Imaging lens and imaging apparatus equipped with the imaging lens
View Patent ↗An imaging lens is constituted essentially by six lenses, including: a first lens of a biconvex shape; a second lens having a negative refractive power and is of a meniscus shape with a concave surface toward the image side; a third lens of a meniscus shape with a convex surface toward the object side; a fourth lens of a meniscus shape with a concave surface toward the object side; a fifth lens having a positive refractive power; and a sixth lens having a negative refractive power and a concave surface toward the image side, provided in this order from the object side.
1. An imaging lens consisting essentially of six lenses, including:
a first lens of a biconvex shape;
a second lens having a negative refractive power and is of a meniscus shape with a concave surface toward the image side;
a third lens of a meniscus shape with a convex surface toward the object side;
a fourth lens of a meniscus shape with a concave surface toward the object side;
a fifth lens having a positive refractive power; and
a sixth lens having a negative refractive power and a concave surface toward the image side, provided in this order from the object side.
2. An imaging lens consisting essentially 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 and is of a meniscus shape with a concave surface toward the image side;
a third lens of a meniscus shape with a convex surface toward the object side;
a fourth lens;
a fifth lens having a positive refractive power; and
a sixth 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 conditional formulae below:
f/f 56<0 (1)
0.7< DDL/f< 0.98 (2)
wherein f56 is the combined focal length of the fifth lens and the sixth lens, f is the focal length of the entire system, and DDL is the distance from the surface of the first lens toward the object side and the surface of the sixth lens toward the image side along the optical axis.
3. An imaging lens consisting essentially 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 and a concave surface toward the image side;
a third lens of a meniscus shape with a convex surface toward the object side;
a fourth lens having a positive refractive power;
a fifth lens having a positive refractive power; and
a sixth 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 conditional formulae below:
f/f 56<0 (1)
0.7< DDL/f< 0.98 (2)
wherein f56 is the combined focal length of the fifth lens and the sixth lens, f is the focal length of the entire system, and DDL is the distance from the surface of the first lens toward the object side and the surface of the sixth lens toward the image side along the optical axis.
4. An imaging lens as defined in claim 1 that further satisfies the conditional formula below:
0< f·P 56<2 (3)
wherein f is the focal length of the entire system, and P56 is the refractive power of an air lens formed between the surface of the fifth lens toward the image side and the surface of the sixth lens toward the object side, the refractive power of the air lens being obtained by Formula (P1) below:
P
56
=
1
-
Nd
5
L
5
r
+
Nd
6
-
1
L
6
f
-
(
1
-
Nd
5
)
×
(
Nd
6
-
1
)
×
D
11
L
5
r
×
L
6
f
(
P1
)
wherein Nd5 is the refractive index of the fifth lens with respect to the d line, Nd6 is the refractive index of the sixth lens with respect to the d line, L5r is the paraxial radius of curvature of the surface of the fifth lens toward the image side, L6f is the paraxial radius of curvature of the surface of the sixth lens toward the object side, and D11 is an air space distance between the fifth lens and the sixth lens along the optical axis.
5. An imaging lens as defined in claim 1 that further satisfies the conditional formula below:
0< f·P 45<1.7 (4)
wherein f is the focal length of the entire system, and P45 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
(
P2
)
wherein Nd4 is the refractive index of the fourth lens with respect to the d line, Nd5 is the refractive index of the fifth lens with respect to the d line, L4r is the paraxial radius of curvature of the surface of the fourth lens toward the image side, L5f is the paraxial radius of curvature of the surface of the fifth lens toward the object side, and D9 is an air space distance between the fourth lens and the fifth lens along the optical axis.
6. An imaging lens as defined in claim 1 that further satisfies the conditional formula below:
0< f/f 5<1 (5)
wherein f is the focal length of the entire system, and f5 is the focal length of the fifth lens.
7. An imaging lens as defined in claim 1 that further satisfies the conditional formula below:
20<ν2<28 (6)
wherein ν2 is the Abbe's number of the second lens with respect to the d line.
8. An imaging lens as defined in claim 1 that further satisfies the conditional formula below:
20<ν5<28 (7)
wherein ν5 is the Abbe's number of the fifth lens with respect to the d line.
9. An imaging lens as defined in claim 1 that further satisfies the conditional formula below:
1< f/f 1<2 (8)
wherein f is the focal length of the entire system, and f1 is the focal length of the first lens.
10. An imaging lens as defined in claim 1 , further comprising:
an aperture stop positioned at the object side of the surface of the first lens toward the object side.
11. An imaging lens as defined in claim 1 further satisfies the conditional formula below:
0.5< f ·tan ω/ L 6 r< 20 (9)
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.
12. An imaging lens as defined in claim 2 that further satisfies the conditional formula below:
−4< f/f 56<−0.1 (1-1)
wherein f56 is the combined focal length of the fifth lens and the sixth lens, and f is the focal length of the entire system.
13. An imaging lens as defined in claim 2 that further satisfies the conditional formula below:
0.8< DDL/f< 0.96 (2-1)
wherein f is the focal length of the entire system, and DDL is the distance from the surface of the first lens toward the object side to the surface of the sixth lens toward the image side along the optical axis.
14. An imaging lens as defined in claim 4 that further satisfies the conditional formula below:
0.1< f·P 56<1.27 (3-1)
wherein f is the focal length of the entire system, and P56 is the refractive power of an air lens formed between the surface of the fifth lens toward the image side and the surface of the sixth lens toward the object side, the refractive power of the air lens being obtained by Formula (P1) below:
P
56
=
1
-
Nd
5
L
5
r
+
Nd
6
-
1
L
6
f
-
(
1
-
Nd
5
)
×
(
Nd
6
-
1
)
×
D
11
L
5
r
×
L
6
f
(
P1
)
wherein Nd5 is the refractive index of the fifth lens with respect to the d line, Nd6 is the refractive index of the sixth lens with respect to the d line, L5r is the paraxial radius of curvature of the surface of the fifth lens toward the image side, L6f is the paraxial radius of curvature of the surface of the sixth lens toward the object side, and D11 is an air space distance between the fifth lens and the sixth lens along the optical axis.
15. An imaging lens as defined in claim 5 that further satisfies the conditional formula below:
0.32< f·P 45<1.65 (4-1)
wherein f is the focal length of the entire system, and P45 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
(
P2
)
wherein Nd4 is the refractive index of the fourth lens with respect to the d line, Nd5 is the refractive index of the fifth lens with respect to the d line, L4r is the paraxial radius of curvature of the surface of the fourth lens toward the image side, L5f is the paraxial radius of curvature of the surface of the fifth lens toward the object side, and D9 is an air space distance between the fourth lens and the fifth lens along the optical axis.
16. An imaging lens as defined in claim 6 that further satisfies the conditional formula below:
0.01< f/f 5<0.98 (5-1)
wherein f is the focal length of the entire system, and f5 is the focal length of the fifth lens.
17. An imaging lens as defined in claim 7 that further satisfies the conditional formula below:
21<ν2<25 (6-1)
wherein ν2 is the Abbe's number of the second lens with respect to the d line.
18. An imaging lens as defined in claim 8 that further satisfies the conditional formula below:
21<ν5<25 (7-1)
wherein ν5 is the Abbe's number of the fifth lens with respect to the d line.
19. An imaging lens as defined in claim 1 , wherein:
the surface of the third lens toward the image side is of an aspherical shape having at least one inflection point at a position in an inwardly radial direction from the intersection of a principal light ray at a maximum angle of view and the surface of the third lens toward the image side to the optical axis.
20. An imaging apparatus equipped with an imaging lens as defined in claim 1 .