Imaging lens

1. An imaging lens which forms an image of an object on a solid-state image sensor, comprising exactly six lenses arranged, in the following order from an object side to an image side:

a first lens with positive refractive power as a meniscus lens having a convex surface on the object side;

a second lens with refractive power having a concave surface on the image side;

a third lens with positive refractive power as a meniscus lens having a concave surface on the image side;

a fourth lens with refractive power having a convex surface on the object side;

a fifth lens that is a double-sided aspheric lens having a convex surface on the image side; and

a sixth lens that is a double-sided aspheric lens with negative refractive power having a concave surface on the object side,

wherein conditional expressions (1) and (2) below are satisfied:

0.18<AG16/Σ d< 0.3  (1)

20< vd 3− vd 4<40  (2)

where

AG16: sum of air gaps on an optical axis from the first lens to the sixth lens

Σd: distance on the optical axis from the object-side surface of the first lens to the image-side surface of the sixth lens

vd3: Abbe number of the third lens at d-ray

vd4: Abbe number of the fourth lens at d-ray.

2. The imaging lens according to claim 1 ,

wherein an aperture stop is located on the object side of the first lens.

3. The imaging lens according to claim 1 , comprising:

a lens group with positive composite refractive power including the first lens, the second lens, and the third lens; and

a lens group with negative composite refractive power including the fourth lens, the fifth lens, and the sixth lens.

4. The imaging lens according to claim 1 ,

wherein the object-side surface of the fifth lens has a pole point off an optical axis.

5. The imaging lens according to claim 4 ,

wherein a conditional expression (3) below is satisfied:

0.2< Ph 51/ih<0.9  (3)

where

Ph51: vertical height of the pole point on the object-side surface of the fifth lens from the optical axis

ih: maximum image height.

6. The imaging lens according to claim 1 ,

wherein a conditional expression (4) below is satisfied:

( f 5+| f 6|)/ f< 1.3  (4)

where

f: focal length of an overall optical system of the imaging lens

f5: focal length of the fifth lens

f6: focal length of the sixth lens.

7. The imaging lens according to claim 1 ,

wherein a conditional expression (5) below is satisfied:

0.5< f 1/ f< 1.5  (5)

where

f: focal length of an overall optical system of the imaging lens

fl: focal length of the first lens.

8. The imaging lens according to claim 1 ,

wherein a conditional expression (6) below is satisfied:

1.5<( r 3+ r 4)/( r 3− r 4)<4.5  (6)

where

r3: curvature radius of the object-side surface of the second lens

r4: curvature radius of the image-side surface of the second lens.

9. The imaging lens according to claim 1 ,

wherein the fourth lens has negative refractive power.

10. The imaging lens according to claim 9 ,

wherein the second lens, and the fourth lens have negative refractive power and the second lens, the fourth lens and the sixth lens satisfy a conditional expression (7) below:

P 4< P 2< P 6  (7)

where

P2: refractive power of the second lens

P4: refractive power of the fourth lens

P6: refractive power of the sixth lens.

11. The imaging lens according to claim 10 ,

wherein the fifth lens has positive refractive power and the first lens, the third lens and the fifth lens satisfy a conditional expression (8) below:

P 3< P 1< P 5  (8)

where

P1: refractive power of the first lens

P3: refractive power of the third lens

P5: refractive power of the fifth lens.

12. The imaging lens according to claim 1 ,

wherein the image-side surface of the sixth lens has a pole point off an optical axis.

13. The imaging lens according to claim 1 ,

wherein a conditional expression (9) below is satisfied:

20< vd 1− vd 2<40  (9)

where

vd1: Abbe number of the first lens at d-ray

vd2: Abbe number of the second lens at d-ray.

14. The imaging lens according to claim 13 ,

wherein conditional expressions (10) and (11) below are satisfied:

50< vd 5<70  (10)

50< vd 6<70  (11)

where

vd5: Abbe number of the fifth lens at d-ray

vd6: Abbe number of the sixth lens at d-ray.

15. The imaging lens according to claim 1 ,

wherein a conditional expression (12) below is satisfied:

0.75< D 5/ D 6<1.50  (12)

where

D 5 : thickness of the fifth lens on an optical axis

D 6 : thickness of the sixth lens on the optical axis.

16. The imaging lens according to claim 15 ,

wherein a conditional expression (13) below is satisfied:

0.35<( T 5/ f )×100<3.00  (13)

where

T5: distance on the optical axis from the image-side surface of the fifth lens to the object-side surface of the sixth lens

f: focal length of an overall optical system of the imaging lens.

17. The imaging lens according to claim 1 ,

wherein a conditional expression (14) below is satisfied:

0.6<| r 7|/ f< 17.0  (14)

where

f: focal length of an overall optical system of the imaging lens

r7: curvature radius of the object-side surface of the fourth lens.

18. The imaging lens according to claim 1 ,

wherein a conditional expression (15) below is satisfied:

0.45< E 5/ D 5<1.20  (15)

where

E5: edge thickness of the fifth lens in a maximum effective diameter

D 5 : thickness of the fifth lens on an optical axis.

19. The imaging lens according to claim 1 ,

wherein a conditional expression (16) below is satisfied:

0.6< f 12/ f< 2.0  (16)

where

f: focal length of an overall optical system of the imaging lens

f12: composite focal length of the first lens and the second lens.

20. The imaging lens according to claim 1 ,

wherein a conditional expression (17) below is satisfied:

0.80<ih/ f <1.0  (17)

where

f: focal length of an overall optical system of the imaging lens

ih: maximum image height.

21. The imaging lens according to claim 1 ,

wherein a conditional expression (18) below is satisfied:

TTL/2ih<1.0  (18)

where

TTL: total track length ih: maximum image height.