Imaging lens

Abstract

To provide a down-sized imaging lens that has various aberrations well corrected across the entire area from the closest image-capturing distance to infinity, even though being low in F-number, and a wide-angle.SOLUTION: An imaging lens is composed of, in order toward an image side from an object side: a first lens L1 that has a negative refractive power; a second lens L2; a third lens L3 that has a positive refractive power; a fourth lens L4 that has a negative refractive power; a fifth lens L5 that has a positive refractive power; and a sixth lens L6 that has a negative refractive power, in which the second lens L2 is a variable focus lens, and the sixth lens L6 has a paraxial concave surface on the image side.SELECTED DRAWING: Figure 1

Description

Technical Field

[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.

Background Art

[0002] Many products and devices such as game machines, home appliances, and automobiles are becoming more highly functional, and it has generally become common to be equipped with a camera function. These cameras are equipped with an autofocus function that automatically focuses when photographing a subject, and can automatically focus and photograph over the entire range from the shortest shooting distance to infinity.

[0003] In addition, with the increase in functionality, the number of cameras installed in each product or device is increasing. Therefore, further miniaturization of the camera module is required, and at the same time, miniaturization of the imaging lens incorporated in the camera module is also required. In addition, the imaging lens is required to have a wide shooting angle of view and high resolution.

[0004] As a camera equipped with an autofocus function, a configuration including a drive mechanism such as a motor for mechanically moving a lens to adjust the focus position is known. However, in this configuration, since a drive mechanism such as a motor is provided, the camera module becomes large. In addition, since it is necessary to secure a space for moving the lens, it is difficult to miniaturize the imaging lens. Furthermore, since a large amount of power is consumed for moving the lens, the power consumption is large.

[0005] On the other hand, as an imaging lens that adjusts the focus position without mechanically moving the lens, for example, an imaging lens as described in Patent Document 1 below is known.

[0006] Patent Document 1 discloses an imaging lens 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 with a convex surface on the object side, and having a focus-variable lens disposed in one of the first to sixth lenses.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] According to Patent Document 1, since the focal position is adjusted by changing the focal length of the focus-variable lens, there is no need for a space for moving the lens or a driving mechanism such as a motor. Therefore, the imaging lens and the camera module can be miniaturized. However, the imaging lens described in Patent Document 1 has an F-number of about 2.49 and a half field angle of about 41.6°, and it is difficult to meet the performance specifications required in recent years.

[0009] The present invention has been made in view of the above-described problems, and an object thereof is to provide a small-sized imaging lens having a high resolution with good correction of various aberrations over the entire range from the shortest shooting distance to infinity while achieving a low F-number and a wide angle.

Means for Solving the Problems

[0010] The imaging lens according to the present invention is composed of, in order from the object side toward the image side, a first lens having a negative refractive power, a second lens, a third lens having a positive refractive power, a fourth lens having a negative refractive power, a fifth lens having a positive refractive power, and a sixth lens having a negative refractive power. The second lens is a focus-variable lens, and the sixth lens has a concave surface on the image side in the paraxial region.

[0011] In this specification, the convex surface, concave surface, and flat surface of the lens refer to the shapes in the paraxial region, and the refractive power refers to the refractive power in the paraxial region unless otherwise specified.

[0012] By having a negative refractive power, the first lens aims to widen the angle of the imaging lens while suppressing the occurrence of various aberrations.

[0013] The second lens is a focus-variable lens composed of a glass substrate, a liquid polymer resin layer, and a film. By arranging the focus-variable lens as the second lens, it aims to widen the angle while suppressing the increase in the diameter of the first lens, and to reduce the thickness and the F-number.

[0014] By having a positive refractive power, the third lens aims to reduce the thickness and correct spherical aberration, coma aberration, astigmatism, field curvature, and distortion well.

[0015] By having a negative refractive power, the fourth lens corrects chromatic aberration, coma aberration, astigmatism, and distortion well.

[0016] By having a positive refractive power, the fifth lens aims to reduce the thickness and correct spherical aberration, coma aberration, astigmatism, field curvature, and distortion well.

[0017] By having a negative refractive power, the sixth lens corrects chromatic aberration, coma aberration, astigmatism, and distortion well. Also, by making the image side concave in the paraxial region, an appropriate back focus is ensured while maintaining the low thickness.

[0018] In the imaging lens with the above configuration, it is desirable that the image side of the first lens is concave in the paraxial region.

[0019] By forming the image-side surface of the first lens as a concave surface in the paraxial region, it becomes possible to widen the angle of the imaging lens while suppressing the occurrence of coma aberration, 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 region.

[0021] By making the third lens biconvex in the paraxial region, the positive refractive power is enhanced to achieve a lower profile, and it becomes possible to correct spherical aberration, coma aberration, astigmatism, field curvature, and distortion favorably.

[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 region.

[0023] By forming the image-side surface of the fourth lens concave in the paraxial region, it becomes possible to correct coma aberration, astigmatism, and distortion favorably.

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

[0025] By making the fifth lens biconvex in the paraxial region, the positive refractive power is enhanced to achieve a lower profile, and it becomes possible to correct spherical aberration, coma aberration, astigmatism, field curvature, and distortion favorably.

[0026] In the imaging lens having the above configuration, it is desirable that the image-side surface of the sixth lens is formed with an aspherical surface having an apex at a position other than on the optical axis.

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

[0028] In the present invention, the apex is defined as a point on the aspherical surface other than on the optical axis where the tangent plane intersects the optical axis perpendicularly.

[0029] It is desirable that the imaging lens having the above configuration satisfies the following conditional expression (1). (1) 0.20 < T5 / D56 < 3.40 However, T5 is the thickness on the optical axis 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.

[0030] By satisfying the range of conditional expression (1), a reduction in thickness can be achieved, and good correction of coma aberration, astigmatism, and distortion aberration becomes possible.

[0031] The imaging lens having the above configuration preferably satisfies the following conditional expression (2). (2) 0.70 < st_IM / L2_IM < 1.10 However, st_IM is the distance on the optical axis from the aperture stop to the imaging surface, and L2_IM is the distance on the optical axis from the object-side surface of the second lens to the imaging surface.

[0032] By satisfying the range of conditional expression (2), it becomes possible to widen the angle of view while suppressing an increase in the diameter of the first lens. In addition, the amount of variation in the angle of view during focusing from the shortest shooting distance to infinity can be suppressed to be smaller.

[0033] The imaging lens having the above configuration preferably satisfies the following conditional expression (3). (3) 0.23 < T4 / T6 < 0.90 However, T4 is the thickness on the optical axis of the fourth lens, and T6 is the thickness on the optical axis of the sixth lens.

[0034] By satisfying the range of conditional expression (3), a reduction in thickness can be achieved, and good correction of spherical aberration, coma aberration, astigmatism, and distortion aberration becomes possible.

[0035] The imaging lens having the above configuration preferably satisfies the following conditional expression (4). (4) 3.40 < r2 / D12 < 14.00 However, r2 is the paraxial curvature radius 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), wide-angle conversion is achieved, and good correction of coma aberration, astigmatism, and distortion aberration becomes possible.

[0037] The imaging lens having the above configuration preferably satisfies the following conditional expression (5). (5) 1.40 < r9 / D56 < 8.25 However, r9 is the paraxial curvature radius 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), good correction of spherical aberration, coma aberration, astigmatism, field curvature, and distortion aberration becomes possible.

[0039] The imaging lens having the above configuration preferably satisfies the following conditional expression (6). (6) 2.75 < r5 / (f / f3) < 9.05 However, r5 is the paraxial curvature radius 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), low-profile design is achieved, and good correction of spherical aberration, astigmatism, field curvature, and distortion aberration becomes possible.

[0041] The imaging lens having the above configuration preferably satisfies the following conditional expression (7). (7) 0.08 < D12 / f < 0.57 However, 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), low-profile design is achieved, and good correction of astigmatism and distortion aberration becomes possible.

[0043] The imaging lens having the above configuration preferably satisfies the following conditional expression (8). (8) 0.13 < D56 / f < 0.76 However, 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 the conditional expression (8), it is possible to reduce the height and achieve good correction of coma aberration, astigmatism, and distortion aberration.

[0045] The imaging lens having the above configuration preferably satisfies the following conditional expression (9). (9) -3.90 < r5 / r6 < -1.00 However, r5 is the paraxial curvature radius of the object-side surface of the third lens, and r6 is the paraxial curvature radius of the image-side surface of the third lens.

[0046] By satisfying the range of the conditional expression (9), it is possible to achieve good correction of spherical aberration, coma aberration, astigmatism, field curvature, and distortion aberration.

[0047] The imaging lens having the above configuration preferably satisfies the following conditional expression (10). (10) 0.20 < r8 / r9 < 1.25 However, r8 is the paraxial curvature radius of the image-side surface of the fourth lens, and r9 is the paraxial curvature radius of the object-side surface of the fifth lens.

[0048] By satisfying the range of the conditional expression (10), it is possible to achieve good correction of coma aberration, astigmatism, and distortion aberration.

[0049] The imaging lens having the above configuration preferably satisfies the following conditional expression (11). (11) -3.20 < r9 / r10 < -0.80 However, r9 is the paraxial curvature radius of the object-side surface of the fifth lens, and r10 is the paraxial curvature radius of the image-side surface of the fifth lens.

[0050] By satisfying the range of the conditional expression (11), it is possible to achieve good correction of spherical aberration, coma aberration, astigmatism, field curvature, and distortion aberration.

[0051] The imaging lens having the above configuration preferably satisfies the following conditional expression (12). (12) 0.78 < D12 / D23 < 6.15 Here, 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 the conditional expression (12), it is possible to reduce the thickness and achieve good correction of spherical aberration, field curvature, and distortion aberration.

[0053] The imaging lens having the above configuration preferably satisfies the following conditional expression (13). (13) 0.64 < D23 / D34 < 2.50 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 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 the conditional expression (13), it is possible to reduce the thickness and achieve good correction of spherical aberration, coma aberration, field curvature, and distortion aberration.

[0055] The imaging lens having the above configuration preferably satisfies the following conditional expression (14). (14) 3.00 < r2 / T1 < 15.30 Here, r2 is the paraxial curvature radius of the image-side surface of the first lens, and T1 is the thickness on the optical axis of the first lens.

[0056] By satisfying the range of the conditional expression (14), it is possible to widen the angle of view and achieve good correction of coma aberration, field curvature, and distortion aberration.

[0057] The imaging lens having the above configuration preferably satisfies the following conditional expression (15). (15) -3.00 < r6 / T3 < -0.75 Here, r6 is the paraxial curvature radius of the image-side surface of the third lens, and T3 is the thickness on the optical axis of the third lens.

[0058] By satisfying the range of conditional expression (15), the height is reduced, and it becomes possible to achieve good correction of coma aberration, astigmatism, field curvature, and distortion aberration.

[0059] The imaging lens having the above configuration preferably satisfies the following conditional expression (16). (16) -3.30 < r5 / r10 < -1.00 However, r5 is the paraxial curvature radius of the object-side surface of the third lens, and r10 is the paraxial curvature radius of the image-side surface of the fifth lens.

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

[0061] The imaging lens having the above configuration preferably satisfies the following conditional expression (17). (17) 0.60 < r2 / f < 5.30 However, r2 is the paraxial curvature radius 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), the angle of view is increased, and it becomes possible to achieve good correction of coma aberration, astigmatism, and distortion aberration.

[0063] The imaging lens having the above configuration preferably satisfies the following conditional expression (18). (18) -3.00 < f1 / f < -0.85 However, 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 increase the angle of view of the imaging lens while suppressing the occurrence of coma aberration, astigmatism, and distortion aberration.

[0065] The imaging lens having the above configuration preferably satisfies the following conditional expression (19). (19) 0.45 < f5 / f < 1.70 However, 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 reduce the thickness and achieve good correction of spherical aberration, coma aberration, astigmatism, field curvature, and distortion aberration.

[0067] The imaging lens with the above configuration preferably satisfies the following conditional expression (20). (20) -2.55 < f6 / f < -0.35 However, 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), it is possible to achieve good correction of chromatic aberration, coma aberration, astigmatism, and distortion aberration.

[0069] The imaging lens with the above configuration preferably satisfies the following conditional expression (21). (21) 0.65 < r9 / f5 < 2.50 However, r9 is the paraxial curvature radius 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 is possible to achieve good correction of spherical aberration, coma aberration, astigmatism, field curvature, and distortion aberration.

[0071] The imaging lens with the above configuration preferably satisfies the following conditional expression (22). (22) 0.70 < T1 / D12 < 1.70 However, T1 is the thickness on the optical axis 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.

[0072] By satisfying the range of conditional expression (22), it is possible to reduce the thickness and achieve good correction of astigmatism and distortion aberration.

[0073] The imaging lens with the above configuration preferably satisfies the following conditional expression (23). (23) 0.26 < (T2 + D23 + T3) / f < 1.35 Here, T2 is the thickness on the optical axis of the second 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, T3 is the thickness on the optical axis of the third lens, 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 reduce the height and achieve good correction of coma aberration, astigmatism, field curvature, and distortion aberration.

[0075] The imaging lens having the above configuration preferably satisfies the following conditional expression (24). (24) -0.70 < (T1 + D12 + T2) / f1 < -0.14 Here, T1 is the thickness on the optical axis 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, T2 is the thickness on the optical axis of the second lens, and f1 is the focal length of the first lens.

[0076] By satisfying the range of conditional expression (24), it is possible to reduce the height and achieve good correction of astigmatism and distortion aberration.

[0077] The imaging lens having the above configuration preferably satisfies the following conditional expression (25). (25) 0.26 < T2 / D12 < 1.30 Here, T2 is the thickness on the optical axis of the second 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.

[0078] By satisfying the range of conditional expression (25), it is possible to reduce the height and achieve good correction of astigmatism and distortion aberration.

[0079] According to the present invention, it is possible to obtain a small imaging lens having high resolution with various aberrations well corrected over the entire range from the shortest shooting distance to infinity while achieving a low F-number and a wide angle. Further, in the imaging lens according to the present invention, since the power consumption when adjusting the focal position can be significantly reduced, an imaging lens friendly to the environment can be provided through the reduction of power consumption.

Brief Description of the Drawings

[0080]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Embodiments for Carrying Out the Invention

[0081] Hereinafter, an embodiment embodying the present invention will be described in detail with reference to the drawings. FIGS. 1, 4, and 7 are cross-sectional views showing the schematic configurations of the imaging lenses according to Examples 1 to 3 of the present embodiment. Since the basic lens configurations are the same in any of the examples, the imaging lens according to the present 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 the present embodiment includes, in order from the object side toward the image side, a first lens L1 having a negative refractive power, a focus-variable lens which is a second lens L2 composed of a glass substrate Gs, a liquid polymer resin layer PL, and a film Me, a third lens L3 having a positive refractive power, a fourth lens L4 having a negative refractive power, a fifth lens L5 having a positive refractive power, and a sixth lens L6 having a negative refractive power.

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

[0084] All the lenses constituting the imaging lens, including the focus-variable lens, have their positions in the direction of the optical axis X fixed with respect to the imaging surface IMG.

[0085] The first lens L1 has a negative refractive power and is a biconcave shape with both the object side and the image side being concave surfaces in the paraxial region. Thereby, the imaging lens is widened while suppressing the occurrence of various aberrations. The occurrence of spherical aberration, coma aberration, astigmatism, field curvature, and distortion aberration 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 a plane in the paraxial region.

[0086] The second lens L2 is a focus-variable lens composed of a glass substrate Gs, a liquid polymer resin layer PL, and a film Me. By disposing the focus-variable lens on the image side of the first lens L1, the imaging lens is widened while suppressing an increase in the diameter of the first lens. Also, a reduction in thickness and a reduction in F-number are achieved.

[0087] Here, the focus-variable lens will be described with reference to FIG. 10. As shown in FIG. 10, the focus-variable lens according to this embodiment includes, 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 disposed on the surface of the film Me on the imaging surface IMG side. The glass substrate Gs serves to support the structure of the focus-variable lens. The surface of the liquid polymer resin layer PL that is in contact with the glass substrate Gs (the surface on the object side in the first embodiment) is always maintained in a flat plane, and the surface of the liquid polymer resin layer PL that is in contact with the film Me (the surface on the imaging surface IMG side in the first embodiment) changes its surface shape according to the shape change of the film Me. By changing the shape of the surface in contact with the film Me, it plays a role of not creating a gap with the film Me. The film Me changes its surface shape by applying a voltage to the actuator Act disposed on the surface, and plays a role of changing the focal length of the lens.

[0088] Since the focus-variable lens can adjust the focus position without moving the lens, it has effects such as miniaturization of the imaging lens, ultra-high speed focusing speed, and reduction of power consumption during focusing. Also, there is an advantage that the variation in the angle of view is small over the entire range from the shortest shooting distance to infinity.

[0089] In addition, the focus-variable lens according to this embodiment is not limited to the above-described configuration, and a configuration in which the object side and the imaging surface IMG side are inverted, that is, a configuration in which the film Me, the liquid polymer resin layer PL, and the glass substrate Gs are arranged in order from the object side toward the imaging surface IMG side may also be used. Note that the actuator Act is disposed on the surface of the film Me on the object side. Embodiment 2 and Embodiment 3 are configurations in which the film Me, the liquid polymer resin layer PL, and the glass substrate Gs are arranged in order from the object side toward the imaging surface IMG side.

[0090] Note that the focus-variable lens according to this embodiment is not limited to the above-described configuration, and other liquid lenses, film lenses, and liquid crystal lenses may also be used.

[0091] The third lens L3 has a positive refractive power and is a biconvex shape with convex surfaces on both the object side and the image side in the paraxial region. This corrects spherical aberration, coma aberration, astigmatism, field curvature, and distortion well while reducing the height of the imaging lens.

[0092] The fourth lens L4 has a negative refractive power and is a biconcave shape with concave surfaces on both the object side and the image side in the paraxial region. This corrects chromatic aberration, coma aberration, astigmatism, and distortion well. The shape of the object-side surface of the fourth lens L4 is not limited to the shape according to the first embodiment and may be a shape that is convex in the paraxial region.

[0093] The fifth lens L5 has a positive refractive power and is a biconvex shape with convex surfaces on both the object side and the image side in the paraxial region. This corrects spherical aberration, coma aberration, astigmatism, field curvature, and distortion well while reducing the height of the imaging lens.

[0094] The sixth lens L6 has a negative refractive power and is a meniscus shape with a concave surface on the image side in the paraxial region. This corrects chromatic aberration, coma aberration, astigmatism, and distortion well. Also, by making the image side concave in the paraxial region, an appropriate back focus is ensured while maintaining the low height. 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 in the paraxial region.

[0095] Moreover, the image-side surface of the sixth lens L6 has an aspherical surface with a vertex at a position other than on the optical axis X. Therefore, not only the axial chromatic aberration but also the off-axis lateral chromatic aberration is corrected well, and the incident angle of the light rays emitted from the imaging lens onto the image plane IMG is preferably suppressed.

[0096] Since the aperture stop ST is disposed between the second lens L2 and the third lens L3, it achieves a wider angle of view while suppressing an increase in the diameter of the first lens L1. Note that the position of the aperture stop ST is not limited to being between the second lens L2 and the third lens L3, and it may be appropriately arranged according to the specifications of the imaging device, but it is preferably arranged near the focus-variable lens. The shorter the distance between the aperture stop ST and the film Me of the focus-variable lens, the smaller the amount of variation in the angle of view during focusing from the shortest shooting distance to infinity can be suppressed.

[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 a single lens, an aspherical surface effective for aberration correction can be formed 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, good correction of various aberrations is performed. Also, since the man-hours can be reduced compared to the case of adopting a cemented lens, the manufacturing cost can be suppressed.

[0098] Note that 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 as aspherical surfaces, but a spherical surface that is easy to manufacture may be adopted depending on the required performance.

[0099] In the imaging lens according to this embodiment, the first lens L1 is preferably formed of a glass material. For example, in an imaging lens mounted on an in-vehicle camera, since the first lens L1 disposed on the most object side is exposed to the outside air, it is desirable to form it of a glass material having high water resistance, heat resistance, weather resistance, etc. By forming the first lens L1 of a glass material, stable optical characteristics can be obtained even in use under severe environments.

[0100] For the imaging lens according to this embodiment, it is preferable that the third lens L3 to the sixth lens L6 are each formed of a plastic material. By using a plastic material, an aspherical shape can be accurately formed, and weight reduction and cost reduction can be achieved.

[0101] Note that the lens material to be adopted is not limited to the material according to this embodiment. For example, by adopting a plastic material for the first lens L1, an aspherical shape can be accurately formed, and further weight reduction and cost reduction can be achieved. Also, for example, by adopting a glass material for the third lens L3 to the sixth lens L6, further high performance can be achieved.

[0102] The imaging lens in this embodiment exhibits preferable 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 However, T1: Thickness on the optical axis X of the first lens L1 T2: Thickness on the optical axis X of the second lens L2 T3: Thickness on the optical axis X of the third lens L3 T4: Thickness on the optical axis X of the fourth lens L4 T5: Thickness on the optical axis X of the fifth lens L5 T6: Thickness on the optical axis X of the sixth lens L6 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 curvature radius of the image side surface of the first lens L1 r5: Paraxial curvature radius of the object side surface of the third lens L3 r6: Paraxial curvature radius of the image side surface of the third lens L3 r8: Paraxial curvature radius of the image side surface of the fourth lens L4 r9: Paraxial curvature radius of the object side surface of the fifth lens L5 r10: Paraxial curvature radius 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 surface IMG L2_IM: Distance on the optical axis X from the object-side surface of the second lens L2 to the imaging surface IMG Note that it is not necessary to satisfy all of the above conditional expressions. By satisfying each conditional expression individually, the operational effects corresponding to each conditional expression can be obtained.

[0103] In addition, the imaging lens in the present embodiment exhibits more preferable effects by satisfying 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 signs of each conditional expression are the same as those described in the previous paragraph. For the conditional expressions (1a) to (25a), the lower and upper limits of the corresponding conditional expressions (1) to (25) may be applied as the lower and upper limits, respectively.

[0104] In this embodiment, the aspherical shape adopted for the aspherical surface of the lens is represented by Equation 1 when the axis in the optical axis direction is Z, the height in the direction orthogonal to the optical axis is H, the paraxial curvature radius is R, the conic coefficient is k, and the aspherical coefficient of the nth order is An.

[0105]

Number

[0106] Next, examples of the imaging lens according to this embodiment are shown. In each example, Fno represents the F-number, ω represents the semi-field angle, ih represents the maximum image height, and TTL represents the overall optical length. Here, the overall optical length is defined as the distance on the optical axis X from the object-side surface of the optical element located farthest on the object side to the imaging surface IMG. Note that the values of the overall optical length and the 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 surface IMG into air.

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

[0108] Regarding the aspherical surface, an asterisk (*) symbol is added after the surface number i for indication.

[0109] (Example 1) Basic lens data [Table 1]

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

[0111] [Table 3]

[0112] Figure 2 is an aberration diagram showing spherical aberration (mm), coma aberration (mm), and distortion (%) of the imaging lens of Example 1 when the object distance is infinite. As shown in Figure 2, according to the imaging lens according to this Example 1, each aberration can be well corrected when the object distance is infinite.

[0113] Figure 3 is an aberration diagram showing spherical aberration (mm), coma aberration (mm), and distortion (%) of the imaging lens of Example 1 when the object distance is 600 mm. As shown in Figure 3, according to the imaging lens according to this Example 1, each aberration can be well corrected even when the object distance is 600 mm.

[0114] Note that the spherical aberration diagram shows the aberration amounts for each wavelength of the F line (486 nm), d line (588 nm), and C line (656 nm). The astigmatism diagram and distortion diagram show the aberration amounts at the reference wavelength d line (588 nm). Also, the astigmatism diagram shows the aberration amount (solid line) on the sagittal image plane S and the aberration amount (dashed line) on the tangential image plane T, respectively (the same applies to FIGS. 5, 6, 8, and 9).

[0115] (Example 2) Basic lens data [Table 4]

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

[0117] [Table 6]

[0118] As shown in FIGS. 5 and 6, the imaging lens according to Example 2 can also correct each aberration well when the object distance is infinite and 600 mm, respectively.

[0119] (Example 3) Basic lens data [Table 7]

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

Table 8

[0121]

Table 9

[0122] As shown in FIGS. 8 and 9, also in the imaging lens according to the third embodiment, each aberration can be favorably corrected in the case where the object distance is infinity and in the case where the object distance is 600 mm.

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

[0124]

Table 10

Industrial Applicability

[0125] When the imaging lens according to the present invention is applied to a product having a camera function, it is possible to achieve both high performance and miniaturization while contributing to reducing the F-number and widening the angle of view of the camera.

Explanation of Signs

[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. A first lens having a negative refractive power, a second lens, a third lens having a positive refractive power, a fourth lens having a negative refractive power, a fifth lens having a positive refractive power, and a sixth lens having a negative refractive power, which are arranged in order from the object side toward the image side, wherein the second lens is a focus variable lens, and the sixth lens has a concave surface on the image side in the paraxial region. An imaging lens characterized by this.

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

3. The imaging lens according to claim 1, characterized by satisfying the following conditional expression (1). (1) 0.20 < T5 / D56 < 3.40 However, T5: The thickness on the optical axis of the fifth lens, D56: 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. An aperture stop is arranged adjacent to the second lens, and the imaging lens according to claim 1, characterized by satisfying the following conditional expression (2). (2) 0.70 < st_IM / L2_IM < 1.10 However, st_IM: The distance on the optical axis from the aperture stop to the imaging surface, L2_IM: The distance on the optical axis from the image-side surface of the second lens to the imaging surface.

5. The imaging lens according to claim 1, characterized by satisfying the following conditional expression (3). (3) 0.23 < T4 / T6 < 0.90 However, T4: The thickness on the optical axis of the fourth lens, T6: The thickness on the optical axis of the sixth lens.

6. The imaging lens according to claim 1, characterized by satisfying the following conditional expression (4). (4) 3.40 < r2 / D12 < 14.00 However, r2: The paraxial curvature radius 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.

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

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