JP2009265354A - Imaging lens, and imaging device using imaging lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To widen an angle, to compactify a size and to enhance optical performance, in an imaging lens. <P>SOLUTION: This imaging device includes the first lens L1 of negative power, the second lens L2 of negative power, the third lens L3 of positive power, a diaphragm, and the fourth lens L4 of positive power, in this order from an object side. The second lens L2 and the fourth lens L4 forms at least one lens face of each of the lenses into a nonspherical face. A conditional expression: 2.4<(D4+D5)/f<5.5 is satisfied therein where D4 represents an air space between the second lens L2 and the third lens L3, D5 represents a center wall thickness of the third lens L3, and f represents a focal distance of the whole imaging lens system. <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 an imaging apparatus 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 (see Patent Document 1). There is also known a wide-angle imaging lens that is configured by four lenses and is aimed at miniaturization and weight reduction (see Patent Documents 2 and 3).
JP 2006-259704 A JP 2007-264676 A JP 2005-227426 A

  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 having positive power, an aperture, and a first lens having positive power. 4 lenses are provided in this order, and in the second lens, the third lens, and the fourth lens, at least one lens surface of each lens forms an aspheric surface, and the following conditional expression (1) is satisfied. It is a feature.

2.4 <(D4 + D5) / f <5.5 (1)
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 lens surface on the object side of the second lens is the lens surface At least one inflection point within the effective diameter of the lens, and 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, or the central portion of the lens surface is convex. None It is desirable that the peripheral portion of the effective diameter has a concave surface.

  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 facing the image side. The lens surface on the object side is aspherical, and the center of this lens surface The second lens having a convex surface and the effective diameter peripheral portion having a positive power weaker than the central portion, or the center portion of the lens surface having a convex surface and a negative power at the effective diameter peripheral portion has a positive power. And a third lens having an aspheric surface on the object side, an aperture, and a fourth lens having a positive power and an aspheric surface on the image side. .

  The second imaging lens preferably satisfies the following conditional expression (1).

2.4 <(D4 + D5) / f <5.5 (1)
However,
D4: air distance between the second lens and the third lens D5: central thickness of the third lens f: focal length of the entire imaging lens system The third lens is an Abbe relative to the d-line of the third lens It is desirable that the number νd3 is made of a material that satisfies the following conditional expression (2).

νd3 <45 (2)
In the third lens, it is desirable that the focal length f3 of the third lens satisfies the following conditional expression (3).

1.0 <f3 / f <3.0 (3)
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.

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

  It is desirable that the lens surface on the image side of the third lens has a lower power at the peripheral portion of the effective diameter than the power at the center of the lens surface.

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

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

  It is desirable that the combined focal length f12 of the first lens and the second lens and the combined focal length f34 of the third lens and the fourth lens satisfy the following conditional expression (4).

0.01 <| f12 / f34 | <0.5 (4)
It is desirable that the distance L from the object-side lens surface of the first lens to the imaging surface of the imaging lens satisfies the following conditional expression (5).

7 <L / f <16 (5)
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 “lens having a positive power” and the “lens having a negative power” define at least the power on the paraxial axis.

  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 effective diameter peripheral portion is a portion formed by a point where a light ray passing through the outermost side among all light rays passing through the effective diameter of each lens intersects each lens surface.

  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 peripheral part of the effective diameter is also convex like the central part 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.

  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.

  Further, “the central part of the lens surface is concave and the peripheral edge of the effective diameter is weaker in negative power than the central part” means that the peripheral part of the effective diameter is concave as well as the central part, 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 the periphery of the effective diameter is also convex like the center, and the periphery of the effective diameter is more positive than the center. Means that the effective diameter peripheral edge portion is concave as well as the central portion, 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 part of the effective diameter is stronger in negative power than the central part” means that the peripheral part of the effective diameter is concave as well as the central part, 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 smaller than the absolute value.

  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 device using the imaging lens of the present invention, from the object side, the first lens having negative power, the second lens having negative power, and the third having positive power. A lens, a diaphragm, and a fourth lens having a positive power in this order, and the second lens, the third lens, and the fourth lens have at least one lens surface of each lens aspherical, and a conditional expression (1): Since 2.4 <(D4 + D5) / f <5.5 is satisfied, 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 on the most object side, it is possible to capture light rays that have been incident at a large angle of view and to widen the angle. 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.

  Further, both the third lens and the fourth lens are lenses having positive power with at least one surface being aspherical, and a diaphragm is disposed between the third lens and the fourth lens, so that curvature of field and coma are reduced. It is possible to correct aberrations well and to reduce the size of the lens system.

  According to the second imaging lens and the imaging apparatus using the imaging lens of the present invention, the first lens that is a meniscus lens having negative power from the object side and having the concave surface directed to the image side, the lens surface on the object side Is an aspherical surface, the center of this lens surface is convex and the effective diameter peripheral edge is weaker in positive power than the center, or the center of this lens surface is convex and negative at the effective diameter peripheral edge. A second lens having power, a third lens having positive power and a lens surface on the object side forming an aspheric surface, and a fourth lens having a positive power and a lens surface having an aspheric surface on the image side. Since they are provided in order, the optical performance can be enhanced while widening and downsizing.

  By disposing the negative first lens and the second lens on the most object side, it is possible to catch a light ray incident at a large angle of view and to widen the angle.

  Further, the first lens is a meniscus lens having negative power on the object side and a concave surface on the image side, so that the Petzval sum can be reduced and the curvature of field can be corrected over a wide field angle. It becomes possible.

  Further, by making the surface of at least one side of the second lens an aspherical surface, it is possible to satisfactorily correct various aberrations and reduce the size of the lens system. 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. From 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.

  By making the surface on the second lens object side an aspherical surface, it becomes easy to make the lens system smaller and wider. Further, the second lens object side surface has a lens surface that is convex in the center, and the effective diameter peripheral portion has a positive power weaker than that of the central portion, or the central portion of this lens surface is convex and has an effective diameter peripheral portion. By using a surface having negative power, it becomes easy to downsize and widen the lens system, and it is possible to satisfactorily correct field curvature.

  Further, both the third lens and the fourth lens are lenses having positive power with at least one surface being aspherical, and a diaphragm is disposed between the third lens and the fourth lens, so that curvature of field and coma are reduced. It is possible to correct aberrations well and to reduce the size of the lens system.

  By making the third lens object side surface an aspherical surface, it is possible to favorably correct curvature of field.

  By making the fourth lens image side surface an aspherical surface, it is possible to satisfactorily correct field curvature and coma.

  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 used in an in-vehicle or crime prevention imaging device for photographing the surrounding situation outdoors, on the light receiving surface Jk of the imaging element 10 made of a CCD, a CMOS, or the like. An object image is formed. 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 a first lens L1, a second lens L2, a third lens L3, an aperture stop St, a fourth lens L4, and an optical member Cg1 in this order from the object side along the optical axis Z1.

  Here, a case where each of the first lens L1 to the fourth lens L4 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 R12 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 a specific wavelength range between the lens system and the image sensor, it is between the adjacent lenses of the first lens L1 to the fourth lens L4. 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 4th lens L4.

  In addition, the code | symbol R1-R12 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 position 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 optical members. The object-side surface and the image-side surface of Cg1, R12, indicate the imaging surface Jk of the imaging lens 20 as described above.

  In addition, each of the lens surfaces R1 to R6 and the lens surfaces R8 to R12 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 third lens L3 has positive power, and the fourth lens L4 has positive power. is there.

  Further, in the imaging lens 20, the second lens L2, the third lens L3, and the fourth lens L4 are such that at least one lens surface of each lens is aspheric. Further, the air distance D4 between the second lens and the third lens, the center thickness D5 of the third lens, and the focal length f of the entire imaging lens system are conditional expression (1): 2.4 <(D4 + D5) / f. <5.5 is satisfied.

  Thus, the imaging lens 20 configured to satisfy the conditional expression (1) and the like can satisfactorily correct spherical aberration, distortion, and coma, and can have a long back focus distance. Further, since the angle of view can be increased, sufficient optical performance can be obtained.

  Note that the back focus distance is the distance (air conversion length) from the image-side lens surface R9 to the imaging surface R12 of the fourth lens L4.

  If the value of (D4 + D5) / f exceeds the upper limit of conditional expression (1), the diameter of the first lens L1 disposed on the object side increases and the overall length of the imaging lens also increases. It becomes difficult.

  On the other hand, if the value of (D4 + D5) / f falls below the lower limit of conditional expression (1), spherical aberration and coma aberration cannot be corrected well, making it difficult to obtain a bright (small F value) lens system. Become.

  The imaging lens 20 is also configured as follows.

  That is, the imaging lens 20 includes a first lens L1, a second lens L2, a third lens L3, an aperture stop St, and a fourth lens L4 in this order from the object side along the optical axis Z1. L1 is a meniscus lens having negative power and having a concave surface facing the image side (the arrow + Z direction side in the figure).

  In the second lens L2, the lens surface R3 on the object side (the arrow-Z direction side in the figure) is an aspheric surface, the central portion of the lens surface R3 is a convex surface, and the effective peripheral edge is more positive than the central portion. Is weak, or the central portion of the lens surface R3 is convex and has a negative power at the periphery of the effective diameter. The third lens L3 has positive power, and the object side lens surface R5 forms an aspherical surface. The fourth lens L4 has positive power, and the image-side lens surface R9 is aspheric.

  The central portion of the lens surface is a portion on the lens surface where the lens surface and the optical axis intersect.

  Hereinafter, the meaning that “the central portion of the lens surface R3 is convex and the peripheral edge portion of the effective diameter is weaker in the positive power than the central portion” will be described. The explanation will be given with reference to FIG. In addition, about the lens surfaces other than the said lens surface R5, illustration of the code | symbol used by description is abbreviate | omitted.

  The above-mentioned “configuration in which the center portion of the lens surface R3 is convex and the peripheral edge portion of the effective diameter is weaker in positive power than the center portion (hereinafter also referred to as a configuration example of the lens surface R3)” is as follows. .

  That is, the point where the normal line H3 and the optical axis Z1 at the point X3 on the periphery of the effective diameter of the lens surface R3 having a convex surface (having a 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 of the lens surface R3 at the point X3. Further, the intersection between the lens surface R3 and the optical axis Z1 is defined as a central portion C3. When the lens surface R3 is determined as described above, the lens surface R3 has a convex surface (positive power) on the optical axis Z1 (center 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 of 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.

  Further, the fact that the center portion of the lens surface R3 is convex and has a negative power at the periphery of the effective diameter means that the center E3 of curvature at the center portion C3 on the lens surface R3 is closer to the image side than the center portion C3, and It means that P3 is on the object side with respect to the central portion C3.

  The surface R3 on the second lens object side is an aspherical surface, and the central portion of this lens surface is a convex surface, and the peripheral portion of the effective diameter has a weaker positive power than the central portion, or the central portion of this lens surface R3 is a convex surface By having a negative power at the periphery of the effective diameter, it becomes easy to reduce the size and widen the lens system, and it is possible to satisfactorily correct the curvature of field.

  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 (2) to (12) 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 (2) to (12), or two or more of conditional expressions (2) to (12). It is good also as satisfying the combination of.

  The meanings of the parameters indicated by symbols in the conditional expressions (2) to (12) 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 fourth lens L4 f2: the focal length of the second lens f3: the focal length of the third lens f12: the first lens and the second lens Synthetic focal length f34: Synthetic focal length D3 of the third lens and the fourth lens D1: Center thickness D3 of the first lens D3: Center thickness D2 of the second lens D4: Air spacing D2 between the second lens and the third lens D5: First Center thickness D7 of the three lenses: Air distance R4c between the aperture stop and the fourth lens R4c: Radius of curvature of the center of the image side lens surface of the second lens νd3: Abbe number L of the third lens with respect to the d line L: First The distance from the lens surface on the object side of the lens to the imaging surface However, the value of the distance L is a value other than the value indicating the back focus distance in terms of air and the back focus distance of the distance L. The value obtained by adding the actual length is there.

  Note that the back focus distance Bf is a distance (air conversion length) from the image-side lens surface R9 to the imaging surface R12 of the fourth lens L4.

N1: Refractive index ED with respect to the d-line of the first lens: the effective ray diameter of the image side lens surface R2 of the first lens L1, that is, the outermost side of the rays passing through the image side lens surface R2 of the first lens L1. This is the diameter of a circle drawn by the intersection of the passing light beam V1 and its lens surface R2 (see FIG. 2).

  “Effective ray diameter of 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. To do. 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.

  In addition, the above-mentioned “effective diameter peripheral edge portion of the lens surface” is a portion formed by each point on the lens surface that intersects the light ray passing through the outermost side among the effective light rays passing through the lens surface, and on the circumference of the effective diameter. means.

Conditional expression (2): νd3 <45 relates to correction of chromatic aberration of magnification and the like.

  If conditional expression (2) is satisfied, it will be easy to satisfactorily correct chromatic aberration of magnification.

  However, if the condition is out of the range of the conditional expression (2), it becomes difficult to correct the chromatic aberration of magnification.

In order to correct the chromatic aberration of magnification more satisfactorily, the Abbe number ν3 with respect to the d-line of the third lens should satisfy the following conditional expression (2-2).
νd3 <32 (2-2)

Furthermore, in order to minimize the chromatic aberration of magnification, the Abbe number ν3 of the third lens with respect to the d-line may satisfy the following conditional expression (2-3).
νd3 <28 (2-3)

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

  In Examples 3, 5, and 6 to be described later, as an optical material for forming the third lens L3, polycarbonate resin manufactured by Teijin Chemicals Ltd., Panlite (registered trademark) SP-1516 (product name, “Panlite (registered trademark)” ) "Is a registered trademark of the company). This material is characterized in that the refractive index with respect to the d-line is 1.60 or more, the Abbe number with respect to the d-line is as small as 25.5, and the optical distortion is small.

  By using this material for the third lens L3, it is possible to correct the chromatic aberration of magnification satisfactorily, and at the same time, to minimize the occurrence of distortion that occurs during molding of the resin material. By using the imaging lens of the present invention as an imaging lens for a high-pixel imaging device having, for example, more than 1 million pixels, it is possible to obtain a good image representing an object.

Conditional expression (3): 1.0 <f3 / f <3.0 relates to aberration correction, assembling ability, and the like.

  If the lens system is configured so as to satisfy the conditional expression (3), it is possible to easily correct the chromatic aberration of magnification and assemble the lens.

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

  On the other hand, if the lens system is configured such that the value of f3 / f is lower than the lower limit of conditional expression (3), the power of the third lens becomes too strong and the sensitivity to decentration becomes high, making it difficult to assemble the lens. .

Conditional expression (4): 0.01 <| f12 / f34 | <0.5 relates to aberration correction and the like.

  If the lens system is configured so as to satisfy the conditional expression (4), it is possible to easily correct field curvature and coma.

  However, if the value of | f12 / f34 | exceeds the upper limit of the conditional expression (4), it becomes difficult to widen the angle and at the same time, the field curvature becomes large, making it difficult to obtain a good image.

  On the other hand, if the value of | f12 / f34 | is less than the lower limit of the conditional expression (4), widening can be easily achieved, but coma increases, and it is difficult to obtain a good image in the periphery. Become.

Conditional expression (5): 7 <L / f <16 relates to downsizing and widening.

  If the lens system is configured to satisfy the conditional expression (5), it is possible to achieve a wide angle as well as a reduction in size.

  However, if the value of L / f is made to exceed the upper limit of conditional expression (5), widening of the angle can be easily achieved, but the size of the imaging lens is increased.

  On the other hand, if the value of L / f is made lower than the lower limit of conditional expression (5), the size of the imaging lens can be reduced, but it is difficult to achieve a wide angle.

Conditional expression (6): 1.70 <N1 <1.90 relates to aberration correction and the like. N1 is a refractive index with respect to the d-line of the first lens as described above.

  If the lens system is configured to satisfy the conditional expression (6), chromatic aberration and distortion can be easily corrected.

  However, if the value of N1 is made to exceed the upper limit of conditional expression (6), the Abbe number of the lens member becomes small and the chromatic aberration becomes large. In addition, the cost of the lens member is increased, leading to an increase in the cost of the imaging lens.

  On the other hand, if the value of N1 is made lower than the lower limit of the conditional expression (6), it is necessary to increase the curvature of the object-side surface in order to achieve a wide angle, and it is difficult to correct distortion well. It becomes.

Conditional expression (7): 1.5 <ED / R4c <1.90 relates to workability and aberration correction.

  If the lens system is configured so as to satisfy the conditional expression (7), it is possible to achieve both good workability and good distortion correction.

  However, if the value of ED / R4c is made to exceed the upper limit of conditional expression (7), the lens surface R4 on the image side of the second lens becomes close to a hemisphere, which makes it difficult to process, thereby increasing the manufacturing cost of the imaging lens. Resulting in.

  On the other hand, when the value of ED / R4c is made lower than the lower limit of conditional expression (7), the processing of the second lens is easy, but the distortion cannot be corrected well.

Conditional expression (8): −2.0 <f2 / f <−1.0 relates to aberration correction and widening of the angle.

  If the lens system is configured so as to satisfy the conditional expression (8), it is possible to achieve both wide angle and good correction of spherical aberration.

  However, if the value of f2 / f is made to exceed the upper limit of conditional expression (8), it will be difficult to correct spherical aberration well.

  On the other hand, if the value of f2 / f is made lower than the lower limit of the conditional expression (8), the negative power of the second lens becomes weak and it becomes difficult to widen the angle.

Conditional expression (9): 0.50 <D3 / f <1.5 relates to the size and workability of the imaging lens.

  If the lens system is configured so as to satisfy the conditional expression (9), it is possible to achieve both good processability and downsizing of the second lens L2 while suppressing a decrease in aberration.

  However, if the value of D3 / f is made to exceed the upper limit of conditional expression (9), the lens system becomes larger and the objective of size reduction cannot be achieved. Further, when trying to prevent an increase in the size of the lens system, the degree of freedom of the aspheric shape of the lens surface R4 on the image side of the second lens L2 is limited, and distortion correction becomes insufficient.

  On the other hand, if the value of D3 / f is made lower than the lower limit of conditional expression (9), the center thickness of the second lens L2 becomes too small to make processing difficult, and the manufacturing cost of the imaging lens increases.

Conditional expression (10): 0.50 <D1 / f relates to impact resistance and the like.

  If the lens system is configured so as to satisfy the conditional expression (10), for example, the impact resistance of the first lens when used in a vehicle-mounted application can be easily improved.

  If the value of D1 / f is made lower than the lower limit of the conditional expression (10), the first lens becomes thin and easily cracked.

Conditional expression (11): 0.50 <D4 / f <2.0 relates to aberration correction.

  If the lens system is configured to satisfy the conditional expression (11), it is possible to easily correct chromatic aberration.

  However, if the value of D4 / f is made to exceed the upper limit of conditional expression (11), the size of the lens system increases and it becomes difficult to correct chromatic aberration.

  On the other hand, if the value of D4 / f is made lower than the lower limit of the conditional expression (11), the chromatic aberration can be corrected well, but the image side lens surface of the second lens L2 and the object side lens surface of the third lens L3. Are too close to each other, so that the aspherical shapes of the lens surface R4 on the image side of the second lens L2 and the lens surface R5 on the object side of the third lens L3 are limited, so that aberration correction is insufficient. In addition, it becomes difficult to assemble, and ghosts caused by reflection between the two lens surfaces also occur.

Conditional expression (12): 0.05 <D7 / f <0.25 relates to the size and telecentricity of the imaging lens.

  If the lens system is configured so as to satisfy the conditional expression (12), it is possible to more easily achieve a reduction in size of the lens system and good telecentricity.

  However, if the value of D7 / f is made to exceed the upper limit of conditional expression (12), the lens system becomes larger, or the attempt to prevent the lens system from becoming larger reduces the distance between the aperture stop and the third lens. Or If the distance between the aperture stop and the third lens is reduced, it becomes difficult to separate the on-axis light beam and off-axis light beam that pass through the first lens, the second lens, and the third lens, which is disadvantageous in terms of aberration correction. Yes, it becomes difficult to correct distortion.

  On the other hand, if the value of D7 / f is made lower than the lower limit of the conditional expression (12), it becomes difficult to reduce the incident angle of the light beam incident on the imaging surface, and it is difficult to form a so-called telecentric lens system. It becomes.

<< 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 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 produce 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 image-side lens surface R4 of the second lens L2 is also an aspherical surface.

  It is desirable that the lens surface R4 has a concave surface at the center, and the peripheral edge of the effective diameter has a weaker negative power than 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 lens surface R4 has a concave surface at the center C4 (having negative power), and by making the peripheral power of the effective diameter weaker than the center portion C4, the peripheral light rays are sharply changed. Since the light can be condensed without bending, the distortion can be corrected well.

  Further, the object-side lens surface R3 of the second lens L2 has at least one inflection point within the effective diameter of the lens surface R3, and the central portion C3 of the lens surface R3 forms a convex surface and has an effective diameter peripheral portion. X3 may have a positive power weaker than that of the center portion, or the center portion C3 of the lens surface R3 may be a convex surface and the effective diameter peripheral edge portion X3 may be a concave surface.

  The surface R3 on the second lens object side is an aspherical surface and has at least one inflection point within the effective diameter of the lens surface R3. The central portion C3 of the lens surface R3 is a convex surface, and the effective diameter peripheral edge portion X4 is The lens system can be reduced in size and widened by making the positive power weaker than the central portion, or by making the central portion C43 of the lens surface R3 convex and the effective diameter peripheral portion X3 concave. Becomes easy, and the curvature of field can be corrected well.

  The radius of curvature at the point X3 on the effective diameter peripheral portion of the lens surface R3 on the object side of the second lens L2 is R3x, and the radius of curvature at the central portion C3 where the lens surface R3 intersects the optical axis Z1 is R3c. In this case, the absolute value of the curvature radius R3x is desirably 1.2 times or more the absolute value of the curvature radius R3c. By setting the absolute value of the curvature radius R3x to a value that is at least 1.2 times 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.

  The radius of curvature at the point X4 on the peripheral portion of the effective diameter of the lens surface R4 on the image side of the second lens L2 is R4x, and the radius of curvature at the central portion C4 where the lens surface R4 intersects the optical axis Z1 is R4c. In this case, the absolute value of the curvature radius R4x is desirably 1.5 times or more the absolute value of the curvature radius 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 The object-side lens surface R5 of the third lens L3 is preferably an aspherical surface.

  It is desirable that this lens surface R5 has a convex surface at the center, and the peripheral portion at the effective diameter has a positive power weaker than that at the center.

  As shown in FIG. 2, the above-mentioned “configuration in which the central portion of the lens surface R5 is convex and the peripheral edge 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 R5)” The configuration is as follows.

  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. The radius R5c of the center portion C5 of the surface R5 is larger than the absolute value of the curvature radius R5c.

  Note that a circle Sp1 having the radius of the line segment X5-P5 with the intersection P5 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 R5c with the center E5 of curvature as the center is shown in the figure.

  As described above, the lens surface R5 has a convex surface at the center C5 (having a positive power), and the effective power is corrected at the periphery of the effective diameter at the periphery of the effective diameter to be better than that at the center. It becomes possible to do.

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

  It is desirable that the lens surface R6 has a weaker power at the periphery of the effective diameter of the lens surface R6 than the power at the center of the lens surface R6.

  The above-described “configuration in which the power at the peripheral portion of the effective diameter of the lens surface R6 is weaker than the power at the center of the lens surface R6 (hereinafter also referred to as a configuration example of the lens surface R6)” is as follows. .

  That is, the point where the normal line H6 at the point X6 on the periphery of the effective diameter of the lens surface R6 intersects the optical axis Z1 is defined as the intersection point P6, and the length of the line segment X6-P6 connecting the point X6 and the intersection point P6 is defined as the lens surface. The absolute value of the radius of curvature at point X6 on R6. Further, an intersection between the lens surface R6 and the optical axis Z1 is defined as a central portion C6. When determined in this way, in the configuration example of the lens surface R6, the center of curvature E6 and the intersection point P6 in the center portion C6 of the lens surface R6 are both on the object side or the image side with respect to the center portion C6. In addition, the length of the line segment X6-P6 (the absolute value of the radius of curvature R6x at the point X6 of the lens surface R6) is made larger than the absolute value of the radius of curvature R6c at the center C6 of the lens surface R6. .

  As described above, the lens surface R6 on the image side of the third lens L3 is made weaker in power at the peripheral portion of the effective diameter of the lens surface R6 than the power at the center of the lens surface R6. It becomes possible to correct the surface curvature satisfactorily.

  Further, the radius of curvature at the point X5 on the effective diameter peripheral portion of the lens surface R5 on the object side of the third lens L3 is R5x, and the radius of curvature at the central portion C5 where the lens surface R5 intersects the optical axis Z1 is R5c. In this case, the absolute value of the curvature radius R5x is desirably 1.2 times or more the absolute value of the curvature radius R5c. By setting the absolute value of the curvature radius R5x to 1.2 or more times the absolute value of the curvature radius R5c, it is possible to correct the curvature of field favorably.

◇ Limitation of components related to the fourth lens It is desirable that the object-side lens surface R8 of the fourth lens L4 be an aspherical surface.

  It is desirable that the lens surface R8 has a concave surface at the center, and the peripheral portion at the effective diameter has a stronger negative power than the center.

  The above “configuration in which the central portion of the lens surface R8 is concave and the peripheral portion of the effective diameter has stronger negative power than the central portion (hereinafter also referred to as a configuration example of the lens surface R8)” is as follows.

  That is, the point where the normal line H8 of the point X8 on the peripheral portion of the effective diameter of the lens surface R8 having a concave surface (having negative power) and the optical axis Z1 intersect is defined as an intersection point P8, and the point X8 and the intersection point P8 Is the absolute value of the radius of curvature at the point X8 on the lens surface R8. Further, the intersection between the lens surface R8 and the optical axis Z1 is defined as a central portion C8. When determined in this way, the configuration example of the lens surface R8 is such that the lens surface R8 has a concave surface (having negative power) on the optical axis Z1 (central portion C8), and the central portion C8 of the lens surface R8 has a point. The center of curvature E8 and the intersection C8 are both on the object side from the center C8, and the length of the line segment X8-P8 (the absolute value of the radius of curvature R8x at the point X8 of the lens surface R8) is the lens. This is smaller than the absolute value of the radius of curvature R8c at the center C8 of the surface R8.

  As described above, the lens surface R8 has a concave surface at the center portion C8 (having negative power), and the coma aberration is corrected well by making the negative power stronger than the center portion C8 at the periphery of the effective diameter. It becomes possible to do.

  The image-side lens surface R9 of the fourth lens L4 is preferably an aspherical surface.

  It is desirable that the lens surface R9 has a convex surface at the center, and the peripheral portion at the effective diameter has a positive power weaker than that at 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 has a central portion C9. The center of curvature E9 and the intersection point P9 are both on the object side from the center C9, and the length of the line segment X9-P9 (the absolute value of the radius of curvature Rx9 at the point X9 of the lens surface R9) is the lens surface. This is larger than the absolute value of the radius of curvature Rc9 at the center C9 of R9.

  As described above, the lens surface R9 has a convex surface at the center C9, and a positive power is weaker than that at the center C9 at the periphery of the effective diameter, thereby favorably correcting curvature of field and coma. Is possible.

  Further, the radius of curvature at the point X9 on the effective diameter peripheral portion of the lens surface R9 on the image side of the fourth lens L4 is R9x, and the radius of curvature at the central portion C9 where the lens surface R9 intersects the optical axis Z1 is R9c. In this case, it is desirable that the absolute value of the curvature radius R9x is 1.2 times or more the absolute value of the curvature radius R9c. 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.

  In this way, by making each lens surface from the object-side lens surface R3 of the second lens L2 to the image-side lens surface R9 of the fourth lens L4 into an aspheric shape as described above, spherical aberration, image surface In addition to curvature and coma, distortion can be corrected well.

◇ Restriction of other components It is desirable that the aperture stop St is 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.

  In this imaging lens, when a cover glass or the like is not disposed on the object side from the first lens, the first lens L1 is a glass lens, and the second lens L2, the third lens L3, and the fourth lens L4 are plastic. It is desirable to use a lens.

  By making the material of the second lens L2 to the fourth lens L4 plastic, the aspherical shape can be accurately reproduced. In addition, the lens system can be manufactured at a low cost.

  As a material for forming each plastic lens from the second lens L2 to the fourth lens L4, 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 lens L1 to the fourth lens L4 is not limited to being formed of a material having a constant refractive index, and a gradient index lens may be used for any one or more of the four lenses. Good.

  Each lens of the second lens L2 to the fourth lens L4 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 L2 to the fourth lens L4.

  The light beam that passes outside the effective light beam diameter of the first lens L1 and the second lens L2 becomes stray light and reaches the imaging surface, which may become a ghost, but it is effective on the first lens L1 and the second lens L2. It is desirable to block stray light by providing light shielding plates Sk1, Sk2 and the like (see FIGS. 1 and 2) as light shielding means in a region outside the beam diameter.

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

  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 light beam diameter on the second lens L3 to the fourth lens L4, or between these lenses.

  In such an imaging lens, it is desirable that the distortion is within ± 10% when the angle of view is θ, the focal length of the entire lens system is f, and the ideal image height is 2f × tan (θ / 2). .

  By making the second to fourth lenses aspherical as described above, the distortion can be within ± 10% when the ideal image height is 2f × tan (θ / 2). .

  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 21, numerical data and the like related to the imaging lenses of Examples 1 to 6 according to the present invention will be described together. FIGS. 3-8 is sectional drawing which shows schematic structure of each imaging lens of Example 1- Example 6, and the code | symbol in FIGS. 3-8 corresponding to the code | symbol in FIGS. The structure to be shown is shown.

  9-14 is a figure which shows the basic data of each imaging lens of Examples 1-6. 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). The lower left part (indicated by reference numeral (c) in the figure) shows each coefficient of the aspherical expression representing the shape of the lens surface (aspherical shape). 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.

  9 to 14, in the upper left lens data, the surface number of an optical member such as a lens is sequentially increased from the object side to the image side, i-th (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 = 10, 11). In addition, the surface number of the imaging surface (i = 12) 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 (air equivalent length / in Air), distance from the lens surface on the object side of the first lens to the imaging surface: L, first Effective ray diameter of image side surface of one lens: ED, focal length of entire lens system (combined focal length of first lens to fourth lens): f, focal length of first lens: f1, focal point of second lens Distance: f2, third lens focal length: f3, fourth lens focal length: f4, first lens, second lens combined focal length: f12, third lens, fourth lens combined focal length: f34 Indicates the value of.

  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, each coefficient K, A3, A4, A5... Of the aspherical expression representing each aspheric surface Ri (i = 3, 4,...) Is effective in the lower left part of each of FIGS. Indicates the value rounded to 3 digits.

  Further, | X3-P3 |, | X4-P4 |,... Shown in the column of “symbol” described in the lower right part of each of FIGS. 9 to 14 are “point X3” described in the specification. Are the lengths of the line segment X3-P3 connecting the point P3 and the intersection point P3 "," the length of the line segment X4-P4 connecting the point X4 and the point of intersection P4 ", and so on.

  FIG. 15 is a diagram illustrating the values of the parameters of the conditional expressions (1) to (12) for each of the examples 1 to 6.

    FIGS. 16-21 is a figure which shows the various aberrations of each imaging lens of Examples 1-6. 16 to 21 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 part of the lens surface which comprises the lens which makes the shape made into a rotation object generally makes | forms circular shape with the constant distance from the optical axis of this lens. This circular area becomes the edge of the effective area on the lens surface.

  As can be seen from the basic data of Examples 1 to 6 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 four 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.

  FIG. 22 is a diagram showing an automobile equipped with an in-vehicle camera, which is an example of an imaging apparatus that includes the imaging lens of the present invention and an imaging device that converts an optical image formed by the imaging lens into an electrical signal. .

  As shown in FIG. 22, on-vehicle cameras 502 to 504 using the imaging lens of the present invention are mounted on an automobile 501 and used. The automobile 501 includes an in-vehicle camera 502 that is an in-vehicle camera for imaging a blind spot range on the side of the passenger seat, and an in-vehicle camera 503 that is an in-vehicle camera for imaging the blind spot range behind the automobile 1. And a vehicle-mounted camera 504 that is attached to the rear surface of the rearview mirror and is an in-vehicle camera for photographing the same field of view in front as the driver.

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. 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 value corresponding to each parameter in conditional expression (1)-(12) 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. A figure showing a car equipped with an in-vehicle camera

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

Claims (14)

From the object side, a first lens having a negative power, a second lens having a negative power, a third lens having a positive power, an aperture, and a fourth lens having a positive power are provided in this order.
In the second lens, the third lens, and the fourth lens, at least one lens surface of each lens forms an aspheric surface,
An imaging lens satisfying the following conditional expression (1):
2.4 <(D4 + D5) / f <5.5 (1)
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 lens surface on the object side of the second lens has at least one inflection point within the effective diameter of the lens surface, the central portion of the lens surface is a convex surface, and the peripheral portion of the effective diameter is more positive than the central portion. 2. The imaging lens according to claim 1, wherein the power of the imaging lens is weak, or the center portion of the lens surface is convex and the peripheral portion of the effective diameter is concave. From the object side,
A first lens that is a meniscus lens having negative power and a concave surface facing the image side;
The lens surface on the object side is an aspheric surface, the central portion of the lens surface is convex, and the effective diameter peripheral portion is weaker in positive power than the central portion, or the central portion of the lens surface is convex and has an effective diameter. A second lens with negative power at the periphery,
A third lens having positive power and an aspheric lens surface on the object side;
Aperture,
An imaging lens comprising a fourth lens having positive power and an image-side lens surface having an aspherical surface in this order. The imaging lens according to claim 3, wherein the following conditional expression (1) is satisfied.
2.4 <(D4 + D5) / f <5.5 (1)
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 5. The imaging lens according to claim 1, wherein an Abbe number νd3 of the third lens with respect to the d-line satisfies the following conditional expression (2).
νd3 <45 (2) The imaging lens according to claim 1, wherein a focal length f3 of the third lens satisfies the following conditional expression (3).
1.0 <f3 / f <3.0 (3)   7. 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.   8. The lens surface on the object side of the third 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 imaging lens according to any one of the above.   The lens surface on the image side of the third lens has a lower effective peripheral edge power than that of the central portion of the lens surface. The imaging lens described.   10. The lens surface on the object side of the fourth lens, wherein the central portion of the lens surface is concave and the peripheral portion of the effective diameter has a stronger negative power than the central portion. The imaging lens according to any one of the above.   11. The lens surface on the image side of the fourth lens, wherein the central portion of the lens surface is convex, and the effective diameter peripheral portion has a positive power weaker than that of the central portion. The imaging lens according to any one of the above. The combined focal length f12 of the first lens and the second lens and the combined focal length f34 of the third lens and the fourth lens satisfy the following conditional expression (4): The imaging lens according to any one of 1 to 11.
0.01 <| f12 / f34 | <0.5 (4) 13. The distance L from the object-side lens surface of the first lens to the imaging surface of the imaging lens satisfies the following conditional expression (5): 13. The imaging lens according to 1.
7 <L / f <16 (5)   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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