Imaging lens system and imaging device

Abstract

To provide an image capturing lens system which can be produced at low cost and offers more stable performance against temperature variations, and to provide an image capturing device having the same.SOLUTION: An image capturing lens system 11 provided herein comprises a front group lens system and a rear group lens system arranged in order form the object side to the image side. The front group lens system consists of, in order from the object side to the image side, a first lens L1 with negative power having a concave surface on the image side, a second lens L2 with negative power having a convex surface on the image side, and a third ens L3 with positive power having a convex surface on the image side. The rear group lens system consists of, in order from the object side to the image side, a fourth lens L4 with positive power having a convex surface of the image side, a fifth lens L5 with negative power, and a sixth lens L6. The fourth lens L4 and the fifth lens L5 constitute a cemented lens. The first lens L1 and the third lens L3 are glass lenses. The second lens L2, the fourth lens L4, and the fifth lens L5 are plastic lenses.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In recent years, the use of wide-angle lenses installed in vehicles has been shifting from viewing to sensing. Sensing requires the resolution required for image analysis, so high-resolution images corresponding to megapixels are in demand. A wide angle of view is also required.

[0003] As such, in-vehicle imaging devices are required to capture images of distant objects in the direction of travel with high resolution, as well as close-up images with a wide angle. Furthermore, they are required to have a bright optical system. Furthermore, imaging lens systems for in-vehicle cameras, in particular, are also required to be compact.

[0004] For example, Patent Document 1 describes an imaging device that uses a mirror to switch between a wide-angle optical system and a telephoto optical system, whose optical axes are arranged perpendicular to each other, and forms an optical image from either optical system on a common imaging element. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-122379 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the imaging device of Patent Document 1 uses two types of lenses: a telephoto optical system for long-distance imaging and a wide-angle optical system for close-distance imaging, which increases the size of the unit and also increases the cost. Furthermore, if all lenses were made of plastic to reduce costs, there was the problem that performance would be unstable against changes in environmental temperature.

[0007] As described above, conventional imaging lens systems have had the problem that it is not possible to realize an imaging lens system and imaging device that are cost-effective and have stable performance against temperature changes. [Means for solving the problem]

[0008] An imaging lens system according to one embodiment is an imaging lens system that is composed of, in order from the object side to the image side, a front lens group system and a rear lens group system, The front lens group system comprises, 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 and a convex shape on the object side and a convex shape on the image side, The rear lens system comprises, 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 composite 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] According to this configuration, it is possible to realize an imaging lens system that uses a large amount of plastic lenses to reduce costs and has 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 an imaging device that are inexpensive and have stable performance against temperature changes. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view showing the configuration of an imaging lens system according to Example 1. FIG. [Figure 2] 4A to 4C are diagrams illustrating spherical aberration in the imaging lens system of Example 1. [Figure 3] FIG. 2 is a diagram showing the curvature of field in the imaging lens system of the first embodiment. [Figure 4] 4A to 4C are diagrams illustrating distortion in the imaging lens system of Example 1. [Figure 5] 10 is a graph showing the relationship between spatial frequency and MTF at 25° C. in the imaging lens system of Example 1. [Figure 6] 10 is a graph showing the relationship between spatial frequency and MTF at −40° C. in the imaging lens system of Example 1. [Figure 7] 10 is a graph showing the relationship between spatial frequency and MTF at 115° C. in the imaging lens system of Example 1. [Figure 8] FIG. 2 is a diagram for explaining an angle of view. [Figure 9] FIG. 10 is a cross-sectional view showing the configuration of an imaging lens system according to Example 2. [Figure 10] 10A and 10B are diagrams illustrating spherical aberration in the imaging lens system of Example 2. [Figure 11] FIG. 10 is a diagram illustrating the curvature of field in the imaging lens system of Example 2. [Figure 12] 10A and 10B are diagrams illustrating distortion in the imaging lens system of Example 2. [Figure 13] 10 is a graph showing the relationship between spatial frequency and MTF at 25° C. in the imaging lens system of Example 2. [Figure 14] 10 is a graph showing the relationship between spatial frequency and MTF at −40° C. in the imaging lens system of Example 2. [Figure 15] 10 is a graph showing the relationship between spatial frequency and MTF at 115° C. in the imaging lens system of Example 2. [Figure 16] FIG. 10 is a cross-sectional view showing the configuration of an imaging lens system according to Example 3. [Figure 17] 10A and 10B are diagrams illustrating spherical aberration in the imaging lens system of Example 3. [Figure 18] FIG. 10 is a diagram illustrating the curvature of field in the imaging lens system of Example 3. [Figure 19] 10A and 10B are diagrams illustrating distortion in the imaging lens system of Example 3. [Figure 20] 10 is a graph showing the relationship between spatial frequency and MTF at 25° C. in the imaging lens system of Example 3. [Figure 21] 10 is a graph showing the relationship between spatial frequency and MTF at −40° C. in the imaging lens system of Example 3. [Figure 22] 11 is a graph showing the relationship between spatial frequency and MTF at 115° C. in the imaging lens system of Example 3. [Figure 23] FIG. 10 is a cross-sectional view showing the configuration of an imaging lens system according to Example 4. [Figure 24] 10A and 10B are diagrams illustrating spherical aberration in the imaging lens system of Example 4. [Figure 25] FIG. 10 is a diagram illustrating the curvature of field in the imaging lens system of Example 4. [Figure 26] 10A and 10B are diagrams illustrating distortion in the imaging lens system of Example 4. [Figure 27] 10 is a graph showing the relationship between spatial frequency and MTF at 25° C. in the imaging lens system of Example 4. [Figure 28] 10 is a graph showing the relationship between spatial frequency and MTF at −40° C. in the imaging lens system of Example 4. [Figure 29] 11 is a graph showing the relationship between spatial frequency and MTF at 115° C. in the imaging lens system of Example 4. [Figure 30] FIG. 10 is a cross-sectional view showing the configuration of an imaging lens system according to a fifth embodiment. [Figure 31] 10A and 10B are diagrams illustrating spherical aberration in the imaging lens system of Example 5. [Figure 32] FIG. 10 is a diagram showing the curvature of field in the imaging lens system of Example 5. [Figure 33] 10A and 10B are diagrams illustrating distortion in the imaging lens system of Example 5. [Figure 34] 10 is a graph showing the relationship between spatial frequency and MTF at 25° C. in the imaging lens system of Example 5. [Figure 35]11 is a graph showing the relationship between spatial frequency and MTF at −40° C. in the imaging lens system of Example 5. [Figure 36] 11 is a graph showing the relationship between spatial frequency and MTF at 115° C. in the imaging lens system of Example 5. [Figure 37] FIG. 10 is a cross-sectional view of an imaging device according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] The optical lens and the imaging device according to this embodiment will be described below. (Embodiment 1: Imaging lens system) The imaging lens system of the first embodiment is an imaging lens system that is composed of, in order from the object side to the image side, a front lens group system and a rear lens group system, The front lens group system comprises, 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 and a convex shape on the object side and a convex shape on the image side, The rear lens system comprises, 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 composite 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, according to the imaging lens system of the first embodiment, it is possible to realize an imaging lens system that is cost-effective and has stable performance against temperature changes.

[0014] The imaging lens system of the first embodiment may be configured to satisfy the following formula (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 the plastic lenses in the front lens group and the plastic lens groups 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 example corresponding to the imaging lens system of the first embodiment will be described with reference to the drawings. Example 1 Fig. 1 is a cross-sectional view showing the configuration of an imaging lens system according to Example 1. In Fig. 1, the imaging lens system 11 is composed of, in order from the object side to the image side, a first lens L1 having negative power, a second lens L2 having negative power, a third lens L3 having positive power, an aperture stop STOP, a fourth lens L4 having positive power, a fifth lens L5 having 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 surface portion facing the object side. The image-side lens surface S2 of the first lens L1 has a concave curved surface portion facing 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 surface portion facing the object side. The image-side lens surface S4 of the second lens L2 has a convex curved surface portion facing the image side.

[0019] The third lens L3 is an aspherical glass lens having a positive power. The object-side lens surface S5 has a convex surface facing the object side, and the image-side lens surface S6 has a convex surface facing the image side.

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

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

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

[0023] The fourth lens L4 and the fifth lens L5 form a cemented lens in which the image side lens surface S9 of the fourth lens L4 and the object side lens surface S10 of the fifth lens L5 are cemented together.

[0024] The sixth lens L6 is an aspherical lens having positive power. The object-side lens surface S12 has a convex surface facing the object side, and the image-side lens surface S13 has a concave surface facing the image side. The sixth lens L6 is a glass lens.

[0025] The IR cut filter 12 is a filter for cutting 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. Table 1 presents the lens data, such as the radius of curvature (mm), surface spacing (mm), refractive index at the d-line, and Abbe number at the d-line, for each surface. The refractive index at the d-line and the Abbe number at the d-line 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 "*" indicate that they are aspherical. [Table 1]

[0027] The aspherical shape used on the lens surface is as follows: Z is the amount of sag, c is the inverse of the radius of curvature, k is the conic coefficient, and r is the ray height from the optical axis Z. The aspherical coefficients of the 4th, 6th, 8th, 10th, and 12th orders are α4, α6, α8, and α 10 ,α 12 When this is the case, it can be expressed by the following equation:

number

[0028] Table 2 shows aspherical 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, "-6.522528E-03" corresponds to "-6.522528×10 -3 " means. [Table 2]

[0029] FIG. 2 is a diagram of spherical aberration in the imaging lens system of Example 1. FIG. 3 is a diagram of field curvature in the imaging lens system of Example 1. FIG. 4 is a diagram of distortion aberration in the imaging lens system of Example 1. As shown in FIGS. 2 to 4, the imaging lens system 11 of Example 1 has a half angle of view ω of 65° and an F-number of 1.6. In the spherical aberration diagram of FIG. 2, the horizontal axis indicates the position where a light ray intersects with the optical axis Z, and the vertical axis indicates the relative height of the light ray at the pupil diameter. In the field curvature diagram of FIG. 3, the horizontal axis indicates the distance of the image formation point in the direction of the optical axis Z, and the vertical axis indicates the image height (field angle). In FIG. 4, Sag indicates field curvature in the sagittal plane, and Tan indicates field curvature in the tangential plane. In the distortion aberration diagram of FIG. 4, the horizontal axis indicates the amount of image distortion (%), and the vertical axis indicates the image height (field angle). 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 results of calculating the characteristic values ​​of the imaging lens system of each example. Table 11 shows the characteristic values ​​for the imaging lens system 11, where 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. The various focal lengths in Table 11 were calculated using light with a wavelength of 555 nm. In Example 1, since the sixth lens is a glass lens, the composite focal length frp of the plastic lenses in the rear lens group system is the composite focal length f45 of the fourth lens L4 and the fifth lens L5.

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

[0032] In this specification, the angle of view means the angle at which the lines extending the incident light on the object-side lens surface intersect with each other for the most off-axis light beam that can actually pass through the first lens L1 in a cross section along the optical axis. Specifically, this corresponds to the "angle of view" in Figure 8.

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

[0034] Example 2 Fig. 9 is a cross-sectional view showing the configuration of an imaging lens system of Example 2. In Fig. 9, the imaging lens system 11 is composed of, in order from the object side to the image side, a first lens L1 having negative power, a second lens L2 having negative power, a third lens L3 having positive power, an aperture STOP, a fourth lens L4 having positive power, a fifth lens L5 having negative power, and a sixth lens L6 having positive power. In Example 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 Fig. 9, the same components as those in Fig. 1 are designated by the same reference numerals, and their description will be omitted.

[0035] Table 3 shows the lens data for each lens surface in the imaging lens system 11 of Example 2. Table 3 presents the lens data, such as the radius of curvature (mm), surface spacing (mm), refractive index at the d-line, and Abbe number at the d-line for each surface. The refractive index at the d-line and the Abbe number at the d-line 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 "*" indicate that they are aspherical. [Table 3]

[0036] Table 4 shows aspherical coefficients for defining the aspherical shape of the aspherical lens surface 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] Fig. 10 is a diagram of spherical aberration in the imaging lens system of Example 2. Fig. 11 is a diagram of field curvature in the imaging lens system of Example 2. Fig. 12 is a diagram of distortion aberration in the imaging lens system of Example 2. As shown in Figs. 10 to 12, the imaging lens system 11 of Example 2 has a half angle of view ω of 65° and an F-number of 1.6. In the spherical aberration diagram of Fig. 10, the horizontal axis indicates the position where the light ray intersects with the optical axis Z, and the vertical axis indicates the relative height of the light ray at the pupil diameter. In the field curvature diagram of Fig. 11, the horizontal axis indicates the distance of the image-forming point in the direction of the optical axis Z, and the vertical axis indicates the image height (field angle). In Fig. 12, Sag indicates field curvature in the sagittal plane, and Tan indicates field curvature in the tangential plane. In the distortion diagram of Figure 12, the horizontal axis represents the amount of image distortion (%), and the vertical axis represents the image height (angle 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 composite focal length frp of the plastic lenses in the rear lens group system is the composite focal length f45 of the fourth lens L4 and the fifth lens L5.

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

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

[0041] Example 3 Fig. 16 is a cross-sectional view showing the configuration of an imaging lens system of Example 3. In Fig. 16, the imaging lens system 11 is composed of, in order from the object side to the image side, a first lens L1 having negative power, a second lens L2 having negative power, a third lens L3 having positive power, an aperture STOP, a fourth lens L4 having positive power, a fifth lens L5 having negative power, and a sixth lens L6 having 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 Fig. 16, the same components as those in Fig. 1 are designated by the same reference numerals, and their description will be omitted.

[0042] Table 5 shows the lens data for each lens surface in the imaging lens system 11 of Example 3. Table 5 presents the lens data, such as the radius of curvature (mm), surface spacing (mm), refractive index at the d-line, and Abbe number at the d-line for each surface. The refractive index at the d-line and the Abbe number at the d-line 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 "*" are aspherical. [Table 5]

[0043] Table 6 shows aspherical coefficients for defining the aspherical shape of the aspherical lens surface 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] FIG. 17 is a diagram of spherical aberration in the imaging lens system of Example 3. FIG. 18 is a diagram of field curvature in the imaging lens system of Example 3. FIG. 19 is a diagram of distortion in the imaging lens system of Example 3. As shown in FIGS. 17 to 19, the imaging lens system 11 of Example 3 has a half angle of view ω of 65° and an F-number of 1.6. In the spherical aberration diagram of FIG. 17, the horizontal axis indicates the position where the light ray intersects with the optical axis Z, and the vertical axis indicates the relative height of the light ray at the pupil diameter. In the field curvature diagram of FIG. 18, the horizontal axis indicates the distance of the image formation point in the direction of the optical axis Z, and the vertical axis indicates the image height (field angle). In FIG. 19, Sag indicates field curvature in the sagittal plane, and Tan indicates field curvature in the tangential plane. In the distortion diagram of FIG. 19, the horizontal axis indicates the amount of image distortion (%), and the vertical axis indicates the image height (field angle). 17 shows the simulation results using light rays with wavelengths of 0.42 μm, 0.55 μm, and 0.68 μm, while FIGS. 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 of Example 3. In Example 3, since the sixth lens is a glass lens, the composite focal length frp of the plastic lenses in the rear lens group system is the composite focal length f45 of the fourth lens L4 and the fifth lens L5.

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

[0047] As shown in FIGS. 20 to 22, the imaging lens system of Example 3 maintains approximately 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 an imaging lens system of Example 4. In Figure 23, imaging lens system 11 consists of, in order from the object side to the image side, a first lens L1 having negative power, a second lens L2 having negative power, a third lens L3 having positive power, an aperture stop STOP, a fourth lens L4 having positive power, a fifth lens L5 having negative power, and a sixth lens L6 having positive power. In Example 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 Fig. 23, the same components as those in Fig. 1 are given the same reference numerals and descriptions thereof will be omitted.

[0049] Table 7 shows the lens data for each lens surface in the imaging lens system 11 of Example 4. Table 7 presents the lens data, such as the radius of curvature (mm), surface spacing (mm), refractive index at the d-line, and Abbe number at the d-line for each surface. The refractive index at the d-line and the Abbe number at the d-line 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 "*" indicate that they are aspherical. [Table 7]

[0050] Table 8 shows aspherical coefficients for defining the aspherical shape of the aspherical lens surface 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] FIG. 24 is a diagram of spherical aberration in the imaging lens system of Example 4. FIG. 25 is a diagram of field curvature in the imaging lens system of Example 4. FIG. 26 is a diagram of distortion in the imaging lens system of Example 4. As shown in FIGS. 24 to 26, the imaging lens system 11 of Example 4 has a half angle of view ω of 65° and an F-number of 1.6. In the spherical aberration diagram of FIG. 24, the horizontal axis indicates the position where the light ray intersects with the optical axis Z, and the vertical axis indicates the relative height of the light ray at the pupil diameter. In the field curvature diagram of FIG. 25, the horizontal axis indicates the distance of the image formation point in the direction of the optical axis Z, and the vertical axis indicates the image height (field angle). In FIG. 26, Sag indicates field curvature in the sagittal plane, and Tan indicates field curvature in the tangential plane. In the distortion diagram of FIG. 26, the horizontal axis indicates the amount of image distortion (%), and the vertical axis indicates the image height (field angle). 24 shows the simulation results using light rays with wavelengths of 0.42 μm, 0.55 μm, and 0.68 μm, while FIGS. 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 of Example 4. In Example 4, since the sixth lens is a plastic lens, the composite focal length frp of the plastic lenses in the rear lens group system is the composite focal length f456 of the fourth lens L4, the fifth lens L5, and the sixth lens.

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

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

[0055] Example 5 Fig. 30 is a cross-sectional view showing the configuration of an imaging lens system according to a fifth embodiment. In Fig. 30, the imaging lens system 11 is composed of, in order from the object side to the image side, a first lens L1 having negative power, a second lens L2 having negative power, a third lens L3 having positive power, an aperture STOP, a fourth lens L4 having positive power, a fifth lens L5 having negative power, and a sixth lens L6 having positive power. In the fifth embodiment, 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 Fig. 30, the same components as those in Fig. 1 are designated by the same reference numerals, and their description will be omitted.

[0056] Table 9 shows the lens data for each lens surface in the imaging lens system 11 of Example 5. Table 9 presents the lens data, such as the radius of curvature (mm), surface spacing (mm), refractive index at the d-line, and Abbe number at the d-line for each surface. The refractive index at the d-line and Abbe number at the d-line 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 "*" indicate that they are aspherical. [Table 9]

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

[0058] FIG. 31 is a diagram of spherical aberration in the imaging lens system of Example 5. FIG. 32 is a diagram of field curvature in the imaging lens system of Example 5. FIG. 33 is a diagram of distortion in the imaging lens system of Example 5. As shown in FIGS. 31 to 33, the imaging lens system 11 of Example 5 has a half angle of view ω of 65° and an F-number of 1.6. In the spherical aberration diagram of FIG. 31, the horizontal axis indicates the position where the light ray intersects with the optical axis Z, and the vertical axis indicates the relative height of the light ray at the pupil diameter. In the field curvature diagram of FIG. 32, the horizontal axis indicates the distance of the image formation point in the direction of the optical axis Z, and the vertical axis indicates the image height (field angle). In FIG. 33, 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. 33, the horizontal axis indicates the amount of image distortion (%), and the vertical axis indicates the image height (field angle). Figure 31 shows the simulation results using light rays with wavelengths of 0.42 μm, 0.55 μm, and 0.68 μm, while 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 of Example 5. In Example 5, since the sixth lens is a plastic lens, the composite focal length frp of the plastic lenses in the rear lens group system is the composite focal length f456 of the fourth lens L4, the fifth lens L5, and the sixth lens.

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

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

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

[0063] (Embodiment 2: Application to an Imaging Device) 37 is a cross-sectional view of an imaging device according to embodiment 2. The imaging device 21 includes an imaging lens system 11, a cover glass 22, and an imaging element 23. The imaging lens system 11, the cover glass 22, and the imaging element 23 are housed in a housing (not shown).

[0064] The imaging element 23 is an element that converts received light into an electrical signal, and may be, for example, a CCD image sensor or a CMOS image sensor. The imaging element 23 is disposed 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 imaging element 23.

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

[0066] The present invention is not limited to the above-described embodiment, and can be modified as appropriate within the scope of the invention. [Explanation of symbols]

[0067] 11 Imaging lens system 12 Cut Filter 21 Imaging device 22 Coverslip 23 Image sensor L1, L2, L3, L4, L5, L6 lenses STOP Aperture IMG Image plane

Claims

1. An imaging lens system consisting of a front lens group system and a rear lens group system, in that order from the object side to the image side, the front lens group system comprises, 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 rear lens group system comprises, in order from the object side to the image side, a fourth lens having positive power and having a convex shape facing 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, The imaging lens system, wherein the second lens, the fourth lens, and the fifth lens are plastic lenses.

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

3. 2. The imaging lens system according to claim 1, wherein the following formula (2) is satisfied, where frp is a composite focal length of the plastic lenses in the rear lens group system, and F is a focal length of the entire lens system: 2<|frp / F| ...(2)

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

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

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

7. an imaging lens system according to any one of claims 1 to 6; an imaging element disposed on the image side of the imaging lens system.

Images