Imaging lens
A compact low-cost imaging lens which provides brightness with an F-value of 2.5 or less and a wide field of view and corrects aberrations properly, meeting the demand for low-profileness. The imaging lens elements are arranged in the following order from an object side to an image side: a first lens with positive refractive power having a convex surface on the object side; a second lens with negative refractive power; a third lens with positive or negative refractive power having at least one aspheric surface; a fourth lens with positive refractive power; a fifth lens as a meniscus double-sided aspheric lens having a concave surface near an optical axis on the image side; and a sixth lens as a meniscus lens having a concave surface near the optical axis on the object side. The both surfaces of the fifth lens have pole-change points off the optical axis.
1. An imaging lens which forms an image of an object on a solid-state image sensor, in which elements are arranged in order from an object side to an image side, comprising:
a first lens with positive refractive power having a convex surface on the object side;
a second lens with negative refractive power;
a third lens with positive or negative refractive power having at least one aspheric surface;
a fourth lens with positive refractive power;
a fifth lens as a meniscus double-sided aspheric lens having a concave surface near an optical axis on the image side; and
a sixth lens as a meniscus lens having a concave surface near the optical axis on the object side,
wherein both surfaces of the fifth lens have pole-change points off the optical axis, and
wherein a conditional expression (5) below is satisfied:
−3.0< f 6/ f<− 0.8 (5)
where
f: focal length of an overall optical system of the imaging lens
f6: focal length of the sixth lens.
2. The imaging lens according to claim 1 ,
wherein a conditional expression (1) below is satisfied:
0.5< f 1/ f< 1.5 (1)
where
f: focal length of an overall optical system of the imaging lens
f1: focal length of the first lens.
3. The imaging lens according to claim 2 ,
wherein a conditional expression (2) below is satisfied:
−2.0< f 2/ f<− 0.5 (2)
where
f: focal length of an overall optical system of the imaging lens
f2: focal length of the second lens.
4. The imaging lens according to claim 2 ,
wherein a conditional expression (3) below is satisfied:
0.3< f 4/ f< 1.0 (3)
where
f: focal length of an overall optical system of the imaging lens
f4: focal length of the fourth lens.
5. The imaging lens according to claim 2 ,
wherein a conditional expression (4) below is satisfied:
−1.5< f 5/ f<− 0.3 (4)
where
f: focal length of an overall optical system of the imaging lens
f5: focal length of the fifth lens.
6. The imaging lens according to claim 2 ,
wherein a conditional expression (5) below is satisfied:
−3.0< f 6/ f<− 0.8 (5)
where
f: focal length of an overall optical system of the imaging lens
f6: focal length of the sixth lens.
7. The imaging lens according to claim 2 ,
wherein a conditional expression (11) below is satisfied:
0.3< f 4/ f 1<1.5 (11)
where
f1: focal length of the first lens
f4: focal length of the fourth lens.
8. The imaging lens according to claim 1 ,
wherein a conditional expression (2) below is satisfied:
−2.0< f 2/ f<− 0.5 (2)
where
f: focal length of an overall optical system of the imaging lens
f2: focal length of the second lens.
9. The imaging lens according to claim 1 ,
wherein a conditional expression (3) below is satisfied:
0.3< f 4/ f< 1.0 (3)
where
f: focal length of an overall optical system of the imaging lens
f4: focal length of the fourth lens.
10. The imaging lens according to claim 1 ,
wherein a conditional expression (4) below is satisfied:
−1.5< f 5/ f<− 0.3 (4)
where
f: focal length of an overall optical system of the imaging lens
f5: focal length of the fifth lens.
11. The imaging lens according to claim 1 ,
wherein the third lens has a meniscus shape with a convex surface near the optical axis on the object side.
12. The imaging lens according to claim 1 ,
wherein a conditional expression (6) below is satisfied:
0.3< r 4/ f< 1.0 (6)
where
f: focal length of an overall optical system of the imaging lens
r4: curvature radius of the image-side surface of the second lens.
13. The imaging lens according to claim 1 ,
wherein conditional expressions (7) and (8) below are satisfied:
20<ν d 1−ν d 2<50 (7)
50 <νd 3 ,νd 4 ,νd 5 ,νd 6<80 (8)
where
νd1: Abbe number of the first lens at d-ray
νd2: Abbe number of the second lens at d-ray
νd3: Abbe number of the third lens at d-ray
νd4: Abbe number of the fourth lens at d-ray
νd5: Abbe number of the fifth lens at d-ray
νd6: Abbe number of the sixth lens at d-ray.
14. The imaging lens according to claim 1 ,
wherein conditional expressions (9) and (10) below are satisfied:
1.0<( r 9+ r 10)/( r 9− r 10)<2.7 (9)
−1.5<( r 11+ r 12)/( r 11− r 12)<−0.5 (10)
where
r9: curvature radius of the object-side surface of the fifth lens
r10: curvature radius of the image-side surface of the fifth lens
r11: curvature radius of the object-side surface of the sixth lens
r12: curvature radius of the image-side surface of the sixth lens.
15. The imaging lens according to claim 1 ,
wherein a conditional expression (11) below is satisfied:
0.3< f 4/ f 1<1.5 (11)
where
f1: focal length of the first lens
f4: focal length of the fourth lens.