Imaging lens system and imaging device

Abstract

To provide an image capturing lens system capable of suppressing focus variation due to temperature changes, and to provide an image capturing device.SOLUTION: An image capturing lens system 11 provided herein at least comprises, in order from the object side to the image side, power lenses L1-L5 that satisfy a condition expressed as: |fi / F|<20.0, where fi represents a focal length of an i-th lens located at the i-th position (i is a positive integer), and F represents a focal length of the entire optical system. Defining a variation of a refractive index Nd of the i-th lens for the d-ray due to temperature changes as (dNd / dt)i, and Pdi as Pdi=(dNd / dt)i / fi, the power lenses L1-L5 are arranged such that the sign of the Pdi value alternately changes in order from the object side to the image side. The image capturing lens system has a half view angle of 50° or greater.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an imaging lens system and an imaging device, and more particularly to an imaging lens system and an imaging device for in-vehicle use or surveillance use, for example.

Background Art

[0002] For cameras mounted on vehicles, an imaging optical system having a wide angle of view is required so as to obtain a wide imaging range. For example, Patent Document 1 describes an imaging lens system with a wide angle of view using plastic lenses. Specifically, Patent Document 1 describes an imaging lens system including, in order from the object side to the image side, a first lens L1 which is a glass lens, a second lens L2 which is a plastic lens, a third lens L3 which is a glass lens, and a fourth lens L4 which is a plastic lens.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] On the other hand, for in-vehicle cameras, since they are placed in a harsh usage environment, an imaging optical system in which defocus (change in the focal position) due to temperature changes is suppressed is required. However, in the lens system described in Patent Document 1, since plastic lenses are used, there is a problem that the focal position easily changes due to temperature changes.

[0005] In particular, in an imaging lens system used for sensing in autonomous driving, if defocus occurs due to temperature changes, problems will arise in the accuracy of the sensing. For example, in an in-vehicle optical system, in order to suppress errors in image recognition in autonomous driving, it is necessary to keep the defocus within ±20 μm in a temperature range of -40°C to 105°C. However, the lens system described in Patent Document 1 does not meet the requirements of the optical system used for sensing.

[0006] On the other hand, by using only glass lenses for the lenses used in the imaging lens system, defocus due to temperature changes can be suppressed. However, since glass lenses are generally more expensive than plastic lenses, the cost will increase.

[0007] The present invention has been made in view of such problems, and an object thereof is to provide an imaging lens system and an imaging device capable of suppressing changes in the focal position due to temperature changes.

Means for Solving the Problems

[0008] In an imaging lens system according to an embodiment, when the focal length of the i-th lens (i is a positive integer) arranged in order from the object side to the image side is fi and the focal length of the entire optical system is F, at least five power lenses satisfying |fi / F| < 20.0 are provided, When the change rate of the refractive index Nd of the d-line of the i-th lens due to temperature change is (dNd / dt)i and Pdi = (dNd / dt)i / fi, the power lenses are arranged such that the signs of the values of Pdi alternate in order from the object side to the image side.

Effects of the Invention

[0009] According to the present invention, it is possible to provide an imaging lens system and an imaging device capable of suppressing changes in the focal position due to temperature changes.

Brief Description of the Drawings

[0010]

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Mode for Carrying Out the Invention

[0011] Hereinafter, the optical lens and the imaging device according to the present embodiment will be described. (Embodiment 1: Imaging Lens System) In the imaging lens system of Embodiment 1, when the focal length of the i-th lens (i is a positive integer) arranged in order from the object side to the image side is fi and the focal length of the entire optical system is F, it has at least five power lenses that satisfy |fi / F| < 20.0. Here, a power lens is a lens having a relatively large power, and means a lens that satisfies |fi / F| < 20.0. In the imaging lens system of Embodiment 1, when the change rate of the refractive index Nd of the d-line of the i-th lens due to temperature change is (dNd / dt)i and Pdi = (dNd / dt)i / fi, the power lenses are arranged such that the positive and negative signs of the values of the Pdi alternate in order from the object side to the image side. Here, the d-line is a light ray with a wavelength of 588 nm. Thereby, the change in the focal position due to the temperature change of the adjacent power lenses can be offset from each other. Specifically, the inventors focused on the fact that the amount of change in the focal position due to the temperature change of the imaging lens system mainly depends on the value of Pdi of the power lens constituting the imaging lens system, that is, the value obtained by multiplying the rate of change in refractive index (dNd / dt)i due to the temperature change of the power lens constituting the imaging lens system by the power (1 / f). More specifically, when the value of (dNd / dt)i is positive in a power lens having positive power, Pdi becomes positive, and the focal position of the power lens is displaced toward the object side at high temperature compared to the focal position at normal temperature. On the other hand, when the value of (dNd / dt)i is negative in a power lens having positive power, Pdi becomes negative, and the focal position of the power lens is displaced toward the image side at high temperature compared to the focal position at normal temperature. Also, when the value of (dNd / dt)i is positive in a power lens having negative power, Pdi becomes negative, and the focal position of the power lens is displaced toward the image side at high temperature compared to the focal position at normal temperature. On the other hand, when the value of (dNd / dt)i is negative in a power lens having negative power, Pdi becomes positive, and the focal position of the power lens is displaced toward the object side at high temperature compared to the focal position at normal temperature. Therefore, by alternately switching the positive and negative signs of the value of Pdi of the power lenses arranged from the object side toward the image side, it is possible to cancel out the changes in the focal position due to the temperature change of the adjacent power lenses with each other.

[0012] For example, even when there are several lenses with a positive Pdi value followed by several lenses with a negative Pdi value from the object side toward the image side, it is possible to suppress the displacement of the focal length due to the temperature change of the entire imaging lens system. However, when lenses with the same sign of Pdi continue, the variation in the position of the light rays due to the temperature change in each lens becomes large, resulting in an increase in aberration and a decrease in resolution. For example, when lenses with a positive Pdi value continue, the deviation of the position of the light rays accumulatively increases during temperature change, and the light rays of a specific angle of view emitted from the image side surface of the lens group with a positive Pdi value have a large variation in the position where they enter the object side surface of the adjacent lens, so that the aberration correction that should be performed in the adjacent lens cannot be sufficiently performed. Therefore, it is preferable that the power lenses arranged from the object side toward the image side are arranged such that the positive and negative signs of the Pdi value alternate.

[0013] In addition, an imaging lens system generally includes a lens having a predetermined power necessary for obtaining a desired overall focal length F finally while performing various corrections, and a lens having a relatively weak power for the purpose of correction only. Since the lens with a relatively weak power does not contribute to the variation in the focal position during temperature change, there is no need to consider the sign of Pdi. Therefore, in the imaging lens system according to Embodiment 1, only the relatively high-power power lenses that satisfy |fi / F| < 20.0 are arranged such that the signs of the Pdi values alternate in order from the object side toward the image side, that is, negative, positive, negative,..., or positive, negative, positive,....

[0014] In addition, the half angle of view of the imaging lens system according to Embodiment 1 is 50° or more, and the imaging lens system according to Embodiment 1 is a wide-angle imaging lens system. Here, the half angle of view of the optical system refers to the angle formed by the optical axis on the object side of the light ray that reaches the position (diagonal point) of the diagonal length of the sensor through the pupil center.

[0015] In addition, in the imaging lens system according to Embodiment 1, it is preferable that the power lens satisfies |Pdi| < 1.5×10 -5 ​When the absolute value of Pdi of a certain power lens becomes larger than the upper limit value, the fluctuation of the focal position due to the temperature change of the power lens becomes too large, and it becomes difficult to correct the fluctuation of the focal position due to the temperature change of the power lens by another power lens adjacent to the power lens. Therefore, the absolute value of Pdi of each power lens is preferably less than 1.5×10 -5 smaller.

[0016] In addition, the imaging lens system according to Embodiment 1 includes, in order from the object side to the image side, a first lens having a negative power and a concave surface on the image side, a second lens having a positive power and a convex surface on the object side, a third lens having a positive power, a fourth lens having a negative power, a fifth lens having a positive power, and a sixth lens. It is preferable to include a diaphragm disposed at any one of the positions between the first lens and the second lens, between the second lens and the third lens, and between the third lens and the fourth lens. Here, the first lens to the fifth lens are power lenses having a relatively large power satisfying |fi / F| < 20.0, and the sixth lens is a lens having a relatively weak power that does not satisfy |fi / F| < 20.0 and is mainly for aberration correction. Generally, an imaging lens system used for automatic driving sensing that requires a wide angle of view and high resolution includes, in order from the object side to the image side, one or two lenses having a concave surface on the image side for realizing a wide angle of view, one or two condenser lenses, a concave lens and a convex lens for correcting chromatic aberration, and an aberration correction lens having a relatively small power mainly for aberration correction as needed. In other words, the imaging lens system requires at least five or more power lenses. However, as the number of power lenses constituting the imaging lens system increases, the cumulative value of the fluctuation of the focal position due to the temperature change increases accordingly. Therefore, the imaging lens system according to Embodiment 1 is preferably composed of the five power lenses of the first lens to the fifth lens described above and one sixth lens for aberration correction.

[0017] In the imaging lens system according to Embodiment 1, it is preferable that the first lens and the second lens are made of a glass material with a refractive index Nd of d-line of 1.7 or more, and the third lens to the sixth lens are made of a glass material with a refractive index Nd of d-line of less than 1.7. By forming the third lens to the sixth lens with a relatively inexpensive glass material having a refractive index Nd of d-line of less than 1.7, the cost of the imaging lens system can be reduced.

[0018] In the imaging lens system according to Embodiment 1, when the combined focal length of the third lens, the fourth lens, the fifth lens, and the sixth lens is f(3-6), it is preferable to satisfy the following formula (1). f(3-6) / F>3.5 ···(1) Since the third lens to the sixth lens are made of a glass material with a refractive index Nd of less than 1.7, for example, plastic, the change rate (dNd / dt)i of the refractive index due to temperature change is large. Therefore, in order to reduce the influence of (dNd / dt)i on the value of Pdi, the combined focal length f(3-6) of the third lens to the sixth lens is preferably relatively large. Therefore, by satisfying the above formula (1), while forming the third lens to the sixth lens with a relatively inexpensive glass material, it is possible to suppress the fluctuation of the focal position due to temperature change in the third lens to the sixth lens.

[0019] In the imaging lens system according to Embodiment 1, when the thickness on the optical axis of the second lens is d2, it is preferable to satisfy the following formula (2). 0.63<d2 / F<0.9 ···(2) Since the thickness on the optical axis of the second lens satisfies the above formula (2), that is, is relatively thick, spherical aberration can be preferably corrected.

[0020] In the imaging lens system according to Embodiment 1, the fourth lens and the fifth lens may be joined to each other. By configuring the fourth lens and the fifth lens as a cemented lens, chromatic aberration can be preferably corrected.

[0021] Next, an example corresponding to the imaging lens system of Embodiment 1 will be described with reference to the drawings. (Example 1) FIG. 1 is a cross-sectional view showing the configuration of the imaging lens system 11 of Example 1. Specifically, the imaging lens system 11 according to Example 1 includes, in order from the object side toward the image side, a first lens L1, a second lens L2, a third lens L3, an aperture stop (STOP), a fourth lens L4, a fifth lens L5, and a sixth lens L6. The imaging plane of the imaging lens system 11 is indicated by IMG.

[0022] The first lens L1 is a spherical glass lens having a negative power. The object-side lens surface S1 of the first lens L1 faces the object side with a concave surface. The image-side lens surface S2 of the first lens L1 has a concave curved surface portion.

[0023] The second lens L2 is a spherical glass lens having a positive power. The object-side lens surface S3 of the second lens L2 faces the object side with a convex surface. Also, the image-side lens surface S4 of the second lens L2 faces the image side with a convex surface.

[0024] The third lens L3 is an aspherical plastic lens having a positive power. The object-side lens surface S5 of the third lens L3 faces the object side with a convex surface. Also, the image-side lens surface S6 of the third lens L3 faces the image plane side with a convex surface.

[0025] The aperture stop STOP is an aperture that determines the F-number (Fno) of the lens system. The aperture stop STOP is disposed between the third lens L3 and the fourth lens L4.

[0026] The fourth lens L4 is an aspherical plastic lens having a negative power. The object-side lens surface S9 of the fourth lens L4 faces the object side with a concave surface. Also, the image-side lens surface S10 of the fourth lens L4 faces the image plane side with a concave surface.

[0027] The fifth lens L5 is an aspherical plastic lens having a positive power. The object-side lens surface S11 of the fifth lens L5 has a convex curved surface portion. Also, the image-side lens surface S12 of the fifth lens L5 faces the convex surface toward the image plane side.

[0028] The fourth lens L4 and the fifth lens L5 form a cemented lens. That is, they are in contact with each other at the image-side lens surface S10 of the fourth lens L4 and the object-side lens surface S11 of the fifth lens L5. For example, it is preferable that the fourth lens L4 and the fifth lens L5 are cemented with an adhesive layer having an axial thickness of 0.02 mm.

[0029] The sixth lens L6 is an aspherical plastic lens having a positive power. The object-side lens surface S13 of the sixth lens L6 has a convex curved surface portion. Also, the image-side lens surface S14 of the sixth lens L6 has a concave curved surface portion.

[0030] The IR cut filter 12 is a filter for cutting light in the infrared region. The IR cut filter 12 is treated as being integrated with the imaging lens system 11 at the time of designing the imaging lens system 11. However, the IR cut filter 12 is not an essential component of the imaging lens system 11.

[0031] Table 1 shows the lens data of each lens surface in the imaging lens system 11 of Example 1. In Table 1, as the lens data, the radius of curvature (mm) of each surface, the interval between surfaces on the central optical axis (mm), the refractive index Nd with respect to the d-line, the Abbe number Vd with respect to the d-line, and the temperature change rate dNd / dt (1 / K) of the refractive index at a wavelength of 588 nm at 25 °C are presented. Also, the refractive index at the d-line and the Abbe number at the d-line shown in Table 1 are the values when the ambient temperature t (°C) around the imaging lens system 11 is 25 (°C). Also, in Table 1, the surfaces marked with "*" indicate that they are aspherical surfaces. Also, in Table 1, for example, "-4.9E-06" means "-4.9×10 -6 ". The numerical expressions are the same for the following tables.

[0032]

Table 1

[0033] The aspherical shape adopted on the lens surface is represented by the following equation, where z is the sag amount, c is the reciprocal of the radius of curvature, k is the conic coefficient, and r is the ray height from the optical axis Z, and the aspherical coefficients of the 3rd, 4th, 5th, 6th, 7th, 8th, 9th, 10th, 12th, 14th, and 16th orders are A3, A4, A5, A6, A7, A8, A9, A10, A12, A14, and A16, respectively.

Equation

[0034] Table 2 shows the aspherical coefficients for defining the aspherical shape of the lens surface that is aspherical in the imaging lens system 11 of Example 1.

[0035]

Table 2

[0036] Next, the aberrations will be described with reference to the drawings. FIG. 2 shows the spherical aberration diagram (longitudinal aberration diagram), the field curvature diagram, and the distortion aberration diagram in the imaging lens system 11 of Example 1. As shown in FIG. 2, in the imaging lens system 11 of Example 1, the semi-field angle is 52.0° and the F-number is 2.0. Also, in the longitudinal aberration diagram of FIG. 2A, the horizontal axis indicates the position where the ray intersects the optical axis Z, and the vertical axis indicates the height at the pupil diameter. Further, FIG. 2A shows the simulation results for rays of 455 nm, 502 nm, 546 nm, 614 nm, and 661 nm. Also, 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). Also, in the field curvature diagram of FIG. 2B, Sag indicates the field curvature in the sagittal plane, and Tan indicates the field curvature in the tangential plane. Further, FIG. 2B shows the simulation results for a ray of wavelength 546 nm. Also, in the distortion aberration diagram of FIG. 2C, the horizontal axis indicates the amount of image distortion (%), and the vertical axis indicates the image height (field angle). Further, FIG. 2C shows the simulation results for light rays with a wavelength of 546 nm. Note that FIG. 2 shows a spherical aberration diagram (longitudinal aberration diagram), a field curvature diagram, and a distortion aberration diagram when the environmental temperature t (°C) is 25 (°C).

[0037] (Example 2) FIG. 3 is a cross-sectional view showing the imaging lens system 11 according to Example 2. Since the configuration of the imaging lens system 11 according to Example 2 is the same as that of Example 1, the description thereof is omitted. Hereinafter, the characteristic data of the imaging lens system 11 according to Example 2 will be described.

[0038] Table 3 shows the lens data of each lens surface of the imaging lens system 11 according to Example 2. Since the items shown in Table 3 are the same as those in Table 1, the description thereof is omitted.

[0039]

Table 3

[0040] Table 4 shows the aspherical coefficients for defining the aspherical shape of the lens surfaces that are aspherical in the imaging lens system 11 of Example 2. In Table 4, the aspherical shape adopted for the lens surface is represented by the same formula as in Example 1.

[0041]

Table 4

[0042] FIG. 4 shows a spherical aberration diagram (longitudinal aberration diagram), a field curvature diagram, and a distortion aberration diagram in the imaging lens system 11 of Example 2. Since the description of each aberration diagram shown in FIG. 4 is the same as that of FIG. 2, the description thereof is omitted.

[0043] (Example 3) FIG. 5 is a cross-sectional view showing the imaging lens system 11 according to Embodiment 3. Since the configuration of the imaging lens system 11 according to Embodiment 3 is the same as that of Embodiment 1 except that the aperture STOP is also arranged between the first lens L1 and the second lens L2, the description thereof is omitted. Hereinafter, the characteristic data of the imaging lens system 11 according to Embodiment 3 will be described.

[0044] Table 5 shows the lens data of each lens surface of the imaging lens system 11 according to Embodiment 3. Since the items shown in Table 5 are the same as those in Table 1, the description thereof is omitted.

[0045] [Table 5]

[0046] Table 6 shows the aspherical coefficients for defining the aspherical shape of the lens surfaces that are aspherical in the imaging lens system 11 of Embodiment 3. In Table 6, the aspherical shape adopted for the lens surface is represented by the same formula as in Embodiment 1.

[0047] [Table 6]

[0048] FIG. 6 shows the spherical aberration diagram (longitudinal aberration diagram), the field curvature diagram, and the distortion aberration diagram in the imaging lens system 11 of Embodiment 3. Since the description of each aberration diagram shown in FIG. 6 is the same as that in FIG. 2, the description thereof is omitted.

[0049] (Embodiment 4) FIG. 7 is a cross-sectional view showing the imaging lens system 11 according to Embodiment 4. Since the configuration of the imaging lens system 11 according to Embodiment 4 is the same as that of Embodiment 1, the description thereof is omitted. Hereinafter, the characteristic data of the imaging lens system 11 according to Embodiment 4 will be described.

[0050] Table 7 shows the lens data of each lens surface of the imaging lens system 11 according to Embodiment 4. Since the items shown in Table 7 are the same as those in Table 1, the description thereof is omitted.

[0051]

Table 7

[0052] Table 8 shows the aspherical coefficients for defining the aspherical shape of the lens surfaces that are aspherical in the imaging lens system 11 of Example 4. In Table 8, the aspherical shape adopted for the lens surface is represented by the same formula as in Example 1.

[0053]

Table 8

[0054] Fig. 8 shows the spherical aberration diagram (longitudinal aberration diagram), field curvature diagram, and distortion aberration diagram in the imaging lens system 11 of Example 4. Since the explanations for each aberration diagram shown in Fig. 8 are the same as those in Fig. 2, the explanations are omitted.

[0055] (Example 5) Fig. 9 is a cross-sectional view showing the imaging lens system 11 according to Example 5. Since the configuration of the imaging lens system 11 according to Example 5 is the same as that in Example 1, the explanation thereof is omitted. Hereinafter, the characteristic data of the imaging lens system 11 according to Example 5 will be described.

[0056] Table 9 shows the lens data of each lens surface of the imaging lens system 11 according to Example 5. Since the items shown in Table 9 are the same as those in Table 1, the explanation thereof is omitted.

[0057]

Table 9

[0058] Table 10 shows the aspherical coefficients for defining the aspherical shape of the lens surfaces that are aspherical in the imaging lens system 11 of Example 5. In Table 10, the aspherical shape adopted for the lens surface is represented by the same formula as in Example 1.

[0059]

Table 10

[0060] Figure 10 shows the spherical aberration diagram (longitudinal aberration diagram), field curvature diagram, and distortion aberration diagram of the imaging lens system 11 of Example 5. Since the explanations for each aberration diagram shown in Figure 10 are the same as those in Figure 2, the explanations are omitted.

[0061] (Example 6) Figure 11 is a cross-sectional view showing the imaging lens system 11 according to Example 6. Since the configuration of the imaging lens system 11 according to Example 6 is the same as that of Example 1, the explanation thereof is omitted. Hereinafter, the characteristic data of the imaging lens system 11 according to Example 6 will be described.

[0062] Table 11 shows the lens data of each lens surface of the imaging lens system 11 according to Example 6. Since the items shown in Table 11 are the same as those in Table 1, the explanation thereof is omitted.

[0063] [Table 11]

[0064] Table 12 shows the aspherical coefficients for defining the aspherical shape of the lens surfaces that are aspherical in the imaging lens system 11 of Example 6. In Table 12, the aspherical shape adopted for the lens surface is represented by the same formula as in Example 1.

[0065] [Table 12]

[0066] Figure 12 shows the spherical aberration diagram (longitudinal aberration diagram), field curvature diagram, and distortion aberration diagram of the imaging lens system 11 of Example 6. Since the explanations for each aberration diagram shown in Figure 12 are the same as those in Figure 2, the explanations are omitted.

[0067] (Example 7) FIG. 13 is a cross-sectional view showing the imaging lens system 11 according to Example 7. Since the configuration of the imaging lens system 11 according to Example 7 is the same as that of Example 3, the description thereof is omitted. Hereinafter, the characteristic data of the imaging lens system 11 according to Example 7 will be described.

[0068] Table 13 shows the lens data of each lens surface of the imaging lens system 11 according to Example 7. Since the items shown in Table 13 are the same as those in Table 1, the description thereof is omitted.

[0069] [Table 13]

[0070] Table 14 shows the aspherical coefficients for defining the aspherical shape of the lens surface that is an aspherical surface in the imaging lens system 11 of Example 7. In Table 14, the aspherical shape adopted for the lens surface is represented by the same formula as in Example 1.

[0071] [Table 14]

[0072] FIG. 14 shows the spherical aberration diagram (longitudinal aberration diagram), field curvature diagram, and distortion aberration diagram in the imaging lens system 11 of Example 7. Since the description of each aberration diagram shown in FIG. 7 is the same as that in FIG. 2, the description thereof is omitted.

[0073] (Example 8) FIG. 15 is a cross-sectional view showing the imaging lens system 11 according to Example 8. Since the configuration of the imaging lens system 11 according to Example 8 is the same as that of Example 3, the description thereof is omitted. Hereinafter, the characteristic data of the imaging lens system 11 according to Example 8 will be described.

[0074] Table 15 shows the lens data of each lens surface of the imaging lens system 11 according to Example 8. Since the items shown in Table 15 are the same as those in Table 1, the description thereof is omitted.

[0075] [Table 15]

[0076] Table 16 shows the aspherical coefficients for defining the aspherical shape of the lens surfaces that are aspherical in the imaging lens system 11 of Example 8. In Table 16, the aspherical shape adopted for the lens surface is represented by the same formula as in Example 1.

[0077] [Table 16]

[0078] FIG. 16 shows the spherical aberration diagram (longitudinal aberration diagram), field curvature diagram, and distortion aberration diagram in the imaging lens system 11 of Example 8. Since the explanations for each aberration diagram shown in FIG. 16 are the same as those in FIG. 2, the explanations are omitted.

[0079] (Example 9) FIG. 17 is a cross-sectional view showing the imaging lens system 11 according to Example 9. Since the configuration of the imaging lens system 11 according to Example 9 is the same as that in Example 1, the explanation thereof is omitted. Hereinafter, the characteristic data of the imaging lens system 11 according to Example 9 will be described.

[0080] Table 17 shows the lens data of each lens surface of the imaging lens system 11 according to Example 9. Since the items shown in Table 17 are the same as those in Table 1, the explanation thereof is omitted.

[0081] [Table 17]

[0082] Table 18 shows the aspherical coefficients for defining the aspherical shape of the lens surfaces that are aspherical in the imaging lens system 11 of Example 9. In Table 18, the aspherical shape adopted for the lens surface is represented by the same formula as in Example 1.

[0083] [Table 18]

[0084] Fig. 18 shows the spherical aberration diagram (longitudinal aberration diagram), the field curvature diagram, and the distortion aberration diagram of the imaging lens system 11 of Example 9. Since the explanations of the respective aberration diagrams shown in Fig. 19 are the same as those in Fig. 2, the explanations are omitted.

[0085] As shown in the longitudinal aberration diagrams of Figs. 2A, 4A, 6A, 8A, 10A, 12A, 14A, 16A, and 18A, according to the imaging lens systems 11 of Examples 1 to 9, the longitudinal aberrations at wavelengths of 455 nm, 502 nm, 546 nm, 614 nm, and 661 nm are well corrected. Therefore, the imaging lens system 11 has high resolution.

[0086] Also, as shown in the field curvature diagrams of Figs. 2B, 4B, 6B, 8B, 10B, 12B, 14B, 16B, and 18B, according to the imaging lens systems 11 of Examples 1 to 9, the field curvature is well corrected. Therefore, the imaging lens system 11 has high resolution.

[0087] Also, as shown in the distortion aberration diagrams of Figs. 2C, 4C, 6C, 8C, 10C, 12C, 14C, 16C, and 18C, according to the imaging lens systems 11 of Examples 1 to 9, the distortion aberration is well corrected. Therefore, the imaging lens system 11 has high resolution.

[0088] Table 19 shows the focal length f of the first lens L1 1 and the focal length f of the second lens L2 2 and the focal length f of the third lens L3 3 and the focal length f of the fourth lens L4 4 and the focal length f of the fifth lens L5 5 and the focal length f of the sixth lens L6 6, the combined focal length f(3~6) of the third lens L3 to the sixth lens L6, the focal length F of the entire optical system of the imaging lens system 11, the values of |f1 / F| to |f6 / F|, the value of f(3~6) / F, the thickness d2 on the optical axis of the second lens, the value of d2 / F, the temperature change rate (dNd / dt)1 of the refractive index of the first lens L1, the temperature change rate (dNd / dt)2 of the refractive index of the second lens L2, the temperature change rate (dNd / dt)3 of the refractive index of the third lens L3, the temperature change rate (dNd / dt)4 of the refractive index of the fourth lens L4, the temperature change rate (dNd / dt)5 of the refractive index of the fifth lens L5, the temperature change rate (dNd / dt)6 of the refractive index of the sixth lens L6, Pd1 of the first lens L1, Pd2 of the second lens L2, Pd3 of the third lens L3, Pd4 of the fourth lens L4, Pd5 of the fifth lens L5, Pd6 of the sixth lens L6, the sum ΣPdi of Pdi from the first lens L1 to the sixth lens L6, the focal position of the imaging lens system 11 at -40°C and the focal position at 105°C when the focal position at 25°C of the imaging lens system 11 is used as a reference (0 mm) are shown. In Table 19, the units of the focal length and the thickness on the optical axis of the second lens are both mm. The unit of the temperature change rate of the refractive index is 1 / K for all. Also, the units of (dNd / dt)1 to (dNd / dt)6 are 1 / K, and the units of Pd1 to Pd6 are 1 / K·mm. Also, the various focal lengths and focal positions in Table 19 were calculated using light rays with a wavelength of 546 nm.

[0089]

Table 19

[0090] As shown in Table 19, in Examples 1 to 9, the first lens L1 to the fifth lens L5, which are power lenses satisfying |fi / F| < 20.0, are arranged such that the signs of the Pdi values alternately change between negative, positive, negative, ··· in order from the object side to the image side. Thereby, the change in the focal position due to the temperature change of the adjacent power lenses can be offset from each other, and the change in the focal position due to the temperature change of the overall focal length F of the imaging lens system 11 can be suppressed. Actually, as shown in Table 19, in Examples 1 to 9, the change in the focal position due to the temperature change of the overall focal length F of the imaging lens system 11 is suppressed within 20 μm.

[0091] Also, in Examples 1 to 9, the half field angle of the imaging lens system 11 is 50° or more, and a wide-angle imaging lens system 11 can be realized.

[0092] Also, as shown in Table 19, in Examples 1 to 9, the first lens L1 to the fifth lens L5, which are power lenses satisfying |fi / F| < 20.0, satisfy |Pdi| < 1.5×10 -5 . Thereby, the fluctuation of the focal position due to the temperature change of the power lenses L1 to L5 can be corrected more reliably.

[0093] Also, in Examples 1 to 9, the imaging lens system 11 is composed of five power lenses of the first lens L1 to the fifth lens L5 and one sixth lens L6 for aberration correction. Thereby, while realizing a wide angle and high resolution, the number of lenses constituting the imaging lens system 11 can be suppressed, and the cumulative value of the fluctuation of the focal position due to the temperature change can be suppressed. Actually, in Examples 1 to 9, as shown in FIGS. 2, 4, 6, 8, 10, 12, 14, 16, 18, various aberrations can be suitably reduced to realize high resolution, and as shown in Table 19, the fluctuation of the focal position due to the temperature change of the imaging lens system 11 can be suppressed.

[0094] In addition, in Examples 1 to 9, the first lens L1 and the second lens L2 are made of a glass material with a refractive index Nd of d-line of 1.7 or more, and the third lens L3 to the sixth lens L6 are made of a glass material with a refractive index Nd of d-line of less than 1.7. Thereby, by forming the third lens to the sixth lens with a relatively inexpensive glass material, the cost of the imaging lens system 11 can be reduced.

[0095] In addition, as shown in Table 19, in Examples 1 to 9, the value of f(3 - 6) / F satisfies the above formula (1). Thereby, while forming the third lens L3 to the sixth lens L6 with a relatively inexpensive glass material, it is possible to suppress the variation in the focal position due to temperature change in the third lens L3 to the sixth lens L6.

[0096] In addition, as shown in Table 19, in Examples 1 to 9, the value of d2 / F satisfies the above formula (2). Since the thickness d2 on the optical axis of the second lens L2 is relatively thick, spherical aberration can be preferably corrected. Actually, in Examples 1 to 9, as shown in FIGS. 2A, 4A, 6A, 8A, 10A, 12A, 14A, 16A, 18A, the spherical aberration at wavelengths of 455 nm, 502 nm, 546 nm, 614 nm, 661 nm is well corrected, and a high-resolution imaging lens system 11 can be realized.

[0097] In addition, in Examples 1 to 9, the fourth lens L4 and the fifth lens L5 are joined to each other. Thereby, chromatic aberration can be preferably corrected.

[0098] (Embodiment 2: Application Example to Imaging Device) FIG. 19 shows that the imaging device 21 includes an imaging lens system 11 and an image sensor 22. The imaging lens system 11 and the image sensor 22 are housed in a housing (not shown). The imaging lens system 11 is the imaging lens system 11 described in the above Embodiment 1.

[0099] The image sensor 22 is an element that converts received light into an electrical signal. For example, a CCD image sensor or a CMOS image sensor is used. The image sensor 22 is disposed at the imaging position of the imaging lens system 11.

[0100] As described above, according to the imaging device of Embodiment 2, it is possible to provide an imaging device that can reduce aberrations and suppress changes in the focal position due to temperature changes at a level required for image recognition in autonomous driving.

[0101] Note that the present invention is not limited to the above embodiments, and can be appropriately modified without departing from the gist. For example, Example 2 may be applied to Examples 1 to 9. For example, the use of the imaging lens system of the present invention is not limited to in-vehicle cameras and surveillance cameras, and can also be used for other applications such as being mounted on small electronic devices such as mobile phones.

Explanation of Reference Numerals

[0102] 11 Imaging lens system 12 IR cut filter 21 Imaging device 22 Image sensor L1 First lens L2 Second lens L3 Third lens L4 Fourth lens L5 Fifth lens L6 Sixth lens STOP Diaphragm IMG Imaging plane

Claims

1. When the focal length of the i-th lens (i is a positive integer) arranged in order from the object side to the image side is fi and the focal length of the entire optical system is F, there are at least five power lenses satisfying |fi / F| < 20.0, When the change rate of the refractive index Nd of the d-line of the i-th lens due to temperature change is (dNd / dt)i and Pdi = (dNd / dt)i / fi, the power lenses are continuously arranged such that the signs of the values of Pdi alternate in order from the object side to the image side, An imaging lens system in which the first lens arranged closest to the object side among the power lenses has a negative power.

2. The power lens satisfies |Pdi| < 1.5×10 －５ The imaging lens system according to claim 1.

3. Comprising, in order from the object side to the image side, the first lens having a concave surface on the image side, the second lens having a positive power and a convex surface on the object side, the third lens having a positive power, the fourth lens having a negative power, the fifth lens having a positive power, and the sixth lens, The imaging lens system according to claim 1 or 2, further comprising a diaphragm disposed at any one of the positions between the first lens and the second lens, between the second lens and the third lens, and between the third lens and the fourth lens.

4. The first lens and the second lens are formed of a glass material having a refractive index Nd of the d-line of 1.7 or more, and the third lens to the sixth lens are formed of a glass material having a refractive index Nd of the d-line of less than 1.

7. The imaging lens system according to claim 3.

5. The imaging lens system according to claim 3, having a half field angle of 50° or more.

6. When the combined focal length of the third lens, the fourth lens, the fifth lens, and the sixth lens is f(3 - 6), the imaging lens system according to any one of claims 3 to 5, satisfying the following formula (1). f(3 - 6) / F > 3.5... (1)

7. When the thickness of the second lens on the optical axis is d2, the imaging lens system according to any one of claims 3 to 6, satisfying the following formula (2). 0.63 < d2 / F < 0.9... (2)

8. An imaging lens system according to any one of claims 1 to 7, And an image sensor disposed at the focal position of the imaging lens system. An imaging device comprising the same.

Images