Image pickup lens and image pickup device
An image pickup lens includes: a first lens which is a positive lens having a positive refractive power; a second lens which is a negative lens having a negative refractive power; a third lens which is a positive lens; a fourth lens having at least one surface with an aspherical shape, wherein the first lens, the second lens, the third lens and the fourth lens are arranged from an object side of the image pickup lens in this order and the image pickup lens is designed using a predefined condition.
1. An image pickup lens comprising:
a first lens which is a positive lens having a positive refractive power;
a second lens which is a negative lens having a negative refractive power;
a third lens which is a positive lens having a positive refractive power;
a fourth lens having at least one surface with an aspherical shape,
wherein the first lens, the second lens, the third lens and the fourth lens are arranged from an object side of the image pickup lens in this order and
the image pickup lens satisfies following conditional expressions:
−3.0<( r 3 + r 4 )/( r 3 − r 4 )<−0.7 (1)
v 1 − v 2 >15.0 (2)
v 3 − v 2 >15.0 (3)
where r 3 is a curvature radius of an object side surface of the second lens, r 4 is a curvature radius of an image side surface of the second lens, v 1 , v 2 , and v 3 are Abbe constants of the first to third lenses respectively.
2. The image pickup lens of claim 1 further comprising an aperture stop at a closest position to an object side of the image pickup lens.
3. The image pickup lens of claim 2 which satisfies a following conditional expression:
−1.5<( r 3 + r 4 )/( r 3 − r 4 )<−0.7 (4)
where r 3 is a curvature radius of an object side surface of the second lens and r 4 is a curvature radius of an image side surface of the second lens.
4. The image pickup lens of claim 2 which satisfies a following conditional expression:
−1.5<( r 3 + r 4 )/( r 3 − r 4 )<−1.0 (5)
where r 3 is a curvature radius of an object side surface of the second lens and r 4 is a curvature radius of an image side surface of the second lens.
5. The image pickup lens of claim 2 which satisfies a following conditional expression:
0.1<( r 1 + r 2 )/( r 1 − r 2 )<1.0 (6)
where r 1 is a curvature radius of an object side surface of the first lens and r 2 is a curvature radius of an image side surface of the first lens.
6. The image pickup lens of claim 2 , wherein the fourth lens comprises a positive lens.
7. The image pickup lens of claim 2 , wherein the fourth lens comprises a negative lens.
8. The image pickup lens of claim 1 further comprising an aperture stop between the first lens and the second lens.
9. The image pickup lens of claim 8 , wherein the first lens has a shape having a convex surface which faces an object side of the optical pickup lens.
10. The image pickup lens of claim 8 which satisfies a following conditional expression:
−1.5 <f 2 / f <−0.7 (7)
where f 2 is a focal length of the second lens and f is a focal length of a total system of the image pickup lens.
11. The image pickup lens of claim 8 , wherein the first and second lenses have meniscus shapes such that the aperture stop is arranged between the first lens and the second lens and the concave surfaces of the first lens and the second lens face the aperture stop.
12. The image pickup lens of claim 8 which satisfies a following conditional expression:
−2.5<( r 3 + r 4 )/( r 3 − r 4 )<−1.2 (8).
13. The image pickup lens of claim 8 , wherein the fourth lens is a negative lens.
14. The image pickup lens of claim 1 , wherein an air lens formed by an image side surface of the third lens and an object side surface of the fourth lens has a biconcave shape.
15. The image pickup lens of claim 1 which satisfies following conditional expressions:
0.30< fa/f <0.60 (9)
0.30< f 7 / f <2.0 (10)
where f is a focal length of an entire system of the image pickup lens,
fa is a focal length of an air lens which is formed by an image side surface of the third lens and an object side surface of the fourth lens and satisfies the following expression:
fa=R 6 × R 7 /{ R 7 ×(1 −N 3 )+ R 6 ×( N 4 −1)− D 6 ×(1 −N 3 )×( N 4 −1)},
N 3 is a refractive index of the third lens for d-line,
N 4 is a refractive index of the fourth lens for d-line,
R 6 is a curvature radius of an image side surface of the third lens,
R 7 is a curvature radius of an object side surface of the fourth lens,
D 6 is an air distance between the third lens and the fourth lens along an optical axis and
r 7 is a curvature radius of an object side surface of the fourth lens.
16. The image pickup lens of claim 15 which satisfies a following conditional expression:
0.30< r 7 / f <1.0 (11).
17. The image pickup lens of claim 1 ,
wherein the first lens comprises a glass material,
the second lens, the third lens and the fourth lens comprise a plastic material and
the image pickup lens satisfies a following conditional expression:
| f/f 234|<0.5 (12)
where f is a focal length of an entire system of the image pickup lens and f234 is a composite focal length of the second lens, the third lens and fourth lens which comprise a plastic material.
18. The image pickup device comprising the image pickup lens of claim 1 and a solid-state image pickup element.