Imaging lens system and imaging device

Abstract

To provide an image capturing lens system and image capturing device, which allow for checking a faraway object without relying on resolution of an image sensor, and for capturing images of a wide field of view.SOLUTION: An image capturing lens system 11 provided herein comprises in order from an object side to an image side: a first lens group G1 comprising a first lens L1 with negative power having a concave surface on an object side and a second lens L2 with positive power; and a second lens group G2 comprising a third lens L3 and succeeding lenses. The system satisfies the following conditional expressions (1), (2): -6.0<f1 / Fr<-1.5 ...(1), 0.7<d12 / F<1.5 ...(2), where f1 represents a focal length of the first lens L1, Fr represents a composite focal length of all lenses other than the first lens L1, d12 represents a distance between an image-side surface S2 of the first lens L1 and an object-side surface S3 of the second lens L2 along an optical axis Z, and F represents a focal length of the entire optical system.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] Recently, there has been an increasing demand for in-vehicle front sensing devices to have the conflicting capabilities of being able to recognize distant objects (telephoto) and capturing images of a wider range (wide-angle). To achieve this, it has been considered to use a high-resolution sensor and a wide-angle imaging lens system. This involves using a wide-angle lens system to view a wider range, and a high-resolution sensor to capture distant objects. As an example, Patent Document 1 describes an imaging device that satisfies both the telephoto and wide-angle requirements by using a wide-angle lens system and a high-resolution imaging element. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2013 / 018306 Summary of the Invention [Problem to be solved by the invention]

[0004] However, Patent Document 1 does not allow for a higher resolution (i.e., a telephoto lens) than the resolution of the image sensor. Furthermore, there are cost and technical limitations on increasing the resolution of the image sensor.

[0005] The present invention has been made in consideration of these problems, and aims to provide an imaging lens system and an imaging device that can capture images of a wide range and enable the identification of distant objects without relying on the resolution of the imaging element. [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 group including a first lens having a concave surface facing the object side and having negative power, a second lens having positive power, and a second lens group including a third lens and subsequent lenses, When the focal length of the first lens is f1 and the composite focal length of all lenses other than the first lens is Fr, the following formula (1) is satisfied: -6.0 <f1 / Fr<-1.5 ···(1) When the distance on the optical axis between the image-side surface of the first lens and the object-side surface of the second lens is d12 and the focal length of the entire optical system is F, the following formula (2) is satisfied. 0.7 <d12 / F<1.5 ···(2) By having the first lens have negative power and a concave surface on the object side, negative distortion is generated, making it possible to realize a wide-angle lens system. Furthermore, by satisfying the above formulas (1) and (2), negative distortion can be effectively generated in the first lens.

[0007] An imaging lens system according to another embodiment includes, in order from the object side to the image side, a first lens group including a first lens having a concave surface on the object side and negative power, a second lens having an aspherical shape on the object side and on the image side, and a third lens having positive power; and a second lens group including a fourth lens and subsequent lenses, the second lens has an inflection point on at least one of its object-side and image-side surfaces, When the focal length of the first lens is f1 and the composite focal length of all lenses other than the first lens is Fr, the following formula (1) is satisfied: -6.0 <f1 / Fr<-1.5 ···(1) When the distance on the optical axis between the image-side surface of the first lens and the object-side surface of the second lens is d12, the thickness on the optical axis of the second lens is d2, the distance on the optical axis between the image-side surface of the second lens and the object-side surface of the third lens is d23, the refractive index of the second lens is n2, D=d12+d2 / n2+d23, and the focal length of the entire optical system is F, the following equation (4) is satisfied. 0.7 <D / F<1.5 ···(4) By having the first lens have negative power and a concave surface on the object side, negative distortion is generated, making it possible to realize a wide-angle imaging lens system. Furthermore, by satisfying the above formulas (1) and (4), negative distortion can be effectively generated in the first lens. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide an imaging lens system and an imaging device that can recognize distant objects and capture images of a wide range without relying on the resolution of the imaging element. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view showing the configurations and light rays of an imaging lens system and an imaging device according to the first embodiment. [Figure 2] 1 is a cross-sectional view showing the configuration of an imaging lens system and an imaging device according to Example 1. FIG. [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 is a cross-sectional view showing the configuration and light rays of an imaging lens system and an imaging device according to a second embodiment. FIG. [Figure 13] FIG. 10 is a diagram illustrating a distance ET2. [Figure 14] FIG. 10 is a cross-sectional view showing the configuration of an imaging lens system and an imaging device according to a sixth embodiment. [Figure 15] 10A to 10C are diagrams showing spherical aberration (longitudinal aberration), curvature of field, and distortion in the imaging lens system of Example 6. [Figure 16] FIG. 10 is a cross-sectional view showing the configuration of an imaging lens system and an imaging device according to a seventh embodiment. [Figure 17] 10A to 10C are diagrams showing spherical aberration (longitudinal aberration), curvature of field, and distortion in the imaging lens system of Example 7. [Figure 18] FIG. 13 is a cross-sectional view showing the configuration of an imaging lens system and an imaging device according to an eighth embodiment. [Figure 19] 13A to 13C are diagrams showing spherical aberration (longitudinal aberration), curvature of field, and distortion in the imaging lens system of Example 8. [Figure 20] FIG. 13 is a cross-sectional view showing the configuration of an imaging lens system and an imaging device according to Example 9. [Figure 21] 13A to 13C are diagrams showing spherical aberration (longitudinal aberration), curvature of field, and distortion in the imaging lens system of Example 9. DETAILED DESCRIPTION OF THE INVENTION

[0010] 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.

[0011] As shown in FIG. 1, imaging lens system 11 of the first embodiment is composed of, in order from the object side to the image side, a first lens group G1 consisting of a first lens L1 having a concave surface facing the object side and negative power, a second lens L2 having positive power, and a second lens group G2 consisting of a third lens L3 and subsequent lenses. Specifically, the first lens group G1 is composed of, from the object side to the image side, a first lens L1, which is a meniscus lens having negative power and a concave surface facing the object side, and a second lens L2, which has positive power and a convex surface facing the object side. The second lens group G2 is composed of a third lens L3, which has negative power and a concave surface facing the image side, a fourth lens L4, which has positive power and a convex surface facing both the object side and the image side, and a fifth lens L5, which has negative power and an aspherical surface facing both the object side and the image side, sandwiching an aperture stop STOP. As shown in FIG. 1, the imaging lens system 11 may include a wavelength filter glass 12 between the image-side lens surface S11 of the fifth lens L5 and an image plane IMG. The third lens L3 and the fourth lens L4 form a cemented lens. A cover glass 22 is provided on the imaging element 21, and the image plane of the imaging lens system 11 is indicated by IMG. The first lens L1 and the second lens L2 are preferably glass lenses, and the third lens L3 to the fifth lens L5 are preferably plastic lenses.

[0012] The first lens L1 and the second lens L2, which are located closer to the object side than the aperture stop STOP, constitute the first lens group G1, and the third lens L3, the fourth lens L4, and the fifth lens L5, which are located closer to the image side than the aperture stop STOP, constitute the second lens group G2. The first lens group G1 has negative power, and the second lens group G2 has positive power. The aperture stop STOP is an aperture that determines the F-number (Fno) of the imaging lens system 11.

[0013] Because the first lens L1 has negative power and the object-side surface S1 of the first lens L1 is concave, the angle of incidence of off-axis rays (rays that form an image off the optical axis, also called "peripheral rays") incident on the first lens L1 can be significantly changed, generating negative distortion. As a result, the image shrinks toward the periphery, widening the range detected by the image sensor 21, achieving a wide angle of view and enabling the realization of a wide-angle imaging lens system 11. Furthermore, because the second lens L2 has positive power, light-collecting performance can be ensured.

[0014] Furthermore, when the focal length of the first lens L1 is f1 and the combined focal length of the lenses L2, L3, L4, and L5 other than the first lens L1 is Fr, it is preferable to satisfy the following formula (1). -6.0 <f1 / Fr<-1.5 ···(1) The above formula (1) expresses the condition for effectively producing negative distortion with the first lens L1, expressed as the ratio between the focal length of the first lens L1 and the combined focal length of the subsequent lenses. If the upper limit is exceeded, the negative power will be too strong, causing distortion to become too large and difficult to correct, and if the lower limit is exceeded, negative distortion will not be sufficient, making it difficult to obtain a wide angle of view. Therefore, it is possible to realize a wide-angle imaging lens system 11, and also a telephoto imaging lens system 11 without requiring a high-resolution imaging element. Therefore, it is possible to provide an imaging lens system and an imaging device that can recognize distant objects and capture images of a wide range without relying on the resolution of the imaging element.

[0015] Furthermore, if the distance on the optical axis Z between the image-side surface S2 of the first lens L1 and the object-side surface S3 of the second lens L2 is d12 and the overall focal length of the imaging lens system 11 is F, then the following equation (2) is satisfied. 0.7 <d12 / F<1.5 ···(2)

[0016] If the distance d12 on the optical axis Z between the image-side surface S2 of the first lens L1 and the object-side surface S3 of the second lens L2 is too small, the incident positions of off-axial rays on the object-side surface S1 of the first lens L1 are close to the axial rays (light rays that form an image on the optical axis, also referred to as "central rays"), resulting in a large angle of incidence of the off-axial rays, and therefore, it is not possible to generate significant negative distortion. On the other hand, if d12 is relatively large, the incident positions of the off-axial rays on the object-side surface S1 of the first lens can be made farther away from the axial rays, thereby reducing the angle of incidence of the off-axial rays, thereby enabling significant negative distortion to be generated. Therefore, it is preferable that d12 / F be greater than 0.7. On the other hand, if d12 / F is greater than 1.5, the lens diameter of the first lens L1 becomes too large, making it difficult to achieve a compact imaging lens system 11.

[0017] Furthermore, the half angle of view of the optical system is 40° or less, and preferably 30° or less. Having a half angle of view of 40° or less allows the focal length of the imaging lens system to be increased. Here, the half angle of view of the optical system refers to the angle between the optical axis on the object side and a ray that passes through the center of the pupil and reaches the diagonal position (diagonal point) of the sensor.

[0018] In the first embodiment, the second lens group G2 is made up of three lenses, but the number of lenses is not limited to this and may be any number. The object of the present invention is achieved with only the first lens L1 for determining the angle of view and the second lens L2 having a light-condensing function, and the lenses located on the image side of these lenses are simply configured to realize imaging, so it does not matter how many lenses there are. In other words, from the third lens L3 onwards, there is little curvature of field, and since they are close to the pupil (aperture), it is sufficient to focus on imaging performance such as spherical aberration, so any configuration is acceptable.

[0019] Furthermore, when the radius of curvature of the object-side surface S1 of the first lens L1 is R11, it is preferable that the following formula (3) be satisfied. -2.5 <R11 / F<-1 ···(3)

[0020] Furthermore, if R11 / F is smaller than -2.5, in other words, if the radius of curvature R11 of the object-side surface S1 of the first lens L1 is relatively small, the distortion caused by the first lens L1 becomes small, making it difficult to ensure a sufficiently large angle of view. On the other hand, if R11 / F is larger than -1, in other words, if the radius of curvature R11 of the object-side surface S1 of the first lens L1 is relatively large, the curvature of field becomes too large, making it difficult to correct the imaging performance of the imaging lens system 11. Therefore, by satisfying the above formula (3), it is possible to ensure sufficient imaging performance while also ensuring a sufficiently large angle of view.

[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 FIG. 2 is a cross-sectional view showing an imaging lens system 11 according to Example 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, and an IR cut filter 12. The first lens L1 has negative power, a concave surface on the object side, and a convex surface on the image side. The second lens L2 has positive power, a convex aspherical surface on the object side, and an aspherical surface on the image side. The third lens L3 has negative power, an aspherical surface on the object side, and a concave aspherical surface on the image side. The fourth lens L4 has positive power, and convex aspherical surfaces on both the object side and the image side. The fifth lens L5 has positive power, and aspherical surfaces on both the object side and the image side. The first lens L1 and the second lens L2 are glass lenses, and the third lens L3 to the fifth lens L5 are plastic lenses. The imaging lens system 11 also includes an IR cut filter 12, which 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 27.0°, an F-number of 1.8, and a focal length F of the entire optical system of 8.269 (mm). The refractive index at the d-line and the Abbe number at the d-line shown in Table 1 are values ​​obtained 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 for the lens surfaces of the second lens L2, the third lens L3, the fourth lens surface L4, and the fifth lens L5 are expressed by the following formula (8), where Y(h) is the amount of sag in the optical axis Z 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, "-6.88301E-06" corresponds to "-6.88301E×10 -6 " 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 27.0° and an F-number of 1.8. In the longitudinal aberration diagram of FIG. 3A, the horizontal axis indicates the position where the light ray intersects with the optical axis Z, and the vertical axis indicates the height in terms of the pupil diameter. In the field curvature diagram of Fig. 3B, the horizontal axis represents the distance along the optical axis Z, 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, 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 27.0°, an F-number of 1.8, and a focal length F of the entire optical system of 8.506 (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 27.0°, an F-number of 1.8, and a focal length F of the entire optical system of 8.29 (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 explanations will be omitted. Here, the imaging lens system 11 according to Example 4 has a half angle of view of 27.0°, an F-number of 1.8, and a focal length F of the entire optical system of 7.98 (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 27.0°, an F-number of 1.8, and a focal length F of the entire optical system of 8.006 (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 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 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 also lists the focal length F (mm) of the entire imaging lens system 11 according to Examples 1 to 5, the focal lengths f1 to f5 (mm) of the first lens L1 through the fifth lens L5, the composite focal length Fr (mm) of all lenses except the first lens, the radius of curvature R11 (mm) of the object-side surface S1 of the first lens L1, the distance d12 (mm) along the optical axis Z between the image-side surface S2 of the first lens L1 and the object-side surface S3 of the second lens L2, the composite focal length f3 / 4 (mm) of the cemented lens formed by the third lens L3 and the fourth lens L4, the optical length tol (mm) of the imaging lens system 11, the value of d12 / F, the value of f1 / Fr, and the value of R11 / F. The values ​​listed in Table 11 are for a light wavelength of 555 nm and an ambient temperature t (°C) of 25°C. [Table 11]

[0047] In Examples 1 to 5, the first lens L1 has negative power and a concave surface on the object side, thereby realizing a wide-angle imaging lens system 11 with a half angle of view of 27.0°. Also, as shown in Table 11, in Examples 1 to 5, the value of f1 / Fr satisfies the above formula (1). This makes it possible to effectively generate negative distortion in the first lens L1, thereby realizing a wide-angle imaging lens system 11. In addition, in Examples 1 to 5, the half angle of view of the entire optical system is 40° or less, and therefore the focal length F of the imaging lens system 11 according to Examples 1 to 5 is 7.98 to 8.51, which makes it possible to realize a telephoto imaging lens system 11. In other words, it is possible to realize a telephoto imaging lens system 11 without relying on the resolution of the image sensor 21.

[0048] Furthermore, as shown in Table 11, in Examples 1 to 5, the value of d12 / F satisfies the above formula (2). Therefore, since d12 / F is greater than 0.7, it is possible to generate a sufficiently large negative distortion (distortion aberration) by the first lens L1. This makes it possible to achieve a wide angle of the imaging lens system 11. In fact, the half angle of view of the imaging lens systems 11 in Examples 1 to 5 is 27.0°, which is sufficiently large. On the other hand, since d12 / F is smaller than 1.5, it is possible to prevent the lens diameter of the first lens L1 from increasing, and it is possible to make the imaging lens system 11 more compact. Furthermore, the second lens L2 has positive power, and the second lens group G2 has positive power, thereby ensuring the light-collecting performance of the imaging lens system 11. For example, as shown in Figures 3, 5, 7, 9, and 11, in Examples 1 to 5, the longitudinal aberration, the curvature of field, and the distortion aberration have good values. Therefore, in Examples 1 to 5, the telephoto capabilities of the imaging lens system 11 can be achieved.

[0049] Furthermore, as shown in Table 11, in Examples 1 to 5, the value of R11 / F satisfies the above formula (3). Because R11 / F is greater than -2.5, the radius of curvature R11 of the object-side surface S1 of the first lens L1 can be made sufficiently large, and the distortion aberration caused by the first lens L1 can be made sufficiently large. Therefore, the angle of view of the imaging lens system 11 can be made sufficiently large. On the other hand, because R11 / F is smaller than -1, the radius of curvature R11 of the object-side surface S1 of the first lens L1 can be prevented from becoming too large, and an increase in field curvature can be prevented. Therefore, it is easy to correct the imaging performance of the imaging lens system 11.

[0050] Embodiment 2 (Imaging lens system and imaging device) 12 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 2. 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).

[0051] 12, the imaging lens system 11 of Embodiment 2 has a configuration in which a correcting lens is inserted between the first lens L1 and the second lens L2 in the imaging lens system 11 of Embodiment 1. That is, from the object side to the image side, the imaging lens system 11 is made up of a first lens group G1 that includes a first lens L1 that has a concave surface facing the object side and has negative power, a second lens L2 that serves as a correcting lens, and a third lens L3 that has positive power, and a second lens group G2 that includes a fourth lens L4 and subsequent lenses. Specifically, the first lens group G1 is composed of, from the object side to the image side, a first lens L1, which is a meniscus lens having negative power and a concave surface facing the object side; a second lens L2, which is a corrector lens having aspherical surfaces facing the object side and the image side; and a third lens L3, which has positive power and a convex surface facing the object side. The second lens group G2, sandwiching the aperture stop STOP, is composed of a fourth lens L4, which has negative power and a concave surface facing the image side; a fifth lens L5, which has positive power and a convex surface facing the object side and the image side; and a sixth lens L6, which has negative power and an aspherical surface facing the object side and the image side. As shown in FIG. 12, the imaging lens system 11 may include a wavelength filter glass 12 between the image-side lens surface S13 of the sixth lens L6 and the image plane IMG. The fourth lens L4 and the fifth lens L5 form a cemented lens. Furthermore, there is a cover glass 22 on the imaging element 21, and the imaging plane of the imaging lens system 11 is indicated by IMG. The first lens L1 to the third lens L3 are preferably glass lenses, and the fourth lens L4 to the sixth lens L6 are preferably plastic lenses. The second lens L2, which serves as a correcting lens, preferably has at least one inflection point on either the object-side or image-side surface, which makes it possible to correct field curvature, one of the various aberrations caused by the negative distortion produced by the first lens L1, from the center to the periphery.

[0052] The first lens L1, second lens L2, and third lens L3, which are arranged closer to the object side than the aperture stop STOP, constitute the first lens group G1, while the fourth lens L4, fifth lens L5, and sixth lens L6, which are arranged closer to the image side than the aperture stop STOP, constitute the second lens group G2. The first lens group G1 has negative power, and the second lens group G2 has positive power. The aperture stop STOP is an aperture that determines the F-number (Fno) of the imaging lens system 11.

[0053] Because the first lens L1 has negative power and the object-side surface S1 of the first lens L1 is concave, the angle of incidence of off-axis rays incident on the first lens L1 can be significantly changed, generating negative distortion. As a result, the image shrinks toward the periphery, widening the range detected by the image sensor 21, achieving a wide angle of view and enabling the realization of a wide-angle imaging lens system 11. Furthermore, because the second lens L2 has positive power, light-collecting performance can be ensured.

[0054] Furthermore, when the focal length of the first lens L1 is f1 and the combined focal length of the lenses L2, L3, L4, L5, and L6 other than the first lens L1 is Fr, it is preferable to satisfy the following formula (1). -6.0 <f1 / Fr<-1.5 ···(1) The above formula (1) expresses the condition for effectively producing negative distortion with the first lens L1, expressed as the ratio between the focal length of the first lens L1 and the combined focal length of the subsequent lenses. If the upper limit is exceeded, the negative power will be too strong, causing distortion to become too large and difficult to correct, and if the lower limit is exceeded, negative distortion will not be sufficient, making it difficult to obtain a wide angle of view. Therefore, it is possible to realize a wide-angle imaging lens system 11, and also a telephoto imaging lens system 11 without requiring a high-resolution imaging element. Therefore, it is possible to provide an imaging lens system and an imaging device that can recognize distant objects and capture images of a wide range without relying on the resolution of the imaging element.

[0055] Furthermore, when the distance on the optical axis Z between the image-side surface S2 of the first lens L1 and the object-side surface S3 of the second lens L2 is d12, the thickness on the optical axis Z of the second lens L2 is d2, the distance on the optical axis Z between the image-side surface S4 of the second lens L2 and the object-side surface S5 of the third lens L3 is d23, the refractive index of the second lens L2 is n2, D = d12 + d2 / n2 + d23, and the overall focal length of the imaging lens system 11 is F, the following equation (4) is satisfied. 0.7 <D / F<1.5 ···(4)

[0056] If the distance D on the optical axis Z between the image-side surface S2 of the first lens L1 and the object-side surface S5 of the third lens L3 is too small, the incident positions of off-axial rays relative to on-axial rays on the object-side surface S1 of the first lens L1 will be close, resulting in a large angle of incidence of the off-axial rays, making it difficult to generate significant negative distortion. On the other hand, if the distance D is relatively large, the incident positions of off-axial rays relative to on-axial rays on the object-side surface S1 of the first lens L1 can be made farther apart, resulting in a smaller angle of incidence of the off-axial rays, making it possible to generate significant negative distortion. Therefore, it is preferable that D / F be greater than 0.7. On the other hand, if D / F is greater than 1.5, the lens diameter of the first lens L1 will be too large, making it difficult to achieve a compact imaging lens system 11.

[0057] Furthermore, the half angle of view of the optical system is 40° or less, and preferably 30° or less. Having a half angle of view of 40° or less allows the focal length of the imaging lens system to be increased. Here, the half angle of view of the optical system refers to the angle between the optical axis on the object side and a ray that passes through the center of the pupil and reaches the diagonal position (diagonal point) of the sensor.

[0058] In the second embodiment, the second lens group G2 is composed of three lenses, but the number of lenses is not limited to this and may be any number. The object of the present invention is achieved with only the first lens L1 for determining the angle of view and the third lens L3 having a light-condensing function, and the lenses located on the image side of these lenses are simply configured to realize imaging, so it does not matter how many lenses there are. In other words, from the fourth lens L4 onwards, there is little curvature of field, and since they are close to the pupil (aperture), it is sufficient to focus on imaging performance such as spherical aberration, so any configuration is acceptable.

[0059] Furthermore, when the radius of curvature of the object-side surface S1 of the first lens L1 is R11, it is preferable that the following formula (3) be satisfied. -2.5 <R11 / F<-1 ···(3)

[0060] If R11 / F is smaller than -2.5, in other words, if the radius of curvature R11 of the object-side surface S1 of the first lens L1 is relatively small, the distortion caused by the first lens L1 will be small, making it difficult to ensure a sufficiently large angle of view. On the other hand, if R11 / F is larger than -1, in other words, if the radius of curvature R11 of the object-side surface S1 of the first lens L1 is relatively large, the field curvature will be too large, making it difficult to correct the imaging performance of the imaging lens system 11. Therefore, by satisfying the above formula (3), it is possible to ensure sufficient imaging performance while also ensuring a sufficiently large angle of view.

[0061] It is also preferable that the following formula (5) be satisfied. 0.05 <d12 / d23<1.0 ···(5)

[0062] When d12 / d23 is smaller than 1.0, the second lens L2 is positioned closer to the first lens L1 than the third lens L3, reducing the overlap of incident rays on the surface of the second lens L2, making it possible to correct each incident ray individually, resulting in effective aberration correction. It is also preferable that d12 / d23 be greater than 0.05. If d12 / d23 is smaller than 0.05, i.e., if the second lens L2 is too close to the first lens L1, there is a high possibility that the first lens L1 and the second lens L2 will interfere with each other when assembling the imaging lens system 11.

[0063] Furthermore, when the focal length of the second lens L2 is f2, it is preferable to satisfy the following formula (6). -0.1 <F / f2<0.1 ···(6) By satisfying this condition, the power of the second lens L2 can be limited, and the image plane can be efficiently corrected as a correction lens.

[0064] Furthermore, as shown in Figure 13, if the distance parallel to the optical axis Z between the intersection P1 of a ray passing through the outermost diameter side of the object-side surface S3 of the second lens L2 and the object-side surface S3 of the second lens L2 and the intersection P2 of the ray passing through the outermost diameter side of the object-side surface S3 of the second lens L2 and the image-side surface S4 is ET2, it is preferable to satisfy the following equation (7): 0.9 <ET2 / d2<1.1 ···(7)

[0065] It is preferable to satisfy at least one of the above formulas (6) and (7). In other words, it is preferable that the lens power of the second lens L2 is weaker than that of the other lenses in the imaging lens system 11. This makes it possible for the second lens L2 to suitably correct various aberrations caused by the negative distortion produced by the first lens L1.

[0066] Next, an example corresponding to the imaging lens system 11 of the second embodiment will be described with reference to the drawings.

[0067] Example 6 FIG. 14 is a cross-sectional view showing an imaging lens system 11 according to Example 6. 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, and an IR cut filter 12. The first lens L1 has negative power, a concave surface on the object side, and a convex surface on the image side. The second lens has positive power, and an aspherical surface with inflection points on the object side and the image side. The third lens L3 has positive power, a convex aspherical surface on the object side, and an aspherical surface on the image side. The fourth lens L4 has negative power, an aspherical surface on the object side, and a concave aspherical surface on the image side. The fifth lens L5 has positive power, and a convex aspherical surface on the object side and the image side. The sixth lens L6 has positive power, and an aspherical surface on the object side and the image side. The first lens L1 to the third lens L3 are glass lenses, and the fourth lens L4 to the sixth lens L6 are plastic lenses. The imaging lens system 11 also includes an IR cut filter 12 that cuts off light in the infrared region. The characteristic data of the imaging lens system 11 according to Example 6 will be described below.

[0068] Table 12 shows lens data for each lens surface of the imaging lens system 11 according to Example 6. The items shown in Table 12 are the same as those in Table 1, and therefore their explanations will be omitted. Here, the imaging lens system 11 according to Example 6 has a half angle of view of 27.0°, an F-number of 1.8, and a focal length F of the entire optical system of 8.623 (mm). [Table 12]

[0069] Table 13 shows aspherical coefficients for defining the aspherical shape of the aspherical lens surface in the imaging lens system 11 of Example 6. [Table 13]

[0070] 15 shows diagrams of spherical aberration (longitudinal aberration), field curvature, and distortion in the imaging lens system 11 of Example 6. The explanation of each aberration diagram shown in Fig. 15 is the same as that in Fig. 3, and therefore will not be repeated.

[0071] Example 7 16 is a cross-sectional view showing an imaging lens system 11 according to Example 7. The configuration of the imaging lens system 11 according to Example 7 is the same as that of Example 6, and therefore a description thereof will be omitted. Below, characteristic data of the imaging lens system 11 according to Example 7 will be described.

[0072] Table 14 shows lens data for each lens surface of the imaging lens system 11 according to Example 7. The items shown in Table 14 are the same as those in Table 1, and therefore their explanations will be omitted. Here, the imaging lens system 11 according to Example 7 has a half angle of view of 27.0°, an F-number of 1.8, and a focal length F of the entire optical system of 8.923 (mm). [Table 14]

[0073] Table 15 shows aspherical coefficients for defining the aspherical shape of the aspherical lens surface in the imaging lens system 11 of Example 7. [Table 15]

[0074] 17 shows diagrams of spherical aberration (longitudinal aberration), field curvature, and distortion in the imaging lens system 11 of Example 7. The explanation of each aberration diagram shown in Fig. 17 is the same as that in Fig. 3, and therefore will not be repeated.

[0075] Example 8 18 is a cross-sectional view showing an imaging lens system 11 according to Example 8. The configuration of the imaging lens system 11 according to Example 8 is the same as that of Example 6, and therefore a description thereof will be omitted. Below, characteristic data of the imaging lens system 11 according to Example 8 will be described.

[0076] Table 16 shows lens data for each lens surface of the imaging lens system 11 according to Example 8. The items shown in Table 16 are the same as those in Table 1, and therefore their explanations will be omitted. Here, the imaging lens system 11 according to Example 8 has a half angle of view of 27.0°, an F-number of 1.8, and a focal length F of the entire optical system of 8.59 (mm). [Table 16]

[0077] Table 17 shows aspherical coefficients for defining the aspherical shape of the aspherical lens surface in the imaging lens system 11 of the eighth embodiment. [Table 17]

[0078] 19 shows diagrams of spherical aberration (longitudinal aberration), field curvature, and distortion in the imaging lens system 11 of Example 8. The explanation of each aberration diagram shown in Fig. 19 is the same as that in Fig. 3, and therefore will not be repeated.

[0079] Example 9 20 is a cross-sectional view showing an imaging lens system 11 according to Example 9. The configuration of the imaging lens system 11 according to Example 9 is the same as that of Example 6, and therefore a description thereof will be omitted. Below, characteristic data of the imaging lens system 11 according to Example 9 will be described.

[0080] Table 18 shows lens data for each lens surface of the imaging lens system 11 according to Example 9. The items shown in Table 18 are the same as those in Table 1, and therefore their explanations will be omitted. Here, the imaging lens system 11 according to Example 9 has a half angle of view of 27.0°, an F-number of 1.8, and a focal length F of the entire optical system of 8.623 (mm). [Table 18]

[0081] Table 19 shows aspherical coefficients for defining the aspherical shape of the aspherical lens surface in the imaging lens system 11 of Example 9. [Table 19]

[0082] 21 shows diagrams of spherical aberration (longitudinal aberration), field curvature, and distortion in the imaging lens system 11 of Example 9. The explanation of each aberration diagram shown in Fig. 21 is the same as that in Fig. 3, and therefore will not be repeated.

[0083] 15A, 17A, 19A, and 21A, 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 6 to 9. Therefore, the imaging lens system 11 has high resolution.

[0084] 15B, 17B, 19B, and 21B, the curvature of field is well corrected according to the imaging lens systems 11 of Examples 6 to 9. Therefore, the imaging lens system 11 has high resolution.

[0085] 15C, 17C, 19C, and 21C, distortion is well corrected according to the imaging lens systems 11 of Examples 6 to 9. Therefore, the imaging lens system 11 has high resolution.

[0086] Table 20 also lists the focal length F (mm) of the entire imaging lens system 11 according to Examples 6 to 9, the focal lengths f1 to f6 (mm) of the first lens L1 to the sixth lens L6, the combined focal length Fr (mm) of all lenses other than the first lens, the radius of curvature R11 (mm) of the object-side surface S1 of the first lens L1, the distance d12 (mm) on the optical axis Z between the image-side surface S2 of the first lens L1 and the object-side surface S3 of the second lens L2, the thickness d2 (mm) on the optical axis Z of the second lens L2, and the distance d12 (mm) on the optical axis Z between the image-side surface S4 of the second lens L2 and the object-side surface S5 of the third lens L3. The table shows the distance d23 (mm) on Z, the distance D (mm) on the optical axis Z between the image-side surface S2 of the first lens L1 and the object-side surface S5 of the third lens L3, the distance ET2 (mm) parallel to the optical axis Z between the intersection of a ray passing through the outermost diameter side of the object-side surface S3 of the second lens L2 and the image-side surface S4, the composite 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 D / F, the value of f1 / Fr, the value of R11 / F, the value of d12 / d23, the value of F / f2, and the value of ET2 / d2. The values ​​shown in Table 20 are those when the wavelength of the light is 555 nm and the ambient temperature t (°C) is 25°C. [Table 20]

[0087] In Examples 6 to 9, the first lens L1 has negative power and a concave surface on the object side, thereby realizing a wide-angle imaging lens system 11 with a half angle of view of 27.0°. Also, as shown in Table 20, in Examples 6 to 9, the value of f1 / Fr satisfies the above formula (1). This makes it possible to effectively generate negative distortion in the first lens L1, thereby realizing a wide-angle imaging lens system 11. In addition, in Examples 6 to 9, the half angle of view of the entire optical system is 40° or less, so the focal length F of the imaging lens system 11 according to Examples 6 to 9 is 8.55 to 8.93, and it is possible to realize a telephoto imaging lens system 11. In other words, it is possible to realize a telephoto imaging lens system 11 without relying on the resolution of the image sensor 21. In addition, in Examples 6 to 9, it is possible to realize a wide-angle imaging lens system 11 with a half angle of view of 27.0° by having the first lens L1 have negative power and a concave surface on the object side. In addition, in Examples 6 to 9, the second lens L2 serving as a correction lens has one inflection point on the object-side and image-side surfaces. This makes it possible to correct field curvature, one of the various aberrations caused by negative distortion produced by the first lens L1, from the center to the periphery. For example, as shown in Figures 15B, 17B, 19B, and 21B, in Examples 6 to 9, the field curvature has a good value.

[0088] As shown in Table 20, in Examples 6 to 9, the values ​​of D / F satisfy the above formula (4). Therefore, since D / F is greater than 0.7, it is possible to generate a sufficiently large negative distortion (distortion aberration) by the first lens L1. This makes it possible to achieve a wide angle of the imaging lens system 11. In fact, the half angle of view of the imaging lens systems 11 in Examples 6 to 9 is 27.0, which is sufficiently large. On the other hand, since D / F is less than 1.5, it is possible to prevent the lens diameter of the first lens L1 from increasing, and it is possible to make the imaging lens system 11 more compact. Furthermore, the third lens L3 has positive power, and the second lens group G2 has positive power, thereby ensuring the light-collecting performance of the imaging lens system 11. For example, as shown in Figures 15, 17, 19, 21, and 23, in Examples 6 to 9, the longitudinal aberration, the curvature of field, and the distortion aberration have good values. Therefore, in Examples 6 to 9, the telephoto capabilities of the imaging lens system 11 can be achieved.

[0089] Furthermore, as shown in Table 20, in Examples 6 to 9, the value of R11 / F satisfies the above formula (3). Because R11 / F is greater than -2.5, the radius of curvature R11 of the object-side surface S1 of the first lens L1 can be made sufficiently large, and the distortion aberration caused by the first lens L1 can be made sufficiently large. Therefore, the angle of view of the imaging lens system 11 can be made sufficiently large. On the other hand, because R11 / F is smaller than -1, the radius of curvature R11 of the object-side surface S1 of the first lens L1 can be prevented from becoming too large, and an increase in field curvature can be prevented. Therefore, it is easy to correct the imaging performance of the imaging lens system 11.

[0090] Furthermore, as shown in Table 20, in Examples 6 to 9, the value of d12 / d23 satisfies the above formula (5). Therefore, when d12 / d23 is smaller than 1.0, aberrations can be effectively corrected. On the other hand, when d12 / d23 is larger than 0.05, interference between the first lens L1 and the second lens L2 can be prevented.

[0091] Furthermore, as shown in Table 20, in Examples 6 to 9, the values ​​of F / f2 satisfy the above formula (6), and the values ​​of ET2 / d2 satisfy the above formula (7). Therefore, the lens power of the second lens L2 is weaker than the other lenses in the imaging lens system 11, and the second lens L2 can suitably correct various aberrations caused by the negative distortion produced by the first lens L1.

[0092] 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]

[0093] 11 Imaging lens system 12 Glass (IR cut filter) 20 Imaging device 21 Image sensor 22 Coverslip L1 First lens L2 Second lens L3 Third lens L4 4th lens L5 Fifth lens L6 6th lens G1 First lens group G2 Second lens group STOP Aperture IMG Image plane

Claims

1. a first lens group consisting of, in order from the object side to the image side, a first lens having a concave surface on the object side and negative power, a second lens having an aspherical shape on the object side and on the image side, and a third lens having positive power; and a second lens group consisting of, in order from the object side to the image side, a fourth lens having negative power, a fifth lens having positive power, and a sixth lens having negative power, the second lens has an inflection point on at least one of its object-side and image-side surfaces, When the focal length of the first lens is f1 and the composite focal length of all lenses other than the first lens is Fr, the following formula (1) is satisfied: -6.0<f1 / Fr<-1.5...(1) When the distance on the optical axis between the image-side surface of the first lens and the object-side surface of the second lens is d12, the thickness on the optical axis of the second lens is d2, the distance on the optical axis between the image-side surface of the second lens and the object-side surface of the third lens is d23, the refractive index of the second lens is n2, D = d12 + d2 / n2 + d23, and the focal length of the entire optical system is F, the following formula (4) is satisfied: 0.7<D / F<1.5...(4) An imaging lens system that satisfies the following formula (3) when the radius of curvature of the object side of the first lens is R11. -2.5<R11 / F<-1...(3)

2. A first lens group consisting of, in order from the object side to the image side, a first lens having a concave surface on the object side and negative power, a second lens having an aspherical shape on the object side and on the image side, and a third lens having positive power; and a second lens group consisting of, in order from the object side to the image side, a fourth lens having negative power, a fifth lens having positive power, and a sixth lens having negative power; the second lens has an inflection point on at least one of its object-side and image-side surfaces, When the focal length of the first lens is f1 and the composite focal length of all lenses other than the first lens is Fr, the following formula (1) is satisfied: -6.0<f1 / Fr<-1.5...(1) When the distance on the optical axis between the image-side surface of the first lens and the object-side surface of the second lens is d12, the thickness on the optical axis of the second lens is d2, the distance on the optical axis between the image-side surface of the second lens and the object-side surface of the third lens is d23, the refractive index of the second lens is n2, D = d12 + d2 / n2 + d23, and the focal length of the entire optical system is F, the following formula (4) is satisfied: 0.7<D / F<1.5...(4) An imaging lens system that satisfies the following formula (5): 0.05<d12 / d23<1.0...(5)

3. 2. The imaging lens system according to claim 1, wherein a half angle of view of the entire optical system is 40[deg.] or less.

4. An imaging lens system as described in claim 2, wherein the half-angle of the entire optical system is 40° or less.

5. 5. The imaging lens system according to claim 1, wherein the following formula (6) is satisfied when the focal length of the second lens is f2: -0.1<F / f2<0.1...(6)

6. 6. The imaging lens system according to claim 1, wherein the following formula (7) is satisfied, when a distance parallel to the optical axis between an intersection of a ray passing through an outermost diameter side of the object-side surface of the second lens and the object-side surface of the second lens and an intersection of a ray passing through an outermost diameter side of the object-side surface of the second lens and an image-side surface is defined as ET2: 0.9<ET2 / d2<1.1 (7)

7. 7. The imaging lens system according to claim 1, wherein the second lens has at least one inflection point on either its object-side or image-side surface.

8. An imaging lens system according to any one of claims 1 to 7; an imaging element disposed at a focal position of the imaging lens system.

Images