Image capturing lens

Abstract

To provide an image capturing lens which features a low F-number, wider angle of view, and lower height and yet offers good optical characteristics in the near-infrared region.SOLUTION: An image capturing lens provided herein consists of a first lens L1 having positive refractive power, a second lens L2 having positive or negative refractive power, a third lens L3 having positive refractive power, and a fourth lens L4 having negative refractive power, arranged in order from the object side to the image side. The first lens L1 has an object-side surface that is convex near an optical axis. The second lens L2 has a meniscus shape near the optical axis. The third lens L3 has an image-side surface that is convex near the optical axis. The fourth lens L4 has an image-side surface that is concave and meniscus-shaped near the optical axis. The image capturing lens satisfies predetermined conditional expressions.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an imaging lens that forms an image of a subject on a solid-state imaging element such as a CCD sensor or a CMOS sensor used in an imaging device. [Background technology]

[0002] In recent years, there has been progress in the development of driver monitoring systems that record the face and eye movements of car drivers to determine whether they are inattentive or drowsy while driving, and then issue warnings or alerts.In addition, there is an increasing number of systems that record not only the driver but also passengers in the passenger seat and back seat to monitor and support the safety of all passengers.

[0003] The cameras used in these systems must be compact because they are installed in the narrow spaces inside the vehicle. This means that the imaging lenses installed in them must also be compact. The imaging lenses must also have a wide angle of view so that they can capture images of passenger seats and rear seats.

[0004] Furthermore, the cameras used in these systems mainly use near-infrared light to capture images of the driver's face and other features even at night or in dark environments such as tunnels, so the imaging lens is also required to be able to capture good images in the near-infrared light range.

[0005] As a conventional lens that aims to have good performance in the near-infrared light region, for example, an imaging lens such as that disclosed in Patent Document 1 below is known.

[0006] Patent Document 1 discloses an imaging lens that is composed of, in order from the object side, a first lens having positive refractive power, a second lens having negative refractive power, a third lens having positive refractive power, and a fourth lens having positive refractive power. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2018-013580 Summary of the Invention [Problem to be solved by the invention]

[0008] The imaging lens disclosed in Patent Document 1 has a small F-number, a wide angle, and good performance in the near-infrared light region. However, the total optical length is 9.5 mm to 16.2 mm, and the total-to-diagonal ratio (the ratio of the total optical length to the diagonal length of the effective imaging surface of the imaging element) is large, at 1.79 to 2.77, so a further reduction in height is desired.

[0009] The present invention has been made in view of the above-mentioned problems, and has an object to provide an imaging lens that satisfies the demands for a low F-number and a wide angle, while also achieving a further reduction in height, and in which various aberrations are well corrected in the near-infrared light region. [Means for solving the problem]

[0010] An imaging lens according to the present invention comprises, arranged in order from the object side to the image side, a first lens having positive refractive power, a second lens having positive or negative refractive power, a third lens having positive refractive power, and a fourth lens having negative refractive power. The first lens has a convex surface on the object side in a paraxial view, the second lens has a meniscus shape in a paraxial view, the third lens has a convex surface on the image side in a paraxial view, and the fourth lens has a meniscus shape with a concave surface on the image side in a paraxial view.

[0011] In this specification, the convex, concave, and flat surfaces of a lens refer to the shape in the paraxial direction, and unless otherwise specified, the refractive power refers to the refractive power in the paraxial direction.

[0012] The first lens has positive refractive power and has a convex surface on the object side in the paraxial direction, thereby suppressing the occurrence of spherical aberration, coma, astigmatism, curvature of field, and distortion while achieving a low height.

[0013] The second lens has positive or negative refractive power and is meniscus shaped paraxially, thereby effectively correcting coma, astigmatism, and distortion.

[0014] The third lens has positive refractive power and is convex on the image side in the paraxial direction, thereby achieving a low profile and providing excellent correction for spherical aberration, coma, astigmatism, field curvature, and distortion.

[0015] The fourth lens element has negative refractive power, which effectively corrects chromatic aberration, coma, astigmatism, field curvature, and distortion. Its paraxial meniscus shape with a concave surface on the image side ensures an appropriate back focus while maintaining a low profile.

[0016] In the imaging lens having the above configuration, it is desirable that the object-side surface of the fourth lens be formed as an aspheric surface having a pole point at a position other than the optical axis.

[0017] By forming an aspherical shape with a pole point at a position other than on the optical axis on the object side surface of the fourth lens, it becomes possible to correct astigmatism and distortion more effectively.

[0018] In the imaging lens having the above configuration, it is desirable that the image-side surface of the fourth lens be formed as an aspheric surface having a pole point at a position other than the optical axis.

[0019] By forming an aspherical shape with a pole point at a position other than on the optical axis on the image-side surface of the fourth lens, it becomes possible to more effectively correct coma, astigmatism, field curvature, and distortion.

[0020] In the present invention, a pole is defined as a point on an aspherical surface other than on the optical axis where a tangent plane intersects the optical axis perpendicularly.

[0021] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (1). (1) 0.86<νd3 / (νd2+νd4)<1.65 Here, νd2 is the Abbe number for the d-line of the second lens, νd3 is the Abbe number for the d-line of the third lens, and νd4 is the Abbe number for the d-line of the fourth lens.

[0022] By satisfying the range of conditional expression (1), chromatic aberration can be corrected satisfactorily.

[0023] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (2). (2) 1.68 <r7 / D23 / bf<4.90 where r7 is the paraxial radius of curvature of the object-side surface of the fourth lens, D23 is the distance on the optical axis from the image-side surface of the second lens to the object-side surface of the third lens, and bf is the back focus.

[0024] By satisfying the range of conditional expression (2), it is possible to achieve a low profile and to make good corrections for astigmatism and distortion.

[0025] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (3). (3) 0.48 <D23 / f / D34<3.00 where D23 is the distance on the optical axis from the image-side surface of the second lens to the object-side surface of the third lens, D34 is the distance on the optical axis from the image-side surface of the third lens to the object-side surface of the fourth lens, and f is the focal length of the entire imaging lens system.

[0026] By satisfying the range of conditional expression (3), it becomes possible to make good correction for astigmatism and distortion.

[0027] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (4). (4)-1.75 <r7 / f4<-0.37 Here, r7 is the paraxial radius of curvature of the object-side surface of the fourth lens, and f4 is the focal length of the fourth lens.

[0028] By satisfying the range of conditional expression (4), chromatic aberration, spherical aberration, astigmatism, and distortion can be corrected satisfactorily.

[0029] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (5). (5) March 10 <D23 / f×100<16.90 Here, D23 is the distance on the optical axis from the image-side surface of the second lens to the object-side surface of the third lens, and f is the focal length of the entire imaging lens system.

[0030] By satisfying the range of conditional expression (5), it becomes possible to make good correction for astigmatism and distortion.

[0031] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (6). (6) 1.50 <f1 / f3<4.80 Here, f1 is the focal length of the first lens, and f3 is the focal length of the third lens.

[0032] By satisfying the range of conditional expression (6), it is possible to achieve a low profile and to make good corrections for spherical aberration, coma, astigmatism, curvature of field, and distortion.

[0033] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (7). (7) 0.58 <T2 / D23<3.70 Here, T2 is the thickness of the second lens on the optical axis, and D23 is the distance on the optical axis from the image-side surface of the second lens to the object-side surface of the third lens.

[0034] By satisfying the range of conditional expression (7), it is possible to achieve a low profile and to make good corrections for astigmatism and distortion.

[0035] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (8). (8) 0.80 <f1 / f<2.30 Here, f1 is the focal length of the first lens, and f is the focal length of the entire imaging lens system.

[0036] By satisfying the range of conditional expression (8), it is possible to appropriately set the positive refractive power and achieve a low height while suppressing the occurrence of spherical aberration, coma, astigmatism, curvature of field, and distortion.

[0037] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (9). (9) 10.45<|r2| / D12<44.00 where r2 is the paraxial radius of curvature of the image-side surface of the first lens, and D12 is the distance on the optical axis from the image-side surface of the first lens to the object-side surface of the second lens.

[0038] By satisfying the range of conditional expression (9), it is possible to achieve a low profile and to make good corrections for spherical aberration, astigmatism, curvature of field, and distortion.

[0039] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (10): (10)0.50 <T1 / T2<3.00 Here, T1 is the thickness of the first lens on the optical axis, and T2 is the thickness of the second lens on the optical axis.

[0040] By satisfying the range of conditional expression (10), it is possible to achieve a low profile and to make good corrections for spherical aberration, astigmatism, and distortion.

[0041] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (11). (11)-0.55 <r8 / f4<-0.13 Here, r8 is the paraxial radius of curvature of the image-side surface of the fourth lens, and f4 is the focal length of the fourth lens.

[0042] By satisfying the range of conditional expression (11), an appropriate back focus can be ensured, and chromatic aberration, coma, astigmatism, curvature of field, and distortion can be corrected satisfactorily.

[0043] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (12). (12)-0.55 <r6 / f<-0.10 Here, r6 is the paraxial radius of curvature of the image-side surface of the third lens, and f is the focal length of the entire imaging lens system.

[0044] By satisfying the range of conditional expression (12), it becomes possible to make good corrections for spherical aberration, coma, astigmatism, curvature of field, and distortion.

[0045] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (13). (13)0.25 <r7 / f<0.86 Here, r7 is the paraxial radius of curvature of the object-side surface of the fourth lens, and f is the focal length of the entire imaging lens system.

[0046] By satisfying the range of conditional expression (13), it becomes possible to make good correction for astigmatism and distortion.

[0047] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (14). (14)0.10 <r8 / f<0.36 Here, r8 is the paraxial radius of curvature of the image-side surface of the fourth lens, and f is the focal length of the entire imaging lens system.

[0048] By satisfying the range of conditional expression (14), it becomes possible to make good corrections for coma, astigmatism, curvature of field, and distortion.

[0049] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (15). (15)-0.37 <T4 / f4<-0.08 Here, T4 is the thickness of the fourth lens on the optical axis, and f4 is the focal length of the fourth lens.

[0050] By satisfying the range of conditional expression (15), coma, astigmatism, and distortion can be corrected satisfactorily.

[0051] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (16). (16)0.24 <f3 / f<0.89 Here, f3 is the focal length of the third lens, and f is the focal length of the entire imaging lens system.

[0052] By satisfying the range of conditional expression (16), it is possible to appropriately set the positive refractive power, achieve a low height, and achieve favorable correction of spherical aberration, coma, astigmatism, curvature of field, and distortion.

[0053] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (17). (17)-1.35 <f4 / f<-0.27 Here, f4 is the focal length of the fourth lens, and f is the focal length of the entire imaging lens system.

[0054] By satisfying the range of conditional expression (17), it is possible to appropriately set the negative refractive power, ensure an appropriate back focus, and achieve favorable correction of chromatic aberration, coma, astigmatism, curvature of field, and distortion.

[0055] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (18). (18)0.25 <f23 / f<1.15 Here, f23 is the combined focal length of the second and third lenses, and f is the focal length of the entire imaging lens system.

[0056] By satisfying the range of conditional expression (18), it is possible to achieve a low profile and to make good corrections for spherical aberration, astigmatism, and distortion.

[0057] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (19): (19)1.48 <r7 / r8<4.75 Here, r7 is the paraxial radius of curvature of the object-side surface of the fourth lens, and r8 is the paraxial radius of curvature of the image-side surface of the fourth lens.

[0058] By satisfying the range of conditional expression (19), it becomes possible to make good corrections for coma, astigmatism, curvature of field, and distortion.

[0059] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (20): (20)1.60 <r7 / T4<7.55 Here, r7 is the paraxial radius of curvature of the object-side surface of the fourth lens, and T4 is the thickness of the fourth lens on the optical axis.

[0060] By satisfying the range of conditional expression (20), it is possible to achieve a low profile and to make good corrections for spherical aberration, astigmatism, and distortion.

[0061] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (21). (21)-23.30 <r6 / D34<-4.70 Here, r6 is the paraxial radius of curvature of the image-side surface of the third lens, and D34 is the distance on the optical axis from the image-side surface of the third lens to the object-side surface of the fourth lens.

[0062] By satisfying the range of conditional expression (21), it becomes possible to make good corrections for spherical aberration, coma, astigmatism, curvature of field, and distortion.

[0063] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (22). (22)0.95 <T3 / (D23+D34)<4.50 where T3 is the thickness of the third lens on the optical axis, D23 is the distance on the optical axis from the image-side surface of the second lens to the object-side surface of the third lens, and D34 is the distance on the optical axis from the image-side surface of the third lens to the object-side surface of the fourth lens.

[0064] By satisfying the range of conditional expression (22), it is possible to achieve a low profile and to make good corrections for astigmatism and distortion.

[0065] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (23). (23)4.00<|r2| / D12 / f3<23.50 where r2 is the paraxial radius of curvature of the image-side surface of the first lens, D12 is the distance on the optical axis from the image-side surface of the first lens to the object-side surface of the second lens, and f3 is the focal length of the third lens.

[0066] By satisfying the range of conditional expression (23), it is possible to achieve a low profile and to make good corrections for spherical aberration, astigmatism, curvature of field, and distortion.

[0067] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (24). (24)-0.35 <r7 / f / f4<-0.06 Here, r7 is the paraxial radius of curvature of the object-side surface of the fourth lens, f is the focal length of the entire imaging lens system, and f4 is the focal length of the fourth lens.

[0068] By satisfying the range of conditional expression (24), it becomes possible to make good correction for astigmatism and distortion.

[0069] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (25). (25)18<νd4<33 Here, νd4 is the Abbe number for the d-line of the fourth lens.

[0070] By satisfying the range of conditional expression (25), chromatic aberration can be corrected satisfactorily.

[0071] The present invention makes it possible to obtain an imaging lens that satisfies the requirements for a low F-number and a wide angle, while also achieving a further reduction in height and that satisfies the requirements for aberrations in the near-infrared light region. Furthermore, because the imaging lens according to the present invention satisfies the requirements for aberrations, the number of lenses can be reduced, and by reducing the amount of lens material used, an environmentally friendly imaging lens can be provided. [Brief explanation of the drawings]

[0072] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of an imaging lens according to a first embodiment of the present invention. [Figure 2] 3A to 3C are aberration diagrams showing spherical aberration, astigmatism, and distortion of the imaging lens according to Example 1 of the present invention. [Figure 3] FIG. 10 is a cross-sectional view showing a schematic configuration of an imaging lens according to a second embodiment of the present invention. [Figure 4] 5A to 5C are aberration diagrams showing spherical aberration, astigmatism, and distortion of the imaging lens according to Example 2 of the present invention. [Figure 5] FIG. 10 is a cross-sectional view showing a schematic configuration of an imaging lens according to a third embodiment of the present invention. [Figure 6] 10A to 10C are aberration diagrams showing spherical aberration, astigmatism, and distortion of the imaging lens according to Example 3 of the present invention. [Figure 7] FIG. 10 is a cross-sectional view showing a schematic configuration of an imaging lens according to a fourth embodiment of the present invention. [Figure 8] 10A to 10C are aberration diagrams showing spherical aberration, astigmatism, and distortion of the imaging lens according to Example 4 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0073] An embodiment of the present invention will be described in detail below with reference to the drawings. Figures 1, 3, 5, and 7 are cross-sectional views showing the schematic configurations of imaging lenses according to Examples 1 to 4 of this embodiment. Since the basic lens configuration is the same in all examples, the imaging lens according to this embodiment will be described here with reference to the cross-sectional view of Example 1.

[0074] As shown in FIG. 1, the imaging lens according to this embodiment is composed of, in order from the object side to the image side, a first lens L1 having positive refractive power, a second lens L2 having positive refractive power, a third lens L3 having positive refractive power, and a fourth lens L4 having negative refractive power.

[0075] A filter FL, such as a visible light cut filter or a dual-pass filter that transmits light in a specific wavelength range, and a cover glass CG are disposed between the fourth lens L4 and the imaging plane IMG. The filter FL and cover glass CG can be omitted. Instead of disposing various filters such as the filter FL, a coating that functions similarly to the various filters can be applied to the lens surface of one of the lenses.

[0076] The aperture stop ST is located on the object side of the first lens L1, which facilitates correction of various aberrations and also facilitates control of the angle at which light rays at high image heights enter the image sensor. Note that the position of the aperture stop ST is not limited to the object side of the first lens L1, and may be located as appropriate depending on the specifications of the image sensor.

[0077] The first lens L1 has positive refractive power and is a meniscus shape with a convex surface on the object side in the paraxial direction. This reduces the height of the imaging lens while suppressing the occurrence of spherical aberration, coma, astigmatism, field curvature, and distortion. The shape of the image-side surface of the first lens L1 is not limited to the shape according to the first embodiment, and may be a shape that is convex in the paraxial direction. A biconvex shape is advantageous for reducing the height of the imaging lens because it can increase the positive refractive power.

[0078] The second lens L2 has positive refractive power and is a meniscus shape with a convex surface on the image side paraxially. This allows for good correction of coma, astigmatism, and distortion. The refractive power of the second lens L2 is not limited to being positive and may be negative. Furthermore, the second lens L2 is not limited to being a meniscus shape with a convex surface on the image side and may be a meniscus shape with a concave surface on the image side.

[0079] The third lens L3 has positive refractive power and a meniscus shape with a convex surface on the image side in the paraxial direction. This allows for a low profile while effectively correcting spherical aberration, coma, astigmatism, field curvature, and distortion. The shape of the object-side surface of the third lens L3 is not limited to the shape according to the first embodiment, and may be a shape that is convex on the paraxial direction.

[0080] The fourth lens L4 has negative refractive power and is a meniscus shape with a concave surface on the image side paraxially. This allows for excellent correction of chromatic aberration, coma, astigmatism, field curvature, and distortion. In addition, by making the surface on the image side paraxially concave, an appropriate back focus is ensured while maintaining a low profile.

[0081] Furthermore, the object-side surface of the fourth lens L4 is formed as an aspheric surface having a pole point at a position other than on the optical axis X. This allows for better correction of astigmatism and distortion.

[0082] Furthermore, the image-side surface of the fourth lens L4 is formed as an aspheric surface with a pole point at a position other than on the optical axis X. This allows for better correction of coma, astigmatism, field curvature, and distortion.

[0083] In the imaging lens according to this embodiment, all of the first lens L1 to the fourth lens L4 are each composed of a single lens. A configuration consisting of only single lenses allows for the frequent use of aspherical surfaces, which are effective in correcting aberrations. In this embodiment, appropriate aspherical surfaces are formed on the lens surfaces of the second lens L2 to the fourth lens L4, thereby achieving good correction of various aberrations. Furthermore, since the number of steps can be reduced compared to when a cemented lens is used, manufacturing costs can be kept down.

[0084] In the imaging lens according to this embodiment, the first lens L1 is preferably made of a glass material. For example, in an imaging lens mounted on an interior camera of a car, the temperature inside the car can be high, so by making the first lens L1 from a highly heat-resistant glass material, performance fluctuations can be suppressed even when the environmental temperature changes. By making the first lens L1 from a glass material, stable optical characteristics can be obtained even when used in a harsh environment.

[0085] In the imaging lens according to this embodiment, both the object-side surface and the image-side surface of the first lens L1 are formed as spherical surfaces. This allows the manufacturing costs of the first lens L1 to be reduced. This is particularly effective when the first lens L1 is made of a glass material. Depending on the required optical performance, the lens surfaces may be formed aspherically.

[0086] In the imaging lens according to this embodiment, the second lens L2 to the fourth lens L4 are preferably made of a plastic material. By using a plastic material, it is possible to form an aspherical shape with high precision, and it is also possible to achieve weight reduction and cost reduction.

[0087] It is desirable that all of the lens surfaces of the second lens L2 to the fourth lens L4 be aspherical, but depending on the required performance, spherical surfaces may be used, which are easier to manufacture.

[0088] The lens materials used are not limited to those used in this embodiment. For example, by using a plastic material for the first lens L1, it is possible to form an aspherical shape with high precision, and it is also possible to aim for further weight reduction and cost reduction. Furthermore, by using a glass material for the second lens L2 to the fourth lens L4, it is also possible to aim for further improvement in performance.

[0089] The imaging lens of this embodiment provides desirable effects by satisfying the following conditional expressions (1) to (25). (1) 0.86<νd3 / (νd2+νd4)<1.65 (2) 1.68 <r7 / D23 / bf<4.90 (3) 0.48 <D23 / f / D34<3.00 (4)-1.75 <r7 / f4<-0.37 (5) March 10 <D23 / f×100<16.90 (6) 1.50 <f1 / f3<4.80 (7) 0.58 <T2 / D23<3.70 (8) 0.80 <f1 / f<2.30 (9) 10.45<|r2| / D12<44.00 (10)0.50 <T1 / T2<3.00 (11)-0.55 <r8 / f4<-0.13 (12)-0.55 <r6 / f<-0.10 (13)0.25 <r7 / f<0.86 (14)0.10 <r8 / f<0.36 (15)-0.37 <T4 / f4<-0.08 (16)0.24 <f3 / f<0.89 (17)-1.35 <f4 / f<-0.27 (18)0.25 <f23 / f<1.15 (19)1.48 <r7 / r8<4.75 (20)1.60 <r7 / T4<7.55 (21)-23.30 <r6 / D34<-4.70 (22)0.95 <T3 / (D23+D34)<4.50 (23)4.00<|r2| / D12 / f3<23.50 (24)-0.35 <r7 / f / f4<-0.06 (25)18<νd4<33 however, r2: paraxial radius of curvature of the image-side surface of the first lens L1, r6: paraxial radius of curvature of the image-side surface of the third lens L3, r7: paraxial radius of curvature of the object side surface of the fourth lens L4, r8: paraxial radius of curvature of the image-side surface of the fourth lens L4, D12: the distance on the optical axis X from the image-side surface of the first lens L1 to the object-side surface of the second lens L2, D23: the distance on the optical axis X from the image-side surface of the second lens L2 to the object-side surface of the third lens L3, D34: the distance on the optical axis X from the image-side surface of the third lens L3 to the object-side surface of the fourth lens L4, T1: thickness of the first lens L1 on the optical axis X, T2: thickness of the second lens L2 on the optical axis X, T3: thickness of the third lens L3 on the optical axis X, T4: thickness of the fourth lens L4 on the optical axis X, f: focal length of the entire imaging lens system, f3: focal length of the third lens L3, f4: focal length of the fourth lens L4, f23: The combined focal length of the second lens L2 and the third lens L3. bf: back focus, νd2: Abbe number of the second lens L2 for the d line, νd3: Abbe number of the third lens L3 for the d line, νd4: Abbe number for the d line of the fourth lens L4, Let's say.

[0090] It is not necessary to satisfy all of the above conditional expressions, and by satisfying each conditional expression individually, it is possible to obtain the effects corresponding to each conditional expression.

[0091] Furthermore, the imaging lens of this embodiment will achieve more desirable effects if it satisfies the following conditional expressions (1a) to (25a). (1a)0.98<νd3 / (νd2+νd4)<1.38 (2a) 1.85 <r7 / D23 / bf<4.50 (3a) 0.55 <D23 / f / D34<2.50 (4a)-1.45 <r7 / f4<-0.45 (5a)4.65 <D23 / f×100<14.50 (6a) 1.80 <f1 / f3<4.00 (7a) 0.65 <T2 / D23<3.05 (8a) 0.95 <f1 / f<1.90 (9a) 14.00<|r2| / D12<37.60 (10a)0.75 <T1 / T2<2.50 (11a)-0.45 <r8 / f4<-0.19 (12a)-0.45 <r6 / f<-0.15 (13a) 0.35 <r7 / f<0.75 (14a)0.15 <r8 / f<0.30 (15a)-0.30 <T4 / f4<-0.10 (16a)0.35 <f3 / f<0.75 (17a)-1.15 <f4 / f<-0.40 (18a)0.35 <f23 / f<0.95 (19a)1.80 <r7 / r8<4.00 (20a)2.40 <r7 / T4<6.30 (21a)-19.40 <r6 / D34<-7.05 (22a)1.45 <T3 / (D23+D34)<3.75 (23a)6.10<|r2| / D12 / f3<19.60 (24a)-0.30 <r7 / f / f4<-0.09 (25a)21<νd4<29 However, the symbols in each conditional expression are the same as those explained in the previous paragraph. Note that for conditional expressions (1a) to (25a), the lower limit and upper limit of each may be the lower limit and upper limit of the corresponding conditional expressions (1) to (25).

[0092] In this embodiment, the aspherical shape adopted for the aspherical lens surface is expressed by Equation 1, where Z is the axis in the optical axis direction, H is the height in the direction perpendicular to the optical axis, R is the paraxial radius of curvature, k is the conic coefficient, and An is the n-th order aspherical coefficient.

[0093]

number

[0094] Next, examples of the imaging lens according to this embodiment are shown. In each example, f denotes the focal length of the entire imaging lens system, Fno denotes the F-number, ω denotes the half angle of view, ih denotes the maximum image height, and TTL denotes the total optical length. Here, the total optical length is the distance on the optical axis from the object-side surface of the optical element located closest to the object to the imaging plane IMG. Note that the values ​​of the total optical length and back focus are the distances obtained by converting the thicknesses of the filter FL, cover glass CG, etc., located between the imaging lens and the imaging plane IMG into air.

[0095] Additionally, i denotes the surface number counted from the object side, r denotes the paraxial radius of curvature, d denotes the distance between lens surfaces (surface spacing) on ​​the optical axis X, Nd denotes the refractive index at the reference wavelength d-line (588 nm), and νd denotes the Abbe number for the reference wavelength d-line. Note that aspherical surfaces are indicated by adding an asterisk (*) after the surface number i.

[0096] Example 1 Basic lens data [Table 1]

[0097] FIG. 2 is an aberration diagram showing the spherical aberration (mm), astigmatism (mm), and distortion (%) of the imaging lens of Example 1. The spherical aberration diagram shows the amount of aberration for each wavelength of 910 nm, 940 nm, 960 nm, and 980 nm. The astigmatism diagram and distortion diagram show the amount of aberration at 940 nm. The astigmatism diagram also shows the amount of aberration (solid line) at the sagittal image plane S and the amount of aberration (dashed line) at the tangential image plane T (the same applies to FIG. 4). As shown in FIG. 2, the imaging lens of Example 1 can satisfactorily correct each aberration in the near-infrared light region.

[0098] Example 2 Basic lens data [Table 2]

[0099] As shown in FIG. 4, the imaging lens according to the second embodiment can also effectively correct each aberration in the near-infrared light range.

[0100] Example 3 Basic lens data [Table 3]

[0101] FIG. 6 is an aberration diagram showing the spherical aberration (mm), astigmatism (mm), and distortion (%) of the imaging lens of Example 3. The spherical aberration diagram shows the amount of aberration for each wavelength of 440 nm, 580 nm, 650 nm, and 940 nm. The astigmatism diagram and distortion diagram show the amount of aberration at 940 nm. The astigmatism diagram also shows the amount of aberration (solid line) at the sagittal image plane S and the amount of aberration (dashed line) at the tangential image plane T. As shown in FIG. 6, the imaging lens of Example 3 can satisfactorily correct each aberration in the visible light range as well as the near-infrared light range.

[0102] The imaging lens according to the third embodiment enables not only imaging using infrared illumination but also color imaging using sunlight during the day.

[0103] Example 4 Basic lens data [Table 4]

[0104] FIG. 8 is an aberration diagram showing the spherical aberration (mm), astigmatism (mm), and distortion (%) of the imaging lens of Example 4. The spherical aberration diagram shows the amount of aberration for each wavelength of 900 nm, 940 nm, 960 nm, and 999 nm. The astigmatism diagram and distortion diagram show the amount of aberration at 940 nm. The astigmatism diagram also shows the amount of aberration (solid line) at the sagittal image plane S and the amount of aberration (dashed line) at the tangential image plane T. As shown in FIG. 8, the imaging lens of Example 4 can also effectively correct each aberration in the near-infrared light region.

[0105] Below, values ​​corresponding to the conditional expressions (1) to (25) according to Examples 1 to 4 (values ​​corresponding to the conditional expressions) are shown.

[0106] [Table 5] [Industrial Applicability]

[0107] When the imaging lens according to the present invention is applied to a product equipped with a camera function, it contributes to reducing the height, widening the angle, and reducing the F-number of the camera, and also provides good optical performance in the near-infrared light region. Note that the imaging lens according to the present invention is not limited to in-vehicle cameras for automobiles, etc., but can also be applied to cameras mounted on surveillance cameras, biometric authentication devices, etc. [Explanation of symbols]

[0108] X optical axis ST aperture stop L1 First lens L2 Second lens L3 Third lens L4 4th lens FL Filter CG cover glass IMG imaging surface

Claims

1. Arranged in order from the object side to the image side, a first lens having a positive refractive power; a second lens having a positive or negative refractive power; a third lens having a positive refractive power; a fourth lens having negative refractive power, the first lens has a convex surface on the object side in a paraxial direction, the second lens has a meniscus shape paraxially; the third lens has a paraxial convex surface facing the image side, the fourth lens has a meniscus shape with a concave surface on the image side in a paraxial direction, An imaging lens characterized by satisfying the following conditional expressions (1), (2), and (3): (1) 0.86<νd3 / (νd2+νd4)<1.65 (2) 1.68<r7 / D23 / bf<4.90 (3) 0.48<D23 / f / D34<3.00 however, νd2: Abbe number of the second lens with respect to the d line, νd3: Abbe number of the third lens with respect to the d line, νd4: Abbe number of the fourth lens with respect to the d line, r7: paraxial radius of curvature of the object side surface of the fourth lens, D23: the distance on the optical axis from the image-side surface of the second lens to the object-side surface of the third lens, bf: back focus, D34: the distance on the optical axis from the image-side surface of the third lens to the object-side surface of the fourth lens, f: focal length of the entire imaging lens system.

2. 2. The imaging lens according to claim 1, wherein the following conditional expression (4) is satisfied: (4) -1.75<r7 / f4<-0.37 however, r7: paraxial radius of curvature of the object side surface of the fourth lens, f4: the focal length of the fourth lens.

3. 2. The imaging lens according to claim 1, wherein the following conditional expression (5) is satisfied: (5) 3.10<D23 / f×100<16.90 however, D23: the distance on the optical axis from the image-side surface of the second lens to the object-side surface of the third lens, f: focal length of the entire imaging lens system.

4. 2. The imaging lens according to claim 1, wherein the following conditional expression (6) is satisfied: (6) 1.50<f1 / f3<4.80 however, f1: focal length of the first lens, f3: the focal length of the third lens.

5. 2. The imaging lens according to claim 1, wherein the following conditional expression (7) is satisfied: (7) 0.58<T2 / D23<3.70 however, T2: the thickness of the second lens on the optical axis, D23: The distance on the optical axis from the image-side surface of the second lens to the object-side surface of the third lens.

6. 2. The imaging lens according to claim 1, wherein the following conditional expression (8) is satisfied: (8) 0.80<f1 / f<2.30 however, f1: focal length of the first lens, f: focal length of the entire imaging lens system.

7. 2. The imaging lens according to claim 1, wherein the following conditional expression (9) is satisfied: (9) 10.45<|r2| / D12<44.00 however, r2: paraxial radius of curvature of the image-side surface of the first lens, D12: The distance on the optical axis from the image-side surface of the first lens to the object-side surface of the second lens.

Images