JP2008299271A - Imaging lens, imaging device having the same, and personal digital assistant - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a miniaturized imaging lens excelling in luminous flux aberration collecting performance. <P>SOLUTION: The imaging lens 1 forming an object image on an image sensor 14 includes a first lens 11a arranged on the object side and having positive refracting power, and a second lens group 12 arranged on the object side of the image sensor 14. The second lens group 12 is formed by laminating a third lens and a fourth lens formed of materials with different optical characteristics from each other. The fourth lens 12b is formed in plane shape on the image sensor 14 side. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an imaging lens used for a small camera such as a digital still camera, and more particularly to an imaging lens having a short overall lens length suitable as a small camera incorporated in a portable information terminal and a cellular phone.

  In recent years, digital still cameras using solid-state image sensors represented by CCD (Charge Coupled Device) and CMOS (Complementary Metal Oxide Semiconductor) have been rapidly spread, and various digital still cameras have been developed. Miniaturization of digital still cameras is progressing year by year with the progress of technology in solid-state imaging devices. Among them, a digital still camera mounted on a portable information terminal or a mobile phone is particularly required to be miniaturized due to the size limitation of the housing.

  In order to reduce the size of a digital still camera, it is effective to increase the number of pixels of a solid-state image sensor first. In recent years, due to technological progress in semiconductor processes, the number of pixels of the solid-state image sensor has increased dramatically, and as a result, the area per pixel can be reduced and the area of the entire image sensor can be reduced. A camera of 3 to 5 million pixels is mounted on the above-described camera mounted on the above-described mobile phone or the like.

  Next, in order to reduce the size of the digital still camera, the lens is also required to be reduced in size. When the lens is downsized in accordance with the ratio of downsizing of the solid-state imaging device, that is, when the focal length of the lens is shortened, downsizing the lens without reducing the number of lens components is the meat per lens. Since the thickness is reduced, it is difficult in the manufacturing process. On the other hand, when the number of lenses is reduced, it is disadvantageous for aberration correction for obtaining good optical performance.

Under such circumstances, for example, Patent Document 1 discloses an imaging lens constituted by two plastic aspheric lenses. According to Patent Document 1, it is possible to provide a downsized imaging lens having good optical characteristics.
JP 2005-121685 A (published on May 12, 2005)

  However, the conventional imaging lens has a problem in correcting the aberration of the luminous flux.

  Specifically, although the imaging lens disclosed in Patent Document 1 realizes a compact optical system with a short overall length, the two lenses correct all light beams including light beams other than the optical axis. There is a problem of having to.

  The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide an imaging lens that is excellent in performance for correcting light beam aberration and is miniaturized.

  In order to solve the above-described problem, an imaging lens according to the present invention is an imaging lens that forms a subject image on an imaging element, and is arranged on the subject side and has at least one lens having a positive refractive power. And an image sensor side lens group disposed on the object side of the image sensor, and the image sensor side lens group includes two or more lens layers made of materials having different optical characteristics. Thus, among the lens layers, the lens layer disposed closest to the image sensor side is characterized in that the image sensor side has a planar shape.

  According to the above invention, the aberration of the luminous flux that cannot be corrected by the subject side lens can be efficiently corrected by the imaging element side lens group. That is, in order to correct the aberration of the light beam off the optical axis, by stacking lenses made of materials having different optical characteristics, a large number of aspheric surfaces necessary for aberration correction can be arranged in a small space. Thereby, it is possible to provide a downsized imaging lens that is excellent in the correction performance of the aberration of the light beam.

  In the imaging lens according to the present invention, it is preferable that a planar plate is provided in contact with the planar shape of the lens layer disposed closest to the imaging element.

  As a result, since the flat plate is provided in contact with the imaging lens group, it is not necessary to provide a new lens holding mechanism in the lens barrel when holding the imaging lens group. That is, in the imaging lens according to the present invention, the number of lenses that need to be provided with a lens holding mechanism can be reduced, and the imaging lens can be further reduced in size.

  Furthermore, the image pickup device side lens group according to the present invention includes two or more lens layers made of materials having different optical characteristics, and further includes a flat plate in contact with the lens layer closest to the image pickup device. Yes. Due to such a configuration, the imaging element side lens group and the plane plate can be handled as a single unit, and the plane imaging unit and the imaging element can be handled as an integrated package. When an element is provided, the image sensor side lens group, the plane plate, and the image sensor can be handled as an integrated package.

  In the imaging lens according to the present invention, the imaging lens group has a curved surface shape, and the lens layer has a positive refractive power that increases from the center to the periphery of the imaging element side lens group. It is preferable that it is the structure to perform.

  With the above configuration, the thickness of the central portion of the imaging lens group can be reduced and the thickness outside the optical axis can be increased by the above configuration. Accordingly, it is possible to suppress an increase in the optical length and to effectively correct a light beam outside the optical.

  In the imaging lens according to the present invention, it is preferable that at least one of the lens layers is made of a resin material.

  This is advantageous in terms of mass productivity and cost in manufacturing the imaging lens.

  In the imaging lens according to the present invention, it is preferable that a material of the lens layer arranged closest to the imaging element is a resin material.

  Thereby, when manufacturing the said imaging lens, it becomes possible to manufacture easily by well-known methods, such as 2P method, for example. Moreover, since a resin material is used, it is advantageous in terms of mass productivity and cost in manufacturing the imaging lens.

  In the imaging lens according to the present invention, it is preferable that the lens layer located closest to the subject among the lens layers is made of a resin material.

  Thereby, when manufacturing the said imaging lens, it becomes further advantageous in terms of mass productivity and cost.

  In the imaging lens according to the present invention, it is preferable that the lens layer located closest to the subject among the lens layers is made of an inorganic material.

  Thereby, an imaging lens excellent in stability and characteristics of the optical system can be provided.

  In the imaging lens according to the present invention, for each of the layers made of different materials, a difference in refractive index due to d-line between at least two arbitrary layers in the lens layer is 0.05 or more and / or a difference in Abbe number. Is preferably 5 or more.

  By using the difference in refractive index and / or Abbe number as described above, the effect of increasing the number of aspheric surfaces of the imaging element side lens is increased.

  In the imaging lens according to the present invention, the area of the planar shape portion in the lens layer closest to the imaging element and the area of the planar shape portion side of the plane plate can be made equal.

  With such a configuration, the size of the flat plate can be minimized, the size of the flat plate can be reduced, and the manufacturing cost can be reduced.

  In the imaging lens according to the present invention, it is preferable that the area of the planar shape portion in the lens layer closest to the imaging element is equal to the area of the surface in contact with the planar shape portion of the plane plate.

  Thereby, the image sensor side lens group and the flat plate can be handled in a more stable state.

  In the imaging lens according to the present invention, it is preferable that the plane plate has at least one function of an infrared cut filter and an optical low-pass filter.

  Since the flat plate has the above function, it is not necessary to separately provide an infrared cut film or an optical low-pass filter. Therefore, the imaging lens can be further downsized as compared with the case where they are provided.

  In addition, the imaging apparatus according to the present invention preferably includes an imaging lens and an imaging element that captures a subject image formed by the imaging lens.

  Since the imaging device is provided with a flat plate in contact with the imaging element side lens group, in the imaging device provided with the imaging lens, the flat plate and the imaging device can be integrated into a package, The image sensor and the image sensor side lens group can be handled as an integrated package. In general, in the imaging lens system, the lens group requires a separate holding mechanism such as a lens barrel and a holder, but it is necessary to provide a holding mechanism for the imaging element side lens group by integrating the imaging element and the imaging element side lens group. Therefore, it is possible to achieve miniaturization, positioning with high accuracy, and a packaged product is less likely to be displaced due to temperature change, impact, etc., and can maintain performance even when there is an environmental change. Furthermore, the imaging device can be reduced in size and weight, and an imaging device with high mass production efficiency can be provided. In addition, it is possible to suppress performance degradation due to environmental changes.

  The portable information terminal according to the present invention preferably includes the imaging device.

  Since the imaging lens has good optical characteristics and is downsized, the optical characteristics of the portable information terminal can be improved and downsized.

  As described above, the imaging lens according to the present invention is formed by laminating two or more lens layers made of materials having different optical characteristics, and among the lens layers, the lens layer arranged closest to the imaging element is The imaging element side has a planar shape.

  Therefore, the aberration of the luminous flux that cannot be corrected by the subject side lens can be efficiently corrected by the imaging element side lens group. That is, in order to correct the aberration of the light beam off the optical axis, by stacking lenses made of materials having different optical characteristics, a large number of aspheric surfaces necessary for aberration correction can be arranged in a small space. As a result, there is an effect that it is possible to provide a downsized imaging lens that is excellent in the correction performance of the aberration of the light beam.

  An embodiment of an imaging lens according to the present invention will be described below with reference to FIGS.

<Imaging lens>
FIG. 1 is a cross-sectional view of the imaging lens 1 according to the present embodiment. As shown in the figure, the imaging lens 1 is composed of a first lens group 11, a second lens group (imaging element side lens group) 12 and a plane plate 13 in order from the subject side (left hand side in FIG. 1). ing. Further, the first lens group 11 includes two first lenses (subject side lenses) 11a and second lenses (subject side lenses) 11b, and the second lens group 12 includes a third lens (lens layer). 12a and a fourth lens (lens layer) 12b.

  An aperture stop 10 is disposed on the subject side of the first lens group 11, and an image sensor (solid-state image sensor) 14 is disposed on the image sensor side of the flat plate 13. The aperture stop 10 and the image sensor 14 are not elements that constitute the imaging lens 1, but are illustrated in the drawing for convenience in order to clarify the positional relationship of the elements that constitute the imaging lens 1.

  The aperture stop 10 is a device for adjusting the amount of light passing through the imaging lens 1. The position where the aperture stop 10 is provided is not particularly limited. In the figure, the configuration in which the aperture stop 10 is provided on the subject side of the subject side lens is illustrated, but the configuration may be provided between the first lens 11a and the second lens 11b. It is good also as a structure with which the image pick-up element 14 side of the 1st lens 11a was equipped.

  The first lens group 11 has a positive refractive power with respect to a light beam incident from the object side, and is sequentially formed by the first lens 11a and the second lens 11b from the aperture stop 10 side that receives light from the object. It is configured.

  As shown in the figure, the first lens group 11 is composed of two lenses, a first lens 11a and a second lens 11b, but is not limited to this number, and is composed of a single lens. It may be. However, from the viewpoint that the imaging lens 1 can be made smaller and lighter and various aberrations such as spherical aberration, astigmatism and distortion can be corrected more favorably, it is preferably about two.

  The first lens 11a has a convex shape on the subject side and a spherical shape. On the other hand, the imaging element 14 side is a lens having a concave shape and a low-order aspherical shape.

  The second lens 11b has a concave shape on the subject side and a convex shape on the image sensor 14 side. In addition, both the subject side surface and the image side surface are aspherical lenses.

  The material of the first lens 11a and the second lens 11b is not particularly limited, and specifically, a resin material such as plastic, an inorganic material such as glass and semiconductor, a liquid crystal, a liquid, or the like may be used. it can. Furthermore, among these, a resin material (plastic) is preferable from the viewpoint of mass productivity and cost, and from the viewpoint of stability and characteristics (for example, refractive index, dispersion characteristics, heat resistance, etc.) of the optical system, it is made of glass. Preferably there is.

  As a method for forming the first lens 11a and the second lens 11b, a conventionally known method can be used. For example, when the first lens 11a and the second lens 11b are made of plastic, it is preferably formed by injection molding.

  As described above, the second lens group 12 is preferably a lens having a curved shape formed so as to be in contact with the subject side surface portion of the flat plate 13. As a result, since the flat plate is provided in contact with the imaging lens group, it is not necessary to provide a new lens holding mechanism in the lens barrel when holding the imaging lens group. That is, in the imaging lens according to the present invention, the number of lenses that need to be provided with a lens holding mechanism can be reduced, and the imaging lens can be further reduced in size.

  The second lens group 12 preferably has a configuration in which the positive refractive power increases from the center to the periphery of the second lens group 12. This is because an increase in the optical length can be suppressed and a light beam outside the optical can be effectively corrected.

  The second lens group 12 includes a third lens 12a on the subject side and a fourth lens 12b on the imaging element side, which are made of materials having different optical characteristics. Further, the third lens 12a has a curved surface on the subject side, and the third lens 12a has a configuration in which the positive refractive power increases from the center to the periphery of the second lens group 12. The positive refractive power increases from the center of 12a to the periphery.

  The shape of the third lens 12a is not particularly limited as long as it is a curved surface shape, but is preferably an aspherical shape, and more preferably an aspherical shape having a concave shape at the center of the optical axis. . By making the shape of the third lens 12a an aspherical shape in which the central portion of the optical axis has a concave shape, the thickness of the central portion of the optical axis can be reduced and the thickness outside the optical axis can be increased. As a result, it is possible to effectively correct the light beam outside the optical axis without increasing the optical length. In the shape of the third lens 12a, the thickness at the center of the optical axis may be zero. This is because there is almost no need to correct aberration at the center of the optical axis. In addition, it is preferable that it is aspherical shape which has positive refractive power in the peripheral part of the 3rd lens 12a.

  The fourth lens 12b is laminated with the third lens 12a, and the imaging element 14 side of the fourth lens 12b has a planar shape. Since the planar shape is thus formed, the fourth lens 12b and the planar plate 13 can be in surface contact.

  The material of the third lens 12a and the fourth lens 12b is not particularly limited as long as the third lens 12a can be formed so as to have the curved surface shape described above. Specifically, a resin material such as plastic, an inorganic material such as glass and a semiconductor, a liquid crystal, a liquid, or the like can be used. Among these, plastic is preferable from the viewpoint of mass productivity and cost, and glass is preferable from the viewpoint of stability and characteristics (for example, refractive index, dispersion characteristics, heat resistance, etc.) of the optical system.

  By using resin as the material of the fourth lens 12b, the fourth lens 12b can be easily formed on the flat plate 13, and further, the flat plate 13 is prevented from being damaged when the third lens 12a is formed. be able to.

  In particular, if at least one of the materials of the third lens 12a and the fourth lens 12b is a resin, the second lens group 12 can be easily formed. Specifically, an optical resin is filled between the third lens 12a obtained by molding or polishing and the flat plate 13, and the fourth lens 12b is fixed by curing and bonding by a 2P (Photoreplication Process) method. Thus, the second lens group 12 can be obtained.

  Further, both the third lens 12a and the fourth lens 12b may be formed by the 2P method. After the fourth lens 12b is formed on the flat plate 13 by the 2P method, the third lens 12a is formed on the fourth lens 12b by the 2P method, and then the third lens 12a is formed on the fourth lens 12b by the 2P method. Thus, the second lens group 12 can be obtained.

  The optical characteristics of the third lens 12a and the fourth lens 12b are different from each other, but when the difference in refractive index or Abbe number (reverse dispersion) between these two lenses is large, the two lenses are This is preferable because the effect of increasing the number of aspherical surfaces to be stacked is increased. Specifically, the difference in refractive index is preferably 0.05 or more. Moreover, it is preferable if the difference in Abbe number is 5 or more.

  In the imaging lens 1, the second lens group 12 has two lenses. However, the imaging lens 1 may be configured to further include a lens between the third lens 12a and the fourth lens 12b. In this case, the second lens group can be manufactured using a conventionally known method such as the 2P method. When the second lens group 12 includes three or more lenses, there is a difference in refractive index due to the d-line between any two lenses in the three or more lenses included in the second lens group 12. The difference of 0.05 or more and / or the Abbe number may be 5 or more.

  The flat plate 13 is usually used to prevent the image sensor 14 from being damaged, and is used to protect the image sensor 14 from foreign matters such as dust and dirt. In the imaging lens 1, since the second lens group 12 is formed on the subject side surface of the flat plate 13, there is no need to provide a lens holding mechanism for holding the third lens 12a. Further, by laminating a plurality of lenses having different optical characteristics on the plane plate 13, a large number of aspheric surfaces necessary for correcting the aberration of the light beam can be formed on the plane, and the second lens group 12 is arranged in a small space. be able to. Note that it is more preferable that the second lens group 12 and the flat plate 13 are integrally molded as one member because the second lens group and the flat plate 13 can be handled stably.

  In addition, the area of the planar portion of the fourth lens 12b closest to the imaging element 14 and the area of the planar plate 13 that is in contact with the planar portion of the fourth lens 12b can be configured to be equal. Thereby, since the magnitude | size of the plane board 13 can be made into a required minimum magnitude | size, manufacturing cost can be reduced. The area of the flat plate 13 and the area of the fourth lens 12b can obtain the above effect even if they are not completely equal, and may be substantially equal.

  The material of the flat plate 13 is not particularly limited, but the flat plate 13 itself needs to have no influence on the light incident on the imaging lens 1 and is therefore made of glass having an optical coating film. It is preferable. That is, a cover glass for protecting the image sensor 14 is preferable. In the present embodiment, the flat plate 13 serves as a cover for the image sensor 14.

  The plane plate 13 preferably has at least one function of an infrared cut filter and an optical low-pass filter, and more preferably has both of the above functions. Thereby, since it is not necessary to provide the imaging lens 1 with an infrared cut film or an optical low-pass filter, the imaging lens 1 can be further downsized.

  The imaging element 14 is an electronic component that includes an electrical conversion unit that converts a light beam that has passed through the imaging lens 1 into an electrical signal. In general, the image sensor 14 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 sequentially drives each pixel to obtain a signal charge, an A / D converter that converts each signal charge into a digital signal, and a signal processing that forms an image signal output using the digital signal. It consists of parts. Note that the type of the image sensor 14 is not particularly limited. Specifically, a CCD, a CMOS, or the like can be used.

  Next, detailed data of the imaging lens 1 will be described. Tables 1 and 2 show specific imaging lens data of the imaging lens 1. Table 1 shows basic data of the imaging lens.

  Here, the “aspheric shape” in this specification and the like will be described. The aspherical shape according to the present specification and the like can be expressed by using the aspherical expression shown in Equation 1 when the Z axis is taken in the optical axis direction and the Y axis is taken in a direction perpendicular to the optical axis.

  Where K is the conic constant, R is the radius of curvature, A, B, C and D are the 4th, 6th, 8th and 10th aspherical coefficients, respectively, and Z is the height Y from the optical axis. The length of a perpendicular line drawn from a point on the aspheric surface at the position to the tangent plane (plane perpendicular to the optical axis) of the apex of the aspheric surface is shown.

  In Table 1, “f” indicates the combined focal length of the entire imaging lens, “FNO” indicates the F number (F value) of the imaging lens, and “d” indicates the diagonal length of the imaging element.

  In the column of the surface number Si in the lens data shown in Tables 1 and 2, the surface of the constituent element closest to the subject is the first, and the i-th (i = 1 to 9). In the column of curvature radius Ri, the value of the curvature radius of the i-th surface from the subject side is shown. 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 Ri and Di is mm (millimeter). In the columns of the refractive index and the Abbe number, the d line (587.6 nm) of lens elements including the flat plate 13 (the first lens 11a, the second lens 11b, the third lens 12a, the fourth lens 12b, and the flat plate 13). ) For the refractive index and Abbe number. As described above, it is preferable that the difference in refractive index is 0.05 or more, or the difference in Abbe number (reverse dispersion ratio) is 5 or more. With such a value, the effect of increasing the number of aspheric surfaces of the imaging element 14 side lens is increased. Specific numerical values of the refractive index and the Abbe number are not particularly limited, but examples include a range where the refractive index is 1.4 to 1.8 and the Abbe number is 45 to 60. it can.

  Table 2 shows data (aspheric coefficient) related to the aspheric shapes of surface numbers 3 to 6.

  In the imaging lens 1 according to the present embodiment, the refractive index nd and Abbe number νd at the d-line are the third lens 12a_nd = 1.75, νd = 45.0, the fourth lens 12b_nd = 1.45, νd = 50.0, flat plate 13_nd = 1.52, and νd = 64.2, and the difference in refractive index is 0.05 or more, or the difference in Abbe number (reverse dispersion ratio) is 5 or more.

  2A is an aberration diagram illustrating spherical aberration of the imaging lens 1, FIG. 2B is astigmatism of the imaging lens 1, and FIG. 2C is an aberration diagram illustrating distortion aberration of the imaging lens 1. FIG. Each aberration diagram shows the aberration with the d-line as the reference wavelength, but the spherical aberration diagram also shows aberrations for 440 nm and 660 nm. In the astigmatism diagram, the solid line indicates the aberration in the tangential (meridional) direction, and the dotted line indicates the aberration in the sagittal direction.

  As can be seen from the figure, by forming the third lens 12a and the fourth lens 12b on the flat plate 13, the imaging lens 1 with sufficient aberration correction can be realized.

<Configuration of Imaging Device 20>
The configuration of the imaging device 20 will be described below with reference to FIG. FIG. 2 is a cross-sectional view of the imaging device 20. In FIG. 4, the configuration of the imaging lens 1 is adopted as the imaging lens. However, the configuration is not limited to this, and can be changed as appropriate within the scope of the present invention.

  As illustrated in FIG. 3, the imaging device 20 includes an imaging lens 1, an imaging element 14, a housing 21, a support substrate 22, a flexible printed circuit board 23, an infrared cut filter 24, and a lens holding unit 25.

  In addition, a large number of pads (not shown) are provided in the vicinity of the outer edge of the light receiving side (subject side) surface of the image sensor 14 in the present embodiment, and are connected to the support substrate 22 via bonding wires W. Yes. Note that the type of the image sensor 14 is not particularly limited. Specifically, a CCD, a CMOS, or the like can be used.

  The support substrate 22 is a hard substrate that supports the imaging device 14 and the housing 21 on one surface thereof. The other surface of the support substrate 22 (the surface opposite to the surface on which the image sensor 14 is supported) is provided with a flexible printed circuit board 23 having one end connected thereto. The support substrate 22 is provided with a large number of signal transmission pads on both the front and back surfaces, and is connected to the image sensor 14 on one side via bonding wires W and connected to the flexible printed board 23 on the other side. Yes.

  The flexible printed circuit board 23 is supplied with a voltage and a clock signal for driving the image pickup device 14 from an external circuit (for example, a control circuit included in the device on which the image pickup device 20 is mounted), or receives a digital YUV signal from the outside. It is a substrate that makes it possible to output to. 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 housing 21 is light-shielding and fixedly disposed so as to cover the image sensor 14 on the surface of the support substrate 22 on the image sensor 14 side. Specifically, the housing 21 is wide open so as to surround the image sensor 14 on the image sensor 14 side and is in contact with the support substrate 22, and a flanged cylinder having a small opening on the other end side. It is formed in a shape.

  The housing 21 includes a lens holding unit 25 therein. The lens holding unit 25 is a member for holding the first lens 11a, the second lens 11b, and the aperture stop 10.

  Further, an infrared cut filter 24 is fixedly disposed on the upper portion of the housing 21. The infrared cut filter 24 may be fixedly disposed between the imaging lens 1 and the imaging element 14. Note that an infrared light cut function may be added to the flat plate 13.

  Since the imaging device 20 is provided with the flat plate 13 in contact with the second lens group 12 described above, in the imaging device 20 including the imaging lens 1, the flat plate 13 and the imaging element can be integrated into a package. Similarly, the image sensor and the image sensor side lens group can be handled as an integrated package.

  In general, in the imaging lens system, the lens group requires a separate holding mechanism such as a lens barrel and a holder, but it is necessary to provide a holding mechanism for the imaging element side lens group by integrating the imaging element and the imaging element side lens group. Therefore, it is possible to achieve miniaturization, positioning with high accuracy, and a packaged product is less likely to be displaced due to temperature change, impact, etc., and can maintain performance even when there is an environmental change. Furthermore, the imaging device can be reduced in size and weight, and an imaging device with high mass production efficiency can be provided. In addition, it is possible to suppress performance degradation due to environmental changes.

  The portable information terminal in the present embodiment includes the imaging lens 1. The portable information terminal according to the present embodiment is not particularly limited as long as it can include an imaging lens. Specific examples include a mobile phone, a mobile device, and a laptop computer.

  As mentioned above, although the specific Example of this invention was shown, this invention is not limited to the specific shape and numerical value of the Example shown previously, In order to obtain a desired optical characteristic and optical length Each parameter can be changed as appropriate.

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

  The imaging lens according to the present invention can be suitably used for an imaging device such as a digital still camera, and can be particularly suitably used for a small-sized imaging device suitable for portable use. Specific examples of the imaging device include a digital camera mounted on a portable information terminal or a mobile phone.

It is sectional drawing of the imaging lens which concerns on this Embodiment. FIG. 6 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging lens according to the present embodiment. It is sectional drawing of the imaging device which concerns on this Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Imaging lens 10 Aperture stop 11 1st lens group 11a 1st lens 11b 2nd lens 12 2nd lens group 12a 3rd lens 12b 4th lens 13 Planar plate 14 Imaging element 20 Imaging device

Claims (13)

In an imaging lens that forms a subject image on an imaging device,
A subject side lens composed of at least one lens having a positive refractive power and disposed on the subject side;
An image sensor side lens group disposed on the subject side of the image sensor,
The imaging element side lens group is formed by laminating two or more lens layers made of materials having different optical characteristics,
Among the lens layers described above, the lens layer arranged closest to the imaging element has a planar shape on the imaging element side.   The imaging lens according to claim 1, wherein a planar plate is provided in contact with a planar shape of the lens layer disposed closest to the imaging element.   The imaging lens according to claim 1, wherein the lens layer has a configuration in which a positive refractive power increases from a center to a periphery of the imaging element side lens group.   The imaging lens according to claim 3, wherein the imaging element side lens group has a curved surface shape.   The imaging lens according to claim 1, wherein at least one of the lens layers is made of a resin material.   6. The imaging lens according to claim 5, wherein the lens layer disposed closest to the imaging element is a resin material.   The imaging lens according to claim 5 or 6, wherein the lens layer located closest to the subject among the lens layers is made of a resin material.   The imaging lens according to claim 5 or 6, wherein the lens layer located closest to the subject among the lens layers is made of an inorganic material.   The difference in refractive index due to d-line between any two of the two or more lens layers made of different materials is 0.05 or more and / or the Abbe number difference is 5 or more. Item 2. The imaging lens according to Item 1.   The imaging lens according to claim 1, wherein an area of the planar shape portion in the lens layer closest to the imaging element is equal to an area of the planar shape portion side of the planar plate.   The imaging lens according to claim 1, wherein the flat plate has a function of at least one of an infrared cut filter and an optical low-pass filter. The imaging lens according to any one of claims 1 to 11,
An image pickup apparatus comprising: an image pickup device that picks up a subject image formed by the image pickup lens.   A portable information terminal comprising the imaging device according to claim 12.

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