JP2009288300A - Imaging lens and imaging device using this imaging lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging lens capable of achieving a wide angle, being miniaturized, and enhancing optical performance. <P>SOLUTION: This imaging lens is constituted by arranging a first lens L1 having negative power, a second lens L2 having negative power, a third lens L3, a fourth lens L4 having positive power, a fifth lens L5 having positive power, and a sixth lens L6 having negative power in this order from an object side. In any three lenses among the lenses including the second lens L2 to the sixth lens L6, at least one lens surface in each lens forms a non-spherical face, and the third lens L3 and the sixth lens L6 are formed by a material having Abbe number of 45 or less for d ray. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an imaging lens that forms an image of a subject and an imaging apparatus using the imaging lens.

  2. Description of the Related Art Conventionally, a wide-angle imaging lens that is reduced in size and weight and is used in imaging devices for in-vehicle use, mobile phone use, monitoring use, and the like is known. Such an imaging lens forms an image of an object as a subject on a light receiving surface of an imaging element such as a CCD element or a CMOS element.

In addition, as a wide-angle imaging lens aiming at miniaturization and weight reduction, 5 to 6 lenses including an imaging lens composed of 6 lenses and a third lens made of a glass material (see Patent Document 1), and a plastic cemented lens. There is known an imaging lens (see Patent Document 2) composed of the above lens. The applicant has applied for the invention of the imaging lens described in Patent Document 3.
JP 2007-249073 A JP 2006-284620 A Japanese Patent Application No. 2007-261626

  However, as in Patent Documents 1 and 3, if the third lens is formed of a glass material, the cost increases. Further, by using an aspheric lens as the third lens, it becomes possible to correct the field curvature more satisfactorily.

  The thing of patent document 2 uses the cemented lens of plastic aspherical lenses. If an aspheric surface is used for the cemented lens, the manufacturing cost is increased.

  By the way, in recent years, the downsizing and the increase in the number of pixels of an image sensor such as a CCD element or a CMOS element are rapidly progressing. Along with this, there is a demand for further widening and downsizing an imaging lens used in an imaging device for in-vehicle use, mobile phone use, monitoring use, etc., and reducing aberrations.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an imaging lens capable of widening and downsizing and enhancing optical performance and an imaging apparatus using the imaging lens. is there.

  The first imaging lens of the present invention has, from the object side, a first lens having negative power, a second lens having negative power, a third lens, a fourth lens having positive power, and a positive power. A fifth lens and a sixth lens having negative power are provided in this order, and the second lens to the sixth lens are such that at least one lens surface of each lens forms an aspheric surface. The third lens and the sixth lens Is formed of a material having an Abbe number of 45 or less with respect to the d-line.

  The second imaging lens of the present invention is a first lens that is a meniscus lens having negative power from the object side and having a concave surface directed to the image side, and at least the lens surface on the image side is an aspheric surface. The central portion of the lens has a concave surface, and the peripheral portion of the effective diameter has a weaker negative power than the central portion, a third lens in which at least one lens surface forms an aspheric surface, and has a positive power, and has at least one lens. A fourth lens having an aspherical surface, a fifth lens having positive power and at least one lens surface being an aspherical surface, and a sixth lens having negative power and at least one lens surface being an aspherical surface. It is the thing provided in this order, It is characterized by the above-mentioned.

  In the first imaging lens and the second imaging lens, it is desirable to dispose a diaphragm between the third lens and the fourth lens.

  It is desirable that the third lens has a positive power and the center of the lens surface on the object side has a convex surface.

  The first lens is preferably a glass lens, and the second to sixth lenses are preferably plastic lenses.

  It is desirable that the first imaging lens and the second imaging lens satisfy the conditional expression (1); 2.0 <f56 / f <5.5.

  Where f: focal length of the entire imaging lens system, f56: combined focal length of the fifth lens and the sixth lens.

  It is desirable that the first imaging lens and the second imaging lens satisfy the conditional expression (2); 2.5 <(D4 + D5) / f <5.5.

  Where f: focal length of the entire imaging lens system, D4: air space between the second lens and the third lens, and D5: center thickness of the third lens.

  It is desirable that the first imaging lens and the second imaging lens satisfy the conditional expression (3); 4.0 <f3 / f <9.0.

  Where f: focal length of the entire imaging lens system, f3: focal length of the third lens.

  It is desirable that the lens surface on the image side of the second lens has a concave surface at the center of the lens surface, and the peripheral edge of the effective diameter has a weaker negative power than the center.

  The lens surface on the object side of the second lens has a convex surface at the center of the lens surface, and the peripheral edge of the effective diameter is weaker in positive power than the center, or the center of the lens surface has a convex surface and has an effective diameter. It is desirable that the peripheral edge has a negative power.

  It is desirable that the lens surface on the object side of the third lens is a convex surface at the center of the lens surface and has a region with a positive power stronger than the center within the effective diameter.

  It is desirable that the lens surface on the image side of the fifth lens has a convex surface at the center of the lens surface and that the peripheral edge of the effective diameter has a weaker positive power than the center.

  It is desirable that the lens surface on the object side of the sixth lens has a concave surface at the center of the lens surface and that the peripheral edge portion of the effective diameter has a weaker negative power than the center portion.

  It is desirable that the lens surface on the image side of the sixth lens has a convex surface at the center of the lens surface, and the peripheral edge of the effective diameter has a weaker positive power than the center.

  It is desirable that the first imaging lens and the second imaging lens satisfy the conditional expression (4); 11 <L / f <18.

  Where f: focal length of the entire imaging lens system, Lf: distance from the object-side lens surface of the first lens to the imaging surface.

  An image pickup apparatus according to the present invention includes a first image pickup lens or a second image pickup lens, and an image pickup element that converts an optical image formed by the image pickup lens into an electric signal.

  The “effective ray diameter of the lens surface” means the diameter of a circle drawn by the intersection of the ray that passes through the outermost side (position farthest from the optical axis) of the effective rays that pass through the lens surface and the lens surface. The effective light beam passing through the lens surface is a light beam used for forming an image of the subject.

  Here, the effective ray diameter of the lens surface matches the effective diameter of the lens surface.

  The “lens portion of the effective diameter of the lens surface” means that the lens surface intersects with the light beam that passes through the outermost side (position farthest from the optical axis of the lens) among all the light beams that pass through the effective diameter of the lens surface. It means the part on the surface.

  “Lens having positive power” means that the lens has positive power in the paraxial region.

  Further, “a lens having negative power” means that the lens has a negative power in a paraxial region.

  In addition, “the central portion of the lens surface is convex and the peripheral portion of the effective diameter is weaker in positive power than the central portion” means that both the peripheral portion of the effective diameter and the central portion are convex, and the curvature of the central portion is This means that the absolute value of the radius of curvature at the periphery of the effective diameter is greater than the absolute value of the radius value.

  In addition, “the central part of the lens surface is convex and the peripheral part of the effective diameter is stronger in positive power than the central part” means that both the peripheral part of the effective diameter and the central part are convex and the curvature of the central part is This means that the absolute value of the radius of curvature of the peripheral portion of the effective diameter is smaller than the absolute value of the radius value.

  Further, “the central portion of the lens surface has a convex surface and has negative power at the peripheral portion of the effective diameter” means that the central portion of the lens surface has a convex surface and the peripheral portion of the effective diameter has a concave surface.

  Furthermore, “the central part of the lens surface is concave and the effective diameter peripheral part is weaker in negative power than the central part” means that both the effective diameter peripheral part and the central part are concave and the curvature of the central part is This means that the absolute value of the radius of curvature at the periphery of the effective diameter is greater than the absolute value of the radius value.

  In addition, “the central portion of the lens surface has a concave surface and has positive power at the peripheral portion of the effective diameter” means that the central portion of the lens surface has a concave surface and the peripheral portion of the effective diameter has a convex surface.

  “The power at the periphery of the effective diameter is weaker than the power at the center of the lens surface” means that both the periphery of the effective diameter and the center are convex, and the periphery of the effective diameter is more positive than the center. Means that the effective diameter peripheral portion and the central portion are both concave, and the effective diameter peripheral portion has a negative power weaker than that of the central portion.

  "The central part of the lens surface is concave and the peripheral part of the effective diameter is stronger in negative power than the central part" means that both the peripheral part of the effective diameter and the central part are concave, and the radius of curvature of the central part is This means that the absolute value of the radius of curvature of the periphery of the effective diameter is smaller than the absolute value.

  “The central part of the lens surface is convex, and there is a region with a positive power stronger than the central part between the central part of the lens surface and the peripheral part of the effective diameter” is effective from the central part of the lens surface. The entire surface is convex up to the peripheral edge of the radius, and there is an area where the absolute value of the radius of curvature is smaller than the absolute value of the radius of curvature of the center between the center and the effective radius Means.

  The radius of curvature at the center means the radius of curvature of the lens surface at the position where the lens surface intersects the optical axis.

  The reason why the value of the radius of curvature is indicated by an absolute value is to clarify the magnitude relationship of the radius of curvature.

  According to the first imaging lens and the imaging apparatus using the imaging lens of the present invention, in order from the object side, the first lens having negative power, the second lens having negative power, the third lens, and positive A fourth lens having power, a fifth lens having positive power, and a sixth lens having negative power are arranged in this order. The second lens to the sixth lens are at least one lens surface in each lens. Since the third lens and the sixth lens are made of a material having an Abbe number of 45 or less with respect to the d-line, it is possible to widen and reduce the size and to improve the optical performance.

  By disposing the first negative lens and the second lens closest to the object side, it is possible to capture light rays that have entered at a large angle of view and to widen the optical system. By making the surface of at least one side of the second lens an aspherical surface, various aberrations can be corrected well, and the lens system can be downsized. In the second lens, the on-axis light beam and the off-axis light beam are separated from each other. Therefore, if this lens is aspherical, it is advantageous in correcting aberrations, and distortion correction is relatively easy.

  In addition, although the axial ray and the off-axis ray are also separated in the first lens, it is preferable to use a glass material as a material of the first lens L1 disposed on the most object side of the lens system as described later. . The first lens is the largest lens in the lens system. In view of these circumstances, it is preferable in terms of lens manufacturing and aberration correction that the second lens to which plastic material is easily applied is an aspherical lens.

  In addition, since the second to sixth lenses are configured such that at least one lens surface of each lens has an aspherical surface, spherical aberration, field curvature, and coma aberration can be corrected well, and the lens system can be made compact. Can be realized.

  By forming the third lens and the sixth lens with a material having an Abbe number of 45 or less with respect to the d-line, it is possible to satisfactorily correct axial chromatic aberration and lateral chromatic aberration.

  According to the second imaging lens of the present invention and the imaging device using the imaging lens, in order from the object side, the first lens that is a meniscus lens having negative power and a concave surface facing the image side, at least on the image side The lens surface is an aspheric surface, the center of the image-side lens surface is a concave surface, and the effective diameter peripheral portion is a second lens having a negative power weaker than that of the central portion, and at least one lens surface is an aspheric surface. A lens, a fourth lens having positive power and at least one lens surface being aspheric, a fifth lens having positive power and at least one lens surface being aspheric, at least one lens having negative power Since the sixth lens whose surface is an aspheric surface is disposed, it is possible to widen the angle and reduce the size and to improve the optical performance.

  By disposing the negative first lens and the second lens in order from the most object side, it is possible to catch a light ray incident at a large angle of view and to widen the optical system. By making the first lens a meniscus lens having a concave surface, it is possible to favorably correct curvature of field.

  In the second lens, at least the image-side surface is aspherical, so that various aberrations can be favorably corrected and the lens system can be downsized. In the second lens, the on-axis light beam and the off-axis light beam are separated from each other. Therefore, if this lens is aspherical, it is advantageous in correcting aberrations, and distortion correction is relatively easy.

  Although the first lens also separates the on-axis light beam and the off-axis light beam, it is preferable to use a glass material as described later as the material of the first lens disposed on the most object side of the lens system. The first lens is the largest lens in the lens system. In view of these circumstances, it is preferable in terms of lens manufacturing and aberration correction that the second lens to which plastic material is easily applied is an aspherical lens.

  The second lens has an aspherical surface on the image side, the center of this lens surface is concave, and the periphery of the effective diameter has a negative power weaker than that of the center. Since the light beam passing through can be condensed without abrupt bending, distortion can be corrected well.

  In addition, by using the third lens as a lens in which at least one lens surface is aspheric, it is possible to favorably correct curvature of field.

  The fourth lens and the fifth lens are both positive power lenses with at least one aspheric surface, the sixth lens is a negative power lens with at least one aspheric surface, and the third lens. By disposing a stop between the first lens and the fourth lens, it is possible to satisfactorily correct spherical aberration, curvature of field, and coma and to reduce the size of the lens system.

  Hereinafter, embodiments of an imaging lens of the present invention and an imaging apparatus using the imaging lens will be described in detail with reference to the drawings.

  FIG. 1 is a cross-sectional view showing a schematic configuration of an image pickup apparatus using the image pickup lens of the present invention, and FIG. 2 is a view in which auxiliary lines for explanation are added to FIG.

  The illustrated imaging lens 20 is a wide-angle imaging lens that is used in an in-vehicle imaging device mainly for imaging situations such as the front, side, and rear of an automobile. The imaging lens 20 includes a CCD, a CMOS, and the like. An object image is formed on the light receiving surface Jk. The image sensor 10 converts an optical image formed by the imaging lens 20 into an electrical signal and obtains an image signal indicating the optical image.

<Basic configuration of imaging lens and its operation and effect>
First, the basic configuration of the imaging lens 20 will be described. The imaging lens 20 includes, from the object side along the optical axis Z1, a first lens L1, a second lens L2, a third lens L3, an aperture stop St, a fourth lens L4, a fifth lens L5, a sixth lens L6, optical The member Cg1 is provided in this order.

  Here, a case where each of the first lens L1 to the sixth lens L6 is a single lens will be described, but these lenses are not limited to a single lens, and may be a cemented lens or the like.

  As described above, the light receiving surface Jk of the image sensor 10 is disposed on the imaging plane R16 on which an image representing an object that is a subject is formed through the imaging lens 20.

  Further, when the imaging lens is applied to the imaging apparatus, it is preferable to arrange a cover glass, a low-pass filter, an infrared cut filter, or the like according to the configuration on the camera side where the lens is mounted. In this example, the parallel plate-shaped optical member Cg1 is disposed between the lens system and the image sensor 10.

  Instead of arranging a low-pass filter or various filters that cut off a specific wavelength range between the lens system and the image sensor, a gap between adjacent lenses among the first lens L1 to the sixth lens L6 is used. These various filters may be arranged. Or you may give the coating which show | plays the effect | action similar to various filters to the lens surface in any one of the 1st lens L1-the 6th lens L6.

  In addition, the code | symbol R1-R16 in FIG. 1 points out the following components. That is, R1 and R2 are the object side lens surface and the image side lens surface of the first lens L1, R3 and R4 are the object side lens surface and the image side lens surface of the second lens L2, and R5 and R6 are the third side. The object-side lens surface and the image-side lens surface of the lens L3, R7 is the aperture of the aperture stop St, R8 and R9 are the object-side lens surface and the image-side lens surface of the fourth lens L4, and R10 and R11 are the first lens surface. The object side lens surface and the image side lens surface of the five lens L5, R12 and R13 are the object side lens surface and the image side lens surface of the sixth lens L6, and R14 and R15 are the object side surface of the optical member Cg1. The surface on the image side, R16, indicates an imaging surface that coincides with the light receiving surface Jk of the imaging lens 20 as described above.

  Further, each of the lens surfaces R1 to R6 and the lens surfaces R8 to R13 is formed by a curved surface smoothly connected from the central portion intersecting the optical axis to the peripheral portion of the effective diameter, and has a discontinuous region such as a step. I do not have.

  In the imaging lens 20, the first lens L1 has negative power, the second lens L2 has negative power, the fourth lens L4 has positive power, the fifth lens L5 has positive power, The 6 lens L6 has negative power.

  Further, the imaging lens 20 includes a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, and a sixth lens, in which at least one lens surface of each lens is aspheric. The third lens and the sixth lens are made of a material having an Abbe number of 45 or less with respect to the d-line.

  When the Abbe number of the material forming the third lens L3 with respect to the d-line is 45 or less, it becomes easy to satisfactorily correct the chromatic aberration of magnification. However, if the Abbe number of the material forming the third lens L3 with respect to the d-line exceeds 45, it is difficult to correct lateral chromatic aberration.

  By setting the Abbe number of the material forming the sixth lens L6 to 45 or less with respect to the d-line, it is easy to satisfactorily correct axial chromatic aberration. However, if the Abbe number of the material forming the sixth lens L6 with respect to the d-line exceeds 45, correction of axial chromatic aberration becomes difficult.

  As a material for forming the third lens L3 or the sixth lens L6, polycarbonate resin manufactured by Teijin Chemicals Ltd., Panlite SP-1516 (product name of the company, “Panlite” is a registered trademark of the company) can be used. This material has a refractive index of 1.6 or more, an Abbe number as small as 25.5, and a small optical distortion.

  By using this material for the third lens L3 or the sixth lens L6, it is possible to satisfactorily correct the chromatic aberration of magnification and the chromatic aberration on the axis, and at the same time minimize the influence of distortion generated during molding, for example, 1 million. A good image can be obtained even when used for a lens for an image sensor having a high pixel size exceeding the pixels.

  In addition, by making the second lens to the sixth lens at least one lens surface of each lens aspherical, spherical aberration, field curvature, coma aberration, and distortion are corrected satisfactorily despite wide angle. can do.

  The imaging lens 20 is also configured as follows.

  That is, the imaging lens 20 has a negative power in order from the object side along the optical axis Z1 and a first lens L1 that is a meniscus lens having a concave surface on the image side, and at least the image-side lens surface is aspheric. None, the central portion of the image-side lens surface is concave, the effective diameter peripheral portion is a second lens L2 having a weaker negative power than the central portion, at least one lens surface is an aspherical third lens L3, positive A fourth lens L4 having power, at least one lens surface forming an aspheric surface, a fifth lens L5 having positive power, and at least one lens surface forming an aspheric surface, having negative power, at least one lens A sixth lens L6 having an aspheric surface is disposed.

  By configuring the image-side lens surface of the second lens L2 as described above, distortion can be corrected well.

  In addition, since the sixth lens L6 has negative power, it is possible to correct axial chromatic aberration more satisfactorily.

  In addition, the center part of the lens surface which comprises a lens is the site | part (intersection of an optical axis and a lens surface) on a lens surface which intersects with the optical axis which passes along this lens.

  The imaging lens of the present invention may satisfy either one of the above two basic configurations or may satisfy both of the above two basic configurations.

  According to the basic configuration of the imaging lens, the imaging lens can be widened and reduced in size, and the optical performance of the imaging lens can be enhanced.

<About the configuration that further restricts the basic configuration of the imaging lens and its operation and effect>
Next, components that further limit the above-described basic configuration of the imaging lens 20, and the operations and effects thereof will be described. Note that these components that further limit the basic configuration are not essential for the imaging lens of the present invention.

<< Construction, action, and effect of the above basic structure limited by conditional expressions >>
First, the following conditional expressions (1) to (9), which further limit the basic configuration of the imaging lens, and their operations and effects will be described. The imaging lens of the present invention may satisfy only one of conditional expressions (1) to (9), or two or more of conditional expressions (1) to (9). It is good also as satisfying the combination of.

  The meanings of the parameters indicated by symbols in conditional expressions (1) to (9) are collectively shown below.

f: the focal length of the entire imaging lens, that is, the combined focal length of the first lens L1 to the sixth lens L6, f1: the focal length of the first lens, f2: the focal length of the second lens, f3: the focal length of the third lens, f4: Focal length f5 of the fourth lens: Focal length f5 of the fifth lens: Focal length f6 of the sixth lens: Composite focal length f56 of the first lens and second lens f56: Synthetic focal length f123 of the fifth lens and sixth lens: Synthetic focal length f456 of the first lens, the second lens, and the third lens: Synthetic focal length D4 of the fourth lens, the fifth lens, and the sixth lens D1: Center thickness D4 of the first lens D4: The second lens and the third lens Air distance D5: center thickness of the third lens νd3: Abbe number of the third lens relative to the d-line νd5: Abbe number of the fifth lens relative to the d-line νd6: Abbe number of the sixth lens relative to the d-line L: first Lens on the object side of the lens However, the value of the distance L is a value indicating the back focus distance in terms of air and a value indicating the actual length of the distance L other than the back focus distance. It is the value which added and.

  The back focus distance Bf is an air-converted length from the image side lens surface R13 to the imaging surface R16 of the sixth lens L6.

Conditional expression (1): 2.0 <f56 / f <5.5 relates to aberration correction.

  If the lens system is configured so as to satisfy the conditional expression (1), chromatic aberration and curvature of field can be easily corrected.

  However, if the lens system is configured so that the value of f56 / f exceeds the upper limit of conditional expression (1), that is, the conditional expression of f56 / f ≧ 5.5 is satisfied, chromatic aberration can be corrected well. It becomes difficult.

  On the other hand, if the lens system is configured so that the value of f56 / f is below the lower limit of conditional expression (1), that is, the conditional expression of 2.0 ≧ f56 / f is satisfied, the field curvature is corrected well. Difficult to do. Conditional expression (2): 2.5 <(D4 + D5) / f <5.5 relates to aberration correction and lens system size.

  If the lens system is configured to satisfy the conditional expression (2), spherical aberration, distortion and coma can be corrected well, and the back focus distance can be increased, so that the angle of view can be increased and imaging can be performed. Optical performance sufficient as a lens can be obtained.

  However, if the lens system is configured so that the value of (D4 + D5) / f exceeds the upper limit of the conditional expression (2), the diameter of the lens surface on the object side of the first lens is increased, and the total length of the lens is increased, resulting in a smaller size. It becomes difficult.

  On the other hand, if the lens system is configured such that the value of (D4 + D5) / f falls below the lower limit of conditional expression (2), spherical aberration and coma aberration cannot be corrected well, and a bright (small F value) lens is configured. It becomes difficult.

Conditional expression (3): 4.0 <f3 / f <9.0 relates to the chromatic aberration of magnification and the back focus distance.

  If the lens system is configured to satisfy the conditional expression (3), the chromatic aberration of magnification can be corrected well without shortening the back focus distance.

  However, if the lens system is configured such that the value of f3 / f exceeds the upper limit of conditional expression (3), it becomes difficult to satisfactorily correct the chromatic aberration of magnification.

  On the other hand, if the lens system is configured so that the value of f3 / f is lower than the lower limit of conditional expression (3), the chromatic aberration of magnification can be corrected well, but the back focus distance is shortened, and the imaging element 10 and the imaging lens 20 It becomes difficult to insert various filters between them.

  Conditional expression (4): 11 <L / f <18 relates to the angle of view and the apparatus size.

  If the lens system is configured so as to satisfy the conditional expression (4), a small and wide-angle lens system can be realized.

  However, if the lens system is configured such that the value of L / f exceeds the upper limit of conditional expression (4), widening of the angle can be easily achieved, but the lens system becomes large.

  On the other hand, if the lens system is configured such that the value of L / f is below the lower limit of conditional expression (4), the lens system can be reduced in size, but it is difficult to achieve a wide angle.

Conditional expression (5): −4.2 <f6 / f <−1.0 relates to chromatic aberration of magnification and chromatic aberration on the axis.

  If the lens system is configured so as to satisfy the conditional expression (5), the lateral chromatic aberration and the axial chromatic aberration can be favorably corrected.

  However, if the lens system is configured such that the value of f6 / f exceeds the upper limit of conditional expression (5), the chromatic aberration of magnification will increase.

  On the other hand, if the lens system is configured such that the value of f6 / f is below the lower limit of conditional expression (5), the negative power of the fifth lens becomes weak, and axial chromatic aberration cannot be corrected well.

Conditional expression (6): −2.0 <f12 / f <−1.0 relates to the angle of view, the apparatus size, and the aberration.

  If the lens system is configured so as to satisfy the conditional expression (6), a lens system having a small size and a wide angle of view can be realized without increasing the field curvature.

  However, if the lens system is configured such that the value of f12 / f exceeds the upper limit of conditional expression (6), widening of the angle can be easily achieved, but the field curvature becomes large.

  On the other hand, when the lens system is configured such that the value of f12 / f is below the lower limit of conditional expression (6), the negative power is weak for the first lens and the second lens having negative power arranged on the object side. Therefore, the light beam passing through these lenses cannot be bent greatly, making it difficult to achieve both wide angle and downsizing of the lens system.

Conditional expression (7): νd5 / νd6> 1.5 relates to axial chromatic aberration and chromatic aberration of magnification.

  If the lens system is configured so as to satisfy the conditional expression (7), it is possible to satisfactorily correct both axial chromatic aberration and lateral chromatic aberration.

  However, if the lens system is configured such that the value of νd5 / νd6 is less than the lower limit of conditional expression (7), it is difficult to satisfactorily correct both axial chromatic aberration and lateral chromatic aberration.

Conditional expression (8): −2.5 <f123 / f456 <−0.5 relates to the angle of view, back focus distance, and aberration.

  If the lens system is configured so as to satisfy the conditional expression (8), it is possible to achieve both a wide angle and a predetermined length of back focus distance without increasing the curvature of field.

  However, if the lens system is configured so that the value of f123 / f456 exceeds the upper limit of conditional expression (8), widening of the angle can be easily achieved, but the field curvature becomes large, and a good image is formed. Becomes difficult.

  On the other hand, if the lens system is configured such that the value of f123 / f456 is less than the lower limit of the conditional expression (8), it is difficult to achieve both widening the angle and ensuring a predetermined length of back focus distance. When the back focus distance is shortened, it is difficult to insert a cover glass or various filters between the lens surface on the image side and the light receiving surface of the image sensor.

Conditional expression (9): 0.8 <D1 / f relates to the impact resistance of the first lens.

  If the lens system is configured so as to satisfy the conditional expression (9), for example, the strength of the first lens with respect to various impacts when used in a vehicle-mounted application can be increased.

  However, if the lens system is configured such that the value of D1 / f is less than the lower limit of conditional expression (9), the first lens becomes thin and easily broken.

<< Other components that limit the above basic configuration and their functions and effects >>
In the following, components other than the conditional expressions that limit the imaging lens, and their functions and effects will be described.

◇ Further limitation regarding the lens forming material By using a glass lens as the first lens, an imaging lens having high weather resistance and being difficult to break can be produced. By producing each lens of the second lens to the sixth lens with a plastic material, it becomes possible to accurately reproduce the aspherical shape, and it is possible to make the lens system inexpensive and lightweight.

  In order to satisfactorily correct the chromatic aberration of magnification, it is desirable that the Abbe number of the material of the third lens L3 and the sixth lens L6 with respect to the d-line is 30 or less.

  Furthermore, in order to correct axial chromatic aberration satisfactorily, it is desirable that the Abbe number of the material of the third lens L3 and the sixth lens L6 with respect to the d-line is 28 or less.

  It is desirable that the Abbe number with respect to the d-line of the material of the first lens, the second lens, the fourth lens, and the fifth lens is 40 or more. By doing so, it is possible to suppress the occurrence of chromatic aberration and obtain good resolution performance.

◇ Limitation of components related to the aperture stop The aperture stop St is desirably disposed between the third lens L3 and the fourth lens L4.

  By disposing the aperture stop St between the third lens L3 and the fourth lens L4, the entire lens system can be reduced in size.

◇ Limitation of components related to the first lens For example, an imaging lens used in harsh environments such as in-vehicle cameras and surveillance cameras should use a material with good water resistance, acid resistance, chemical resistance, etc. as the first lens. Is desirable.

  As a material for forming the first lens, it is desirable to use a material having a powder method water resistance of 1st to 4th grades according to the Japan Optical Glass Industry Association standard.

  Further, as a material for forming the first lens, it is desirable to use a material having a powder method acid resistance of 1st to 4th grades of the Japan Optical Glass Industry Association standard.

  Further, it is desirable to use a hard material as a material for forming the first lens. For example, a glass material is desirably used as the first lens forming material, and a transparent ceramic material may be used.

  By using the first lens L1 as a glass lens, it is possible to create an imaging lens that has high weather resistance and is difficult to break.

  The first lens L1 is not limited to a glass spherical lens, and one or both lens surfaces of the first lens L1 may be aspherical. By using the first lens L1 as an aspheric glass lens, it is possible to form an imaging lens that is excellent in water resistance, acid resistance, chemical resistance, and the like and that can correct various aberrations better.

  A cover glass for protecting the lens may be disposed closer to the object side than the first lens, or a hard coat or a glassy thin film for improving weather resistance may be disposed on the lens surface on the first lens object side.

  When a cover glass or the like is disposed on the object side of the first lens and the first lens is not easily affected by the external environment, the first lens can be a plastic aspheric lens. When the first lens is a plastic aspheric lens, it is possible to correct field curvature and distortion more satisfactorily.

◇ Limitation of components related to the second lens It is desirable that the object-side lens surface R3 of the second lens L2 be an aspherical surface.

  Further, the lens surface R3 on the object side of the second lens L2 has a convex surface at the center (having positive power), and the effective diameter peripheral portion has a positive power weaker than the center portion or an effective diameter. The peripheral edge is preferably concave (has negative power).

  As shown in FIG. 2, “the central portion of the lens surface R3 is convex (having positive power), and the peripheral portion of the effective diameter has a weaker positive power than the central portion (hereinafter, the configuration of the lens surface R3). (Also referred to as an example) ”has the following configuration.

  That is, the point where the normal line H3 and the optical axis Z1 intersect at the point X3 on the effective diameter peripheral portion of the lens surface R3 having a convex surface at the center is the intersection point P3, and the line segment X3-P3 connecting the point X3 and the intersection point P3. Is the absolute value of the radius of curvature at the point X3 on the lens surface R3. Further, the intersection between the lens surface R3 and the optical axis Z1 is defined as a central portion C3. When determined in this way, the configuration example of the lens surface R3 is such that the lens surface R3 has a convex surface (having positive power) on the optical axis Z1 (central portion C3), and the lens surface R3 has a central surface C3. The center of curvature E3 and the intersection point P3 are both on the image side from the center C3, and the length of the line segment X3-P3 (the absolute value of the radius of curvature R3x at the point X3 of the lens surface R3) is the lens surface. This is larger than the absolute value of the radius of curvature R3c at the center C3 of R3.

  A circle Sp1 having the radius of the line segment X3-P3 with the intersection P3 as the center is shown in the figure. Further, a circle Sp2 having the radius of curvature as the absolute value of the curvature radius R3c with the center E3 of curvature as the center is shown in the figure.

  The reason why the value of the radius of curvature is indicated by an absolute value is to clarify the magnitude relationship of the radius of curvature.

  Moreover, in the same description regarding the lens surfaces to be described later other than the lens surface R3, the reference numerals used in the description are omitted.

In the following description, the reason why the radius of curvature is indicated by an absolute value is the same as described above.

  Further, “the lens surface on the object side of the second lens has a positive power at the center and a peripheral power at the effective diameter has a negative power (concave)” means that the center surface C3 of the lens surface R3 A point E3 indicating the center of curvature is located on the image side of the center portion C3 that is the intersection of the lens surface R3 and the optical axis Z1, and a point P3 indicating the center of curvature of the point X3 that is the effective diameter peripheral portion on the lens surface R3 is This is a case of being located on the object side with respect to the center portion C3.

  As described above, the center portion of the object-side lens surface R3 of the second lens L2 is a convex surface, and the effective diameter peripheral edge portion has a positive power weaker than the central portion, or the effective diameter peripheral edge portion is concave. By doing so, it is possible to satisfactorily correct field curvature while maintaining a wide angle.

  The image-side lens surface R4 of the second lens L2 is preferably an aspherical surface.

  Further, it is desirable that the image side lens surface R4 of the second lens L2 has a concave surface at the center (having negative power), and the negative power is weaker at the periphery of the effective diameter than at the center.

  The above “configuration in which the central portion of the lens surface R4 is concave and the peripheral portion of the effective diameter has a weaker negative power than the central portion (hereinafter also referred to as a configuration example of the lens surface R4)” has the following configuration. .

  That is, the point where the normal line H4 and the optical axis Z1 at the point X4 on the effective diameter peripheral part of the lens surface R4 having a concave surface (having negative power) intersect with each other is defined as an intersection point P4, and the point X4 and the intersection point P4 Is the absolute value of the radius of curvature at the point X4 on the lens surface R4. In addition, the intersection between the lens surface R4 and the optical axis Z1 is defined as a central portion C4. When the lens surface R4 is determined as described above, the lens surface R4 has a concave surface (having a negative power) on the optical axis Z1 (center portion C4), and the lens surface R4 has a central surface C4. The center of curvature E4 and the intersection point P4 are both on the image side from the center C4, and the length of the line segment X4-P4 (the absolute value of the radius of curvature R4x at the point X4 of the lens surface R4) is the lens surface. The radius of curvature R4c at the center C4 of R4 is larger than the absolute value.

  As described above, the central portion of the image side lens surface R4 of the second lens is concave, and the periphery of the second lens is reduced by reducing the negative power at the peripheral portion of the effective diameter compared to the central portion. Since the passing light beam can be condensed without abrupt bending, distortion can be corrected well.

  When the radius of curvature of the effective diameter peripheral edge portion X3 of the lens surface R3 on the object side of the second lens 2L is R3x, the absolute value (| X3-P3 |) of the radius of curvature R3x is the radius of curvature at the center portion C3. It is desirable that the value is 1.5 times or more the absolute value of R3c.

  By setting the absolute value of the curvature radius R3x to a value that is 1.5 times or more the absolute value of the curvature radius R3c, it is possible to facilitate widening of the angle and at the same time correct the curvature of field well.

  Further, when the radius of curvature at the effective peripheral edge portion X4 of the image side lens surface R4 of the second lens L2 is R4x, the absolute value (| X4-P4 |) of the radius of curvature R4x is the radius of curvature at the central portion C4. It is desirable that the value is 1.5 times or more the absolute value of R4c.

  By setting the absolute value of the radius of curvature R4x to be 1.5 times or more the absolute value of the radius of curvature R3c, it is possible to correct distortion well.

◇ Limitation of components related to the third lens It is desirable that the third lens L3 has a positive power, and the lens surface R5 on the object side has a convex surface at the center. By doing in this way, it becomes possible to correct | amend field curvature further favorably.

  The third lens may have negative power.

  The object-side lens surface R5 of the third lens L3 is preferably an aspherical surface.

  The lens surface R5 on the object side of the third lens L3 has a convex surface at the center (has positive power), and the positive power is stronger between the center and the effective diameter peripheral edge than the center. It is desirable to have a configuration that has a certain area.

  The above-mentioned “configuration in which the central portion of the lens surface R5 is convex, and there is a region where the positive power is stronger than the central portion between the central portion and the peripheral portion of the effective diameter (hereinafter, also examples of the configuration of the lens surface R5) ")" Has the following configuration.

  That is, the point where the normal line H5A and the optical axis Z1 intersect at a certain point X5A on the effective diameter of the lens surface R5 having a convex surface (having positive power) at the center is defined as the intersection point P5A, and the point X5A and the intersection point P5A The length of the connecting line segment X5A-P5A is the absolute value of the radius of curvature at the point X5A of the lens surface R5. When determined in this way, there is a configuration in which the absolute value of the radius of curvature is smaller than that of the central portion between the central portion and the peripheral portion of the effective diameter.

  Further, the object-side lens surface R5 of the third lens L3 may have a convex surface at the center, and a positive power may be stronger at the periphery of the effective diameter than at the center.

  The above-mentioned “configuration in which the central portion of the lens surface R5 is convex and the peripheral portion of the effective diameter has a stronger positive power than the central portion” has the following configuration.

  That is, the point where the normal line H5 and the optical axis Z1 at the point X5 on the periphery of the effective diameter of the lens surface R5 having a convex surface (having a positive power) intersect with the optical axis Z1 is an intersection point P5, and the point X5 and the intersection point P5 Is the absolute value of the radius of curvature at the point X5 on the lens surface R5. Further, the intersection between the lens surface R5 and the optical axis Z1 is defined as a central portion C5. When determined in this way, in the configuration example of the lens surface R5, the lens surface R5 has a convex surface (having positive power) on the optical axis Z1 (central portion C5), and the lens surface R5 is in the central portion C5 of the lens surface R5. The center of curvature E5 and the intersection point P5 are both on the image side of the center C5, and the length of the line segment X5-P5 (the absolute value of the radius of curvature R5x at the point X5 on the lens surface R5) is the lens. This is smaller than the absolute value of the radius of curvature R5c at the center C5 of the surface R5.

  As described above, the central part of the lens surface on the object side of the third lens has a convex surface, and a structure having a positive power stronger than the central part between the central part and the effective diameter peripheral part, Or, the central part of the lens surface on the object side of the third lens is convex, and the positive power is stronger at the peripheral part of the effective diameter than the central part, so that the curvature of field is good while taking a long back focus distance. It becomes possible to correct to.

  The lens surface R5 on the object side of the third lens L3 has a convex surface at the center (has positive power), and the positive power is stronger between the center and the effective diameter peripheral edge than the center. It is also possible to have a structure in which the positive power is weaker in the peripheral portion of the effective diameter than in the central portion.

  The image-side lens surface R6 of the third lens L3 is preferably an aspherical surface.

  Further, it is desirable that the image side lens surface R6 of the third lens L3 has a concave surface at the center, and has a negative power stronger at the periphery of the effective diameter than at the center.

  That is, it is desirable that the absolute value of the radius of curvature at the peripheral portion of the effective diameter of the lens surface R6 is smaller than the absolute value of the radius of curvature at the center of the lens surface R6.

  In this way, the central portion of the image-side lens surface R6 of the third lens L3 is a concave surface, and the negative power is increased at the peripheral portion of the effective diameter compared to the central portion, so that the field curvature and coma aberration are increased. Can be corrected satisfactorily.

  When the curvature radius at the effective diameter peripheral edge portion X5 of the lens surface R5 on the object side of the third lens L3 is R5x, the absolute value (| X5-P5 |) of the curvature radius R5x is the curvature radius R5c at the center portion C5. A value between 0.4 and 1.5 times the absolute value is desirable.

  By setting the absolute value of the curvature radius R5x to a value between 0.4 times and 1.5 times the absolute value of the curvature radius R5c, it is possible to satisfactorily correct the chromatic aberration of magnification.

◇ Limitation of components related to the fourth lens It is desirable that the image-side lens surface R9 of the fourth lens L4 be an aspherical surface.

  It is desirable that the image side lens surface R9 of the fourth lens L4 has a convex surface at the center, and has a weak positive power at the periphery of the effective diameter compared to the center.

  The above “configuration in which the central portion of the lens surface R9 is convex and the peripheral portion of the effective diameter has a weaker positive power than the central portion (hereinafter also referred to as a configuration example of the lens surface R9)” has the following configuration.

  That is, the point where the normal line H9 and the optical axis Z1 at the point X9 on the effective diameter peripheral portion of the lens surface R9 having a convex surface (having a positive power) intersect with the optical axis Z1 is defined as an intersection point P9. Is the absolute value of the radius of curvature at the point X9 on the lens surface R9. Further, the intersection between the lens surface R9 and the optical axis Z1 is defined as a central portion C9. When determined in this way, the configuration example of the lens surface R9 is such that the lens surface R9 has a convex surface (having positive power) on the optical axis Z1 (central portion C9), and the lens surface R9 is in the central portion C9 of the lens surface R9. The center of curvature E9 and the intersection point P9 are both on the image side from the center C9, and the length of the line segment X9-P9 (the absolute value of the radius of curvature R9x at the point X9 of the lens surface R9) is the lens surface. It is made larger than the absolute value of the radius of curvature R9c at the center C9 of R9.

  As described above, the curvature of the field can be favorably corrected by making the lens surface R9 have a convex surface at the center C9 and making the positive power weaker at the peripheral edge of the effective diameter than at the center C9. .

◇ Limitation of components related to the fifth lens It is desirable that the object-side lens surface R10 of the fifth lens L5 be an aspherical surface.

  Furthermore, it is desirable that the object-side lens surface R10 of the fifth lens L5 has a concave surface at the center (having negative power), and that the negative power is stronger than the center at the effective diameter end.

  The above “configuration in which the central portion of the lens surface R10 is concave and the peripheral portion of the effective diameter has a stronger negative power than the central portion (hereinafter also referred to as a configuration example of the lens surface R10)” is as follows.

  That is, a point where the normal line H10 of the point X10 on the peripheral edge portion of the effective diameter of the lens surface R10 having a concave surface (having a negative power) and the optical axis Z1 intersect is defined as an intersection point P10, and the point X10 and the intersection point P10 Is the absolute value of the radius of curvature at the point X10 on the lens surface R10. Further, an intersection between the lens surface R10 and the optical axis Z1 is defined as a central portion C10. When determined in this way, in the configuration example of the lens surface R10, the lens surface R10 has a concave surface (having negative power) on the optical axis Z1 (central portion C10), and the lens surface R10 is in the central portion C10 of the lens surface R10. Both the center of curvature E10 and the intersection point P10 are closer to the object side than the center C10, and the length of the line segment X10-P10 (the absolute value of the radius of curvature R10x at the point X10 of the lens surface R10) is the lens surface. This is smaller than the absolute value of the radius of curvature R10c at the center C10 of R10.

  In addition, the object-side lens surface R10 of the fifth lens L5 may have a convex surface at the center (having positive power) and negative power at the effective diameter end.

  The above-mentioned “configuration in which the central portion of the lens surface R10 has a convex surface and the peripheral portion of the effective diameter has negative power” has the following configuration.

  That is, a point where the normal line H10 of the point X10 on the peripheral portion of the effective diameter of the lens surface R10 having a convex surface (having positive power) and the optical axis Z1 intersect is defined as an intersection point P10, and the point X10 and the intersection point P10 Is the absolute value of the radius of curvature at the point X10 on the lens surface R10. Further, an intersection between the lens surface R10 and the optical axis Z1 is defined as a central portion C10. When determined in this way, “the configuration in which the central portion of the lens surface R10 has a convex surface and the peripheral portion of the effective diameter has negative power” means that the lens surface R10 is a convex surface on the optical axis Z1 (central portion C10). (Having positive power), the center of curvature E10 of the center portion C10 of the lens surface R10 is located on the object side of the center portion C10, and the intersection P10 is located on the image side of the center portion C10. It is.

  As described above, the lens surface R10 on the object side of the fifth lens L5 has a concave surface at the center (having negative power), and the peripheral portion of the effective diameter has a negative power stronger than that at the center, or The curvature of the field can be corrected satisfactorily by making the central portion a convex surface and making the peripheral portion of the effective diameter concave.

  The image-side lens surface R11 of the fifth lens L5 is preferably an aspherical surface.

  Furthermore, it is desirable that the image-side lens surface R11 of the fifth lens L5 has a convex surface at the center (having positive power), and the peripheral portion at the effective diameter has a lower positive power than the center portion.

  The above “configuration in which the central portion of the lens surface R11 is convex and the peripheral portion of the effective diameter has a weaker positive power than the central portion (hereinafter also referred to as a configuration example of the lens surface R11)” is as follows.

  That is, the point where the normal line H11 and the optical axis Z1 at the point X11 on the peripheral portion of the effective diameter of the lens surface R11 having a convex surface (having positive power) intersect is the intersection point P11, and the point X11 and the intersection point P11 Is the absolute value of the radius of curvature at the point X11 on the lens surface R11. Further, the intersection between the lens surface R11 and the optical axis Z1 is defined as a center portion C11. When determined in this way, in the configuration example of the lens surface R11, the lens surface R11 has a convex surface (having positive power) on the optical axis Z1 (center portion C11), and the lens surface R11 is in the center portion C11 of the lens surface R11. Both the center of curvature E11 and the intersection point P11 are closer to the object side than the center C11, and the length of the line segment X11-P11 (the absolute value of the radius of curvature R11x at the point X11 of the lens surface R11) is the lens surface. It is made larger than the absolute value of the radius of curvature R11c at the center C11 of R11.

  As described above, the central portion of the image-side lens surface R11 of the fifth lens L5 has a convex surface (having positive power), and the effective diameter peripheral portion weakens the positive power than the central portion, It becomes possible to correct spherical aberration satisfactorily.

◇ Limitation of components related to the sixth lens It is desirable that the object-side lens surface R12 of the sixth lens L6 be an aspherical surface.

  Further, it is desirable that the lens surface R12 on the object side of the sixth lens L6 has a concave surface at the center (having negative power), and the negative power is weaker at the periphery of the effective diameter than at the center. .

  The above “configuration in which the center portion of the lens surface R12 is concave and the peripheral portion of the effective diameter has a weaker negative power than the center portion (hereinafter also referred to as a configuration example of the lens surface R12)” has the following configuration. .

  That is, the point where the normal line H12 and the optical axis Z1 at the point X12 on the peripheral portion of the effective diameter of the lens surface R12 having a concave surface (having negative power) intersect with each other is defined as an intersection point P12, and the point X12 and the intersection point P12. Is the absolute value of the radius of curvature at the point X12 on the lens surface R12. Further, an intersection between the lens surface R12 and the optical axis Z1 is defined as a center portion C12. When determined in this way, the configuration example of the lens surface R12 is such that the lens surface R12 has a concave surface (has negative power) on the optical axis Z1 (central portion C12), and is in the central portion C12 of the lens surface R12. The center of curvature E12 and the intersection point P12 are both on the object side from the center C12, and the length of the line segment X12-P12 (the absolute value of the radius of curvature R12x at the point X12 of the lens surface R12) is the lens surface. The radius of curvature R12c at the center C12 of R12 is larger than the absolute value.

  Furthermore, the center part of the lens surface R12 on the sixth lens object side is concave (having negative power) in this way, and the effective diameter peripheral part is shaped so that the negative power is weaker than the center part, It is possible to satisfactorily correct field curvature as well as chromatic aberration.

  The image-side lens surface R13 of the sixth lens L6 is preferably an aspherical surface.

  Further, it is desirable that the image-side lens surface R13 of the sixth lens L6 has a convex surface at the center (having positive power), and that the effective diameter peripheral portion has a lower positive power than the center.

  The above “configuration in which the central portion of the lens surface R13 is convex and the peripheral portion of the effective diameter has a weaker positive power than the central portion (hereinafter also referred to as a configuration example of the lens surface R13)” has the following configuration.

  That is, the point where the normal line H13 and the optical axis Z1 at the point X13 on the effective diameter peripheral part of the lens surface R13 having a convex surface (having a positive power) intersect is the intersection point P13, and the point X13 and the intersection point P13 are Is the absolute value of the radius of curvature at the point X13 on the lens surface R13. Further, an intersection between the lens surface R13 and the optical axis Z1 is defined as a central portion C13. When determined in this way, in the configuration example of the lens surface R13, the lens surface R13 has a convex surface (having positive power) on the optical axis Z1 (central portion C13), and the lens surface R13 has a central portion C13. The center of curvature E13 and the intersection point P13 are both on the object side from the center C13, and the length of the line segment X13-P13 (the absolute value of the radius of curvature R13x at the point X13 of the lens surface R13) is the lens surface. This is larger than the absolute value of the radius of curvature R13c at the center C13 of R13.

  As described above, the center portion of the image-side lens surface R13 of the sixth lens has a convex surface, and a positive power is weaker at the periphery of the effective diameter than the center portion, or the center portion of the lens surface R13 is It is possible to correct spherical aberration and coma aberration satisfactorily by forming a convex surface and having an effective-diameter peripheral portion having a concave surface (having negative power).

  Furthermore, when the curvature radius at the effective diameter peripheral edge portion X12 of the object side lens surface R12 of the sixth lens L6 is R12x, the absolute value (| X12−P12 |) of the curvature radius R12x is the curvature of the center portion C12. It is desirable that the value is 1.5 times or more the absolute value of the radius R12c.

  Thus, by setting the absolute value of the radius of curvature R12x to a value that is 1.5 times or more the absolute value of the radius of curvature R12c, it is possible to satisfactorily correct field curvature as well as chromatic aberration.

  Further, when the radius of curvature at the effective peripheral edge portion X13 of the lens surface R13 on the image side of the sixth lens L6 is R13x, the absolute value (| X13−P13 |) of the radius of curvature RX13 is the curvature of the central portion C13. It is desirable that the value is twice or more the absolute value of the radius R13c.

  Thus, spherical aberration and coma can be favorably corrected by setting the absolute value of the radius of curvature R13x to a value that is at least twice the absolute value of the radius of curvature R13c.

◇ Restriction of Other Components The imaging lens of the present invention desirably has a distortion within ± 10% when the ideal image height is 2f × tan (θ / 2).

  The luminous flux that passes outside the effective diameter of the first lens L1 and the second lens L2 becomes stray light and a ghost is generated when it reaches the imaging surface. Therefore, the light beam that is outside the effective diameter on the first lens L1 and the second lens L2 It is desirable to block stray light by providing light shielding plates Sk1 and Sk2 which are light shielding means in the region.

  The light shielding means may employ a configuration in which a plate material that blocks light is disposed in an area outside the effective diameter on the lens, or a film made of light shielding paint is applied to an area outside the effective diameter on the lens. .

  Further, the light shielding unit may be disposed in a space between the first lens L1 and the second lens L2 as necessary. Further, the light shielding means may be disposed on the area outside the effective diameter on the second lens L3 to the sixth lens L6, or between these lenses.

  The material of each lens from the second lens to the sixth lens is preferably plastic (resin material).

  As a material of the lenses from the second lens to the sixth lens, a so-called nanocomposite material in which particles having a size smaller than the wavelength of light are mixed with a resin material may be used.

  Each of the first to sixth lenses is not limited to a material having a constant refractive index, and a gradient index lens may be used for any one or more of the six lenses.

  Each lens of the second lens to the sixth lens is not limited to the case where one surface or both surfaces are aspherical surfaces, and may be diffractive optical surfaces. That is, the diffractive optical element may be formed on any one or more lens surfaces from the second lens to the sixth lens.

  By making the second lens to the sixth lens aspherical at least one lens surface of each lens, it is possible to satisfactorily correct spherical aberration, curvature of field, coma, and distortion while maintaining a wide angle. it can.

  It is desirable that the first lens is a glass lens and the second to sixth lenses are plastic lenses.

  For example, when used in a harsh environment such as an in-vehicle camera or a surveillance camera, the material of the first lens is required to have high weather resistance. Therefore, a material having good water resistance, acid resistance, chemical resistance, etc. should be used. desirable.

  Further, it is desirable to use a hard material as the material of the first lens.

  It is desirable to use a glass lens as the first lens. A lens made of transparent ceramics may be used as the first lens.

  By using glass as the material of the first lens, it is possible to create a lens that has high weather resistance and is difficult to break.

  The first lens is not limited to a glass spherical lens. As the first lens, a glass aspheric lens in which one lens surface or both lens surfaces are aspherical surfaces may be used. By making the lens surface of the first lens an aspherical surface, various aberrations can be corrected more satisfactorily.

  By using plastic as the material from the second lens to the sixth lens, the aspherical shape can be accurately reproduced. In addition, the lens system can be manufactured at a low cost.

  Each lens from the second lens to the sixth lens may be aspheric on both sides.

  Further, it is desirable not to use a cemented lens in the lens system.

  Chromatic aberration can be easily corrected by using a cemented lens, but using a cemented lens causes an increase in cost. By using the configuration of the present invention, it is possible to manufacture a lens with good performance in which chromatic aberration is corrected without using a cemented lens.

<Specific Examples>
Next, with reference to FIGS. 3 to 15, numerical data and the like related to the imaging lenses of Examples 1 to 4 according to the present invention will be described together. FIGS. 3-6 is sectional drawing which shows schematic structure of each imaging lens of Example 1-4, and the code | symbol in FIGS. 3-6 corresponding to the code | symbol in FIG. 1, 2 respond | corresponds mutually. The configuration is shown.

  7-20 is a figure which shows the basic data of each imaging lens of Example 1- Example 4. FIG. Lens data is shown in the upper left part (indicated by symbol (a) in the figure) in each figure, and schematic specifications of the imaging lens are shown in the upper center part (indicated by sign (b) in the figure). Furthermore, each coefficient of the aspherical expression representing the shape of the lens surface (aspherical shape) is shown in the lower left part (indicated by symbol (d) in the figure). The lower right part (indicated by reference sign (e) in the figure) shows the absolute value of the radius of curvature at the periphery of the effective shape of each lens surface.

  7 to 10, in the upper left lens data, the surface number of an optical member such as a lens is sequentially increased from the object side toward the image side (i = 1 (i = 1, 2, 3,...)). ) Surface number. These lens data include the surface number of the aperture stop St (i = 7) and the surface numbers of the object-side surface and the image-side surface of the optical member Cg1, which is a parallel flat plate (i = 14, 15). In addition, the surface number (i = 16) of the imaging surface is also included. In addition, the surface number is marked with * for those in which the lens surface is aspherical.

  Ri represents the paraxial radius of curvature of the i-th (i = 1, 2, 3,...) Surface, and Di (i = 1, 2, 3,...) Represents light from the i-th surface and the i + 1-th surface. The surface interval on the axis Z1 is shown. Note that the symbol Ri of the lens data corresponds to the symbol Ri (i = 1, 2, 3,...) Indicating the lens surface in FIG.

  In each lens data, Ndj represents the refractive index with respect to the d-line (wavelength 587.6 nm) of the j-th (j = 1, 2, 3,...) Optical element that sequentially increases from the object side to the image side. Νdj represents the Abbe number of the j-th optical element with respect to the d-line.

  The unit of the paraxial radius of curvature and the surface interval is mm, and the paraxial radius of curvature is positive when convex on the object side and negative when convex on the image side.

Each aspheric surface is defined by the following aspheric expression.

  Each of the following values is shown in the schematic specifications of the upper center portion in each of FIGS.

  F value: Fno, half angle of view: ω, image height: IH, back focus distance: Bf (in Air), distance from the object side lens surface to the imaging surface of the first lens: L, focal point of the entire lens system Distance (combined focal length of first lens to sixth lens): f, focal length of first lens: f1, focal length of second lens: f2, focal length of third lens: f3, focal length of fourth lens : F4, focal length of the fifth lens: f5, focal length of the sixth lens: f6. Further, the combined focal length of the first lens and the second lens: f12, the combined focal length of the fifth lens and the sixth lens: f56, the combined focal length of the first lens, the second lens, and the third lens: f123, the fourth. The combined focal lengths f456 of the lens, the fifth lens, and the sixth lens are shown.

  As described above, the value of the distance L is a value obtained by adding the value indicating the back focus distance as an air-converted length and the value indicating the actual length other than the back focus distance among the values of the distance L. .

  Further, in the lower left part of each figure of FIGS. 7 to 10, the values of the coefficients K, A3, A4, A5... Of the aspheric expression representing each aspheric surface Ri (i = 3,4,...). Indicates.

  FIG. 11 is a diagram illustrating the values of the parameters of the conditional expressions (1) to (9) for each of the examples 1 to 4.

  12 to 15 are diagrams illustrating various aberrations of the imaging lenses of Examples 1 to 4. FIG. 12 to 15 show aberrations with respect to the d-line (wavelength 587.6 nm), the F-line (wavelength 486.1 nm), and the C-line (wavelength 656.3 nm) for each imaging lens of each example.

  The distortion diagram shows the ideal image height of 2f × tan (θ / 2) using the focal length f of the entire lens system and the angle of view θ (variable treatment, 0 ≦ θ ≦ ω), and the amount of deviation from that. Indicates.

  In addition, the effective diameter peripheral portion of the lens surface constituting the lens that forms the shape to be rotated is generally a circular region in which the distance from the optical axis of the lens is constant. The area having this shape is the edge of the effective area on the lens surface.

  As can be seen from the basic data of Examples 1 to 4 and diagrams showing various aberrations, according to the wide-angle imaging lens of the present invention, by optimizing the shape and material of each of the six lenses, Optical performance can be improved and miniaturization can be realized.

  In addition, this invention is not limited to the said embodiment and each Example, A various deformation | transformation implementation is possible. For example, the radius of curvature, the surface interval, and the refractive index of each lens component are not limited to the numerical values shown in the above drawings, and may take other values.

  In the imaging lens of the present invention, by using many aspheric surfaces after the second lens, the lens system can be downsized and manufactured at low cost, and aberrations such as field curvature and distortion can be corrected more favorably. It becomes.

The figure which shows schematic structure of the imaging lens of this invention Figure with auxiliary lines etc. for explanation added to FIG. Sectional drawing which shows schematic structure of the imaging lens of Example 1. FIG. Sectional drawing which shows schematic structure of the imaging lens of Example 2. Sectional drawing which shows schematic structure of the imaging lens of Example 3. Sectional drawing which shows schematic structure of the imaging lens of Example 4. The figure which shows the basic data of the imaging lens of Example 1. The figure which shows the basic data of the imaging lens of Example 2. The figure which shows the basic data of the imaging lens of Example 3. The figure which shows the basic data of the imaging lens of Example 4. The figure which shows the value corresponding to each parameter in conditional expression (1)-(9) for every Example FIG. 5 is a diagram illustrating various aberrations of the imaging lens of Example 1. FIG. 6 is a diagram illustrating various aberrations of the imaging lens of Example 2. FIG. 6 is a diagram illustrating various aberrations of the imaging lens of Example 3. FIG. 5 is a diagram illustrating various aberrations of the imaging lens of Example 4.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image sensor 20 Imaging lens L1 1st lens L2 2nd lens L3 3rd lens L4 4th lens L5 5th lens L6 6th lens

Claims (15)

From the object side, the first lens with negative power, the second lens with negative power, the third lens, the fourth lens with positive power, the fifth lens with positive power, the first lens with negative power 6 lenses in this order,
The second lens to the sixth lens are such that at least one lens surface of each lens forms an aspheric surface,
The imaging lens, wherein the third lens and the sixth lens are made of a material having an Abbe number of 45 or less with respect to the d-line. From the object side,
A first lens that is a meniscus lens having negative power and a concave surface facing the image side;
At least the image-side lens surface is an aspherical surface, the central portion of the lens surface is concave, and the effective diameter peripheral portion is a second lens having a weaker negative power than the central portion,
A third lens in which at least one lens surface is aspheric;
A fourth lens having positive power and at least one lens surface being aspheric;
A fifth lens having positive power and at least one lens surface being aspheric;
An imaging lens comprising a sixth lens having negative power and at least one lens surface forming an aspherical surface in this order.   The imaging lens according to claim 1, wherein a diaphragm is disposed between the third lens and the fourth lens.   4. The imaging lens according to claim 1, wherein the third lens has a positive power, and a center portion of a lens surface on the object side forms a convex surface. 5. The imaging lens according to claim 1, wherein the following conditional expression (1) is satisfied.
2.0 <f56 / f <5.5 (1)
However,
f: focal length of the entire imaging lens system f56: combined focal length of the fifth lens and the sixth lens The imaging lens according to claim 1, wherein the following conditional expression (2) is satisfied.
2.5 <(D4 + D5) / f <5.5 (2)
However,
f: Focal length D4 of the entire imaging lens system: Air space between the second lens and the third lens D5: Center thickness of the third lens The imaging lens according to claim 1, wherein the following conditional expression (3) is satisfied.
4.0 <f3 / f <9.0 (3)
However,
f: focal length of the entire imaging lens system f3: focal length of the third lens   8. The lens surface on the image side of the second lens, wherein the central portion of the lens surface is a concave surface, and the peripheral portion of the effective diameter is weaker in negative power than the central portion. The imaging lens according to any one of the above.   The lens surface on the object side of the second lens has a convex surface at the center of the lens surface, and the peripheral edge portion of the effective diameter has a weaker positive power than the central portion, or the central portion of the lens surface has a convex surface and is effective The imaging lens according to any one of claims 1 to 8, wherein the radial peripheral portion has negative power.   The lens surface on the object side of the third lens has a convex portion at the center of the lens surface, and has a region having a positive power stronger than the center within the effective diameter. The imaging lens according to any one of the above.   11. The lens surface on the image side of the fifth lens, wherein the central portion of the lens surface is convex, and the peripheral portion of the effective diameter has a positive power weaker than that of the central portion. The imaging lens according to any one of the above.   12. The lens surface on the object side of the sixth lens, wherein the central portion of the lens surface is a concave surface, and the peripheral portion of the effective diameter is weaker in negative power than the central portion. The imaging lens according to any one of the above.   The lens surface on the image side of the sixth lens is such that the central portion of the lens surface is convex, and the peripheral portion of the effective diameter is weaker in positive power than the central portion. The imaging lens according to any one of the above. The imaging lens according to claim 1, wherein the following conditional expression (4) is satisfied.
11 <L / f <18 (4)
However,
f: Focal length of the entire imaging lens system
Lf: distance from the object-side lens surface of the first lens to the imaging plane   15. An imaging apparatus comprising: the imaging lens according to claim 1; and an imaging element that converts an optical image formed by the imaging lens into an electrical signal.

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