JP4894222B2 - Imaging lens, imaging unit, and portable terminal - Google Patents

Description

  The present invention relates to a small imaging lens, an imaging unit, and a portable terminal equipped with the imaging lens using a solid-state imaging device such as a CCD image sensor or a CMOS image sensor.

  In recent years, along 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, Portable information terminals are becoming popular. In addition, there is an increasing demand for further downsizing of imaging lenses mounted on these imaging apparatuses.

  As an imaging lens for such an application, a lens having a three-lens configuration is known because it can achieve higher performance than a lens having one or two lenses. A so-called triplet-type imaging lens including, in order from the object side, a first lens having a positive refractive power, a second lens having a negative refractive power, and a third lens having a positive refractive power is disclosed in Patent Document 1, for example. .

A so-called telephoto type imaging lens including a first lens having a positive refractive power, a second lens having a positive refractive power, and a third lens having a negative refractive power in order from the object side is disclosed in Patent Document 2, for example. Has been.
JP 2001-750006 A JP 2003-322792 A

  However, although 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, on the other hand, the entire length of the imaging lens (the most object side of the imaging lens). The distance on the optical axis from the surface to the image side focal point) is relatively long, and is not necessarily suitable for miniaturization. Further, the imaging lens of the type described in Patent Document 2 has an advantageous configuration for shortening the overall length of the imaging lens, but there is room for improvement in further downsizing.

  In view of such problems, the present invention provides a three-lens imaging lens in which various aberrations are favorably corrected while being smaller than the conventional type, an imaging unit including the imaging lens, and a portable terminal. Objective.

Here, although it is a scale of a small image pickup lens, the present invention aims at downsizing the level satisfying the following expression. By satisfying this range, the overall length of the imaging lens 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 / f <1.40 (7)
However,
L: Distance on the optical axis from the lens surface closest to the object side to the image side focal point of the entire imaging lens system f: Focal length of the entire imaging lens system

Here, the image-side focal point refers to an image point when a parallel light beam parallel to the optical axis is incident on the imaging 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 following formula is good.
L / f <1.30 (7 ′)

The imaging lens according to claim 1 is a single-focus imaging lens that forms a subject image on a solid-state imaging device, and has a first refractive power and a convex surface directed toward the object side in order from the object side. lens, an aperture stop, a positive second lens having a meniscus shape with a convex surface facing the has image side refractive power, Ri Do a third lens having a concave surface facing the has image side a negative refractive power, the following It satisfies the conditional expression.
0.20 <R1 / f <0.42 (1)
0.15 <D2 / f <0.30 (2 ′)
However,
R1: curvature radius D2 of the object side surface of the first lens D2: air spacing on the axis of the first lens and the second lens f2: focal length of the entire imaging lens system The imaging lens according to claim 2 , The invention described in item 1 is characterized in that the following conditional expression is satisfied.
0.23 <R1 / f <0.38 (1 ′)

  The basic configuration of the present invention for obtaining a small imaging lens with good aberration correction is, in order from the object side, a first lens having a positive refractive power and a convex surface facing the object side, an aperture stop, a positive lens A second meniscus lens having a refractive power and having a convex surface facing the image side, and a third lens having a negative refractive power and having a concave surface facing the image side. The so-called telephoto type lens configuration in which a positive lens group consisting of a first lens and a second lens and a negative third lens with a concave surface facing the image side are arranged in order from the object side shortens the overall length of the imaging lens. However, this configuration is advantageous for downsizing.

  Regarding aberration correction, since the positive refractive power is shared by the first lens and the second lens, it is possible to suppress the occurrence of spherical aberration and coma. 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 is easily corrected.

Conditional expression (1) sets the radius of curvature of the first lens on the object side appropriately. When R1 / f is less than the upper limit, the entire length of the imaging lens can be shortened. In addition, the field curvature can be corrected favorably. On the other hand, when R1 / f exceeds the lower limit, higher-order spherical aberration and coma aberration can be reduced. In addition, the radius of curvature does not become too small, and the processability of the lens is improved. More preferably, the range of the following formula is good.
0.23 <R1 / f <0.38 (1 ′)

Conditional expression (2) is a condition for appropriately setting the distance between the first lens and the second lens to satisfactorily correct coma and field curvature. When D2 / f is lower than the upper limit, coma aberration and field curvature can be favorably corrected. Further, since the distance between the aperture stop and the first lens and the second lens is reduced, the outer diameters of the first lens and the second lens are not increased, which is advantageous for downsizing the imaging lens. On the other hand, when D2 / f exceeds the lower limit, a sufficient interval for inserting the aperture stop can be secured. More preferably, the range of the following formula is good.
0.15 <D2 / f <0.3 (2 ′)

The imaging lens described in claim 3 is characterized in that, in the invention described in claim 1 or 2 , the following conditional expression is satisfied.
−5 <P _air / P ₀ <−1.3 (3)
However,
P ₀ : refractive power of the entire imaging lens system P _air : refractive power of a so-called air lens formed by the image side surface (R2) of the first lens and the object side surface (R3) of the second lens, and The refractive power is the reciprocal of the focal length, and the P _air can be obtained by the following equation (4).
P _air = (1-N1) / R2 + (N2-1) / R3-{((1-N1) · (N2-1)) / (R2 · R3)} · D2 (4)
However,
N1: Refractive index N2 with respect to d line of the first lens R2: Refractive index R2 with respect to d line of the second lens R2: Radius of curvature R3 of the image side surface of the first lens D2: Radius of curvature D2 of the object side surface of the second lens: Air spacing on the axis of the first lens and the second lens

Conditional expression (3) is a condition for improving the image plane correction and lens processability by making the refractive power of the air lens formed by the first lens and the second lens appropriate. If P _air / P ₀ is less than the upper limit, the negative refractive power by the air lens can be maintained, and the Petzval sum does not become too large, and the image plane can be flattened. On the other hand, if P _air / P ₀ exceeds the lower limit, the negative refracting power by the air lens does not become too strong, so that the radius of curvature of the second surface and the third surface sandwiching the stop can be increased, and the workability of the lens is improved. Become. Further, since the second surface and the third surface are separated from each other outside the axis, a sufficient air space for inserting the diaphragm can be secured without increasing the axial space, which is advantageous for downsizing of the imaging lens. More preferably, the range of the following formula is good.
-4 <P _air / P ₀ <-2 (3 ′)

An imaging lens according to a fourth aspect of the invention is characterized in that, in the invention according to any one of the first to third aspects, the following conditional expression is satisfied.
−2.0 <f3 / f <−0.4 (5)
However,
f3: focal length of the third lens f: focal length of the entire imaging lens system

Conditional expression (5) sets the refractive power of the third lens appropriately. When f3 / f exceeds the lower limit, the negative refracting power of the third lens can be appropriately maintained, and it is effective for shortening the entire lens length and favorably correcting various off-axis aberrations such as field curvature and distortion. There is. On the other hand, since f3 / f is less than the upper limit, the negative refractive power of the third lens is not increased more than necessary, and as a result, the exit pupil position can be moved away from the solid-state image sensor to the object side. It is possible to reduce the principal ray incident angle of the light beam that forms an image on the periphery of the imaging surface of the element (the angle formed by the principal ray and the optical axis is 0 ° when the optical axis is parallel to the optical axis). As a result, it is possible to suppress a phenomenon (shading) in which the substantial aperture efficiency decreases in the periphery of the imaging surface. More preferably, the range of the following formula is better.
−1.5 <f3 / f <−0.5 (5 ′)

According to a fifth aspect of the present invention, in the image pickup lens according to the fourth aspect of the invention, the third lens has a biconcave shape, so that negative refractive power is dispersed on the object side surface and the image side surface. Therefore, the negative refractive power of the third lens can be increased without the curvature radius of the image side surface becoming too small. When the negative refracting power of the third lens is set under the conditional expression (5), the distance between the most convex part on the image side surface of the third lens and the imaging surface can be increased, and the assembling property can be increased. And an imaging lens excellent in ease of adjustment.

An imaging lens according to a sixth aspect of the invention is characterized in that, in the invention according to any one of the first to fifth aspects, the following conditional expression is satisfied.
20 <{(ν1 + ν2) / 2} −ν3 <65 (6)
However,
ν1: Abbe number of the first lens ν2: Abbe number of the second lens ν3: Abbe number of the third lens

Conditional expression (6) is a condition for satisfactorily correcting the chromatic aberration of the entire imaging lens system. When the value of equation (6) exceeds the lower limit, axial chromatic aberration and lateral chromatic aberration can be corrected in a well-balanced manner. On the other hand, when the value of the formula (6) is lower than the upper limit, the lens can be constituted by an optical material that is highly available. More preferably, the range of the following formula is good.
25 <{(ν1 + ν2) / 2} −ν3 <65 (6 ′)

The imaging lens according to claim 7, characterized in the invention according to any one of claims 1 to 6, wherein the first lens, the second lens, and said third lens are formed of plastic material And

  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, in comparison with a glass lens manufactured by laborious polishing, the first lens, the second lens, and the third lens are made of plastic lenses manufactured by injection molding, so that the radius of curvature and the outer diameter are increased. Even small lenses can be mass-produced at low cost. In addition, since plastic lenses can be easily aspherical, it is advantageous in terms of aberration correction. Furthermore, compared to the case of adopting a glass mold lens that can be manufactured relatively easily even with a small-diameter lens, the plastic lens can reduce the press temperature, and therefore, the wear of the molding die can be suppressed. In addition, it is possible to reduce the cost by reducing the number of replacements and maintenance of the molding die.

  The phrase “formed from a plastic material” includes a case where a plastic material is used as a base material and a coating treatment is performed on the surface for the purpose of preventing reflection or improving surface hardness. In addition, for the purpose of suppressing the temperature change of the refractive index of the plastic material to be small, the case where inorganic fine particles are mixed in the plastic material is also included.

An imaging unit according to an eighth aspect of the present invention is a solid-state imaging device including a photoelectric conversion unit, and an imaging according to any one of the first to seventh aspects, wherein a subject image is formed on 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 formed in a manner that the height of the image pickup unit in the optical axis direction of the image pickup lens is 10 [mm] or less.

  By using the imaging lens of the present invention, a smaller and higher performance imaging unit can be obtained.

  Here, the “light entrance opening” is not necessarily limited to a space such as a hole, and refers to a portion where a region capable of transmitting incident light from the object side is formed. Further, “the height of the imaging unit in the optical axis direction of the imaging lens is equal to or less than 10 mm” means the total length along the optical axis direction of the imaging unit having all the above-described configurations. Therefore, for example, when a housing is provided on the front surface of the substrate and an electronic component or the like is mounted on the back surface of the substrate, the electronic component that protrudes on the back surface from the front end on the object side of the housing It is assumed that the distance (Δ in FIG. 2) to the front end of the lens is 10 [mm] or less.

A mobile terminal according to a ninth aspect includes the imaging unit according to the eighth aspect.

  By using the imaging unit of the present invention, a smaller and higher performance portable terminal can be obtained.

  According to the present invention, it is possible to provide an imaging lens having a three-lens configuration in which various aberrations are favorably corrected while being smaller than the conventional type, and an imaging unit and a portable terminal including the imaging lens.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. 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.

  As shown in FIG. 1, the imaging unit 50 includes a CMOS type imaging device 51 as a solid-state imaging device having a photoelectric conversion unit 51a, an imaging lens 10 that causes the photoelectric conversion unit 51a of the imaging device 51 to capture a subject image, A substrate 52 having an external connection terminal (also referred to as an external connection terminal) 54 (see FIG. 1) for holding the image sensor 51 and transmitting / receiving an electric signal thereof, and an opening for light incidence from the object side A housing 53 as a lens barrel made of a light shielding member is provided, and these are integrally formed.

  As shown in FIG. 2, the imaging element 51 has a photoelectric conversion part 51 a as a light receiving part in which pixels (photoelectric conversion elements) are two-dimensionally arranged at the center of the plane on the light receiving side. A signal processing circuit 51b is formed around the periphery. 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 it 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 includes a support flat plate 52a that supports the image sensor 51 and the housing 53 on the upper surface thereof, and a flexible substrate 52b having one end connected to the lower surface of the support flat plate 52a (the surface opposite to the image sensor 51). It has.

  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 imaging element 51 described above on the upper surface side and connected to the flexible substrate 52b on the lower surface side. .

  In FIG. 1, as described above, one end of the flexible substrate 52b is connected to the support flat plate 52a, and the support flat plate 52a and an external circuit (for example, an image pickup unit are mounted) via an external connection terminal 54 provided at the other end. Connected to the control circuit of the host device, and can be supplied with a voltage and a clock signal for driving the imaging device 51 from an external circuit, or can output a digital YUV signal to the external circuit. And 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 connection terminals 54 with respect to the support flat plate 52a.

  In FIG. 2, the housing 53 is fixedly disposed on the surface of the support plate 52 a of the substrate 52 on which the image sensor 51 is provided so as to cover the image sensor 51. That is, the housing 53 is formed in a cylindrical shape with a flange having a wide opening so that a portion on the image pickup device 51 side surrounds the image pickup device 51 and the other end portion having a small opening, and the image pickup is performed on the support plate 52a. The end on the element 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 housing 53 is used with the other end provided with a small opening (opening portion for light incidence) facing the object side, and inside the housing 53, between the imaging lens 10 and the imaging element 51, An IR (infrared) cut filter F is fixedly arranged.

  The imaging lens 10 includes, in order from the object side, a first lens L1 having a positive refractive power and a convex surface facing the object side, an aperture stop S, a meniscus shape having a positive refractive power and a convex surface facing the image side. The second lens L2 includes a third lens L3 having negative refractive power and a concave surface facing the image side, and has a function of forming a subject image on the image sensor. 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.

  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 first lens L1. The aperture stop S is a member that determines the F number of the entire imaging lens system.

  The lenses L1 and L2 are held by a lens frame 55, and the lens L3 is held by a lens frame 56. The lens frames 55 and 56 arranged in series are abutted against the flange of the casing 53 in a state where the optical axes thereof coincide with the center line of the casing 53, so that each lens L <b> 1 is placed inside the casing 53. ˜L3 can be positioned at a predetermined optical axis position. The lens and the lens frame may be integrally formed.

  Although not shown, these lenses L1, L2, and L3 are set to an effective diameter range having a function as an imaging lens from each center to a predetermined range, for example, and an outer portion as the imaging lens. It may be set to a flange portion that does not function. In this case, each lens L 1, L 2, L 3 can be held inside the casing 53 by fitting the outer periphery of the flange portion into a predetermined position of the casing 53. The IR cut filter F is a member formed in, for example, a substantially rectangular shape or a circular shape.

  In recent years, for the purpose of downsizing the entire imaging unit 50, 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. Yes. 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. Note that when the imaging unit 50 wants to suppress the image point position variation of the entire imaging lens system when the temperature changes, the first lens L1 may be a glass mold lens.

  Furthermore, although illustration is omitted, a light shielding mask may be disposed between each of the second lens L2 and the third lens L3, and in this case, imaging of the third lens L3 close to the solid-state imaging device. By preventing unnecessary light from entering the outside of the lens effective diameter, it is possible to suppress the occurrence of ghost and flare.

  The operation 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 housing 53 is provided on the back surface of the mobile phone 100 (see FIG. 3B), and is disposed at a position corresponding to the lower side of the liquid crystal display unit.

  The external connection terminal 54 (arrow in FIG. 4) 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. System program for input unit 60, liquid crystal display unit 70 for displaying captured images in addition to predetermined data, wireless communication unit 80 for realizing various information communications with an external server, and mobile phone 100 Storage unit (ROM) 91 storing necessary data such as various processing programs and terminal IDs, various processing programs and data executed by the control unit 101, or processing data, or imaging data by the imaging unit 50 Etc. are used as a work area for temporarily storing and the like, and a temporary storage part (RAM) 92 is provided.

  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 externally as video information via the wireless communication unit 80. Sent to.

(Example)
Examples of imaging lenses suitable for the above-described embodiments will be described below. 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 imaging device R: Radius of curvature D: Axial distance Nd: Refractive index νd of lens material with respect to d-line: Lens material Abbe number of

  In each embodiment, the shape of the aspheric surface is expressed by the following “Equation 1” where the vertex of the surface is the origin, the X axis is taken in the optical axis direction, and the height in the direction perpendicular to the optical axis is h.

Example 1
Tables 1 and 2 show lens data of the imaging lens according to the first example.

In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻⁰² ) is expressed using E (for example, 2.5E-02).

  5 is a cross-sectional view of the imaging lens of Example 1. FIG. In the figure, L1 is a first lens, L2 is a second lens, L3 is a third lens, and S is an aperture stop. Further, F is a parallel plate assuming an optical low-pass filter, an IR cut filter, and the like, and 51a is a photoelectric conversion unit of the image sensor 51. FIG. 6 is an aberration diagram (spherical aberration (a), astigmatism (b), distortion aberration (c), meridional coma aberration (d)) relating to the imaging lens of Example 1. In the following aberration diagrams, in the spherical aberration diagram and the meridional coma aberration diagram, the solid line represents the d line and the dotted line represents the g line, and in the astigmatism diagram, the solid line represents the sagittal image plane and the dotted line represents the meridional image plane. It shall represent.

(Example 2)
Tables 3 and 4 show lens data of the imaging lens according to Example 2.

  FIG. 7 is a cross-sectional view of the imaging lens of 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. Further, F is a parallel plate assuming an optical low-pass filter, an IR cut filter, and the like, and 51a is a photoelectric conversion unit of the image sensor 51. FIG. 8 is an aberration diagram of Example 2 (spherical aberration (a), astigmatism (b), distortion (c), and meridional coma aberration (d)).

(Example 3)
Tables 5 and 6 show lens data of the imaging lens according to Example 3.

  FIG. 9 is a cross-sectional view of the imaging lens of Example 3. In the figure, L1 is a first lens, L2 is a second lens, L3 is a third lens, S is an aperture stop, F is a parallel plate such as an optical low-pass filter or IR cut filter, and CG is an image sensor. 51 is a parallel plate assuming 51 sealing glass, and 51 a is a photoelectric conversion part of the image sensor 51. FIG. 10 is an aberration diagram of Example 3 (spherical aberration (a), astigmatism (b), distortion (c), and meridional coma (d)).

Example 4
Tables 7 and 8 show lens data of the imaging lens according to Example 4.

  FIG. 11 is a cross-sectional view of the imaging lens of Example 4. In the figure, L1 is a first lens, L2 is a second lens, L3 is a third lens, S is an aperture stop, and F is an optical low-pass filter, an IR cut filter, a seal glass for a solid-state image sensor, or the like. Reference numeral 51 a denotes a photoelectric conversion unit of the image sensor 51. FIG. 12 is an aberration diagram of Example 4 (spherical aberration (a), astigmatism (b), distortion (c), and meridional coma aberration (d)).

(Example 5)
Tables 9 and 10 show lens data of the imaging lens according to Example 5.

  FIG. 13 is a cross-sectional view of the imaging lens of Example 5. In the figure, L1 is a first lens, L2 is a second lens, L3 is a third lens, S is an aperture stop, and F is an optical low-pass filter, an IR cut filter, a seal glass for a solid-state image sensor, or the like. Reference numeral 51 a denotes a photoelectric conversion unit of the image sensor 51. FIG. 14 is an aberration diagram of Example 5 (spherical aberration (a), astigmatism (b), distortion (c), and meridional coma aberration (d)).

  Table 11 shows values of the respective examples corresponding to the respective conditional expressions.

  In the above-described Examples 1, 2, 3, 4, and 5, 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 formed of a polycarbonate plastic material and has a saturated water absorption rate of 0.4% or less. Plastic lenses have a larger saturated water absorption rate than glass lenses, so if there is a sudden change in humidity, a non-uniform distribution of water absorption will occur transiently, and the refractive index will not be uniform and good imaging performance will be obtained. There is a tendency to disappear. In order to suppress performance deterioration due to humidity change, it is desirable to use a plastic material having a saturated water absorption rate of 0.7% or less.

  Further, since the plastic material has a large change in 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 can be used when the ambient temperature changes greatly. There is a risk that the image point position of the entire system will fluctuate. 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 (for example, a glass mold lens) formed of a glass material, 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 to some extent, thereby reducing this temperature characteristic problem. Can do. When a glass mold lens is used, it is desirable to use a glass material having a glass transition point (Tg) of 400 ° C. or lower 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 dependency of the refractive index is obtained. For example, by dispersing fine particles of niobium oxide (Nb ₂ 0 ₅ ) in acrylic, the refractive index change due to temperature change can be reduced. In this embodiment, by using a plastic material in which such inorganic particles are dispersed in one of the two positive lenses (L1, L2) or in all the lenses (L1, L2, L3), It is possible to suppress image point position fluctuations when the temperature of the entire imaging lens system changes.

  In the present embodiment, the principal ray incident angle of the light beam incident on the imaging surface of the solid-state imaging device is not necessarily designed to be sufficiently small in the periphery of the imaging surface. However, recent techniques have made it possible to reduce shading by reviewing the arrangement of the color filters of the solid-state imaging device and the on-chip microlens array. Specifically, if the pitch of the arrangement of the color filters and the on-chip microlens array is set slightly smaller than the pixel pitch of the image pickup surface of the image pickup device, the color filter or Since the on-chip microlens array is shifted to the optical axis side of the imaging lens, the obliquely incident light beam can be efficiently guided to the light receiving portion of each pixel. Thereby, the shading which generate | occur | produces with a solid-state image sensor can be restrained small. The present embodiment is a design example in which the miniaturization is sought for the amount that the demand is relaxed.

It is a perspective view of the imaging unit 50 concerning this Embodiment. 3 is a diagram schematically showing a cross section along the optical axis of an imaging optical system of the imaging unit 50. FIG. It is the front view (a) of the mobile phone to which the imaging unit is applied, and the rear view (b) 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. 3 is a cross-sectional view in the optical axis direction of the imaging lens of Example 1. FIG. FIG. 4 is an aberration diagram of Example 1 (spherical aberration (a), astigmatism (b), distortion (c), and meridional coma (d)). FIG. 6 is a cross-sectional view in the optical axis direction of the imaging lens of Example 2. FIG. 6 is an aberration diagram of Example 2 (spherical aberration (a), astigmatism (b), distortion (c), and meridional coma (d)). 6 is a cross-sectional view in the optical axis direction of the imaging lens of Embodiment 3. FIG. 6 is an aberration diagram of Example 3 (spherical aberration (a), astigmatism (b), distortion (c), and meridional coma (d)). 6 is a cross-sectional view in the optical axis direction of an imaging lens of Example 4. FIG. FIG. 6 is an aberration diagram of Example 4 (spherical aberration (a), astigmatism (b), distortion (c), and meridional coma (d)). 6 is a cross-sectional view in the optical axis direction of the imaging lens of Example 5. FIG. FIG. 6 is an aberration diagram of Example 5 (spherical aberration (a), astigmatism (b), distortion (c), and meridional coma (d)).

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Imaging lens 50 Imaging unit 51 Imaging element 51a Photoelectric conversion part 51b Signal processing circuit 52 Board | substrate 52a Support flat plate 52b Flexible board 53 Case 54 External connection terminal 55 Mirror frame 56 Mirror frame 60 Input part 70 Liquid crystal display part 80 Wireless communication part 91 Storage unit 92 Storage unit 100 Mobile phone 101 Control unit CG Seal glass F Filters L1 to L3 Lens S Aperture stop W Wire

Claims (9)

A single-focus imaging lens that forms a subject image on a solid-state imaging device,
In order from the object side, a first lens having a positive refractive power and 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, negative refraction Ri Do a third lens having a concave surface facing the image has a force side, an image pickup lens satisfies the conditional expression below.
0.20 <R1 / f <0.42 (1)
0.15 <D2 / f <0.30 (2 ′)
However,
R1: curvature radius D2 of the object side surface of the first lens D2: air space on the axis of the first lens and the second lens f: focal length of the entire imaging lens system The imaging lens according to claim 1, wherein the following conditional expression is satisfied.
0.23 <R1 / f <0.38 (1 ′) The imaging lens according to claim 1 or 2, characterized by satisfying the following conditional expression.
−5 <P _air / P ₀ <−1.3 (3)
However,
P ₀ : refractive power of the entire imaging lens system P _air : refractive power of a so-called air lens formed by the image side surface (R2) of the first lens and the object side surface (R3) of the second lens, and The refractive power is the reciprocal of the focal length, and the P _air can be obtained by the following equation (4).
P _air = (1-N1) / R2 + (N2-1) / R3-{((1-N1) · (N2-1)) / (R2 · R3)} · D2 (4)
However,
N1: Refractive index N2 with respect to d line of the first lens R2: Refractive index R2 with respect to d line of the second lens R2: Radius of curvature R3 of the image side surface of the first lens D2: Radius of curvature D2 of the object side surface of the second lens: Air spacing on the axis of the first lens and the second lens The imaging lens according to any one of claims 1 to 3, characterized by satisfying the following conditional expression.
−2.0 <f3 / f <−0.4 (5)
However,
f3: focal length of the third lens f: focal length of the entire imaging lens system The imaging lens according to claim 4 , wherein the third lens has a biconcave shape. The imaging lens according to any one of claims 1 to 5, characterized by satisfying the following conditional expression.
20 <{(ν1 + ν2) / 2} −ν3 <65 (6)
However,
ν1: Abbe number of the first lens ν2: Abbe number of the second lens ν3: Abbe number of the third lens Said first lens, said second lens, and an imaging lens according to any one of claims 1 to 6, wherein the third lens is characterized in that it is formed from a plastic material. A solid-state imaging device including a photoelectric conversion unit;
An imaging lens according to any one of claims 1 to 7 , which forms 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 blocking member having an opening for light incidence from the object side,
The imaging unit, wherein the imaging unit has a height in the optical axis direction of the imaging lens of 10 [mm] or less. A portable terminal comprising the imaging unit according to claim 8 .

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