JP2005242286A - Imaging lens, imaging unit and portable terminal with the unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging lens that is smaller than the conventional lenses and the various aberrations of which are satisfactorily corrected. <P>SOLUTION: The imaging lens comprises, from the object side in order, a first lens L1 which has positive refracting power and whose convex face is in the direction of the object side, an opening diaphragm S, a second lens L2, in the form of a meniscus, which has a positive refracting power and whose convex face is in the direction of the image side, and a third lens L3 which has a negative refracting power and whose convex face is in the direction the image side. In the imaging lens, the following conditional formulae are satisfied: 0.8<f1/f<2.0 and 20<ä(v1+v2)/2}-v3<70, wherein f1 is the focal distance of the first lens, f is the focal distance of the entire system of the imaging lens, v1 is the Abbe's number of the first lens, v2 is the Abbe's number of the second lens and v3 is the Abbe's number of the third lens. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an imaging lens suitable as an optical system of a solid-state imaging device such as a CCD type image sensor or a CMOS type image sensor, an imaging unit having the imaging lens, and a portable terminal including the imaging unit.

In recent years, with the improvement in performance and size of solid-state imaging devices such as CCD (Charged Coupled Device) type image sensors or CMOS (Complementary Metal Oxide Semiconductor) type image sensors, mobile phones equipped with imaging devices Personal computers are becoming popular.
With the miniaturization of these mobile phones and personal computers or the increase in density due to the increase in functions, there is a demand for further miniaturization of the imaging lens mounted on the imaging device in order to reduce the size of these imaging devices. Is growing.

In recent years, as such an imaging lens for a small imaging device, it is possible to improve performance as compared with an imaging lens having one or two lenses, and in recent years, a first lens having positive refractive power in order from the object side. An imaging lens having a three-lens configuration in which a second lens having a negative refractive power and a third lens having a positive refractive power are arranged is becoming common. Such a so-called triplet type imaging lens is disclosed in Patent Document 1.
JP 2001-750006 A

However, the imaging lens of the type described in Patent Document 1 is a type in which various aberrations are favorably corrected while ensuring a wide angle of view, but on the other hand, the entire length of the imaging lens (the most object of the entire imaging lens system). This is not suitable for downsizing the distance from the side surface to the image side focal point (however, the distance between the aperture stop and the image side focal point in an imaging lens in which the aperture stop is disposed closest to the object side).
In view of such problems, an object of the present invention is to provide a three-lens imaging lens, an imaging unit, and a portable terminal that are more compact than the conventional type and have various aberrations corrected satisfactorily.

Here, although it is a scale of a small imaging lens, the present invention aims at miniaturization at a level that satisfies the following conditional expression (7). By satisfying this range, the overall lens length can be shortened and the lens outer diameter can be reduced synergistically. Thereby, the whole imaging device can be reduced in size and weight.
L / 2Y <1.50 (7)
However,
L: Distance on the optical axis from the object side surface of the first lens to the image-side focal point of the entire imaging lens system
2Y: Diagonal length of the imaging surface of the solid-state imaging device (diagonal length of the rectangular effective pixel area of the solid-state imaging device)
Here, the image side focal point means an image point when a parallel light beam parallel to the optical axis is incident on the lens. When a parallel plate such as an optical low-pass filter, an infrared cut filter, or a seal glass of a solid-state image sensor package is disposed between the image-side surface of the imaging lens and the image-side focal position, the imaging lens is parallel. The flat plate portion is calculated as the above L value after the air conversion distance.
More preferably, the range of the conditional expression (8) below is better.
L / 2Y <1.30 (8)

The invention according to claim 1 has, in order from the object side, a first lens having a positive refractive power, a convex surface facing the object side, an aperture stop, a positive refractive power, and a convex surface on the image side. An imaging lens composed of a second meniscus lens directed to the third lens having negative refractive power and a concave surface facing the image side, wherein the focal length of the first lens is f1, and the focal point of the entire imaging lens system When the distance is f, the Abbe number of the first lens is ν1, the Abbe number of the second lens is ν2, and the Abbe number of the third lens is ν3, the following conditional expressions (1) and (2) are satisfied. The structure is adopted.
0.8 <f1 / f <2.0 (1)
20 <{(ν1 + ν2) / 2} −ν3 <70 (2)

According to the first aspect of the present invention, a so-called telephoto type in which a positive lens group including a first lens and a second lens and a negative third lens with a concave surface facing the image side are arranged in this order from the object side. This lens configuration is advantageous in reducing the overall length of the lens and can correct aberrations satisfactorily.
That is, with respect to aberration correction, since the positive refractive power is shared by the first lens and the second lens, the occurrence of spherical aberration and coma can be suppressed. Further, since the aperture stop is disposed between the first lens and the second lens, the first lens has a shape with a convex surface facing the object side, and the second lens has a meniscus shape with the convex surface facing the image side. And distortion are easily corrected.

Here, the conditional expression (1) defines the refractive power of the first lens. By falling below the upper limit value in Expression (1), the positive refractive power of the first lens can be appropriately maintained, and the entire length of the imaging lens can be reduced. On the other hand, by exceeding the lower limit value, the positive refractive power of the first lens does not become unnecessarily large, and higher-order spherical aberration and coma aberration generated in the first lens can be suppressed to a small value. The value of f1 / f in conditional expression (1) is more preferably in the range of conditional expression (9) below.
0.8 <f1 / f <1.65 (9)
Conditional expression (2) is a condition for satisfactorily correcting chromatic aberration of the entire imaging lens system. By exceeding the lower limit in the expression (2), the longitudinal chromatic aberration and the lateral chromatic aberration can be corrected with a good balance. Further, the upper limit value of the expression (2) is set in consideration that there is no actual lens material that exceeds this value and is suitable as a lens material.
The value of conditional expression (2) is more preferably within the range of conditional expression (10) below.
25 <{(ν1 + ν2) / 2} −ν3 <70 (10)

  In addition, since the lens configuration as described above can ensure a large tolerance for the eccentricity of each lens, for example, in mass production, the optical axis of each lens is slightly smaller than the same straight line on an imaging unit or the like. Even when they are incorporated with a small amount of deviation, there is an effect that image quality is hardly deteriorated and lens performance can be properly maintained.

The invention described in claim 2 has the same configuration as that of the invention described in claim 1, and satisfies the following conditional expression (3) when the focal length of the third lens is f3. Adopted.
-1.5 <f3 / f <-0.5 (3)

  According to the second aspect of the present invention, the conditional expression (3) defines the refractive power of the third lens. Beyond the lower limit in equation (3), the negative refracting power of the third lens can be maintained moderately, and the overall length of the lens can be reduced and off-axis aberrations such as field curvature and distortion can be corrected. It can be done well. On the other hand, when the value falls below the upper limit, the negative refractive power of the third lens is not increased more than necessary, and the light flux that forms an image on the periphery of the imaging surface of the solid-state imaging device is not excessively jumped up. The telecentric characteristic of the side light flux can be easily ensured.

  Here, the image side telecentric characteristic means that the principal ray of the light beam that forms an image on the imaging surface of the solid-state imaging device becomes substantially parallel to the optical axis after exiting the last lens surface. The exit pupil position of the lens is sufficiently away from the image plane. When the telecentric characteristic is deteriorated, a light beam is incident on the solid-state imaging device obliquely, and a shading phenomenon occurs in which the substantial aperture efficiency is reduced at the periphery of the imaging surface, resulting in insufficient peripheral light amount. Therefore, the image side telecentric characteristic is a characteristic necessary for an imaging lens using a solid-state imaging element.

The invention described in claim 3 has the same configuration as that of the invention described in claim 1 or 2, and when the radius of curvature of the image side surface of the second lens is R4, the following condition (11) The structure that satisfies the formula is adopted.
0.15 <| R4 | / f <0.40 (11)

According to the third aspect of the present invention, the conditional expression (11) appropriately sets the absolute value of the curvature radius R4 on the second lens image plane side. By exceeding the lower limit in the expression (11), the refractive power on the second lens image surface side does not become excessively large, and the occurrence of coma flare of off-axis light flux and barrel distortion can be suppressed. Further, the radius of curvature on the second lens image surface side is not too small, which is preferable from the viewpoint of lens processability.
By falling below the upper limit in Expression (11), the refractive power of the second lens image side surface can be appropriately secured, so that off-axis aberrations generated by the third lens having negative refractive power can be corrected in a balanced manner. it can. In addition, it is possible to easily ensure the telecentric characteristics of the image-side light beam.
The value of conditional expression (11) is more preferably within the range of conditional expression (12) below.
0.18 <| R4 | / f <0.30 (12)

  The invention described in claim 4 has the same configuration as that of any one of claims 1 to 3, and the first lens has a meniscus shape with a convex surface facing the object side. Is adopted.

  According to the fourth aspect of the invention, the shapes of the first lens and the second lens are symmetrical with respect to the aperture stop, and the spherical aberration and coma generated in the first lens are corrected more satisfactorily. be able to. Further, the chromatic aberration of magnification and distortion of the entire imaging lens system can be corrected more easily.

  The invention described in claim 5 has the same configuration as that of the invention described in claim 1, and the third lens has a meniscus shape with a concave surface facing the image side.

According to the invention described in claim 5, since the third lens has a meniscus shape with the concave surface facing the image side, the principal point position of the third lens can be moved to the image side. A sufficient back focus can be ensured while reducing the overall lens length.
In addition, since the air lens between the second lens and the third lens has a biconcave shape, the positive refractive power makes it easy to ensure the telecentric characteristics of the light beam formed on the periphery of the imaging surface of the solid-state imaging device. can do.

The invention according to claim 6 has the same configuration as the invention according to any one of claims 1 to 5, and the image side surface of the third lens has an apex of the image side surface as an origin, and light. Taking the X axis in the axial direction, the height in the direction perpendicular to the optical axis is h, the i-th order aspheric coefficient of the image side surface of the third lens is Ai, and the radius of curvature of the image side surface of the third lens is R6, when the conical coefficient of the image side surface of the third lens is K6, the aspherical displacement amount X expressed by the following equation (5) and the aspheric rotating quadratic surface expressed by the following equation (6) The component displacement amount X0 satisfies the following conditional expression (4) in the range of the height h in the vertical direction of the optical axis where hmax × 0.7 <h <hmax with respect to the maximum effective radius hmax. Is adopted.
X − X0 <0 (4)

  Here, the vertex of the image side surface of the third lens means an intersection of the image side surface and the optical axis.

  According to the sixth aspect of the present invention, the shape of the side surface of the third lens image is such that the negative refracting power decreases as it moves away from the optical axis and goes to the periphery by making it an aspherical shape that satisfies conditional expression (4). (Furthermore, the shape has an inflection point that is a concave shape in the vicinity of the optical axis but a convex shape in the peripheral portion), so that the telecentric characteristics of the light beam that forms an image on the periphery of the imaging surface of the solid-state imaging device Can be easily secured.

  The invention described in claim 7 has the same configuration as that of the invention described in any one of claims 1 to 6, and the first lens, the second lens, and the third lens are made of a plastic material. The structure is formed.

According to the seventh aspect of the present invention, even if the first lens, the second lens, and the third lens are made of a plastic lens manufactured by injection molding, even a lens having a small curvature radius or outer diameter can be used. Mass production is possible.
That is, in recent years, for the purpose of downsizing the entire solid-state imaging device, even a solid-state imaging device having the same number of pixels has been developed with a small pixel pitch and consequently a small imaging surface size. In such an imaging lens for a solid-state imaging device having a small imaging surface size, it is necessary to proportionally shorten the focal length of the entire system, so that the curvature radius and the outer diameter of each lens are considerably reduced. Therefore, it becomes difficult to process with a glass lens manufactured by polishing.
In addition, by forming each lens with a plastic lens manufactured by injection molding, it becomes easy to make an aspheric surface, and aberration correction can be performed satisfactorily. Here, as a lens that can be manufactured relatively easily even with a small-diameter lens, the use of a glass mold lens is also conceivable, but in general, a glass with a high glass transition point (Tg) is set to a high press temperature when performing mold pressing. It is necessary to do so, and the mold is easily worn out. As a result, the number of times the mold is replaced and the number of maintenance increases, leading to an increase in cost.

  “It is made of a plastic material” means that a plastic material is used as a base material and inorganic fine particles are mixed in the plastic material, or that the surface is coated for the purpose of preventing reflection or improving surface hardness. Including the case where it went.

  The invention according to claim 8 is the solid-state imaging device having a photoelectric conversion unit and the subject image according to any one of claims 1 to 7 for forming a subject image on the photoelectric conversion unit of the solid-state imaging device. An imaging lens, a substrate having an external connection terminal that holds the solid-state imaging device and transmits / receives an electrical signal, and a housing made of a light shielding member having an opening for light incidence from the object side. The imaging unit is integrally formed, and the height of the imaging unit in the optical axis direction of the imaging lens is 10 [mm] or less.

According to the invention described in claim 8, by using the imaging lens according to any one of claims 1 to 7, an imaging unit having advantages such as a smaller size and higher image quality can be obtained. .
The “light entrance opening” is not necessarily limited to a space such as a hole, and refers to a portion where a region through which incident light from the object side can be transmitted is formed.
Further, “the length in the optical axis direction of the imaging lens of the imaging unit is 10 [mm] or less” means the total length along the optical axis direction of the imaging unit having all the above-described configurations. Therefore, for example, in the case where a housing is provided on the front surface of the board and an electronic component or the like is mounted on the back surface of the board, the electrons projecting on the back surface from the front end on the object side of the housing. Assume that the distance to the tip of the component is 10 mm or less.

  A portable terminal according to a ninth aspect of the invention employs a configuration including the imaging unit according to the eighth aspect.

  According to the ninth aspect of the invention, by mounting the imaging unit according to the eighth aspect described above, a portable terminal capable of achieving the above-described miniaturization and weight reduction and capable of high-quality imaging is realized. be able to.

The invention according to claim 10 has, in order from the object side, a first lens having a positive refractive power, a convex surface facing the object side, an aperture stop, a positive refractive power, and a convex surface facing the image side. A second meniscus-shaped second lens having a negative refractive power and a third lens having a concave surface facing the image side, wherein the focal length of the first lens is f1, and the focal point of the third lens When the distance is f3 and the focal length of the entire imaging lens system is f, the following conditional expressions (1) and (3) are satisfied.
0.8 <f1 / f <2.0 (1)
-1.5 <f3 / f <-0.5 (3)

According to the invention described in claim 10, in order from the object side, a so-called telephoto type in which a positive lens group including a first lens and a second lens and a negative third lens having a concave surface facing the image side are arranged. This lens configuration is advantageous in reducing the overall length of the lens and can correct aberrations satisfactorily.
That is, with respect to aberration correction, since the positive refractive power is shared by the first lens and the second lens, the occurrence of spherical aberration and coma can be suppressed. Further, since the aperture stop is disposed between the first lens and the second lens, the first lens has a shape with a convex surface facing the object side, and the second lens has a meniscus shape with the convex surface facing the image side. And distortion are easily corrected.
Here, the conditional expression (1) defines the refractive power of the first lens. By falling below the upper limit value in Expression (1), the positive refractive power of the first lens can be appropriately maintained, and the entire length of the imaging lens can be reduced. On the other hand, by exceeding the lower limit value, the positive refractive power of the first lens does not become unnecessarily large, and higher-order spherical aberration and coma aberration generated in the first lens can be suppressed to a small value.
Conditional expression (2) defines the refractive power of the third lens. Beyond the lower limit in equation (2), the negative refracting power of the third lens can be maintained moderately, and the overall length of the lens can be reduced, and off-axis aberrations such as field curvature and distortion can be corrected. It can be done well. On the other hand, when the value falls below the upper limit, the negative refractive power of the third lens is not increased more than necessary, and the light flux that forms an image on the periphery of the imaging surface of the solid-state imaging device is not excessively jumped up. The telecentric characteristic of the side light flux can be easily ensured.

The invention described in claim 11 has the same configuration as that of the invention described in claim 10, and satisfies the following conditional expression (11) when the radius of curvature of the image side surface of the second lens is R4. , Is adopted.
0.15 <| R4 | / f <0.40 (11)

According to the eleventh aspect of the present invention, the conditional expression (11) appropriately sets the absolute value of the curvature radius R4 on the second lens image plane side. By exceeding the lower limit in the expression (11), the refractive power on the second lens image surface side does not become excessively large, and the occurrence of coma flare of off-axis light flux and barrel distortion can be suppressed. Further, the radius of curvature on the second lens image surface side is not too small, which is preferable from the viewpoint of lens processability.
By falling below the upper limit in Expression (11), the refractive power of the second lens image side surface can be appropriately secured, so that off-axis aberrations generated by the third lens having negative refractive power can be corrected in a balanced manner. it can. In addition, it is possible to easily ensure the telecentric characteristics of the image-side light beam.
The value of conditional expression (11) is more preferably within the range of conditional expression (12) below.
0.18 <| R4 | / f <0.30 (12)

  The invention described in claim 12 has the same configuration as that of the invention described in claim 10 or 11, and adopts a configuration in which the first lens has a meniscus shape with a convex surface facing the object side.

  According to the twelfth aspect of the present invention, the shapes of the first lens and the second lens are symmetrical with respect to the aperture stop, and the spherical aberration and coma generated in the first lens are corrected more satisfactorily. be able to. Further, the chromatic aberration of magnification and distortion of the entire imaging lens system can be corrected more easily.

  The invention described in claim 13 has the same configuration as that of the invention described in claim 10, and the third lens has a meniscus shape with a concave surface facing the image side.

According to the invention described in claim 13, since the third lens has a meniscus shape with the concave surface facing the image side, the principal point position of the third lens can be moved to the image side, and the entire imaging lens system A sufficient back focus can be ensured while reducing the overall lens length.
In addition, since the air lens between the second lens and the third lens has a biconcave shape, the positive refractive power makes it easy to ensure the telecentric characteristics of the light beam formed on the periphery of the imaging surface of the solid-state imaging device. can do.

The invention according to a fourteenth aspect has the same configuration as that of the invention according to any one of the tenth to thirteenth aspects, and the image side surface of the third lens has the apex of the image side surface as an origin and an optical axis. Taking the X axis as the direction, the height in the direction perpendicular to the optical axis is h, the i-th order aspheric coefficient of the image side surface of the third lens is Ai, and the radius of curvature of the image side surface of the third lens is R6. When the cone coefficient of the image side surface of the third lens is K6, the aspherical displacement amount X expressed by the following equation (5) and the aspheric rotating quadratic surface component expressed by the following equation (6): The displacement X0 satisfies the following conditional expression (4) in the range of the height h in the vertical direction of the optical axis where hmax × 0.7 <h <hmax with respect to the maximum effective radius hmax. Adopted.
X − X0 <0 (4)

  Here, the vertex of the image side surface of the third lens means an intersection of the image side surface and the optical axis.

  According to the fourteenth aspect of the present invention, the shape of the side surface of the third lens image is such that the negative refractive power decreases as it moves away from the optical axis and goes to the periphery by making it an aspherical shape that satisfies conditional expression (4). (Furthermore, the shape has an inflection point that is a concave shape in the vicinity of the optical axis but a convex shape in the peripheral portion), so that the telecentric characteristics of the light beam that forms an image on the periphery of the imaging surface of the solid-state imaging device Can be easily secured.

  The invention according to a fifteenth aspect includes the same configuration as that of the invention according to any one of the tenth to fourteenth aspects, and the first lens, the second lens, and the third lens are made of a plastic material. It has been configured to be.

According to the invention described in claim 15, even if the first lens, the second lens, and the third lens are made of a plastic lens manufactured by injection molding, even a lens having a small curvature radius or outer diameter can be used. Mass production is possible.
That is, in recent years, for the purpose of downsizing the entire solid-state imaging device, even a solid-state imaging device having the same number of pixels has been developed with a small pixel pitch and consequently a small imaging surface size. In such an imaging lens for a solid-state imaging device having a small imaging surface size, it is necessary to proportionally shorten the focal length of the entire system, so that the curvature radius and the outer diameter of each lens are considerably reduced. Therefore, it becomes difficult to process with a glass lens manufactured by polishing.
In addition, by forming each lens with a plastic lens manufactured by injection molding, it becomes easy to make an aspheric surface, and aberration correction can be performed satisfactorily. Here, as a lens that can be manufactured relatively easily even with a small-diameter lens, the use of a glass mold lens is also conceivable, but in general, a glass with a high glass transition point (Tg) is set to a high press temperature when performing mold pressing. It is necessary to do so, and the mold is easily worn out. As a result, the number of times the mold is replaced and the number of maintenance increases, leading to an increase in cost.

  “It is made of a plastic material” means that a plastic material is used as a base material and inorganic fine particles are mixed in the plastic material, or that the surface is coated for the purpose of preventing reflection or improving surface hardness. Including the case where it went.

  The invention according to claim 16 is the imaging according to any one of claims 10 to 15 for forming a subject image on the solid-state imaging device having a photoelectric conversion unit and the photoelectric conversion unit of the solid-state imaging device. A lens, a substrate having an external connection terminal for holding the solid-state imaging device and transmitting / receiving an electric signal, and a housing made of a light-shielding member having an opening for light incidence from the object side are integrated. The image pickup unit is configured to be configured such that the height of the image pickup unit in the optical axis direction of the image pickup lens is 10 [mm] or less.

According to the invention described in claim 16, by using the imaging lens according to any one of claims 10 to 15, it is possible to obtain an imaging unit having advantages such as further miniaturization and higher image quality. .
The “light entrance opening” is not necessarily limited to a space such as a hole, and refers to a portion where a region through which incident light from the object side can be transmitted is formed.
Further, “the length in the optical axis direction of the imaging lens of the imaging unit is 10 [mm] or less” means the total length along the optical axis direction of the imaging unit having all the above-described configurations. Therefore, for example, in the case where a housing is provided on the front surface of the board and an electronic component or the like is mounted on the back surface of the board, the electrons projecting on the back surface from the front end on the object side of the housing. Assume that the distance to the tip of the component is 10 mm or less.

  The invention described in claim 17 is configured to include the imaging unit described in claim 16.

  According to the seventeenth aspect of the present invention, by mounting the imaging unit according to the sixteenth aspect described above, a portable terminal capable of achieving the above-described reduction in size and weight and high-quality imaging can be realized. be able to.

  According to the present invention, it is possible to obtain a three-lens imaging lens, an imaging unit, and a portable terminal that are more compact than the conventional type and that correct various aberrations.

An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a perspective view of an imaging unit 50 according to the present embodiment, and FIG. 2 is a diagram schematically showing a cross section along the optical axis of the imaging optical system of the imaging unit 50.
The imaging unit 50 includes a CMOS image sensor 51 as a solid-state imaging device having a photoelectric conversion unit 51a, an imaging optical system 10 as an imaging lens that causes the photoelectric conversion unit 51a of the image sensor 51 to capture a subject image, and an image. A substrate 52 having an external connection terminal 54 that holds the sensor 51 and transmits / receives an electrical signal thereof, and a housing 53 as a lens barrel having a light incident opening from the object side and made of a light shielding member. These are formed integrally.

In the image sensor 51, a photoelectric conversion unit 51a as a light receiving unit in which pixels (photoelectric conversion elements) are two-dimensionally arranged is formed in the center of a plane on the light receiving side. A processing circuit 51b is formed. Such a signal processing circuit includes a drive circuit unit that sequentially drives each pixel to obtain a signal charge, an A / D conversion unit that converts each signal charge into a digital signal, and a signal that forms an image signal output using the digital signal. It consists of a processing unit and the like. A number of pads (not shown) are arranged near the outer edge of the plane on the light receiving side of the image sensor 51, and are connected to the substrate 52 via wires W. The image sensor 51 converts the signal charge from the photoelectric conversion unit 51 a into an image signal such as a digital YUV signal and outputs the image signal to a predetermined circuit on the substrate 52 via the wire W. Here, Y is a luminance signal, U (= R−Y) is a color difference signal between red and the luminance signal, and V (= BY) is a color difference signal between blue and the luminance signal.
Note that the image sensor is not limited to the above CMOS image sensor, and other devices such as a CCD may be used.

The substrate 52 has a flat plate 52a for supporting the image sensor 51 and the housing 53 on one plane, and a flexible substrate having one end connected to the back surface (the surface opposite to the image sensor 51) of the support plate 52a. 52b.
The support flat plate 52a has a large number of signal transmission pads provided on the front and back surfaces, and is connected to the wire W of the image sensor 51 described above on one plane side and connected to the flexible substrate 52b on the back side. Yes.
As described above, one end of the flexible substrate 52b is connected to the support plate 52a, and the support plate 52a and an external circuit (for example, a host device on which an imaging unit is mounted) is connected via the external output terminal 54 provided at the other end. Control circuit), a voltage for driving the image sensor 51 and a clock signal are supplied from an external circuit, and a digital YUV signal can be output to the external circuit. Furthermore, the intermediate portion in the longitudinal direction of the flexible substrate 52b has flexibility or deformability, and the deformation gives the freedom to the orientation and arrangement of the external output terminals with respect to the support flat plate 52a.

The housing 53 is fixedly mounted by bonding in a state where the image sensor 51 is housed inside the flat surface of the support plate 52a of the substrate 52 on which the image sensor 51 is provided. That is, the casing 53 is formed in a cylindrical shape with a bottom having a wide opening so that the portion on the image sensor 51 side surrounds the image sensor 51 and the other end having an opening, and the image is formed on the support plate 52a. The end on the sensor 51 side is fixed in contact. Note that the end of the housing 53 on the image sensor 51 side may be fixed in contact with the periphery of the photoelectric conversion unit 51 a on the image sensor 51.
The casing 53 is used with the other end provided with an opening facing the object side, and an IR (infrared) cut filter 23 of the imaging optical system 10 described later is provided inside the opening.
The imaging optical system 10 is stored and held inside the housing 53.

The imaging optical system 10 includes an IR cut filter 23 that prevents the incidence of infrared rays from the object side, a first lens L1 having a positive refractive power from the object side, and a convex surface facing the object side, and a positive refractive power. A second lens L2 having a meniscus shape having a convex surface facing the image side, a third lens L3 having negative refractive power and having a concave surface facing the image side, and an imaging lens arranged in this order, and the first lens L1 , And an aperture stop S disposed between the second lens L2.
The imaging optical system 10 is for forming an object image on a solid-state imaging device using the aperture stop S and the lenses L1, L2, and L3 as optical systems. In FIG. 1, the upper side is the object side and the lower side is the image side, and the alternate long and short dash line in FIG. 2 is the optical axis common to the lenses L1, L2, and L3.

The IR cut filter 23 is a member formed in, for example, a substantially rectangular shape or a circular shape. Although illustration is omitted, an external light shielding mask for minimizing the incidence of unnecessary light from outside may be provided on the object side further than the IR cut filter 23.
The aperture stop S is a member that determines the F number of the entire imaging lens system.

Each lens L1, L2, L3 is housed inside the housing in a state where the optical axis thereof matches the center line of the housing 53.
These lenses L1, L2, L3 are not shown in the figure, but for example, the range from each center to a predetermined range is set to an effective diameter range that functions as an imaging lens, and the outer portion is used as an imaging lens. It may be set to a flange portion that does not function. In this case, the lenses L1, L2, and L3 can be held inside the casing 53 by fitting the outer peripheral portion of the flange portion into a predetermined position of the casing 53.

In recent years, for the purpose of downsizing the entire imaging apparatus, even a solid-state imaging device having the same number of pixels has been developed with a small pixel pitch and as a result, a light receiving unit (photoelectric conversion unit) with a small screen size. . Imaging lenses for solid-state imaging devices with such a small screen size need to shorten the focal length of the entire system in order to ensure the same angle of view, so the radius of curvature and outer diameter of each lens is considerably small. turn into. Therefore, it becomes difficult to process with a glass lens manufactured by polishing. Therefore, it is desirable that each of the lenses L1, L2, and L3 is formed by injection molding using plastic as a material. Further, when the image pickup apparatus is desired to suppress the image point position fluctuation of the entire image pickup lens system when the temperature changes, it is desirable that the first lens is a glass mold lens.
The detailed specifications of the lenses L1, L2, and L3 will be described using a plurality of specific examples in the examples described later.

  Further, although not shown, a light shielding mask may be disposed between the IR cut filter 23 and the first lens L1, and between the second lens L2 and the third lens L3. Prevents the light incident from the IR cut filter from entering the outside of the effective diameter of the imaging lens of the first lens L1 due to the mutual action of each of the light shielding masks and the aperture stop S, and from the aperture stop S. The incident light can be prevented from entering outside the effective diameter of the imaging lens of the second lens L2 and the third lens L3, and the occurrence of ghost and flare can be suppressed.

A usage mode of the imaging unit 50 described above will be described. FIG. 3 shows a state in which the imaging unit 50 is installed in a mobile phone 100 as a mobile terminal or an imaging device. FIG. 4 is a control block diagram of the mobile phone 100.
In the imaging unit 50, for example, the object side end surface of the casing 53 in the imaging optical system is provided on the back surface of the mobile phone 100 (the liquid crystal display unit side is the front surface), and is disposed at a position corresponding to the lower side of the liquid crystal display unit. Is done.
The external connection terminal 54 of the imaging unit 50 is connected to the control unit 101 of the mobile phone 100 and outputs an image signal such as a luminance signal or a color difference signal to the control unit 101 side.
On the other hand, as shown in FIG. 4, the mobile phone 100 controls each unit in an integrated manner, and also supports a control unit (CPU) 101 that executes a program corresponding to each process, and inputs a number and the like with keys. An input unit 60, a display unit 70 for displaying captured images in addition to predetermined data, a wireless communication unit 80 for realizing various information communication with an external server, a system program for the mobile phone 100, A storage unit (ROM) 91 storing various processing programs and necessary data such as a terminal ID, and various processing programs and data executed by the control unit 101, or processing data, or imaging data by the imaging unit 50, etc. And a temporary storage unit (RAM) 92.
Then, the image signal input from the imaging unit 50 is stored in the storage unit 92 or displayed on the display unit 70 by the control system of the mobile phone 100, and further, video information is transmitted via the wireless communication unit 80. Sent to the outside.

Next, although the specification of an imaging lens is demonstrated based on Examples 1-5, each specification is not limited to this. Here, symbols used in each example are as follows.
f: Focal length of the entire imaging lens system fB: Back focus
F: F number
2Y: Diagonal length of the imaging surface of the solid-state image sensor
R: radius of curvature of refractive surface
D: Distance between the top surfaces of the refractive surfaces
Nd: Refractive index of lens material at d-line νd: Abbe number of lens material

  In each embodiment, the aspherical shape has the vertex of the surface as the origin, the X axis in the optical axis direction, the height in the direction perpendicular to the optical axis is h, the vertex radius of curvature is R, the conic constant is K, The i-th aspherical coefficient is represented by the following expression expressed by the following “Equation 3” where Ai is Ai.

(First embodiment)
Imaging lens data are shown in Tables 1 and 2, and numerical values corresponding to the conditional expressions are shown in Table 3.

  FIG. 5 is an explanatory diagram showing the arrangement of the imaging lenses of the first embodiment. In the figure, L1 is a first lens, L2 is a second lens, L3 is a third lens, and S is an aperture stop. FIG. 6 is an aberration diagram of Example 1 (spherical aberration, astigmatism, distortion, and meridional coma).

(Example 2)
Imaging lens data are shown in Tables 4 and 5, and numerical values corresponding to the conditional expressions are shown in Table 6.

  FIG. 7 is an explanatory diagram illustrating the arrangement of the imaging lenses according to the second embodiment. In the figure, L1 is a first lens, L2 is a second lens, L3 is a third lens, and S is an aperture stop. FIG. 8 is an aberration diagram of Example 2 (spherical aberration, astigmatism, distortion, and meridional coma).

(Example 3)
Imaging lens data are shown in Tables 7 and 8, and numerical values corresponding to the conditional expressions are shown in Table 9.

  FIG. 9 is an explanatory diagram illustrating the arrangement of the imaging lenses according to the third embodiment. In the figure, L1 is a first lens, L2 is a second lens, L3 is a third lens, and S is an aperture stop. FIG. 10 is an aberration diagram of Example 3 (spherical aberration, astigmatism, distortion, and meridional coma).

(Example 4)
Imaging lens data are shown in Tables 10 and 11, and numerical values corresponding to the conditional expressions are shown in Table 12.

  FIG. 11 is an explanatory diagram illustrating the arrangement of the imaging lenses according to the fourth embodiment. In the figure, L1 is a first lens, L2 is a second lens, L3 is a third lens, and S is an aperture stop. FIG. 12 is an aberration diagram of Example 4 (spherical aberration, astigmatism, distortion, and meridional coma).

(Example 5)
Imaging lens data are shown in Tables 13 and 14, and numerical values corresponding to the conditional expressions are shown in Table 15.

  FIG. 13 is an explanatory diagram illustrating an imaging lens arrangement according to the fifth embodiment. In the figure, L1 is a first lens, L2 is a second lens, L3 is a third lens, and S is an aperture stop. FIG. 14 is an aberration diagram of Example 5 (spherical aberration, astigmatism, distortion, and meridional coma).

In the first, second, and third embodiments, the first lens L1 and the second lens L2 are formed of a polyolefin-based plastic material, and the saturated water absorption is 0.01% or less. The third lens L3 is made of a polycarbonate plastic material and has a saturated water absorption rate of 0.4%.
Here, since the plastic lens has a larger saturated water absorption rate than the glass lens, a sudden non-uniform distribution of water absorption occurs when there is a sudden change in humidity, and the refractive index is not uniform and good imaging is achieved. There is a tendency that performance cannot be obtained. Therefore, in order to suppress performance degradation due to humidity changes, it is desirable to use a plastic material having a saturated water absorption rate of 0.7% or less.

In Example 4 described above, the first lens L1 is made of a glass material. The second lens L2 is formed from a polyolefin-based plastic material, and the saturated water absorption is 0.01% or less, and the third lens L3 is formed from a polyester-based plastic material, and the saturated water absorption is 0.7%.
In the fifth embodiment, the first lens L1 is made of a glass material. The second lens L2 is formed from a polyolefin plastic material, and the saturated water absorption is 0.01% or less. The third lens L3 is formed from a polycarbonate plastic material, and the saturated water absorption is 0.4.
%.

  In addition, since the plastic material has a large change in the refractive index when the temperature changes, if the first lens L1, the second lens L2, and the third lens L3 are all made of plastic lenses, the imaging lens lens changes when the ambient temperature changes. There is a problem that the image point position of the entire system fluctuates. In the imaging unit having such a specification that the image point position variation cannot be ignored, for example, the positive first lens L1 is a lens formed of a glass material (for example, a glass mold lens), and the positive second lens L2 and the negative third lens are used. The lens L3 is a plastic lens, and the second lens L2 and the third lens L3 have a refractive power distribution that cancels the image point position fluctuation at the time of temperature change. it can. When a glass mold lens is used, it is desirable to use a glass material having a glass transition point (Tg) of 400 ° C. (400 degrees Celsius) or less in order to prevent the mold from being consumed as much as possible.

Recently, it has been found that inorganic fine particles can be mixed in a plastic material to suppress the temperature change of the refractive index of the plastic material to a small value. More specifically, mixing fine particles with a transparent plastic material generally causes light scattering and lowers the transmittance, so it was difficult to use as an optical material. By making it smaller than the wavelength, it is possible to substantially prevent scattering. The refractive index of the plastic material decreases with increasing temperature, but the refractive index of inorganic particles increases with increasing temperature. Therefore, it is possible to make almost no change in the refractive index by using these temperature dependencies so as to cancel each other.
Specifically, by dispersing inorganic particles having a maximum length of 20 nanometers or less in a plastic material as a base material, a plastic material with extremely low temperature dependence of the refractive index is obtained. For example, by dispersing fine particles of niobium oxide (Nb ₂ O ₅ ) in acrylic, the refractive index change due to temperature change can be reduced.
In the present invention, imaging is performed by using a plastic material in which such inorganic particles are dispersed in one of two positive lenses (L1, L2) or in all lenses (L1, L2, L3). It is possible to suppress the fluctuation of the image point position when the temperature of the entire lens system changes.

  The first and second embodiments are design examples in which an optical low-pass filter and an infrared cut filter are not arranged on the image side of the imaging lens. However, the third embodiment is an infrared cut on the image side of the imaging lens and on the object side. This is a design example in which a coated infrared cut filter F is disposed. Example 4 and Example 5 are design examples in which the above-described infrared cut filter F and the seal glass P of the solid-state image element package are arranged on the image side of the imaging lens. Of course, an optical low-pass filter may be arranged in each embodiment as necessary.

  In this embodiment, the telecentric characteristic of the image side light beam is not always designed sufficiently. However, with recent technology, shading can be reduced by reviewing the arrangement of the color filters of the solid-state image sensor and the microlens array, and the angle between the principal ray and the optical axis is 25 ° at the periphery of the imaging surface. A solid-state imaging device has also been developed that does not cause noticeable shading if it is less than or equal to about. Therefore, the present embodiment is a design example aiming at further miniaturization for the part where the requirement of the telecentric characteristic is relaxed.

It is a perspective view of the imaging unit which is an embodiment of the present invention. 1 is a schematic cross-sectional view of a cross section including an optical axis of each lens of an imaging unit according to an embodiment of the present invention. 3A is a front view of a mobile phone to which the imaging unit is applied, and FIG. 3B is a rear view of the mobile phone to which the imaging unit is applied. FIG. 4 is a control block diagram of the mobile phone in FIG. 3. FIG. 3 is an explanatory diagram illustrating a lens arrangement of Example 1. FIG. 4 is an aberration diagram of Example 1 (spherical aberration, astigmatism, distortion, and meridional coma). FIG. 6 is an explanatory diagram illustrating an imaging lens arrangement of Example 2. FIG. 6 is an aberration diagram of Example 2 (spherical aberration, astigmatism, distortion, and meridional coma). FIG. 6 is an explanatory diagram showing a lens arrangement of Example 3. FIG. 6 is an aberration diagram of Example 3 (spherical aberration, astigmatism, distortion, and meridional coma). FIG. 6 is an explanatory diagram illustrating a lens arrangement of Example 4. FIG. 6 is an aberration diagram of Example 4 (spherical aberration, astigmatism, distortion, and meridional coma). FIG. 10 is an explanatory diagram showing a lens arrangement of Example 5. FIG. 10 is an aberration diagram of Example 5 (spherical aberration, astigmatism, distortion, and meridional coma).

Explanation of symbols

10 Imaging optical system (imaging lens)
50 Imaging unit 51 Image sensor (solid-state imaging device)
51a Photoelectric conversion unit 52 Substrate 53 Housing 54 External connection terminal 100 Mobile phone (mobile terminal)
L1 1st lens L2 2nd lens L3 3rd lens S Aperture stop

Claims (17)

In order from the object side, a first lens having a positive refractive power and having a convex surface facing the object side, an aperture stop, a second meniscus lens having a positive refractive power and a convex surface facing the image side, An imaging lens comprising a third lens having negative refractive power and having a concave surface facing the image side,
The focal length of the first lens is f1, the focal length of the entire imaging lens is f, the Abbe number of the first lens is ν1, the Abbe number of the second lens is ν2, and the Abbe number of the third lens is ν3. An imaging lens satisfying the following conditional expressions (1) and (2):
0.8 <f1 / f <2.0 (1)
20 <{(ν1 + ν2) / 2} −ν3 <70 (2) 2. The imaging lens according to claim 1, wherein the following conditional expression (3) is satisfied when a focal length of the third lens is f3.
-1.5 <f3 / f <-0.5 (3) The imaging lens according to claim 1 or 2, wherein the following conditional expression (11) is satisfied when a radius of curvature of an image side surface of the second lens is R4.
0.15 <| R4 | / f <0.40 (11)   The imaging lens according to any one of claims 1 to 3, wherein the first lens has a meniscus shape with a convex surface facing the object side.   The imaging lens according to claim 1, wherein the third lens has a meniscus shape with a concave surface facing the image side. The image side surface of the third lens has an apex of the image side surface as an origin, the X axis in the optical axis direction, a height in a direction perpendicular to the optical axis, h, and i on the image side surface of the third lens. When the following aspheric coefficient is Ai, the radius of curvature of the image side surface of the third lens is R6, and the cone coefficient of the image side surface of the third lens is K6,
The aspherical displacement amount X expressed by the following equation (5) and the aspherical rotating quadric surface component displacement amount X0 expressed by the following equation (6) are expressed as hmax × 0.7 <h with respect to the maximum effective radius hmax. 6. The imaging lens according to claim 1, wherein the following conditional expression (4) is satisfied within a range of the height h in the direction perpendicular to the optical axis where <hmax is satisfied.
X − X0 <0 (4)

  The imaging lens according to claim 1, wherein the first lens, the second lens, and the third lens are formed of a plastic material. A solid-state imaging device having a photoelectric conversion unit;
The imaging lens according to any one of claims 1 to 7, for forming a subject image on the photoelectric conversion unit of the solid-state imaging device,
A substrate having external connection terminals for holding the solid-state imaging device and transmitting and receiving electrical signals;
An imaging unit integrally formed with a housing made of a light shielding member having an opening for light incidence from the object side,
An imaging unit, wherein a height of the imaging unit in an optical axis direction of the imaging lens is 10 [mm] or less.   A portable terminal comprising the imaging unit according to claim 8. In order from the object side, a first lens having a positive refractive power and having a convex surface facing the object side, an aperture stop, a second meniscus lens having a positive refractive power and a convex surface facing the image side, An imaging lens comprising a third lens having negative refractive power and having a concave surface facing the image side,
When the focal length of the first lens is f1, the focal length of the third lens is f3, and the focal length of the entire imaging lens system is f, the following conditional expressions (1) and (3) are satisfied. A characteristic imaging lens.
0.8 <f1 / f <2.0 (1)
-1.5 <f3 / f <-0.5 (3) The imaging lens according to claim 10, wherein the following conditional expression (11) is satisfied when a radius of curvature of the image side surface of the second lens is R4.
0.15 <| R4 | / f <0.40 (11)   The imaging lens according to claim 10 or 11, wherein the first lens has a meniscus shape with a convex surface facing the object side.   The imaging lens according to claim 10, wherein the third lens has a meniscus shape with a concave surface facing the image side. The image side surface of the third lens is
The vertex of the image side surface is the origin, the X axis is taken in the optical axis direction, the height in the direction perpendicular to the optical axis is h, the i-th order aspheric coefficient of the image side surface of the third lens is Ai When the radius of curvature of the image side surface of the third lens is R6 and the cone coefficient of the image side surface of the third lens is K6,
The aspherical displacement amount X expressed by the following equation (5) and the aspherical rotating quadric surface component displacement amount X0 expressed by the following equation (6) are expressed as hmax × 0.7 <h with respect to the maximum effective radius hmax. The imaging lens according to any one of claims 10 to 13, wherein the following conditional expression (4) is satisfied in a range of an arbitrary height h in the vertical direction of the optical axis where hmax is satisfied.
X − X0 <0 (4)

  The imaging lens according to claim 10, wherein the first lens, the second lens, and the third lens are made of a plastic material. A solid-state imaging device having a photoelectric conversion unit;
The imaging lens according to any one of claims 10 to 15, for forming a subject image on the photoelectric conversion unit of the solid-state imaging device,
A substrate having external connection terminals for holding the solid-state imaging device and transmitting and receiving electrical signals;
An imaging unit integrally formed with a housing made of a light shielding member having an opening for light incidence from the object side,
An imaging unit, wherein a height of the imaging unit in an optical axis direction of the imaging lens is 10 [mm] or less.   A portable terminal comprising the imaging unit according to claim 16.

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