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 to be mounted on a vehicle. [Background technology]

[0002] Patent Document 1 describes a telephoto imaging lens system with an angle of view of about 50°. Since the brightness of a 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 is generally characterized by a long focal length and brightness. Moreover, Patent Document 2 describes a projection lens system for projecting an image onto a screen. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2012-220741 A [Patent Document 2] JP 2001-194584 A Summary of the Invention [Problem to be solved by the invention]

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

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

[0006] An imaging lens system of one embodiment includes, 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 aspheric 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 aspheric 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) Effect 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 appropriately correcting various aberrations. [Brief description of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view showing the configurations of an imaging lens system and an imaging device according to a first embodiment. [Diagram 2] FIG. 11 is a diagram for explaining distances ET3 and ET6. [Diagram 3] 3A to 3C are diagrams showing spherical aberration (longitudinal aberration), field curvature, and distortion in the imaging lens system of Example 1. [Figure 4] FIG. 11 is a cross-sectional view showing the configuration of an imaging lens system and an imaging device according to a second embodiment. [Diagram 5] 11A to 11C are diagrams showing spherical aberration (longitudinal aberration), field curvature, and distortion in the imaging lens system of Example 2. [Figure 6] FIG. 11 is a cross-sectional view showing the configuration of an imaging lens system and an imaging device according to a third embodiment. [Figure 7] 11A to 11C are diagrams showing spherical aberration (longitudinal aberration), field curvature, and distortion in the imaging lens system of Example 3. [Figure 8]FIG. 11 is a cross-sectional view showing the configuration of an imaging lens system and an imaging device according to a fourth embodiment. [Figure 9] 11A to 11C are diagrams showing spherical aberration (longitudinal aberration), field curvature, and distortion in the imaging lens system of Example 4. [Figure 10] FIG. 11 is a cross-sectional view showing the configuration of an imaging lens system and an imaging device according to a fifth embodiment. [Figure 11] 13A to 13C are diagrams showing spherical aberration (longitudinal aberration), field curvature, and distortion in the imaging lens system of Example 5. [Figure 12] 13 shows MTF curves at −40° C., 25° C., and 115° C. of the imaging lens system according to Example 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. First embodiment (Imaging lens system and imaging device) 1 is a cross-sectional view showing the configurations 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 an image forming position of the imaging lens system 11. The imaging lens system 11 will now be described in detail.

[0010] As shown in Fig. 1, the 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 on the object side, a second lens L2 having negative power and a convex surface on the object side, a third lens L3 having an aspheric surface 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 a convex surface on the object side and the image side, and a sixth lens L6 having an aspheric surface on the object side and the image side. 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 image forming surface IMG. The fourth lens L4 and the fifth lens L5 may form a cemented lens. The image forming 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] Furthermore, if 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 those 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 aspheric 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, when 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 image forming surface 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 those 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, when 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 FIG. 2, when 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 is weaker than those 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. Specifically, it is preferable that the power of the entire third lens L3, not just the central portion thereof, is relatively weak. 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 portion and the peripheral portion thereof, and makes it possible to suitably correct spherical aberration by the aspheric 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 is weaker than those 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. Specifically, it is preferable that the power of the sixth lens L6 is 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 the field curvature by the aspheric surface of the sixth lens L6.

[0015] Moreover, it is preferable that the angle of view of the imaging lens system 11 is equal to or smaller than 40°. 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 angle of view is the angle of view 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. Thereby, imaging performance can be ensured by the first lens L1 and the second lens L2, and chromatic aberration correction performance can be ensured by the fourth lens L4 and the fifth lens L5.

[0017] The fourth lens L4 and the fifth lens L5 constitute a cemented lens. ,When the environmental temperature is 25℃, At d-line wavelengths relative When the temperature change coefficient of the refractive index Nd5 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 expressions (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 problem 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. In particular, when changes in the focal length of the lens increase due to temperature changes, this causes a shift in the focal length of the entire lens system (out of focus), resulting in 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 formula (6) and formula (7) are 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 larger 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 change 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 the material of the fifth lens L5 makes it easier to correct the deviation of the focal length F of the entire imaging lens system 11 due to temperature change.

[0020] In addition, by satisfying the above formula (5), that is, the material of the fifth lens L5 relative When the temperature coefficient of refractive index change dNd5 / dt satisfies the above formula (5), it is possible to correct the deviation of the overall focal length F of the imaging lens system 11 due to temperature change. relativeBy selecting a material whose refractive index temperature change coefficient dNd5 / dt satisfies the above formula (5), it is possible to correct the deviation of the entire focal length F of the imaging lens system 11 due to temperature change. Specifically, by making dNd5 / dt satisfy the above formula (5), it is possible to correct the amount of focus shift due to temperature change. This allows the fifth lens L5 to correct the deviation of the entire focal length F of the imaging lens system 11 due to temperature change.

[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 The imaging lens system 11 according to the first embodiment has a configuration shown in FIG. 1. Specifically, the imaging lens system 11 according to the first embodiment is composed of 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, in that order from the object side to the image side. The first lens L1 has a positive power, a convex surface on the object side, and a concave surface on the image side. The second lens L2 has a negative power, a convex surface on the object side, and a concave surface on the image side. The third lens L3 has a positive power, a meniscus shape convex to the image side, and an aspheric surface on the object side and the image side. The fourth lens L4 has a negative power, a convex surface on the object side, and a concave surface on the image side. The fifth lens L5 has a positive power, and a convex surface on the object side and the image side. The sixth lens L6 has a negative power, a meniscus shape convex to the object side, and an aspheric surface 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. Hereinafter, characteristic data of the imaging lens system 11 according to the first embodiment will be described.

[0023] Table 1 shows lens data of each lens surface of the imaging lens system 11 according to Example 1. In Table 1, the lens data includes 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. 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). The refractive index at the d-line and the Abbe number at the d-line shown in Table 1 are values ​​when the environmental temperature t (°C), which is the temperature around the imaging lens system 11, is 25 (°C). In Table 1, the surfaces marked with an "*" are aspheric. [Table 1]

[0024] The aspheric shape adopted for the lens surfaces of the third lens L3 and the sixth lens L6 is expressed by the following formula (8), where Y(h) is the amount of sag in the optical axis direction, c is the inverse 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 conical coefficient, and A4, A6, A8, A10, A12, A14, and A16 are the aspheric coefficients of the fourth, sixth, eighth, tenth, twelfth, fourteenth, and sixteenth orders, respectively. The meanings of each symbol and the formulas representing the aspheric shapes are the same in the examples described later.

number

[0025] Table 2 shows aspheric coefficients for defining the aspheric shape of the lens surface that is made aspheric 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 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 indicates the distance in the optical axis direction, and the vertical axis indicates the image height (angle of view). In the field curvature diagram of Fig. 3B, Sag indicates the field curvature on the sagittal plane, and Tan indicates 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 in FIG. 3B and FIG. 3C show the results of a simulation using a light beam 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 similar to that of Example 1, except that the third lens L3 has a meniscus shape 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 explanations are 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 aspheric coefficients for defining the aspheric shape of the lens surface that is made aspheric 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 similar to 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 explanations are 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 aspheric coefficients for defining the aspheric shape of the lens surface that is made aspheric 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 similar to 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 aspheric coefficients for defining the aspheric shape of the lens surface that is made aspheric 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 similar to that of Example 1, and therefore a description thereof will be omitted. Hereinafter, 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 the explanations thereof 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 aspheric coefficients for defining the aspheric shape of the lens surface that is made aspheric in the imaging lens system 11 of the fifth embodiment. [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 system 11 of Examples 1 to 5. Therefore, the imaging lens system 11 has high resolution.

[0044] 3B, 5B, 7B, 9B, and 11B, the field curvature is well corrected according to the imaging lens system 11 of the present embodiments 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 the present embodiments 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 environmental 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 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 aspheric surface of the third lens L3 can appropriately correct the spherical aberration. Also, as shown in Table 11, in Examples 1 to 5, the value of F / f6 satisfies 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 aspheric surface of the sixth lens L6 can appropriately correct the 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 to say, in Examples 1 to 5, various aberrations can be suitably corrected even though the lens is a telephoto lens.

[0048] Furthermore, as shown in Table 11, the value of ET3 / d3 satisfies 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] Also, as shown in Table 11, in Examples 1 to 5, the value of ET6 / d6 satisfies the above formula (4). 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 the field curvature.

[0050] Also, 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 shift in the overall focal length F of the imaging lens system 11 caused by temperature change can be easily corrected by selecting the material of the fifth lens L5.

[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 entire focal length F of the imaging lens system 11 due to temperature change. For example, FIG. 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 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 the room temperature of 25° C. and the high temperature of 115° C. In addition, in the imaging lens system 11 according to Example 4, there is almost no difference in the shape of the MTF curve between the room temperature of 25° C. and the low temperature of −40° C., and the deviation of the peak position in the low temperature of −40° C. environment from the room temperature of 25° C. environment is suppressed to about 0.01 mm. That is, in the imaging lens system 11 according to the fourth embodiment, the deviation of the focal length F of the entire optical system due to temperature change 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 and scope of the present invention. For example, the use of the imaging lens system of the present invention is not limited to vehicle-mounted cameras and surveillance cameras, and the imaging lens system may be used for other purposes, 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 5th lens L6 6th lens STOP Squeeze 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 aspheric 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 aspheric 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) an imaging lens system which satisfies the following expressions (5) to (7), where a temperature change coefficient of the relative refractive index of the fifth lens at the wavelength of the d-line when an environmental temperature is 25° C. is dNd5 / dt, a focal length of a cemented lens formed of the fourth lens and the fifth lens is f4_5, and a focal length of the fifth lens is f5: -3.0<dNd5 / dt≦4.9 (5) 1<F / f4_5<1.3...(6) 0.6<f5 / f4_5<0.8...(7)

2. 2. The imaging lens system according to claim 1, wherein the angle of view of the imaging lens system is equal to or greater than 20 degrees and equal to or less than 50 degrees.

3. the first lens has a positive power, the second lens has a negative power, the fourth lens has a negative power, and the fifth lens has a positive power; The imaging lens system according to claim 1 , further comprising a diaphragm disposed between the third lens and the fourth lens.

4. The imaging lens system according to claim 1 , wherein the fourth lens and the fifth lens form a cemented lens.

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