Imaging lens system and imaging device

Abstract

To provide an imaging lens system and imaging device which can suppress the occurrence of a ghost even when a plastic lens is used.SOLUTION: An imaging lens system 11 comprises first lens to sixth lens L6 in the order from the object side to the image side, the image side lens surfaces S4, S8 and S14 of the second lens L2, the third lens L3 and the fifth lens L5 have the concave surface shape on the object side, the sixth lens L6 satisfies the following formula (1) and formula (2) when a sag amount at a height H1 in an effective diameter of an object side lens surface S15 is Sg1H and a sag amount at a height H2 in an effective diameter of the image side lens surface is Sg2H, (1) Sg1H / H1<-0.10, (2) Sg2H / H2<-0.10. Here, H1 and H2 are light beam heights at a position through which a light beam that is incident on the outer side of the diagonal length of an imaging element passes.SELECTED DRAWING: Figure 2

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] In recent years, there has been a trend toward requiring cameras mounted on vehicles to have sensing functions, for example, to realize autonomous driving. To achieve stability and accuracy in the sensing function, in-vehicle cameras are often constructed entirely with glass lenses, as in the in-vehicle camera described in Patent Document 1, for example. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-211598 Summary of the Invention [Problem to be solved by the invention]

[0004] On the other hand, glass lenses are more expensive than plastic lenses, so replacing some glass lenses with plastic lenses is required to reduce costs. However, the extensive use of plastic lenses has the disadvantage that the effects of ghosting cannot be ignored. Specifically, the AR coating (anti-reflection coating) formed on the lens surface of a plastic lens has a reflectivity approximately 5 to 10% higher than that of the AR coating formed on the lens surface of a glass lens. Therefore, the effects of ghosting are more likely to be significant in cameras that use plastic lenses than in cameras that are composed only of glass lenses. Ghosting affects the imaging performance of optical systems, and when optical systems are used for sensing applications, the occurrence of ghosting can lead to false recognition and reduce the sensing function of the optical system.

[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 can suppress the occurrence of ghosts even when a plastic lens is used. [Means for solving the problem]

[0006] The imaging lens system of one embodiment includes, in order from the object side to the image side, a first lens which is a meniscus lens having negative power and having a convex surface facing the object side. 、 The optical system comprises a second lens element which is a meniscus lens element with a convex surface facing the image side, an aperture stop, a third lens element which has positive power and is biconvex, a fourth lens element which has negative power and has a convex surface on the image side facing the object side, a fifth lens element which has positive power and is biconvex, and a sixth lens element. When a plane that includes the intersection of the lens surface and the optical axis and is perpendicular to the optical axis is defined as a reference plane, the distance in the optical axis direction from the reference plane to the lens surface at the height of the effective diameter of the lens surface is defined as the amount of sag, and when the direction from the reference plane to the lens surface is directed from the object side to the image side, the sag amount is defined as positive. The sixth lens satisfies the following formulas (1) and (2), where Sg1H is a sag amount at a height H1 at the effective diameter of the object-side lens surface and Sg2H is a sag amount at a height H2 at the effective diameter of the image-side lens surface: Sg1H / H1<-0.10 (1) Sg2H / H2<-0.10 (2) Here, H1 and H2 are the heights of light rays at positions where light rays passing outside the diagonal length of the image sensor pass. "Outside the diagonal length of the image sensor" refers to the area outside the range of a circle on the image sensor whose center is the intersection of the image sensor and the optical axis and whose diameter is equal to the diagonal length of the image sensor. "Height at the effective diameter of the lens surface" refers to the height from the optical axis at a position within the effective diameter of the lens surface. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an imaging lens system and an imaging device that can suppress the occurrence of ghosts even when using plastic lenses. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 10 is a cross-sectional view illustrating the amount of sag of a lens. [Figure 2] 1 is a cross-sectional view showing the configuration of an imaging device and an imaging lens system 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 device and an imaging lens system 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. DETAILED DESCRIPTION OF THE INVENTION

[0009] An optical lens and an imaging device according to the present embodiment will be described below. (Embodiment 1: Imaging lens system) The imaging lens system of the first embodiment includes, in order from the object side to the image side, a first lens which is a meniscus lens having negative power and whose convex surface faces the object side. 、 It consists of the second lens, which is a meniscus lens with a convex surface facing the image side, an aperture stop, a biconvex third lens with positive power, a fourth lens with negative power whose image side is convex facing the object side, a biconvex fifth lens with positive power, and a sixth lens. Furthermore, in the imaging lens system of the first embodiment, when the amount of sag at a height H1 at the effective diameter of the object-side lens surface is Sg1H and the amount of sag at a height H2 at the effective diameter of the image-side lens surface is Sg2H, the sixth lens satisfies the following formulas (1) and (2): Sg1H / H1<-0.10 (1) Sg2H / H2<-0.10 (2)

[0010] Here, the amount of sag of a lens will be described with reference to FIG. 1. As shown in FIG. 1, when a plane PO, which includes the intersection of the object-side lens surface SO of lens L and the optical axis Z and is perpendicular to the optical axis, is defined as a reference plane, the distance along the optical axis Z from the reference plane PO to the object-side lens surface SO at a height H1 at the effective diameter of the object-side lens surface SO is defined as a sag amount Sg1H. Similarly, when a plane PI, which includes the intersection of the image-side lens surface SI of lens L and the optical axis Z and is perpendicular to the optical axis, is defined as a reference plane, the distance along the optical axis Z from the reference plane PI to the image-side lens surface SI at a height H2 at the effective diameter of the image-side lens surface SI is defined as a sag amount Sg2H. The direction from the reference planes PO and PI to the lens surfaces SO and SI is defined as a positive value when directed from the object side to the image side. That is, when the object-side lens surface SO is convex at the height H1, the sag amount Sg1H is a positive value. When the image-side lens surface SI is convex at the height H2, the sag amount Sg2H is a negative value.

[0011] Furthermore, heights H1 and H2 are the heights of light rays at positions where light rays incident outside the diagonal length of the image sensor pass through. "Outside the diagonal length of the image sensor" refers to the area outside the range of a circle on the imaging surface, centered at the intersection of the imaging surface and the optical axis, with a diameter equal to the diagonal length of the image sensor. The reason for using the term "outside the diagonal length of the image sensor" is that the shape of the lens surface where light rays pass through to enter the image sensor is originally designed based on imaging performance, etc., and therefore this excludes this area. Furthermore, "height of the lens surface at the effective diameter" means the height from the optical axis at a position within the effective diameter of the lens surface. That is, heights H1 and H2 are positions on the lens surface within the effective diameter of the lens surface, and are heights from the optical axis to positions through which light rays incident outside the diagonal length of the imaging element pass.

[0012] This makes it possible to suppress the occurrence of ghost images even when a plastic lens is used. Specifically, ghosting occurs when light reflected from the lens surfaces of lenses constituting the optical system enters an image sensor. In particular, strong ghosting occurs when light reflected from the image-side lens surface of a lens enters an image sensor. However, in the imaging lens system according to the first embodiment, the image-side lens surfaces of the second, third, and fifth lenses have a concave surface shape toward the object side, and the reflected light from the image-side lens surfaces of the second, third, and fifth lenses is reflected in a diverging direction (away from the optical axis Z), thereby preventing the reflected light from entering the image sensor. Furthermore, the sag amount Sg1H at a position on the object-side lens surface of the sixth lens through which a ray incident outside the diagonal length of the image sensor passes satisfies the above formula (1). Therefore, the overall shape of the object-side lens surface of the sixth lens is concave toward the object side, preventing the light reflected at that position from entering the image sensor. Furthermore, the sag Sg2H at a position on the image-side lens surface of the sixth lens through which a ray of light incident on a portion outside the diagonal length of the image sensor passes satisfies the above formula (2). Therefore, the overall shape of the image-side lens surface of the sixth lens is concave toward the object side, and light reflected at that position can be prevented from entering the image sensor. Therefore, in the imaging lens system according to the first embodiment, it is possible to prevent light reflected from the lens surface from entering the imaging element, and to prevent the occurrence of ghosts.

[0013] In addition, the sixth lens, which is closest to the image sensor in the imaging lens system, has an aspherical shape that makes the optical axis and the chief ray nearly parallel, which reduces the sensor incident angle to the image-forming surface of the image sensor. This ensures sufficient peripheral light intensity and realizes an imaging lens system with excellent sensing capabilities.

[0014] It is also preferable to dispose an infrared cut filter between the third lens and the fourth lens, which can prevent reflected light from the infrared cut filter from entering the imaging element, thereby further suppressing the occurrence of ghost images. Specifically, because infrared cut filters are more expensive than lenses, lens systems are typically designed without an infrared cut filter, and then an infrared cut filter is placed closest to the image side of the lens system. However, there is a problem in that light reflected from the object-side surface of the infrared cut filter is re-reflected, for example, by the object-side lens surface of the second lens and enters the image sensor, causing ghosting. However, in the imaging lens system according to the first embodiment, the infrared cut filter is placed between the third lens and the fourth lens, so that even if light reflected from the object-side surface of the infrared cut filter is re-reflected by the lens surface of a lens located closer to the object than the infrared cut filter, it is less likely to enter the image sensor. This makes it possible to prevent reflected light from the infrared cut filter from entering the image sensor.

[0015] It is also preferable that the fourth lens and the fifth lens form a cemented lens, which makes it possible to suitably correct chromatic aberration.

[0016] It is also preferable that at least the object-side and image-side lens surfaces of the second lens, the third lens, and the sixth lens have aspherical shapes, which makes it possible to effectively correct spherical aberration, field curvature, and distortion, and to realize an imaging lens system with excellent imaging performance.

[0017] Next, an example corresponding to the imaging lens system of the first embodiment will be described with reference to the drawings. Example 1 2 is a cross-sectional view showing the configuration of the imaging device 10 of Example 1. Specifically, the imaging device 10 includes an imaging lens system 11 and an imaging element 12. The imaging lens system 11 and the imaging element 12 are housed in a housing (not shown).

[0018] The imaging element 12 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 12 is disposed at the imaging position (focal position) of the imaging lens system 11.

[0019] The imaging lens system 11 according to the first embodiment includes, in order from the object side to the image side, a first lens L1, a second lens L2, an aperture stop (STOP), and a third lens L3. 、 Infrared cut filter (IRCF), Fourth lens L4, The imaging lens system 11 is made up of a fifth lens L5 and a sixth lens L6. The imaging plane of the imaging lens system 11 is indicated by IMG.

[0020] The first lens L1 is a glass lens having negative power. The object-side lens surface S1 of the first lens L1 has a spherical shape convex toward the object side. The image-side lens surface S2 of the first lens L1 has a spherical shape convex toward the object side.

[0021] The second lens L2 is a plastic lens with positive power. The object-side lens surface S3 of the second lens L2 has an aspherical shape concave toward the object side. The image-side lens surface S4 of the second lens L2 also has an aspherical shape concave toward the object side.

[0022] The aperture stop STOP is an aperture that determines the F-number (F-number, Fno) of the lens system. The aperture stop STOP is disposed between the second lens L2 and the third lens L3.

[0023] The third lens L3 is a glass lens having positive power. The object-side lens surface S7 of the third lens L3 has an aspherical shape convex toward the object side. The image-side lens surface S8 of the third lens L3 has an aspherical shape concave toward the object side.

[0024] The infrared cut filter (IRCF) is a filter for cutting light in the infrared region. When designing the imaging lens system 11, the infrared cut filter is treated as an integral part of the imaging lens system 11. However, the infrared cut filter is not an essential component of the imaging lens system 11. The infrared cut filter is disposed between the third lens L3 and the fourth lens L4.

[0025] The fourth lens L4 is a plastic lens having negative power. The object-side lens surface S11 of the fourth lens L4 has an aspherical shape convex toward the object side. The image-side lens surface S12 of the fourth lens L4 also has an aspherical shape convex toward the object side.

[0026] The fifth lens L5 is a plastic lens having positive power. The object-side lens surface S13 of the fifth lens L5 has an aspherical shape convex toward the object side. The image-side lens surface S14 of the fifth lens L5 has an aspherical shape concave toward the object side.

[0027] The fourth lens L4 and the fifth lens L5 form a cemented lens. That is, the image-side lens surface S12 of the fourth lens L4 and the object-side lens surface S13 of the fifth lens L5 are in contact with each other. The fourth lens L4 and the fifth lens L5 are cemented together with an adhesive layer having an axial thickness of 0.020 mm.

[0028] The sixth lens L6 is a plastic lens with negative power. The object-side lens surface S15 of the sixth lens L6 has an aspherical shape that is concave toward the object side overall. The image-side lens surface S16 of the sixth lens L6 also has an aspherical shape that is concave toward the object side overall.

[0029] Table 1 shows lens data for each lens surface in the imaging lens system 11 of Example 1. Table 1 presents the lens data, such as the glass material, refractive index Nd at the d-line, Abbe number Vd at the d-line, curvature of each surface, radius of curvature (mm) of each surface, surface spacing (mm) at the central optical axis, and effective diameter (mm). The refractive index at the d-line and 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.

[0030] [Table 1]

[0031] The aspherical shape used on the lens surface is expressed as follows: z is the amount of sag, c is the inverse of the radius of curvature, k is the conic coefficient, and r is the ray height from the optical axis Z. The aspherical coefficients of the 4th, 6th, 8th, 10th, 12th, 14th, and 16th orders are A4, A6, A8, and A9, respectively. 10 , A 12 , A 14 , A 16 When this is the case, it is expressed by the following equation:

number

[0032] 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, "-2.119E-03" corresponds to "-2.119×10 -3 The same applies to the numerical expressions in the following tables.

[0033] [Table 2]

[0034] Next, aberrations will be described with reference to the drawings. Fig. 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 pupil radius of 0.7303 and a half angle of view of 47.228°. The F-number is 2.8. In the longitudinal aberration diagram of FIG. 3(A), the horizontal axis indicates the position where the light ray intersects with the optical axis Z, and the vertical axis indicates the height at the pupil diameter. , 473 nm The simulation results for the ray of light are shown. In the field curvature diagram of Figure 3(B), the horizontal axis represents the distance in the optical axis Z direction, and the vertical axis represents the image height (angle of view). In the field curvature diagram of Figure 3(B), Sag represents the field curvature on the sagittal plane, and Tan represents the field curvature on the tangential plane. Figure 3(B) also shows the results of a simulation using light with a wavelength of 538 nm. In the distortion diagram of Figure 3(C), the horizontal axis represents the amount of image distortion (%) and the vertical axis represents the image height (angle of view). Figure 3(C) also shows the results of a simulation using light with a wavelength of 538 nm. FIG. 3 shows diagrams of spherical aberration (longitudinal aberration), field curvature, and distortion when the environmental temperature t (° C.) is 25 (° C.).

[0035] Example 2 4 is a cross-sectional view showing an imaging lens system 11 according to Example 2. Similar to Example 1, the imaging lens system 11 according to Example 2 comprises, in order from the object side to the image side, a first lens L1, a second lens L2, an aperture stop (STOP), and a third lens L3. 、 Infrared cut filter (IRCF), Fourth lens L4, The imaging lens system 11 according to Example 2 is composed of a fifth lens L5 and a sixth lens L6. The imaging lens system 11 according to Example 2 differs from Example 1 in that the second lens L2 has negative power, the sixth lens L6 has positive power, the object-side lens surface S11 and the image-side lens surface S12 of the fourth lens L4 have spherical shapes, and the object-side lens surface S13 and the image-side lens surface S14 of the fifth lens L5 have spherical shapes. The characteristic data of the imaging lens system 11 according to Example 2 will be described below.

[0036] 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 the explanation thereof will be omitted.

[0037] [Table 3]

[0038] Table 4 shows aspherical coefficients for defining the aspherical shape of the aspherical lens surface in the imaging lens system 11 of Example 2. In Table 4, the aspherical shape adopted for the lens surface is expressed by the same formula as in Example 1.

[0039] [Table 4]

[0040] 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.

[0041] Table 5 shows the total length TL of the optical system of imaging lens system 11, the focal length f1 of first lens L1, the focal length f2 of second lens L2, the focal length f3 of third lens L3, the focal length f4 of fourth lens L4, the focal length f5 of fifth lens L5, the focal length f6 of sixth lens L6, the combined focal length f45 of fourth lens L4 through fifth lens L5, the focal length F of the entire optical system of imaging lens system 11, the values ​​of f1 / F through f6 / F, the value of f45 / F, the height H1 of the object-side lens surface S15 of sixth lens L6 at the effective diameter, the sag Sg1H of the object-side lens surface S15 of sixth lens L6, the height H2 of the image-side lens surface S16 of sixth lens L6 at the effective diameter, and the sag Sg2H of the object-side lens surface S16 of sixth lens L6. In Table 5, the total length, focal length, height, and sag are all in millimeters. The focal length, height, and sag shown in Table 5 were calculated using light with a wavelength of 538 nm.

[0042] [Table 5]

[0043] In Examples 1 and 2, the image-side lens surfaces S4, S8, and S14 of the second lens L2, the third lens L3, and the fifth lens L5 have a surface shape concave toward the object side, and reflected light from the image-side lens surfaces S4, S8, and S14 of the second lens L2, the third lens L3, and the fifth lens L5 is reflected in a diverging direction (a direction away from the optical axis Z), thereby preventing the light from entering the image sensor 12. Also, as shown in Table 5, in Examples 1 and 2, the value of Sg1H / H1 satisfies the above formula (1), and the value of Sg2H / H2 satisfies the above formula (2). As a result, the imaging lens systems 11 according to Examples 1 and 2 can prevent reflected light from the object-side lens surface S15 and the image-side lens surface S16 of the sixth lens L6 from entering the image sensor 12. As a result, the imaging lens systems 11 according to Examples 1 and 2 can prevent the occurrence of ghosts, achieve excellent imaging performance, and achieve high resolution. In fact, as shown in FIGS. 3 and 5, the imaging lens systems 11 according to Examples 1 and 2 can effectively reduce various aberrations, have excellent imaging performance, and achieve high resolution.

[0044] Furthermore, in Examples 1 and 2, the sixth lens L6, which is located closest to the image sensor 12, has an aspheric shape that brings the optical axis and the chief ray closer to being parallel to each other, which reduces the sensor incident angle to the image plane IMG of the image sensor 12. This ensures a sufficient amount of peripheral light, and makes it possible to realize an imaging lens system 11 with excellent sensing capabilities.

[0045] In addition, an infrared cut filter IRCF is disposed between the third lens L3 and the fourth lens L4, which prevents reflected light from the infrared cut filter IRCF from entering the image sensor 12, thereby further suppressing the occurrence of ghost images.

[0046] Furthermore, the fourth lens L4 and the fifth lens L5 form a cemented lens, which makes it possible to appropriately correct chromatic aberration.

[0047] It is also preferable that at least the object-side lens surfaces S3, S7, and S15 and the image-side lens surfaces S4, S8, and S16 of the second lens L2, the third lens L3, and the sixth lens L6 have aspheric shapes, thereby making it possible to effectively correct spherical aberration, field curvature, and distortion, and to realize an imaging lens system 11 with excellent imaging performance.

[0048] Furthermore, the imaging device 10 includes the imaging lens system 11, which makes it possible to provide an imaging device that suppresses the occurrence of ghosts and has excellent imaging performance at a level required for image recognition in autonomous driving.

[0049] It should be noted that the present invention is not limited to the above-described embodiments, and modifications can be made 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 it can also be used for other purposes, such as being mounted on small electronic devices such as mobile phones. [Explanation of symbols]

[0050] 10. Imaging device 11 Imaging lens system 12 Image sensor L1 First lens L2 Second lens L3 Third lens L4 4th lens L5 Fifth lens L6 6th lens STOP Aperture IRCF Infrared Cut Filter IMG Image plane Z optical axis

Claims

1. The optical system comprises, in order from the object side to the image side, a first lens which is a meniscus lens having negative power and whose convex surface faces the object side, a second lens which is a meniscus lens having a convex surface facing the image side, a stop, a third lens which is a biconvex lens having positive power, a fourth lens which is a biconvex lens having negative power and whose image side surface faces the object side, a fifth lens which is a biconvex lens having positive power, and a sixth lens, When a plane that includes the intersection of the lens surface and the optical axis and is perpendicular to the optical axis is defined as a reference plane, the distance in the optical axis direction from the reference plane to the lens surface at the height of the effective diameter of the lens surface is defined as the amount of sag, and when the direction from the reference plane to the lens surface is directed from the object side to the image side, the sag amount is defined as positive. The sixth lens satisfies the following formulas (1) and (2), where Sg1H is a sag amount at a height H1 at the effective diameter of the object-side lens surface and Sg2H is a sag amount at a height H2 at the effective diameter of the image-side lens surface: Sg1H / H1<-0.10...(1) Sg2H / H2<-0.10...(2) Here, H1 and H2 are the heights of light rays at positions where light rays incident on the outside of the diagonal length of the image sensor pass through, an infrared cut filter disposed between the third lens and the fourth lens;

2. The imaging lens system of claim 1 , wherein the sixth lens is a meniscus lens.

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

4. 4. The imaging lens system according to claim 1, wherein at least the object-side and image-side lens surfaces of the second lens, the third lens, and the sixth lens have aspherical shapes.

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.

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