Imaging lens system and imaging device

Abstract

To provide an imaging lens system and imaging device that reduce costs and stabilize performance against temperature changes. [Solution] The imaging lens system 11 is an imaging lens system consisting of a front lens group system and a rear lens group system, arranged in order from the object side to the image side. The front lens group system consists of a first lens L1 having negative power and a concave shape on the image side, a second lens L2 having negative power and a convex shape on the image side, and a third lens L3 having positive power and a convex shape on the image side, arranged in order from the object side to the image side. The rear lens group system consists of a fourth lens L4 having positive power and a convex shape on the image side, a fifth lens L5 having negative power, and a sixth lens L6, arranged in order from the object side to the image side. The fourth lens L4 and the fifth lens L5 are cemented lenses, the first lens L1 and the third lens L3 are glass lenses, and the second lens L2, the fourth lens L4, and the fifth lens L5 are plastic lenses.

Description

Technical Field

[0001] The present invention relates to an imaging lens system and an imaging device.

Background Art

[0002] In recent years, the applications of wide-angle lenses mounted on vehicles have changed from viewing to sensing. Since sensing requires a resolution necessary for image analysis, high-resolution images corresponding to megapixels are required. Also, a wide angle of view is required.

[0003] Thus, in an in-vehicle imaging device, it is required to image a distant object in the traveling direction with high resolution and to image a nearby object with a wide angle. Furthermore, it is required to be a bright optical system. Also, particularly in an imaging lens system for an in-vehicle camera, compactness is required.

[0004] For example, Patent Document 1 describes an imaging device that switches between a wide-angle optical system and a telephoto optical system arranged such that their optical axes are orthogonal to each other by a mirror, and forms an optical image by either optical system on a common image sensor.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the imaging device of Patent Document 1, since two types of lenses, a telephoto optical system for long-distance imaging and a wide-angle optical system for short-distance imaging, are used, the size of the unit becomes large and the cost also increases. Also, when all the lenses are made of plastic lenses for cost reduction, there is a problem that the performance stability is lacking with respect to changes in the environmental temperature.

[0007] Thus, conventional imaging lens systems have faced the challenge of not being able to realize imaging lens systems and imaging devices that are cost-effective and have stable performance against temperature changes. [Means for solving the problem]

[0008] One embodiment of the imaging lens system is an imaging lens system consisting of a front lens group system and a rear lens group system, arranged in order from the object side to the image side. The aforementioned front lens group consists of, in order from the object side to the image side, a first lens having negative power and a concave shape on the image side, a second lens having negative power and a concave shape on the object side, and a third lens having positive power, a convex shape on the object side, and a convex shape on the image side. The aforementioned rear lens group consists of, in order from the object side to the image side, a fourth lens having positive power and a convex shape on the object side and a convex shape on the image side, a fifth lens having negative power, and a sixth lens, The fourth lens and the fifth lens are cemented lenses, the first lens and the third lens are glass lenses, and the second lens, the fourth lens and the fifth lens are plastic lenses. When the focal length of the second lens is f2, the combined focal length of the plastic lenses in the rear lens group is frp, and the focal length of the entire lens system is F, the following equations (1) and (2) are satisfied. 2<|f2 / F| ···(1) 2<|frp / F| ···(2)

[0009] This configuration allows for cost reduction through the extensive use of plastic lenses, while also enabling the realization of an imaging lens system with stable performance against temperature changes. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an imaging lens system and imaging device that reduce costs and stabilize performance against temperature changes. [Brief explanation of the drawing]

[0011] [Figure 1] It is a cross-sectional view showing the configuration of the imaging lens system according to Example 1. [Figure 2] It is a spherical aberration diagram of the imaging lens system of Example 1. [Figure 3] It is a field curvature diagram of the imaging lens system of Example 1. [Figure 4] It is a distortion aberration diagram of the imaging lens system of Example 1. [Figure 5] It is a graph showing the relationship between the spatial frequency and MTF at 25°C in the imaging lens system of Example 1. [Figure 6] It is a graph showing the relationship between the spatial frequency and MTF at -40°C in the imaging lens system of Example 1. [Figure 7] It is a graph showing the relationship between the spatial frequency and MTF at 115°C in the imaging lens system of Example 1. [Figure 8] [Figure 8] It is a diagram for explaining the angle of view. [Figure 9] It is a cross-sectional view showing the configuration of the imaging lens system according to Example 2. [Figure 10] It is a spherical aberration diagram of the imaging lens system of Example 2. [Figure 11] It is a field curvature diagram of the imaging lens system of Example 2. [Figure 12] It is a distortion aberration diagram of the imaging lens system of Example 2. [Figure 13] It is a graph showing the relationship between the spatial frequency and MTF at 25°C in the imaging lens system of Example 2. [Figure 14] It is a graph showing the relationship between the spatial frequency and MTF at -40°C in the imaging lens system of Example 2. [Figure 15] It is a graph showing the relationship between the spatial frequency and MTF at 115°C in the imaging lens system of Example 2. [Figure 16] It is a cross-sectional view showing the configuration of the imaging lens system according to Example 3. [Figure 17] It is a spherical aberration diagram of the imaging lens system of Example 3. [Figure 18] It is a field curvature diagram of the imaging lens system of Example 3. [Figure 19] It is a distortion aberration diagram of the imaging lens system of Example 3. [Figure 20] It is a graph showing the relationship between the spatial frequency and MTF at 25°C in the imaging lens system of Example 3. [Figure 21] It is a graph showing the relationship between the spatial frequency and MTF at -40°C in the imaging lens system of Example 3. [Figure 22] It is a graph showing the relationship between the spatial frequency and MTF at 115°C in the imaging lens system of Example 3. [Figure 23] It is a cross-sectional view showing the configuration of the imaging lens system according to Example 4. [Figure 24] It is a spherical aberration diagram of the imaging lens system of Example 4. [Figure 25] It is a field curvature diagram of the imaging lens system of Example 4. [Figure 26] It is a distortion aberration diagram of the imaging lens system of Example 4. [Figure 27] It is a graph showing the relationship between the spatial frequency and MTF at 25°C in the imaging lens system of Example 4. <所 [Figure 28] It is a graph showing the relationship between the spatial frequency and MTF at -40°C in the imaging lens system of Example 4. [Figure 29] It is a graph showing the relationship between the spatial frequency and MTF at 115°C in the imaging lens system of Example 4. [Figure 30] It is a cross-sectional view showing the configuration of the imaging lens system according to Example 5. [Figure 31] It is a spherical aberration diagram of the imaging lens system of Example 5. [Figure 32] It is a field curvature diagram of the imaging lens system of Example 5. [Figure 33] It is a distortion aberration diagram of the imaging lens system of Example 5. [Figure 34] It is a graph showing the relationship between the spatial frequency and MTF at 25°C in the imaging lens system of Example 5. [Figure 35]This graph shows the relationship between spatial frequency and MTF at -40°C in the imaging lens system of Example 5. [Figure 36] This graph shows the relationship between spatial frequency and MTF at 115°C in the imaging lens system of Example 5. [Figure 37] This is a cross-sectional view of the imaging device according to Embodiment 2. [Modes for carrying out the invention]

[0012] The optical lens and imaging device according to this embodiment will be described below. (Embodiment 1: Imaging lens system) The imaging lens system of Embodiment 1 is an imaging lens system consisting of a front lens group system and a rear lens group system, arranged in order from the object side to the image side, The aforementioned front lens group consists of, in order from the object side to the image side, a first lens having negative power and a concave shape on the image side, a second lens having negative power and a concave shape on the object side, and a third lens having positive power, a convex shape on the object side, and a convex shape on the image side. The aforementioned rear lens group consists of, in order from the object side to the image side, a fourth lens having positive power and a convex shape on the object side and a convex shape on the image side, a fifth lens having negative power, and a sixth lens, The fourth lens and the fifth lens are cemented lenses, the first lens and the third lens are glass lenses, and the second lens, the fourth lens and the fifth lens are plastic lenses. When the focal length of the second lens is f2, the combined focal length of the plastic lenses in the rear lens group is frp, and the focal length of the entire lens system is F, the following equations (1) and (2) are satisfied. 2<|f2 / F| ···(1) 2<|frp / F| ···(2)

[0013] Thus, the imaging lens system of Embodiment 1 makes it possible to realize an imaging lens system that is cost-effective and has stable performance against temperature changes.

[0014] The imaging lens system of Embodiment 1 described above may satisfy the following equation (3) when the sixth lens is a glass lens and the second lens is f2. 0.5 < |f² / frp| < 2 ···(3)

[0015] With these configurations, the refractive power changes that occur in both the plastic lens in the front lens group and the plastic lens group in the rear lens group due to temperature changes can be compensated for by each other, thereby suppressing changes in the performance of the entire optical system due to temperature changes.

[0016] Next, an embodiment corresponding to the imaging lens system of Embodiment 1 will be described with reference to the drawings. (Example 1) Figure 1 is a cross-sectional view showing the configuration of the imaging lens system according to Embodiment 1. In Figure 1, the imaging lens system 11 consists of, in order from the object side to the image side, a first lens L1 with negative power, a second lens L2 with negative power, a third lens L3 with positive power, an aperture stop, a fourth lens L4 with positive power, a fifth lens L5 with negative power, and a sixth lens L6. The imaging plane of the imaging lens system 11 is indicated by IMG. The imaging lens system 11 also includes an IR cut filter 12.

[0017] The first lens L1 is an aspherical glass lens with negative power. The object-side lens surface S1 of the first lens L1 has a convex curved portion on the object side. The image-side lens surface S2 of the first lens L1 has a concave curved portion on the image side.

[0018] The second lens L2 is an aspherical plastic lens with negative power. The object-side lens surface S3 of the second lens L2 has a concave curved portion on the object side. The image-side lens surface S4 of the second lens L2 has a convex curved portion on the image side.

[0019] The third lens L3 is an aspherical glass lens with positive power. The object-side lens surface S5 faces convexly towards the object, and the image-side lens surface S6 faces convexly towards the image.

[0020] The aperture stop is the aperture that determines the F-number (Fno) of the lens system. The aperture stop is located between the third lens L3 and the fourth lens L4.

[0021] The fourth lens L4 is an aspherical plastic lens with positive power. The object-side lens surface S8 faces convexly towards the object, and the image-side lens surface S9 faces convexly towards the image.

[0022] The fifth lens L5 is an aspherical plastic lens with negative power. The object-side lens surface S10 faces the object, with a concave surface facing the object, and the image-side lens surface S11 faces the image, with a convex surface facing the image.

[0023] The fourth lens L4 and the fifth lens L5 form a cemented lens by joining the image-side lens surface S9 of the fourth lens L4 and the object-side lens surface S10 of the fifth lens L5.

[0024] The sixth lens L6 is a positive-power aspherical lens. The object-side lens surface S12 faces convexly towards the object, and the image-side lens surface S13 faces concavely towards the image. The sixth lens L6 is a glass lens.

[0025] The IR cut filter 12 is a filter for cutting out light in the infrared region. When designing the imaging lens system 11, the IR cut filter 12 is treated as an integral part of the imaging lens system 11. However, the IR cut filter 12 is not an essential component of the imaging lens system 11.

[0026] Table 1 shows the lens data for each lens surface in the imaging lens system 11 of Example 1. In Table 1, the lens data for each surface includes the radius of curvature (mm), interplanar spacing (mm), refractive index at line d, and Abbe number at line d. The refractive index at line d and Abbe number at line d are values ​​when the ambient temperature t (°C), which is the temperature around the imaging lens system 11, is 25 (°C). Surfaces marked with an asterisk (*) indicate that they are aspherical. [Table 1]

[0027] The aspherical shapes used on the lens surface are determined by using α4, α6, α8, and α6 aspherical coefficients, respectively, where Z is the sag, c is the reciprocal of the radius of curvature, k is the conicity coefficient, and r is the ray height from the optical axis Z. 10 ,α 12 When this is the case, it can be expressed by the following equation.

number

[0028] Table 2 shows the aspheric coefficients used to define the aspheric shape of the aspheric lens surface in the imaging lens system 11 of Example 1. In Table 2, for example, "-6.522528E-03" is equivalent to "-6.522528×10 -3 It means "...". [Table 2]

[0029] Figure 2 is a spherical aberration diagram for the imaging lens system of Example 1. Figure 3 is an image field curvature diagram for the imaging lens system of Example 1. Figure 4 is a distortion aberration diagram for the imaging lens system of Example 1. As shown in Figures 2 to 4, in the imaging lens system 11 of Example 1, the half-angle of view ω is 65° and the F-number is 1.6. In the spherical aberration diagram of Figure 2, the horizontal axis shows the position where the light ray intersects the optical axis Z, and the vertical axis shows the relative height of the light ray at the pupil diameter. In the image field curvature diagram of Figure 3, the horizontal axis shows the distance to the image point in the direction of the optical axis Z, and the vertical axis shows the image height (angle of view). In Figure 4, Sag shows the image field curvature in the sagittal plane, and Tan shows the image field curvature in the tangential plane. In the distortion aberration diagram of Figure 4, the horizontal axis shows the amount of image distortion (%), and the vertical axis shows the image height (angle of view). Figure 2 shows the simulation results using light rays with wavelengths of 0.42 μm, 0.55 μm, and 0.68 μm. Figures 3 and 4 show the simulation results using light rays with a wavelength of 0.55 μm.

[0030] Table 11 below shows the calculated characteristic values ​​of the imaging lens system for each embodiment. In Table 11, the characteristic values ​​are shown for the imaging lens system 11 when the focal length of the first lens L1 is f1, the focal length of the second lens L2 is f2, the focal length of the third lens L3 is f3, the focal length of the fourth lens L4 is f4, the focal length of the fifth lens L5 is f5, the focal length of the sixth lens L6 is f6, the focal length of the entire lens system is F, the combined focal length of the fourth lens L4 and the fifth lens L5 is f45, the combined focal length of the fourth lens L4, the fifth lens L5, and the sixth lens L6 is f456, the combined focal length of the front group of plastic lenses is ffp, and the combined focal length of the rear group of plastic lenses is frp. Furthermore, the various focal lengths in Table 11 were calculated using light rays with a wavelength of 555 nm. In Example 1, since the sixth lens is a glass lens, the combined focal length frp of the plastic lenses in the rear lens group is the combined focal length f45 of the fourth lens L4 and the fifth lens L5.

[0031] Figure 5 is a graph showing the relationship between spatial frequency and MTF at 25°C for the imaging lens system of Example 1. Figure 6 is a graph showing the relationship between spatial frequency and MTF at -40°C for the imaging lens system of Example 1. Figure 7 is a graph showing the relationship between spatial frequency and MTF at 115°C for the imaging lens system of Example 1. In Figures 5 to 7, the vertical axis represents MTF (Modulation Transfer Function), and the horizontal axis represents spatial frequency (cycles / mm). Figures 5 to 7 show the relationship between spatial frequency and MTF for different fields of view. In Figures 5 to 7, the dashed lines show the relationship between spatial frequency and MTF in the tangential plane, and the solid lines show the relationship between spatial frequency and MTF in the sagittal plane.

[0032] In this specification, the field of view refers to the angle at which lines extending from the incident light to the object-side lens surface intersect each other in a cross-sectional view along the optical axis, for the outermost light beam that can actually pass through the first lens L1. Specifically, it corresponds to the "field of view" in Figure 8.

[0033] As shown in Figures 5 to 7, the imaging lens system of Example 1 maintains almost the same relationship between spatial frequency and MTF even at different temperatures.

[0034] (Example 2) Figure 9 is a cross-sectional view showing the configuration of the imaging lens system of Embodiment 2. In Figure 9, the imaging lens system 11 consists of, in order from the object side to the image side, a first lens L1 with negative power, a second lens L2 with negative power, a third lens L3 with positive power, an aperture stop, a fourth lens L4 with positive power, a fifth lens L5 with negative power, and a sixth lens L6 with positive power. In Embodiment 2, the sixth lens L6 is a glass lens. The imaging plane of the imaging lens system 11 is indicated by IMG. The imaging lens system 11 also includes an IR cut filter 12. In Figure 9, components identical to those in Figure 1 are denoted by the same reference numerals and their description is omitted.

[0035] Table 3 shows the lens data for each lens surface in the imaging lens system 11 of Example 2. In Table 3, the lens data for each surface includes the radius of curvature (mm), interplanar spacing (mm), refractive index at line d, and Abbe number at line d. The refractive index at line d and Abbe number at line d are values ​​when the ambient temperature t (°C), which is the temperature around the imaging lens system 11, is 25 (°C). Surfaces marked with an asterisk (*) indicate that they are aspherical. [Table 3]

[0036] Table 4 shows the aspheric coefficients used to define the aspherical shape of the lens surface designated as aspherical in the imaging lens system 11 of Example 2. In Table 4, the aspherical shape adopted for the lens surface is expressed by the same formula as in Example 1. [Table 4]

[0037] Figure 10 is a spherical aberration diagram for the imaging lens system of Example 2. Figure 11 is an image field curvature diagram for the imaging lens system of Example 2. Figure 12 is a distortion aberration diagram for the imaging lens system of Example 2. As shown in Figures 10 to 12, in the imaging lens system 11 of Example 2, the half-angle of view ω is 65° and the F-number is 1.6. In the spherical aberration diagram of Figure 10, the horizontal axis shows the position where the light ray intersects the optical axis Z, and the vertical axis shows the relative height of the light ray at the pupil diameter. In the image field curvature diagram of Figure 11, the horizontal axis shows the distance to the image point in the direction of the optical axis Z, and the vertical axis shows the image height (angle of view). In Figure 12, Sag shows the image field curvature in the sagittal plane, and Tan shows the image field curvature in the tangential plane. In the distortion diagram in Figure 12, the horizontal axis represents the amount of image distortion (%), and the vertical axis represents the image height (field of view). Figure 10 shows the simulation results using light rays with wavelengths of 0.42 μm, 0.55 μm, and 0.68 μm. Figures 11 and 12 show the simulation results using light rays with a wavelength of 0.55 μm.

[0038] Table 11 shows the results of calculating the characteristic values ​​of the imaging lens system 11 in Example 2. In Example 2, since the sixth lens is a glass lens, the combined focal length frp of the plastic lenses in the rear lens group system is the combined focal length f45 of the fourth lens L4 and the fifth lens L5.

[0039] Figure 13 is a graph showing the relationship between spatial frequency and MTF at 25°C for the imaging lens system of Example 2. Figure 14 is a graph showing the relationship between spatial frequency and MTF at -40°C for the imaging lens system of Example 2. Figure 15 is a graph showing the relationship between spatial frequency and MTF at 115°C for the imaging lens system of Example 2. In Figures 13 to 15, the vertical axis represents MTF (Modulation Transfer Function), and the horizontal axis represents spatial frequency (cycles / mm). Figures 13 to 15 show the relationship between spatial frequency and MTF for different fields of view. In Figures 13 to 15, the dashed lines show the relationship between spatial frequency and MTF in the tangential plane, and the solid lines show the relationship between spatial frequency and MTF in the sagittal plane.

[0040] As shown in Figures 13 to 15, the imaging lens system of Example 2 maintains almost the same relationship between spatial frequency and MTF even at different temperatures.

[0041] (Example 3) Figure 16 is a cross-sectional view showing the configuration of the imaging lens system of Embodiment 3. In Figure 16, the imaging lens system 11 consists of, in order from the object side to the image side, a first lens L1 with negative power, a second lens L2 with negative power, a third lens L3 with positive power, an aperture stop, a fourth lens L4 with positive power, a fifth lens L5 with negative power, and a sixth lens L6 with positive power. In Embodiment 2, the sixth lens L6 is a glass lens. The imaging plane of the imaging lens system 11 is indicated by IMG. The imaging lens system 11 also includes an IR cut filter 12. In Figure 16, components identical to those in Figure 1 are denoted by the same reference numerals and their description is omitted.

[0042] Table 5 shows the lens data for each lens surface in the imaging lens system 11 of Example 3. In Table 5, the lens data for each surface includes the radius of curvature (mm), interplanar spacing (mm), refractive index at line d, and Abbe number at line d. The refractive index at line d and Abbe number at line d are values ​​when the ambient temperature t (°C), which is the temperature around the imaging lens system 11, is 25 (°C). Surfaces marked with an asterisk (*) indicate that they are aspherical. [Table 5]

[0043] Table 6 shows the aspheric coefficients used to define the aspherical shape of the lens surface designated as aspherical in the imaging lens system 11 of Example 3. In Table 6, the aspherical shape adopted for the lens surface is expressed by the same formula as in Example 1. [Table 6]

[0044] Figure 17 is a spherical aberration diagram for the imaging lens system of Example 3. Figure 18 is a field curvature diagram for the imaging lens system of Example 3. Figure 19 is a distortion aberration diagram for the imaging lens system of Example 3. As shown in Figures 17 to 19, in the imaging lens system 11 of Example 3, the half-angle of view ω is 65° and the F-number is 1.6. In the spherical aberration diagram of Figure 17, the horizontal axis shows the position where the light ray intersects the optical axis Z, and the vertical axis shows the relative height of the light ray at the pupil diameter. In the field curvature diagram of Figure 18, the horizontal axis shows the distance to the image point in the direction of the optical axis Z, and the vertical axis shows the image height (angle of view). In Figure 19, Sag shows the field curvature in the sagittal plane, and Tan shows the field curvature in the tangential plane. In the distortion aberration diagram of Figure 19, the horizontal axis shows the amount of image distortion (%), and the vertical axis shows the image height (angle of view). Figure 17 shows the simulation results using light rays with wavelengths of 0.42 μm, 0.55 μm, and 0.68 μm. Figures 18 and 19 show the simulation results using light rays with a wavelength of 0.55 μm.

[0045] Table 11 shows the results of calculating the characteristic values ​​of the imaging lens system 11 in Example 3. In Example 3, since the sixth lens is a glass lens, the combined focal length frp of the plastic lenses in the rear lens group is the combined focal length f45 of the fourth lens L4 and the fifth lens L5.

[0046] Figure 20 is a graph showing the relationship between spatial frequency and MTF at 25°C for the imaging lens system of Example 3. Figure 21 is a graph showing the relationship between spatial frequency and MTF at -40°C for the imaging lens system of Example 3. Figure 22 is a graph showing the relationship between spatial frequency and MTF at 115°C for the imaging lens system of Example 3. In Figures 20 to 22, the vertical axis represents MTF (Modulation Transfer Function), and the horizontal axis represents spatial frequency (cycles / mm). Figures 20 to 22 show the relationship between spatial frequency and MTF for different fields of view. In Figures 20 to 22, the dashed line shows the relationship between spatial frequency and MTF in the tangential plane, and the solid line shows the relationship between spatial frequency and MTF in the sagittal plane.

[0047] As shown in Figures 20 to 22, the imaging lens system of Example 3 maintains almost the same relationship between spatial frequency and MTF even at different temperatures.

[0048] (Example 4) Figure 23 is a cross-sectional view showing the configuration of the imaging lens system of Embodiment 4. In Figure 23, the imaging lens system 11 consists of, in order from the object side to the image side, a first lens L1 with negative power, a second lens L2 with negative power, a third lens L3 with positive power, an aperture stop, a fourth lens L4 with positive power, a fifth lens L5 with negative power, and a sixth lens L6 with positive power. In Embodiment 4, the sixth lens L6 is a plastic lens. The imaging plane of the imaging lens system 11 is indicated by IMG. The imaging lens system 11 also includes an IR cut filter 12. In Figure 23, components identical to those in Figure 1 are denoted by the same reference numerals and their descriptions are omitted.

[0049] Table 7 shows the lens data for each lens surface in the imaging lens system 11 of Example 4. In Table 7, the lens data for each surface includes the radius of curvature (mm), interplanar spacing (mm), refractive index at line d, and Abbe number at line d. The refractive index at line d and Abbe number at line d are values ​​when the ambient temperature t (°C), which is the temperature around the imaging lens system 11, is 25 (°C). Surfaces marked with an asterisk (*) indicate that they are aspherical. [Table 7]

[0050] Table 8 shows the aspheric coefficients used to define the aspherical shape of the lens surface designated as aspherical in the imaging lens system 11 of Example 4. In Table 8, the aspherical shape adopted for the lens surface is expressed by the same formula as in Example 1. [Table 8]

[0051] Figure 24 is a spherical aberration diagram for the imaging lens system of Example 4. Figure 25 is a field curvature diagram for the imaging lens system of Example 4. Figure 26 is a distortion aberration diagram for the imaging lens system of Example 4. As shown in Figures 24 to 26, in the imaging lens system 11 of Example 4, the half-angle of view ω is 65° and the F-number is 1.6. In the spherical aberration diagram of Figure 24, the horizontal axis shows the position where the light ray intersects the optical axis Z, and the vertical axis shows the relative height of the light ray at the pupil diameter. In the field curvature diagram of Figure 25, the horizontal axis shows the distance to the image point in the direction of the optical axis Z, and the vertical axis shows the image height (angle of view). In Figure 26, Sag shows the field curvature in the sagittal plane, and Tan shows the field curvature in the tangential plane. In the distortion aberration diagram of Figure 26, the horizontal axis shows the amount of image distortion (%), and the vertical axis shows the image height (angle of view). Figure 24 shows the simulation results using light rays with wavelengths of 0.42 μm, 0.55 μm, and 0.68 μm. Figures 25 and 26 show the simulation results using light rays with a wavelength of 0.55 μm.

[0052] Table 11 shows the results of calculating the characteristic values ​​of the imaging lens system 11 in Example 4. In Example 4, since the sixth lens is a plastic lens, the combined focal length frp of the plastic lenses in the rear lens group is the combined focal length f456 of the fourth lens L4, the fifth lens L5, and the sixth lens.

[0053] Figure 27 is a graph showing the relationship between spatial frequency and MTF at 25°C for the imaging lens system of Example 4. Figure 28 is a graph showing the relationship between spatial frequency and MTF at -40°C for the imaging lens system of Example 4. Figure 29 is a graph showing the relationship between spatial frequency and MTF at 115°C for the imaging lens system of Example 4. In Figures 27 to 29, the vertical axis represents MTF (Modulation Transfer Function), and the horizontal axis represents spatial frequency (cycles / mm). Figures 27 to 29 show the relationship between spatial frequency and MTF for different fields of view. In Figures 27 to 29, the dashed lines show the relationship between spatial frequency and MTF in the tangential plane, and the solid lines show the relationship between spatial frequency and MTF in the sagittal plane.

[0054] As shown in Figures 27 to 29, the imaging lens system of Example 4 maintains almost the same relationship between spatial frequency and MTF even at different temperatures.

[0055] (Example 5) Figure 30 is a cross-sectional view showing the configuration of the imaging lens system of Embodiment 5. In Figure 30, the imaging lens system 11 consists of, in order from the object side to the image side, a first lens L1 with negative power, a second lens L2 with negative power, a third lens L3 with positive power, an aperture stop, a fourth lens L4 with positive power, a fifth lens L5 with negative power, and a sixth lens L6 with positive power. In Embodiment 5, the sixth lens L6 is a plastic lens. The imaging plane of the imaging lens system 11 is indicated by IMG. The imaging lens system 11 also includes an IR cut filter 12. In Figure 30, components identical to those in Figure 1 are denoted by the same reference numerals and their description is omitted.

[0056] Table 9 shows the lens data for each lens surface in the imaging lens system 11 of Example 5. In Table 9, the lens data for each surface includes the radius of curvature (mm), interplanar spacing (mm), refractive index at line d, and Abbe number at line d. The refractive index at line d and Abbe number at line d are values ​​when the ambient temperature t (°C), which is the temperature around the imaging lens system 11, is 25 (°C). Surfaces marked with an asterisk (*) indicate that they are aspherical. [Table 9]

[0057] Table 10 shows the aspheric coefficients used to define the aspheric shape of the lens surface designated as aspheric in the imaging lens system 11 of Example 5. In Table 10, the aspheric shape adopted for the lens surface is expressed by the same formula as in Example 1. [Table 10]

[0058] Figure 31 is a spherical aberration diagram for the imaging lens system of Example 5. Figure 32 is an image field curvature diagram for the imaging lens system of Example 5. Figure 33 is a distortion aberration diagram for the imaging lens system of Example 5. As shown in Figures 31 to 33, in the imaging lens system 11 of Example 5, the half-angle of view ω is 65° and the F-number is 1.6. In the spherical aberration diagram of Figure 31, the horizontal axis shows the position where the light ray intersects the optical axis Z, and the vertical axis shows the relative height of the light ray at the pupil diameter. In the image field curvature diagram of Figure 32, the horizontal axis shows the distance to the image point in the direction of the optical axis Z, and the vertical axis shows the image height (angle of view). In Figure 33, Sag shows the image field curvature in the sagittal plane, and Tan shows the image field curvature in the tangential plane. In the distortion aberration diagram of Figure 33, the horizontal axis shows the amount of image distortion (%), and the vertical axis shows the image height (angle of view). Figure 31 shows the simulation results using light rays with wavelengths of 0.42 μm, 0.55 μm, and 0.68 μm. Figures 32 and 33 show the simulation results using light rays with a wavelength of 0.55 μm.

[0059] Table 11 shows the results of calculating the characteristic values ​​of the imaging lens system 11 in Example 5. In Example 5, since the sixth lens is a plastic lens, the combined focal length frp of the plastic lenses in the rear lens group is the combined focal length f456 of the fourth lens L4, the fifth lens L5, and the sixth lens.

[0060] Figure 34 is a graph showing the relationship between spatial frequency and MTF at 25°C for the imaging lens system of Example 5. Figure 35 is a graph showing the relationship between spatial frequency and MTF at -40°C for the imaging lens system of Example 5. Figure 36 is a graph showing the relationship between spatial frequency and MTF at 115°C for the imaging lens system of Example 5. In Figures 34 to 36, the vertical axis represents MTF (Modulation Transfer Function), and the horizontal axis represents spatial frequency (cycles / mm). Figures 34 to 36 show the relationship between spatial frequency and MTF for different fields of view. In Figures 34 to 36, the dashed lines show the relationship between spatial frequency and MTF in the tangential plane, and the solid lines show the relationship between spatial frequency and MTF in the sagittal plane.

[0061] As shown in Figures 34 to 36, the imaging lens system of Example 5 maintains almost the same relationship between spatial frequency and MTF even at different temperatures.

[0062] Table 11 lists the numerical values ​​corresponding to each condition in this embodiment according to the above conditional formulas. Clearly, the imaging lens system of this embodiment satisfies the above conditional formulas. [Table 11]

[0063] (Embodiment 2: Example of application to an imaging device) Figure 37 is a cross-sectional view of an imaging device according to Embodiment 2. The imaging device 21 comprises an imaging lens system 11, a cover glass 22, and an image sensor 23. The imaging lens system 11, the cover glass 22, and the image sensor 23 are housed in a housing (not shown).

[0064] The image sensor 23 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 image sensor 23 is positioned at the imaging position of the imaging lens system 11. The horizontal angle of view is the angle of view corresponding to the horizontal direction of the image sensor 23.

[0065] The cover glass 22 is provided on the image sensor 23 to protect the image sensor 23 from foreign matter.

[0066] It should be noted that the present invention is not limited to the embodiments described above, and can be modified as appropriate without departing from the spirit of the invention. [Explanation of Symbols]

[0067] 11 Imaging lens system 12-cut filter 21 Imaging device 22 Cover glass 23 Image sensor L1, L2, L3, L4, L5, L6 lenses STOP aperture IMG imaging plane

Claims

1. The imaging lens system consists of a front lens group and a rear lens group, arranged in order from the object side to the image side. The aforementioned front lens group consists of, in order from the object side to the image side, a first lens having negative power and a concave shape on the image side, a second lens having negative power and a convex shape on the image side, and a third lens having positive power and a convex shape on the image side. The aforementioned rear lens group consists of, in order from the object side to the image side, a fourth lens having positive power and a convex shape on the image side, a fifth lens having negative power, and a sixth lens. The first lens and the third lens are glass lenses. The second lens, the fourth lens, and the fifth lens are plastic lenses in this imaging lens system.

2. The imaging lens system according to claim 1, wherein the focal length of the second lens is f2 and the focal length of the entire lens system is F, and the following equation (1) is satisfied. 2<|f2 / F| ...(1)

3. The imaging lens system according to claim 1, wherein the combined focal length of the plastic lenses in the rear lens group is frp, and the focal length of the entire lens system is F, satisfies the following equation (2). 2<|frp / F| ...(2)

4. The imaging lens system according to claim 1, wherein the focal length of the second lens is f2 and the combined focal length of the plastic lenses in the rear lens group is frp, and the following equation (3) is satisfied. 0.5<|f2 / frp|<2...(3)

5. The imaging lens system according to claim 1, wherein the sixth lens is a glass lens.

6. The imaging lens system according to claim 1, wherein the sixth lens is a plastic lens.

7. The imaging lens system according to any one of claims 1 to 6, An imaging device comprising an image sensor disposed on the image side of the imaging lens system.

Images