JP2009008956A - Imaging lens, imaging unit, and personal digital assistance incorporating the imaging unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging unit that has an imaging lens section with a short entire lens length, and to provide a personal digital assistance incorporating the imaging unit. <P>SOLUTION: The imaging unit includes: a first lens L1, the biconvex lens having positive power; a second lens L2, the meniscus lens having positive power with its convex face oriented to the imaging face side; a third lens L3, the meniscus lens having negative power with its convex face oriented to the object side; and a fourth lens L4 having positive power, which is located near the imaging face 31a of the solid imaging element, one face of which is flat and the other face of which has a curvature. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an imaging lens body, an imaging unit including a solid-state imaging device and an imaging lens unit, and a portable information terminal equipped with the imaging unit, and in particular, suitable as a small camera such as a digital still camera. The present invention relates to an imaging unit including an imaging lens unit having a short overall lens length, and a portable information terminal equipped with the imaging unit.

  In recent years, portable information terminals called PDA (Personal Digital Assistant), cellular phones, and the like have become widespread, and many of them are equipped with an imaging device such as a digital camera. These image pickup devices are miniaturized by using a small CCD (Charged Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor) sensor. In addition, along with the widespread use of these devices, image pickup devices are required to be smaller and have higher resolution and higher performance.

Therefore, as the performance of such a small imaging device increases, the number of lenses increases from the conventional two-lens configuration to the three-lens / four-lens configuration. As the four-lens configuration, for example, an imaging lens unit with positive / negative / positive power distribution as proposed in Patent Documents 1 and 2 has been proposed. By making the power of the fourth lens closest to the imaging surface positive, the incident angle of the off-axis luminous flux that becomes a problem when the size of the imaging lens unit is reduced is prevented from becoming too large. The distortion is corrected.
JP 2004-102234 A (published April 2, 2004) Japanese Patent Laying-Open No. 2005-164872 (released on June 23, 2005)

  However, in the above-described conventional technology, the fourth lens is relatively far from the imaging surface. Therefore, if the fourth lens tries to suppress the incident angle on the imaging surface from becoming too large, the fourth lens is associated with it. Since astigmatism occurs, the resolution of the periphery deteriorates, and the assembling tolerance of the lens becomes severe due to the influence of astigmatism. In addition, since astigmatism occurs, the incident angle cannot be strongly corrected by the fourth lens, and therefore it is difficult to shorten the overall length of the lens system.

  Accordingly, the present invention has been made in view of the above-described problems, and an object of the present invention is to make it easy to assemble a lens and to reduce the overall length of the lens system while having a four-lens configuration. Body, an imaging unit including an imaging lens body (imaging lens unit), and a portable information terminal equipped with the imaging unit.

  In order to solve the above-described problems, an imaging lens body according to the present invention is an imaging lens body that forms an image of a subject on an imaging surface of a solid-state imaging device. The imaging lens body includes four lenses and is sequentially arranged from the subject side. A first lens that is a biconvex lens having a positive power, a meniscus second lens having a positive power with a concave surface facing the subject, and a meniscus having a negative power with a concave surface facing the imaging surface A third lens having a shape and a fourth lens having a positive power in which one surface is a flat surface and the other surface is a curved surface, and the fourth lens includes the first to first lenses. It is characterized by being arranged in the vicinity of a focal position obtained by combining four lenses.

  By adopting the above-described configuration, the imaging lens body according to the present invention can facilitate the assembly of the lens and can shorten the overall length of the lens system even though it has a four-lens configuration.

Specifically, the present invention is configured as described above,
(A) The first lens is a biconvex lens having a positive power, the second lens is a meniscus shape having a concave surface facing the object side, and the power of the two positive lenses is relatively strong and negative to the third lens. By giving power, the overall length of the lens system can be shortened.

  (B) Further, by making the third lens a meniscus lens having a negative power with the concave surface facing the imaging surface side, it is possible to correct field curvature and to obtain a high optical performance of the lens system. The overall length can be shortened.

  (C) Also, the fourth lens is a lens having a positive power and is disposed in the vicinity of the imaging surface, so that the fourth lens has only the functions of reducing the incident angle of the off-axis light beam on the imaging surface and correcting the distortion. Can be made. This also allows the third lens to give a strong negative power and can increase the positive power of the first lens and the second lens, so that the overall length of the lens system can be shortened as a whole. In addition, high optical properties can be obtained.

  (D) Further, by arranging the fourth lens in the vicinity of the imaging surface, astigmatism hardly occurs even if the light beam is bent by the fourth lens, so that the incident angle can be strongly corrected by the fourth lens. Therefore, the total length of the lens system can be shortened despite the four-lens configuration.

  (E) Moreover, since one surface of the fourth lens is a flat surface, it is possible to reduce the deterioration of performance due to decentering and tilting of the lens during assembly. Further, at the time of assembling, the plane can be used as an assembling reference surface, the assembling can be simplified and the mass production efficiency can be improved.

  (F) Moreover, since one surface of the fourth lens is a flat surface, it is easy to form various optical coating films, and other optical elements / components can be attached. For example, it is easy to attach a light shielding member, a shutter, various filters, an optical film, a prism, and the like.

  (G) Also, by making one surface of the fourth lens flat, the center thickness of the fourth lens can be reduced, which can contribute to the miniaturization of the lens system.

  (H) Moreover, it is possible to arrange | position a solid-state imaging device on the plane of a 4th lens by making one surface of a 4th lens into a plane. As a result, the fourth lens and the image sensor can be handled as a unit, which contributes to reducing the size and weight of the image pickup optical system. Further, in a general imaging lens unit system, the lens requires a separate holding mechanism such as a lens barrel and a holder, but it is not necessary to provide a holding mechanism for the fourth lens by being integrated with the imaging element. The imaging lens unit can be further reduced in size and weight.

  From the above, according to the configuration of the present invention, it is possible to provide an imaging unit including an imaging lens unit having a short overall length of the lens system and having high optical performance while ensuring an appropriate exit pupil position. In addition, high mass production efficiency is achieved, and the optical performance is prevented from deteriorating due to decentering and tilting of the lens.

Specifically, in the imaging lens body according to the present invention, when the distance between the center of the surface having the curvature of the fourth lens and the focal position is L and the size of the effective image circle diameter is 2Y, Conditional expression (1):
0.03 <L / Y <1.0 (1)
The fourth lens is arranged so as to satisfy the above.

  In the present specification, the refractive power is referred to as “power”.

  In addition to the above configuration, the imaging lens body according to the present invention preferably includes an aperture stop on the subject side of the first lens.

  By adopting the above configuration, the overall length of the lens system can be shortened compared to a configuration in which the aperture stop is disposed between the first lens and the second lens (FIG. 2 of Patent Document 1).

In addition to the above configuration, the imaging lens body according to the present invention has the above-described configuration, where f3 is the focal length of the third lens, and f is the focal length of the focal point obtained by combining the first to fourth lenses. The imaging lens unit has the following formula (2):
−6.0 <f3 / f <−0.5 (2)
Is preferably satisfied.

  By adopting the above configuration, the imaging lens body according to the present invention can bring the positions of the first lens and the second lens closer to the imaging surface side with respect to the principal point of the lens system, and the entire length of the lens system. Can be shortened. Further, each aberration such as curvature of field can be corrected more satisfactorily.

  In addition to the above configuration, the imaging lens body according to the present invention has an aspherical surface in which the surface of the fourth lens having the curvature is stronger at the periphery of the lens than at the center of the lens. The shape is preferred.

  By adopting the above configuration, the imaging lens body according to the present invention can bend more off-axis light beams that increase the angle of incidence on the imaging surface than the center. As a result, the radius of curvature of the peripheral portion can be reduced while increasing the radius of curvature of the central portion of the fourth lens, so that the off-axis light beam can be corrected well even if the thickness of the fourth lens is thin.

  An imaging unit including the imaging lens body having the above-described configuration and a solid-state imaging device having an imaging surface is also included in the present invention.

  In order to solve the above-described problem, an imaging unit according to the present invention is an imaging unit including a solid-state imaging device having an imaging surface and an imaging lens unit that forms an image of a subject on the imaging surface. The imaging lens unit is composed of four lenses, and in order from the subject side, a first lens that is a biconvex lens having positive power, and a second meniscus shape having positive power with a concave surface facing the subject side. A lens, a third meniscus lens having a negative power with the concave surface facing the imaging surface, and a positive lens disposed in the vicinity of the imaging surface, where one surface is a flat surface and the other surface is a curved surface. And a fourth lens having the following power.

  By adopting the above-described configuration, the imaging unit according to the present invention can facilitate the assembly of the lens with respect to the imaging lens unit, and can shorten the total length of the lens system even though the configuration is four.

Specifically, in the present invention, the imaging lens unit is configured as described above,
(A) The first lens is a biconvex lens having a positive power, the second lens is a meniscus shape having a concave surface facing the object side, and the power of the two positive lenses is relatively strong and negative to the third lens. By giving power, the overall length of the lens system can be shortened.

  (B) Further, by making the third lens a meniscus lens having a negative power with the concave surface facing the imaging surface side, it is possible to correct field curvature and to obtain a high optical performance of the lens system. The overall length can be shortened.

(C) Further, the fourth lens is a lens having a positive power and is disposed in the vicinity of the imaging surface. Specifically, the distance between the center of the surface having the curvature of the fourth lens and the imaging surface is set to L. When the effective image circle diameter is 2Y, the imaging lens unit has the following formula (1);
0.03 <L / Y <1.0 (1)
By arranging so as to satisfy the condition, the fourth lens can have only the functions of reducing the incident angle of the off-axis light beam on the imaging surface and correcting the distortion. This also allows the third lens to give a strong negative power and can increase the positive power of the first lens and the second lens, so that the overall length of the lens system can be shortened as a whole. In addition, high optical properties can be obtained.

  (D) Further, by arranging the fourth lens in the vicinity of the imaging surface, astigmatism hardly occurs even if the light beam is bent by the fourth lens, so that the incident angle can be strongly corrected by the fourth lens. Therefore, the total length of the lens system can be shortened despite the four-lens configuration.

  (E) Moreover, since one surface of the fourth lens is a flat surface, it is possible to reduce the deterioration of performance due to decentering and tilting of the lens during assembly. Further, at the time of assembling, the plane can be used as an assembling reference surface, the assembling can be simplified and the mass production efficiency can be improved.

  (F) Moreover, since one surface of the fourth lens is a flat surface, it is easy to form various optical coating films, and other optical elements / components can be attached. For example, it is easy to attach a light shielding member, a shutter, various filters, an optical film, a prism, and the like.

  (G) Also, by making one surface of the fourth lens flat, the center thickness of the fourth lens can be reduced, which can contribute to the miniaturization of the lens system.

  (H) Moreover, it is possible to arrange | position a solid-state imaging device on the plane of a 4th lens by making one surface of a 4th lens into a plane. As a result, the fourth lens and the image sensor can be handled as a unit, which contributes to reducing the size and weight of the image pickup optical system. Further, in a general imaging lens unit system, the lens requires a separate holding mechanism such as a lens barrel and a holder, but it is not necessary to provide a holding mechanism for the fourth lens by being integrated with the imaging element. The imaging lens unit can be further reduced in size and weight.

  From the above, according to the configuration of the present invention, it is possible to provide an imaging unit including an imaging lens unit having a short overall length of the lens system and having high optical performance while ensuring an appropriate exit pupil position. In addition, high mass production efficiency is achieved, and the optical performance is prevented from deteriorating due to decentering and tilting of the lens.

  In addition to the above-described configuration, the imaging unit according to the present invention preferably includes an aperture stop on the subject side of the imaging lens unit.

  By adopting the above configuration, the overall length of the lens system can be shortened compared to a configuration in which the aperture stop is disposed between the first lens and the second lens (FIG. 2 of Patent Document 1).

  In addition to the above configuration, the imaging unit according to the present invention further includes a translucent cover member for protecting the imaging surface, and the translucent cover member is the flat surface of the fourth lens. It is preferable to have a surface in contact with.

  By adopting the above configuration, the imaging unit according to the present invention can dispose the fourth lens in the vicinity of the imaging surface. Accordingly, it is possible to correct the aberration and the incident angle with respect to the imaging surface with respect to the light beam incident on the imaging surface. Since the fourth lens is disposed in contact with the translucent cover member, it is not necessary to provide a new lens holding mechanism in the lens barrel that holds the lens. That is, the number of lenses that need to be provided with a lens holding mechanism can be reduced. Therefore, the imaging lens unit can be reduced in size and weight.

  In addition, since the fourth lens is disposed in contact with the translucent cover member, it is possible to suppress the influence of the inclination of the fourth lens on the solid-state imaging device, and it is possible to suppress the eccentricity deviation.

  Moreover, in order to arrange | position the 4th lens in contact with a translucent cover member, when a 4th lens is used as the positioning part with respect to the optical axis of an imaging lens part, the influence of the inclination of a 1st-3rd lens is suppressed. It is also possible to suppress eccentric deviation.

  Further, since the fourth lens is disposed in contact with the translucent cover member, the thickness of the fourth lens can be reduced. That is, by forming the fourth lens on the cover glass by 2P molding or the like, a thin fourth lens that cannot be held alone can be formed on the cover glass. Thereby, the optical characteristics can be improved while minimizing the total length of the lens system.

  As a result, it is possible to reduce the number of lenses that need to be provided with a lens holding mechanism, and to suppress performance deterioration due to decentering and tilting of the lens.

  Moreover, when the imaging unit according to the present invention includes the translucent cover member, the translucent cover may be disposed on the imaging surface side of the fourth lens, or the fourth lens is translucent. May be disposed on the imaging surface side of the cover member.

  In the imaging unit according to the present invention, in addition to the above configuration, the fourth lens is preferably made of a resin material.

  By adopting the above configuration, the imaging unit according to the present invention can easily form the fourth lens on the cover glass. As a result, the cover glass can be prevented from being damaged during the formation of the fourth lens.

  The portable information terminal according to the present invention is characterized by including the imaging unit having the above-described configuration in order to solve the above-described problems.

  By adopting the above configuration, the portable information terminal according to the present invention includes an imaging unit that exhibits the above-described effects, and a small portable information terminal including a high-performance imaging unit can be obtained.

  As described above, the imaging lens body according to the present invention is an imaging lens body that forms an image of a subject on the imaging surface of a solid-state imaging device, and is composed of four lenses. A first lens which is a biconvex lens having a positive surface, a meniscus second lens having a positive power with a concave surface facing the object side, and a meniscus third lens having a negative power with a concave surface facing the imaging surface side. A lens and a fourth lens having a positive power in which one surface is a flat surface and the other surface is a curved surface are arranged, and the fourth lens is a combination of the first to fourth lenses. It is characterized by being arranged in the vicinity of the focal position obtained by Moreover, as described above, the imaging unit according to the present invention is an imaging unit including a solid-state imaging device having an imaging surface and an imaging lens unit that forms an image of a subject on the imaging surface. A first lens which is a biconvex lens having a positive power in order from the subject side, a meniscus second lens having a positive power with a concave surface facing the subject side, and imaging A third meniscus lens having a negative power with a concave surface facing the surface side, and a first lens having a positive power that is disposed in the vicinity of the imaging surface, one surface being a flat surface and the other surface having a curvature. 4 lenses are arranged. In addition, as described above, the portable information terminal according to the present invention includes the imaging unit having the above-described configuration.

  With the above configuration, an imaging lens body that facilitates lens assembly and can shorten the overall length of the lens system while having a four-lens configuration, and an imaging unit including the imaging lens body (imaging lens unit) In addition, a portable information terminal equipped with the imaging unit can be provided.

[Embodiment 1]
An embodiment of the present invention will be described with reference to FIGS. In the following description, various technically preferable limitations for carrying out the present invention are given, but the scope of the present invention is not limited to the following embodiments and drawings.

  FIGS. 1A to 1C are diagrams showing a configuration of a mobile phone (portable information terminal) according to the present embodiment. 1A is a front side of the mobile phone 1, FIG. 1B is a back side of the mobile phone 1, and FIG. 1C is a side side of the mobile phone 1. .

  The mobile phone 1 according to the present embodiment has an imaging function (camera function). Therefore, as shown in FIGS. 1A to 1C, the mobile phone 1 includes a housing 2, an imaging unit 3 a, a speaker unit 4, a microphone unit 5, an input unit 6, a monitor unit 7, and a light unit. 8 and a shutter button 9. In the present embodiment, the surface shown in FIG. 1A where the input unit 6 and the monitor unit 7 are provided is referred to as a front surface.

  The speaker unit 4 and the microphone unit 5 are used for inputting and outputting audio information. The monitor unit 7 is used to output video information. In the present embodiment, the monitor unit 7 is also used to display information obtained from the imaging unit 3a. The light unit 8 is used as an illuminating device for illuminating the subject when the subject is imaged by the imaging unit 3a.

  By operating the shutter button 9 or the input unit 6, the subject can be imaged by the imaging unit 3a. The captured image is signal-processed in the mobile phone 1 and displayed on the monitor unit 7. The captured image can be stored as electronic data in the mobile phone 1 or stored in an external recording device.

  The imaging unit 3a will be described in detail with reference to FIG.

  FIG. 2 is a cross-sectional view of the image pickup unit 3a, and shows a state in which the image pickup unit 3a shown in FIG. 1C is cut in parallel to the side surface of the mobile phone 1 shown in FIG. . As shown in FIG. 2, the imaging unit 3a includes a solid-state imaging unit (solid-state imaging device) 30a, a unit package 30b, and an imaging lens unit (imaging lens body) 30c.

  The solid-state imaging unit 30a includes a solid-state imaging element 31, which is an electronic component including an electrical conversion unit for converting a light beam that has passed through the imaging lens unit 30c into an electrical signal, a support substrate 32, and a flexible printed circuit board 33. Have.

  The solid-state imaging device 31 is formed with an electrical conversion unit in which pixels are two-dimensionally arranged at the center of the light receiving side surface, and a signal processing circuit is formed around the electrical conversion unit. The signal processing circuit 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. A large number of pads (not shown) are provided in the vicinity of the outer edge of the light-receiving side surface of the solid-state image sensor 31 in the present embodiment, and the solid-state image sensor 31 is connected to the support substrate 32. The kind of solid-state image sensor 31 is not specifically limited. Specifically, a CCD sensor, a CMOS sensor, or the like can be used.

  The support substrate 32 is a hard substrate that supports the solid-state imaging device 31 and the unit package 30b on one surface thereof. The other surface of the support substrate 32 (the surface opposite to the surface on which the solid-state imaging device 31 is supported) is provided with a flexible printed circuit board 33 having one end connected thereto. The support substrate 32 is provided with a large number of signal transmission pads on both the front and back surfaces. One surface is connected to the solid-state imaging device 31 and the other surface is connected to the flexible printed circuit 33.

  The flexible printed circuit board 33 is supplied with a voltage and a clock signal for driving the solid-state imaging device 31 from an external circuit (for example, a control circuit included in an apparatus equipped with the imaging unit 3a), and receives a digital YUV signal. It is a substrate that enables output to the outside. Y is a luminance signal, U is a color difference signal between red and the luminance signal, and V is a color difference signal between blue and the luminance signal.

  The unit package 30 b includes a light shielding body 34 and an infrared light cut filter 35.

  The light shielding body 34 is fixedly disposed so as to cover the solid-state imaging device 31 on the surface of the support substrate 32 on the solid-state imaging device 31 side. Specifically, the light-shielding body 34 is wide open so as to surround the solid-state image pickup device 31 on the solid-state image pickup device 31 side and is in contact with the support substrate 32, and has a flange having a small opening on the other end side. It is formed in a cylindrical shape. The light blocking body 34 can have the imaging lens unit 30c disposed therein.

  The infrared light cut filter 35 is disposed at a light incident portion of the unit package 30 b and is fixedly disposed on the light shield 34. The infrared light cut filter 35 may be fixedly disposed between the imaging lens unit 30 c and the solid-state imaging element 31. Note that an infrared light cut function may be added to the cover glass.

  The imaging lens unit 30c includes an aperture stop 37, a lens holding unit 36, and a four-lens group of lenses.

  The aperture stop 37 is disposed closer to the subject than the lens group, and keeps the exit pupil away from the image plane. In the present embodiment, the opening provided in the upper part of the light shield 34 shown in FIG. Thus, by arranging the aperture stop on the subject side of the first lens L1, the overall length of the lens system can be shortened compared to the configuration in which the aperture stop is disposed between the first lens and the second lens. Can do.

  The lens holding unit 36 holds the lens group and is fixed inside the light shielding body 34 using a flange provided on the inner wall of the light shielding body 34.

  The four-lens group includes a first lens L1, a second lens L2, a third lens L3, and a fourth lens L4 from the subject side. The lens group will be described in detail with reference to FIG.

  FIG. 3 is a cross-sectional view illustrating a state in which the lens group of the imaging lens unit 30c is cut along the center of the optical axis. In FIG. 3, the left side of the drawing is the subject side, and the right side of the drawing is the solid-state imaging device 31 side shown in FIG. In FIG. 3, the position of the imaging surface (imaging surface) of the lens group is shown as 31a. The imaging plane is a focal position obtained by combining the first to fourth lenses, and corresponds to the position of the electrical conversion unit of the solid-state imaging device 31.

  The four-lens group includes a first lens L1 that is a biconvex lens having positive power, a meniscus second lens L2 having positive power with a concave surface facing the object, and a concave surface on the imaging surface side. Meniscus third lens L3 having negative power directed to the fourth lens L4, which is disposed in the vicinity of the imaging surface 31a, and has a positive power, one surface being a flat surface and the other surface having a curvature. L4.

  The material of each lens can be an optical material such as plastic or glass, and is preferably plastic from the viewpoint of mass productivity and cost, and the stability and characteristics of the optical system (for example, refractive index, dispersion characteristics, heat resistance). Etc.) is preferable.

  In the above configuration, the first lens is a biconvex lens having positive power, the second lens is a meniscus shape having a concave surface facing the object side, and the power of the two positive lenses is relatively strong and negative to the third lens. By giving this power, the overall length of the lens system can be shortened. The third lens L3 is the only lens having negative power and functions to reduce the Petzval sum related to field curvature. Further, off-axis rays that diverge when the third lens L3 has negative power are corrected by the fourth lens L4 having positive power disposed in the vicinity of the imaging surface. By disposing the fourth lens L4 in the vicinity of the image formation surface, the incident angle of the off-axis light beam on the image formation surface can be relaxed and the distortion can be corrected. With this effect, the negative power of the third lens L3 can be made relatively strong.

  Further, by disposing the fourth lens L4 in the vicinity of the image plane, the function of the fourth lens L4 can be limited as described above, and astigmatism and the like in the fourth lens L4 can be suppressed. For this reason, one surface of the fourth lens L4 can be flat. By making one surface of the fourth lens L4 a flat surface, it is possible to reduce deterioration in performance due to decentering and tilting during lens assembly. Furthermore, by making one surface of the fourth lens L4 flat, the center thickness of the fourth lens L4 can be reduced, which can contribute to the downsizing of the lens system.

Next, configuration conditions of the lens group will be described. The lens group has the following formula (1);
0.03 <L / Y <1.0 (1)
However,
L: distance between the center of the surface having the curvature of the fourth lens L4 and the imaging plane (focal position obtained by combining the first to fourth lenses) Y: configured to satisfy the radius of the effective image circle diameter Yes. The above expression (1) is an expression for defining the position of the fourth lens L4. By satisfying the above formula (1), the fourth lens L4 can be disposed in the vicinity of the imaging plane (the focal position obtained by combining the first to fourth lenses), and the off-axis light beam enters the imaging plane. Angle relaxation and distortion correction can be performed, and the occurrence of astigmatism can be suppressed. If the lower limit of the formula is not reached, the distortion correction effect in the fourth lens L4 cannot be said to be sufficient. If the upper limit of the formula is exceeded, aberrations such as astigmatism occur in the fourth lens L4, and sufficient characteristics are obtained. I can't.

The lens group is represented by the following formula (2):
−6.0 <f3 / f <−0.5 (2)
However,
f3: Focal length of the third lens L3 f: It is also configured to satisfy the focal length of the entire lens system. By satisfying the above expression (2), the positions of the first lens L1 and the second lens L1 can be brought closer to the image plane side with respect to the principal point of the lens system, and the overall length of the lens system can be shortened. . In addition, each aberration can be corrected more satisfactorily. Note that if the lower limit of the expression (2) is not reached, the effect of correcting the curvature of field is not sufficiently obtained, and if the upper limit of the expression (2) is exceeded, the distortion becomes strong.

Hereinafter, the lens group of the present embodiment will be described in detail by showing numerical examples.
(Numerical example 1)
Tables 1 and 2 show specific numerical data of the lens group according to the present embodiment. Table 1 shows surface data, and Table 2 shows data relating to the aspherical shape among the surface data in Table 1.

  In the field of the surface number Si in the lens data shown in Tables 1 and 2, the surface of the component on the most object side is the first, and the i-th number is assigned so as to increase sequentially toward the imaging surface side. The number of the surface of (i = 1-9) is shown. The column of the curvature radius Ri shows the value of the curvature radius of the i-th surface from the subject side. The column of the surface interval Di indicates the interval on the optical axis between the i-th surface Si and the i + 1-th surface Si + 1 from the subject side. The unit of the Ri and Di values is mm (millimeter). The columns of refractive index and Abbe number indicate the refractive index and Abbe number values for the d-line (587.6 nm) of the lens element.

  Further, the aspherical shape in this specification and the like is expressed by using the following aspherical expression (3) when taking the Z axis in the optical axis direction and the Y axis in the direction orthogonal to the optical axis.

However,
K: Conic constant R: Curvature radius A, B, C and D: Fourth, sixth, eighth and tenth aspheric coefficients Z: Aspheric surface at height Y from the optical axis The length of the perpendicular line drawn from the upper point to the tangent plane (plane perpendicular to the optical axis) of the apex of the aspherical surface is shown.

In addition, the numerical value of each aspheric surface data in the specification of the present application represents a power of 10 using “E”. That is, for example, 2.5 × 10 ⁻⁰² is represented as 2.5E-02.

  “F” shown in Table 1 is the combined focal length of the entire lens group, and “Fno” is the F number (F value) of the imaging lens. In this example, since L = 0.87 and Y = 2.2, L / Y = 0.40, which satisfies the above formula (1).

  In this example, since the focal length f3 = −3.7 and f = 3.3 of the third lens L3, f3 / f = −1.1, which satisfies the above formula (2).

  As shown in Table 1, in this example, the image surface side S3 of the first lens L1, the image surface side S5 of the second lens L2, and both surfaces S6 and S7 of the third lens L3 are aspherical. Yes. In the basic lens data, numerical values of the radius of curvature near the optical axis are shown as the radius of curvature of these aspheric surfaces.

  In addition, FIG. 4 shows spherical aberration, astigmatism, and distortion in this example. Each aberration diagram shows the aberration with the e-line (546.1 nm) as the reference wavelength, but the spherical aberration diagram also shows the aberration for the g-line (435.8 nm) and the C-line (656.3 nm). In the astigmatism diagram, the solid line indicates the sagittal aberration, and the dotted line indicates the tangential (meridional) aberration.

  As can be seen from FIG. 4, by arranging the fourth lens L4 in the vicinity of the imaging surface, it is possible to optimize the power arrangement of the entire imaging lens and to realize sufficient aberration correction.

  Therefore, by adopting the above configuration, it is possible to realize an image pickup unit including a small and high-performance lens group.

  In the present embodiment, the imaging unit 3a is arranged on the back surface of the monitor unit 7 shown in FIG. 1, but the arrangement method and the orientation of the imaging unit 3a are not limited to this.

  Further, as shown in FIGS. 1A to 1C, the mobile phone 1 according to the present embodiment is a so-called folding in which an upper casing and a lower casing are connected via a hinge. As an example, the portable cellular phone 1 is not limited to the folding cellular phone 1 in which the imaging unit 3a can be mounted.

[Embodiment 2]
Another embodiment according to the present invention will be described below with reference to FIGS. In addition, in this embodiment, in order to explain a difference from the first embodiment, for the sake of convenience of explanation, members having the same functions as those described in the first embodiment are denoted by the same member numbers. The description is omitted.

  FIG. 5 is a cross-sectional view showing a configuration of an imaging unit provided in the mobile phone according to the present embodiment. FIG. 6 is a cross-sectional view showing the configuration of the lens group of the imaging unit shown in FIG. In the first embodiment described above, as shown in FIG. 2, the fourth lens L4 is also held by the lens holding portion 36 in the same manner as the first lens L1 to the third lens L3. On the other hand, in the imaging unit 3b of the present embodiment shown in FIG. 5, a cover glass (translucent cover member) 38 is provided on the surface of the solid-state imaging device 31 on the imaging lens unit 30c side, and the fourth lens. L4 is not held by the lens holding portion 36, but is formed on the surface of the cover glass 38 on the imaging lens portion 30c side.

  In this embodiment, as shown in FIGS. 5 and 6, the power of the two positive lenses is such that the first lens is a biconvex lens having a positive power and the second lens is a meniscus shape having a concave surface facing the object side. By making the lens relatively strong and giving negative power to the third lens, the total length of the lens system can be shortened. The third lens L3 is the only lens having negative power and functions to reduce the Petzval sum related to field curvature. Further, off-axis rays that diverge when the third lens L3 has negative power are corrected by the fourth lens L4 having positive power disposed in the vicinity of the imaging surface. By disposing the fourth lens L4 in the vicinity of the image plane, the incident angle of the off-axis light beam on the image plane can be relaxed and the distortion can be corrected. With this effect, the negative power of the third lens L3 can be made relatively strong.

  In addition, the fourth lens L4 of the present embodiment is disposed on the cover glass 38 provided on the solid-state image sensor 31 so as to protect the solid-state image sensor 31 so that the plane of the fourth lens L4 is in contact therewith. By directly fixing the fourth lens L4 on the cover glass 38, it is not necessary to separately provide a lens holding mechanism for holding the fourth lens L4. Accordingly, since the lens holding mechanism of the fourth lens L4 can be omitted, the imaging unit can be reduced in size and weight. Moreover, when the 4th lens L4 is used as the positioning part with respect to an optical axis, the influence of the inclination of a 1st-3rd lens can be suppressed, and eccentricity deviation can also be suppressed.

  Further, as shown in FIGS. 5 and 6, the fourth lens L4 can be arranged in the vicinity of the imaging surface 31a, so that the function of the lens is limited as described above, and the generation of astigmatism and the like in the fourth lens L4 is suppressed. can do. For this reason, one surface of the fourth lens L4 can be flat. By making one surface of the fourth lens L4 into a planar shape, it is possible to reduce performance degradation due to eccentricity and tilt during lens assembly. Furthermore, by making one surface of the fourth lens L4 into a planar shape, the center thickness of the fourth lens L4 can be reduced, which can contribute to the downsizing of the lens system.

  By using resin as the material of the fourth lens L4, the fourth lens L4 can be easily formed on the cover glass 38, and the cover glass 38 is prevented from being damaged when the fourth lens L4 is formed. Can do.

  As a forming method for forming the fourth lens L4 on the cover glass 38, a conventionally known method can be used. Specifically, when the fourth lens L4 is made of a resin, molding using a 2P (Photoreplication Process) method can be given. Or you may affix the 4th lens L4 formed with glass or resin.

  The configuration conditions of the lens group are the same as those in the first embodiment described above, and thus description thereof is omitted.

Hereinafter, the lens group of the present embodiment will be described in detail by showing numerical examples.
(Numerical example 2)
Tables 3 and 4 show specific numerical data of the lens group according to the present embodiment. Table 3 shows surface data, and Table 4 shows data related to the aspherical shape among the surface data in Table 3.

  The surface number Si, the curvature radius Ri, and the surface interval Di in the lens data shown in Tables 3 and 4 are the same as those described in (Numerical Example 1). The definitions of the refractive index and the Abbe number are the same as those described in (Numerical Example 1).

  The aspheric shape is an aspheric shape represented by the above aspheric formula (3).

  In this example, since L = 0.90 and Y = 2.2, L / Y = 0.41, which satisfies the above formula (1).

  In this example, since the focal length f3 = −6.5 and f = 3.1 of the third lens L3, f3 / f = −2.1, which satisfies the above formula (2).

  As shown in Table 3, in the present example, the second surface to the seventh surface are aspherical.

  FIG. 7 shows spherical aberration, astigmatism, and distortion (distortion) in this example. Each aberration diagram shows the aberration with the e-line (546.1 nm) as the reference wavelength, but the spherical aberration diagram also shows the aberration for the g-line (435.8 nm) and the C-line (656.3 nm). In the astigmatism diagram, the solid line indicates the sagittal aberration, and the dotted line indicates the tangential (meridional) aberration.

  As can be seen from FIG. 7, the fourth lens L4 is formed on the cover glass 38 as shown in FIG. 5, and the fourth lens L4 is disposed in the vicinity of the image plane 31a, whereby the power of the entire imaging lens is increased. The arrangement can be optimized, and sufficient aberration correction can be realized.

  In addition, by directly fixing the fourth lens L4 on the cover glass 38, a mechanism for holding the fourth lens L4 is not necessary, so that the imaging unit can be reduced in size and weight. Moreover, since it fixes directly on the cover glass 38, the 4th lens L4 can be made very thin, and there exists an effect which shortens an optical system.

  Therefore, by adopting the above configuration, it is possible to realize an image pickup unit including a small and high-performance lens group.

[Embodiment 3]
Another embodiment according to the present invention will be described below with reference to FIGS. In addition, in this embodiment, in order to explain the difference from the second embodiment, for the sake of convenience of explanation, members having the same functions as those described in the second embodiment are denoted by the same member numbers. The description is omitted.

  FIG. 8 is a cross-sectional view showing the configuration of the lens group of the imaging unit provided in the mobile phone according to the present embodiment. In Embodiment 2 described above, as shown in FIG. 5 and Table 3, the surface on the subject side of the fourth lens L4 formed on the cover glass 38 is a spherical surface. On the other hand, in the lens group of the present embodiment shown in FIG. 8, the surface on the subject side of the fourth lens L4 has an aspherical shape, as will be described in detail later. Hereinafter, the lens group and the aperture stop of this embodiment will be described with reference to FIG.

  In this embodiment, as shown in FIG. 8, the first lens is a biconvex lens having positive power, the second lens is a meniscus shape having a concave surface facing the object side, and the power of the two positive lenses is relatively high. The total length of the lens system can be shortened by strengthening and applying negative power to the third lens. The third lens L3 is the only lens having negative power and functions to reduce the Petzval sum related to field curvature. Further, off-axis rays that diverge when the third lens L3 has negative power are corrected by the fourth lens L4 having positive power disposed in the vicinity of the imaging surface. By disposing the fourth lens L4 in the vicinity of the image formation surface, the incident angle of the off-axis light beam on the image formation surface can be relaxed and the distortion can be corrected. With this effect, the negative power of the third lens L3 can be made relatively strong.

  In addition, the fourth lens L4 of the present embodiment is disposed on the cover glass 38 provided on the solid-state image sensor 31 so as to protect the solid-state image sensor 31 so that the plane of the fourth lens L4 is in contact therewith. By directly fixing the fourth lens L4 on the cover glass 38, it is not necessary to separately provide a lens holding mechanism for holding the fourth lens L4. Accordingly, since the lens holding mechanism of the fourth lens L4 can be omitted, the imaging unit can be reduced in size and weight. Moreover, when the 4th lens L4 is used as the positioning part with respect to an optical axis, the influence of the inclination of a 1st-3rd lens can be suppressed, and eccentricity deviation can also be suppressed.

  Further, as shown in FIG. 8, the fourth lens L4 can be arranged in the vicinity of the image forming surface 31a, so that the function of the lens is limited as described above, and the generation of astigmatism and the like in the fourth lens L4 is suppressed. it can. For this reason, one surface of the fourth lens L4 can be flat. By making one surface of the fourth lens L4 into a planar shape, it is possible to reduce performance degradation due to eccentricity and tilt during lens assembly. Furthermore, by making one surface of the fourth lens L4 into a planar shape, the center thickness of the fourth lens L4 can be reduced, which can contribute to the downsizing of the lens system.

  In the present embodiment, the object side surface of the fourth lens is aspherical, the radius of curvature at the center of the surface is increased, the radius of curvature at the periphery is reduced, and the power at the periphery is increased. I am doing so. Accordingly, it is possible to enhance the effects of off-axis light incident angle correction and distortion correction while keeping the center thickness of the fourth lens L4 thin.

  The configuration conditions of the lens group are the same as those in the first embodiment described above, and thus the description thereof is omitted.

Hereinafter, the lens group of the present embodiment will be described in detail by showing numerical examples.
(Numerical Example 3)
Tables 5 and 6 show specific numerical data of the lens group according to the present embodiment. Table 5 shows surface data, and Table 6 shows data relating to the aspherical shape among the surface data in Table 5.

  The surface number Si, the curvature radius Ri, and the surface interval Di in the lens data shown in Tables 5 and 6 are the same as the definitions described in (Numerical Example 1). The definitions of the refractive index and the Abbe number are the same as those described in (Numerical Example 1).

  The aspheric shape is an aspheric shape represented by the above aspheric formula (3).

  In this example, since L = 0.90 and Y = 2.2, L / Y = 0.41, which satisfies the above formula (1).

  In the present example, since the focal length f3 = −5.5 and f = 3.2 of the third lens L3, f3 / f = −1.7, which satisfies the above formula (2).

  As shown in Table 5, in the present example, the second surface to the eighth surface are aspherical.

  FIG. 9 shows spherical aberration, astigmatism, and distortion (distortion) in this example. Each aberration diagram shows the aberration with the e-line (546.1 nm) as the reference wavelength, but the spherical aberration diagram also shows the aberration for the g-line (435.8 nm) and the C-line (656.3 nm). In the astigmatism diagram, the solid line indicates the sagittal aberration, and the dotted line indicates the tangential (meridional) aberration.

  As can be seen from FIG. 9, by arranging the fourth lens L4 in the vicinity of the imaging surface, it is possible to optimize the power arrangement of the entire imaging lens, and to realize sufficient aberration correction.

  In addition, by directly fixing the fourth lens L4 on the cover glass 38, a mechanism for holding the fourth lens L4 is not necessary, so that the imaging unit can be reduced in size and weight. Moreover, since it fixes directly on the cover glass 38, the 4th lens L4 can be made very thin, and there exists an effect which shortens an optical system.

  Therefore, with the above configuration, a small and high-performance imaging lens and imaging unit can be obtained.

[Embodiment 4]
Another embodiment according to the present invention will be described below with reference to FIGS. In addition, in this embodiment, in order to explain a difference from the first embodiment, for the sake of convenience of explanation, members having the same functions as those described in the first embodiment are denoted by the same member numbers. The description is omitted.

  FIG. 10 is a cross-sectional view showing the configuration of the imaging unit provided in the mobile phone according to the present embodiment. FIG. 11 is a cross-sectional view showing the configuration of the lens group of the imaging unit shown in FIG. In the first embodiment described above, as shown in FIGS. 2 and 3, the fourth lens L4 has a flat surface on the image plane side. On the other hand, in the imaging unit 3c of this embodiment shown in FIG. 10, the subject side of the fourth lens L4 is a flat surface, and the imaging surface side is a surface having a curvature.

  In this embodiment, as shown in FIGS. 10 and 11, the power of the two positive lenses is such that the first lens is a biconvex lens having a positive power and the second lens is a meniscus shape having a concave surface facing the object side. By making the lens relatively strong and giving negative power to the third lens, the total length of the lens system can be shortened. The third lens L3 is the only lens having negative power and functions to reduce the Petzval sum related to field curvature. Further, off-axis rays that diverge when the third lens L3 has negative power are corrected by the fourth lens L4 having positive power disposed in the vicinity of the imaging surface. By disposing the fourth lens L4 in the vicinity of the image formation surface, the incident angle of the off-axis light beam on the image formation surface can be relaxed and the distortion can be corrected. With this effect, the negative power of the third lens L3 can be made relatively strong.

  In addition, by disposing the fourth lens L4 in the vicinity of the imaging surface, the function of the lens is limited as described above, and the occurrence of astigmatism or the like in the fourth lens L4 can be suppressed. For this reason, one surface of the fourth lens L4 can be flat. By making one surface of the fourth lens L4 into a planar shape, it is possible to reduce performance degradation due to eccentricity and tilt during lens assembly. Furthermore, by making one surface of the fourth lens L4 into a planar shape, the center thickness of the fourth lens L4 can be reduced, which can contribute to the downsizing of the lens system.

  The configuration conditions of the lens group are the same as those in the first embodiment, and a description thereof will be omitted.

Hereinafter, the lens group of the present embodiment will be described in detail by showing numerical examples.
(Numerical example 4)
Tables 7 and 8 show specific numerical data of the lens group according to the present embodiment. Table 7 shows surface data, and Table 8 shows data related to the aspherical shape among the surface data in Table 7.

  The surface number Si, the curvature radius Ri, and the surface interval Di in the lens data shown in Tables 7 and 8 are the same as those described in (Numerical Example 1). The definitions of the refractive index and the Abbe number are the same as those described in (Numerical Example 1).

  The aspheric shape is an aspheric shape represented by the above aspheric formula (3).

  In this example, since L = 0.56 and Y = 2.2, L / Y = 0.25, which satisfies the above formula (1).

  In this example, since the focal length f3 = −3.7 and f = 3.4 of the third lens L3, f3 / f = −1.1, which satisfies the above formula (2).

  As shown in Table 7, in the present example, the third, fifth, sixth and seventh surfaces are aspherical.

  In addition, FIG. 12 shows spherical aberration, astigmatism, and distortion (distortion) in this example. Each aberration diagram shows the aberration with the e-line (546.1 nm) as the reference wavelength, but the spherical aberration diagram also shows the aberration for the g-line (435.8 nm) and the C-line (656.3 nm). In the astigmatism diagram, the solid line indicates the sagittal aberration, and the dotted line indicates the tangential (meridional) aberration.

  As can be seen from FIG. 12, the fourth lens L4 is formed on the surface of the cover glass 38 as shown in FIG. 10, and the fourth lens L4 is disposed in the vicinity of the image plane 31a, so that the power of the entire imaging lens is increased. The arrangement can be optimized, and sufficient aberration correction can be realized.

  Therefore, by adopting the above configuration, it is possible to realize an image pickup unit including a small and high-performance lens group.

[Embodiment 5]
Another embodiment according to the present invention will be described below with reference to FIGS. In addition, in this embodiment, in order to explain the difference from the second embodiment, for the sake of convenience of explanation, members having the same functions as those described in the second embodiment are denoted by the same member numbers. The description is omitted.

  FIG. 13 is a cross-sectional view illustrating the configuration of the imaging unit provided in the mobile phone according to the present embodiment. FIG. 14 is a cross-sectional view showing the configuration of the lens group of the imaging unit shown in FIG. In the above-described third embodiment, as shown in FIG. 5, the fourth lens L4 is disposed on the surface of the cover glass 38 on the imaging lens portion 30c side so that the plane is in contact with the surface. On the other hand, in the imaging unit 3d of the present embodiment, the fourth lens L4 is disposed on the surface of the cover glass 38 on the solid-state imaging device 31 side so that the plane is in contact with the surface.

  In this embodiment, as shown in FIGS. 13 and 14, the power of the two positive lenses is such that the first lens is a biconvex lens having positive power and the second lens is a meniscus shape having a concave surface facing the object side. By making the lens relatively strong and giving negative power to the third lens, the total length of the lens system can be shortened. The third lens L3 is the only lens having negative power and functions to reduce the Petzval sum related to field curvature. Further, off-axis rays that diverge when the third lens L3 has negative power are corrected by the fourth lens L4 having positive power disposed in the vicinity of the imaging surface. By disposing the fourth lens L4 in the vicinity of the image formation surface, the incident angle of the off-axis light beam on the image formation surface can be relaxed and the distortion can be corrected. With this effect, the negative power of the third lens L3 can be made relatively strong.

  Further, by disposing the fourth lens L4 in the vicinity of the image plane, the function of the fourth lens L4 can be limited as described above, and astigmatism and the like in the fourth lens L4 can be suppressed. For this reason, one surface of the fourth lens L4 can be flat. By making one surface of the fourth lens L4 a flat surface, it is possible to reduce deterioration in performance due to decentering and tilting during lens assembly. Furthermore, by making one surface of the fourth lens L4 flat, the center thickness of the fourth lens L4 can be reduced, which can contribute to the downsizing of the lens system.

  The configuration conditions of the lens group are the same as those in the first embodiment described above, and thus the description thereof is omitted.

Hereinafter, the lens group of the present embodiment will be described in detail by showing numerical examples.
(Numerical example 5)
Tables 9 and 10 show specific numerical data of the lens group according to the present embodiment. Table 9 shows surface data, and Table 10 shows data related to the aspherical shape among the surface data in Table 9.

  The surface number Si, the curvature radius Ri, and the surface interval Di in the lens data shown in Tables 9 and 10 are the same as the definitions described in (Numerical Example 1). The definitions of the refractive index and the Abbe number are the same as those described in (Numerical Example 1).

  The aspheric shape is an aspheric shape represented by the above aspheric formula (3).

  In this example, since L = 0.27 and Y = 2.2, L / Y = 0.12, which satisfies the above formula (1).

  In this example, since the focal length f3 = −5.5 and f = 3.3 of the third lens L3, f3 / f = −1.7, which satisfies the above formula (2).

  As shown in Table 9, in the present example, the second to seventh surfaces are aspherical.

  Further, FIG. 15 shows spherical aberration, astigmatism and distortion in this example. Each aberration diagram shows the aberration with the e-line (546.1 nm) as the reference wavelength, but the spherical aberration diagram also shows the aberration for the g-line (435.8 nm) and the C-line (656.3 nm). In the astigmatism diagram, the solid line indicates the sagittal aberration, and the dotted line indicates the tangential (meridional) aberration.

  As can be seen from FIG. 15, the fourth lens L4 is formed on the surface of the cover glass 38 as shown in FIG. 13, and the fourth lens L4 is disposed in the vicinity of the image plane 31a, so that the power of the entire imaging lens is increased. The arrangement can be optimized, and sufficient aberration correction can be realized.

  Further, by directly fixing the fourth lens L4 to the cover glass 38, there is no need for a mechanism for holding the fourth lens L4, so that the imaging unit can be reduced in size and weight. Moreover, since it fixes directly on the cover glass 38, the 4th lens L4 can be made very thin, and there exists an effect which shortens an optical system.

  Therefore, by adopting the above configuration, it is possible to realize an image pickup unit including a small and high-performance lens group.

[Embodiment 6]
Another embodiment according to the present invention will be described below with reference to FIGS. In this embodiment, in order to explain the differences from the fifth embodiment, for the sake of convenience of explanation, members having the same functions as those described in the fifth embodiment are denoted by the same member numbers. Description is omitted.

  FIG. 16 is a cross-sectional view illustrating the configuration of the imaging unit provided in the mobile phone according to the present embodiment. FIG. 17 is a cross-sectional view showing the configuration of the lens group of the imaging unit shown in FIG. In Embodiment 5 described above, as shown in FIG. 13, the surface of the fourth lens L4 disposed in contact with the surface of the cover glass 38 on the solid-state imaging device 31 side is a spherical surface. On the other hand, in the present embodiment, the surface of the fourth lens L4 on the solid-state imaging device 31 side has an aspheric shape.

  In this embodiment, as shown in FIGS. 16 and 17, the power of the two positive lenses is such that the first lens is a biconvex lens having positive power and the second lens is a meniscus shape having a concave surface facing the object side. By making the lens relatively strong and giving negative power to the third lens, the total length of the lens system can be shortened. The third lens L3 is the only lens having negative power and functions to reduce the Petzval sum related to field curvature. Further, off-axis rays that diverge when the third lens L3 has negative power are corrected by the fourth lens L4 having positive power disposed in the vicinity of the imaging surface. By disposing the fourth lens L4 in the vicinity of the image formation surface, the incident angle of the off-axis light beam on the image formation surface can be relaxed and the distortion can be corrected. With this effect, the negative power of the third lens L3 can be made relatively strong.

  In addition, by disposing the fourth lens L4 in the vicinity of the imaging surface, the function of the lens is limited as described above, and the occurrence of astigmatism or the like in the fourth lens L4 can be suppressed. For this reason, one surface of the fourth lens L4 can be flat. By making one surface of the fourth lens L4 into a planar shape, it is possible to reduce performance degradation due to eccentricity and tilt during lens assembly. Furthermore, by making one surface of the fourth lens L4 into a planar shape, the center thickness of the fourth lens L4 can be reduced, which can contribute to the downsizing of the lens system.

  The configuration conditions of the lens group are the same as those in the first embodiment, and a description thereof will be omitted.

Hereinafter, the lens group of the present embodiment will be described in detail by showing numerical examples.
(Numerical example 6)
Tables 11 and 12 show specific numerical data of the lens group according to the present embodiment. Table 11 shows surface data, and Table 12 shows data related to the aspherical shape among the surface data in Table 11.

  The surface number Si, the curvature radius Ri, and the surface interval Di in the lens data shown in Tables 11 and 12 are the same as those described in (Numerical Example 1). The definitions of the refractive index and the Abbe number are the same as those described in (Numerical Example 1).

  The aspheric shape is an aspheric shape represented by the above aspheric formula (3).

  In this example, since L = 0.29 and Y = 2.2, L / Y = 0.13, which satisfies the above formula (1).

  In the present example, since the focal length f3 = −5.5 and f = 3.2 of the third lens L3, f3 / f = −1.7, which satisfies the above formula (2).

  As shown in Table 11, in this example, the 2nd to 7th and 11th surfaces are aspherical.

  Further, FIG. 18 shows spherical aberration, astigmatism and distortion in this example. Each aberration diagram shows the aberration with the e-line (546.1 nm) as the reference wavelength, but the spherical aberration diagram also shows the aberration for the g-line (435.8 nm) and the C-line (656.3 nm). In the astigmatism diagram, the solid line indicates the sagittal aberration, and the dotted line indicates the tangential (meridional) aberration.

  As can be seen from FIG. 18, the fourth lens L4 is formed on the surface of the cover glass 38 as shown in FIG. 16, and the fourth lens L4 is disposed in the vicinity of the image plane 31a, so that the power of the entire imaging lens is increased. The arrangement can be optimized, and sufficient aberration correction can be realized.

  Further, by directly fixing the fourth lens L4 to the cover glass 38, there is no need for a mechanism for holding the fourth lens L4, so that the imaging unit can be reduced in size and weight. Moreover, since it fixes directly on the cover glass 38, the 4th lens L4 can be made very thin, and there exists an effect which shortens an optical system.

  Therefore, by adopting the above configuration, it is possible to realize an image pickup unit including a small and high-performance lens group.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and technical means disclosed in different embodiments can be appropriately combined. The obtained embodiments are also included in the technical scope of the present invention.

  An imaging unit of the present invention facilitates assembly of a lens and has an imaging lens unit that can shorten the overall length of a lens system while having a four-lens configuration, and a portable type equipped with the imaging unit An information terminal can be provided.

  Therefore, the present invention can be applied to any device equipped with an image pickup device such as a digital camera or a mobile phone having an image pickup function.

It is sectional drawing which showed the structure of one Embodiment of the portable telephone which concerns on this invention. It is sectional drawing which showed the structure of the imaging unit which is one structure of the principal part of the portable telephone shown in FIG. It is sectional drawing which showed one structure of the principal part of the portable telephone shown in FIG. FIG. 3 is a diagram illustrating each aberration of the imaging unit illustrated in FIG. 2. It is sectional drawing which showed the structure of the lens group provided in other embodiment of the portable telephone which concerns on this invention. It is sectional drawing which showed the structure of the lens group provided in other embodiment of the portable telephone which concerns on this invention. It is the figure which showed each aberration of the imaging unit provided with the lens group shown in FIG. It is sectional drawing which showed the structure of the lens group provided in other embodiment of the portable telephone which concerns on this invention. It is the figure which showed each aberration of the imaging unit provided with the lens group shown in FIG. It is sectional drawing which showed the structure of the imaging unit provided in other embodiment of the portable telephone which concerns on this invention. It is sectional drawing which showed the structure of the lens group provided in other embodiment of the portable telephone which concerns on this invention. It is the figure which showed each aberration of the imaging unit provided with the lens group shown in FIG. It is sectional drawing which showed the structure of the imaging unit provided in other embodiment of the portable telephone which concerns on this invention. It is sectional drawing which showed the structure of the lens group provided in other embodiment of the portable telephone which concerns on this invention. It is the figure which showed each aberration of the imaging unit provided with the lens group shown in FIG. It is sectional drawing which showed the structure of the imaging unit provided in other embodiment of the portable telephone which concerns on this invention. It is sectional drawing which showed the structure of the lens group provided in other embodiment of the portable telephone which concerns on this invention. It is the figure which showed each aberration of the imaging unit provided with the lens group shown in FIG.

Explanation of symbols

1 Mobile phone (portable information terminal)
2 Housings 3a, 3b, 3c, 3d Imaging unit 4 Speaker unit 5 Microphone unit 6 Input unit 7 Monitor unit 8 Light unit 9 Shutter button 30a Solid-state imaging unit 30b Unit package 30c Imaging lens unit (imaging lens body)
31 Solid-state imaging device 31a Imaging surface (imaging surface) (focal position obtained by combining first to fourth lenses)
32 Support substrate 33 Flexible printed circuit board 34 Light shield 35 Infrared light cut filter 36 Lens holding part 37 Aperture stop 38 Cover glass L1 First lens L1 Second lens L2 Second lens L3 Third lens L4 Fourth lens

Claims (13)

An imaging lens body that forms an image of a subject on an imaging surface of a solid-state imaging device,
Consists of four lenses, in order from the subject side,
A first lens that is a biconvex lens having positive power;
A meniscus second lens having a positive power with a concave surface facing the subject side;
A meniscus third lens having a negative power with the concave surface facing the imaging surface;
A fourth lens having a positive power, in which one surface is a flat surface and the other surface is a surface having a curvature;
The imaging lens body, wherein the fourth lens is disposed in the vicinity of a focal position obtained by combining the first to fourth lenses.   The imaging lens body according to claim 1, wherein an aperture stop is disposed on the subject side of the first lens. When the distance between the center of the surface having the curvature of the fourth lens and the focal position is L and the size of the effective image circle diameter is 2Y, the fourth lens has the following formula (1);
0.03 <L / Y <1.0 (1)
The imaging lens body according to claim 1, wherein the imaging lens body is disposed so as to satisfy the above. When the focal length of the third lens is f3, and the focal length of the focal point obtained by combining the first to fourth lenses is f,
The following formula (2);
−6.0 <f3 / f <−0.5 (2)
The imaging lens body according to any one of claims 1 to 3, wherein:   5. The surface of the fourth lens having the curvature has an aspherical shape in which power is increased in a peripheral portion of the lens as compared with a central portion of the lens. The imaging lens body described in 1.   An imaging unit comprising: the imaging lens body according to any one of claims 1 to 5; and a solid-state imaging device having an imaging surface. In an imaging unit comprising a solid-state imaging device having an imaging surface and an imaging lens unit that forms an image of a subject on the imaging surface,
The imaging lens unit is composed of four lenses, and in order from the subject side,
A first lens that is a biconvex lens having positive power;
A meniscus second lens having a positive power with a concave surface facing the subject side;
A meniscus third lens having a negative power with the concave surface facing the imaging surface;
An imaging unit, comprising: a fourth lens having a positive power, arranged in the vicinity of the imaging surface, wherein one surface is a flat surface and the other surface is a curved surface.   The imaging unit according to claim 7, wherein an aperture stop is disposed on a subject side of the imaging lens unit. A light-transmitting cover member for protecting the imaging surface;
The imaging unit according to claim 7 or 8, wherein the translucent cover member has a surface in contact with the flat surface of the fourth lens.   The imaging unit according to claim 9, wherein the translucent cover is disposed on the imaging surface side of the fourth lens.   The imaging unit according to claim 9, wherein the fourth lens is arranged on the imaging surface side of the translucent cover member.   The imaging unit according to any one of claims 7 to 11, wherein the fourth lens is made of a resin material.   A portable information terminal comprising the imaging unit according to any one of claims 6 to 12.

Images