Imaging lens

Abstract

Provided is a small-sized imaging lens that has a low F-number and is of wide angle and yet has high resolving power in which various aberrations are satisfactorily corrected throughout the entire range from the closest imaging distance to infinity.　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; a third lens L3 having positive refractive power; a fourth lens L4 having negative refractive power; a fifth lens L5 having positive refractive power; and a sixth lens L6 having negative refractive power. The second lens L2 is a variable-focus lens, and the sixth lens L6 has a concave surface in a paraxial region on the image side.

Description

Imaging lens

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

[0002] Many products and devices, such as game consoles, home appliances, and automobiles, are becoming increasingly sophisticated and equipped with cameras. These cameras are equipped with autofocus functions that automatically adjust the focus when photographing a subject, and can automatically focus over the entire range from the minimum focusing distance to infinity.

[0003] Furthermore, as functionality becomes more sophisticated, the number of cameras installed per product or device is increasing. This requires camera modules to be made even smaller, and at the same time, the imaging lenses incorporated into camera modules must also be made smaller. Furthermore, imaging lenses must have a wide angle of view and high resolution.

[0004] A known camera with an autofocus function is one that includes a drive mechanism, such as a motor, for mechanically moving the lens to adjust the focal position. However, this configuration results in a large camera module due to the inclusion of a drive mechanism, such as a motor. Furthermore, since space must be secured for lens movement, miniaturizing the imaging lens is difficult. Furthermore, the lens movement consumes a lot of power, resulting in high power consumption.

[0005] On the other hand, as an imaging lens that adjusts the focal position without mechanically moving the lens, 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, a second lens, a third lens, a fourth lens, a fifth lens, and a sixth lens whose surface facing the object side is convex, and that has a variable-focus lens disposed in one of the first to sixth lenses.

[0007] Chinese Utility Model No. 219266645

[0008] According to Patent Document 1, the focal position is adjusted by changing the focal length of the variable-focus lens, eliminating the need for space for moving the lens or a drive mechanism such as a motor. This allows the imaging lens and camera module to be made smaller. However, the imaging lens described in Patent Document 1 has an F-number of approximately 2.49 and a half angle of view of approximately 41.6°, making it difficult to meet the performance specifications required in recent years.

[0009] The present invention has been made in view of the above-mentioned problems, and has as its object to provide a small imaging lens that has a low F-number, a wide angle, and high resolving power in which various aberrations are well corrected over the entire range from the shortest shooting distance to infinity.

[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 negative refractive power, a second lens, a third lens having positive refractive power, a fourth lens having negative refractive power, a fifth lens having positive refractive power, and a sixth lens having negative refractive power. The second lens is a variable-focus lens, and the sixth lens has 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 negative refractive power, thereby achieving a wide angle of the imaging lens while suppressing the occurrence of various aberrations.

[0013] The second lens is a variable-focus lens composed of a glass substrate, a liquid polymer resin layer, and a film. By using the variable-focus lens as the second lens, it is possible to achieve a wide angle while suppressing the increase in the diameter of the first lens, as well as a low height and a low F-number.

[0014] The third lens has a positive refractive power, thereby achieving a low profile and effectively correcting spherical aberration, coma, astigmatism, curvature of field, and distortion.

[0015] The fourth lens has a negative refractive power, and thereby effectively corrects chromatic aberration, coma, astigmatism, and distortion.

[0016] The fifth lens has a positive refractive power, thereby achieving a low height and effectively correcting spherical aberration, coma, astigmatism, curvature of field, and distortion.

[0017] The sixth lens element has negative refractive power, which effectively corrects chromatic aberration, coma, astigmatism, and distortion. Furthermore, by making the image-side surface paraxially concave, it ensures an appropriate back focus while maintaining a low profile.

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

[0019] By forming the image-side surface of the first lens as a concave surface paraxially, it becomes possible to achieve a wider angle of view for the imaging lens while suppressing the occurrence of coma, astigmatism, and distortion.

[0020] In the imaging lens having the above configuration, it is desirable that the third lens has a biconvex shape in the paraxial direction.

[0021] By making the third lens paraxially biconvex, the positive refractive power is strengthened to achieve a low profile, and spherical aberration, coma, astigmatism, curvature of field, and distortion can be corrected satisfactorily.

[0022] In the imaging lens having the above configuration, it is desirable that the fourth lens has a concave surface on the image side in the paraxial direction.

[0023] By forming the image-side surface of the fourth lens as a concave surface paraxially, it becomes possible to make good corrections for coma, astigmatism, and distortion.

[0024] In the imaging lens having the above configuration, it is desirable that the fifth lens has a biconvex shape in the paraxial direction.

[0025] By making the fifth lens paraxially biconvex, the positive refractive power is strengthened to reduce the height, and spherical aberration, coma, astigmatism, curvature of field, and distortion can be corrected satisfactorily.

[0026] In the imaging lens having the above configuration, it is desirable that the image-side surface of the sixth lens be formed as an aspheric surface having a pole point at a position other than the optical axis.

[0027] By forming an aspherical shape having a pole point at a position other than on the optical axis on the image-side surface of the sixth lens, not only can on-axis chromatic aberration be effectively corrected but also off-axis chromatic aberration of magnification, and the angle of the light rays emitted from the imaging lens can be suitably suppressed.

[0028] 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.

[0029] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (1): (1) 0.20<T5 / D56<3.40 where T5 is the thickness of the fifth lens on the optical axis, and D56 is the distance on the optical axis from the image-side surface of the fifth lens to the object-side surface of the sixth lens.

[0030] By satisfying the range of conditional expression (1), it is possible to achieve a low profile and to make good corrections for coma, astigmatism, and distortion.

[0031] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (2): (2) 0.70<st_IM / L2_IM<1.10 where st_IM is the distance on the optical axis from the aperture stop to the imaging plane, and L2_IM is the distance on the optical axis from the object-side surface of the second lens to the imaging plane.

[0032] By satisfying the range of conditional expression (2), it is possible to achieve a wider angle of view without increasing the diameter of the first lens, and it is also possible to further reduce the amount of fluctuation in the angle of view when focusing from the shortest shooting distance to infinity.

[0033] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (3): (3) 0.23<T4 / T6<0.90 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.

[0034] By satisfying the range of conditional expression (3), it is possible to achieve a low profile and to make good corrections for spherical aberration, coma, astigmatism, and distortion.

[0035] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (4): (4) 3.40<r2 / D12<14.00 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.

[0036] By satisfying the range of conditional expression (4), it is possible to widen the angle of view and to make good corrections for coma, astigmatism, and distortion.

[0037] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (5): (5) 1.40<r9 / D56<8.25, where r9 is the paraxial radius of curvature of the object-side surface of the fifth lens, and D56 is the distance on the optical axis from the image-side surface of the fifth lens to the object-side surface of the sixth lens.

[0038] By satisfying the range of conditional expression (5), it becomes possible to make good corrections for spherical aberration, coma, astigmatism, curvature of field, and distortion.

[0039] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (6): (6) 2.75<r5 / (f / f3)<9.05 where r5 is the paraxial radius of curvature of the object-side surface of the third lens, f is the focal length of the entire imaging lens system, and f3 is the focal length of the third lens.

[0040] By satisfying the range of conditional expression (6), it is possible to achieve a low profile and to make good corrections for spherical aberration, astigmatism, curvature of field, and distortion.

[0041] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (7): (7) 0.08<D12 / f<0.57 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.

[0042] 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.

[0043] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (8): (8) 0.13<D56 / f<0.76, where D56 is the distance on the optical axis from the image-side surface of the fifth lens to the object-side surface of the sixth lens, and f is the focal length of the entire imaging lens system.

[0044] By satisfying the range of conditional expression (8), it is possible to achieve a low profile and to make good corrections for coma, astigmatism, and distortion.

[0045] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (9): (9) −3.90<r5 / r6<−1.00 where r5 is the paraxial radius of curvature of the object-side surface of the third lens, and r6 is the paraxial radius of curvature of the image-side surface of the third lens.

[0046] By satisfying the range of conditional expression (9), it becomes possible to make good corrections for spherical aberration, coma, astigmatism, curvature of field, and distortion.

[0047] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (10): (10) 0.20<r8 / r9<1.25 where r8 is the paraxial radius of curvature of the image-side surface of the fourth lens, and r9 is the paraxial radius of curvature of the object-side surface of the fifth lens.

[0048] By satisfying the range of conditional expression (10), coma, astigmatism, and distortion can be corrected satisfactorily.

[0049] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (11): (11) −3.20<r9 / r10<−0.80, where r9 is the paraxial radius of curvature of the object-side surface of the fifth lens, and r10 is the paraxial radius of curvature of the image-side surface of the fifth lens.

[0050] By satisfying the range of conditional expression (11), it becomes possible to make good corrections for spherical aberration, coma, astigmatism, curvature of field, and distortion.

[0051] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (12): (12) 0.78<D12 / D23<6.15, 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 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.

[0052] By satisfying the range of conditional expression (12), it is possible to achieve a low profile and to make good corrections for astigmatism, curvature of field, and distortion.

[0053] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (13): (13) 0.64<D23 / D34<2.50, 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 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.

[0054] By satisfying the range of conditional expression (13), it is possible to achieve a low profile and to make good corrections for spherical 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 (14): (14) 3.00<r2 / T1<15.30 where r2 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.

[0056] By satisfying the range of conditional expression (14), it is possible to widen the angle of view and to make good corrections for coma, astigmatism, and distortion.

[0057] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (15): (15) −3.00<r6 / T3<−0.75 where r6 is the paraxial radius of curvature of the image-side surface of the third lens, and T3 is the thickness of the third lens on the optical axis.

[0058] By satisfying the range of conditional expression (15), it is possible to achieve a low profile and 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 (16): (16) −3.30<r5 / r10<−1.00 where r5 is the paraxial radius of curvature of the object-side surface of the third lens, and r10 is the paraxial radius of curvature of the image-side surface of the fifth lens.

[0060] By satisfying the range of conditional expression (16), it becomes possible to make good corrections for spherical aberration, astigmatism, curvature of field, and distortion.

[0061] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (17): (17) 0.60<r2 / f<5.30 where r2 is the paraxial radius of curvature of the image-side surface of the first lens, and f is the focal length of the entire imaging lens system.

[0062] By satisfying the range of conditional expression (17), it is possible to widen the angle of view and to make good corrections for coma, astigmatism, and distortion.

[0063] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (18): (18) -3.00<f1 / f<-0.85 where f1 is the focal length of the first lens, and f is the focal length of the entire imaging lens system.

[0064] By satisfying the range of conditional expression (18), it becomes possible to widen the angle of the imaging lens while suppressing the occurrence of coma, astigmatism, and distortion.

[0065] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (19): (19) 0.45<f5 / f<1.70 where f5 is the focal length of the fifth lens, and f is the focal length of the entire imaging lens system.

[0066] By satisfying the range of conditional expression (19), it is possible to achieve a low profile and to make good corrections for spherical aberration, coma, astigmatism, curvature of field, and distortion.

[0067] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (20): (20) -2.55<f6 / f<-0.35 where f6 is the focal length of the sixth lens, and f is the focal length of the entire imaging lens system.

[0068] By satisfying the range of conditional expression (20), chromatic aberration, coma, astigmatism, and distortion can be corrected satisfactorily.

[0069] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (21): (21) 0.65<r9 / f5<2.50 where r9 is the paraxial radius of curvature of the object-side surface of the fifth lens, and f5 is the focal length of the fifth lens.

[0070] 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.

[0071] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (22): (22) 0.70<T1 / D12<1.70 where T1 is the thickness of the first lens on the optical axis, 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.

[0072] 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.

[0073] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (23): (23) 0.26<(T2+D23+T3) / f<1.35 where T2 is the thickness of the second 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, T3 is the thickness of the third lens on the optical axis, and f is the focal length of the entire imaging lens system.

[0074] By satisfying the range of conditional expression (23), it is possible to achieve a low profile and to make good corrections for coma, astigmatism, curvature of field, and distortion.

[0075] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (24): (24) -0.70<(T1+D12+T2) / f1<-0.14 where T1 is the thickness of the first lens on the optical axis, 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, T2 is the thickness of the second lens on the optical axis, and f1 is the focal length of the first lens.

[0076] By satisfying the range of conditional expression (24), it is possible to achieve a low profile and to make good corrections for astigmatism and distortion.

[0077] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (25): (25) 0.26<T2 / D12<1.30 where T2 is the thickness of the second lens on the optical axis, 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.

[0078] By satisfying the range of conditional expression (25), it is possible to achieve a low profile and to make good corrections for astigmatism and distortion.

[0079] The present invention makes it possible to provide a compact imaging lens that has a low F-number, a wide angle of view, and high resolving power with various aberrations well corrected over the entire range from the shortest shooting distance to infinity. Furthermore, the imaging lens according to the present invention can reduce power consumption when adjusting the focal position, thereby providing an environmentally friendly imaging lens.

[0080] 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 aberration diagrams showing spherical aberration, astigmatism, and distortion when the object distance of the imaging lens according to Example 1 of the present invention is infinity. FIG. 3 is aberration diagrams showing spherical aberration, astigmatism, and distortion when the object distance of the imaging lens according to Example 1 of the present invention is 600 mm. FIG. 4 is a cross-sectional view showing a schematic configuration of an imaging lens according to Example 2 of the present invention. FIG. 5 is aberration diagrams showing spherical aberration, astigmatism, and distortion when the object distance of the imaging lens according to Example 2 of the present invention is infinity. FIG. 6 is aberration diagrams showing spherical aberration, astigmatism, and distortion when the object distance of the imaging lens according to Example 2 of the present invention is 600 mm. FIG. 7 is a cross-sectional view showing a schematic configuration of an imaging lens according to Example 3 of the present invention. FIG. 8 is aberration diagrams showing spherical aberration, astigmatism, and distortion when the object distance of the imaging lens according to Example 3 of the present invention is infinity. FIG. 9 is aberration diagrams showing spherical aberration, astigmatism, and distortion when the object distance of the imaging lens according to Example 3 of the present invention is 600 mm. 1 is a cross-sectional view showing a schematic configuration of a variable focus lens included in a lens configuration of the present invention.

[0081] An embodiment of the present invention will be described in detail below with reference to the drawings. Figures 1, 4, and 7 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.

[0082] 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 which is a variable-focus lens made up of a glass substrate Gs, a liquid polymer resin layer PL, and a film Me, a third lens L3 having positive refractive power, a fourth lens L4 having negative refractive power, a fifth lens L5 having positive refractive power, and a sixth lens L6 having negative refractive power.

[0083] A filter IR, such as an infrared cut filter or a cover glass, is disposed between the sixth lens L6 and the imaging surface IMG. Note that this filter IR can be omitted.

[0084] All lenses that make up the imaging lens, including the variable focus lens, are fixed in position in the optical axis X direction relative to the imaging surface IMG.

[0085] The first lens L1 has negative refractive power and is biconcave, with both the object side and the image side concave in the paraxial direction. This allows the imaging lens to have a wide angle while suppressing the occurrence of various aberrations. The occurrence of spherical aberration, coma, astigmatism, field curvature, and distortion is suppressed. The shape of the object-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 flat in the paraxial direction.

[0086] The second lens L2 is a variable-focus lens made up of a glass substrate Gs, a liquid polymer resin layer PL, and a film Me. By placing the variable-focus lens on the image side of the first lens L1, a wide angle is achieved without increasing the diameter of the first lens. This also allows for a low height and a low F-number.

[0087] The variable-focus lens will now be described with reference to FIG. 10 . As shown in FIG. 10 , the variable-focus lens according to this embodiment is composed of, in order from the object side toward the imaging surface IMG side, a glass substrate Gs, a liquid polymer resin layer PL, a film Me, and an actuator Act arranged on the surface of the film Me facing the imaging surface IMG. The glass substrate Gs supports the structure of the variable-focus lens. The surface of the liquid polymer resin layer PL that contacts the glass substrate Gs (the object-side surface in this Example 1) is always maintained flat, while the surface that contacts the film Me (the surface facing the imaging surface IMG in this Example 1) changes its surface shape in response to changes in the shape of the film Me. By changing the shape of the surface that contacts the film Me, the liquid polymer resin layer PL prevents a gap from forming between the film Me and the film Me. The film Me changes its surface shape by applying a voltage to the actuator Act arranged on its surface, thereby changing the focal length of the lens.

[0088] Variable-focus lenses allow you to adjust the focal position without moving the lens, which allows for smaller imaging lenses, ultra-fast focusing speeds, and reduced power consumption during focusing. Another advantage is that the angle of view remains constant over the entire range from the shortest focusing distance to infinity.

[0089] Furthermore, the variable-focus lens according to the present embodiment is not limited to the configuration described above, and may have a configuration in which the object side and the imaging surface IMG side are reversed, i.e., a configuration in which the film Me, the liquid polymer resin layer PL, and the glass substrate Gs are arranged in this order from the object side toward the imaging surface IMG side. The actuator Act is arranged on the object-side surface of the film Me. Examples 2 and 3 have a configuration in which the film Me, the liquid polymer resin layer PL, and the glass substrate Gs are arranged in this order from the object side toward the imaging surface IMG side.

[0090] The variable focus lens according to this embodiment is not limited to the above-described configuration, and may be a liquid lens, a film lens, or a liquid crystal lens.

[0091] The third lens L3 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 spherical aberration, coma, astigmatism, curvature of field, and distortion.

[0092] The fourth lens L4 has negative refractive power and a biconcave shape with concave surfaces on both the object side and the image side in the paraxial direction. This allows for good correction of chromatic aberration, coma, astigmatism, and distortion. The shape of the object-side surface of the fourth lens L4 is not limited to the shape in Example 1, and may be a shape that is convex in the paraxial direction.

[0093] The fifth lens L5 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 spherical aberration, coma, astigmatism, curvature of field, and distortion.

[0094] The sixth lens L6 has negative refractive power and is a meniscus shape with a concave surface on the image side paraxially. This allows for good correction of chromatic aberration, coma, astigmatism, and distortion. Furthermore, by making the image side concave on the paraxial side, an appropriate back focus is ensured while maintaining a low profile. The shape of the object-side surface of the sixth lens L6 is not limited to the shape according to the first embodiment, and may be a shape that is concave on the paraxial side.

[0095] Furthermore, an aspheric surface having a pole point at a position other than on the optical axis X is formed on the image-side surface of the sixth lens L6. This allows for excellent correction of not only on-axis chromatic aberration but also off-axis lateral chromatic aberration, and also effectively suppresses the angle of incidence of light rays emitted from the imaging lens onto the image plane IMG.

[0096] The aperture stop ST is located between the second lens L2 and the third lens L3, thereby achieving a wide angle of view while preventing the diameter of the first lens L1 from becoming too large. The position of the aperture stop ST is not limited to between the second lens L2 and the third lens L3 and may be appropriately positioned depending on the specifications of the image sensor, but it is preferable to position it near the variable-focus lens. The shorter the distance between the aperture stop ST and the membrane Me of the variable-focus lens, the smaller the amount of fluctuation in the angle of view when focusing from the minimum shooting distance to infinity.

[0097] In the imaging lens according to this embodiment, the first lens L1, the third lens L3, the fourth lens L4, the fifth lens L5, and the sixth lens L6 are each composed of a single lens. By using single lenses, it is possible to form aspherical surfaces effective for correcting aberrations on the object-side and image-side surfaces. In this embodiment, by forming appropriate aspherical surfaces on the lens surfaces of the first lens L1, the third lens L3, the fourth lens L4, the fifth lens L5, and the sixth lens L6, various aberrations are effectively corrected. Furthermore, since the number of steps can be reduced compared to when a cemented lens is used, manufacturing costs can be suppressed.

[0098] It is desirable to form the lens surfaces of the first lens L1, the third lens L3, the fourth lens L4, the fifth lens L5, and the sixth lens L6 aspherical, but depending on the required performance, spherical surfaces, which are easier to manufacture, may also be used.

[0099] 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 in-vehicle camera, the first lens L1, which is positioned closest to the object, is exposed to the outside air and is therefore desirably made of a glass material that is highly water-resistant, heat-resistant, weather-resistant, etc. By making the first lens L1 of a glass material, stable optical characteristics can be obtained even when used in harsh environments.

[0100] In the imaging lens according to this embodiment, the third lens L3 to the sixth lens L6 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.

[0101] 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 third lens L3 to the sixth lens L6, it is also possible to aim for further improvement in performance.

[0102] The imaging lens of this embodiment provides desirable effects by satisfying the following conditional expressions (1) to (25). (1) 0.20<T5 / D56<3.40 (2) 0.70<st_IM / L2_IM<1.10 (3) 0.23<T4 / T6<0.90 (4) 3.40<r2 / D12<14.00 (5) 1.40<r9 / D56<8.25 (6) 2.75<r5 / (f / f3)<9.05 (7) 0.08<D12 / f<0.57 (8) 0.13<D56 / f<0.76 (9) -3.90<r5 / r6<-1.00 (10) 0.20<r8 / r9<1.25 (11) -3.20<r9 / r10<-0.80 (12) 0.78<D12 / D23<6.15 (13) 0.64<D23 / D34<2.50 (14) 3.00<r2 / T1<15.30 (15) -3.00<r6 / T3<-0.75 (16) -3.30<r5 / r10<-1.00 (17) 0.60<r2 / f<5.30 (18) -3.00<f1 / f<-0.85 (19) 0.45<f5 / f<1.70 (20) -2.55<f6 / f<-0.35 (21) 0.65<r9 / f5<2.50 (22) 0.70<T1 / D12<1.70 (23) 0.26<(T2+D23+T3) / f<1.35 (24) -0.70<(T1+D12+T2) / f1<-0.14 (25) 0.26<T2 / D12<1.30 where, 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 T5: thickness of the fifth lens L5 on the optical axis X T6: thickness of the sixth lens L6 on the optical axis X D12: 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 D34: 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. D56: Distance on the optical axis X from the image-side surface of the fifth lens L5 to the object-side surface of the sixth lens L6. r2: Paraxial radius of curvature of the image-side surface of the first lens L1. r5: Paraxial radius of curvature of the object-side surface of the third lens L3. r6: Paraxial radius of curvature of the image-side surface of the third lens L3. r8: Paraxial radius of curvature of the image-side surface of the fourth lens L4.r9: paraxial radius of curvature of the object-side surface of the fifth lens L5 r10: paraxial radius of curvature of the image-side surface of the fifth lens L5 f: focal length of the entire imaging lens system f1: focal length of the first lens L1 f3: focal length of the third lens L3 f5: focal length of the fifth lens L5 f6: focal length of the sixth lens L6 st_IM: distance on the optical axis X from the aperture stop ST to the imaging plane IMG L2_IM: distance on the optical axis X from the object-side surface of the second lens L2 to the imaging plane IMG It should be noted that it is not necessary to satisfy all of the above conditional expressions; by satisfying each conditional expression individually, it is possible to obtain the effect corresponding to each conditional expression.

[0103] Furthermore, the imaging lens of this embodiment will achieve more preferable effects if it satisfies the following conditional expressions (1a) to (25a). (1a) 0.37<T5 / D56<2.80 (2a) 0.77<st_IM / L2_IM<1.00 (3a) 0.35<T4 / T6<0.75 (4a) 5.00<r2 / D12<11.70 (5a) 2.10<r9 / D56<6.90 (6a) 4.10<r5 / (f / f3)<7.50 (7a) 0.12<D12 / f<0.47 (8a) 0.20<D56 / f<0.62 (9a) -3.20<r5 / r6<-1.50 (10a) 0.32<r8 / r9<1.00 (11a) -2.65<r9 / r10<-1.20 (12a) 1.10<D12 / D23<5.10 (13a) 0.95<D23 / D34<2.10 (14a) 4.50<r2 / T1<12.70 (15a) -2.50<r6 / T3<-1.15 (16a) -2.75<r5 / r10<-1.50 (17a) 0.90<r2 / f<4.40 (18a) -2.50<f1 / f<-1.30 (19a) 0.65<f5 / f<1.40 (20a) -2.10<f6 / f<-0.55 (21a) 0.95<r9 / f5<2.05 (22a) 0.60<T1 / D12<1.65 (23a) 0.38<(T2+D23+T3) / f<1.13 (24a) -0.59<(T1+D12+T2) / f1<-0.20 (25a) 0.39<T2 / D12<1.05 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 the corresponding conditional expressions (1) to (25) may be applied as the respective lower limit and upper limit.

[0104] 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.

[0105]

[0106] Next, examples of the imaging lens according to this embodiment will be shown. In each example, 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 thickness of a filter IR or the like disposed between the imaging lens and the imaging plane IMG into air.

[0107] i is the surface number counted from the object side, r is the paraxial radius of curvature, d is the distance (surface spacing) between lens surfaces on the optical axis X, Nd is the refractive index at the reference wavelength d line (588 nm), and vd is the Abbe number for the reference wavelength d line. Also, OBJ is the object distance, and MeR is the paraxial radius of curvature of the variable-focus lens.

[0108] Aspherical surfaces are indicated by adding an asterisk (*) after the surface number i.

[0109] (Example 1) Basic lens data

[0110] Table 2 shows the focal length (f) of the entire imaging lens system and the paraxial radii of curvature (MeR) of surfaces 5 and 6 of the variable-focus lens when the object distance (OBJ) in Example 1 is infinity and 600 mm.

[0111]

[0112] 2 is an aberration diagram showing spherical aberration (mm), astigmatism (mm), and distortion (%) for the imaging lens of Example 1 when the object distance is infinity. As shown in FIG. 2, the imaging lens of Example 1 can effectively correct each aberration when the object distance is infinity.

[0113] 3 is an aberration diagram showing spherical aberration (mm), astigmatism (mm), and distortion (%) when the object distance is 600 mm for the imaging lens of Example 1. As shown in FIG. 3, the imaging lens of Example 1 can satisfactorily correct each aberration even when the object distance is 600 mm.

[0114] The spherical aberration diagram shows the amount of aberration for each wavelength: F-line (486 nm), d-line (588 nm), and C-line (656 nm). The astigmatism diagram and distortion diagram show the amount of aberration at 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. 5, 6, 8, and 9).

[0115] (Example 2) Basic lens data

[0116] Table 5 shows the focal length (f) of the entire imaging lens system and the paraxial radii of curvature (MeR) of surfaces 3 and 4 of the variable-focus lens when the object distance (OBJ) in Example 2 is infinity and 600 mm.

[0117]

[0118] As shown in FIGS. 5 and 6, the imaging lens according to the second embodiment can also effectively correct each aberration when the object distance is infinity and when the object distance is 600 mm.

[0119] (Example 3) Basic lens data

[0120] Table 8 shows the focal length (f) of the entire imaging lens system and the paraxial radii of curvature (MeR) of surfaces 3 and 4 of the variable-focus lens when the object distance (OBJ) in Example 3 is infinity and when it is 600 mm.

[0121]

[0122] As shown in FIGS. 8 and 9, the imaging lens according to the third embodiment can also effectively correct each aberration when the object distance is infinity and when the object distance is 600 mm.

[0123] Below, values ​​corresponding to the conditional expressions (1) to (25) according to the first to third embodiments (values ​​corresponding to the conditional expressions) are shown.

[0124]

[0125] When the imaging lens according to the present invention is applied to a product equipped with a camera function, it contributes to lowering the F-number and widening the angle of view of the camera, and also makes it possible to achieve both high performance and miniaturization.

[0126] X Optical axis ST Aperture stop L1 First lens L2 Second lens L3 Third lens L4 Fourth lens L5 Fifth lens L6 Sixth lens Gs Glass substrate PL Liquid polymer resin layer Me Film IR filter IMG Imaging surface Act Actuator

Claims

1. An imaging lens comprising, arranged in order from the object side to the image side, a first lens having negative refractive power, a second lens, a third lens having positive refractive power, a fourth lens having negative refractive power, a fifth lens having positive refractive power, and a sixth lens having negative refractive power, wherein the second lens is a variable focus lens, and the sixth lens has a concave surface on the image side in the paraxial direction.

2. The imaging lens according to claim 1, wherein the fifth lens has a biconvex shape on the paraxial plane.

3. The imaging lens according to claim 1, which satisfies the following conditional expression (1): (1) 0.20<T5 / D56<3.40, where T5 is the thickness of the fifth lens on the optical axis, and D56 is the distance on the optical axis from the image-side surface of the fifth lens to the object-side surface of the sixth lens.

4. The imaging lens according to claim 1, characterized in that an aperture stop is disposed adjacent to the second lens, and the following conditional expression (2) is satisfied: (2) 0.70<st_IM / L2_IM<1.10, where st_IM is the distance on the optical axis from the aperture stop to the imaging plane, and L2_IM is the distance on the optical axis from the image-side surface of the second lens to the imaging plane.

5. The imaging lens according to claim 1, which satisfies the following conditional expression (3): (3) 0.23<T4 / T6<0.90, 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.

6. The imaging lens according to claim 1, which satisfies the following conditional expression (4): (4) 3.40<r2 / D12<14.00, 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.

7. The imaging lens according to claim 1, which satisfies the following conditional expression (5): (5) 1.40<r9 / D56<8.25, where r9 is the paraxial radius of curvature of the object-side surface of the fifth lens, and D56 is the distance on the optical axis from the image-side surface of the fifth lens to the object-side surface of the sixth lens.

Images