Imaging lens and imaging apparatus equipped with the imaging lens
View Patent ↗An imaging lens is essentially constituted by five lenses, including: a first lens having a positive refractive power and a convex surface toward the object side; a second lens of a biconcave shape; a third lens having a positive refractive power and is of a meniscus shape with a concave surface toward the object side; a fourth lens having a negative refractive power and a concave surface toward the object side; and a fifth lens having a negative refractive power and a concave surface toward the image side, provided in this order from the object side. The imaging lens satisfies predetermined conditional formulae.
1. An imaging lens consisting essentially of five lenses, including:
a first lens having a positive refractive power and a convex surface toward the object side;
a second lens of a biconcave shape;
a third lens having a positive refractive power and is of a meniscus shape with a concave surface toward the object side;
a fourth lens having a negative refractive power and a concave surface toward the object side; and
a fifth lens having a negative refractive power and a concave surface toward the image side, provided in this order from the object side;
the imaging lens satisfying the following conditional formulae:
−1.2 <f/f 4<−0.2 (1)
−1.18 <f/f 5<−0.35 (2)
1.5 <f·P 34<5 (3)
wherein f is the focal length of the entire system, f 4 is the focal length of the fourth lens, and f 5 is the focal length of the fifth lens, and
P 34 is the refractive power of an air lens formed between the surface of the third lens toward the image side and the surface of the fourth lens toward the object side, the refractive power of the air lens being obtained by Formula (P1) below:
P
34
=
1
-
Nd
3
L
3
r
+
Nd
4
-
1
L
4
f
-
(
1
-
Nd
3
)
×
(
Nd
4
-
1
)
×
D
7
L
3
r
×
L
4
f
(
P
1
)
wherein Nd 3 is the refractive index of the third lens with respect to the d line, Nd 4 is the refractive index of the fourth lens with respect to the d line, L 3 r is the paraxial radius of curvature of the surface of the third lens toward the image side, L 4 f is the paraxial radius of curvature of the surface of the fourth lens toward the object side, and D 7 is an air space distance between the third lens and the fourth lens along the optical axis.
2. The imaging lens as defined in claim 1 , wherein:
the fifth lens is of a biconcave shape.
3. The imaging lens as defined claim 1 , wherein:
the first lens is of a biconvex shape.
4. The imaging lens as defined in claim 1 that further satisfies the following conditional formula:
−2 <f·P 45<1.1 (4)
wherein P 45 is the refractive power of an air lens formed between the surface of the fourth lens toward the image side and the surface of the fifth lens toward the object side, the refractive power of the air lens being obtained by Formula (P2) below:
P
45
=
1
-
Nd
4
L
4
r
+
Nd
5
-
1
L
5
f
-
(
1
-
Nd
4
)
×
(
Nd
5
-
1
)
×
D
9
L
4
r
×
L
5
f
(
P
2
)
wherein Nd 4 is the refractive index of the fourth lens with respect to the d line, Nd 5 is the refractive index of the fifth lens with respect to the d line, L 4 r is the paraxial radius of curvature of the surface of the fourth lens toward the image side, L 5 f is the paraxial radius of curvature of the surface of the fifth lens toward the object side, and D 9 is an air space distance between the fourth lens and the fifth lens along the optical axis.
5. The imaging lens as defined in claim 1 that further satisfies the following conditional formula:
0.08<( L 2 r+L 2 f )/( L 2 r−L 2 f )<1 (5)
wherein L 2 r is the paraxial radius of curvature of the surface of the second lens toward the image side, and L 2 f is the paraxial radius of curvature of the surface of the second lens toward the object side.
6. The imaging lens as defined in claim 1 that further satisfies the following conditional formula:
0 <f ·tan ω/ L 5 r< 0.7 (6)
wherein L 5 r is the paraxial radius of curvature of the surface of the fifth lens toward the object side, and ω is the half value of a maximum angle of view when focused on an object at infinity.
7. The imaging lens as defined in claim 1 that further satisfies the following conditional formula:
1 <f/f 1<3 (7)
wherein f 1 is the focal length of the first lens.
8. The imaging lens as defined in claim 1 that further satisfies the following conditional formula:
−1 <f/f 4<−0.25 (1-1).
9. The imaging lens as defined in claim 1 that further satisfies the following conditional formula:
−1.17 <f/f 5<−0.44 (2-1).
10. The imaging lens as defined in claim 1 that further satisfies the following conditional formula:
1.6 <f·P 34<4 (3-1)
wherein P 34 is the refractive power of an air lens formed between the surface of the third lens toward the image side and the surface of the fourth lens toward the object side, the refractive power of the air lens being obtained by Formula (P1) below:
P
34
=
1
-
Nd
3
L
3
r
+
Nd
4
-
1
L
4
f
-
(
1
-
Nd
3
)
×
(
Nd
4
-
1
)
×
D
7
L
3
r
×
L
4
f
(
P
1
)
wherein Nd 3 is the refractive index of the third lens with respect to the d line, Nd 4 is the refractive index of the fourth lens with respect to the d line, L 3 r is the paraxial radius of curvature of the surface of the third lens toward the image side, L 4 f is the paraxial radius of curvature of the surface of the fourth lens toward the object side, and D 7 is an air space distance between the third lens and the fourth lens along the optical axis.
11. The imaging lens as defined in claim 1 that further satisfies the following conditional formula:
−1.5 <f·P 45<0 (4-1)
wherein P 45 is the refractive power of an air lens formed between the surface of the fourth lens toward the image side and the surface of the fifth lens toward the object side, the refractive power of the air lens being obtained by Formula (P2) below:
P
45
=
1
-
Nd
4
L
4
r
+
Nd
5
-
1
L
5
f
-
(
1
-
Nd
4
)
×
(
Nd
5
-
1
)
×
D
9
L
4
r
×
L
5
f
(
P
2
)
wherein Nd 4 is the refractive index of the fourth lens with respect to the d line, Nd 5 is the refractive index of the fifth lens with respect to the d line, L 4 r is the paraxial radius of curvature of the surface of the fourth lens toward the image side, L 5 f is the paraxial radius of curvature of the surface of the fifth lens toward the object side, and D 9 is an air space distance between the fourth lens and the fifth lens along the optical axis.
12. The imaging lens as defined in claim 1 that further satisfies the following conditional formula:
0.09<( L 2 r+L 2 f )/( L 2 r−L 2 f )<0.99 (5-1)
wherein L 2 r is the paraxial radius of curvature of the surface of the second lens toward the image side, and L 2 f is the paraxial radius of curvature of the surface of the second lens toward the object side.
13. The imaging lens as defined in claim 1 that further satisfies the following conditional formula:
−0.85 <f/f 4<−0.3 (1-2).
14. The imaging lens as defined in claim 1 that further satisfies the following conditional formula:
2.4 <f·P 34<3 (3-2)
wherein P 34 is the refractive power of an air lens formed between the surface of the third lens toward the image side and the surface of the fourth lens toward the object side, the refractive power of the air lens being obtained by Formula (P1) below:
P
34
=
1
-
Nd
3
L
3
r
+
Nd
4
-
1
L
4
f
-
(
1
-
Nd
3
)
×
(
Nd
4
-
1
)
×
D
7
L
3
r
×
L
4
f
(
P
1
)
wherein Nd 3 is the refractive index of the third lens with respect to the d line, Nd 4 is the refractive index of the fourth lens with respect to the d line, L 3 r is the paraxial radius of curvature of the surface of the third lens toward the image side, L 4 f is the paraxial radius of curvature of the surface of the fourth lens toward the object side, and D 7 is an air space distance between the third lens and the fourth lens along the optical axis.
15. The imaging lens as defined in claim 1 that further satisfies the following conditional formula:
−1.2 <f·P 45<−0.5 (4-2)
wherein P 45 is the refractive power of an air lens formed between the surface of the fourth lens toward the image side and the surface of the fifth lens toward the object side, the refractive power of the air lens being obtained by Formula (P2) below:
P
45
=
1
-
Nd
4
L
4
r
+
Nd
5
-
1
L
5
f
-
(
1
-
Nd
4
)
×
(
Nd
5
-
1
)
×
D
9
L
4
r
×
L
5
f
(
P
2
)
wherein Nd 4 is the refractive index of the fourth lens with respect to the d line, Nd 5 is the refractive index of the fifth lens with respect to the d line, L 4 r is the paraxial radius of curvature of the surface of the fourth lens toward the image side, L 5 f is the paraxial radius of curvature of the surface of the fifth lens toward the object side, and D 9 is an air space distance between the fourth lens and the fifth lens along the optical axis.
16. The imaging lens as defined in claim 1 that further satisfies the following conditional formula:
0.1<( L 2 r+L 2 f )/( L 2 r−L 2 f )<0.985 (5-2)
wherein L 2 r is the paraxial radius of curvature of the surface of the second lens toward the image side, and L 2 f is the paraxial radius of curvature of the surface of the second lens toward the object side.
17. An imaging apparatus equipped with an imaging lens as defined in Claim 1 .
18. An imaging lens consisting essentially of five lenses, including:
a first lens having a positive refractive power and a convex surface toward the object side;
a second lens of a biconcave shape;
a third lens having a positive refractive power and is of a meniscus shape with a concave surface toward the object side;
a fourth lens having a negative refractive power and a concave surface toward the object side; and
a fifth lens having a negative refractive power and a concave surface toward the image side, provided in this order from the object side;
the imaging lens satisfying the following conditional formulae:
−1.2 <f/f 4<−0.2 (1)
−1.18 <f/f 5<−0.35 (2)
wherein f is the focal length of the entire system, f 4 is the focal length of the fourth lens, and f 5 is the focal length of the fifth lens, and
the fourth lens is of a biconcave shape.
19. An imaging lens consisting essentially of five lenses, including:
a first lens having a positive refractive power and a convex surface toward the object side;
a second lens of a biconcave shape;
a third lens having a positive refractive power and is of a meniscus shape with a concave surface toward the object side;
a fourth lens having a negative refractive power and a concave surface toward the object side; and
a fifth lens having a negative refractive power and a concave surface toward the image side, provided in this order from the object side;
the imaging lens satisfying the following conditional formulae:
−1.2 <f/f 4<−0.2 (1)
−1.18 <f/f 5<−0.35 (2)
wherein f is the focal length of the entire system, f 4 is the focal length of the fourth lens, and f 5 is the focal length of the fifth lens, and that further satisfies the following conditional formula:
−1.1 <f/f 5<−0.7 (2-2).