JP4940704B2 - IMAGING LENS, IMAGING DEVICE, AND PORTABLE TERMINAL HAVING THE IMAGING DEVICE - Google Patents

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 not only providing voice information to a remote place. Image information can also be transmitted to each other.

  As an image pickup element used in these image pickup apparatuses, a solid-state image pickup element such as a CCD (Charge Coupled Device) type image sensor and a CMOS (Complementary Metal-Oxide Semiconductor) type image sensor is used.

  In recent years, with the widespread use of these portable terminals, an apparatus equipped with an imaging device using an imaging element having a high pixel number is being supplied to the market so that a higher quality image can be obtained. Some image pickup apparatuses use an image pickup lens composed of a plurality of lenses for the purpose of improving the resolution, corresponding to an image pickup element having a high pixel count.

  As an imaging lens used in a small and high-performance imaging apparatus having such a high-pixel imaging device, a four-lens imaging lens capable of achieving higher performance than a two- to three-lens configuration has been proposed. ing.

  As this four-lens imaging lens, in order from the object side, a first lens having a positive refractive power, a second lens having a negative refractive power, a third lens having a positive refractive power, and a first lens having a positive refractive power. A so-called reverse Ernostar type imaging lens that is configured with four lenses and aims at high performance is disclosed (for example, see Patent Document 1).

Further, in order from the object side, the first lens having positive refractive power, the second lens having negative refractive power, the third lens having positive refractive power, and the fourth lens having negative refractive power are imaged. A so-called telephoto type imaging lens that aims to reduce the total lens length (distance on the optical axis from the aperture stop to the image side focal point) is disclosed (for example, see Patent Document 2).
JP 2004-341010 A JP 2002-365530 A

  However, since the imaging lens described in Patent Literature 1 is an inverted Ernostar type, the fourth lens is a positive lens, and the fourth lens is a negative lens as in the telephoto type. Since the principal point position is on the image side and the back focus is long, this is a disadvantageous type for downsizing. Furthermore, one of the four lenses has a negative refractive power, and correction of the Petzval sum is difficult, and good performance cannot be secured at the periphery of the screen.

  In addition, the imaging lens described in Patent Document 2 has a problem in that the imaging angle of view is narrow and the aberration correction is insufficient, so that the number of pixels of the imaging element can be increased.

  Furthermore, if all the lenses that make up the imaging lens with priority given to cost, etc. are made of plastic lenses by injection molding, it is advantageous for miniaturization and cost reduction of the imaging lens. Since the refractive index change is large, when all the lenses are made of plastic lenses, the entire image point position varies depending on the temperature. In the so-called pan focus type imaging apparatus of the fixed focus type, there is a problem that the fluctuation of the image point position when the temperature changes cannot be ignored.

  In view of the above problems, the present invention is compatible with a high-pixel imaging device that is small in size and can secure a wide angle of view, that various aberrations are corrected well, and that image point position fluctuations during temperature changes can be kept small. The object is to obtain an imaging lens.

  Said subject is solved by the following structures.

1) An imaging lens for forming a subject image on a photoelectric conversion unit of a solid-state imaging device, in order from the object side, an aperture stop, a first lens having a positive refractive power, and a second having a negative refractive power. A lens, a third lens having a positive refractive power, a fourth lens having a negative refractive power,
The following conditional expression (1) is satisfied ,
The imaging lens, wherein the second lens satisfies the following conditional expression (3) .

0.8 <f ₁ /f<2.0 (1)
0 <(R ₃ + R ₄ ) / (R ₃ −R ₄ ) <2.5 (3)
However,
f ₁ : focal length of the first lens f: focal length of the entire imaging lens system
R ₃ : radius of curvature of the object side surface of the second lens
R ₄ : radius of curvature of the image side surface of the second lens 2) The third lens is an imaging lens of 1) that satisfies the following conditional expression (2).

0.3 <f ₃ /f<1.5 (2)
However,
f ₃ : focal length of the third lens f: focal length of the entire imaging lens system

3) The imaging lens according to 1) or 2) , wherein the fourth lens satisfies the following conditional expression (4):

0.15 <R ₈ /f<0.5 (4)
However,
R ₈ : radius of curvature of the image side surface of the fourth lens f: focal length of the entire imaging lens system
4) The imaging lens according to any one of 1) to 3) , wherein the first lens is formed of a glass material.

5) The imaging lens according to any one of 1) to 4) , wherein the second lens, the third lens, and the fourth lens are formed of a plastic material.

6) A substrate on which a connection terminal portion for holding a solid-state image sensor and transmitting / receiving an electric signal is formed; an imaging lens according to any one of 1) to 5) ; An imaging device integrally formed with a housing made of a light-shielding material having an opening for incident light from the side, wherein the height of the imaging device in the optical axis direction of the imaging lens is 10 (Mm) or less, The imaging device characterized by the above-mentioned.

7) A portable terminal comprising the imaging device of 6) .

  According to the first aspect of the invention, by adopting a telephoto type lens configuration, the principal point position of the optical system can be placed on the object side, and an imaging lens with a short overall length can be obtained. Furthermore, by using two negative lenses in the four-lens configuration, the number of surfaces that have a diverging effect can be increased, facilitating correction of Petzval sum, and good results up to the periphery of the screen while having a wide angle of view. An imaging lens that ensures image performance can be obtained.

  In addition, by disposing the aperture stop closest to the object side, the exit pupil position can be further distant, and the chief ray incident angle (principal ray and light) of the light beam that forms an image on the periphery of the imaging surface of the solid-state imaging device. The angle formed by the shaft can be kept small, and so-called telecentricity can be ensured. Even when a mechanical shutter is required, it is possible to obtain an imaging lens with a short overall length because it can be arranged closest to the object side.

  Conditional expression (1) sets the refractive power of the first lens appropriately. When the lower limit is exceeded, the refractive power of the first lens does not increase more than necessary, and the spherical aberration and coma aberration are reduced and improved. Can be suppressed. In addition, when the value is below the upper limit, the refractive power of the first lens is appropriately secured, and the entire length of the imaging lens can be shortened, and the size can be reduced.

  Conditional expression (1) is more preferably within the range of the following expression.

0.9 <f ₁ /f<1.5
Conditional expression (3) is a condition for appropriately setting the shape of the second lens. Within the range of this conditional expression, the second lens has a shape having a negative refractive power stronger on the image side surface than on the object side surface. The imaging lens of the present invention has a configuration in which the positive refractive power of the first lens is relatively weak and the positive refractive power of the third lens is relatively strong. Occurrence of chromatic aberration increases. Therefore, the second lens can reduce the occurrence of coma aberration and chromatic aberration in the entire lens system by allocating negative refractive power more strongly to the image side surface than to the object side surface.
Further, by exceeding the lower limit, the refractive power of the image side surface of the second lens can be increased, and correction of coma, curvature of field, astigmatism, and chromatic aberration can be easily performed. On the other hand, the curvature of the object side surface of the second lens becomes gentle, and the aberration of the off-axis light beam passing near the periphery of this surface can be suppressed. By falling below the upper limit value, it is possible to suppress the negative refracting power of the image side surface of the second lens from becoming too strong and correct aberrations in a balanced manner. In addition, the radius of curvature of the image-side surface does not become too small, and the shape has no problem in lens processing.
Conditional expression (3) is more preferably in the range of the following expression.
0 <(R ₃ + R ₄ ) / (R ₃ −R ₄ ) <2.0
Conditional expression (2) of the above invention 2) sets the refractive power of the third lens appropriately. By exceeding the lower limit, the refractive power of the third lens does not become excessive, the principal point of the optical system is arranged on the object side, and the total lens length can be reduced. On the other hand, since the positive refractive power of the third lens can be appropriately maintained by being below the upper limit, and as a result, the exit pupil position can be moved away from the solid-state image sensor toward the object side, the imaging surface of the solid-state image sensor The chief ray incident angle (the angle between the chief ray and the optical axis) of the light beam that forms an image on the peripheral portion can be kept small, and so-called telecentricity can be secured. 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.

  Conditional expression (2) is more preferably within the range of the following expression.

0.3 <f ₃ /f<1.0
Furthermore, in order to suppress the principal ray incident angle of the light beam focused on the imaging surface of the solid-state imaging device to 23 ° or less, conditional expression (2) is more preferably in the range of the following expression.

0.3 <f ₃ /f<0.7
The third lens is preferably a biconvex lens. If the third lens is a biconvex lens, it has a double-sided converging function, so that a positive refractive power can be ensured without reducing the radius of curvature, and the occurrence of higher-order aberrations can be suppressed. It becomes a problem-free shape.

Conditional expression (4 ) of the invention of 3) above is a condition for appropriately setting the radius of curvature of the image side surface of the fourth lens. Beyond the lower limit, the radius of curvature does not become too small, the distance from the imaging surface of the solid-state imaging device can be ensured, and the shape has no problem in lens processing. By falling below the upper limit, the negative refractive power of the image-side surface of the fourth lens can be maintained moderately, and the overall length of the lens is shortened and various off-axis aberrations such as field curvature and distortion are corrected well. be able to.

  Conditional expression (4) is more preferably in the range of the following expression.

0.15 <R ₈ /f<0.4
According to the above invention 4) or 5) , the first lens having a positive refractive power is formed of a glass material that hardly changes the refractive index when the temperature changes, and the second lens, the third lens, and the fourth lens. By using a plastic material, it is possible to compensate for image point position fluctuations when the temperature changes in the entire imaging lens system, while using many plastic lenses. More specifically, the positive third lens made of a plastic material has a relatively large positive refractive power, and the two negative lenses of the second lens and the fourth lens share the negative refractive power. Therefore, the distribution of refractive power of the plastic lens can be optimized, and the contribution to the image point position fluctuation at the time of temperature change will cancel out, and the image point position at the time of temperature change in the entire imaging lens system Variations can be kept small.

  In addition, by forming the first lens from a glass material, the plastic lens can be configured without being exposed, and problems such as scratches on the first lens can be avoided, which is a preferable configuration.

  The term “formed from a plastic material” as used in the present invention includes a case where a coating material is applied to the surface of the plastic material for the purpose of preventing reflection and improving the surface hardness. Moreover, the case where inorganic fine particles are mixed in the plastic material is included for the purpose of minimizing the temperature change of the refractive index of the plastic material.

According to the above invention 6) , 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 10 (mm) or less” means that a substrate on which a solid-state imaging device is held and a connection terminal portion for transmitting and receiving electrical signals is formed. Meaning the total length along the optical axis direction of an imaging device including an imaging lens and a housing that includes the imaging lens and is formed of a light-shielding material having an opening for light incidence from the object side It is. Therefore, for example, when a case is provided on the front surface of the board and an electronic component or the like is mounted on the back side of the board, the electrons projecting on the back side from the front end portion on the object side of the case. This means that the distance to the tip of the component is 10 (mm) or less.

According to the above invention 7) , it is possible to obtain a portable terminal capable of recording a smaller and higher quality image.

  That is, according to the present invention, an image pickup lens having a four-lens structure in which various aberrations are well corrected and a high-quality image is obtained while eliminating the problem of focal shift due to temperature change, which is smaller than the conventional one, It is possible to obtain an imaging device and a portable terminal including

  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. .

  In the housing 53, an infrared light cut filter F is fixedly disposed between the imaging lens 10 and the imaging element 51.

  The imaging lens 10 includes, in order from the object side, an aperture stop S, a first lens L1 having a positive refractive power, a second lens L2 having a negative refractive power, a third lens L3 having a positive refractive power, and a negative refraction. The fourth lens L4 having power 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 to L4.

  Each lens L <b> 1 to L <b> 4 constituting the imaging lens 10 is 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 lenses L1 to L4. In particular, it is preferable to dispose between the third lens L3 and the fourth lens L4 or between the fourth lens 4 and the infrared light cut filter F. By disposing a rectangular fixed stop outside the light path, the ghost , Flare generation can be suppressed.

  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: Spacing on the axis Nd: Refractive index of lens material with respect to d-line νd: Lens material Abbe number In each example, the shape of the aspherical surface is expressed by the following (Equation 1), where the vertex of the surface is the origin, the X axis is the optical axis direction, and the height 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 the 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 of the first lens as one surface.

Example 1
Tables 1 and 2 show lens data of the imaging lens of Example 1.

  FIG. 5 is a cross-sectional view of the imaging lens shown in the first embodiment. In the figure, S is an aperture stop, L1 is a first lens, L2 is a second lens, L3 is a third lens, and L4 is a fourth lens. Further, F is a parallel plate assuming an optical low-pass filter, an IR cut filter, a seal glass of a solid-state image sensor, or the like.

  FIG. 6 is an aberration diagram (spherical aberration, astigmatism, distortion, meridional coma) of the imaging lens shown in Example 1.

  The first lens is made of a glass lens, the second lens and the fourth lens are made of a polycarbonate plastic material, and the saturated water absorption is 0.4%. The third lens is formed of a polyolefin-based plastic material and has a saturated water absorption of 0.01% or less.

  The imaging element is assumed to be a 1 / 3.2 inch type, a pixel pitch of 2.2 μm, and 2048 × 1536 pixels.

  Table 3 shows changes in the refractive index nd depending on the temperature of the plastic material.

  The imaging lens shown in Example 1 has an image point position fluctuation (back focus change amount (ΔfB)) of −0.0004 (mm) when the temperature rises by +30 (° C.) with respect to room temperature of 20 (° C.). Become.

  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 caused by the refractive index change of the plastic lens, and the influence of the thermal expansion of the plastic lens at the time of temperature rise and the thermal expansion of the lens barrel holding the lens. The impact is not taken into account.

  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 ± 0.0158 (mm), and the fluctuation of the image point position of the image pickup lens shown in the first embodiment is represented by this focus. The depth can be kept very small. It is said that the image point position variation must be less than or equal to the depth of focus at the maximum, and desirably it is preferably suppressed to half or less. On the other hand, the imaging lens of Example 1 has an image point with respect to the depth of focus. The position fluctuation amount can be set to a small value of about 2.5%, and there can be no problem at all.

(Example 2)
Tables 4 and 5 show lens data of the imaging lens of Example 2.

  FIG. 7 is a cross-sectional view of the imaging lens shown in the second embodiment. In the figure, S is an aperture stop, L1 is a first lens, L2 is a second lens, L3 is a third lens, and L4 is a fourth lens. Further, F is a parallel plate assuming an optical low-pass filter, an IR cut filter, a seal glass of a solid-state image sensor, or the like.

  FIG. 8 is an aberration diagram (spherical aberration, astigmatism, distortion, meridional coma) of the imaging lens shown in Example 2.

  The first lens is made of a glass lens, the second lens and the fourth lens are made of a polycarbonate plastic material, and the saturated water absorption is 0.4%. The third lens is formed of a polyolefin-based plastic material and has a saturated water absorption of 0.01% or less.

  The imaging element is assumed to be a 1 / 3.2 inch type, a pixel pitch of 2.2 μm, and 2048 × 1536 pixels.

  Table 6 shows changes in the refractive index nd depending on the temperature of the plastic material.

  The imaging lens shown in Example 2 has an image point position fluctuation (back focus change amount (ΔfB)) of −0.0005 (mm) when +30 (° C.) is raised with respect to room temperature 20 (° C.). .

  The focal depth on the image sensor side assumed in the second embodiment is ± 0.0141 (mm), whereas the imaging lens of the second embodiment has an image point position variation amount of 3.5 with respect to the focal depth amount. %, Which can be as small as possible.

(Example 3)
Tables 7 and 8 show lens data of the imaging lens of Example 3.

  FIG. 9 is a cross-sectional view of the imaging lens shown in Example 3. In the figure, S is an aperture stop, L1 is a first lens, L2 is a second lens, L3 is a third lens, and L4 is a fourth lens. Further, F is a parallel plate assuming an optical low-pass filter, an IR cut filter, a seal glass of a solid-state image sensor, or the like.

  FIG. 10 is an aberration diagram (spherical aberration, astigmatism, distortion, and meridional coma) of the imaging lens shown in Example 3.

  The first lens is made of a glass lens, the second lens and the fourth lens are made of a polycarbonate plastic material, and the saturated water absorption is 0.4%. The third lens is formed of a polyolefin-based plastic material and has a saturated water absorption of 0.01% or less.

  The imaging element is assumed to be a 1 / 3.2 inch type, a pixel pitch of 2.2 μm, and 2048 × 1536 pixels.

  Table 9 shows changes in the refractive index nd depending on the temperature of the plastic material.

  The imaging lens shown in Example 3 has an image point position fluctuation (back focus change amount (ΔfB)) of −0.0077 (mm) when +30 (° C.) is raised with respect to room temperature 20 (° C.). .

  The focal depth on the image sensor side assumed in the third embodiment is ± 0.0158 (mm). On the other hand, the imaging lens of the third embodiment displays the image point position variation amount with respect to the focal depth amount. It can be less than half, and can be a problem-free one.

Example 4
Tables 10 and 11 show lens data of the imaging lens of Example 4.

  FIG. 11 is a cross-sectional view of the imaging lens shown in Example 4. In the figure, S is an aperture stop, L1 is a first lens, L2 is a second lens, L3 is a third lens, and L4 is a fourth lens. Further, F is a parallel plate assuming an optical low-pass filter, an IR cut filter, a seal glass of a solid-state image sensor, or the like.

  FIG. 12 is an aberration diagram (spherical aberration, astigmatism, distortion, and meridional coma) of the imaging lens shown in Example 4.

  The first lens is made of a glass lens, the second lens and the fourth lens are made of a polycarbonate plastic material, and the saturated water absorption is 0.4%. The third lens is formed of a polyolefin-based plastic material and has a saturated water absorption of 0.01% or less.

  The imaging element is assumed to be a 1 / 3.2 inch type, a pixel pitch of 2.25 μm, and 2048 × 1536 pixels.

  Table 12 shows changes in the refractive index nd depending on the temperature of the plastic material.

  The imaging lens shown in Example 4 has an image point position fluctuation (back focus change amount (ΔfB)) of −0.0012 (mm) when +30 (° C.) is raised with respect to room temperature 20 (° C.). .

  The focal depth on the image sensor side assumed in the fourth embodiment is ± 0.0144 (mm). On the other hand, the imaging lens of the fourth embodiment has the image point position variation amount 8.3 with respect to the focal depth amount. %, Which can be as small as possible.

(Example 5)
Tables 13 and 14 show lens data of the imaging lens of Example 5.

  FIG. 13 is a cross-sectional view of the imaging lens shown in Example 5. In the figure, S is an aperture stop, L1 is a first lens, L2 is a second lens, L3 is a third lens, and L4 is a fourth lens. Further, F is a parallel plate assuming an optical low-pass filter, an IR cut filter, a seal glass of a solid-state image sensor, or the like.

  FIG. 14 is an aberration diagram (spherical aberration, astigmatism, distortion, meridional coma) of the imaging lens shown in Example 5.

  The first lens is made of a glass lens, the second lens and the fourth lens are made of a polycarbonate plastic material, and the saturated water absorption is 0.4%. The third lens is formed of a polyolefin-based plastic material and has a saturated water absorption of 0.01% or less.

  The imaging element is assumed to be a 1 / 3.2 inch type, a pixel pitch of 2.2 μm, and 2048 × 1536 pixels.

  Table 15 shows changes in the refractive index nd depending on the temperature of the plastic material.

  In the imaging lens shown in Example 5, the image point position fluctuation (back focus change amount (ΔfB)) when +30 (° C.) is raised with respect to room temperature 20 (° C.) is +0.0047 (mm).

  The focal depth on the image sensor side assumed in the fifth embodiment is ± 0.0141 (mm). On the other hand, the imaging lens of the fifth embodiment displays the image point position variation amount with respect to the focal depth amount. It can be less than half, and can be a problem-free one.

(Example 6)
Tables 16 and 17 show lens data of the imaging lens of Example 6.

  FIG. 15 is a cross-sectional view of the imaging lens shown in Example 6. In the figure, S is an aperture stop, L1 is a first lens, L2 is a second lens, L3 is a third lens, and L4 is a fourth lens. Further, F is a parallel plate assuming an optical low-pass filter, an IR cut filter, a seal glass of a solid-state image sensor, or the like.

  FIG. 16 is an aberration diagram (spherical aberration, astigmatism, distortion, and meridional coma) of the imaging lens shown in Example 6.

  The first lens is made of a glass lens, the second lens and the fourth lens are made of a polycarbonate plastic material, and the saturated water absorption is 0.4%. The third lens is formed of a polyolefin-based plastic material and has a saturated water absorption of 0.01% or less.

  The imaging element is assumed to be a 1 / 3.2 inch type, a pixel pitch of 2.2 μm, and 2048 × 1536 pixels.

  Table 18 shows changes in the refractive index nd depending on the temperature of the plastic material.

  In the imaging lens shown in Example 6, the image point position fluctuation (back focus change amount (ΔfB)) when the temperature is raised by +30 (° C.) with respect to the normal temperature of 20 (° C.) is −0.0042 (mm). .

  The focal depth on the image sensor side assumed in the sixth embodiment is ± 0.0141 (mm). On the other hand, the imaging lens of the sixth embodiment displays the image point position variation amount with respect to the focal depth amount. It can be less than half, and can be a problem-free one.

(Example 7)
Tables 19 and 20 show lens data of the imaging lens of Example 7.

  FIG. 17 is a cross-sectional view of the imaging lens shown in Example 7. In the figure, S is an aperture stop, L1 is a first lens, L2 is a second lens, L3 is a third lens, and L4 is a fourth lens. Further, F is a parallel plate assuming an optical low-pass filter, an IR cut filter, a seal glass of a solid-state image sensor, or the like.

  FIG. 18 is an aberration diagram (spherical aberration, astigmatism, distortion, meridional coma) of the imaging lens shown in Example 7.

  The first lens is made of a glass lens, the second lens and the fourth lens are made of a polycarbonate plastic material, and the saturated water absorption is 0.4%. The third lens is formed of a polyolefin-based plastic material and has a saturated water absorption of 0.01% or less.

  The imaging element is assumed to be a 1 / 3.2 inch type, a pixel pitch of 2.2 μm, and 2048 × 1536 pixels.

  Table 21 shows changes in the refractive index nd depending on the temperature of the plastic material.

  The imaging lens shown in Example 7 has an image point position fluctuation (back focus change amount (ΔfB)) of −0.0073 (mm) when +30 (° C.) is raised with respect to room temperature 20 (° C.). .

  The focal depth on the image sensor side assumed in the seventh embodiment is ± 0.0158 (mm). On the other hand, the imaging lens of the seventh embodiment displays the image point position variation amount with respect to the focal depth amount. It can be less than half, and can be a problem-free one.

  Table 22 below shows values corresponding to the conditional expressions in Examples 1 to 7.

  In Examples 1 to 7, the first lens is formed of a glass lens, the second lens and the fourth lens are formed of a polycarbonate plastic material, and the saturated water absorption is 0.4%. The third lens is formed of a polyolefin-based plastic material and has a saturated water absorption of 0.01% 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. 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.

  In addition, when a glass mold lens is used for the first lens, it is desirable to use a glass material having a glass transition point (Tg) of 400 (° 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, in order to suppress fluctuations in the image point position of the entire imaging lens system due to temperature changes, the positive first lens is a glass lens, the second lens, the third lens, and the fourth lens are plastic lenses, and when the temperature changes The problem of the temperature characteristic is solved by allocating the refractive power of the plastic lens so as to offset the image point position fluctuation to a certain extent.

  In recent years, it has been found that inorganic fine particles can be mixed in a plastic material to suppress a temperature change in the refractive index of the plastic material. 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 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 addition to the second lens, the third lens, and the fourth lens, it is also possible to use a plastic material in which the inorganic particles are dispersed in the first lens, so that the image point position fluctuation at the time of temperature change is offset to some extent. As described above, by distributing the respective refractive powers, it is possible to further suppress the image point position fluctuation of the entire imaging lens system when the temperature changes.

  Further, each plastic lens may be made of a plastic material in which the above-mentioned fine particles having different refractive index temperature change values are dispersed. In this case, the contribution of the image point position variation when the temperature of each lens changes. By distributing the refractive power in consideration of the size of the image, it is possible to prevent the image point position variation of the entire imaging lens system from occurring 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 in 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. 2 is a cross-sectional view of the imaging lens shown in Example 1. FIG. FIG. 4 is an aberration diagram (spherical aberration, astigmatism, distortion, and meridional coma) of the imaging lens illustrated in Example 1. 6 is a cross-sectional view of an imaging lens shown in Example 2. FIG. FIG. 6 is an aberration diagram (spherical aberration, astigmatism, distortion, meridional coma) of the imaging lens shown in Example 2. 6 is a cross-sectional view of an imaging lens shown in Example 3. FIG. FIG. 6 is an aberration diagram (spherical aberration, astigmatism, distortion, and meridional coma) of the imaging lens illustrated in Example 3. 6 is a cross-sectional view of an imaging lens shown in Example 4. FIG. FIG. 6 is an aberration diagram (spherical aberration, astigmatism, distortion, meridional coma) of the imaging lens shown in Example 4. 6 is a cross-sectional view of an imaging lens shown in Example 5. FIG. FIG. 10 is an aberration diagram (spherical aberration, astigmatism, distortion, meridional coma) of the imaging lens shown in Example 5. 7 is a cross-sectional view of an imaging lens shown in Example 6. FIG. FIG. 10 is an aberration diagram (spherical aberration, astigmatism, distortion, and meridional coma) of the imaging lens shown in Example 6. 10 is a cross-sectional view of an imaging lens shown in Example 7. FIG. FIG. 10 is an aberration diagram (spherical aberration, astigmatism, distortion, meridional coma) of the imaging lens shown in Example 7.

Explanation of symbols

L1 1st lens L2 2nd lens L3 3rd lens L4 4th lens F Infrared light cut filter S Aperture stop 50 Imaging device 51 Imaging element 52 Substrate 53 Housing 55 Mirror frame

Claims (7)

An imaging lens for forming a subject image on a photoelectric conversion unit of a solid-state imaging device,
In order from the object side, an aperture stop, a first lens having a positive refractive power, a second lens having a negative refractive power, a third lens having a positive refractive power, and a fourth lens having a negative refractive power,
The following conditional expression (1) is satisfied ,
The imaging lens, wherein the second lens satisfies the following conditional expression (3) .
0.8 <f ₁ /f<2.0 (1)
0 <(R ₃ + R ₄ ) / (R ₃ −R ₄ ) <2.5 (3)
However,
f ₁ : focal length of the first lens f: focal length of the entire imaging lens system
R ₃ : radius of curvature of the object side surface of the second lens
R ₄ : radius of curvature of the image side surface of the second lens The imaging lens according to claim 1, wherein the third lens satisfies the following conditional expression (2).
0.3 <f ₃ /f<1.5 (2)
However,
f ₃ : focal length of the third lens f: focal length of the entire imaging lens system The imaging lens according to claim 1 or 2 , wherein the fourth lens satisfies the following conditional expression (4).
0.15 <R ₈ /f<0.5 (4)
However,
R ₈ : radius of curvature of the image side surface of the fourth lens f: focal length of the entire imaging lens system It said first lens The imaging lens according to any one of claims 1 to 3, characterized in that it is formed of a glass material. And the second lens, the third lens, and the fourth lens, the imaging lens according to any one of claims 1 to 4, characterized in that it is formed 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 5 , and the imaging lens. And an imaging device integrally formed with a housing made of a light-shielding material having an opening for light incidence from the object side,
The imaging apparatus, wherein the imaging apparatus has a height in the optical axis direction of the imaging lens of 10 (mm) or less. A portable terminal comprising the imaging device according to claim 6 .

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