Imaging lens
An imaging lens includes, in order from an object side to an image side, a first lens being a double-sided aspheric lens, a second lens, a third lens having positive refractive power, a fourth lens, a fifth lens, and a sixth lens being a double-sided aspheric lens and having negative refractive power and a concave surface facing the image side near an optical axis, wherein an image-side surface of said sixth lens is an aspheric surface changing to the convex surface at a peripheral area, and a below conditional expression (1) is satisfied: −0.68<( N 1−1)/( r 1× f )×1000<0.68 (1) where N 1 : refractive index at d-ray of the first lens, r1: paraxial curvature radius of the object-side surface of the first lens, and f: focal length of an overall optical system.
1. An imaging lens comprising, in order from an object side to an image side,
a first lens being a double-sided aspheric lens having negative refractive power,
a second lens having a concave surface facing the image side near an optical axis,
a third lens having positive refractive power,
a fourth lens,
a fifth lens, and
a sixth lens being a double-sided aspheric lens and having negative refractive power and a concave surface facing the image side near the optical axis, wherein an image-side surface of said sixth lens is an aspheric surface changing to the convex surface at a peripheral area, and a below conditional expressions (7), (8a), and (11) are satisfied:
0.5< f 3/ f< 1.9 (7)
3.0< |f 4|/ f (8a)
0.1< r 12/ f< 0.5 (11)
where
f3: focal length of the third lens,
f4: focal length of the fourth lens,
r12: paraxial curvature radius of the image-side surface of the sixth lens, and
f: focal length of an overall optical system.
2. The imaging lens according to claim 1 , wherein an image-side surface of said first lens is the concave surface facing the image side near the optical axis.
3. The imaging lens according to claim 1 , wherein an image-side surface of said third lens is the convex surface facing the image side near the optical axis.
4. The imaging lens according to claim 1 , wherein said fourth lens is a meniscus lens having the convex surface facing the object side near the optical axis.
5. The imaging lens according to claim 1 , wherein said fifth lens has the positive refractive power.
6. The imaging lens according to claim 1 , wherein said fifth lens is a meniscus lens having the concave surface facing the object side near the optical axis.
7. The imaging lens according to claim 1 , wherein an object-side surface of said sixth lens is the convex surface facing the object side near the optical axis, is an aspheric surface having an off-axial pole point.
8. The imaging lens according to claim 1 , wherein a below conditional expression (2) is satisfied:
0.25< vd 1/( vd 2+ vd 3)<1.10 (2)
where
vd1: abbe number at d-ray of a first lens,
vd2: abbe number at d-ray of a second lens, and
vd3: abbe number at d-ray of a third lens.
9. The imaging lens according to claim 1 , wherein a below conditional expression (3) is satisfied:
1.3< vd 5/ vd 6<4.1 (3)
where
vd5: abbe number at d-ray of a fifth lens, and
vd6: abbe number at d-ray of a sixth lens.
10. The imaging lens according to claim 1 , wherein a below conditional expression (4) is satisfied:
−18< f 1/ f<− 2 (4)
where
f1: focal length of the first lens, and
f: focal length of the overall optical system.
11. The imaging lens according to claim 1 , wherein a below conditional expression (5) is satisfied:
1.8<| f 2|/ f (5)
where
f2: focal length of the second lens, and
f: focal length of the overall optical system.
12. The imaging lens according to claim 1 , wherein a below conditional expression (6) is satisfied:
−24.0< f 12/ f<− 0.8 (6)
where
f12: composite focal length of the first lens and the second lens, and
f: focal length of the overall optical system of the imaging lens.
13. The imaging lens according to claim 1 , wherein a below conditional expression (9) is satisfied:
0.35< f 5/ f< 1.20 (9)
where
f5: focal length of the fifth lens, and
f: focal length of the overall optical system.
14. The imaging lens according to claim 1 , wherein a below conditional expression (10) is satisfied:
−1.45< f 6/ f<− 0.35 (10)
where
f6: focal length of the sixth lens, and
f: focal length of the overall optical system.
15. The imaging lens according to claim 1 , wherein a below conditional expression (12) is satisfied:
Fno≤2.4 (12)
where
Fno: F-number.