Imaging lens system and imaging device

Abstract

To provide an imaging lens system and imaging device that can suitably correct various aberrations while being telephoto. [Solution] The imaging lens system 11 consists of, in order from the object side to the image side, a first lens L1 having a convex surface on the object side, a second lens L2 having a convex surface on the object side, a third lens L3 having a meniscus shape and aspherical surfaces on both the object side and the image side, a fourth lens L4 having a concave surface on the image side, a fifth lens L5 having convex surfaces on both the object side and the image side, and a sixth lens L6 having a convex surface on the object side and aspherical surfaces on both the object side and the image side. When the focal length of the entire optical system is F, the focal length of the third lens L3 is f3, and the focal length of the sixth lens L6 is f6, the following equations (1) and (2) are satisfied. -0.3 <F / f3<0.1 ···(1) -0.2

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 vehicle-mounted use, for example.

Background Art

[0002] Patent Document 1 describes a telephoto imaging lens system having an angle of view of around 50°. Since the brightness of the lens system is proportional to the focal length and inversely proportional to the lens aperture diameter, the longer the focal length of the lens system, the brighter the lens system becomes. Therefore, a telephoto imaging lens system with a relatively long focal length generally has the characteristics of a long focal length and high brightness. In addition, Patent Document 2 describes a projection lens system for projecting an image onto a screen.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, for example, as described in Patent Document 2, there is a problem that as the focal length increases, various aberrations such as field curvature and coma increase.

[0005] 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 that are telephoto and can suitably correct various aberrations.

Means for Solving the Problems

[0006] In one embodiment, the imaging lens system consists of, in order from the object side to the image side, a first lens having a convex surface on the object side, a second lens having a convex surface on the object side, a third lens having a meniscus shape and aspherical surfaces on both the object and image sides, a fourth lens having a concave surface on the image side, a fifth lens having convex surfaces on both the object and image sides, and a sixth lens having a convex surface on the object side and aspherical surfaces on both the object and image sides. When the focal length of the entire optical system is F and the focal length of the third lens is f3, the following equation (1) is satisfied, -0.3 <F / f3<0.1 ···(1) When the focal length of the sixth lens is set to f6, the following equation (2) is satisfied. -0.2 <F / f6<0.3 ···(2) [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an imaging lens system and imaging device that can suitably correct various aberrations while being telephoto. [Brief explanation of the drawing]

[0008] [Figure 1] This is a cross-sectional view showing the configuration of the imaging lens system and imaging device according to Embodiment 1. [Figure 2] This diagram illustrates distances ET3 and ET6. [Figure 3] These are the spherical aberration diagram (longitudinal aberration diagram), field curvature diagram, and distortion aberration diagram for the imaging lens system of Example 1. [Figure 4] This is a cross-sectional view showing the configuration of the imaging lens system and imaging device according to Example 2. [Figure 5] These are the spherical aberration diagram (longitudinal aberration diagram), field curvature diagram, and distortion aberration diagram for the imaging lens system of Example 2. [Figure 6] This is a cross-sectional view showing the configuration of the imaging lens system and imaging device according to Example 3. [Figure 7] These are the spherical aberration diagram (longitudinal aberration diagram), field curvature diagram, and distortion aberration diagram for the imaging lens system of Example 3. [Figure 8]This is a cross-sectional view showing the configuration of the imaging lens system and imaging device according to Example 4. [Figure 9] These are the spherical aberration diagram (longitudinal aberration diagram), field curvature diagram, and distortion aberration diagram for the imaging lens system of Example 4. [Figure 10] This is a cross-sectional view showing the configuration of the imaging lens system and imaging device according to Example 5. [Figure 11] These are the spherical aberration diagram (longitudinal aberration diagram), field curvature diagram, and distortion aberration diagram for the imaging lens system of Example 5. [Figure 12] These are the MTF curves of the imaging lens system according to Example 4 at -40°C, 25°C, and 115°C. [Modes for carrying out the invention]

[0009] Embodiments of the present invention will be described below with reference to the drawings. Embodiment 1 (Imaging lens system and imaging device) Figure 1 is a cross-sectional view showing the configuration and light rays of the imaging lens system 11 and imaging device 20 according to Embodiment 1. The imaging device 20 comprises the imaging lens system 11 and the image sensor 21. The imaging lens system 11 and the image sensor 21 are housed in a housing (not shown). The image sensor 21 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 21 is positioned at the imaging position of the imaging lens system 11. The imaging lens system 11 will be described in detail below.

[0010] As shown in FIG. 1, the imaging lens system 11 of Embodiment 1 includes, in order from the object side to the image side, a first lens L1 having positive power and a convex surface on the object side, a second lens L2 having negative power and a convex surface on the object side, a third lens L3 having aspherical surfaces on the object side and the image side, an aperture STOP, a fourth lens L4 having negative power and a concave surface on the image side, a fifth lens L5 having positive power and convex surfaces on the object side and the image side, and a sixth lens L6 having aspherical surfaces on the object side and the image side. Further, as shown in FIG. 1, the imaging lens system 11 may include glass 12 such as a wavelength filter glass and a cover glass between the image-side lens surface S13 of the sixth lens L6 and the imaging surface IMG. Further, the fourth lens L4 and the fifth lens L5 may form a cemented lens. The imaging surface of the imaging lens system 11 is indicated by IMG. The aperture STOP is an aperture that determines the F-number (Fno) of the imaging lens system 11.

[0011] When the focal length of the entire optical system of the imaging lens system 11 is F and the focal length of the third lens L3 is f3, the following formula (1) is satisfied. -0.3 < F / f3 < 0.1 ···(1) In other words, the lens power of the third lens L3 is weaker than that of the other lenses of the imaging lens system 11, namely, the first lens L1, the second lens L2, the fourth lens L4, and the fifth lens L5. Thereby, spherical aberration can be suitably corrected by the aspherical surface of the third lens L3. Specifically, when F / f3 is less than -0.3, the negative power of the third lens L3 becomes stronger and the overall length of the imaging lens system 11 becomes longer. When F / f3 is greater than 0.1, the positive power of the third lens L3 becomes stronger and it becomes difficult to secure the back focus (BF). Here, the back focus (BF) means the distance on the optical axis Z between the image-side surface of the sixth lens L6 and the imaging surface IMG of the imaging device 21.

[0012] When the focal length of the sixth lens L6 is f6, the following formula (2) is satisfied. -0.2 <F / f6<0.3 ···(2) In other words, the lens power of the sixth lens L6 is weaker than that of the other lenses in the imaging lens system 11: the first lens L1, the second lens L2, the fourth lens L4, and the fifth lens L5. This allows the aspherical surface of the sixth lens L6 to effectively correct field curvature. Specifically, when F / f6 is less than -0.2, the power of the sixth lens L6 increases, making it difficult to correct field curvature. Furthermore, if the f / f6 is greater than 0.3, the power of the sixth lens, L6, increases, making it more difficult to correct field curvature.

[0013] Furthermore, as shown in Figure 2, when ET3 is the distance parallel to the optical axis Z between the intersection point P1 of the object-side surface S5 of the third lens L3 and the object-side surface S5 of the third lens L3, and the intersection point P2 of the object-side surface S5 of the third lens L3 and the image-side surface S6, and d3 is the thickness of the third lens L3 along the optical axis Z, it is preferable that the following equation (3) is satisfied. 0.848 ≤ ET3 / d3 ≤ 1.191 ···(3) In other words, it is preferable that the lens power of the third lens L3 is weaker than that of the other lenses in the imaging lens system 11, namely the first lens L1, the second lens L2, the fourth lens L4, and the fifth lens L5. Specifically, it is preferable that the power of the third lens L3 is relatively weak not only in the central part but throughout the entire lens. This makes it possible to reduce the difference in the distance of light rays passing through the inside of the third lens L3 between the central and peripheral parts, and allows spherical aberration to be suitably corrected by the aspherical surface of the third lens L3.

[0014] In the same manner as ET3 / d3 described above, it is preferable that the following equation (4) is satisfied when ET6 is the distance parallel to the optical axis Z between the point of intersection of the light ray transmitted through the outermost diameter side of the object-side surface S12 of the sixth lens L6 and the object-side surface S12 of the sixth lens L6, and the point of intersection of the light ray transmitted through the outermost diameter side of the object-side surface S12 of the sixth lens L6 and the image-side surface S13, and when d6 is the thickness of the sixth lens L6 on the optical axis Z. 0.820 ≤ ET6 / d6 < 1.1 ···(4) In other words, it is preferable that the lens power of the sixth lens L6 is weaker than that of the other lenses in the imaging lens system 11, namely the first lens L1, the second lens L2, the fourth lens L4, and the fifth lens L5. Specifically, it is preferable that the power of the sixth lens L6 is relatively weak not only in the central part but throughout the entire lens. This makes it possible to reduce the difference in the distance of light rays passing through the inside of the sixth lens L6 between the central and peripheral parts, and allows the aspherical surface of the sixth lens L6 to suitably correct field curvature.

[0015] Furthermore, it is preferable that the angle of view of the imaging lens system 11 is 40° or less. This allows the overall focal length F of the imaging lens system 11's optical system to be increased. In other words, the imaging lens system 11 can be made into a telephoto optical system. Here, the angle of view is the angle of view based on the diagonal length of the image sensor 21.

[0016] Furthermore, it is preferable that the first lens L1 has positive power, the second lens L2 has negative power, the fourth lens L4 has negative power, the fifth lens L5 has positive power, and that the aperture is positioned between the third lens L3 and the fourth lens L4. This ensures imaging performance through the first lens L1 and the second lens L2, and chromatic aberration correction performance through the fourth lens L4 and the fifth lens L5.

[0017] It is preferable that the fourth lens L4 and the fifth lens L5 constitute a cemented lens, and that the temperature coefficient of change of the relative refractive index Nd5 of the fifth lens L5 at the wavelength of the d line when the ambient temperature is 25°C is dNd5 / dt, the focal length of the cemented lens composed of the fourth lens L4 and the fifth lens L5 is f4_5, and the focal length of the fifth lens L5 is f5, then the following equations (5) to (7) are satisfied. -3.0 <dNd5 / dt≦4.9 ···(5) 1 <F / f4_5<1.3 ···(6) 0.6 <f5 / f4_5<0.8 ···(7)

[0018] A common challenge with lens systems, as described in Patent Document 2, for example, is that they must be able to adapt to environmental changes in order to ensure stable images. In particular, if the change in focal length of the lens increases due to temperature changes, the overall focal length shift (out of focus) of the lens system will cause a deterioration in resolution. However, by satisfying equations (5) to (7) above, it is possible to suppress the shift in the overall focal length F of the imaging lens system 11 due to temperature changes.

[0019] Specifically, it is preferable that equations (6) and (7) above are satisfied, that is, that the focal length f4_5 of the cemented lens formed by the fourth lens L4 and the fifth lens L5 is close to the total focal length F of the imaging lens system 11, and that the contribution of the focal length f5 of the fifth lens L5 to the focal length f4_5 of the cemented lens is greater than that of the focal length f4 of the fourth lens L4. This makes it easier to correct the shift in the total focal length F of the imaging lens system 11 due to temperature changes by selecting the material of the fifth lens L5. In other words, it is preferable that the power of the cemented lens formed by the fourth lens L4 and the fifth lens L5 is close to the total power of the imaging lens system 11, and that the contribution of the power of the fifth lens L5 to the power of the cemented lens is large, making it easier to correct the shift in the total focal length F of the imaging lens system 11 due to temperature changes by selecting the material of the fifth lens L5.

[0020] Furthermore, by satisfying equation (5) above, that is, by the temperature change coefficient dNd5 / dt of the relative refractive index of the material of the fifth lens L5 satisfying equation (5), the shift in the overall focal length F of the imaging lens system 11 due to temperature changes can be corrected. In other words, by selecting a material for the fifth lens L5 whose temperature change coefficient dNd5 / dt of the relative refractive index satisfies equation (5) above, the shift in the overall focal length F of the imaging lens system 11 due to temperature changes can be corrected. Specifically, by dNd5 / dt satisfying equation (5) above, the amount of focus shift due to temperature changes can be corrected. As a result, the fifth lens L5 can correct the shift in the overall focal length F of the imaging lens system 11 due to temperature changes.

[0021] Next, an embodiment corresponding to the imaging lens system 11 of Embodiment 1 will be described with reference to the drawings.

[0022] (Example 1) The imaging lens system 11 according to Embodiment 1 has the configuration shown in Figure 1. Specifically, the imaging lens system 11 according to Embodiment 1 consists of, in order from the object side to the image side, a first lens L1, a second lens L2, a third lens L3, an aperture stop, a fourth lens L4, a fifth lens L5, a sixth lens L6, and an IR cut filter 12. The first lens L1 has positive power, a convex surface on the object side, and a concave surface on the image side. The second lens L2 has negative power, a convex surface on the object side, and a concave surface on the image side. The third lens L3 has positive power, a convex meniscus shape on the image side, and aspherical surfaces on both the object side and the image side. The fourth lens L4 has negative power, a convex surface on the object side, and a concave surface on the image side. The fifth lens L5 has positive power, and convex surfaces on both the object side and the image side. The sixth lens L6 has negative power, a convex meniscus shape on the object side, and aspherical surfaces on both the object side and the image side. The first lens L1 to the sixth lens L6 are glass lenses. The IR cut filter 12 is a filter for cutting out light in the infrared region. The characteristic data of the imaging lens system 11 according to Example 1 will be described below.

[0023] Table 1 shows the lens data for each lens surface of the imaging lens system 11 according to Example 1. In Table 1, the lens data for each surface includes the radius of curvature (mm), the interplanar spacing (mm) at the central optical axis Z, the refractive index Nd at the d line, and the Abbe number Vd at the d line. Here, the half-angle of view of the imaging lens system 11 according to Example 1 is 18.0°, the F-number is 1.64, and the focal length F of the entire optical system is 15.24 (mm). Also, the refractive index at the d line and the Abbe number at the d line shown in Table 1 are values ​​when the ambient temperature t (°C), which is the temperature around the imaging lens system 11, is 25 (°C). Furthermore, in Table 1, surfaces marked with an asterisk (*) indicate that they are aspherical surfaces. [Table 1]

[0024] Furthermore, the aspherical shapes adopted for the lens surfaces of the third lens L3 and the sixth lens L6 are expressed by the following equation (8), where Y(h) is the sag in the optical axis direction, c is the reciprocal of the radius of curvature, h is the height from the central optical axis Z in the direction perpendicular to the central optical axis Z, K is the conicity coefficient, and A4, A6, A8, A10, A12, A14, and A16 are the 4th, 6th, 8th, 10th, 12th, 14th, and 16th order aspherical coefficients, respectively. Note that the meaning of each symbol and the equations representing the aspherical shapes are the same in the embodiments described later.

number

[0025] 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, "4.88076E-04" is equivalent to "4.88076E×10 -4 It means "...". [Table 2]

[0026] Figure 3 shows the spherical aberration diagram (longitudinal aberration diagram), field curvature diagram, and distortion aberration diagram for the imaging lens system 11 of Example 1. As shown in Figure 3, the imaging lens system 11 of Example 1 has a half-angle of view of 18° and an F-number of 1.64. Furthermore, in the longitudinal aberration diagram in Figure 3A, the horizontal axis indicates the position where the light ray intersects the optical axis, and the vertical axis indicates the height at the pupil diameter. Furthermore, in the field curvature diagram of Figure 3B, the horizontal axis represents the distance along the optical axis, and the vertical axis represents the image height (field of view). Also, in the field curvature diagram of Figure 3B, Sag represents the field curvature in the sagittal plane, and Tan represents the field curvature in the tangential plane. Furthermore, in the distortion diagram in Figure 3C, the horizontal axis represents the amount of image distortion (%), and the vertical axis represents the image height (angle of view). Furthermore, the image field curvature and distortion aberration diagrams in Figures 3B and 3C show the simulation results using light with a wavelength of 555 nm. Figure 3 shows the spherical aberration diagram (longitudinal aberration diagram), field curvature diagram, and distortion diagram when the ambient temperature t (°C) is 25 (°C).

[0027] (Example 2) Figure 4 is a cross-sectional view showing the imaging lens system 11 according to Example 2. The configuration of the imaging lens system 11 according to Example 2 is the same as that of Example 1, except that the third lens L3 has a meniscus shape that is convex toward the object side, so its explanation will be omitted. The characteristic data of the imaging lens system 11 according to Example 2 will be described below.

[0028] Table 3 shows the lens data for each lens surface of the imaging lens system 11 according to Example 2. The items shown in Table 3 are the same as those in Table 1, so their explanation is omitted. Here, the half-angle of view of the imaging lens system 11 according to Example 2 is 18.0°, the F-number is 1.8, and the focal length F of the entire optical system is 11.00 (mm). [Table 3]

[0029] Table 4 shows the aspheric coefficients used to define the aspherical shape of the aspherical lens surface in the imaging lens system 11 of Example 2. [Table 4]

[0030] Figure 5 shows the spherical aberration diagram (longitudinal aberration diagram), field curvature diagram, and distortion aberration diagram for the imaging lens system 11 of Example 2. The explanation of each aberration diagram shown in Figure 5 is the same as in Figure 3, so the explanation is omitted.

[0031] (Example 3) Figure 6 is a cross-sectional view showing the imaging lens system 11 according to Example 3. The configuration of the imaging lens system 11 according to Example 3 is the same as that of Example 1, so its explanation will be omitted. The characteristic data of the imaging lens system 11 according to Example 3 will be described below.

[0032] Table 5 shows the lens data for each lens surface of the imaging lens system 11 according to Example 3. The items shown in Table 5 are the same as those in Table 1, so their explanation is omitted. Here, the half-angle of view of the imaging lens system 11 according to Example 3 is 18.0°, the F-number is 1.8, and the focal length F of the entire optical system is 12.86 (mm). [Table 5]

[0033] Table 6 shows the aspheric coefficients used to define the aspherical shape of the aspherical lens surface in the imaging lens system 11 of Example 3. [Table 6]

[0034] Figure 7 shows the spherical aberration diagram (longitudinal aberration diagram), field curvature diagram, and distortion aberration diagram for the imaging lens system 11 of Example 3. The explanation of each aberration diagram shown in Figure 7 is the same as in Figure 3, so the explanation is omitted.

[0035] (Example 4) Figure 8 is a cross-sectional view showing the imaging lens system 11 according to Example 4. The configuration of the imaging lens system 11 according to Example 4 is the same as that of Example 1, so its explanation will be omitted. The characteristic data of the imaging lens system 11 according to Example 4 will be described below.

[0036] Table 7 shows the lens data for each lens surface of the imaging lens system 11 according to Example 4. The items in Table 7 are the same as those in Table 1, so their explanation is omitted. Here, the half-angle of view of the imaging lens system 11 according to Example 4 is 18.0°, the F-number is 1.65, and the focal length F of the entire optical system is 15.203 (mm). [Table 7]

[0037] Table 8 shows the aspheric coefficients used to define the aspherical shape of the aspherical lens surface in the imaging lens system 11 of Example 4. [Table 8]

[0038] Figure 9 shows the spherical aberration diagram (longitudinal aberration diagram), field curvature diagram, and distortion aberration diagram for the imaging lens system 11 of Example 4. The explanation of each aberration diagram shown in Figure 9 is the same as in Figure 3, so the explanation is omitted.

[0039] (Example 5) Figure 10 is a cross-sectional view showing the imaging lens system 11 according to Example 5. The configuration of the imaging lens system 11 according to Example 5 is the same as that of Example 1, so its explanation will be omitted. The characteristic data of the imaging lens system 11 according to Example 5 will be described below.

[0040] Table 9 shows the lens data for each lens surface of the imaging lens system 11 according to Example 5. The items in Table 9 are the same as those in Table 1, so their explanation is omitted. Here, the half-angle of view of the imaging lens system 11 according to Example 5 is 18.0°, the F-number is 1.6, and the focal length F of the entire optical system is 15.17 (mm). [Table 9]

[0041] 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. [Table 10]

[0042] Figure 11 shows the spherical aberration diagram (longitudinal aberration diagram), field curvature diagram, and distortion aberration diagram for the imaging lens system 11 of Example 5. The explanation of each aberration diagram shown in Figure 11 is the same as in Figure 3, so the explanation is omitted.

[0043] As shown in the longitudinal aberration diagrams of Figures 3A, 5A, 7A, 9A, and 11A, the imaging lens system 11 of these embodiments 1 to 5 effectively corrects longitudinal aberrations at wavelengths of 486.1 nm, 587.6 nm, and 656.3 nm. Therefore, the imaging lens system 11 achieves high resolution.

[0044] Furthermore, as shown in the field curvature diagrams in Figures 3B, 5B, 7B, 9B, and 11B, the field curvature is well corrected in the imaging lens systems 11 of these embodiments 1 to 5. Therefore, the imaging lens system 11 achieves high resolution.

[0045] Furthermore, as shown in the distortion diagrams in Figures 3C, 5C, 7C, 9C, and 11C, distortion is well corrected in the imaging lens system 11 of these embodiments 1 to 5. Therefore, the imaging lens system 11 achieves high resolution.

[0046] Table 11 also shows the total focal length F (mm) of the imaging lens system 11 according to Examples 1 to 5, the focal lengths f1 to f6 (mm) of the first lens L1 to the sixth lens L6, the focal length f4_5 (mm) of the cemented lens consisting of the fourth lens L4 and the fifth lens L5, the optical length tol (mm) of the imaging lens system 11, the values ​​of F / f3, F / f6, ET3 / d3, ET6 / d6, dNd5 / dt, F / f4_5, and f5 / f4_5. The values ​​shown in Table 11 are for when the wavelength of the light is 555 nm and the ambient temperature t (°C) is 25 (°C). [Table 11]

[0047] As shown in Table 11, in Examples 1 to 5, the value of F / f3 satisfies equation (1) above. Therefore, as shown in Figures 3A, 5A, 7A, 9A, and 11A, the imaging lens system 11 according to Examples 1 to 5 is able to suitably correct spherical aberration by the aspherical surface of the third lens L3. Also, as shown in Table 11, in Examples 1 to 5, the value of F / f6 satisfies equation (2) above. Therefore, as shown in Figures 3B, 5B, 7B, 9B, and 11B, the imaging lens system 11 according to Examples 1 to 5 is able to suitably correct field curvature by the aspherical surface of the sixth lens L6. Furthermore, in Examples 1 to 5, the angle of view is 36°, and the overall focal length F of the imaging lens system 11 is relatively long. In other words, in Examples 1 to 5, the imaging lens system 11 has a telephoto optical system. In other words, in Examples 1 to 5, various aberrations can be suitably corrected even with a telephoto lens.

[0048] Furthermore, as shown in Table 11, in Examples 1 to 5, the value of ET3 / d3 satisfies the above equation (3). In other words, in Examples 1 to 5, the lens power of the third lens L3 is weaker than that of the other lenses in the imaging lens system 11. Therefore, for the same reasons as above, spherical aberration can be suitably corrected by the third lens L3.

[0049] Furthermore, as shown in Table 11, in Examples 1 to 5, the value of ET6 / d6 satisfies the above equation (4). In other words, in Examples 1 to 5, the lens power of the sixth lens L6 is weaker than that of the other lenses in the imaging lens system 11. Therefore, for the same reasons as above, the sixth lens L6 can suitably correct field curvature.

[0050] Furthermore, as shown in Table 11, in Examples 1 to 5, the value of F / f4_5 satisfies equation (6) above, and the value of f5 / f4_5 satisfies equation (7) above. Therefore, in Examples 1 to 5, the material selection of the fifth lens L5 makes it easier to correct the shift in the overall focal length F of the imaging lens system 11 due to temperature changes.

[0051] Furthermore, as shown in Table 11, in Examples 4 and 5, the value of dNd5 / dt satisfies the above equation (5). Therefore, in Examples 4 and 5, the fifth lens L5 is able to correct the shift in the overall focal length F of the imaging lens system 11 due to temperature changes. For example, Figure 12 shows the MTF curves of the imaging lens system 11 according to Example 4 at -40°C, 25°C, and 115°C. As shown in Figure 12, in the imaging lens system 11 according to Example 4, there is almost no difference in the peak position and shape of the MTF curve between a room temperature of 25°C and a high temperature of 115°C. Also, in the imaging lens system 11 according to Example 4, there is almost no difference in the shape of the MTF curve between a room temperature of 25°C and a low temperature of -40°C, and the shift in the peak position from the room temperature of 25°C in the low temperature of -40°C is suppressed to about 0.01 mm. In other words, the imaging lens system 11 according to Example 4 is able to sufficiently correct the shift in the focal length F of the entire optical system due to temperature changes.

[0052] 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. For example, the applications of the imaging lens system of the present invention are not limited to in-vehicle cameras and surveillance cameras, but may also be used for other applications such as mounting on small electronic devices such as mobile phones. [Explanation of symbols]

[0053] 11 Imaging lens system 12 Glass (IR cut filter) 20 Imaging device 21 Image sensor L1 First Lens L2 Second Lens L3 3rd lens L4 4th lens L5 5th lens L6 6th lens STOP aperture IMG imaging plane

Claims

1. The lenses, arranged in order from the object side towards the image side, consist of a first lens with a convex surface on the object side, a second lens with a convex surface on the object side, a third lens with a meniscus shape and aspherical surfaces on both the object and image sides, a fourth lens with a concave surface on the image side, a fifth lens with convex surfaces on both the object and image sides, and a sixth lens with a convex surface on the object side and aspherical surfaces on both the object and image sides. The first lens has positive power, An aperture is positioned between the third lens and the fourth lens. An imaging lens system that satisfies the following equations (1) and (2), where F is the focal length of the entire optical system, f3 is the focal length of the third lens, and f6 is the focal length of the sixth lens. -0.3<F / f3<0.1...(1) -0.2<F / f6<0.3...(2)

2. The imaging lens system according to claim 1, wherein the temperature coefficient of change of the relative refractive index of the fifth lens at the wavelength of the d line when the ambient temperature is 25°C is dNd5 / dt, the focal length of the cemented lens composed of the fourth lens and the fifth lens is f4_5, and the focal length of the fifth lens is f5, satisfies the following equations (5) to (7). -3.0<dNd5 / dt≦4.9 (5) 1<F / f4_5<1.3...(6) 0.6<f5 / f4_5<0.8...(7)

3. The imaging lens system according to claim 1 or 2, wherein the angle of view of the imaging lens system is 20° or more and 50° or less.

4. The imaging lens system according to any one of claims 1 to 3, wherein the second lens has negative power, the fourth lens has negative power, and the fifth lens has positive power.

5. An imaging lens system according to any one of claims 1 to 4, An imaging device comprising an image sensor positioned at the focal position of the imaging lens system.

Images