wherein a conditional expression (11) below is satisfied:
8.0 <D 3 /T 2 (11)
where
D3: thickness on the optical axis of the third lens, and
T2: distance along the optical axis from the image-side surface of the second lens to the object-side surface of the third lens.
9. An imaging lens comprising, in order from an object side to an image side,
a first lens having a concave surface facing the object side and a convex surface facing an image side, and positive refractive power,
a second lens having a concave surface facing the image side near an optical axis and negative refractive power,
a third lens having the convex surface facing the image side and the positive refractive power, and
a fourth lens being a meniscus lens having the convex surface facing an object side near the optical axis and having the negative refractive power, wherein said fourth lens is a double-sided aspheric lens and has a pole point at an off-axial position on the image-side surface, and below conditional expressions (1), (4), (5) and (12) are satisfied:
0.5<Σ d /TTL<0.9 (1)
30< νd 1− νd 2 (4)
20< νd 4<32 (5)
−8.5<═ r 5═/ r 6<3.0 (12)
where
Σd: distance along the optical axis from the object-side surface of the first lens to the image-side surface of the fourth lens,
TTL: total track length,
νd1: abbe number at d-ray of the first lens,
νd2: abbe number at d-ray of the second lens,
νd4: abbe number at d-ray of a fourth lens,
r5: curvature radius near the optical axis of the object-side surface of the third lens, and
r6: curvature radius near the optical axis of the image-side surface of the third lens.
10. The imaging lens according to claim 9 , wherein a conditional expression (13) below is satisfied:
0.45 <r 4 /f< 4.0 (13)
where
r4: curvature radius near the optical axis of the image-side surface of the second lens,
f: focal length of the overall optical system.
11. The imaging lens according to claim 9 , wherein a conditional expression (6) below is satisfied:
0.5<( T 3/ f )×100<2.0 (6)
where
T3: distance along the optical axis from the image-side surface of the third lens to the object-side surface of the fourth lens, and
f: focal length of the overall optical system.
12. The imaging lens according to claims 9 , wherein a conditional expression (7) below is satisfied:
1.0<═ r 3 /r 4═<4.2 (7)
where
r3: curvature radius near the optical axis of the object-side surface of the second lens, and
r4: curvature radius near the optical axis of the image-side surface of the second lens.
13. The imaging lens according to claims 9 , wherein a conditional expression (8) below is satisfied:
0.3< D 3 /f <0.9 (8)
where
D3: thickness on the optical axis of the third lens, and
f: focal length of the overall optical system.
14. An imaging lens comprising, in order from an object side to an image side,
a first lens having a concave surface facing an object side and a convex surface facing an image side, and having positive refractive power,
a second lens having a concave surface facing the image side near an optical axis and negative refractive power,
a third lens having the convex surface facing the image side and the positive refractive power, and
a fourth lens being a meniscus lens having the convex surface facing an object side near the optical axis and having the negative refractive power, wherein said fourth lens is a double-sided aspheric lens and has a pole point at an off-axial position on the image-side surface, and below conditional expressions (1) and (6) are satisfied:
0.5<Σ d/TTL< 0.9 (1)
0.5<(T3/ f )×100<2.0 (6)
where
Σd: distance along the optical axis from the object-side surface of the first lens to the image-side surface of the fourth lens,
TTL: total track length,
T3: distance along the optical axis from the image-side surface of the third lens to the object-side surface of the fourht lens, and
f: focal length of the overall optical system.
15. The imaging lens according to claim 14 , wherein a conditional expression (2) below is satisfied:
0.7<| r 5| /f< 3.5 (2)
where
r5: curvature radius near the optical axis of the object-side surface of the third lens, and
f: focal length of the overall optical system.
16. The imaging lens according to claim 14 , wherein a conditional expression (3) below is satisfied:
1.0 <f 1/ f (3)
where
f1: focal length of the first lens, and
f: focal length of the overall optical system.
17. The imaging lens according to claim 14 , wherein a conditional expression (6) below is satisfied:
0.5<( T 3 /f )×100<2.0 (6)
where
T3: distance along the optical axis from the image-side surface of the third lens to the object-side surface of the fourth lens, and
f: focal length of the overall optical system.
18. The imaging lens according to claims 14 , wherein a conditional expression (7) below is satisfied:
1.0<═ r 3 /r 4═<4.2 (7)
where
r3: curvature radius near the optical axis of the object-side surface of the second lens, and
r4: curvature radius near the optical axis of the image-side surface of the second lens.