Imaging lens, imaging device, and mobile terminal
Provided is an imaging lens, including, in order from an object side: a positive first lens; a second lens having a concave shape toward the object side; and (i−2) number of lens, wherein the i-th lens, which is the most image-side lens, includes: an i-th lens flat plate; and a positive or negative lens element on at least one of the opposite surfaces of the i-th lens flat plate, wherein the following conditional relationship is satisfied: 0.9>Y max /Y>0.61, where: Y max is a height of the most off-axial ray on an image-side surface of the (i−1)th lens; and Y is a maximum image height.
1. An imaging lens, comprising, in order from an object side:
a first lens having a positive refractive power;
a second lens having a concave shape toward the object side; and
(i−2) number of lens, where i is equal to or greater than 3, wherein an i-th lens, which is counted from the object side, includes:
an i-th lens flat plate; and
a lens element which is provided on at least one of an object-side surface and an image-side surface of the i-th lens flat plate, has a refractive index different than the i-th lens flat plate, and has a positive refracting power or a negative refracting power,
wherein the following conditional relationship is satisfied:
0.9 >Y max /Y >0.61 (1)
where:
Y max is a distance from an optical axis to a point, which is on an image-side surface of an (i−1)th lens, which is counted from the object side, and at which a principal ray of the most outer light beam passes through; and
Y is a maximum image height depending on the imaging lens and a size of an imaging device.
2. The imaging lens of claim 1 , wherein an (i−1)th lens, which is counted from the object side, includes:
a lens flat plate; and
a lens element on an image side surface of the (i−1)th lens has a convex shape toward the image side at the point where the principle ray of the maximum image height passes through.
3. The imaging lens of claim 1 , wherein the following conditional relationship is satisfied:
0.6
≤
f
s
1
f
≤
1.3
(
2
)
where:
f s1 is a focal length of an object-side surface of the first lens; and
f is a focal length of the imaging lens.
4. The imaging lens of claim 1 , wherein the i-th lens includes:
an ib-th lens element formed on an image-side surface of the i-th lens flat plate, wherein the following relationship is satisfied:
X
-
X
0
Y
<
0.16
(
3
)
where:
X is an aspherical deviation given by the following Equation (a);
X 0 is an aspherical deviation of a rotational quadric surface given by the following Equation (b); and
Y is a maximum image height in the imaging lens,
X
=
h
2
/
R
ib
1
+
1
-
(
1
+
K
ib
)
h
2
/
R
ib
2
+
∑
A
m
h
m
Equation
(
a
)
X
0
=
h
2
/
R
ib
1
+
1
-
(
1
+
K
ib
)
h
2
/
R
ib
2
Equation
(
b
)
where:
A im is an m-order aspherical coefficient of an image-side surface of the ib-th lens element;
R ib is a radius of curvature of the image-side surface of the ib-th lens element;
K ib is a conical coefficient of the image-side surface of the ib-th lens element; and
h is a distance between the optical axis and a point, on the image-side surface of the ib-th lens element, and at which the principal ray of the maximum image height passes through.
5. The imaging lens of claim 1 , wherein the first lens is a cemented lens configured of a first lens piece having a positive refracting power and a second lens piece having a negative refracting power, and the following relationship is satisfied:
5<|ν2−ν1|<70 (4)
where:
ν 1 is an Abbe's number of the first lens piece; and
ν 2 is an Abbe's number of the second lens piece.
6. The imaging lens of claim 1 , wherein the first lens includes:
a first lens flat plane;
a 1f-th lens element formed on an object-side surface of the first lens flat plate and having a positive refracting power; and
a 1b-th lens element formed on an image-side surface of the first lens flat plate and having a negative refracting power,
wherein the following relationship is satisfied:
5<|ν 2 −ν 1 |<70 (4′)
where:
ν 1 is an Abbe's number of the lens element, of the first lens, having a positive refracting power; and
ν 2 is an Abbe's number of the lens element, of the first lens, having a negative refracting power.
7. The imaging lens of claim 1 , wherein the second lens is a meniscus lens which has a convex surface toward the image side.
8. The imaging lens of claim 1 , wherein the second lens includes:
a second lens flat plane;
a 2f-th lens element which is formed on an object-side surface of the second lens flat plane and has a negative refracting power; and
a 2b-th lens element which is formed on an image-side surface of the second lens flat plane and has a positive refracting power.
9. The imaging lens of claim 1 , wherein an object-side surface of the if-th lens element is aspheric surface having a concave shape toward the object side in the vicinity of the optical axis.
10. The imaging lens of claim 1 , wherein at least one of the lenses and lens elements is made of resin material.
11. The imaging lens of claim 1 , wherein each of the first lens to the (i−1)th lens has a lens flat plate and a lens element, and each lens element and each lens flat plate have a different refractive index in each of the first lens to the (i−1)th lens.
12. The imaging lens of claim 1 , wherein the lens element included in the i-th lens is made of UV hardening resin material, and the following relationship is satisfied:
5<|ν 1 −ν 2 |<40 Equation (5)
where:
ν 1 is an Abbe's number of an object-side surface of the first lens; and
ν 2 is an Abbe's number of an object-side of the first lens.
13. The imaging lens of claim 1 , wherein i=3.
14. The imaging lens of claim 1 , wherein the i-th lens flat plate includes an optical functional thin film on the surface thereof.
15. The imaging lens of claim 1 , wherein an optical surface, of each of the lenses, contacting with air is aspherical.
16. An imaging device, comprising:
the imaging lens of claim 1 ; and
a solid-state image sensor.
17. A mobile terminal, comprising:
the imaging device of claim 16 .