An imaging lens is provided and includes: in order from an object side of the imaging lens, a first lens having a positive refractive power; a second lens having a positive refractive power and being a spherical glass lens having a convex surface on an image side thereof; a third lens having a negative refractive power and having a concave surface on the object side in the vicinity of an optical axis thereof; and a fourth lens having a positive refractive power and having a meniscus shape in the vicinity of the optical axis thereof, a convex surface in the meniscus shape being directed to the object side, the imaging lens satisfying a specific condition.
1. An imaging lens comprising: in order from an object side of the imaging lens,
a first lens having a positive refractive power;
a second lens having a positive refractive power and being a spherical glass lens having a convex surface on an image side thereof;
a third lens having a negative refractive power and having a concave surface on the object side in the vicinity of an optical axis thereof; and
a fourth lens having a positive refractive power and having a meniscus shape in the vicinity of the optical axis thereof, a convex surface in the meniscus shape being directed to the object side,
the imaging lens satisfying conditional expression:
0.8< f 2/ f< 2.0 (1)
wherein
f is a focal length of the imaging lens, and
f 2 is a focal length of the second lens.
2. The imaging lens according to claim 1 , wherein the imaging lens further satisfies conditional expressions:
1.2< f 1/ f< 2.5 (2)
0.45<| f 3 /f|< 0.8 (3)
0.8< f 4/ f <1.5 (4)
wherein
f is a focal length of the imaging lens,
f 1 is a focal length of the first lens,
f 3 is a focal length of the third lens, and
f 4 is a focal length of the fourth lens.
3. The imaging lens according to claim 1 , wherein
an object-side surface of the first lens is an aspherical surface in which a shape in the vicinity of the optical axis is convex directed to the object side and a positive refractive power becomes weaker as advancing toward a periphery of the first lens, and
an image-side surface of the first lens is an aspherical surface in which a shape in the vicinity of the optical axis is concave directed to the image side and a negative refractive power becomes weaker as advancing toward the periphery of the first lens.
4. The imaging lens according to claim 1 , wherein the third lens has a bi-concave shape in the vicinity of the optical axis, and
the fourth lens satisfies conditional expression:
0.20< R 4 A/f< 0.35 (5)
wherein
f is a focal length of the imaging lens, and
R4A is a paraxial radius of curvature of an object-side surface of the fourth lens.
5. The imaging lens according to claim 1 , further satisfying conditional expression:
12< v 2 −v 3 (6)
wherein
v2 is an Abbe number of the second lens, and
v3 is an Abbe number of the third lens.
6. The imaging lens according to claim 2 , wherein
an object-side surface of the first lens is an aspherical surface in which a shape in the vicinity of the optical axis is convex directed to the object side and a positive refractive power becomes weaker as advancing toward a periphery of the first lens, and
an image-side surface of the first lens is an aspherical surface in which a shape in the vicinity of the optical axis is concave directed to the image side and a negative refractive power becomes weaker as advancing toward the periphery of the first lens.
7. The imaging lens according to claim 2 , wherein the third lens has a bi-concave shape in the vicinity of the optical axis, and
the fourth lens satisfies conditional expression:
0.20 <R 4 A/f< 0.35 (5)
wherein
f is a focal length of the imaging lens, and
R4A is a paraxial radius of curvature of an object-side surface of the fourth lens.
8. The imaging lens according to claim 3 , wherein the third lens has a bi-concave shape in the vicinity of the optical axis, and
the fourth lens satisfies conditional expression:
0.20< R 4 A/f< 0.35 (5)
wherein
f is a focal length of the imaging lens, and
R4A is a paraxial radius of curvature of an object-side surface of the fourth lens.
9. The imaging lens according to claim 6 , wherein the third lens has a bi-concave shape in the vicinity of the optical axis, and
the fourth lens satisfies conditional expression:
0.20< R 4 A/f< 0.35 (5)
wherein
f is a focal length of the imaging lens, and
R4A is a paraxial radius of curvature of an object-side surface of the fourth lens.
10. The imaging lens according to claim 2 , further satisfying conditional expression:
12< v 2− v 3 (6)
wherein
v2 is an Abbe number of the second lens, and
v3 is an Abbe number of the third lens.
11. The imaging lens according to claim 3 , further satisfying conditional expression:
12< v 2 −v 3 (6)
wherein
v2 is an Abbe number of the second lens, and
v3 is an Abbe number of the third lens.
12. The imaging lens according to claim 4 , further satisfying conditional expression:
12< v 2 −v 3 (6)
wherein
v2 is an Abbe number of the second lens, and
v3 is an Abbe number of the third lens.
13. The imaging lens according to claim 6 , further satisfying conditional expression:
12< v 2 −v 3 (6)
wherein
v2 is an Abbe number of the second lens, and
v3 is an Abbe number of the third lens.
14. The imaging lens according to claim 7 , further satisfying conditional expression:
12< v 2 −v 3 (6)
wherein
v2 is an Abbe number of the second lens, and
v3 is an Abbe number of the third lens.
15. The imaging lens according to claim 8 , further satisfying conditional expression:
12< v 2 −v 3 (6)
wherein
v2 is an Abbe number of the second lens, and
v3 is an Abbe number of the third lens.
16. The imaging lens according to claim 9 , further satisfying conditional expression:
12< v 2 −v 3 (6)
wherein
v2 is an Abbe number of the second lens, and
v3 is an Abbe number of the third lens.