Imaging lens system and imaging device

Abstract

To provide an imaging lens system and an imaging device with which, although being a telephoto, it is possible to suitably correct various aberrations.SOLUTION: An imaging lens system 11 comprises, in order from the object side toward the image side, a first lens L1 having a projection on the object side, a second lens L2 having a projection on the object side, a third lens L3 having a meniscus shape and having an aspheric surface on the object and image sides, a fourth lens L4 having a recess on the image side, a fifth lens L5 having a projection on the object and image sides, and a sixth lens L6 having a projection on the object side and having an aspheric surface on the object and image sides. Assuming that F represents the focal distance of the entire optical system, f3 represents the focal distance of the third lens L3 and f6 represents the focal distance of the sixth lens L6, then formulae (1): -0.3<F / f3<0.1 and (2): -0.2<F / f6<0.3 are satisfied.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an imaging lens system and an imaging device, for example, an imaging lens system and an imaging device for vehicle use. [Background technology]

[0002] Patent Document 1 describes a telephoto imaging lens system with an angle of view of approximately 50°. The brightness of a lens system is proportional to the focal length and inversely proportional to the lens aperture diameter, so the longer the focal length of the lens system, the brighter the lens system. Therefore, telephoto imaging lens systems with a relatively long focal length are generally characterized by their long focal length and brightness. Furthermore, Patent Document 2 describes a projection lens system for projecting an image onto a screen. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-220741 [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-194584 Summary of the Invention [Problem to be solved by the invention]

[0004] However, as described in Patent Document 2, for example, the longer the focal length, the greater the increase in various aberrations such as field curvature and coma aberration.

[0005] The present invention has been made in view of the above problems, and has as its object to provide an imaging lens system and an imaging device that are telephoto and yet capable of correcting various aberrations in an appropriate manner. [Means for solving the problem]

[0006] An imaging lens system of one embodiment comprises, 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 having aspherical surfaces on the object side and the image side, a fourth lens having a concave surface on the image side, a fifth lens having convex surfaces on the object side and the image side, and a sixth lens having a convex surface on the object side and having aspherical surfaces on the object side and the image side, When the focal length of the entire optical system is F and the focal length of the third lens is f3, the following formula (1) is satisfied: -0.3 <F / f3<0.1 ···(1) When the focal length of the sixth lens is f6, the following formula (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 an imaging device that are telephoto and yet capable of correcting various aberrations in an appropriate manner. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view showing the configuration of an imaging lens system and an imaging device according to a first embodiment. [Figure 2] FIG. 10 is a diagram illustrating a distance ET3 and a distance ET6. [Figure 3] 3A to 3C are diagrams showing spherical aberration (longitudinal aberration), curvature of field, and distortion in the imaging lens system of Example 1. [Figure 4] FIG. 10 is a cross-sectional view showing the configuration of an imaging lens system and an imaging device according to a second embodiment. [Figure 5] 10A to 10C are diagrams showing spherical aberration (longitudinal aberration), curvature of field, and distortion in the imaging lens system of Example 2. [Figure 6] FIG. 10 is a cross-sectional view showing the configuration of an imaging lens system and an imaging device according to Example 3. [Figure 7] 10A to 10C are diagrams showing spherical aberration (longitudinal aberration), curvature of field, and distortion in the imaging lens system of Example 3. [Figure 8]FIG. 10 is a cross-sectional view showing the configuration of an imaging lens system and an imaging device according to a fourth embodiment. [Figure 9] 10A to 10C are diagrams showing spherical aberration (longitudinal aberration), curvature of field, and distortion in the imaging lens system of Example 4. [Figure 10] FIG. 10 is a cross-sectional view showing the configuration of an imaging lens system and an imaging device according to a fifth embodiment. [Figure 11] 10A to 10C are diagrams showing spherical aberration (longitudinal aberration), curvature of field, and distortion in the imaging lens system of Example 5. [Figure 12] 10 shows MTF curves at −40° C., 25° C., and 115° C. of the imaging lens system according to Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Embodiment 1 (Imaging lens system and imaging device) 1 is a cross-sectional view showing the configuration and light rays of an imaging lens system 11 and an imaging device 20 according to Embodiment 1. The imaging device 20 includes an imaging lens system 11 and an imaging element 21. The imaging lens system 11 and the imaging element 21 are housed in a housing (not shown). The imaging element 21 is an element that converts received light into an electrical signal, and is, for example, a CCD image sensor or a CMOS image sensor. The imaging element 21 is disposed at the imaging position of the imaging lens system 11. The imaging lens system 11 will now be described in detail.

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

[0011] Furthermore, 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, namely the first lens L1, the second lens L2, the fourth lens L4, and the fifth lens L5, in the imaging lens system 11. This makes it possible to suitably correct spherical aberration by the aspherical surface of the third lens L3. Specifically, when F / f3 is smaller than −0.3, the negative power of the third lens L3 becomes strong, and the overall length of the imaging lens system 11 becomes long. Furthermore, if F / f3 is greater than 0.1, the positive power of the third lens L3 becomes strong, making it difficult to ensure the back focus (BF). Here, the back focus (BF) refers to the distance on the optical axis Z between the image-side surface of the sixth lens L6 and the imaging plane IMG of the image sensor 21.

[0012] Furthermore, 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, namely the first lens L1, the second lens L2, the fourth lens L4, and the fifth lens L5, in the imaging lens system 11. This makes it possible to suitably correct field curvature by the aspheric surface of the sixth lens L6. Specifically, when F / f6 is smaller than -0.2, the power of the sixth lens L6 becomes strong, making it difficult to correct the curvature of field. Furthermore, if F / f6 is greater than 0.3, the power of the sixth lens L6 becomes strong, making it difficult to correct the curvature of field.

[0013] Furthermore, as shown in Figure 2, if ET3 is the distance parallel to the optical axis Z between an intersection P1 of a ray passing through the outermost diameter side of the object-side surface S5 of the third lens L3 and the object-side surface S5 of the third lens L3, and an intersection P2 of a ray passing through the outermost diameter side 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 on the optical axis Z, it is preferable to satisfy the following equation (3): 0.848≦ET3 / d3≦1.191 (3) In other words, it is preferable that the lens power of the third lens L3 be 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 be relatively weak not only in the central portion but also throughout the entire lens. This reduces the difference in the distance of light rays passing through the inside of the third lens L3 between the central portion and the peripheral portion, and makes it possible to suitably correct spherical aberration using the aspherical surface of the third lens L3.

[0014] Similarly to the above ET3 / d3, if ET6 is the distance parallel to the optical axis Z between the intersection of a ray passing 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 intersection of a ray passing through the outermost diameter side of the object-side surface S12 of the sixth lens L6 and the image-side surface S13, and d6 is the thickness of the sixth lens L6 on the optical axis Z, it is preferable to satisfy the following equation (4): 0.820≦ET6 / d6<1.1 (4) In other words, it is preferable that the lens power of the sixth lens L6 be weaker than those 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 be relatively weak not only in the central portion but also in 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 portion and the peripheral portion, and makes it possible to suitably correct field curvature by the aspheric surface of the sixth lens L6.

[0015] Furthermore, it is preferable that the angle of view of the imaging lens system 11 is 40° or less. This makes it possible to increase the focal length F of the entire optical system of the imaging lens system 11. In other words, the imaging lens system 11 can be made into a telephoto optical system. Here, the field angle is the field angle based on the diagonal length of the imaging element 21.

[0016] It is also 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 an aperture is disposed between the third lens L3 and the fourth lens L4. As a result, the first lens L1 and the second lens L2 can ensure imaging performance, and the fourth lens L4 and the fifth lens L5 can ensure chromatic aberration correction performance.

[0017] When the fourth lens L4 and the fifth lens L5 form a cemented lens, and the temperature change coefficient 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 formed by the fourth lens L4 and the fifth lens L5 is f4_5, and the focal length of the fifth lens L5 is f5, it is preferable that the following formulas (5) to (7) be 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 issue with lens systems is that they need to be able to adapt to environmental changes in order to ensure stable images, as described in Patent Document 2, for example. In particular, when the change in focal length of the lens increases due to temperature changes, the focal length of the entire lens system shifts (out of focus), causing degradation of resolution. However, by satisfying the above formulas (5) to (7), it is possible to suppress deviations in the overall focal length F of the imaging lens system 11 due to temperature changes.

[0019] Specifically, it is preferable that the above formulas (6) and (7) be satisfied, that is, the focal length f4_5 of the cemented lens of the fourth lens L4 and the fifth lens L5 is close to the focal length F of the entire imaging lens system 11, and 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 the focal length f4 of the fourth lens L4. This makes it easier to correct the deviation of the focal length F of the entire imaging lens system 11 due to temperature changes by selecting the material of the fifth lens L5. In other words, the power of the cemented lens of the fourth lens L4 and the fifth lens L5 is close to the overall power of the imaging lens system 11, and the contribution of the power of the fifth lens L5 to the power of the cemented lens is large, so that it is easier to correct the deviation of the focal length F of the entire imaging lens system 11 due to temperature changes by selecting the material of the fifth lens L5.

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

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

[0022] Example 1 An imaging lens system 11 according to Example 1 has the configuration shown in FIG. 1. Specifically, the imaging lens system 11 according to Example 1 includes, 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 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 meniscus shape convex on the image side, and aspherical surfaces on 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 the object side and the image side. The sixth lens L6 has negative power, a meniscus shape convex on the object side, and aspherical surfaces on 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 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 lens data for each lens surface of the imaging lens system 11 according to Example 1. Table 1 presents the lens data, including the radius of curvature (mm) of each surface, the surface 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. The imaging lens system 11 according to Example 1 has a half angle of view of 18.0°, an F-number of 1.64, and a focal length F of the entire optical system of 15.24 (mm). 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). In Table 1, surfaces marked with an asterisk (*) are aspherical. [Table 1]

[0024] The aspherical shapes used on the lens surfaces of the third lens L3 and the sixth lens L6 are expressed by the following formula (8), where Y(h) is the amount of 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 a direction perpendicular to the central optical axis Z, K is the conic coefficient, and A4, A6, A8, A10, A12, A14, and A16 are the aspherical coefficients of the fourth, sixth, eighth, tenth, twelfth, fourteenth, and sixteenth orders, respectively. The meanings of the symbols and the formulas representing the aspherical shapes are the same in the examples described below.

number

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

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

[0027] Example 2 4 is a cross-sectional view showing an 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, and therefore a description thereof will be omitted. Below, characteristic data of the imaging lens system 11 according to Example 2 will be described.

[0028] Table 3 shows 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, and therefore their explanation will be omitted. Here, the imaging lens system 11 according to Example 2 has a half angle of view of 18.0°, an F-number of 1.8, and a focal length F of the entire optical system of 11.00 (mm). [Table 3]

[0029] Table 4 shows aspherical coefficients for defining the aspherical shape of the aspherical lens surface in the imaging lens system 11 of the second embodiment. [Table 4]

[0030] 5 shows diagrams of spherical aberration (longitudinal aberration), field curvature, and distortion in the imaging lens system 11 of Example 2. The explanation of each aberration diagram shown in Fig. 5 is the same as that in Fig. 3, and therefore will not be repeated.

[0031] Example 3 6 is a cross-sectional view showing an 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, and therefore a description thereof will be omitted. Below, characteristic data of the imaging lens system 11 according to Example 3 will be described.

[0032] Table 5 shows 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, and therefore their explanation will be omitted. Here, the imaging lens system 11 according to Example 3 has a half angle of view of 18.0°, an F-number of 1.8, and a focal length F of the entire optical system of 12.86 (mm). [Table 5]

[0033] Table 6 shows aspherical coefficients for defining the aspherical shape of the aspherical lens surface in the imaging lens system 11 of the third embodiment. [Table 6]

[0034] 7 shows diagrams of spherical aberration (longitudinal aberration), field curvature, and distortion in the imaging lens system 11 of Example 3. The explanation of each aberration diagram shown in Fig. 7 is the same as that in Fig. 3, and therefore will not be repeated.

[0035] Example 4 8 is a cross-sectional view showing an 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, and therefore a description thereof will be omitted. Below, characteristic data of the imaging lens system 11 according to Example 4 will be described.

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

[0037] Table 8 shows aspherical coefficients for defining the aspherical shape of the aspherical lens surface in the imaging lens system 11 of the fourth embodiment. [Table 8]

[0038] 9 shows diagrams of spherical aberration (longitudinal aberration), field curvature, and distortion in the imaging lens system 11 of Example 4. The explanation of each aberration diagram shown in FIG. 9 is the same as that in FIG. 3, and therefore will not be repeated.

[0039] Example 5 10 is a cross-sectional view showing an 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, and therefore a description thereof will be omitted. Below, characteristic data of the imaging lens system 11 according to Example 5 will be described.

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

[0041] Table 10 shows aspherical coefficients for defining the aspherical shape of the aspherical lens surface in the imaging lens system 11 of Example 5. [Table 10]

[0042] 11 shows diagrams of spherical aberration (longitudinal aberration), field curvature, and distortion in the imaging lens system 11 of Example 5. The explanation of each aberration diagram shown in Fig. 11 is the same as that in Fig. 3, and therefore will not be repeated.

[0043] 3A, 5A, 7A, 9A, and 11A, longitudinal aberrations at wavelengths of 486.1 nm, 587.6 nm, and 656.3 nm are well corrected in the imaging lens systems 11 of Examples 1 to 5. Therefore, the imaging lens system 11 has high resolution.

[0044] 3B, 5B, 7B, 9B, and 11B, the curvature of field is well corrected according to the imaging lens systems 11 of Examples 1 to 5. Therefore, the imaging lens system 11 has high resolution.

[0045] 3C, 5C, 7C, 9C, and 11C, distortion is well corrected according to the imaging lens systems 11 of Examples 1 to 5. Therefore, the imaging lens system 11 has high resolution.

[0046] Table 11 shows the focal length F (mm) of the entire 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 value of F / f3, the value of F / f6, the value of ET3 / d3, the value of ET6 / d6, the value of dNd5 / dt, the value of F / f4_5, and the value of f5 / f4_5. The values ​​shown in Table 11 are those 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 values ​​of F / f3 satisfy the above formula (1). Therefore, as shown in FIGS. 3A, 5A, 7A, 9A, and 11A, in the imaging lens systems 11 according to Examples 1 to 5, the aspherical surface of the third lens L3 can appropriately correct spherical aberration. Also, as shown in Table 11, in Examples 1 to 5, the values ​​of F / f6 satisfy the above formula (2). Therefore, as shown in FIGS. 3B, 5B, 7B, 9B, and 11B, in the imaging lens systems 11 according to Examples 1 to 5, the aspherical surface of the sixth lens L6 can appropriately correct field curvature. In addition, in Examples 1 to 5, the angle of view is 36°, and the focal length F of the entire optical system of the imaging lens system 11 is relatively long. That is, in Examples 1 to 5, the imaging lens system 11 is a telephoto optical system. That is, in Examples 1 to 5, various aberrations can be suitably corrected despite being telephoto.

[0048] Furthermore, as shown in Table 11, the values ​​of ET3 / d3 satisfy the above formula (3) in Examples 1 to 5. In other words, in Examples 1 to 5, the lens power of the third lens L3 is weaker than the other lenses in the imaging lens system 11. Therefore, for the same reason as above, the third lens L3 can suitably correct spherical aberration.

[0049] Furthermore, as shown in Table 11, the values ​​of ET6 / d6 satisfy the above formula (4) in Examples 1 to 5. In other words, in Examples 1 to 5, the lens power of the sixth lens L6 is weaker than the other lenses in the imaging lens system 11. Therefore, for the same reason 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 the above formula (6), and the value of f5 / f4_5 satisfies the above formula (7). Therefore, in Examples 1 to 5, the selection of the material of the fifth lens L5 makes it easier to correct deviations 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 formula (5). Therefore, in Examples 4 and 5, the fifth lens L5 can correct the deviation of the overall focal length F of the imaging lens system 11 due to temperature changes. For example, FIG. 12 shows MTF curves of the imaging lens system 11 according to Example 4 at −40° C., 25° C., and 115° C. As shown in FIG. 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. Furthermore, 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 deviation of the peak position in the low temperature environment of −40° C. from that in the room temperature of 25° C. is suppressed to about 0.01 mm. That is, in the imaging lens system 11 according to Example 4, deviation of the focal length F of the entire optical system due to temperature changes can be sufficiently corrected.

[0052] It should be noted that the present invention is not limited to the above-described embodiments and can be modified as appropriate without departing from the spirit of the present invention. For example, the applications of the imaging lens system of the present invention are not limited to vehicle-mounted cameras and surveillance cameras, and the imaging lens system may also be used for other applications, such as being mounted 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 Third lens L4 4th lens L5 Fifth lens L6 6th lens STOP Aperture IMG Image plane

Claims

1. The optical system comprises, 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 having aspherical surfaces on the object side and the image side, a fourth lens having a concave surface on the image side, a fifth lens having convex surfaces on the object side and the image side, and a sixth lens having a convex surface on the object side and having aspherical surfaces on the object side and the image side, the first lens has a positive power; the fourth lens and the fifth lens form a cemented lens, a diaphragm is disposed between the third lens and the fourth lens; An imaging lens system that satisfies the following formulas (1) and (2), where F is a focal length of the entire optical system, f3 is a focal length of the third lens, and f6 is a focal length of the sixth lens. -0.3<F / f3<0.1...(1) -0.2<F / f6<0.3...(2)

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

3. 3. The imaging lens system according to claim 1, wherein the angle of view of the imaging lens system is between 20 degrees and 50 degrees.

4. 4. The imaging lens system according to claim 1, wherein the second lens has a negative power, the fourth lens has a negative power, and the fifth lens has a positive power.

5. An imaging lens system according to any one of claims 1 to 4; an imaging element disposed at a focal position of the imaging lens system.

Images