Imaging lens and imaging apparatus

1. An imaging lens consisting of, in order from the object side, a first lens having a negative power, a second lens having a positive power, a third lens having a positive power, a fourth lens having a negative power, a fifth lens having a positive power, a sixth lens having a positive power, and a seventh lens having a negative power, wherein

the following conditional formulae are satisfied:

ν d 7<55  (2)

1.25< f 5/ f   (10)

where,

νd7 is the Abbe's number of the material of the seventh lens with respect to the d line,

f is the focal length of the entire system, and

f5 is the focal length of the fifth lens.

2. The imaging lens as defined in claim 1 , wherein the following conditional formula is further satisfied:

40<ν d 3  (3)

where,

νd3 is the Abbe's number of the material for the third lens with respect to the d line.

3. The imaging lens as defined in claim 1 , wherein the following conditional formula is further satisfied:

25<ν d 5  (13)

where,

νd5 is the Abbe's number of the material for the fifth lens with respect to the d line.

4. The imaging lens as defined in claim 1 , wherein the following conditional formula is further satisfied:

0.5< f 3/ f< 10  (14)

where,

f3 is the focal length of the third lens, and

f is the focal length of the entire system.

5. The imaging lens as defined in claim 1 , wherein the following conditional formula is further satisfied:

0.5< f 2/ f< 7  (15)

where,

f2 is the focal length of the second lens, and

f is the focal length of the entire system.

6. The imaging lens as defined in claim 1 , wherein the following conditional formula is satisfied:

f 1/ f<− 0.25  (16)

where,

f1 is the focal length of the first lens, and

f is the focal length of the entire system.

7. The imaging lens as defined in claim 1 , wherein the following conditional formula is satisfied:

0.3< f 123/ f< 15  (17)

where,

f123 is the combined focal length of the first lens, the second lens, and the third lens, and

f is the focal length of the entire system.

8. The imaging lens as defined in claim 1 , wherein the following conditional formula is further satisfied:

0.5< f 234/ f< 18  (18)

where,

f234 is the combined focal length of the second lens, the third lens, and the fourth lens, and

f is the focal length of the entire system.

9. The imaging lens as defined in claim 1 , wherein the following conditional formula is further satisfied:

0.5< f 12345/ f< 10  (19)

where,

f12345 is the combined focal length of the first lens, the second lens, the third lens, the fourth lens, and the fifth lens, and

f is the focal length of the entire system.

10. The imaging lens as defined in claim 1 , wherein the following conditional formula is further satisfied:

−5.0<( R 14+ R 15)/( R 14− R 15)<−0.01  (8)

where,

R14 is the radius of curvature of the object-side surface of the seventh lens, and

R15 is the radius of curvature of the image-side surface of the seventh lens.

11. The imaging lens as defined in claim 1 , wherein the following conditional formula is further satisfied:

0.4< f 2345/ f< 10  (20)

where,

f2345 is the combined focal length of the second lens, the third lens, the fourth lens, and the fifth lens, and

f is the focal length of the entire system.

12. The imaging lens as defined in claim 1 , wherein the following conditional formula is further satisfied:

0.1< f 3456/ f< 5.0  (21)

where,

f3456 is the combined focal length of the third lens, the fourth lens, the fifth lens, and the sixth lens, and

f is the focal length of the entire system.

13. The imaging lens as defined in claim 1 , wherein the following conditional formula is further satisfied:

−4.0<( R 8+ R 9)/( R 8− R 9)<4.0  (22)

where,

R8 is the radius of curvature of the object-side surface of the fourth lens, and

R9 is the radius of curvature of the image-side surface of the fourth lens.

14. The imaging lens as defined in claim 1 , wherein the following conditional formula is further satisfied:

−3< f/f 45<3  (23)

where,

f45 is the combined focal length of the fourth lens and the fifth lens, and

f is the focal length of the entire system.

15. An imaging apparatus equipped with the imaging lens as defined in claim 1 .

16. An imaging lens consisting of, in order from the object side, a first lens having a negative power, a second lens having a positive power, a third lens having a positive power, a fourth lens having a negative power, a fifth lens having a positive power, a sixth lens having a positive power, and a seventh lens having a negative power, wherein

the following conditional formulae are satisfied:

ν d 7<55  (2)

D 4/ f< 0.39  (4)

0.65<( R 10+ R 11)/( R 10− R 11)  (11-1)

where,

νd7 is the Abbe's number of the material of the seventh lens with respect to the d line,

f is the focal length of the entire system,

D4 is the air space between the second lens and the third lens,

R10 is the radius of curvature of the object-side surface of the fifth lens, and

R11 is the radius of curvature of the image-side surface of the fifth lens.

17. An imaging lens consisting of, in order from the object side, a first lens having a negative power, a second lens having a positive power, a third lens having a positive power, a fourth lens having a negative power, a fifth lens having a positive power, a sixth lens having a positive power, and a seventh lens having a negative power, wherein

the following conditional formulae are satisfied:

D 4/ f< 0.39  (4)

0.5<( R 10+ R 11)/( R 10− R 11)  (11)

( R 12+ R 13)/( R 12− R 13)<1.0  (12)

where,

f is the focal length of the entire system,

D4 is the air space between the second lens and the third lens,

R10 is the radius of curvature of the object-side surface of the fifth lens,

R11 is the radius of curvature of the image-side surface of the fifth lens,

R12 is the radius of curvature of the object-side surface of the sixth lens, and

R13 is the radius of curvature of the image-side surface of the sixth lens.