Imaging lens
There is provided an imaging lens which is low-profile, has a small f-value, and obtains wide field of view which aberrations are properly corrected, in order from an object side to an image side, comprising a first lens having positive refractive power and a convex surface on an object side near an optical axis, a second lens having negative refractive power and a concave surface on the object side near the optical axis, a third lens having positive refractive power and a convex surface on the image side as a double-sided aspheric lens and a fourth lens having negative refractive power and a concave surface on an image side near the optical axis as a double-sided aspheric lens, wherein a conditional expression (1) below is satisfied: 8.5< ih/f <1.0 (1) where f denotes the focal length of the overall optical system, and ih denotes maximum image height.
1. An imaging lens, in order from an object side to an image side, comprising:
a first lens having a meniscus shape with positive refractive power and a convex surface on the object side near an optical axis;
a second lens having negative refractive power and a concave surface on the object side near the optical axis;
a third lens having positive refractive power and a convex surface on the image side as a double-sided aspheric lens; and
a fourth lens having a meniscus shape with negative refractive power and a concave surface on the image side near the optical axis as a double-sided aspheric lens, wherein:
conditional expressions (1), (7), (10), (11a), and (13) below are satisfied:
0.85< ih/f< 1.0 (1)
0.14< |r 1 /r 2|<0.7 (7)
−0.9< f 4/ f<− 0.6 (10)
−1.5< r 5/ f<− 0.6 (11a)
9.0<( T 1/ f )*100<16.0 (13)
where f denotes a focal length of an overall optical system, ih denotes maximum image height, r1 denotes a curvature radius near the optical axis on an object-side surface of the first lens, r2 denotes a curvature radius near the optical axis on an image-side surface of the first lens, f4 denotes a focal length of the fourth lens, r5 denotes a curvature radius near the optical axis of an object-side surface of the third lens, and T1 denotes a distance on the optical axis from the image-side surface of the first lens to an object-side surface of the second lens.
2. The imaging lens according to claim 1 , wherein a conditional expression (2) below is satisfied:
Fno≤ 2.4 (2)
where Fno denotes a F-number.
3. The imaging lens according to claim 2 , wherein a conditional expression (3) below is satisfied:
0.1< |r 3/ r 4|<0.6 (3)
where r3 denotes a curvature radius near an optical axis of the object-side surface of the second lens, and r4 denotes a curvature radius near the optical axis of an image-side surface of the second lens.
4. The imaging lens according to claim 3 , wherein a conditional expression (4) below is satisfied:
1.2<( r 7+ r 8)/( r 7 −r 8)<2.5 (4)
where r7 denotes a curvature radius near an optical axis of an object-side surface of the fourth lens, and r8 denotes a curvature radius near the optical axis of an image-side surface of the fourth lens.
5. The imaging lens according to claim 4 , wherein a conditional expression (5) below is satisfied:
0.15<|Sag4/ D 2|<0.4 (5)
where Sag4 denotes an amount of Sag at a maximum effective diameter on the image-side surface of the second lens, and D2 denotes a thickness on the optical axis of the second lens.
6. The imaging lens according to claim 4 , wherein a conditional expression (6) below is satisfied:
0.02<|Sag5/ D 3|<0.13 (6)
where Sag5 denotes an amount of Sag at maximum effective diameter on the object-side surface of the third lens, and D3 denotes a thickness on the optical axis of the third lens.
7. The imaging lens according to claim 3 , wherein a conditional expression (8) below is satisfied:
−7.5< f 2/ f<− 2.0 (8)
where f2 denotes a focal length of the second lens.
8. The imaging lens according to claim 2 , wherein a conditional expression (9) below is satisfied:
0.3< f 3/ f< 1.2 (9)
where f3 denotes a focal length of the third lens.
9. The imaging lens according to claim 2 , wherein a refractive power of the third lens is most strong among a refractive power of the first lens, the second lens, the third lens, and the fourth lens.
10. The imaging lens according to claim 2 , wherein a conditional expression (12) below is satisfied:
0.035< T 3/ D 3<0.2 (12)
where T3 denotes a distance on the optical axis from an image-side surface of the third lens to an object-side surface of the fourth lens, and D3 denotes a thickness on the optical axis of the third lens.
11. The imaging lens according to claim 1 , wherein a conditional expression (14) below is satisfied:
0.55<TTL/2 ih< 0.85 (14)
where TTL is a total track length.