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:

D 4/ f< 0.39  (4)

1.8< f 345/ f   (6)

f 1/ f 2<−0.42  (7)

where,

f is the focal length of the entire system,

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

f345 is the combined focal length of the third lens, the fourth lens, and the fifth lens,

f1 is the focal length of the first lens, and

f2 is the focal length of the second lens.

2. 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:

1.8< f 345/ f   (6)

−2.2<( R 14+ R 15)/( R 14− R 15)<−0.01  (8)

where,

f is the focal length of the entire system,

f345 is the combined focal length of the third lens, the fourth lens, and the fifth lens,

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.

3. 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)

1.8< f 345/ f   (6)

−0.8<( R 5+ R 6)/( R 5− R 6)  (9)

where,

f is the focal length of the entire system,

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

f345 is the combined focal length of the third lens, the fourth lens, and the fifth lens,

R5 is the radius of curvature of the object-side surface of the third lens, and

R6 is the radius of curvature of the image-side surface of the third lens.

4. 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.

5. 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.

6. 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.

7. 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.

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

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

10. 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.

11. 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.

12. 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.

13. 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.

14. 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.

15. 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.

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