Imaging lens and imaging apparatus equipped with the imaging lens
View Patent ↗An imaging lens is provided and includes: in order from the object side, a first lens group including a biconcave lens; a second lens including two lenses whose convex surfaces are arranged opposite to each other and having a positive refractive power as a whole; a third lens group including a biconcave lens; and a fourth lens group including two lenses whose convex surfaces are arranged opposite to each other and having positive refractive power, as a whole, the imaging lens satisfying the specific condition.
1. An imaging lens comprising: in order from an object side of the imaging lens, a first lens group including a biconcave lens;
a second lens group including two lenses whose convex surfaces are arranged opposite to each other, the second lens group having a positive refractive power as a whole;
a third lens group including a biconcave lens; and
a fourth lens group including two lenses whose convex surfaces are arranged opposite to each other, the fourth lens group having positive refractive power, as a whole,
the imaging lens satisfying conditional expressions (1) and (2):
0.20 <BF/L< 0.44 (1)
N 4 >1.8 (2)
wherein BF represents a back focal length BF of the imaging lens, L represents a length L in a optical axial direction from a surface of the imaging lens nearest to an object to a surface of the imaging lens nearest to an image, and N 4 represents a refractive index of the third lens group at the d-line,
wherein each of the convex surfaces of the fourth lens group has a radius of curvature whose absolute value is smaller than that of the other surface of each lens.
2. The imaging lens according to claim 1 , further satisfying conditional expression (3):
0.97 <|f 1 |/f< 1.92 (3)
wherein f 1 represents a focal length of the first lens group, and f represents a focal length of the imaging lens.
3. The imaging lens according to claim 2 , further satisfying conditional expression (4):
0.65 <|f 2 |/f< 1.30 (4)
wherein f 2 represents a focal length of the second group, and f represents a focal length of the imaging lens.
4. The imaging lens according to claim 3 , further satisfying conditional expression (5):
0.49 <|f 3 |/f< 1.03 (5)
wherein f 3 represents a focal length of the third lens group, and f represents a focal length of the imaging lens.
5. The imaging lens according to claim 4 , further satisfying conditional expression (6):
ν 4 <30 (6)
wherein ν 4 represents an Abbe number of the biconcave lens of the third lens group at the d-line.
6. The imaging lens according to claim 5 , wherein each of the convex surfaces of the second lens group, which are arranged opposite to each other, has a radius of curvature whose absolute value is smaller than that of the other surface of each lens.
7. An imaging apparatus comprising:
an imaging lens according to claim 6 ; and
an imaging device that converts an optical image formed by the imaging lens into an electric signal.
8. The imaging lens according to claim 1 , further satisfying conditional expression (4):
0.65 <|f 2 |/f< 1.30 (4)
wherein f 2 represents a focal length of the second group, and f represents a focal length of the imaging lens.
9. The imaging lens according to claim 8 , further satisfying conditional expression (5):
0.49< |f 3 |/f< 1.03 (5)
wherein f 3 represents a focal length of the third lens group, and f represents a focal length of the imaging lens.
10. The imaging lens according to claim 9 , further satisfying conditional expression (6):
ν 4 <30 (6)
wherein ν 4 represents an Abbe number of the biconcave lens of the third lens group at the d-line.
11. The imaging lens according to claim 1 , further satisfying conditional expression (5):
0.49 <|f 3 |/f< 1.03 (5)
wherein f 3 represents a focal length of the third lens group, and f represents a focal length of the imaging lens.
12. The imaging lens according to claim 11 , further satisfying conditional expression (6):
ν 4 <30 (6)
wherein ν 4 represents an Abbe number of the biconcave lens of the third lens group at the d-line.
13. The imaging lens according to claim 1 , further satisfying conditional expression (6):
ν 4 <30 (6)
wherein ν 4 represents an Abbe number of the biconcave lens of the third lens group at the d-line.
14. An imaging apparatus comprising:
an imaging lens according to claim 1 ; and
an imaging device that converts an optical image formed by the imaging lens into an electric signal.
15. The imaging lens according to claim 1 , wherein an aperture diaphragm is located in back of the second lens group.