Imaging lens

Abstract

Provided is an imaging lens that is compact, has a small f-number, and can be satisfactorily corrected for various aberrations in a wavelength region from visible light to near-infrared light although being wide-angle.　This imaging lens comprises, in order from the object side to the image side: a first lens L1 having negative refractive power; a second lens L2 having positive refractive power; a third lens L3 having positive refractive power; a fourth lens L4 having positive refractive power; a fifth lens L5 having negative refractive power; and a sixth lens L6 having positive refractive power. The second lens L2 has a concave surface on the image side in a paraxial region, and the fifth lens L5 has a convex surface on the image side in the paraxial region. When the distance on an optical axis X from an image-side surface of the first lens L1 to an object-side surface of the second lens L2 is defined as D12, and the focal length of the entire imaging lens system is defined as f, the following conditional expression is satisfied. (1): 1.10 < D12 / f < 3.55

Description

Imaging lens

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

[0002] In recent years, the number of automobiles equipped with onboard cameras has been increasing, and their functions, such as obstacle detection and driver monitoring, are evolving further to improve vehicle safety and ensure a comfortable driving experience for drivers.

[0003] Imaging lenses for vehicle-mounted cameras are required to be compact and have a wide angle of view. They are also required to have a small F-number and high resolution performance in the visible to near-infrared light range so that they can be used not only in bright environments such as daytime but also in dark environments such as nighttime.

[0004] As an imaging lens that is small in size, has a small F-number, and has good performance in the visible light to near-infrared light range, for example, an imaging lens such as that disclosed in Patent Document 1 below is known.

[0005] Patent Document 1 discloses an imaging lens that includes, in order from the object side, a first lens having negative power and a concave surface facing the image side, a second lens having positive power, an aperture stop, a third lens having negative power, a fourth lens having positive power, a fifth lens having a convex surface facing the image side and positive power, and a sixth lens having negative power.

[0006] JP 2010-72622 A

[0007] The imaging lens of Patent Document 1 has a bright F-number of 1.50 to 2.0 and provides good correction of aberrations in the visible to near-infrared light range. However, the total optical length is 16 mm or more and the total angle of view is approximately 43 to 58°, making it difficult to satisfy the specifications for miniaturization and wide-angle viewing that are currently required.

[0008] 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 compactness and a wide angle, while having a small F-number and high resolving power with various aberrations well corrected in the wavelength region from visible light to near-infrared light.

[0009] An imaging lens according to the present invention comprises, arranged in order from the object side to the image side, a first lens having negative refractive power, a second lens having positive refractive power, a third lens having positive refractive power, a fourth lens having positive refractive power, a fifth lens having negative refractive power, and a sixth lens having positive refractive power. The second lens has a concave surface on the image side in a paraxial view, and the fifth lens has a convex surface on the image side in a paraxial view. In this specification, the terms "convex," "concave," and "flat" refer to the shape on the paraxial view, and the term "refractive power" refers to the refractive power on the paraxial view unless otherwise specified.

[0010] The first lens has negative refractive power, thereby achieving a wider angle of view and effectively correcting chromatic aberration, spherical aberration, coma, astigmatism, and curvature of field.

[0011] The second lens has positive refractive power and is concave on the image side in the paraxial direction, thereby effectively correcting chromatic aberration, spherical aberration, coma, astigmatism, and field curvature.

[0012] The third lens has a positive refractive power, and thus effectively corrects chromatic aberration and astigmatism.

[0013] The fourth lens has a positive refractive power, thereby reducing the height of the imaging lens and effectively correcting chromatic aberration, spherical aberration, coma, and astigmatism.

[0014] The fifth lens has negative refractive power and has a convex surface on the image side in the paraxial direction, thereby effectively correcting chromatic aberration, spherical aberration, coma, astigmatism, and curvature of field.

[0015] The sixth lens has a positive refractive power, thereby reducing the height of the imaging lens and effectively correcting chromatic aberration, spherical aberration, coma, and curvature of field.

[0016] In the imaging lens having the above configuration, it is desirable that the first lens has a meniscus shape with a convex surface on the object side in the paraxial direction.

[0017] By making the first lens a meniscus shape with a convex surface on the object side in the paraxial direction, it becomes possible to take in a wide range of ray bundles while suppressing the occurrence of various aberrations.

[0018] In the imaging lens having the above configuration, it is desirable that the second lens has a convex surface on the object side in the paraxial direction.

[0019] By forming the object-side surface of the second lens as a paraxial convex surface, it becomes possible to suppress the occurrence of various aberrations while achieving good correction of chromatic aberration, spherical aberration, coma, astigmatism, and curvature of field.

[0020] In the imaging lens having the above configuration, it is desirable that the third lens has a meniscus shape with a concave surface on the object side in the paraxial direction.

[0021] By forming the object-side surface of the third lens as a paraxially concave surface, chromatic aberration and astigmatism can be effectively corrected, and by forming the third lens as a paraxially meniscus shape, field curvature and distortion can be effectively corrected.

[0022] In the imaging lens having the above configuration, it is desirable that the fourth lens has a biconvex shape in the paraxial direction.

[0023] By making the fourth lens have a biconvex shape in the paraxial direction, the positive refractive power is strengthened to achieve a low profile, and chromatic aberration and astigmatism can be corrected satisfactorily.

[0024] In the imaging lens having the above configuration, it is desirable that the fifth lens has a concave surface on the object side in the paraxial direction.

[0025] By forming the object-side surface of the fifth lens as a concave surface in the paraxial direction, it becomes possible to make good corrections for chromatic aberration, spherical aberration, coma, astigmatism, curvature of field, and distortion.

[0026] In the imaging lens having the above configuration, it is desirable that the sixth lens has a convex surface on the object side in the paraxial direction.

[0027] By forming the object-side surface of the sixth lens to be a convex surface on the paraxial line, chromatic aberration, spherical aberration, coma, and curvature of field can be corrected satisfactorily.

[0028] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (1): (1) 1.10<D12 / f<3.55, where 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 f is the focal length of the entire imaging lens system.

[0029] By satisfying the range of conditional expression (1), it is possible to achieve a low profile and to make good corrections for chromatic aberration, spherical aberration, coma, curvature of field, and distortion.

[0030] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (2): (2) 0.50<T1 / f<1.95 where T1 is the thickness of the first lens on the optical axis, and f is the focal length of the entire imaging lens system.

[0031] By satisfying the range of conditional expression (2), it is possible to achieve a low profile and to make good corrections for chromatic aberration, spherical aberration, coma, curvature of field, and distortion.

[0032] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (3): (3) 0.20<D23 / f<0.85 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, and f is the focal length of the entire imaging lens system.

[0033] By satisfying the range of conditional expression (3), it is possible to achieve a low profile and to make good corrections for chromatic aberration, spherical aberration, coma, astigmatism, and curvature of field.

[0034] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (4): (4) 1.00<T6 / bf<4.30 where T6 is the thickness of the sixth lens on the optical axis, and bf is the back focus.

[0035] By satisfying the range of conditional expression (4), an appropriate back focus can be ensured, and chromatic aberration, spherical aberration, coma, and curvature of field can be corrected satisfactorily.

[0036] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (5): (5) 1.20<T1 / T2<4.20 where 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.

[0037] By satisfying the range of conditional expression (5), chromatic aberration, spherical aberration, coma, astigmatism, and curvature of field can be corrected satisfactorily.

[0038] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (6): (6) 0.30<R1r / T1<1.60 where R1r is the paraxial radius of curvature of the image-side surface of the first lens, and T1 is the thickness of the first lens on the optical axis.

[0039] By satisfying the range of conditional expression (6), chromatic aberration, spherical aberration, coma, curvature of field, and distortion can be corrected satisfactorily.

[0040] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (7): (7) 0.35<R6f / T6<1.40 where R6f is the paraxial radius of curvature of the object-side surface of the sixth lens, and T6 is the thickness of the sixth lens on the optical axis.

[0041] By satisfying the range of conditional expression (7), chromatic aberration, spherical aberration, coma, and curvature of field can be corrected satisfactorily.

[0042] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (8): (8) 2.35<D12 / T2<8.55, where 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 T2 is the thickness of the second lens on the optical axis.

[0043] By satisfying the range of conditional expression (8), it is possible to achieve a low profile and to make good corrections for curvature of field and distortion while suppressing the occurrence of various aberrations.

[0044] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (9): (9) 0.35<T2 / D23<1.25 where 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.

[0045] By satisfying the range of conditional expression (9), chromatic aberration, spherical aberration, coma, astigmatism, and curvature of field can be corrected satisfactorily.

[0046] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (10): (10) 0.25<T4 / T6<0.80 where T4 is the thickness of the fourth lens on the optical axis, and T6 is the thickness of the sixth lens on the optical axis.

[0047] By satisfying the range of conditional expression (10), it is possible to achieve a low profile and to make good corrections for chromatic aberration, spherical aberration, coma, astigmatism, curvature of field, and distortion.

[0048] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (11): (11) 2.10<T4 / D45<10.80 where T4 is the thickness of the fourth lens on the optical axis, and D45 is the distance on the optical axis from the image-side surface of the fourth lens to the object-side surface of the fifth lens.

[0049] By satisfying the range of conditional expression (11), chromatic aberration, spherical aberration, coma, and curvature of field can be corrected satisfactorily.

[0050] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (12): (12) 0.07<R1r / R1f<0.30 where R1r is the paraxial radius of curvature of the image-side surface of the first lens, and R1f is the paraxial radius of curvature of the object-side surface of the first lens.

[0051] By satisfying the range of conditional expression (12), it becomes possible to take in a wide range of ray bundles while suppressing the occurrence of various aberrations, and also to make good corrections for curvature of field and distortion.

[0052] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (13): (13) −0.35<R2r / R3f<−0.07 where R2r is the paraxial radius of curvature of the image-side surface of the second lens, and R3f is the paraxial radius of curvature of the object-side surface of the third lens.

[0053] By satisfying the range of conditional expression (13), it becomes possible to make good correction for curvature of field and distortion.

[0054] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (14): (14) 2.30<R3f / R3r<8.50 where R3f is the paraxial radius of curvature of the third lens on the object side, and R3r is the paraxial radius of curvature of the third lens on the image side.

[0055] By satisfying the range of conditional expression (14), chromatic aberration and distortion can be corrected satisfactorily.

[0056] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (15): (15) −2.30<R5r / R6f<−0.64 where R5r is the paraxial radius of curvature on the image side of the fifth lens, and R6f is the paraxial radius of curvature on the object side of the sixth lens.

[0057] By satisfying the range of conditional expression (15), chromatic aberration, spherical aberration, coma, astigmatism, curvature of field, and distortion can be corrected satisfactorily.

[0058] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (16): (16) −0.25<R6f / R6r<−0.05 where R6f is the paraxial radius of curvature of the sixth lens on the object side, and R6r is the paraxial radius of curvature of the sixth lens on the image side.

[0059] By satisfying the range of conditional expression (16), chromatic aberration, spherical aberration, coma, and curvature of field can be corrected satisfactorily.

[0060] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (17): (17) 0.20<R1r / D12<0.70 where R1r 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.

[0061] By satisfying the range of conditional expression (17), it is possible to achieve a low profile and to make good corrections for chromatic aberration, spherical aberration, coma, astigmatism, and curvature of field.

[0062] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (18): (18) 1.55<R2r / D23<4.90 where R2r is the paraxial radius of curvature of the image-side surface of the second lens, 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.

[0063] By satisfying the range of conditional expression (18), chromatic aberration, spherical aberration, coma, astigmatism, and curvature of field can be corrected satisfactorily.

[0064] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (19): (19) -22.80<R6r / bf<-6.40 where R6r is the paraxial radius of curvature of the image-side surface of the sixth lens, and bf is the back focus.

[0065] By satisfying the range of conditional expression (19), an appropriate back focus can be ensured, and chromatic aberration, spherical aberration, coma, and curvature of field can be corrected satisfactorily.

[0066] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (20): (20) −7.10<R6r / f6<−1.80 where R6r is the paraxial radius of curvature of the image-side surface of the sixth lens, and f6 is the focal length of the sixth lens.

[0067] By satisfying the range of conditional expression (20), it is possible to achieve a low profile and to make good corrections for chromatic aberration, spherical aberration, coma, and curvature of field.

[0068] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (21): (21) −19.0<R3f / f<−4.0 where R3f is the paraxial radius of curvature of the object-side surface of the third lens, and f is the focal length of the entire imaging lens system.

[0069] By satisfying the range of conditional expression (21), chromatic aberration and astigmatism can be corrected satisfactorily.

[0070] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (22): (22) −4.80<R3f / f3<−1.00 where R3f is the paraxial radius of curvature of the object-side surface of the third lens, and f3 is the focal length of the third lens.

[0071] By satisfying the range of conditional expression (22), chromatic aberration and distortion can be corrected satisfactorily.

[0072] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (23): (23) 0.55<R5r / f5<1.80 where R5r is the paraxial radius of curvature of the image-side surface of the fifth lens, and f5 is the focal length of the fifth lens.

[0073] By satisfying the range of conditional expression (23), chromatic aberration, spherical aberration, coma, astigmatism, curvature of field, and distortion can be corrected satisfactorily.

[0074] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (24): (24) 0.35<D23 / bf<1.45 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, and bf is the back focus.

[0075] By satisfying the range of conditional expression (24), chromatic aberration, spherical aberration, coma, astigmatism, and curvature of field can be corrected satisfactorily.

[0076] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (25): (25) 0.10<R2r / f2<0.40 where R2r is the paraxial radius of curvature of the image-side surface of the second lens, and f2 is the focal length of the second lens.

[0077] By satisfying the range of conditional expression (25), chromatic aberration, spherical aberration, coma, astigmatism, and curvature of field can be corrected satisfactorily.

[0078] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (26): (26) -3.70<f1 / f<-1.35 where f1 is the focal length of the first lens, and f is the focal length of the entire imaging lens system.

[0079] By satisfying the range of conditional expression (26), it is possible to widen the angle of view and to make good corrections for chromatic aberration, spherical aberration, coma, and distortion.

[0080] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (27): (27) 3.10<f2 / f<12.50 where f2 is the focal length of the second lens, and f is the focal length of the entire imaging lens system.

[0081] By satisfying the range of conditional expression (27), chromatic aberration, spherical aberration, coma, astigmatism, and curvature of field can be corrected satisfactorily.

[0082] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (28): (28) 1.80<f3 / f<6.30 where f3 is the focal length of the third lens, and f is the focal length of the entire imaging lens system.

[0083] By satisfying the range of conditional expression (28), chromatic aberration and astigmatism can be corrected satisfactorily.

[0084] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (29): (29) 0.90<f6 / f<3.00 where f6 is the focal length of the sixth lens, and f is the focal length of the entire imaging lens system.

[0085] By satisfying the range of conditional expression (29), it is possible to achieve a low profile and to make good corrections for chromatic aberration, spherical aberration, coma, and curvature of field.

[0086] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (30): (30) -700<f45 / f<-12 where f45 is the combined focal length of the fourth and fifth lenses, and f is the focal length of the entire imaging lens system.

[0087] By satisfying the range of conditional expression (30), coma, astigmatism, and distortion can be corrected satisfactorily.

[0088] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (31): (31) -350<f45 / f6<-7 where f45 is the combined focal length of the fourth and fifth lenses, and f6 is the focal length of the sixth lens.

[0089] By satisfying the range of conditional expression (31), it becomes possible to make good correction for curvature of field and distortion.

[0090] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (32): (32) 60°<ω<120°, where ω is the half angle of view.

[0091] By satisfying the range of conditional expression (32), it becomes possible to make the imaging lens smaller and to widen the angle of view.

[0092] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (33): (33) 13<νd2<28 where νd2 is the Abbe number for the d-line of the second lens.

[0093] By satisfying the range of conditional expression (33), chromatic aberration can be corrected satisfactorily.

[0094] The present invention makes it possible to obtain an imaging lens that has a wide angle, is compact, has a small F-number, and has high resolving power with various aberrations well corrected in the wavelength range from visible light to near-infrared light. Furthermore, because the imaging lens according to the present invention well corrects various 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.

[0095] FIG. 1 is a cross-sectional view showing a schematic configuration of an imaging lens according to Example 1 of the present invention. FIG. 2 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging lens according to Example 1 of the present invention. FIG. 3 is a cross-sectional view showing a schematic configuration of an imaging lens according to Example 2 of the present invention. FIG. 4 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging lens according to Example 2 of the present invention. FIG. 5 is a cross-sectional view showing a schematic configuration of an imaging lens according to Example 3 of the present invention. FIG. 6 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging lens according to Example 3 of the present invention.

[0096] An embodiment of the present invention will now be described in detail with reference to the drawings. Figures 1, 3, and 5 are cross-sectional views showing the schematic configurations of imaging lenses according to Examples 1 to 3 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.

[0097] 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 negative refractive power, a second lens L2 having positive refractive power, a third lens L3 having positive refractive power, a fourth lens L4 having positive refractive power, a fifth lens L5 having negative refractive power, and a sixth lens L6 having positive refractive power.

[0098] A filter FL, such as a low-pass filter or a band-pass filter that cuts off a specific wavelength range, and a cover glass CG are disposed between the sixth lens L6 and the imaging plane IMG. Note that the filter FL and the cover glass CG can be omitted. Furthermore, instead of disposing various filters such as the filter FL, a coating that functions similarly to the various filters may be applied to the lens surface of one of the lenses.

[0099] The first lens L1 has negative refractive power and a meniscus shape with a convex surface on the object side in the paraxial direction. This allows the imaging lens to capture a wide range of light rays while suppressing the occurrence of various aberrations, thereby achieving a wide angle of view. It also effectively corrects chromatic aberration, spherical aberration, coma, astigmatism, and field curvature.

[0100] The second lens L2 has positive refractive power and a meniscus shape with a concave surface on the image side paraxially, thereby suppressing the occurrence of various aberrations while effectively correcting chromatic aberration, spherical aberration, coma, astigmatism, and field curvature.

[0101] The third lens L3 has positive refractive power and is a meniscus lens with a concave surface on the object side in the paraxial direction, thereby effectively correcting chromatic aberration and astigmatism.

[0102] The fourth lens L4 has positive refractive power and a biconvex shape with convex surfaces on both the object side and the image side in the paraxial direction, thereby achieving a low profile for the imaging lens while effectively correcting chromatic aberration, spherical aberration, coma, and astigmatism.

[0103] The fifth lens L5 has negative refractive power and a meniscus shape with a convex surface on the image side paraxially, thereby providing excellent correction for chromatic aberration, spherical aberration, coma, astigmatism, field curvature, and distortion.

[0104] The sixth lens L6 has positive refractive power and is biconvex with convex surfaces on both the object side and the image side in the paraxial direction, thereby achieving a low profile for the imaging lens while effectively correcting chromatic aberration, spherical aberration, coma, and field curvature.

[0105] In the imaging lens according to this embodiment, the aperture stop ST is disposed between the second lens L2 and the third lens L3, thereby effectively correcting distortion. It also has the effect of blocking stray light unnecessary for imaging. The position of the aperture stop ST is not limited to between the second lens L2 and the third lens L3, and may be disposed as appropriate depending on the specifications of the imaging device.

[0106] In the imaging lens according to this embodiment, it is preferable that all of the first lens L1 to the sixth lens L6 are made of plastic material. By using plastic material, it is possible to form aspherical shapes with high precision, and it is also possible to achieve weight reduction and cost reduction.

[0107] Furthermore, when a camera or the like equipped with an imaging lens is used in a harsh environment, it is desirable that the first lens L1, which is positioned closest to the object, be made of a material that is highly water-resistant, heat-resistant, weather-resistant, etc., such as a glass material.

[0108] In the imaging lens according to this embodiment, all of the first lens L1 through the sixth lens L6 are each constructed as a single lens. A construction using only single lenses allows for the frequent use of aspherical surfaces, which are effective in correcting aberrations. In this embodiment, by forming appropriate aspherical surfaces on the lens surfaces of the first lens L1 through the sixth lens L6, various aberrations are corrected satisfactorily. Furthermore, compared to the case of using cemented lenses, the number of steps can be reduced, thereby suppressing manufacturing costs.

[0109] In the imaging lens according to this embodiment, it is desirable to form all lens surfaces aspherical, but depending on the required performance, spherical surfaces may be used, which are easier to manufacture, and manufacturing costs can be reduced.

[0110] The imaging lens of this embodiment provides desirable effects by satisfying the following conditional expressions (1) to (33). (1) 1.10<D12 / f<3.55 (2) 0.50<T1 / f<1.95 (3) 0.20<D23 / f<0.85 (4) 1.00<T6 / bf<4.30 (5) 1.20<T1 / T2<4.20 (6) 0.30<R1r / T1<1.60 (7) 0.35<R6f / T6<1.40 (8) 2.35<D12 / T2<8.55 (9) 0.35<T2 / D23<1.25 (10) 0.25<T4 / T6<0.80 (11) 2.10<T4 / D45<10.80 (12) 0.07<R1r / R1f<0.30 (13) -0.35<R2r / R3f<-0.07 (14) 2.30<R3f / R3r<8.50 (15) -2.30<R5r / R6f<-0.64 (16) -0.25<R6f / R6r<-0.05 (17) 0.20<R1r / D12<0.70 (18) 1.55<R2r / D23<4.90 (19) -22.80<R6r / bf<-6.40 (20) -7.10<R6r / f6<-1.80 (21) -19.0<R3f / f<-4.0 (22) -4.80<R3f / f3<-1.00 (23) 0.55<R5r / f5<1.80 (24) 0.35<D23 / bf<1.45 (25) 0.10<R2r / f2<0.40 (26) -3.70<f1 / f<-1.35 (27) 3.10<f2 / f<12.50 (28) 1.80<f3 / f<6.30 (29) 0.90<f6 / f<3.00 (30) -700<f45 / f<-12 (31) -350<f45 / f<-7 (32) 60°<ω<120° (33) 13<νd2<28 where R1f: paraxial radius of curvature of the object-side surface of the first lens L1 R1r: paraxial radius of curvature of the image-side surface of the first lens L1 R2f: paraxial radius of curvature of the object-side surface of the second lens L2 R2r: paraxial radius of curvature of the image-side surface of the second lens L2 R3f: paraxial radius of curvature of the object-side surface of the third lens L3 R3r: paraxial radius of curvature of the image-side surface of the third lens L3 R5r: paraxial radius of curvature of the image-side surface of the fifth lens L5 R6f: paraxial radius of curvature of the object-side surface of the sixth lens L6 R6r: paraxial radius of curvature of the image-side surface of the sixth lens L6D12: 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: 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 D45: distance on the optical axis X from the image-side surface of the fourth lens L4 to the object-side surface of the fifth lens L5 T1: thickness on the optical axis X of the first lens L1 T2: thickness on the optical axis X of the second lens L2 T4: thickness on the optical axis X of the fourth lens L4 T6: thickness on the optical axis X of the sixth lens L6 f: focal length of the entire imaging lens system f1: focal length of the first lens L1 f2: focal length of the second lens L2 f3: focal length of the third lens L3 f5: focal length of the fifth lens L5 f6: focal length of the sixth lens L6 f45: composite focal length of the fourth lens L4 and the fifth lens L5 bf: back focus ω: half angle of view νd2: Abbe number for the d-line of the second lens L2 Note that 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.

[0111] Furthermore, the imaging lens of this embodiment achieves more preferable effects by satisfying the following conditional expressions (1a) to (33a). (1a) 1.55<D12 / f<2.95 (2a) 0.75<T1 / f<1.60 (3a) 0.30<D23 / f<0.70 (4a) 1.50<T6 / bf<3.55 (5a) 1.80<T1 / T2<3.60 (6a) 0.47<R1r / T1<1.32 (7a) 0.55<R6f / T6<1.17 (8a) 3.50<D12 / T2<7.10 (9a) 0.55<T2 / D23<1.10 (10a) 0.40<T4 / T6<0.72 (11a) 3.10<T4 / D45<9.70 (12a) 0.10<R1r / R1f<0.23 (13a) -0.28<R2r / R3f<-0.10 (14a) 3.50<R3f / R3r<7.60 (15a) -1.90<R5r / R6f<-0.95 (16a) -0.20<R6f / R6r<-0.09 (17a) 0.30<R1r / D12<0.58 (18a) 2.35<R2r / D23<4.40 (19a) -18.90<R6r / bf<-9.60 (20a) -5.90<R6r / f6<-2.70 (21a) -15.7<R3f / f<-6.0 (22a) -4.00<R3f / f3<-1.55 (23a) 0.80<R5r / f5<1.60 (24a) 0.54<D23 / bf<1.20 (25a) 0.15<R2r / f2<0.33 (26a) -3.00<f1 / f<-1.66 (27a) 4.75<f2 / f<10.35 (28a) 2.75<f3 / f<5.23 (29a) 1.36<f6 / f<2.50 (30a) -580<f45 / f<-19 (31a) -288<f45 / f6<-10 (32a) 70°<ω<105° (33a) 16<νd2<23 However, the symbols in each conditional expression are the same as those explained in the previous paragraph. Note that for the conditional expressions (1a) to (33a), the lower limit and upper limit of each may be the lower limit and upper limit of the corresponding conditional expression (1) to (33).

[0112] In this embodiment, the aspherical shape adopted for the aspherical surface of the 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.

[0113]

[0114] Next, examples of the imaging lens according to this embodiment will be shown. In each example, f represents the focal length of the entire imaging lens system, Fno represents the F-number, ω represents the half angle of view, ih represents the maximum image height, and TTL represents the total optical length. Here, the total optical length is the distance on the optical axis X 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., that are arranged between the imaging lens and the imaging plane IMG into air equivalents.

[0115] In addition, 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 vd 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.

[0116] (Example 1) Basic lens data

[0117]

[0118] FIG. 2 is an aberration diagram showing spherical aberration (mm), astigmatism (mm), and distortion (%) for the imaging lens of Example 1. The spherical aberration diagram shows the amount of aberration for each wavelength of the F-line (486 nm), d-line (588 nm), C-line (656 nm), and near-infrared light at 940 nm. The astigmatism diagram and distortion diagram show the amount of aberration for the reference wavelength d-line (588 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 FIGS. 4 and 6 ). As shown in FIG. 2 , the imaging lens of Example 1 can effectively correct each aberration.

[0119] (Example 2) Basic lens data

[0120]

[0121] As shown in FIG. 4, the imaging lens according to the second embodiment can also effectively correct each aberration.

[0122] (Example 3) Basic lens data

[0123]

[0124] As shown in FIG. 6, the imaging lens according to the third embodiment can also effectively correct each aberration.

[0125] Below, values ​​corresponding to the conditional expressions (1) to (33) according to the first to third embodiments (values ​​corresponding to the conditional expressions) are shown.

[0126]

[0127] When the imaging lens according to the present invention is applied to a product such as an in-vehicle camera, the camera can be made smaller while achieving both a wider angle and higher performance.

[0128] X Optical axis ST Aperture stop L1 First lens L2 Second lens L3 Third lens L4 Fourth lens L5 Fifth lens L6 Sixth lens FL Filter CG Cover glass IMG Imaging surface

Claims

1. An imaging lens comprising, in order from the object side to the image side, a first lens having negative refractive power, a second lens having positive refractive power, a third lens having positive refractive power, a fourth lens having positive refractive power, a fifth lens having negative refractive power, and a sixth lens having positive refractive power, wherein the second lens has a concave surface on the image side paraxially, and the fifth lens has a convex surface on the image side paraxially, and wherein the imaging lens satisfies the following conditional formula (1): (1) 1.10<D12 / f<3.55, where 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 f is the focal length of the entire imaging lens system.

2. The imaging lens according to claim 1, which satisfies the following conditional expression (2): (2) 0.50<T1 / f<1.95, where T1 is the thickness of the first lens on the optical axis, and f is the focal length of the entire imaging lens system.

3. The imaging lens according to claim 1, which satisfies the following conditional expression (3): (3) 0.20<D23 / f<0.85, 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, and f is the focal length of the entire imaging lens system.

4. The imaging lens according to claim 1, which satisfies the following conditional expression (4): (4) 1.00<T6 / bf<4.30, where T6 is the thickness of the sixth lens on the optical axis, and bf is the back focus.

5. The imaging lens according to claim 1, which satisfies the following conditional expression (5): (5) 1.20<T1 / T2<4.20, where 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.

6. The imaging lens according to claim 1, which satisfies the following conditional expression (6): (6) 0.30<R1r / T1<1.60, where R1r is the paraxial radius of curvature of the image-side surface of the first lens, and T1 is the thickness of the first lens on the optical axis.

7. The imaging lens according to claim 1, which satisfies the following conditional expression (7): (7) 0.35<R6f / T6<1.40, where R6f is the paraxial radius of curvature of the object-side surface of the sixth lens, and T6 is the thickness of the sixth lens on the optical axis.

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