JP2007293176A - Imaging lens, imaging apparatus, and personal digital assistant equipped with imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging lens whose back focus is short, which is compact, whose aberration is satisfactorily corrected, and which is suitable for a compact solid-state imaging device. <P>SOLUTION: The imaging lens to form a subject image on the solid-state imaging device comprises an aperture diaphragm, a first biconvex lens having positive refractive power, an infrared cut filter and a second meniscus lens having positive refractive power and turning its convex surface to an object side in order from the object side, and the first lens and the second lens respectively have at least one aspherical surface. The imaging lens satisfies a following conditional expression: 0.7<DA/fB<2.0, provided that DA: distance from the image side surface of the first lens to the object side surface of the second lens, and fB: back focus of the entire system. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an imaging lens, and more particularly to an imaging lens suitable for a small and thin imaging device built in a portable terminal.

  Conventionally, a small and thin imaging device is mounted on a portable terminal which is a small and thin electronic device such as a mobile phone or a PDA (Personal Digital Assistant), thereby enabling not only an image to be transmitted to a remote place but also an image. Information can also be transmitted between each other.

  As an imaging device used in these imaging devices, a solid-state imaging device such as a CCD (Charged Coupled Device) type image sensor or a CMOS (Complementary Metal Oxide Semiconductor) type image sensor is used.

  In recent years, in these portable terminals, the number of pixels and the size of the image sensor have been increased by reducing the pixel pitch of the image sensor so that a small and high-quality image can be obtained. Yes.

  On the other hand, even in an image sensor with a relatively small number of pixels, the size of the image sensor has become very small due to the small pixel pitch. For this reason, there is an increasing demand for an imaging lens having sufficient performance in an imaging apparatus equipped with such an imaging device having a relatively small number of pixels and having a small size and a small number of components.

As an imaging lens mounted on a small imaging device, it is generally preferable to use a two-lens configuration lens that is more advantageous than a single lens lens and that is advantageous for downsizing compared to a three-lens configuration lens. For example, the following patent publications are disclosed.
JP 2004-4620 A JP 2004-252067 A JP 2004-246168 A

  However, although the imaging lens described in Patent Document 1 and Patent Document 2 has a two-lens configuration and is downsized, an infrared cut filter is arranged between the final lens and the imaging element. For this reason, the back focus is long and the entire length of the imaging lens is large. Moreover, it cannot be said that the performance required for an image sensor with a small pixel pitch is sufficiently satisfied, and there is room for improvement.

  The imaging lens described in Patent Document 3 is designed to be downsized by shortening the back focus with a two-lens configuration, but for the configuration in which the infrared cut filter is disposed between the final lens and the imaging element, The back focus cannot be said to be sufficiently short, and there is room for improvement. Moreover, it cannot be said that the performance required for an image sensor with a small pixel pitch is sufficiently satisfied, and further improvement is desired.

  The present invention has been made in view of such a problem, and has an imaging lens suitable for a small solid-state imaging device having a short back focus, a small size, and favorable correction of various aberrations, an imaging device having the imaging lens, and An object is to propose a portable terminal equipped with the imaging device.

The object is achieved by the invention described below.
1. An imaging lens for forming a subject image on a solid-state imaging device, in order from the object side, an aperture stop, a first biconvex lens having a positive refractive power, an infrared cut filter, and a positive refractive power And a meniscus second lens having a convex surface facing the object side, and each of the first lens and the second lens has at least one aspheric surface and satisfies the following conditional expression: An imaging lens characterized by.

0.7 <DA / fB <2.0 (1)
However,
DA: Distance from the image side surface of the first lens to the object side surface of the second lens fB: Back focus of the entire system 2. The imaging lens according to 1, wherein the following conditional expression is satisfied.

-0.8 <(R1 + R2) / (R1-R2) <0.8 (2)
However,
R1: radius of curvature of the object side surface of the first lens R2: radius of curvature of the image side surface of the first lens 3. The imaging lens according to 1 or 2, wherein the following conditional expression is satisfied.

0 <f1 / f2 <0.7 (3)
However,
f1: focal length of the first lens f2: focal length of the second lens The imaging lens according to any one of claims 1 to 3, wherein the first lens and the second lens are made of a plastic material.
5). An imaging lens for forming a subject image on a solid-state imaging device, in order from an object side, an aperture stop, a first biconvex lens having a positive refractive power, and an object side having a positive refractive power And a second lens having a meniscus shape with a convex surface facing the surface, and each of the first lens and the second lens has at least one aspherical surface and satisfies the following conditional expression: lens.

0.6 <DB / f <1.0 (4)
0 <f1 / f2 <0.7 (5)
However,
DB: distance from the image side surface of the first lens to the image side surface of the second lens f: focal length f1 of the entire system f1: focal length f2 of the first lens f: focal length of the second lens 6. The imaging lens according to 5, wherein an infrared cut filter is disposed between the first lens and the second lens, and satisfies the following conditional expression.

0.7 <DA / fB <2.0 (6)
However,
DA: Distance from the image side surface of the first lens to the object side surface of the second lens fB: Back focus of the entire system The imaging lens according to 5 or 6, wherein the following conditional expression is satisfied.

-0.8 <(R1 + R2) / (R1-R2) <0.8 (7)
However,
R1: radius of curvature of the object side surface of the first lens R2: radius of curvature of the image side surface of the first lens The imaging lens according to any one of claims 5 to 7, wherein the first lens and the second lens are made of a plastic material.
9. While holding the solid-state imaging device, a substrate on which a connection terminal portion for transmitting and receiving electrical signals is formed, the imaging lens according to any one of 1 to 8, and the imaging lens are included, An imaging apparatus in which a housing made of a light-shielding material having an opening for light incidence from the object side is integrally formed, and the height of the imaging lens in the optical axis direction is 5 mm or less An imaging device characterized by being:
A portable terminal comprising the imaging device according to 10.9.

・ Claim 1
According to the first aspect of the present invention, it is possible to obtain an image pickup lens that is small and has good aberration correction.

  When the image pickup device is downsized, the focal length of the image pickup lens is shortened to secure a necessary angle of view, and the back focus is also shortened accordingly. As in the past, when an infrared cut filter is placed between the final lens and the image sensor, it is necessary to increase the back focus even though the focal length is shortened. Will not be sufficient and will cause performance degradation.

  Accordingly, when the infrared cut filter is arranged between the first lens and the second lens, it is not necessary to lengthen the back focus, so that the field curvature can be easily corrected and good performance can be obtained.

  In recent years, a film-like thin infrared cut filter has been developed. For example, Sumitomo 3M Co., Ltd. has commercialized a reflective filter having a thickness of 90 μm formed of an organic material having a multilayer structure. Since it is much thinner than conventional infrared absorption glass filters and vapor-deposited multilayer glass filters, it is suitable for an imaging lens with a short focal length for a small solid-state imaging device. Moreover, it can respond to a free shape such as a rectangle, a round shape, a hole, a rib, and the like, and is advantageous for being arranged between lenses.

  However, the reflection type infrared cut filter is not preferable because the half-value wavelength for cutting infrared rays shifts when the incident angle on the filter surface increases. Therefore, it is necessary to suppress the angle of the light beam that exits the image side surface of the first lens. The angle is represented by an angle formed between the principal ray of the light beam and the optical axis, and is zero when the principal ray is located on the optical axis or parallel to the optical axis. In general, it is said that the angle of incidence on the filter surface is preferably 30 ° or less.

  When the first lens is a biconvex lens, the image side surface of the first lens has a positive refracting action, so that it is possible to suppress the jumping of the off-axis light beam. As a result, the angle of the emitted light beam from the image side surface of the first lens can be reduced, so that the incident angle of the principal ray to the infrared cut filter can be reduced.

  Furthermore, by arranging the aperture stop closest to the object side and making the second lens a meniscus lens having a convex surface facing the object side, the exit pupil can be separated further, so the imaging surface of the solid-state image sensor It becomes possible to suppress the chief ray incident angle of the light beam focused on the peripheral portion.

  Further, by using at least one aspherical surface for each of the first lens and the second lens, better aberration correction can be performed. Using an aspherical surface for the first lens is effective in correcting spherical aberration and coma. On the other hand, since the second lens is arranged on the most image side away from the aperture stop, there is a difference in passing height between the on-axis light beam and the off-axis light beam at the periphery of the screen. Various aberrations in the periphery of the screen such as field curvature and distortion can be corrected well.

  Conditional expression (1) is a conditional expression for appropriately setting the distance between the first lens and the second lens and the back focus. By exceeding the lower limit, a sufficient interval for inserting the infrared cut filter can be secured, and correction of field curvature becomes easy. On the other hand, since the back focus can be prevented from being shortened by falling below the upper limit, an increase in the diameter of the second lens can be prevented. It becomes possible to suppress the chief ray incident angle of the light beam that forms an image on the periphery of the imaging surface of the solid-state imaging device.

  It is more desirable to use the following equation instead of conditional equation (1).

0.7 <DA / fB <1.5
・ Claim 2
Conditional expression (2) is a conditional expression for appropriately setting the radius of curvature between the object side surface and the image side surface of the first lens. By exceeding the lower limit, the radius of curvature of the object side surface can be prevented from becoming too small compared to the radius of curvature of the image side surface, and the refractive power of the image side surface can be ensured appropriately. It becomes possible to keep the angle small. As a result, the incident angle to the infrared cut filter is not increased, and good performance can be ensured. On the other hand, by falling below the upper limit, the radius of curvature of the object side surface can be prevented from becoming too large compared to the radius of curvature of the image side surface, and the refracting power of the object side surface can be secured appropriately, resulting in a short back focus and imaging. An increase in the total lens length can be suppressed.

  It is more desirable to use the following equation instead of conditional equation (2).

-0.75 <(R1 + R2) / (R1-R2) <0.6
・ Claim 3
Conditional expression (3) is a conditional expression for appropriately setting the focal lengths of the first lens and the second lens. By exceeding the lower limit, it is possible to prevent the principal point of the entire imaging lens system from passing on the image side, so that the back focus does not become too short, and the principal ray of the light beam that forms an image on the periphery of the imaging surface of the solid-state imaging device It is possible to keep the incident angle small. On the other hand, by being below the upper limit value, the main point of the entire imaging lens system can be brought closer to the object side, and the back focus can be shortened appropriately, so that the overall length of the imaging lens can be shortened.

  It is more desirable to use the following equation instead of conditional equation (3).

0 <f1 / f2 <0.5
・ Claim 4
If all the lenses constituting the imaging lens are made of plastic lenses by injection molding, it is advantageous for downsizing and cost reduction of the imaging lens.

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.
・ Claim 5
According to the fifth aspect of the present invention, it is possible to obtain an image pickup lens that is small and has a well-corrected aberration.

  In particular, by making the first lens a biconvex lens, it becomes easy to give a strong refractive power compared to the second lens, so that the principal point of the entire imaging lens system can be brought closer to the object side. Thus, the entire length of the imaging lens can be reduced.

  Furthermore, by arranging the aperture stop closest to the object side and making the second lens a meniscus lens with a convex surface facing the object side, the exit pupil can be further distant, so that the imaging surface of the solid-state image sensor It becomes possible to suppress the chief ray incident angle of the light beam focused on the peripheral portion.

  Further, by using at least one aspherical surface for each of the first lens and the second lens, better aberration correction can be performed. Using an aspherical surface for the first lens is effective in correcting spherical aberration and coma. On the other hand, since the second lens is arranged on the most image side away from the aperture stop, there is a difference in passing height between the on-axis light beam and the off-axis light beam at the periphery of the screen. Various aberrations in the periphery of the screen such as field curvature and distortion can be corrected well.

  Conditional expression (4) is a conditional expression for appropriately setting the distance DB from the first lens image side surface to the second lens image side surface. By exceeding the lower limit, it is avoided that DB becomes extremely small, and correction of field curvature and distortion becomes easy. On the other hand, when the value is below the upper limit, the DB is prevented from becoming excessively large, and the entire length of the imaging lens can be reduced while ensuring the necessary lens thickness and back focus.

  It is more desirable to use the following equation instead of conditional equation (4).

0.6 <DB / f <0.8
Conditional expression (5) is a conditional expression for appropriately setting the focal lengths of the first lens and the second lens. By exceeding the lower limit, it is possible to prevent the principal point of the entire imaging lens system from passing on the image side, so that the back focus does not become too short, and the principal ray of the light beam that forms an image on the periphery of the imaging surface of the solid-state imaging device It is possible to keep the incident angle small. On the other hand, by being below the upper limit value, the main point of the entire imaging lens system can be brought closer to the object side, and the back focus can be shortened appropriately, so that the overall length of the imaging lens can be shortened.

  It is more desirable to use the following equation instead of conditional equation (5).

0 <f1 / f2 <0.5
・ Claim 6
When the image sensor is downsized, the focal length of the lens is shortened to ensure a necessary angle of view, and the back focus is also shortened accordingly. As in the past, when an infrared cut filter is placed between the final lens and the image sensor, it is necessary to increase the back focus even though the focal length is shortened. Will not be sufficient, leading to performance degradation.

  If the infrared cut filter is arranged between the first lens and the second lens, it is not necessary to lengthen the back focus, so that the field curvature can be easily corrected and good performance can be obtained.

  Conditional expression (6) is a conditional expression for appropriately setting the distance between the first lens and the second lens and the back focus. By exceeding the lower limit, a sufficient interval for inserting the infrared cut filter can be secured, and correction of field curvature becomes easy. On the other hand, since the back focus can be prevented from being shortened by falling below the upper limit, an increase in the diameter of the second lens can be prevented. It becomes possible to suppress the chief ray incident angle of the light beam that forms an image on the periphery of the imaging surface of the solid-state imaging device.

  It is more desirable to use the following equation instead of conditional equation (6).

0.7 <DA / fB <1.5
・ Claim 7
The effect is the same as that of the second aspect.
・ Claim 8
The effect is the same as that of the fourth aspect.
・ Claim 9
According to the ninth aspect, it is possible to obtain a smaller and higher quality image pickup apparatus.

Here, the “opening portion for light incidence” does not necessarily include a space such as a hole but also includes a portion in which a region capable of transmitting incident light from the object side is formed. Further, “the height of the imaging device in the optical axis direction of the imaging lens is 5 mm or less” means that a substrate on which a connection terminal unit for holding a solid-state imaging device and transmitting and receiving an electrical signal is formed, and an imaging lens And the total length along the optical axis direction of an imaging apparatus including a housing that includes an imaging lens and is formed of a light-shielding material having an opening for light incidence from the object side. Therefore, for example, when a housing is provided on the surface of the substrate and an electronic component or the like is mounted on the back surface of the substrate, the electronic component protruding on the back surface from the front end portion on the object side of the housing. This means that the distance to the tip is 5 mm or less.
・ Claim 10
According to the tenth aspect, it is possible to obtain a portable terminal capable of recording a smaller and higher quality image.

  That is, according to the present invention, it is possible to obtain an imaging apparatus and a portable terminal including a two-lens imaging lens that is suitable for a small imaging element and that has various aberrations corrected well.

  Hereinafter, the present invention will be described in detail with reference to embodiments, but the present invention is not limited thereto.

  FIG. 1 is a perspective view of an imaging apparatus 50 according to the present embodiment. FIG. 2 is a diagram schematically showing a cross section along the optical axis of the imaging lens of the imaging device 50 according to the present embodiment.

  As shown in FIG. 1 or FIG. 2, the imaging device 50 includes a CMOS type imaging device 51 as a solid-state imaging device having a photoelectric conversion unit 51a, and an imaging lens that forms a subject image on the photoelectric conversion unit 51a of the imaging device 51. 10, a housing 53 as a lens barrel made of a light-shielding member having an opening for light incidence from the object side, a support substrate 52 a that holds the image sensor 51, and an external connection terminal that transmits and receives electrical signals. And a flexible printed circuit board 52b having 54 (also referred to as an external connection terminal), which are integrally formed.

  As shown in FIG. 2, the image sensor 51 is formed with a photoelectric conversion unit 51a as a light receiving unit in which pixels (photoelectric conversion elements) are two-dimensionally arranged at the center of the light receiving side surface, and around it. A signal processing circuit 51b is formed. The signal processing circuit 51b includes a driving 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 large number of pads (not shown) are provided in the vicinity of the outer edge of the light receiving side surface of the image sensor 51, and are connected to the support substrate 52 a via bonding wires W. The image sensor 51 converts the signal charge from the photoelectric conversion unit 51a into an image signal such as a digital YUV signal and outputs the image signal to a predetermined circuit on the support substrate 52a through the bonding wire W. 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 pickup element is not limited to the above-described CMOS type image sensor, and may be one to which another one such as a CCD is applied.

  One end of the substrate 52 is connected to the other surface of the support substrate 52a (the surface opposite to the image sensor 51) of the hard support substrate 52a that supports the image sensor 51 and the housing 53 on one surface. It is comprised with the flexible printed circuit board 52b. The support substrate 52a is provided with a large number of signal transmission pads on both the front and back surfaces, and is connected to the imaging device 51 via bonding wires W on one surface and to the flexible printed circuit board 52b on the other surface. .

  As shown in FIG. 1, the flexible printed circuit board 52b is connected to the support substrate 52a at one end and is connected to the support substrate 52a and an external circuit (not shown) via an external connection terminal 54 provided at the other end (for example, A control circuit included in a host device on which the image pickup apparatus is mounted), a voltage and a clock signal for driving the image pickup device 51 are supplied from an external circuit, and a digital YUV signal is output to the external circuit. It is possible to do. Further, the flexible printed circuit board 52b has flexibility and an intermediate portion is deformed to give a degree of freedom to the orientation and arrangement of the external connection terminals 54 with respect to the support board 52a.

  As shown in FIG. 2, the housing 53 is fixedly disposed so as to cover the image sensor 51 on the surface of the support substrate 52 a on the image sensor 51 side. In other words, the housing 53 is formed in a cylindrical shape with a flange having a wide opening on the image pickup device 51 side so as to surround the image pickup device 51 and being in contact with and fixed to the support substrate 52a, and the other end portion having a small opening. .

  The imaging lens 10 is fixedly disposed inside the housing 53.

  The imaging lens 10 has, in order from the object side, an aperture stop S, a positive refractive power, a biconvex first lens L1, an infrared cut filter F, a positive refractive power, and a convex surface facing the object side. The second lens L2 having a meniscus shape is configured to form a subject image on the photoelectric conversion surface 51a of the image sensor 51. 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 and L2.

  The first lens L <b> 1, the second lens L <b> 2, and the infrared cut filter F that constitute the imaging lens 10 are held by a lens frame 55. The housing 53 includes the lens frame 55 and the imaging lens 10 held by the lens frame 55, and the lens frame 55 is a flange portion that is fitted to the housing 53 on the outer periphery and has a small opening of the housing 53. It is abutted and positioned.

  Further, although not shown, a fixed diaphragm for cutting unnecessary light may be disposed between the first lens L1 and the second lens L2.

  FIG. 3 is an external view of a mobile phone 100 that is an example of a mobile terminal including the imaging device 50.

  In the mobile phone 100 shown in the figure, an upper casing 71 as a case having display screens D1 and D2 and a lower casing 72 having an operation button 60 as an input unit are connected via a hinge 73. Yes. The imaging device 50 is built below the display screen D <b> 2 in the upper casing 71, and is arranged so that the imaging device 50 can capture light from the outer surface side of the upper casing 71.

  Note that the position of the imaging device may be disposed above or on the side of the display screen D2 in the upper casing 71. Of course, the mobile phone is not limited to a folding type.

  FIG. 4 is a control block diagram of the mobile phone 100.

  As shown in the figure, an external connection terminal 54 (shown by an arrow) of the imaging device 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.

  On the other hand, the mobile phone 100 controls each part in an integrated manner, and also executes a control part (CPU) 101 that executes a program corresponding to each process, an operation button 60 that is an input part for inputting a number and the like, Display screens D1 and D2 for displaying predetermined data and captured images, a wireless communication unit 80 for realizing various information communications with an external server, a system program for mobile phone 100, various processing programs, and a terminal A storage unit (ROM) 91 that stores necessary data such as an ID, and various processing programs and data executed by the control unit 101 or processing data, image data from the imaging device 50, and the like are temporarily stored. Or a temporary storage unit (RAM) 92 used as a work area.

  Further, the image signal input from the imaging device 50 is stored in the storage unit 91 by the control unit 101 of the mobile phone 100, or displayed on the display screens D1 and D2, and further via the wireless communication unit 80. It is transmitted to the outside as image information.

  Examples of the imaging lens applied to the above embodiment will be described below. Symbols used in each example are as follows.

f: Focal length of the entire imaging lens fB: Back focus F: F number 2Y: Diagonal length of the imaging surface of the solid-state imaging device R: Radius of curvature D: Spatial distance between axes Nd: Refractive index of lens material with respect to d-line νd: Lens material In each example, the shape of the aspherical surface is expressed by the following mathematical formula 1, where the vertex of the surface is the origin, the X axis is the optical axis direction, and the height in the direction perpendicular to the optical axis is h.

However,
Ai: i-th order aspherical coefficient R: radius of curvature K: conical constant In the following (including lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻⁰² ) is changed to E (for example, 2.5E). -02). The surface number of the lens data was given in order with the object side surface of the first lens as one surface.
Example 1
Table 1 shows lens data of the imaging lens in Example 1, and Table 2 shows aspheric coefficients.

f = 1.70
fB = 0.60
F = 2.88
2Y = 2.24

  FIG. 5 is a cross-sectional view of the imaging lens in the first embodiment. In the figure, S is an aperture stop, L1 is a first lens, F is an infrared cut filter, L2 is a second lens, and 51 is an image sensor.

  FIG. 6 is an aberration diagram (spherical aberration, astigmatism, distortion) of the imaging lens in the first example.

  The first lens L1 and the second lens L2 are made of a polyolefin-based plastic material and have a saturated water absorption rate of 0.01% or less.

  The image sensor 51 is assumed to be a 1/8 inch type, a pixel pitch of 2.8 μm, and 640 × 480 pixels.

  The incident angle of the principal ray on the infrared cut filter F is 26 ° or less.

  The change in the refractive index nd depending on the temperature of the plastic material is as shown in Table 3.

  The image pickup lens in Example 1 has an image point position fluctuation (back focus change amount (ΔfB)) of +0.009 (mm) when the temperature rises by +30 (° C.) with respect to room temperature 20 (° C.). The amount of change in back focus (ΔfB) when the temperature rises is obtained based on the refractive index change of the plastic lens shown in Table 3. This is because the image point position fluctuation at the time of temperature change is mainly due to the refractive index change of the plastic lens, the influence of the thermal expansion of the plastic lens at the time of temperature change and the influence of the thermal expansion of the lens barrel holding the lens. Is not taken into consideration.

  In general, the depth of focus is expressed by the following equation.

Depth of focus = ± F number × 2 × pixel pitch The depth of focus on the image sensor side assumed in the first embodiment is ± 0.016 (mm).

The image point position variation must be less than or equal to the depth of focus at the maximum. On the other hand, the imaging lens of Example 1 can reduce the image point position variation amount to about half of the focal depth amount, and there is no problem. can do.
(Example 2)
Table 4 shows lens data of the imaging lens in Example 2, and Table 5 shows aspheric coefficients.

f = 1.71
fB = 0.79
F = 2.88
2Y = 2.24

  FIG. 7 is a cross-sectional view of the imaging lens in the second embodiment. In the figure, S is an aperture stop, L1 is a first lens, F is an infrared cut filter, L2 is a second lens, and 51 is an image sensor.

  FIG. 8 is an aberration diagram (spherical aberration, astigmatism, distortion) of the imaging lens in the second embodiment.

  The first lens L1 and the second lens L2 are made of a polyolefin-based plastic material and have a saturated water absorption rate of 0.01% or less.

  The image sensor 51 is assumed to be a 1/8 inch type, a pixel pitch of 2.8 μm, and 640 × 480 pixels.

  The incident angle of the principal ray on the infrared cut filter F is 25 ° or less.

  The change in the refractive index nd depending on the temperature of the plastic material is as shown in Table 6.

The image pickup lens in Example 2 has an image point position fluctuation (back focus change amount (ΔfB)) of +0.009 (mm) when the temperature rises by +30 (° C.) with respect to room temperature 20 (° C.). The focal depth on the image sensor side assumed in the second embodiment is ± 0.016 (mm). On the other hand, the imaging lens of the second embodiment can reduce the image point position fluctuation amount to about half of the focal depth amount. Yes, and no problem.
(Example 3)
Table 7 shows lens data of the imaging lens in Example 3, and Table 8 shows aspheric coefficients.

f = 1.80
fB = 0.58
F = 2.88
2Y = 2.24

  FIG. 9 is a cross-sectional view of the imaging lens in the third embodiment. In the figure, S is an aperture stop, L1 is a first lens, F is an infrared cut filter, L2 is a second lens, and 51 is an image sensor.

  FIG. 10 is an aberration diagram (spherical aberration, astigmatism, distortion) of the imaging lens in the third example.

  The first lens L1 and the second lens L2 are made of a polyolefin-based plastic material and have a saturated water absorption rate of 0.01% or less.

  The image sensor 51 is assumed to be a 1/8 inch type, a pixel pitch of 2.8 μm, and 640 × 480 pixels.

  The incident angle of the principal ray on the infrared cut filter F is 25 ° or less.

  The change in refractive index nd depending on the temperature of the plastic material is as shown in Table 9.

In the image pickup lens in Example 3, the image point position fluctuation (back focus change amount (ΔfB)) when +30 (° C.) is raised with respect to room temperature 20 (° C.) is +0.010 (mm). The focal depth on the image sensor side assumed in the third embodiment is ± 0.016 (mm). On the other hand, the imaging lens of the third embodiment can reduce the image point position variation amount to about half of the focal depth amount. Yes, and no problem.
Example 4
Table 10 shows lens data of the imaging lens in Example 4, and Table 11 shows aspheric coefficients.

f = 1.80
fB = 0.64
F = 2.88
2Y = 2.24

  FIG. 11 is a cross-sectional view of the imaging lens in the fourth embodiment. In the figure, S is an aperture stop, L1 is a first lens, F is an infrared cut filter, L2 is a second lens, and 51 is an image sensor.

  FIG. 12 is an aberration diagram (spherical aberration, astigmatism, distortion) of the imaging lens in the fourth example.

  The first lens L1 and the second lens L2 are made of a polyolefin-based plastic material and have a saturated water absorption rate of 0.01% or less.

  The image sensor 51 is assumed to be a 1/8 inch type, a pixel pitch of 2.8 μm, and 640 × 480 pixels.

  The incident angle of the principal ray on the infrared cut filter F is 27 ° or less.

  The change in the refractive index nd depending on the temperature of the plastic material is as shown in Table 12.

In the imaging lens of Example 4, the image point position fluctuation (back focus change amount (ΔfB)) when +30 (° C.) is raised with respect to the normal temperature 20 (° C.) is +0.009 (mm). The focal depth on the image sensor side assumed in the fourth embodiment is ± 0.016 (mm). On the other hand, the imaging lens of the fourth embodiment can reduce the image point position variation amount to about half of the focal depth amount. Yes, and no problem.
(Example 5)
Table 13 shows the lens data of the imaging lens in Example 5, and Table 14 shows the aspheric coefficient.

f = 1.55
fB = 0.55
F = 2.88
2Y = 2.24

  FIG. 13 is a cross-sectional view of the imaging lens in the fifth embodiment. In the figure, S is an aperture stop, L1 is a first lens, F is an infrared cut filter, L2 is a second lens, and 51 is an image sensor.

  FIG. 14 is an aberration diagram of the image pickup lens in Example 5 (spherical aberration, astigmatism, distortion).

  The first lens L1 and the second lens L2 are made of a polyolefin-based plastic material and have a saturated water absorption rate of 0.01% or less.

  The image sensor 51 is assumed to be a 1/8 inch type, a pixel pitch of 2.8 μm, and 640 × 480 pixels.

The incident angle of the principal ray on the infrared cut filter F is 25 ° or less.
The change in refractive index nd depending on the temperature of the plastic material is as shown in Table 15.

In the imaging lens in Example 5, the image point position fluctuation (back focus change amount (ΔfB)) when +30 (° C.) is raised with respect to the normal temperature 20 (° C.) is +0.008 (mm). The focal depth on the image sensor side assumed in the fifth embodiment is ± 0.016 (mm). On the other hand, the imaging lens of the fifth embodiment can reduce the image point position fluctuation amount to about half of the focal depth amount. Yes, and no problem.
(Example 6)
Table 16 shows lens data of the imaging lens in Example 6, and Table 17 shows aspheric coefficients.

f = 1.56
fB = 0.52
F = 2.88
2Y = 2.24

  FIG. 15 is a cross-sectional view of the imaging lens in the sixth embodiment. In the figure, S is an aperture stop, L1 is a first lens, F is an infrared cut filter, L2 is a second lens, and 51 is an image sensor.

  FIG. 16 is an aberration diagram (spherical aberration, astigmatism, distortion) of the imaging lens in the sixth embodiment.

  The first lens L1 and the second lens L2 are made of a polyolefin-based plastic material and have a saturated water absorption rate of 0.01% or less.

  The image sensor 51 is assumed to be a 1/8 inch type, a pixel pitch of 2.8 μm, and 640 × 480 pixels.

  The incident angle of the principal ray on the infrared cut filter F is 23 ° or less.

  The change in the refractive index nd depending on the temperature of the plastic material is as shown in Table 18.

In the imaging lens in Example 6, the image point position fluctuation (back focus change amount (ΔfB)) when +30 (° C.) rises with respect to room temperature 20 (° C.) is +0.008 (mm). The focal depth on the image sensor side assumed in the sixth embodiment is ± 0.016 (mm). On the other hand, the imaging lens of the sixth embodiment can reduce the image point position fluctuation amount to about half of the focal depth amount. Yes, and no problem.
(Example 7)
Table 19 shows lens data of the imaging lens in Example 7, and Table 20 shows aspheric coefficients.

f = 1.71
fB = 0.59
F = 2.88
2Y = 2.24

  FIG. 17 is a cross-sectional view of the imaging lens in the seventh embodiment. In the figure, S is an aperture stop, L1 is a first lens, F is an infrared cut filter, L2 is a second lens, and 51 is an image sensor.

  FIG. 18 is an aberration diagram (spherical aberration, astigmatism, distortion) of the imaging lens in the seventh embodiment.

  The first lens L1 is formed of a polyolefin-based plastic material and has a saturated water absorption rate of 0.01% or less. The second lens L2 is made of a polycarbonate plastic material and has a saturated water absorption rate of 0.4%.

  The image sensor 51 is assumed to be a 1/8 inch type, a pixel pitch of 2.8 μm, and 640 × 480 pixels.

  The incident angle of the principal ray on the infrared cut filter F is 25 ° or less.

  The change in refractive index nd depending on the temperature of the plastic material is as shown in Table 21.

In the imaging lens in Example 7, the image point position fluctuation (back focus change amount (ΔfB)) when +30 (° C.) rises with respect to the normal temperature 20 (° C.) is +0.009 (mm). The focal depth on the image sensor side assumed in the seventh embodiment is ± 0.016 (mm). On the other hand, the imaging lens of the seventh embodiment can reduce the image point position variation amount to about half of the focal depth amount. Yes, and no problem.
(Example 8)
Table 22 shows the lens data of the imaging lens in Example 8, and Table 23 shows the aspheric coefficient.

f = 1.71
fB = 0.53
F = 2.88
2Y = 2.24

  FIG. 19 is a cross-sectional view of the imaging lens in the eighth embodiment. In the figure, S is an aperture stop, L1 is a first lens, F is an infrared cut filter, L2 is a second lens, and 51 is an image sensor.

  FIG. 20 is an aberration diagram (spherical aberration, astigmatism, distortion) of the imaging lens in the eighth embodiment.

  The first lens L1 is formed of a polyolefin-based plastic material and has a saturated water absorption rate of 0.01% or less. The second lens L2 is made of a polycarbonate plastic material and has a saturated water absorption rate of 0.4%.

  The image sensor 51 is assumed to be a 1/8 inch type, a pixel pitch of 2.8 μm, and 640 × 480 pixels.

  The incident angle of the principal ray on the infrared cut filter F is 24 ° or less.

  The change in the refractive index nd depending on the temperature of the plastic material is as shown in Table 24.

  In the imaging lens shown in Example 8, the image point position fluctuation (back focus change amount (ΔfB)) when +30 (° C.) is raised with respect to room temperature 20 (° C.) is +0.009 (mm). . The focal depth on the image sensor side assumed in the eighth embodiment is ± 0.016 (mm). On the other hand, the imaging lens of the eighth embodiment can reduce the image point position fluctuation amount to about half the focal depth amount. Yes, and no problem.

  Next, Table 25 shows values of the respective examples corresponding to the respective conditional expressions.

  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. It tends 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.

  Moreover, when using a glass mold lens, it is desirable to use the glass material whose glass transition point (Tg) is 400 degrees C or less. Thereby, consumption of a molding die can be prevented as much as possible, and die durability can be improved.

  In the present invention, the image point position fluctuation of the entire imaging lens system due to the temperature change of the refractive index of the plastic material assumes a very small imaging element of 1/8 inch type, so the focal length of the imaging lens is short. Although it is suppressed within the depth of focus as described above, it is desirable that the image point position fluctuation is preferably suppressed to half or less of the depth of focus.

  In recent years, it has been found that inorganic fine particles can be mixed in a plastic material, and the temperature change of the refractive index of the plastic material can be suppressed small. 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 as the temperature increases, but the refractive index of the inorganic particles increases as the temperature increases. Therefore, it is possible to make almost no change in the refractive index by using both of 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 O ₅ ) in acrylic, the refractive index change due to temperature change can be reduced.

  Also in the above-described embodiments, it is possible to use a plastic material in which such inorganic particles are dispersed, and it is possible to suppress the image point position fluctuation of the entire imaging lens system when the temperature changes.

  In the above-described embodiment, the chief 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 at the periphery of the imaging surface. However, with recent technology, shading can be reduced 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.

It is a perspective view of the imaging device concerning this embodiment. It is the figure which showed typically the cross section along the optical axis of the imaging lens of the imaging device which concerns on this Embodiment. It is an external view of a mobile phone which is an example of a mobile terminal provided with an imaging device. It is a control block diagram of a mobile phone. 3 is a cross-sectional view of an imaging lens in Embodiment 1. FIG. FIG. 6 is an aberration diagram (spherical aberration, astigmatism, distortion) of the imaging lens in Example 1. 6 is a cross-sectional view of an imaging lens in Example 2. FIG. FIG. 6 is an aberration diagram (spherical aberration, astigmatism, distortion) of the imaging lens in Example 2. 6 is a cross-sectional view of an imaging lens in Example 3. FIG. FIG. 10 is an aberration diagram (spherical aberration, astigmatism, distortion) of the imaging lens in Example 3. 6 is a cross-sectional view of an imaging lens in Embodiment 4. FIG. FIG. 10 is an aberration diagram (spherical aberration, astigmatism, distortion) of the imaging lens in Example 4. FIG. 6 is a cross-sectional view of an imaging lens in Example 5. FIG. 10 is an aberration diagram (spherical aberration, astigmatism, distortion) of the imaging lens in Example 5. 10 is a cross-sectional view of an imaging lens in Example 6. FIG. FIG. 10 is an aberration diagram (spherical aberration, astigmatism, distortion) of the imaging lens in Example 6. FIG. 10 is a cross-sectional view of an imaging lens in Example 7. FIG. 10 is an aberration diagram (spherical aberration, astigmatism, distortion) of the imaging lens in Example 7. 10 is a cross-sectional view of an imaging lens in Example 8. FIG. FIG. 10 is an aberration diagram (spherical aberration, astigmatism, distortion) of the imaging lens in Example 8.

Explanation of symbols

L1 First lens L2 Second lens F Infrared cut filter S Aperture stop 50 Imaging device 51 Imaging device 52 Substrate 53 Housing 55 Mirror frame

Claims (10)

An imaging lens for forming a subject image on a solid-state imaging device,
From the object side,
An aperture stop,
A biconvex first lens having positive refractive power;
An infrared cut filter,
A second meniscus lens having positive refractive power and having a convex surface facing the object side,
Each of the first lens and the second lens has at least one aspheric surface;
An imaging lens satisfying the following conditional expression:
0.7 <DA / fB <2.0 (1)
However,
DA: Distance from the image side surface of the first lens to the object side surface of the second lens fB: Back focus of the entire system The imaging lens according to claim 1, wherein the following conditional expression is satisfied.
-0.8 <(R1 + R2) / (R1-R2) <0.8 (2)
However,
R1: radius of curvature of the object side surface of the first lens R2: radius of curvature of the image side surface of the first lens The imaging lens according to claim 1, wherein the following conditional expression is satisfied.
0 <f1 / f2 <0.7 (3)
However,
f1: Focal length of the first lens f2: Focal length of the second lens The imaging lens according to claim 1, wherein the first lens and the second lens are made of a plastic material. An imaging lens for forming a subject image on a solid-state imaging device,
From the object side,
An aperture stop,
A biconvex first lens having positive refractive power;
A second meniscus lens having positive refractive power and having a convex surface facing the object side,
Each of the first lens and the second lens has at least one aspheric surface;
An imaging lens satisfying the following conditional expression:
0.6 <DB / f <1.0 (4)
0 <f1 / f2 <0.7 (5)
However,
DB: distance from the image side surface of the first lens to the image side surface of the second lens f: focal length f1 of the entire system f1: focal length f2 of the first lens f: focal length of the second lens An infrared cut filter is disposed between the first lens and the second lens,
The imaging lens according to claim 5, wherein the following conditional expression is satisfied.
0.7 <DA / fB <2.0 (6)
However,
DA: Distance from the image side surface of the first lens to the object side surface of the second lens fB: Back focus of the entire system The imaging lens according to claim 5 or 6, wherein the following conditional expression is satisfied.
-0.8 <(R1 + R2) / (R1-R2) <0.8 (7)
However,
R1: radius of curvature of the object side surface of the first lens R2: radius of curvature of the image side surface of the first lens The imaging lens according to claim 5, wherein the first lens and the second lens are made of a plastic material. A substrate on which a connection terminal portion for holding the solid-state imaging device and transmitting and receiving an electrical signal is formed, the imaging lens according to any one of claims 1 to 8, and the imaging lens included And a housing formed of a light-shielding material having an opening for light incidence from the object side, and an imaging device integrally formed,
An image pickup apparatus, wherein a height of the image pickup lens in an optical axis direction is 5 mm or less. A portable terminal comprising the imaging device according to claim 9.

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