Imaging lens
There is provided an imaging lens with high resolution which satisfies in well balance wide field of view, low-profileness and low F-number and properly corrects aberrations. An imaging lens comprises a first lens having negative refractive power, a second lens having the negative refractive power, a third lens, a fourth lens having the negative refractive power and a convex surface facing the image side near an optical axis, a fifth lens having at least one aspheric surface, and a sixth lens being double-sided aspheric lens and having a concave surface facing the image side near the optical axis, wherein the image-side surface of the sixth lens is an aspheric surface changing to the convex surface at a peripheral area.
1. An imaging lens comprising in order from an object side to an image side,
a first lens having negative refractive power,
a second lens having negative refractive power and a concave surface facing the image side near an optical axis,
a third lens having positive refractive power,
a fourth lens having refractive power and a concave surface facing the object side near the optical axis,
a fifth lens having refractive power and a concave surface facing the object side near the optical axis, and having at least one aspheric surface, and
a sixth lens being a double-sided aspheric lens and having positive refractive power and a concave surface facing the image side near the optical axis, wherein the image-side surface of said sixth lens changes to the convex surface at a peripheral area, and the following conditional expressions (8a) and (9a) are satisfied:
1.65 <f 6 /f< 5.2 (8a)
4<( D 4 /TTL )×100<8 (9a)
where
f6: focal length of the sixth lens,
f: focal length of the overall optical system of the imaging,
D 4 : thickness along the optical axis of the fourth lens, and
TTL: distance along the optical axis from an object-side surface of the first lens to an image plane.
2. The imaging lens according to claim 1 , wherein an object-side surface of said first lens has a concave surface facing the object side near the optical axis.
3. The imaging lens according to claim 2 , wherein the object-side surface of said first lens is an aspheric surface changing to a convex surface at the peripheral area.
4. The imaging lens according to claim 1 , wherein an image-side surface of said first lens has a convex surface facing the image side near the optical axis.
5. The imaging lens according to claim 4 , wherein the image-side surface of said first lens is an aspheric surface changing to a concave surface at the peripheral area.
6. The imaging lens according to claim 1 , wherein said second lens has a meniscus shape near the optical axis, said third lens has a biconvex shape near the optical axis, said fourth lens has the meniscus shape near the optical axis, and said fifth lens has the meniscus shape near the optical axis.
7. The imaging lens according to claim 1 , wherein an object-side surface of said sixth lens is a convex surface facing the object side near the optical axis and an aspheric surface changing from the convex surface to the concave surface at the peripheral area.
8. The imaging lens according to claim 1 , wherein said fourth lens has negative refractive power.
9. The imaging lens according to claim 1 , wherein the following conditional expression (1) is satisfied:
0.15 <vd 1/( vd 2 −vd 3)<0.50 (1)
where
vd1: abbe number at d-ray of the first lens,
vd2: abbe number at d-ray of the second lens, and
vd3: abbe number at d-ray of the third lens.
10. The imaging lens according to claim 1 , wherein the following conditional expression (2) is satisfied:
0.15 <vd 4 /vd 5<0.55 (2)
where
vd4: abbe number at d-ray of the fourth lens, and
vd5: abbe number at d-ray of the fifth lens.
11. The imaging lens according to claim 1 , wherein the following conditional expression (3) is satisfied:
−32 <f 1 /f<− 7 (3)
where
f1: focal length of the first lens, and
f: focal length of the overall optical system of the imaging lens.
12. The imaging lens according to claim 1 , wherein the following conditional expression (4) is satisfied:
−28 <f 12 /f<− 6 (4)
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 the following conditional expression (5) is satisfied:
0.35 <f 3 /f< 1.20 (5)
where
f3: focal length of the third lens, and
f: focal length of the overall optical system of the imaging lens.
14. The imaging lens according to claim 1 , wherein the following conditional expression (6) is satisfied:
−2.5 <f 4 /f<− 0.6 (6)
where
f4: focal length of the fourth lens, and
f: focal length of the overall optical system of the imaging lens.
15. The imaging lens according to claim 1 , wherein the following conditional expression (7) is satisfied:
10 <|f 5 |/f (7)
where
f5: focal length of the fifth lens, and
f: focal length of the overall optical system of the imaging lens.
16. The imaging lens according to claim 1 , wherein the following conditional expression (10) is satisfied:
0.6<Σ( L 1 F−L 6 R )/ f< 2.4 (10)
where
Σ(L 1 F−L 6 R): distance along the optical axis from the object-side surface of the first lens to the image-side surface of the sixth lens, and
f: focal length of the overall optical system of the imaging lens.
17. The imaging lens according to claim 1 , wherein the following conditional expression (11) is satisfied:
0.40 <T 2 /T 3<1.80 (11)
where
T 2 : distance along the optical axis from the image-side surface of the second lens to the object-side surface of the third lens, and
T 3 : distance along the optical axis from the image-side surface of the third lens to the object-side surface of the fourth lens.
18. The imaging lens according to claim 1 , wherein the following conditional expression (12) is satisfied:
0.2 <r 12 /f< 0.9 (12)
where
r12: paraxial curvature radius of the image-side surface of the sixth lens, and
f: focal length of the overall optical system of the imaging lens.
19. The imaging lens according to claim 1 , wherein the following conditional expression (13) is satisfied:
Fno≤ 2.4 (13)
where
Fno: F-number.
20. An imaging lens comprising in order from an object side to an image side,
a first lens having negative refractive power,
a second lens having refractive power and a concave surface facing the image side near an optical axis,
a third lens having positive refractive power,
a fourth lens having refractive power and a concave surface facing the object side near the optical axis,
a fifth lens having refractive power and a concave surface facing the object side near the optical axis, and having at least one aspheric surface, and
a sixth lens being a double-sided aspheric lens and having positive refractive power and a concave surface facing the image side near the optical axis, wherein the image-side surface of said sixth lens changes to the convex surface at a peripheral area, and the following conditional expressions (2), (8a) and (9a) are satisfied:
0.15 <vd 4 /vd 5<0.55 (2)
1.65 <f 6 /f< 5.2 (8a)
4<( D 4 /TTL )×100<8 (9a)
where
vd4: abbe number at d-ray of the fourth lens, and
vd5: abbe number at d-ray of the fifth lens,
f6: focal length of the sixth lens,
f: focal length of the overall optical system of the imaging,
D 4 : thickness along the optical axis of the fourth lens, and
TTL: distance along the optical axis from an object-side surface of the first lens to an image plane.