JP6449083B2 - Imaging lens system and imaging apparatus - Google Patents

Description

  The present invention relates to an imaging lens system and an imaging apparatus.

  In recent years, a lens corresponding to a wide field of view is required as an imaging lens system for use in automobiles. As an imaging lens system for use in an automobile, for example, there is an imaging lens system used for an in-vehicle camera for confirming a front, a back, and a side for ensuring safety when driving an automobile.

  An imaging lens system of an in-vehicle camera is required to be a bright imaging lens system having an extremely wide field of view, high resolution, and an F value of about 2.0. In addition, an imaging lens system for a vehicle-mounted camera is also required to be compact.

  In Patent Document 1, in order from the object side, a first lens having negative power, a second lens having negative power, a third lens having positive power, a diaphragm, a fourth lens having positive power, a negative power An imaging lens system composed of a fifth lens having the following power is described.

JP 2014-89241 A

  The imaging lens system described in Patent Document 1 is wide-angle, bright, and has high imaging performance. However, in an imaging lens system used for a vehicle-mounted camera, it is desired to further reduce the outer diameter of the lens disposed closest to the object side in order to make it as inconspicuous as possible when mounted on a vehicle. At the same time, with the increase in the number of pixels of the image sensor used, higher resolution is required for the imaging lens system of the in-vehicle camera. In order to achieve high resolution, it is necessary to correct field curvature well in a region from the center to the periphery of the image sensor.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide an imaging lens system and an imaging apparatus that have favorable imaging performance, are small, and are bright.

The imaging lens system of the present invention is
From the object side,
A first lens having a concave shape on the image side and having negative power;
A second meniscus lens with a concave surface facing the object side;
A third lens having a biconvex shape near the optical axis and having a positive power;
Aperture,
A fourth lens having negative power;
A fifth lens having positive power;
And a sixth lens having at least one lens surface having an aspherical surface.

  In the imaging lens system of the present invention, the effective diameter of the first lens can be reduced by making the second lens concave on the object side. Furthermore, since the curvature of field can be corrected by making the second lens into a meniscus shape with the concave surface facing the object side, good imaging performance can be obtained. Thereby, it is possible to provide a small and bright imaging lens system having good imaging performance.

In the present invention, it is preferable that the following conditional expression (1) is satisfied when the focal length of the first lens is f ₁ and the focal length of the third lens is f ₃ .
0.6 <| f ₁ / f ₃ | <1.3 (1)

Conditional expression (1) is a condition for suppressing the coma aberration and the curvature of field while ensuring a long back focus and preventing the total length of the lens system from becoming long. If the upper limit of conditional expression (1) is exceeded, the positive power of the third lens will be greater than the negative power of the first lens, so that the image plane will fall and it will be difficult to lengthen the back focus. If the lower limit value of conditional expression (1) is not reached, the negative power of the first lens becomes larger than the positive power of the third lens, so that it is easy to secure the back focus, but the total length of the imaging lens system is reduced. As the length increases, it becomes difficult to correct aberrations caused by the power of the first lens being increased.
In the imaging lens system of the present invention, it is more preferable that 0.7 <| f ₁ / f ₃ | <1.1.

In the present invention, it is preferable that the following conditional expression (2) is satisfied, where f is the focal length of the entire lens system and f ₂ is the focal length of the second lens.
−0.25 <f / f ₂ <0.25 (2)

Conditional expression (2) is a conditional expression for performing image plane correction. If the lower surface of the conditional expression (2) is below the lower limit of the conditional expression (2) with the concave surface facing the object side, the negative power of the second lens increases, so that distortion increases and the control of the angle of view becomes difficult. If the upper limit value of conditional expression (2) is exceeded, the positive power of the second lens increases, so that the image plane collapse increases and the imaging performance deteriorates.
In the imaging lens system of the present invention, it is more preferable that −0.1 <f / f ₂ <0.25.

In the present invention, it is preferable that the following conditional expression (3) is satisfied, where f _{4 is} the focal length of the fourth lens and f ₅ is the focal length of the fifth lens.
−1.6 <f ₄ / f ₅ <−0.6 (3)
In the imaging lens system of the present invention, it is more preferable that −1.1 <f ₄ / f ₅ <−0.6.

  Conditional expression (3) is a conditional expression for correcting chromatic aberration. If the lower limit of conditional expression (3) is not reached, the negative power of the fourth lens becomes smaller than the positive power of the fifth lens, so that chromatic aberration correction is insufficient and imaging performance deteriorates. If the upper limit value of conditional expression (3) is exceeded, the negative power of the fourth lens becomes larger than the positive power of the fifth lens, so that chromatic aberration correction becomes excessive and imaging performance deteriorates.

In the present invention, it is preferable that the following conditional expression (4) is satisfied, where f is the focal length of the entire lens system and f ₁ is the focal length of the first lens.
0.9 <| f ₁ /f|<2.0 (4)

Conditional expression (4) defines the total length of the imaging lens system. When the lower limit value of conditional expression (4) is not reached, the negative power of the first lens becomes larger than the power of the entire lens system, which leads to an increase in the overall length of the imaging lens system. If the upper limit of conditional expression (4) is exceeded, the negative power of the first lens becomes smaller than the power of the entire lens system, so it is difficult to ensure a predetermined back focus.
In the imaging lens system of the present invention, it is more preferable that 0.9 <| f ₁ /f|<1.4.

In the present invention, when the radius of curvature of the image side lens surface of the first lens is R ₂ and the radius of curvature of the object side lens surface of the second lens is R ₃ , the following conditional expression (5) is satisfied. Is preferred.
−1.4 <R ₂ / R ₃ <−0.6 (5)

  Conditional expression (5) defines coma, curvature of field and distortion. If the lower limit value of conditional expression (5) is not reached, the image plane falls, so that correction of curvature of field becomes difficult and imaging performance deteriorates. If the upper limit value of conditional expression (5) is exceeded, distortion will increase, making it difficult to control the angle of view.

In the present invention, the focal length of the first lens is f ₁ , the combined focal length of the second lens and the third lens is f ₂₃ , the Abbe number of the first lens is ν _d1 , and the Abbe number of the second lens is When the number is ν _d2 and the Abbe number of the third lens is ν _d3 , the following conditional expressions (6) and (7) are preferably satisfied.
_{-1.1 <f 1 / f 23 <} -0.7 (6)
35 <(ν _d1 + ν _d2 + ν _d3 ) / 3 <60 (7)

  In the imaging lens system of the present invention, by satisfying conditional expression (6), it is possible to secure the back focus while keeping the entire length of the imaging lens system short, and to perform good chromatic aberration correction. If the upper limit of conditional expression (6) is exceeded, it is advantageous for securing the back focus, but it becomes difficult to correct chromatic aberration and the overall length of the imaging lens system becomes long. If the lower limit of conditional expression (6) is not reached, chromatic aberration correction becomes excessive and it is difficult to ensure back focus. Moreover, satisfactory chromatic aberration correction can be achieved by satisfying conditional expression (7) simultaneously.

In the present invention, the focal length of the entire lens system f, and the combined focal length of said second lens and said third lens is taken as f _23, it is preferable to satisfy the following conditional expression (8).
0.9 <f ₂₃ /f<1.6 (8)

In the imaging lens system of the present invention, by satisfying conditional expression (8), a long back focus can be secured and good chromatic aberration correction can be performed. If the lower limit of conditional expression (8) is not reached, it is effective in reducing axial chromatic aberration and lateral chromatic aberration, but it is difficult to ensure back focus. If the upper limit of conditional expression (8) is exceeded, the back focus can be easily lengthened, but it becomes difficult to correct chromatic aberration well.
In the imaging lens system of the present invention, it is more preferable that 0.9 <f ₂₃ /f<1.2.

The imaging apparatus of the present invention
The imaging lens system described above;
An image pickup device disposed at a focal position of the image pickup lens system.

  According to the present invention, it is possible to provide a small and bright imaging lens system and imaging apparatus having good imaging performance.

1 is a cross-sectional view of an imaging lens system according to Example 1. FIG. FIG. 4 is an aberration diagram of the imaging lens system according to Example 1. 6 is a cross-sectional view of an imaging lens system according to Example 2. FIG. 6 is an aberration diagram of the imaging lens system according to Example 2. FIG. 6 is a cross-sectional view of an imaging lens system according to Example 3. FIG. FIG. 6 is an aberration diagram of the imaging lens system according to Example 3. 6 is a cross-sectional view of an imaging lens system according to Example 4. FIG. FIG. 10 is an aberration diagram of the imaging lens system according to Example 4. 6 is a cross-sectional view of an imaging lens system according to Example 5. FIG. FIG. 10 is an aberration diagram of the imaging lens system according to Example 5. 10 is a cross-sectional view of an imaging lens system according to Example 6. FIG. 10 is an aberration diagram of the imaging lens system according to Example 6. FIG. 10 is a cross-sectional view of an imaging lens system according to Example 7. FIG. 10 is an aberration diagram of the imaging lens system according to Example 7. FIG. 10 is a cross-sectional view of an imaging lens system according to Example 8. FIG. 10 is an aberration diagram of the imaging lens system according to Example 8. FIG. It is sectional drawing of the imaging device which concerns on embodiment.

  Examples of the imaging lens system 11 according to the embodiment of the present invention will be described below.

[Example 1]
FIG. 1 is a diagram illustrating a configuration of the imaging lens system 11 according to the first embodiment. As shown in FIG. 1, the imaging lens system 11 of Example 1 includes, in order from the object side, a first lens L1 having a concave shape on the image side and negative power, and a meniscus having a concave surface facing the object side. A second lens L2 having a shape, a third lens L3 having a biconvex shape in the vicinity of the optical axis Z, having a positive power, a stop STOP, a fourth lens L4 having a negative power, and a positive power. And a sixth lens L6 having at least one lens surface having an aspherical surface. The imaging plane of the imaging lens system 11 is indicated by IMG. In the imaging lens system 11 of Example 1, the second lens L2, the fourth lens L4, the fifth lens L5, and the sixth lens L6 are plastic lenses, and the first lens L1 and the third lens L3 are glass lenses.

  The first lens L1 is a spherical meniscus lens having negative power. The object side lens surface S1 of the first lens L1 is a flat surface, and the image side lens surface S2 is a spherical surface having a positive curvature. The image side lens surface S2 has a concave curved surface portion that is recessed toward the object side.

  The second lens L2 is an aspheric lens having a positive power. The object side lens surface S3 of the second lens L2 is an aspheric surface having a negative curvature, and the image side lens surface S4 is an aspheric surface having a negative curvature. The object side lens surface S3 has a concave curved surface portion that is recessed toward the image side. The image side lens surface S4 has a convex curved surface portion protruding toward the image side.

  The third lens L3 is a spherical lens having positive power. The object side lens surface S5 is a spherical surface having a positive curvature, and the image side lens surface S6 is a spherical surface having a negative curvature. The object side lens surface S5 has a convex curved surface portion protruding toward the object side, and the image side lens surface S6 has a convex curved surface portion protruding toward the image side.

  The first lens L1 has a function of converting incident light from a large incident angle into a small angle along the optical axis Z. The image side lens surface S2 of the first lens L1 has a negative power in order to expand the light beam. Since the second lens L2 has a meniscus shape with the concave surface facing the object side, the curvature of field can be corrected well. The third lens L3 is a positive lens having a convex shape on the object side, and has a function of converging the light beam diverged by the first lens L1.

  The fourth lens L4 is an aspheric lens having negative power. The object side lens surface S8 of the fourth lens L4 is an aspheric surface having a negative curvature, and the image side lens surface S9 is an aspheric surface having a positive curvature. The object side lens surface S8 has a concave curved surface that is recessed toward the image side. The image side lens surface S9 has a concave curved surface that is recessed toward the object side.

  The fifth lens L5 is an aspheric lens having positive power. The object side lens surface S10 of the fifth lens L5 is an aspherical surface having a positive curvature, and the image side lens surface S11 is an aspherical surface having a negative curvature. The object side lens surface S10 has a convex curved surface portion protruding toward the object side. The image side lens surface S11 has a convex curved surface portion protruding toward the image side. The object side lens surface S10 of the fifth lens L5 is bonded to the image side lens surface S9 of the fourth lens L4 with an adhesive.

  The sixth lens L6 is an aspheric lens having negative power. The object side lens surface S12 of the sixth lens L6 is an aspheric surface having a negative curvature, and the image side lens surface S13 is an aspheric surface having a negative curvature. The object side lens surface S12 has a concave curved surface portion that is recessed toward the image side. The image side lens surface S13 has a convex curved surface portion protruding toward the image side.

  The fourth lens L4 is a highly dispersed lens having negative power. The fifth lens L5 is a lens with positive power and small dispersion. Therefore, by combining the fourth lens L4 and the fifth lens L5, axial chromatic aberration and lateral chromatic aberration can be corrected.

  The sixth lens L6 has negative power, and the object side lens surface S12 and the image side lens surface S13 are aspheric. This ensures telecentricity and corrects field curvature.

  The cover glass 12 is a glass plate for protecting the image sensor. The cover glass 12 is handled as an integral part of the imaging lens system 11 when the imaging lens system 11 is designed. However, the cover glass 12 is not an essential component of the imaging lens system 11.

  Table 1 shows lens data of each lens surface of the imaging lens system 11. The lens data includes the radius of curvature, surface spacing, refractive index, and Abbe number of each surface. A surface marked with “*” indicates an aspherical surface.

  The aspherical shape adopted for the lens surface is 4th, 6th, 8th, 10th, where z is the sag amount, c is the reciprocal of the radius of curvature, k is the cone coefficient, and r is the height of the light beam from the optical axis. , 12th order, 14th order, and 16th order aspherical coefficients are represented by the following equations when A4, A6, A8, A10, A12, and A14, respectively.

Table 2 shows the aspheric coefficients for defining the aspherical shape of the aspherical lens surface in the imaging lens system 11 of Example 1. In Table 2, for example, “−1.673481E-03” means “−1.673481 × 10 ⁻³ ”.

  2A to 2C are a longitudinal aberration diagram, a field curvature diagram, and a distortion diagram of the imaging lens system 11 of Example 1. FIG. As shown in FIGS. 2A to 2C, in the imaging lens system 11 of Example 1, the half angle of view ω is 67.5 ° and the F value is 2.0. In the longitudinal aberration diagram of FIG. 2A, the horizontal axis indicates the position where the light beam intersects the optical axis Z, and the vertical axis indicates the height at the pupil diameter. In the field curvature diagram of FIG. 2B, the horizontal axis indicates the distance in the optical axis Z direction, and the vertical axis indicates the image height (field angle). In FIG. 2B, Sag indicates the field curvature in the sagittal plane, and Tan indicates the field curvature in the tangential plane. In the distortion diagram of FIG. 2C, the horizontal axis represents the amount of image distortion (%), and the vertical axis represents the image height (field angle). 2A shows simulation results with light beams with wavelengths of 656 nm, 546 nm, and 436 nm, and FIGS. 2B and 2C show simulation results with light beams with a wavelength of 546 nm.

Table 3 shows the result of calculating the characteristic value of the imaging lens system 11 of Example 1. In the imaging lens system 11, the F value is FNo, the distance from the object side lens surface S1 of the first lens L1 to the imaging plane IMG of the imaging lens system 11 is “optical total length”, the focal length of the entire lens system is f, focal length _{f 1} of the first lens L1, the focal distance _{f 2} of the second lens L2, the focal length of the third lens L3 _{f 3,} a focal length of the fourth lens L4 _{f 4,} a focal length of the fifth lens L5 These characteristic values are as shown in Table 3 where f _{5 is} the focal length of the sixth lens L6 and f _{6 is} the focal length of the sixth lens L6. Various focal lengths were calculated using light rays with a wavelength of 546 nm.

[Example 2]
FIG. 3 is a diagram illustrating a configuration of the imaging lens system 11 according to the second embodiment. As shown in FIG. 3, the first lens L <b> 1 to the sixth lens L <b> 6 have the same shape as in the first embodiment. In the imaging lens system 11 of Example 2, the second lens L2, the fourth lens L4, the fifth lens L5, and the sixth lens L6 are plastic lenses, and the first lens L1 and the third lens L3 are glass lenses.

  Table 4 shows lens data of each lens surface of the imaging lens system 11 of Example 2.

  Table 5 shows the aspheric coefficients for defining the aspherical shape of the aspherical lens surface in the imaging lens system 11 of Example 2.

  4A to 4C are a longitudinal aberration diagram, a field curvature diagram, and a distortion diagram of the imaging lens system 11 of Example 2. FIG. As shown in FIGS. 4A to 4C, in the imaging lens system 11 of Example 2, the half field angle ω is 68.2 ° and the F value is 2.0.

  Table 6 shows the result of calculating the characteristic value of the imaging lens system 11 of Example 2.

[Example 3]
FIG. 5 is a diagram illustrating a configuration of the imaging lens system 11 according to the third embodiment. The first lens L1 to the fifth lens L5 have the same shape as in the first embodiment. The shape of the sixth lens L6 is different from that of the first embodiment.

  The sixth lens L6 is an aspheric lens having negative power. The object side lens surface S12 of the sixth lens L6 is an aspheric surface having a negative curvature, and the image side lens surface S13 is an aspheric surface having a positive curvature. The object side lens surface S12 has a concave curved surface portion that is recessed toward the image side in the vicinity of the optical axis Z. The image side lens surface S13 has a concave curved surface portion that is recessed toward the object side in the vicinity of the optical axis Z.

  In the imaging lens system 11 of Example 3, the second lens L2, the fourth lens L4, the fifth lens L5, and the sixth lens L6 are plastic lenses, and the first lens L1 and the third lens L3 are glass lenses.

  Table 7 shows lens data of each lens surface of the imaging lens system 11 of Example 3.

  Table 8 shows aspherical coefficients for defining the aspherical shape of the aspherical lens surface in the imaging lens system 11 of Example 3.

  6A to 6C are a longitudinal aberration diagram, a field curvature diagram, and a distortion diagram of the imaging lens system 11 of Example 3. FIG. As shown in FIGS. 6A to 6C, in the imaging lens system 11 of Example 3, the half field angle ω is 67.1 ° and the F value is 2.0.

  Table 9 shows the results of calculating the characteristic values of the imaging lens system 11 of Example 3.

[Example 4]
FIG. 7 is a diagram illustrating a configuration of the imaging lens system 11 according to the fourth embodiment. The imaging lens system 11 of Example 4 shown in FIG. 7 will be described. In the imaging lens system 11 of Example 4, the first lens L1 to the sixth lens L6 are glass lenses.

  The first lens L1 is a spherical lens having negative power. The object side lens surface S1 of the first lens L1 is a spherical surface having a negative curvature, and the image side lens surface S2 is a spherical surface having a positive curvature. That is, the first lens L1 is a biconcave lens.

  The second lens L2 is a spherical meniscus lens having negative power. The object side lens surface S3 of the second lens L2 is a spherical surface having a negative curvature, and the image side lens surface S4 is a spherical surface having a negative curvature.

  The third lens L3 is an aspheric lens having positive power. The object side lens surface S5 is an aspherical surface having a positive curvature, and the image side lens surface S6 is an aspherical surface having a negative curvature. The object side lens surface S5 has a convex curved surface portion protruding toward the object side, and the image side lens surface S6 has a convex curved surface portion protruding toward the image side.

  The first lens L1 has a function of converting incident light from a large incident angle into a small angle along the optical axis Z. The object side lens surface S1 and the image side lens surface S2 of the first lens L1 have negative power in order to spread the light rays. Since the second lens L2 has a meniscus shape with the concave surface facing the object side, the curvature of field can be corrected well. The third lens L3 is a positive lens having a convex shape on the object side, and has a function of converging the light beam diverged by the first lens L1.

  The fourth lens L4 is a spherical lens having negative power. The object side lens surface S8 of the fourth lens L4 is a spherical surface having a negative curvature, and the image side lens surface S9 is a spherical surface having a positive curvature. The object side lens surface S8 has a concave curved surface that is recessed toward the image side. The image side lens surface S9 has a concave curved surface that is recessed toward the object side.

  The fifth lens L5 is a spherical lens having positive power. The object side lens surface S9 of the fifth lens L5 is a spherical surface having a positive curvature, and the image side lens surface S10 is a spherical surface having a negative curvature. The object side lens surface S9 has a convex curved surface protruding toward the object side. The image side lens surface S10 has a convex curved surface protruding toward the image side. Since the object side lens surface of the fifth lens L5 and the image side lens surface of the fourth lens L4 are bonded together with an adhesive, the values of the radius of curvature are the same, and the surface numbers in Table 10 are also common.

  The sixth lens L6 is an aspheric lens having positive power. The object side lens surface S11 of the sixth lens L6 is an aspherical surface having a positive curvature, and the image side lens surface S12 is a spherical surface having a negative curvature. The object side lens surface S11 has a convex curved surface portion protruding toward the object side. The image side lens surface S12 has a convex curved surface protruding toward the image side.

  The fourth lens L4 is a highly dispersed lens having negative power. The fifth lens L5 is a lens with positive power and small dispersion. Therefore, by combining the fourth lens L4 and the fifth lens L5, axial chromatic aberration and lateral chromatic aberration can be corrected.

  The sixth lens L6 has a positive power, and the object side lens surface S11 is an aspherical surface. This ensures telecentricity and corrects field curvature.

  Table 10 shows lens data of each lens surface of the imaging lens system 11 of Example 4.

  Table 11 shows aspherical coefficients for defining the aspherical shape of the aspherical lens surface in the imaging lens system 11 of Example 4.

  8A to 8C are a longitudinal aberration diagram, a field curvature diagram, and a distortion diagram of the imaging lens system 11 of Example 4. FIG. As shown in FIGS. 8A to 8C, in the imaging lens system 11 of Example 4, the half angle of view ω is 32.2 ° and the F value is 1.6.

  Table 12 shows the result of calculating the characteristic value of the imaging lens system 11 of Example 4.

[Example 5]
FIG. 9 is a diagram illustrating a configuration of the imaging lens system 11 according to the fifth embodiment. As shown in FIG. 9, the first lens L1 to the fifth lens L5 have the same shape as that of the fourth embodiment. The shape of the sixth lens L6 is different from that of the fourth embodiment.

  The sixth lens L6 is an aspheric lens having positive power. The object side lens surface S11 of the sixth lens L6 is an aspherical surface having a negative curvature, and the image side lens surface S12 is a spherical surface having a negative curvature. The object side lens surface S11 has a concave curved surface portion that is recessed toward the image side in the vicinity of the optical axis Z. The image side lens surface S12 has a convex curved surface protruding toward the image side.

  Table 13 shows lens data of each lens surface of the imaging lens system 11 of Example 5.

  Table 14 shows the aspheric coefficients for defining the aspherical shape of the aspherical lens surface in the imaging lens system 11 of Example 5.

  10A to 10C are a longitudinal aberration diagram, a field curvature diagram, and a distortion diagram of the imaging lens system 11 of Example 5. FIG. As shown in FIGS. 10A to 10C, in the imaging lens system 11 of Example 5, the half field angle ω is 32.5 ° and the F value is 1.6.

  Table 15 shows the result of calculating the characteristic value of the imaging lens system 11 of Example 5.

[Example 6]
FIG. 11 is a diagram illustrating a configuration of the imaging lens system 11 according to the sixth embodiment. As shown in FIG. 11, the first lens L1 and the third lens L3 to the fifth lens L5 have the same shape as in the fourth embodiment. The shapes of the second lens L2 and the sixth lens L6 are different from those in the fourth embodiment. In the imaging lens system 11 of Example 6, the first lens L1 to the sixth lens L6 are glass lenses.

  The second lens L2 is a spherical meniscus lens having a positive power. The object side lens surface S3 of the second lens L2 is a spherical surface having a negative curvature, and the image side lens surface S4 is a spherical surface having a negative curvature.

  The sixth lens L6 is an aspheric lens having positive power. The object side lens surface S11 of the sixth lens L6 is an aspheric surface having a positive curvature, and the image side lens surface S12 is an aspheric surface having a positive curvature. The object side lens surface S11 has a convex curved surface portion projecting toward the object side in the vicinity of the optical axis Z. The image side lens surface S12 has a concave curved surface that is recessed toward the object side in the vicinity of the optical axis Z.

  Table 16 shows lens data of each lens surface of the imaging lens system 11 of Example 6.

  The object side lens surface S5 and the image side lens surface S6 of the third lens L3 and the object side lens surface S11 and the image side lens surface S12 of the sixth lens L6 use odd-order aspheric surfaces. Different from 4 and 5.

The aspherical shape adopted for the lens surface is such that z is the sag amount, c is the reciprocal of the radius of curvature, k is the conic coefficient, r is the ray height from the optical axis Z, and the i-th aspherical coefficient is α _i . Sometimes expressed by the following equation: Here, i is a natural number. The minimum value of i is 3, and the maximum value N of i is N = 20 in this embodiment.

  Table 17 shows the aspheric coefficients for defining the aspherical shape of the aspherical lens surface in the imaging lens system 11 of Example 6.

  12A to 12C are a longitudinal aberration diagram, a field curvature diagram, and a distortion diagram of the imaging lens system 11 of the sixth example. As shown in FIGS. 12A to 12C, in the imaging lens system 11 of Example 6, the half angle of view ω is 34.5 ° and the F value is 1.6.

  Table 18 shows the result of calculating the characteristic value of the imaging lens system 11 of Example 6.

[Example 7]
FIG. 13 is a diagram illustrating a configuration of the imaging lens system 11 according to the seventh embodiment. As shown in FIG. 13, the first lens L1, the third lens L3, and the fourth lens L4 have the same shape as in the fourth embodiment. The shapes of the second lens L2, the fifth lens L5, and the sixth lens L6 are different from those in the fourth embodiment. In the imaging lens system 11 of Example 7, the first lens L1 to the sixth lens L6 are glass lenses.

  The second lens L2 is a spherical meniscus lens having a positive power. The object side lens surface S3 of the second lens L2 is a spherical surface having a negative curvature, and the image side lens surface S4 is a spherical surface having a negative curvature.

  The fifth lens L5 is a spherical meniscus lens having a positive power. The object side lens surface S10 of the fifth lens L5 is a spherical surface having a positive curvature, and the image side lens surface S11 is a spherical surface having a negative curvature. The difference from the imaging lens system 11 according to Example 4 is that the fourth lens L4 and the fifth lens L5 are not pasted together.

  The sixth lens L6 is an aspheric lens having positive power. The object side lens surface S12 of the sixth lens L6 is an aspheric surface having a positive curvature, and the image side lens surface S13 is an aspheric surface having a positive curvature. The object side lens surface S12 has a convex curved surface portion protruding toward the object side in the vicinity of the optical axis Z. The image side lens surface S12 has a concave curved surface portion that is recessed toward the object side in the vicinity of the optical axis Z.

  Table 19 shows lens data of each lens surface of the imaging lens system 11 of Example 7.

  Table 20 shows the aspheric coefficients for defining the aspheric shape of the aspheric lens surface in the imaging lens system 11 of Example 7.

  14A to 14C are a longitudinal aberration diagram, a field curvature diagram, and a distortion diagram of the imaging lens system 11 of the seventh embodiment. As shown in FIGS. 14A to 14C, in the imaging lens system 11 of Example 7, the half field angle ω is 34.7 ° and the F value is 1.6.

  Table 21 shows the results of calculating the characteristic values of the imaging lens system 11 of Example 7.

[Example 8]
FIG. 15 is a diagram illustrating a configuration of the imaging lens system 11 according to the eighth embodiment. As shown in FIG. 15, the first lens L1 to the fifth lens L5 have the same shape as in the seventh embodiment. The shape of the sixth lens L6 is different from that of the seventh embodiment. In the imaging lens system 11 of Example 8, the first lens L1 to the sixth lens L6 are glass lenses.

  The sixth lens L6 is an aspheric lens having positive power. The object side lens surface S12 of the sixth lens L6 is an aspheric surface having a positive curvature, and the image side lens surface S13 is an aspheric surface having a negative curvature. The object side lens surface S12 has a convex curved surface portion protruding toward the object side in the vicinity of the optical axis Z. The image side lens surface S12 has a convex curved surface portion that protrudes toward the object side in the vicinity of the optical axis Z.

  Table 22 shows lens data of each lens surface of the imaging lens system 11 of Example 8.

  Table 23 shows aspheric coefficients for defining the aspheric shape of the aspheric lens surface in the imaging lens system 11 of Example 8.

  16A to 16C are a longitudinal aberration diagram, a field curvature diagram, and a distortion diagram of the imaging lens system 11 of the eighth example. As shown in FIGS. 16A to 16C, in the imaging lens system 11 of Example 8, the half field angle ω is 34.6 ° and the F value is 1.6.

  Table 24 shows the result of calculating the characteristic values of the imaging lens system 11 of Example 8.

[Summary of conditional expressions]
Table 25 shows the results of calculating various parameters used in conditional expressions (1) to (8) in the imaging lens systems 11 of Examples 1 to 8. The combined focal length of the second lens L2 and the third lens L3 is f ₂₃ , the combined focal length of the fourth lens L4 and the fifth lens L5 is f ₄₅ , and the radius of curvature of the image side lens surface of the first lens L1 is R _2. The radius of curvature of the object side lens surface of the second lens L2 is R ₃ , the Abbe number of the first lens L1 is ν _d1 , the Abbe number of the second lens L2 is ν _d2 , and the Abbe number of the third lens L3 is ν _d3. As a result, various parameters are calculated.

[Application example to imaging device]
FIG. 17 is a diagram illustrating a configuration of the imaging apparatus 10 using the imaging lens system 11. The imaging device 10 includes an imaging lens system 11, a cover glass 12, and an imaging element 13. The imaging lens system 11, the cover glass 12, and the imaging element 13 are accommodated in a housing (not shown).

  The imaging element 13 is an element that converts received light into an electrical signal, and for example, a CCD image sensor or a CMOS image sensor is used. The imaging element 13 is disposed at the focal position of the imaging lens system 11. The horizontal angle of view is an angle of view corresponding to the horizontal direction of the image sensor 13.

  The cover glass 12 is provided on the image sensor 13 in order to protect the image sensor 13 from foreign matter.

  Note that the present invention is not limited to the above-described embodiment, and can be changed as appropriate without departing from the spirit of the present invention. For example, the use of the imaging lens system 11 of the present invention is not limited to the in-vehicle camera, but can be used for other uses such as a surveillance camera and a camera mounted on a small electronic device such as a mobile phone.

DESCRIPTION OF SYMBOLS 10 Imaging device 11 Imaging lens system 12 Cover glass 13 Imaging element L1-L6 1st lens-6th lens

Claims (9)

From the object side,
A first lens having a concave shape on the image side and having negative power;
A second meniscus lens with a concave surface facing the object side;
A third lens having a biconvex shape near the optical axis and having a positive power;
Aperture,
A fourth lens having negative power;
A fifth lens having positive power;
A sixth lens having at least one lens surface having an aspheric surface ,
The sixth lens has a negative power, the imaging lens system you characterized by having an image side surface of the concave object side surface and a convex shape. 2. The imaging lens system according to claim ₁ , wherein the following conditional expression (1) is satisfied, where f _{1 is} a focal length of the first lens and f ₃ is a focal length of the third lens.
0.6 <| f ₁ / f ₃ | <1.3 (1) The focal length of the entire lens system f, and the focal length of the second lens is taken as f _2, the imaging lens system according to claim 1 or 2, characterized by satisfying the following conditional expression (2).
−0.25 <f / f ₂ <0.25 (2) The following conditional expression (3) is satisfied, where the focal length of the fourth lens is f ₄ and the focal length of the fifth lens is f _{5. 5.} The imaging lens system described in 1.
−1.6 <f ₄ / f ₅ <−0.6 (3) The following conditional expression (4) is satisfied, where f is the focal length of the entire lens system, and f ₁ is the focal length of the first lens. Imaging lens system.
0.9 <| f ₁ /f|<2.0 (4) When the radius of curvature of the image side lens surface of the first lens is R ₂ and the radius of curvature of the object side lens surface of the second lens is R ₃ , the following conditional expression (5) is satisfied: The imaging lens system according to any one of claims 1 to 5.
−1.4 <R ₂ / R ₃ <−0.6 (5) The focal length of the first lens is f ₁ , the combined focal length of the second lens and the third lens is f ₂₃ , the Abbe number of the first lens is ν _d1 , and the Abbe number of the second lens is ν _d2. The imaging lens system according to claim 1, wherein the following conditional expressions (6) and (7) are satisfied when the Abbe number of the third lens is ν _d3. .
_{-1.1 <f 1 / f 23 <} -0.7 (6)
35 <(ν _d1 + ν _d2 + ν _d3 ) / 3 <60 (7) The following conditional expression (8) is satisfied, where f is a focal length of the entire lens system, and f ₂₃ is a combined focal length of the second lens and the third lens. The imaging lens system according to any one of the above.
0.9 <f ₂₃ /f<1.6 (8) The imaging lens system according to any one of claims 1 to 8,
An image pickup device disposed at a focal position of the image pickup lens system.