Imaging lens and imaging apparatus including the imaging lens
An imaging lens consists of three lenses of, in order from an object side, a first lens having a biconcave shape, and an object-side surface of which is aspherical, a second lens having negative refractive power and a third lens having positive refractive power with a convex surface facing an image side. The absolute value of a curvature radius of an image-side surface of the third lens is less than the absolute value of a curvature radius of an object-side surface of the third lens.
1. An imaging lens consisting of three lenses of, in order from an object side:
a first lens having a biconcave shape, and an object-side surface of which is aspherical;
a second lens having negative refractive power; and
a third lens having positive refractive power with a convex surface facing an image side,
wherein the absolute value of a curvature radius of an image-side surface of the third lens is less than the absolute value of a curvature radius of an object-side surface of the third lens.
2. The imaging lens, as defined in claim 1 , further comprising:
an aperture stop located between the second lens and the third lens.
3. The imaging lens, as defined in claim 2 , wherein the object-side surface of the first lens includes at least one inflection point at a radially inward position toward an optical axis from an intersection of the object-side surface of the first lens and a principal ray at a maximum angle of view.
4. The imaging lens, as defined in claim 1 , wherein the following conditional expression is further satisfied:
−10< L 1 f/L 1 r<− 0.1 (1), where
L1f: a paraxial curvature radius of the object-side surface of the first lens, and
L1r: a paraxial curvature radius of an image-side surface of the first lens.
5. The imaging lens, as defined in claim 1 , wherein the following conditional expression is further satisfied:
−0.9<( L 1 f+L 1 r )/( L 1 f−L 1 r )<0.9 (2), where
L1f: a paraxial curvature radius of the object-side surface of the first lens, and
L1r: a paraxial curvature radius of an image-side surface of the first lens.
6. The imaging lens, as defined in claim 1 , wherein the following conditional expression is further satisfied:
−0.2< f/f 1<−0.05 (3), where
f1: a focal length of the first lens at a wavelength of 850 nm, and
f: a focal length of an entire system at the wavelength of 850 nm.
7. The imaging lens, as defined in claim 1 , wherein the following conditional expression is further satisfied:
0.5< f 1/ f 2<5 (4), where
f1: a focal length of the first lens at a wavelength of 850 nm, and
f2: a focal length of the second lens at the wavelength of 850 nm.
8. The imaging lens, as defined in claim 1 , wherein the second lens has a meniscus shape with a convex surface facing the object side.
9. The imaging lens, as defined in claim 1 , wherein the following conditional expression is further satisfied:
0.1<( L 2 f−L 2 r )/( L 2 f+L 2 r )<1 (5), where
L2f: a paraxial curvature radius of an object-side surface of the second lens, and
L2r: a paraxial curvature radius of an image-side surface of the second lens.
10. The imaging lens, as defined in claim 1 , wherein the following conditional expression is further satisfied:
−3< d 23/ f 12<−1 (6), where
d23: a distance on an optical axis between the second lens and the third lens, and
f12: a combined focal length of the first lens and the second lens at a wavelength of 850 nm.
11. The imaging lens, as defined in claim 4 , wherein the following conditional expression is further satisfied:
−5< L 1 f/L 1 r<− 0.2 (1-1), where
L1f: a paraxial curvature radius of the object-side surface of the first lens, and
L1r: a paraxial curvature radius of an image-side surface of the first lens.
12. The imaging lens, as defined in claim 5 , wherein the following conditional expression is further satisfied:
−0.7<( L 1 f+L 1 r )/( L 1 f−L 1 r )<0.7 (2-1), where
L1f: a paraxial curvature radius of the object-side surface of the first lens, and
L1r: a paraxial curvature radius of an image-side surface of the first lens.
13. The imaging lens, as defined in claim 6 , wherein the following conditional expression is further satisfied:
−0.17< f/f 1<−0.07 (3-1), where
f1: a focal length of the first lens at a wavelength of 850 nm, and
f: a focal length of an entire system at the wavelength of 850 nm.
14. The imaging lens, as defined in claim 7 , wherein the following conditional expression is further satisfied:
0.7< f 1/ f 2<3.5 (4-1), where
f1: a focal length of the first lens at a wavelength of 850 nm, and
f2: a focal length of the second lens at the wavelength of 850 nm.
15. The imaging lens, as defined in claim 9 , wherein the following conditional expression is further satisfied:
0.5<( L 2 f−L 2 r )/( L 2 f+L 2 r )<0.98 (5-1), where
L2f: a paraxial curvature radius of an object-side surface of the second lens, and
L2r: a paraxial curvature radius of an image-side surface of the second lens.
16. The imaging lens, as defined in claim 10 , wherein the following conditional expression is further satisfied:
−2.5< d 23/ f 12<−1.2 (6-1), where
d23: a distance on an optical axis between the second lens and the third lens, and
f12: a combined focal length of the first lens and the second lens at a wavelength of 850 nm.
17. An imaging apparatus comprising:
an imaging lens, as defined in claim 1 .