Imaging lens and imaging apparatus equipped with the imaging lens
View Patent ↗An imaging lens is substantially constituted by six lenses, including: a first lens having a positive refractive power and a convex surface toward the object side; a second lens having a negative refractive power; a third lens having a negative refractive power; a fourth lens having a positive refractive power; a fifth lens having a negative refractive power; and a sixth lens having a biconcave shape, provided in this order from the object side.
1. An imaging lens substantially consisting of six lenses, including:
a first lens having a positive refractive power and a convex surface toward the object side;
a second lens having a negative refractive power;
a third lens having a negative refractive power;
a fourth lens having a positive refractive power;
a fifth lens having a negative refractive power; and
a sixth lens having a biconcave shape, provided in this order from the object side.
2. An imaging lens as defined in claim 1 , wherein:
the fifth lens is of a meniscus shape having a concave surface toward the object side.
3. An imaging lens as defined in claim 1 , wherein:
the fourth lens has a convex surface toward the image side.
4. An imaging lens as defined in claim 1 , wherein:
the second lens has a concave surface toward the image side.
5. An imaging lens as defined in claim 1 that further satisfies the following conditional formula:
−10< f/f 6<−0.8 (1)
wherein f is the focal length of the entire system, and f6 is the focal length of the sixth lens.
6. An imaging lens as defined in claim 1 that further satisfies the following conditional formula:
−1.1< f·P 23<0 (2)
wherein f is the focal length of the entire system, P23 is the refractive power of an air lens formed between the surface of the second lens toward the image side and the surface of the third lens toward the object side, the refractive power of the air lens being obtained by Formula (P) below:
P
23
=
1
-
N
d
2
L
2
r
+
Nd
3
-
1
L
3
f
-
(
1
-
Nd
2
)
×
(
Nd
3
-
1
)
×
D
5
L
2
r
×
L
3
f
(
P
)
wherein Nd2 is the refractive index of the second lens with respect to the d line, Nd3 is the refractive index of the third lens with respect to the d line, L2r is the paraxial radius of curvature of the surface of the second lens toward the image side, L3f is the paraxial radius of curvature of the surface of the third lens toward the object side, and D5 is an air space distance between the second lens and the third lens along the optical axis.
7. An imaging lens as defined in claim 1 that further satisfies the following conditional formula:
−0.088< f/f 5<0 (3)
wherein f is the focal length of the entire system, and f5 is the focal length of the fifth lens.
8. An imaging lens as defined in claim 1 that further satisfies the following conditional formula:
0<( L 5 r−L 5 f )/( L 5 r+L 5 f )<0.073 (4)
wherein L5f is the paraxial radius of curvature of the surface of the fifth lens toward the object side, and L5r is the paraxial radius of curvature of the surface of the fifth lens toward the image side.
9. An imaging lens as defined in claim 1 that further satisfies the following conditional formula:
0.5< f ·tan ω/ L 6 r< 20 (5)
wherein f is the focal length of the entire system, ω is half the maximum angle of view when focused on an object at infinity, and L6r is the paraxial radius of curvature of the surface of the sixth lens toward the image side.
10. An imaging lens as defined in claim 1 that further satisfies the following conditional formula:
−5< f/f 6<−0.85 (1-1)
wherein f is the focal length of the entire system, and f6 is the focal length of the sixth lens.
11. An imaging lens as defined in claim 1 that further satisfies the following conditional formula:
−1.1< f·P 23<−0.2 (2-1)
wherein f is the focal length of the entire system, P23 is the refractive power of an air lens formed between the surface of the second lens toward the image side and the surface of the third lens toward the object side, the refractive power of the air lens being obtained by Formula (P) below:
P
23
=
1
-
N
d
2
L
2
r
+
Nd
3
-
1
L
3
f
-
(
1
-
Nd
2
)
×
(
Nd
3
-
1
)
×
D
5
L
2
r
×
L
3
f
(
P
)
wherein Nd2 is the refractive index of the second lens with respect to the d line, Nd3 is the refractive index of the third lens with respect to the d line, L2r is the paraxial radius of curvature of the surface of the second lens toward the image side, L3f is the paraxial radius of curvature of the surface of the third lens toward the object side, and D5 is an air space distance between the second lens and the third lens along the optical axis.
12. An imaging lens as defined in claim 1 that further satisfies the following conditional formula:
−0.088< f/f 5<−0.02 (3-1)
wherein f is the focal length of the entire system, and f5 is the focal length of the fifth lens.
13. An imaging lens as defined in claim 1 that further satisfies the following conditional formula:
0.02<( L 5 r−L 5 f )/( L 5 r+L 5 f )<0.068 (4-1)
wherein L5f is the paraxial radius of curvature of the surface of the fifth lens toward the object side, and L5r is the paraxial radius of curvature of the surface of the fifth lens toward the image side.
14. An imaging lens as defined in claim 1 that further satisfies the following conditional formula:
0.7< f ·tan ω/ L 6 r< 10 (5-1)
wherein f is the focal length of the entire system, ω is half the maximum angle of view when focused on an object at infinity, and L6r is the paraxial radius of curvature of the surface of the sixth lens toward the image side.
15. An imaging lens as defined in claim 1 that further satisfies the following conditional formula:
−3< f/f 6<−0.89 (1-2)
wherein f is the focal length of the entire system, and f6 is the focal length of the sixth lens.
16. An imaging lens as defined in claim 1 that further satisfies the following conditional formula:
−1.1< f·P 23<−0.4 (2-2)
wherein f is the focal length of the entire system, P23 is the refractive power of an air lens formed between the surface of the second lens toward the image side and the surface of the third lens toward the object side, the refractive power of the air lens being obtained by Formula (P) below:
P
23
=
1
-
N
d
2
L
2
r
+
Nd
3
-
1
L
3
f
-
(
1
-
Nd
2
)
×
(
Nd
3
-
1
)
×
D
5
L
2
r
×
L
3
f
(
P
)
wherein Nd2 is the refractive index of the second lens with respect to the d line, Nd3 is the refractive index of the third lens with respect to the d line, L2r is the paraxial radius of curvature of the surface of the second lens toward the image side, L3f is the paraxial radius of curvature of the surface of the third lens toward the object side, and D5 is an air space distance between the second lens and the third lens along the optical axis.
17. An imaging lens as defined in claim 1 that further satisfies the following conditional formula:
−0.085< f/f 5<−0.03 (3-2)
wherein f is the focal length of the entire system, and f5 is the focal length of the fifth lens.
18. An imaging lens as defined in claim 1 that further satisfies the following conditional formula:
0.03<( L 5 r−L 5 f )/( L 5 r+L 5 f )<0.063 (4-2)
wherein L5f is the paraxial radius of curvature of the surface of the fifth lens toward the object side, and L5r is the paraxial radius of curvature of the surface of the fifth lens toward the image side.
19. An imaging lens as defined in claim 1 that further satisfies the following conditional formula:
1< f ·tan ω/ L 6 r< 5 (5-2)
wherein f is the focal length of the entire system, ω is half the maximum angle of view when focused on an object at infinity, and L6r is the paraxial radius of curvature of the surface of the sixth lens toward the image side.
20. An imaging apparatus comprising an imaging lens as defined in claim 1 .