JP2010009028A - Imaging lens and image pickup apparatus using this imaging lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the optical performance in an imaging lens while realizing a wide angle and miniaturization. <P>SOLUTION: The imaging lens is provided with a first lens L1 with a negative power, a second lens L2 with a negative power, a third lens L3, a fourth lens L4 with a positive power, a fifth lens L5, and a sixth lens L6 with a positive power in this order from the object side. The first lens L1 is a glass lens, and the second lens L2 to the sixth lens L6 are plastic lenses. At least one lens surface of the second lens L2 to the sixth lens L6 is a non-spherical face. The third lens L3 and the fifth lens L5 are formed with a material of a 45 or less Abbe's number with respect to a d line. <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 having high weather resistance, which is reduced in size and weight and used in imaging devices for in-vehicle use, mobile phone use, monitoring use, and the like is known. Such an imaging lens is used to form an image of an object as a subject on the light receiving surface of an imaging element such as a CCD element or a CMOS element. Targeted wide-angle imaging lenses are also known. As such a wide-angle imaging lens including six lenses, a lens using a spherical lens as the third lens from the object side is known (see Patent Document 1). By using an aspherical lens as the third lens as in the present invention, it becomes possible to correct the field curvature more satisfactorily. The applicant has applied for the one described in Patent Document 2.

JP 2007-249073 A Japanese Patent Application No. 2007-261625

  By the way, in recent years, downsizing and increase in the number of pixels of image pickup devices such as CCD devices and CMOS devices 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 includes, 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, a fifth lens, In this order, the first lens is a glass lens, the second to sixth lenses are plastic lenses, and the second to sixth lenses are At least one lens surface has an aspherical surface, and the third lens and the fifth lens are made 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, has negative power, and at least one lens surface forms an aspherical surface. The second lens has positive power, at least the object-side lens surface is aspheric, the center of the lens surface is convex, and the lens surface is between the center and the effective peripheral edge. A third lens having a region where the positive power is stronger than the central portion, a fourth lens having positive power, at least one lens surface being an aspheric surface, and at least one lens surface being an aspheric surface, A sixth lens having positive power and at least one lens surface forming an aspherical surface is provided in this order.

  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 fifth lens preferably has negative power.

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

  It is desirable that the first imaging lens and the second imaging lens satisfy the conditional expression (1); 2.0 <f45 / f <5.0.

  Where f45 is the combined focal length of the fourth lens and the fifth lens, and f is the focal length of the entire imaging lens system.

  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.

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

  It is desirable that the first imaging lens and the second imaging lens satisfy the conditional expression (3); −0.1 <f / f3 <0.5.

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

  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 has a weaker positive power than the center, or the center of the lens surface has a convex surface and an effective diameter peripheral edge. It is desirable that the part has negative power.

  It is desirable that the lens surface on the object side of the fifth 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.

  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 the peripheral edge of the effective diameter has a weaker positive power than the center.

  The fifth lens is preferably a meniscus lens having a concave surface facing the object side.

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

  It is desirable that the image-side lens surface of the sixth lens has a convex surface at the center of the lens surface and a negative power at the periphery of the effective diameter.

  It is desirable that the first imaging lens and the second imaging lens satisfy the conditional expression (4); 7 <L / f <18.

  Where f: focal length of the entire imaging lens system, and L: 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 the first image pickup lens or the 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 negative power in the paraxial region.

  In addition, “the central part of the lens surface is convex and the peripheral part of the effective diameter is weaker in positive power than the central part” means that the central part and the peripheral part of the effective diameter are both convex 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 larger than the absolute value of the value of.

  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 central part and the effective diameter peripheral part are concave, and the radius of curvature of this central part is This means that the absolute value of the radius of curvature of the periphery of the effective diameter is larger than the absolute value of the value of.

  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 the center and the periphery of the effective diameter are both convex, and the periphery of the effective diameter is more positive than the center. It means that the center portion and the effective diameter peripheral edge portion are both concave surfaces, and the effective diameter peripheral edge portion has a negative power weaker than that of the central portion.

  “The central part of the lens surface is concave and the peripheral edge of the effective diameter has a stronger negative power than the central part” means that the central part and the peripheral edge of the effective diameter are both concave, and the absolute radius of curvature of this 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 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 lens has a region where the positive power is stronger than the central portion between the central portion of the lens surface and the effective diameter peripheral portion, and the effective diameter peripheral portion is less positive than the central portion" means that the lens The entire surface is convex from the center of the surface to the periphery of the effective diameter, and 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 diameter of the periphery. This means that the absolute value of the radius of curvature is larger than the absolute value of the radius of curvature at the center at the periphery of the effective diameter.

  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, the first lens having negative power, the second lens having negative power, the third lens, and positive power from the object side. A fourth lens having a first lens, a fifth lens, and a sixth lens having positive power in this order, the first lens being a glass lens, the second to sixth lenses being a plastic lens, Each of the lenses from the second lens to the sixth lens is such that at least one lens surface is aspherical, and the third lens and the fifth lens are formed of a material having an Abbe number of 45 or less with respect to the d-line. As a result, the optical performance can be increased while the angle and size are reduced.

  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.

  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.

  In addition, the third lens, the fourth lens, and the sixth lens are all lenses having a positive power with at least one surface being aspherical, and a stop is disposed between the third lens and the fourth lens, whereby a spherical surface is obtained. It is possible to satisfactorily correct aberration, curvature of field, and coma and reduce the size of the lens system.

  By forming the third lens and the fifth 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.

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

  According to the second imaging lens and the imaging device using the imaging lens of the present invention, the first lens which is a meniscus lens having negative power from the object side and having a concave surface directed to the image side, has negative power. A second lens in which at least one lens surface forms an aspherical surface, has a positive power, and at least the lens surface on the object side has an aspherical surface, and between the central portion of the lens surface and the peripheral portion of the effective diameter, A third lens having a region where the positive power is stronger than the central portion, a fourth lens having positive power, at least one lens surface being an aspheric surface, and at least one lens surface being an aspheric surface, Since the sixth lens having positive power and at least one lens surface being an aspherical surface is arranged in this order, 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 directed to the image side, it becomes possible to favorably correct curvature of field.

  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.

  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.

  Further, in the third lens, at least the lens surface on the object side is an aspherical surface, the central portion of the lens surface is a convex surface, and between the central portion of the lens surface and the peripheral portion of the effective diameter, than the central portion. By using a lens having a region with a strong positive power, it is possible to satisfactorily correct field curvature while taking a long back focus distance.

  Both the fourth lens and the sixth lens are lenses having positive power with at least one surface being aspherical, and at least one surface of the fifth lens is aspherical, and a diaphragm is formed between the third lens and the fourth lens. By arranging the lens, it is possible to satisfactorily correct spherical aberration, curvature of field, and coma and to reduce the size of the lens system.

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. Sectional drawing which shows schematic structure of the imaging lens of Example 5. Sectional drawing which shows schematic structure of the imaging lens of Example 6. Sectional drawing which shows schematic structure of the imaging lens of Example 7. Sectional drawing which shows schematic structure of the imaging lens of Example 8. 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 basic data of the imaging lens of Example 5. The figure which shows the basic data of the imaging lens of Example 6. The figure which shows the basic data of the imaging lens of Example 7. The figure which shows the basic data of the imaging lens of Example 8. The figure which shows the value corresponding to each parameter in conditional expression (1)-(8) 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. FIG. 5 is a diagram illustrating various aberrations of the imaging lens of Example 5. FIG. 6 is a diagram showing various aberrations of the imaging lens of Example 6. FIG. 10 is a diagram illustrating various aberrations of the imaging lens of Example 7. FIG. 10 is a diagram illustrating various aberrations of the imaging lens of Example 8.

  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 lens surface on the object side and the lens surface on the image side of the lens L3, R7 is the aperture of the aperture stop St, R8 and R9 are the lens surface on the object side 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, and the sixth lens L6 has positive power. is there.

  Further, in the imaging lens 20, the first lens L1 is a glass lens, the second lens L2 to the sixth lens L6 are plastic lenses, and the second lens L2 to the sixth lens L6 are At least one lens surface is aspherical, and the third lens L3 and the fifth lens L5 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 fifth lens L5 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 fifth lens L5 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 fifth lens L5, 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 fifth lens L5, it is possible to satisfactorily correct the chromatic aberration of magnification and the axial chromatic aberration, and at the same time minimize the influence of distortion generated during molding. A good image can be obtained even when used for a lens for an image sensor having a high pixel size exceeding the pixels.

  Moreover, the weather resistance of an imaging lens can be improved by making the 1st lens L1 into a glass lens. Furthermore, by using the second lens L2 to the sixth lens L6 as aspherical lenses, it is possible to satisfactorily correct spherical aberration, curvature of field, and distortion while having a wide angle.

  The imaging lens 20 is also configured as follows.

  That is, the imaging lens 20 includes a first lens L1 that is a meniscus lens having negative power from the object side along the optical axis Z1 and having a concave surface facing the image side, and has negative power, and at least one lens surface is The second lens L2 having an aspherical surface has a positive power, and at least the lens surface on the object side is an aspherical surface. A third lens L3 having a region with a positive power stronger than the central portion, an aperture stop St, a fourth lens L4 having a positive power and at least one lens surface being an aspherical surface, at least one A fifth lens having one aspheric surface and a sixth lens having positive power and at least one aspheric surface are provided in this order.

  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 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 (8) that further limit the basic configuration of the imaging lens, and the operation and effect thereof will be described. The imaging lens of the present invention may satisfy only one of conditional expressions (1) to (8), or two or more of conditional expressions (1) to (8). It is good also as satisfying the combination of.

  The meanings of the parameters indicated by symbols in conditional expressions (1) to (8) 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 fourth lens: focal length f5 of fifth lens: focal length f45 of sixth lens: combined focal length D4 of fourth lens and fifth lens D1: center thickness D4 of first lens: second lens Air spacing with the third lens D5: Center thickness νd4 of the third lens: Abbe number νd5 with respect to the d-line of the fourth lens L: Abbe number L with respect to the d-line of the fifth lens L: From the lens surface on the object side of the first lens The distance to the imaging plane However, the value of the distance L is the sum of the value indicating the back focus distance in terms of air and the value indicating the actual length of the distance L other than the back focus distance. It is the value.

  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 <f45 / f <5.0 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 f45 / f exceeds the upper limit of conditional expression (1), that is, the conditional expression of f45 / f ≧ 5.0 is satisfied, chromatic aberration can be corrected well. Becomes difficult.

  On the other hand, if the lens system is configured such that the value of f45 / f is below the lower limit of conditional expression (1), that is, the conditional expression of 2.0 ≧ f45 / 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 can be increased, so that the angle of view can be increased and the imaging lens can be used. Sufficient optical performance 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): −0.1 <f / f3 <0.5 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 f / f3 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 such that the value of f / f3 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 the two.

  Conditional expression (4): 7 <L / f <14 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 <f5 / 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 f5 / 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 f5 / f falls 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): 0.70 <D4 / f relates to aberration correction.

  If the conditional expression (6) is satisfied, the enlargement of the lens system, the occurrence of aberrations, the occurrence of ghosts, etc. can be easily prevented.

  Chromatic aberration can be corrected satisfactorily if the lower limit of conditional expression (6) is not reached, but the second lens L2 and the third lens L3 are too close together, so that the image side lens surface R4 and the second lens L2 and the second lens L2 are too close. Since the aspherical shape of the lens surface R5 on the object side of the three lenses L3 is limited, correction of aberrations is insufficient. In addition, it becomes difficult to assemble, and a ghost caused by reflection between the two lens surfaces R4 and R5 also occurs.

Conditional expression (7): 1.5 <νd4 / νd5 relates to axial chromatic aberration and lateral chromatic aberration.

  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 νd4 / νd5 is below the lower limit of the conditional expression (7), it is difficult to satisfactorily correct both the longitudinal chromatic aberration and the chromatic aberration of magnification.

Conditional expression (8): 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 (8), it is possible to increase the strength of the first lens with respect to various impacts when used in applications such as in-vehicle use.

  However, if the lens system is configured such that the value of D1 / f is less than the lower limit of conditional expression (8), 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.

◇ 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 the components related to the first lens When the imaging lens is used in harsh environments such as in-vehicle cameras and surveillance cameras, the first lens is a material with good water resistance, acid resistance, chemical resistance, etc. It is appropriate to use

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

  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.

  By making the lens surface of the first lens an aspherical surface, various aberrations can be corrected more satisfactorily.

  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, and the effective diameter periphery has a weaker positive power than the center, or the effective diameter periphery has a negative power. It is desirable to have (concave).

  As shown in FIG. 2, the above-mentioned “the center portion of the lens surface R3 on the object side of the second lens has a convex surface (having positive power), and the peripheral portion of the effective diameter has a weaker positive power than the center portion ( Hereinafter, it is also referred to as the configuration of the lens surface R3) ”.

  That is, the point where the normal line H3 and the optical axis Z1 at the point X3 on the peripheral portion of the effective diameter of the lens surface R3 having a convex surface (having positive power) intersect is the intersection point P3, and 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 convex surface at the center (having positive power) and a peripheral portion with an effective diameter having negative power (having a concave surface)” means that the lens surface R3. The point E3 indicating the center of curvature of the center portion C3 of the lens 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 the center of curvature of the point X3 that is the peripheral portion of the effective diameter on the lens surface R3 This is a case where the point P3 indicating is located on the object side of 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 a negative power) intersect with the optical axis Z1 is 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 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 is larger than the absolute value of the radius of curvature R4c at the center C4 of R4.

  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 can be condensed without abrupt bending, distortion can be corrected well.

  Note that when the radius of curvature at the effective peripheral edge portion X3 of the lens surface R3 on the object side of the second lens L2 is R3x, the absolute value (| X3-P3 |) of the radius of curvature R3x is the radius of curvature at the central 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 a value that is 1.5 times or more the absolute value of the radius of curvature R4c, distortion can be corrected satisfactorily.

◇ Limitation of components related to the third lens It is desirable that the object-side lens surface R5 of the third lens L3 be 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, it is desirable that the lens surface R5 on the object side of the third lens L3 has a convex surface at the center (having positive power), and the peripheral portion at the effective diameter has a positive power stronger than that 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.

  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 adopt a configuration in which the positive power is weaker at the peripheral portion of the effective diameter than at the central portion.

  The lens surface R5 on the object side of the third lens L3 can have a positive power stronger at the periphery of the effective diameter than at the center. Further, the lens surface R5 may have a region where the positive power is stronger than that of the central portion between the central portion and the peripheral portion of the effective diameter. Further, the lens surface R5 has a region where the positive power is stronger than the central portion between the central portion and the effective diameter peripheral portion, and the effective diameter peripheral portion has a positive power weaker than the central portion. You can also

  As described above, there is a region where the positive power is stronger than the central portion between the central portion of the lens surface on the object side of the third lens and the peripheral portion of the effective diameter, or the central portion is convex. The effective diameter peripheral portion has a positive power stronger than the central portion, or a region having a positive power stronger than the central portion between the central portion and the effective diameter peripheral portion, and the effective diameter peripheral portion. Then, by adopting a configuration in which the positive power is weaker than that at the center, it is possible to favorably correct curvature of field while increasing the back focus distance.

  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 (having negative power), and the peripheral portion at the effective diameter has stronger negative power than 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 0.3 and 1.5 times the absolute value is desirable.

  By setting the absolute value of the curvature radius R5x to a value between 0.3 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 (having positive power), and the peripheral portion at the effective diameter has a lower positive power than 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 intersect at the point X9 on the effective diameter peripheral portion of the lens surface R9 having a convex surface at the center is the intersection point P9, and the line segment X9-P9 connecting the point X9 and the 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 has a central portion C9. 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 lens surface R9 on the image side of the fourth lens has a convex surface at the center (having positive power), and the positive power is weakened at the periphery of the effective diameter compared to the center portion. It is possible to satisfactorily correct spherical aberration and curvature of field.

  When the radius of curvature at the effective peripheral edge portion X9 of the lens surface R9 on the image side of the fourth lens L4 is R9x, the absolute value of the radius of curvature R9x (| X9−P9 |) is the absolute value of the radius of curvature R9c at the central portion C9. The value is desirably 1.2 times or more of the value.

  By setting the absolute value of the curvature radius R9x to a value that is at least 1.2 times the absolute value of the curvature radius R9c, it is possible to satisfactorily correct spherical aberration and curvature of field.

◇ Limitation of components related to the fifth lens It is desirable that the fifth lens has negative power. With this configuration, axial chromatic aberration can be corrected more satisfactorily.

  In addition, the object-side lens surface R10 of the fifth lens L5 is preferably an aspherical surface.

  Further, 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 the peripheral edge portion of the effective diameter has a negative power weaker than the center.

  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 weaker 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. The radius is larger than the absolute value of the radius of curvature R10c at the center C10 of R10.

  As described above, the center part of the object-side lens surface R10 of the fifth lens L5 has a concave surface (has negative power), and its effective diameter peripheral part weakens negative power than the center part, It is possible to satisfactorily correct field curvature as well as chromatic aberration.

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

  The fifth lens L5 is preferably a meniscus lens having a concave surface facing the object side.

  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.

  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, Spherical aberration and coma can be corrected well.

◇ 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 object-side lens surface R12 of the sixth lens L6 has a convex surface at the center, and that the peripheral portion at the effective diameter has a positive power stronger than that at the center.

  The above “configuration in which the central portion of the lens surface R12 is convex and the peripheral portion of the effective diameter has a stronger positive power than the central portion (hereinafter also referred to as a configuration example of the lens surface R12)” is as follows.

  That is, the point where the normal line H12 and the optical axis Z1 at the point X12 on the periphery of the effective diameter of the lens surface R12 having a convex surface (having positive power) intersect is the 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, in the configuration example of the lens surface R12, the lens surface R12 has a convex surface (having positive power) on the optical axis Z1 (central portion C12), and the lens surface R12 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 image 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. This is smaller than the absolute value of the radius of curvature R12c at the center C12 of R12.

  By configuring the object-side lens surface R12 of the sixth lens L6 in this way, it is possible to satisfactorily correct spherical aberration and field curvature.

  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 a negative power at the peripheral portion of the effective diameter.

  “The lens surface on the image side of the sixth lens has a convex surface at the center (having positive power) and a negative power at the periphery of the effective diameter” means that the curvature of the center portion C13 of the lens surface R13 The center point K13c is located closer to the object side than the intersection C13 of the lens surface R13 and the optical axis Z1 (which coincides with the point C13 indicating the center), and the curvature of the point X13 on the effective diameter peripheral portion of the lens surface R13. This is a case where the center point P13 is located closer to the image side than the intersection point C13.

  By configuring the image-side lens surface R13 of the sixth lens L6 in this manner, coma and curvature of field can be corrected well.

  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 R13x is the absolute value of the radius of curvature R13c at the central portion C13. It is desirable that the value is 0.2 to 2.5 times the value.

  By setting the absolute value of the curvature radius R13x to a value that is 0.2 to 2.5 times the absolute value of the curvature radius R13c, it is possible to satisfactorily correct spherical aberration and curvature of field.

◇ 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, but it is outside the effective diameter on the first lens L1 and 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 L2 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 lens material 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.

  The lenses from the second lens to the sixth lens are not limited to the case where one or both surfaces are aspherical surfaces, but 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.

  In order to more appropriately correct chromatic aberration of magnification, it is desirable to form at least one of the third lens and the fifth lens with a material having an Abbe number of 30 or less with respect to the d-line.

  Furthermore, in order to satisfactorily correct axial chromatic aberration, it is desirable to form at least one of the third lens and the fifth lens with a material having an Abbe number of 28 or less with respect to the d-line.

  Furthermore, it is desirable to form the first lens, the second lens, the fourth lens, and the sixth lens with a material having an Abbe number of 40 or more with respect to the d-line.

  By forming the first lens, the second lens, the fourth lens, and the sixth lens with a material having an Abbe number of 40 or more with respect to the d-line, it is possible to suppress the occurrence of chromatic aberration and obtain a good resolution performance. Become.

  As described above, when the first lens is made of glass, an imaging lens having good weather resistance can be manufactured. In addition, by using the second lens to the sixth lens as aspherical lenses, it is possible to satisfactorily correct spherical aberration, curvature of field, and distortion while having a wide angle.

  As described above, according to the wide-angle imaging lens of the present invention, the optical performance can be improved and the size can be reduced as compared with the conventional wide-angle imaging lens.

<Specific Examples>
Next, with reference to FIGS. 3 to 27, numerical data and the like relating to the imaging lenses of Examples 1 to 8 according to the present invention will be described together. 3 to 10 are cross-sectional views showing schematic configurations of the imaging lenses of Examples 1 to 8, respectively. The reference numerals in FIGS. 3 to 8 that are the same as those in FIGS. The corresponding configuration is shown.

  FIGS. 11 to 18 are diagrams illustrating basic data of the imaging lenses of Examples 1 to 8. FIGS. 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.

  11 to 18, 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.

  The following values are 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 lens surface on the object side of the first lens to the imaging surface: L, effective beam diameter: ED The focal length of the entire lens system (the combined focal length of the first lens to the sixth lens): f, the focal length of the first lens: f1, the focal length of the second lens: f2, the focal length of the third lens: f3, The focal length of the fourth lens is f4, the focal length of the fifth lens is f5, the focal length of the sixth lens is f6, and the combined focal length of the fourth lens and the fifth lens is f45.

  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. .

  Furthermore, in the lower left part of each figure of FIGS. 11-18, the value of each coefficient K, A3, A4, A5... Of the aspheric expression representing each aspheric surface Ri (i = 3,4,...). Indicates.

  FIG. 19 is a diagram illustrating the values of the parameters of the conditional expressions (1) to (8) for each of the examples 1 to 8.

  20 to 27 are diagrams illustrating various aberrations of the imaging lenses of Examples 1 to 8. FIG. 20 to 27 show aberrations for 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 rotationally symmetric lens is generally a circular region having a constant distance from the optical axis of the lens. 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 8 and the 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.

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 (16)

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, and the sixth lens with positive power in this order In preparation,
The first lens is a glass lens;
Each of the second lens to the sixth lens is a plastic lens,
Each of the second to sixth lenses has at least one lens surface that is aspheric.
The imaging lens, wherein the third lens and the fifth 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,
A second lens having negative power and at least one lens surface being an aspheric surface;
It has a positive power, at least the object-side lens surface is aspherical, the central portion of the lens surface is convex, and the lens surface is between the central portion and the effective diameter peripheral portion from the central portion. A third lens with a strong positive power area,
A fourth lens having positive power and at least one lens surface being aspheric;
A fifth lens in which at least one lens surface is aspheric;
An imaging lens comprising a sixth lens having positive power and at least one lens surface being an aspherical surface in this order.   3. 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. 4.   The imaging lens according to claim 1, wherein the fifth lens has a negative power.   The imaging lens according to any one of claims 1 to 4, wherein a stop is disposed between the third lens and the fourth lens. The imaging lens according to claim 1, wherein the following conditional expression (1) is satisfied.
2.0 <f45 / f <5.0 (1)
However,
f45: Composite focal length of the fourth lens and fifth lens f: Focal length of the entire imaging lens system The imaging lens according to claim 1, wherein the following conditional expression (2) is satisfied.
2.5 <(D4 + D5) / f <5.5 (2)
However,
D4: Air distance between the second lens and the third lens D5: Center thickness of the third lens f: Focal length of the entire imaging lens system The imaging lens according to claim 1, wherein the following conditional expression (3) is satisfied.
−0.1 <f / f3 <0.5 (3)
However,
f3: focal length of the third lens f: focal length of the entire imaging lens system   9. The lens surface on the image side of the second lens, wherein the central portion of the lens surface is concave, 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 of the effective diameter is weaker in positive power than the central part, or the central part has a convex surface and an effective diameter peripheral edge. The imaging lens according to claim 1, wherein the imaging lens has negative power.   The lens surface on the object side of the fifth 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 imaging lens according to any one of the above.   12. 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 is weaker in positive power than the central portion. The imaging lens according to any one of the above.   13. The lens surface on the object side of the sixth lens, wherein the central portion of the lens surface is a convex surface, and the peripheral portion of the effective diameter has a stronger positive power than the central portion. The imaging lens according to any one of the above.   14. The lens surface on the image side of the sixth lens, wherein the central portion of the lens surface is a convex surface, and the peripheral portion of the effective diameter has a negative power. The imaging lens described. The imaging lens according to claim 1, wherein the following conditional expression (4) is satisfied.
7 <L / f <18 (4)
However,
f: Focal length of the entire imaging lens system L: Distance from the object-side lens surface of the first lens to the imaging surface   16. 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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