Imaging lens

1. An imaging lens comprising: in order from an object side of the imaging lens,

a first lens having a convex surface on the object side thereof and having a positive power;

an aperture diaphragm;

a second lens having a concave surface on the object side thereof and having a negative power;

a third lens having a positive power; and

a fourth lens having a convex surface on the object side thereof and near an optical axis thereof, the fourth lens having a meniscus shape,

wherein the imaging lens satisfies conditional expressions:

0.2< D 2/ f< 0.4  (1)

TL/f< 1.3  (2)

wherein

f represents a focal distance of the imaging lens;

D 2 represents an air interval between the first lens and second lens along an optical axis of the imaging lens; and

TL represents a distance along the optical axis from an object-side surface of the first lens to an image forming surface.

2. The imaging lens according to claim 1 , further satisfying conditional expressions:

0.7< f 1/ f< 1.2  (3)

1.45< n 1<1.6  (4)

v 1>60  (5)

0.8<| f 2/ f|< 1.3  (6)

1.0< f 3/ f< 20  (7)

wherein

f 1 represents a focal distance of the first lens;

n 1 represents a refractive index of the first lens at the d-line;

v 1 represents an Abbe number of the first lens at the d-line;

f 2 represents a focal distance of the second lens; and

f 3 represents a focal distance of the third lens.

3. The imaging lens according to claim 1 , wherein each of the second, third and fourth lenses has at least one aspherical surface.

4. The imaging lens according to claim 1 , wherein the first lens has at least one aspherical surface.

5. The imaging lens according to claim 1 , wherein each of the second, third and fourth lenses is made of a resin material.

6. The imaging lens according to claim 1 , wherein the first lens is made of optical glass.

7. The imaging lens according to claim 2 , wherein each of the second, third and fourth lenses has at least one aspherical surface.

8. The imaging lens according to claim 2 , wherein the first lens has at least one aspherical surface.

9. The imaging lens according to claim 2 , wherein each of the second, third and fourth lenses is made of a resin material.

10. The imaging lens according to claim 3 , wherein the first lens has at least one aspherical surface.

11. The imaging lens according to claim 3 , wherein each of the second, third and fourth lenses is made of a resin material.

12. The imaging lens according to claim 4 , wherein each of the second, third and fourth lenses is made of a resin material.

13. The imaging lens according to claim 7 , wherein the first lens has at least one aspherical surface.

14. The imaging lens according to claim 7 , wherein each of the second, third and fourth lenses is made of a resin material.

15. The imaging lens according to claim 8 , wherein each of the second, third and fourth lenses is made of a resin material.

16. The imaging lens according to claim 10 , wherein each of the second, third and fourth lenses is made of a resin material.

17. The imaging lens according to claim 13 , wherein each of the second, third and fourth lenses is made of a resin material.

18. The imaging lens according to claim 17 , wherein the first lens is made of optical glass.

19. The imaging lens according to claim 15 , wherein the first lens is made of optical glass.

20. The imaging lens according to claim 9 , wherein the first lens is made of optical glass.

21. The imaging lens according to claim 16 , wherein the first lens is made of optical glass.

22. The imaging lens according to claim 12 , wherein the first lens is made of optical glass.