Imaging lens

Abstract

To provide an image capturing lens which has a low height and yet is well corrected for aberrations.SOLUTION: An image capturing lens disclosed herein comprises a first lens L1 having positive refractive power, a second lens L2, a third lens L3, a fourth lens L4 having negative refractive power, a fifth lens L5, a sixth lens L6, a seventh lens L7 having positive refractive power, and an eighth lens L8 having negative refractive power, arranged in order from an object side to an image plane IM side. The fifth lens L5 has an image-side surface that is convex near an optical axis and the sixth lens L6 has an object-side surface that is concave near the optical axis. The image capturing lens satisfies the following conditional expression: -50.0<f8 / f<-3.0, where f represents a focal length of the entire lens system and f8 represents a focal length of the eighth lens L8.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an imaging lens that forms a subject image on an imaging element such as a CCD sensor or a CMOS sensor. [Background technology]

[0002] With the advancement of IoT (Internet of Things) technology, many products and devices, including not only mobile information devices such as smartphones and mobile phones, but also game consoles, home appliances, and automobiles, are now connected to networks, and various information is being shared between these devices. In an IoT environment, various services can be provided by using image information from cameras built into devices. The amount of image information transmitted over networks continues to increase every year, and the cameras required to be compact and have high resolution are required.

[0003] To obtain clear images with high resolution, it is necessary to effectively correct various aberrations in the imaging lens built into the camera. A lens configuration consisting of eight lenses allows for a high degree of freedom in design due to the large number of lenses that make up the imaging lens, and enables effective correction of various aberrations. Patent Document 1 discloses such an imaging lens with an eight-lens configuration.

[0004] The imaging lens described in Patent Document 1 consists of a positive first lens, a negative second lens, a positive third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, and a negative eighth lens. Of these, the first lens has a refractive power weaker than the refractive power of the entire lens system. The second lens has a thickness determined in relation to the distance between the second and third lenses. The third lens has a shape defined by the radii of curvature of the object-side surface and the image-plane-side surface. The imaging lens described in Patent Document 1 can correct various aberrations relatively well despite its wide angle. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Chinese Patent Application Publication No. 111007631 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, products and devices incorporating cameras have rapidly become smaller and more functional. For imaging lenses built into cameras, there is an ever-increasing demand for higher resolution and lower height. With the imaging lens described in Patent Document 1, it is difficult to achieve a low height while adequately correcting various aberrations.

[0007] An object of the present invention is to provide an imaging lens that is low in height yet can effectively correct various aberrations. [Means for solving the problem]

[0008] The imaging lens of the present invention is an imaging lens that forms a subject image on an imaging element, and is configured by arranging, in order from the object side to the image plane side, a first lens having positive refractive power, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens having positive refractive power, and an eighth lens having negative refractive power.

[0009] By making the refractive power of the first lens positive, the imaging lens can be made low-profile. Furthermore, by disposing an eighth lens with negative refractive power on the image plane side of the seventh lens with positive refractive power, the imaging lens can be made low-profile while effectively correcting chromatic aberration. In this specification, "low profile" refers to a small optical length, i.e., a small ratio of the optical axial distance from the object-side surface of the first lens to the image plane to the diagonal length of the image plane of the imaging element (optical length / diagonal length = total-to-diagonal ratio).

[0010] In the imaging lens having the above configuration, the second lens is preferably a meniscus lens with a convex surface facing the object side in the paraxial direction. By forming the second lens in this shape, coma, astigmatism, field curvature, and chromatic aberration can be effectively corrected.

[0011] In the imaging lens having the above configuration, it is desirable that the fourth lens has negative refractive power, and that the object-side surface of the fourth lens is a concave surface in the paraxial direction.

[0012] In the imaging lens having the above configuration, it is desirable that the image-side surface of the fifth lens be a paraxial convex surface. Also, it is desirable that the object-side surface of the sixth lens be a paraxial concave surface. With such shapes of the fifth lens and the sixth lens, it is possible to effectively correct field curvature.

[0013] In the imaging lens having the above configuration, it is desirable that the seventh lens has a paraxially concave surface on the object side. By forming the object side surface of the seventh lens in this shape, coma, astigmatism, and field curvature can be effectively corrected.

[0014] In the imaging lens having the above configuration, it is desirable that the eighth lens have an aspherical image-side surface with an inflection point. By forming the image-side surface of the eighth lens aspherical with an inflection point, it is possible to ensure back focus while satisfactorily correcting curvature of field and distortion in the peripheral areas of the image. In addition, it is possible to satisfactorily correct paraxial and peripheral aberrations while suppressing the angle of incidence of light rays emitted from the imaging lens onto the image plane of the imaging element within the range of the chief ray angle (CRA).

[0015] Furthermore, in the imaging lens having the above configuration, it is desirable that the surface of the eighth lens on the image side be a paraxially concave surface. By forming the eighth lens in this shape, it is possible to preferably achieve a low profile of the imaging lens while ensuring a sufficient back focus.

[0016] In this invention, the term "lens" refers to an optical element having refractive power. Therefore, optical elements such as prisms and flat filters that change the direction of light are not included in the "lens" of this invention, and these optical elements can be placed in front of or behind the imaging lens or between lenses as appropriate.

[0017] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (1). -50.0 <f8 / f<-3.0 (1) however, f: focal length of the entire lens system, f8: focal length of the eighth lens, Let's say.

[0018] By satisfying conditional expression (1), it is possible to reduce the height of the imaging lens while ensuring back focus, and it is also possible to correct field curvature, distortion, and coma in a well-balanced manner.

[0019] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (2). 0.70 <f1 / f<1.30 (2) however, f: focal length of the entire lens system, f1: focal length of the first lens, Let's say.

[0020] By satisfying conditional expression (2), it is possible to preferably achieve a low profile imaging lens while ensuring a sufficient back focus.

[0021] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (3). -2.20 <f2 / f3<-0.80 (3) however, f2: focal length of the second lens, f3: focal length of the third lens, Let's say.

[0022] By satisfying conditional expression (3), it is possible to reduce the height of the imaging lens and to effectively correct astigmatism.

[0023] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (4). -6.50 <f4 / f3<-1.50 (4) however, f3: focal length of the third lens, f4: focal length of the fourth lens, Let's say.

[0024] By satisfying conditional expression (4), the imaging lens can be made low-profile while effectively correcting spherical aberration and astigmatism.

[0025] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (5). 1.00 <f34 / f<4.00 (5) however, f: focal length of the entire lens system, f34: The combined focal length of the third and fourth lenses. Let's say.

[0026] By satisfying conditional expression (5), it is possible to reduce the height of the imaging lens and to effectively correct astigmatism and curvature of field.

[0027] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (6). -15.0 <f4 / f<-2.0 (6) however, f: focal length of the entire lens system, f4: focal length of the fourth lens, Let's say.

[0028] By satisfying conditional expression (6), it is possible to appropriately reduce the height of the imaging lens while ensuring a sufficient back focus, and also to effectively correct astigmatism and chromatic aberration of magnification.

[0029] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (7). -6.00 <f56 / f<-1.00 (7) however, f: focal length of the entire lens system, f56: The combined focal length of the fifth and sixth lenses, Let's say.

[0030] By satisfying conditional expression (7), the imaging lens can be made low-profile and spherical aberration and astigmatism can be corrected satisfactorily.

[0031] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (8). 2.0 <f7 / f<30.0 (8) however, f: focal length of the entire lens system, f7: focal length of the seventh lens, Let's say.

[0032] By satisfying conditional expression (8), it is possible to appropriately realize a low-profile imaging lens while ensuring a sufficient back focus, and also to appropriately correct spherical aberration, coma, astigmatism, distortion, and curvature of field in a well-balanced manner.

[0033] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (9). -4.00 <f7 / f8<-0.20 (9) however, f7: focal length of the seventh lens, f8: focal length of the eighth lens, Let's say.

[0034] By satisfying conditional expression (9), it is possible to reduce the height of the imaging lens while effectively correcting the curvature of field, and also to ensure the back focus.

[0035] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (10): 0.50 <f67 / f56<8.50 (10) however, f56: The combined focal length of the fifth and sixth lenses, f67: The combined focal length of the sixth and seventh lenses, Let's say.

[0036] By satisfying conditional expression (10), spherical aberration can be corrected well.

[0037] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (11). 0.10 <R2r / R3f<0.85 (11) however, R2r: paraxial radius of curvature of the image-side surface of the second lens, R3f: paraxial radius of curvature of the object side surface of the third lens, Let's say.

[0038] By satisfying conditional expression (11), it is possible to reduce the height of the imaging lens and to effectively correct astigmatism and chromatic aberration of magnification.

[0039] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (12). -90.0 <R4f / D34<-15.0 (12) however, R4f: paraxial radius of curvature of the object side surface of the fourth lens, D34: the distance on the optical axis between the third and fourth lenses, Let's say.

[0040] By satisfying conditional expression (12), it is possible to reduce the height of the imaging lens and to effectively correct astigmatism and chromatic aberration.

[0041] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (13). 0.15<|R5f / R5r|<1.35 (13) however, R5f: paraxial radius of curvature of the object side surface of the fifth lens, R5r: paraxial curvature radius of the image-side surface of the fifth lens element, Let's say.

[0042] By satisfying conditional expression (13), spherical aberration can be corrected well.

[0043] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (14). -2.00 <R6f / f<-0.40 (14) however, f: focal length of the entire lens system, R6f: paraxial radius of curvature of the object side surface of the sixth lens, Let's say.

[0044] By satisfying conditional expression (14), it is possible to realize a low-profile imaging lens while ensuring a sufficient back focus, and also to effectively correct spherical aberration and lateral chromatic aberration.

[0045] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (15). 0.80 <D34 / D45<2.00 (15) however, D34: the distance on the optical axis between the third and fourth lenses, D45: the distance on the optical axis between the fourth and fifth lenses, Let's say.

[0046] By satisfying conditional expression (15), it is possible to reduce the height of the imaging lens and to effectively correct astigmatism.

[0047] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (16). 0.01 <D56 / f<0.08 (16) however, f: focal length of the entire lens system, D56: the distance on the optical axis between the fifth and sixth lenses, Let's say.

[0048] By satisfying conditional expression (16), the imaging lens can be made low-profile and spherical aberration can be corrected satisfactorily.

[0049] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (17). 12.0 <f3 / T3<25.0 (17) however, f3: focal length of the third lens, T3: Thickness of the third lens on the optical axis, Let's say.

[0050] By satisfying conditional expression (17), the imaging lens can be made low-profile and spherical aberration and astigmatism can be corrected satisfactorily.

[0051] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (18). 0.50 <T8 / T7<1.50 (18) however, T7: Thickness of the seventh lens on the optical axis, T8: Thickness of the eighth lens on the optical axis, Let's say.

[0052] By satisfying conditional expression (18), it is possible to reduce the height of the imaging lens and to effectively correct astigmatism.

[0053] It is desirable that the imaging lens having the above configuration satisfy the following conditional expression (19): By satisfying conditional expression (19), chromatic aberration can be corrected well. 35.0<νd4 (19) however, νd4: Abbe number of the fourth lens, Let's say.

[0054] In order to correct chromatic aberration better, it is desirable that the imaging lens having the above configuration satisfy the following conditional expression (20). νd5<35.0 (20) however, νd5: Abbe number of the fifth lens, Let's say.

[0055] In order to correct chromatic aberration better, it is desirable that the imaging lens having the above configuration satisfy the following conditional expression (21). 35.0<νd6 (21) however, νd6: Abbe number of the sixth lens, Let's say.

[0056] In order to correct chromatic aberration better, it is desirable that the imaging lens having the above configuration satisfy the following conditional expression (22). 35.0<νd7 (22) however, νd7: Abbe number of the seventh lens, Let's say.

[0057] In order to correct chromatic aberration better, it is desirable that the imaging lens having the above configuration satisfy the following conditional expression (23). 35.0<νd8 (23) however, νd8: Abbe number of the 8th lens, Let's say.

[0058] In the imaging lens having the above configuration, it is desirable that the focal length of the eighth lens be longer than twice the focal length of the entire lens system. The seventh and eighth lenses are positioned closest to the image plane of the imaging element among the eight lenses. By using low-dispersion materials as defined by the above conditional expressions (22) and (23), chromatic aberration can be corrected even better.

[0059] However, in a high-pixel image sensor, the light receiving area of ​​each pixel is reduced, so the captured image may appear dark. As a method to correct this, an electric circuit is used to There are ways to improve sensitivity. However, increasing light sensitivity does not directly contribute to image formation. Noise components are also amplified. Therefore, it is necessary to create a sufficiently bright image without using electrical circuits. To obtain this, it is desirable that the imaging lens having the above configuration satisfy the following conditional expression (24): 0.55 <Dep / ih (24) however, Dep: entrance pupil diameter, ih: maximum image height on the image plane of the image sensor, Let's say.

[0060] In order to suitably reduce the height of the imaging lens of the present invention, it is desirable that the overall length to diagonal ratio expressed by the following conditional expression (25) be satisfied. 0.5 <TTL / (2×ih)<1.0 (25) however, TTL: The distance on the optical axis from the object side surface of the first lens to the image plane. ih: maximum image height on the image plane of the image sensor, Let's say.

[0061] It should be noted that, although an infrared cut filter, cover glass, or other insert is usually placed between the imaging lens and the image plane, in this specification the air equivalent length is used to indicate the distance on the optical axis of these inserts.

[0062] In the imaging lens of the present invention, it is desirable to arrange each of the lenses from the first lens to the eighth lens with an air gap between them. By arranging each lens with an air gap between them, the imaging lens of the present invention has a lens configuration that does not include any cemented lenses. With such a lens configuration, all eight lenses that make up the imaging lens can be made from plastic material, which reduces the manufacturing cost of the imaging lens.

[0063] In the imaging lens of the present invention, it is desirable to form both surfaces of each of the first through eighth lenses aspherical. By forming both surfaces of each lens aspherical, various aberrations can be corrected more effectively from the paraxial to the peripheral portions of the lenses.

[0064] It is desirable that the imaging lens of the present invention satisfy the condition 70°≦2ω, where ω is the angle of view. By satisfying this condition, the imaging lens can have a wider angle of view, and therefore the imaging lens can be made thinner and have a wider angle of view.

[0065] In this specification, the surface shape of each lens is specified by the sign of the radius of curvature. Whether the radius of curvature is positive or negative follows the general definition, i.e., the direction of light travel is positive, and the radius of curvature is positive when the center of the radius of curvature is on the image side of the lens surface, and negative when the center of the radius of curvature is on the object side. Therefore, "the object-side surface with a positive radius of curvature" refers to a convex surface on the object side, and "the object-side surface with a negative radius of curvature" refers to a concave surface on the object side. Furthermore, "the image-side surface with a positive radius of curvature" refers to a concave surface on the image side, and "the image-side surface with a negative radius of curvature" refers to a convex surface on the image side. Note that the radius of curvature in this specification refers to the paraxial radius of curvature, which may not match the general shape of the lens in a cross-sectional view. [Effects of the Invention]

[0066] The imaging lens of the present invention can provide an imaging lens that has high resolution with various aberrations well corrected, and yet is low in height and particularly suitable for incorporation into small cameras. [Brief explanation of the drawings]

[0067] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic configuration of an imaging lens according to Numerical Example 1. [Figure 2] 2 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging lens shown in FIG. [Figure 3] FIG. 10 is a cross-sectional view showing a schematic configuration of an imaging lens according to Numerical Example 2. [Figure 4] 4 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging lens shown in FIG. 3. [Figure 5] FIG. 10 is a cross-sectional view showing a schematic configuration of an imaging lens according to Numerical Example 3. [Figure 6] 6 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging lens shown in FIG. 5. [Figure 7] FIG. 10 is a cross-sectional view showing a schematic configuration of an imaging lens according to Numerical Example 4. [Figure 8]8A to 8C are aberration diagrams showing spherical aberration, astigmatism, and distortion of the imaging lens shown in FIG. [Figure 9] FIG. 10 is a cross-sectional view showing a schematic configuration of an imaging lens according to Numerical Example 5. [Figure 10] 10 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging lens shown in FIG. [Figure 11] FIG. 10 is a cross-sectional view showing a schematic configuration of an imaging lens according to Numerical Example 6. [Figure 12] 12A to 12C are aberration diagrams showing spherical aberration, astigmatism, and distortion of the imaging lens shown in FIG. [Figure 13] FIG. 11 is a cross-sectional view showing a schematic configuration of an imaging lens according to Numerical Example 7. [Figure 14] 14 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging lens shown in FIG. 13. [Figure 15] FIG. 13 is a cross-sectional view showing a schematic configuration of an imaging lens according to Numerical Example 8. [Figure 16] 16 is an aberration diagram showing spherical aberration, astigmatism, and distortion of the imaging lens shown in FIG. 15. FIG. [Figure 17] FIG. 13 is a cross-sectional view showing a schematic configuration of an imaging lens according to Numerical Example 9. [Figure 18] 18A to 18C are aberration diagrams showing spherical aberration, astigmatism, and distortion of the imaging lens shown in FIG. 17. DETAILED DESCRIPTION OF THE INVENTION

[0068] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described in detail with reference to the accompanying drawings. 1, 3, 5, 7, 9, 11, 13, 15, and 17 are cross-sectional views showing the schematic configurations of imaging lenses according to Numerical Examples 1 to 9 of this embodiment. Since the basic lens configurations are the same in all of the Numerical Examples, the imaging lens according to this embodiment will be described here with reference to the cross-sectional view of Numerical Example 1.

[0069] As shown in FIG. 1, the imaging lens according to this embodiment includes, in order from the object side to the image plane side, a first lens L1 having positive refractive power, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, a seventh lens L7 having positive refractive power, and an eighth lens L8 having negative refractive power. The first lens L1 through the eighth lens L8 are arranged with an air gap between them. A filter IR is disposed between the eighth lens L8 and the image plane IM of the image sensor. This filter IR can be omitted. Unless otherwise specified, the refractive power of each lens in this specification refers to the paraxial refractive power.

[0070] The first lens L1 has a shape in which the radius of curvature r2 of the object-side surface and the radius of curvature r3 of the image-plane-side surface are both positive. The first lens L1 is shaped as a meniscus lens with a convex surface facing the object side in a paraxial view. The shape of the first lens L1 is not limited to the shape according to Numerical Example 1. The shape of the first lens L1 may be any shape that gives it positive refractive power. For example, the shape of the first lens L1 may be a shape in which the radius of curvature r2 is positive and the radius of curvature r3 is negative, resulting in a biconvex lens in a paraxial view, or a shape in which the radii of curvature r2 and r3 are both negative, resulting in a meniscus lens with a concave surface facing the object side in a paraxial view. From the perspective of reducing the height of the imaging lens, it is desirable that the shape of the first lens L1 be a shape in which the radius of curvature r2 is positive, i.e., a shape in which the object-side surface is convex in a paraxial view.

[0071] The second lens L2 has a negative refractive power. The refractive power of the second lens L2 is not limited to being negative. The refractive power of the second lens L2 may be positive.

[0072] The second lens L2 has a shape in which the radius of curvature r4 of the object-side surface and the radius of curvature r5 (=R2r) of the image-plane-side surface are both positive. The second lens L2 has a shape that forms a meniscus lens with a convex surface facing the object side in a paraxial direction. The shape of the second lens L2 is not limited to the shape according to Numerical Example 1. For example, the shape of the second lens L2 may be a shape in which the radius of curvature r4 is negative and the radius of curvature r5 is positive, and may be a shape that forms a biconcave lens in a paraxial direction, or a shape that forms a biconvex lens in a paraxial direction. The second lens L2 may also be a shape that forms a meniscus lens with a concave surface facing the object side in a paraxial direction. From the perspective of reducing the height of the imaging lens, it is desirable that the shape of the second lens L2 be a shape in which the object-side surface is convex in a paraxial direction, similar to the first lens L1.

[0073] The third lens L3 has a positive refractive power. The refractive power of the third lens L3 is not limited to being positive. The refractive power of the third lens L3 may be negative.

[0074] The third lens L3 has a shape in which the radius of curvature r6 (= R3f) of the object-side surface and the radius of curvature r7 of the image-plane-side surface are both positive. The third lens L3 has a shape that forms a meniscus lens with a convex surface facing the object side paraxially. The shape of the third lens L3 is not limited to the shape according to Numerical Example 1. The third lens L3 in Numerical Example 9 is an example of a shape that forms a biconvex lens paraxially. The third lens L3 may also have a shape that forms a meniscus lens with a concave surface facing the object side paraxially or a shape that forms a biconcave lens paraxially. In consideration of reducing the height of the imaging lens, it is desirable that the shape of the third lens L3 be a shape in which the object-side surface is convex paraxially.

[0075] The fourth lens L4 has negative refractive power. The refractive power of the fourth lens L4 is not limited to being negative. The refractive power of the fourth lens L4 may be positive. Furthermore, the refractive power of the fourth lens L4 may be zero paraxially and may be positive or negative in the peripheral portion.

[0076] The fourth lens L4 has a shape in which the radius of curvature r8 (=R4f) of the object-side surface and the radius of curvature r9 of the image-plane-side surface are both negative. The fourth lens L4 has a shape that forms a meniscus lens with a concave surface facing the object side paraxially. The shape of the fourth lens L4 is not limited to the shape according to Numerical Example 1. The shape of the fourth lens L4 may be any shape that provides negative refractive power. The fourth lens L4 in Numerical Examples 4, 5, and 7 to 9 are examples of a shape that forms a biconcave lens paraxially. The shape of the fourth lens L4 may also be a shape that forms a meniscus lens with a convex surface facing the object side paraxially. In consideration of good correction of various aberrations, it is desirable that the shape of the fourth lens L4 be a shape in which the object-side surface is concave paraxially.

[0077] The fifth lens L5 has positive refractive power. The refractive power of the fifth lens L5 is not limited to being positive. The imaging lenses according to Numerical Examples 6 to 9 are examples of lens configurations in which the refractive power of the fifth lens L5 is negative. Furthermore, the refractive power of the fifth lens L5 is zero paraxially, and may be positive or negative in the peripheral portion.

[0078] The fifth lens L5 has a shape in which the radius of curvature r10 (= R5f) of the object-side surface and the radius of curvature r11 (= R5r) of the image-plane-side surface are both negative. The fifth lens L5 has a shape that forms a meniscus lens with a concave surface facing the object side paraxially. The shape of the fifth lens L5 is not limited to the shape according to Numerical Example 1. The fifth lens L5 in Numerical Example 3 is an example of a shape that forms a biconvex lens paraxially. In addition to this, the shape of the fifth lens L5 may also be a shape that forms a meniscus lens with a convex surface facing the object side paraxially, or a shape that forms a biconcave lens paraxially.

[0079] The sixth lens L6 has negative refractive power. The refractive power of the sixth lens L6 is not limited to being negative. The refractive power of the sixth lens L6 may be positive. Furthermore, the refractive power of the sixth lens L6 may be zero paraxially and may be positive or negative in the peripheral portion.

[0080] The sixth lens L6 has a shape in which the radius of curvature r12 (=R6f) of the object-side surface and the radius of curvature r13 of the image-plane-side surface are both negative. The sixth lens L6 has a shape that forms a meniscus lens with a concave surface facing the object side paraxially. The shape of the sixth lens L6 is not limited to the shape according to Numerical Example 1. The fifth lens L5 in Numerical Examples 2, 3, and 8 is an example of a shape that forms a biconcave lens paraxially. The shape of the sixth lens L6 may be a shape that forms a meniscus lens with a convex surface facing the object side paraxially, or a shape that forms a biconcave lens paraxially. In order to achieve a low profile of the imaging lens and to effectively correct spherical aberration, it is desirable that the shape of the sixth lens be a shape in which the object-side surface is concave paraxially.

[0081] The seventh lens L7 has a shape in which the radius of curvature r14 of the object-side surface and the radius of curvature r15 of the image-plane-side surface are both positive. The seventh lens L7 has a shape that forms a meniscus lens with a convex surface facing the object side in a paraxial view. The shape of the seventh lens L7 is not limited to the shape according to Numerical Example 1, and may have any shape that has positive refractive power. The shape of the seventh lens L7 may be a shape that forms a meniscus lens with a concave surface facing the object side in a paraxial view, or a shape that forms a biconvex lens in a paraxial view.

[0082] The eighth lens L8 has a shape in which the radius of curvature r16 of the object-side surface and the radius of curvature r17 of the image-side surface are both positive. The eighth lens L8 has a shape that forms a meniscus lens with a convex surface facing the object side in a paraxial direction. The shape of the eighth lens L8 is not limited to the shape according to Numerical Example 1. The shape of the eighth lens L8 may be any shape that has negative refractive power. The shape of the eighth lens L8 may be a meniscus lens with a concave surface facing the object side in a paraxial direction, or a biconcave lens in a paraxial direction. In order to reduce the height of the imaging lens and achieve good correction of various aberrations, it is desirable that the shape of the eighth lens L8 be a shape in which the surface on the image side is concave in a paraxial direction.

[0083] Both surfaces of the seventh lens L7 and the eighth lens L8 are aspherical surfaces with inflection points. Here, an inflection point refers to a point on a curve where the sign of curvature changes, or a point on a lens surface where the direction of curvature of the curve changes. Both surfaces of the seventh lens L7 and the eighth lens L8 in the imaging lens according to this embodiment are aspherical surfaces with polar points. The shapes of the seventh lens L7 and the eighth lens L8 allow for excellent correction of not only on-axis chromatic aberration but also off-axis chromatic aberration of magnification, and also allow the angle of incidence of light rays emerging from the imaging lens onto the image plane IM to be suitably controlled within the CRA range. Depending on the required optical performance and the degree of height reduction of the imaging lens, the surfaces of the seventh lens L7 and the eighth lens L8, except for the surface of the eighth lens L8 facing the image plane, may be formed as aspherical surfaces without inflection points.

[0084] The imaging lens according to this embodiment satisfies the following conditional expressions (1) to (24). -50.0 <f8 / f<-3.0 (1) 0.70 <f1 / f<1.30 (2) -2.20 <f2 / f3<-0.80 (3) -6.50 <f4 / f3<-1.50 (4) 1.00 <f34 / f<4.00 (5) -15.0 <f4 / f<-2.0 (6) -6.00 <f56 / f<-1.00 (7) 2.0 <f7 / f<30.0 (8) -4.00 <f7 / f8<-0.20 (9) 0.50 <f67 / f56<8.50 (10) 0.10 <R2r / R3f<0.85 (11) -90.0 <R4f / D34<-15.0 (12) 0.15<|R5f / R5r|<1.35 (13) -2.00 <R6f / f<-0.40 (14) 0.80 <D34 / D45<2.00 (15) 0.01 <D56 / f<0.08 (16) 12.0 <f3 / T3<25.0 (17) 0.50 <T8 / T7<1.50 (18) 35.0<νd4 (19) νd5<35.0 (20) 35.0<νd6 (21) 35.0<νd7 (22) 35.0<νd8 (23) 0.55 <Dep / ih (24) however, f: focal length of the entire 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, f4: focal length of the fourth lens L4, f7: focal length of the seventh lens L7, f8: focal length of the eighth lens L8, f34: The combined focal length of the third lens L3 and the fourth lens L4, f56: The combined focal length of the fifth lens L5 and the sixth lens L6, f67: The combined focal length of the sixth lens L6 and the seventh lens L7 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, R4f: paraxial radius of curvature of the object side surface of the fourth lens L4, R5f: paraxial radius of curvature of the object side surface of the fifth lens L5, R5r: paraxial curvature radius 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, D34: the distance on the optical axis between the third lens L3 and the fourth lens L4, D45: the distance on the optical axis between the fourth lens L4 and the fifth lens L5, D56: the distance on the optical axis between the fifth lens L5 and the sixth lens L6, T3: thickness of the third lens L3 on the optical axis X, T7: thickness of the seventh lens L7 on the optical axis X, T8: thickness of the eighth lens L8 on the optical axis X, νd4: Abbe number of the fourth lens L4, νd5: Abbe number of the fifth lens L5, νd6: Abbe number of the sixth lens L6, νd7: Abbe number of the seventh lens L7, νd8: Abbe number of the eighth lens L8, Dep: entrance pupil diameter, ih: maximum image height on the image plane IM of the image sensor, Let's say.

[0085] The imaging lens according to this embodiment satisfies the overall length to diagonal ratio shown in the following conditional expression (25). 0.5 <TTL / (2×ih)<1.0 (25) however, TTL: the distance on the optical axis X from the object-side surface of the first lens L1 to the image plane IM, Let's say.

[0086] Moreover, the imaging lens according to this embodiment satisfies the following conditional expression. 70°≦2ω however, ω: Half angle of view, Let's say.

[0087] It is not necessary to satisfy all of the above conditional expressions, and by satisfying each of the above conditional expressions individually, it is possible to obtain the respective effects corresponding to each conditional expression.

[0088] The imaging lens according to this embodiment achieves more preferable effects by satisfying the following conditional expressions (2a) to (23a). 0.80 <f1 / f<1.20 (2a) -2.00 <f2 / f3<-1.00 (3a) -6.00 <f4 / f3<-2.00 (4a) 1.50 <f34 / f<3.00 (5a) -12.0 <f4 / f<-3.0 (6a) -5.00 <f56 / f<-1.00 (7a) 3.0 <f7 / f<28.0 (8a) -3.00 <f7 / f8<-0.30 (9a) 0.80 <f67 / f56<8.00 (10a) 0.25 <R2r / R3f<0.70 (11a) -90.0 <R4f / D34<-20.0 (12a) 0.15<|R5f / R5r|<1.25 (13a) -1.80 <R6f / f<-0.50 (14a) 1.00 <D34 / D45<1.90 (15a) 0.01 <D56 / f<0.07 (16a) 13.0 <f3 / T3<23.0 (17a) 0.70 <T8 / T7<1.40 (18a) 35.0<νd4<95.0 (19a) 13.0<νd5<35.0 (20a) 35.0<νd6<95.0 (21a) 35.0<νd7<95.0 (22a) 35.0<νd8<95.0 (23a)

[0089] For the above conditional expressions (2a) to (23a), the lower limit value or upper limit value of the corresponding conditional expressions (2) to (23) may be applied.

[0090] In this embodiment, the lens surfaces of the lenses are aspherical. The aspherical formula for these aspherical surfaces is given by the following equation:

number

[0091] Next, numerical examples of the imaging lens according to this embodiment are shown. In each table showing basic lens data, f denotes the focal length of the entire lens system, Fno denotes the F-number, ω denotes the half angle of view, ih denotes the maximum image height on the image plane IM, and TTL denotes the distance on the optical axis from the object-side surface of the first lens L1 to the image plane IM. Also, i denotes the surface number counted from the object side, r denotes the paraxial radius of curvature, d denotes the inter-surface distance on the optical axis X, nd denotes the refractive index at a reference wavelength of 588 nm, and νd denotes the Abbe number at that reference wavelength. Note that a surface with an asterisk (*) next to the surface number indicates that it is aspherical.

[0092] Numerical Example 1 Basic lens data [Table 1]

[0093] [Table 2]

[0094] FIG. 2 is an aberration diagram showing spherical aberration (mm), astigmatism (mm), and distortion (%). The astigmatism diagram and distortion diagram show the amount of aberration at a reference wavelength (588 nm). The astigmatism diagram also shows the sagittal image plane (S) and tangential image plane (T), respectively (the same applies to FIGS. 4, 6, 8, 10, 12, 14, 16, and 18). As shown in FIG. 2, the imaging lens according to Numerical Example 1 can effectively correct various aberrations.

[0095] Numerical Example 2 Basic lens data [Table 3]

[0096] [Table 4]

[0097] As shown in FIG. 4, the imaging lens according to Numerical Example 2 can also effectively correct various aberrations.

[0098] Numerical Example 3 Basic lens data [Table 5]

[0099] [Table 6]

[0100] As shown in FIG. 6, the imaging lens according to Numerical Example 3 also makes it possible to correct various aberrations satisfactorily.

[0101] Numerical Example 4 Basic lens data [Table 7]

[0102] [Table 8]

[0103] As shown in FIG. 8, the imaging lens according to Numerical Example 4 can also effectively correct various aberrations.

[0104] Numerical Example 5 Basic lens data [Table 9]

[0105] [Table 10]

[0106] As shown in FIG. 10, the imaging lens according to Numerical Example 5 also makes it possible to correct various aberrations satisfactorily.

[0107] Numerical Example 6 Basic lens data [Table 11]

[0108] [Table 12]

[0109] As shown in FIG. 12, the imaging lens according to Numerical Example 6 can also effectively correct various aberrations.

[0110] Numerical Example 7 Basic lens data [Table 13]

[0111] [Table 14]

[0112] As shown in FIG. 14, the imaging lens according to Numerical Example 7 can also effectively correct various aberrations.

[0113] Numerical Example 8 Basic lens data [Table 15]

[0114] [Table 16]

[0115] As shown in FIG. 16, the imaging lens according to Numerical Example 8 can also effectively correct various aberrations.

[0116] Numerical Example 9 Basic lens data [Table 17]

[0117] [Table 18]

[0118] As shown in FIG. 18, the imaging lens according to Numerical Example 9 also makes it possible to correct various aberrations satisfactorily.

[0119] As described above, the imaging lens according to this embodiment can effectively correct various aberrations despite its small overall length-to-angle ratio. Below, values ​​corresponding to conditional expressions (1) to (24) of each numerical example according to this embodiment are shown. [Table 19]

[0120] Therefore, when the imaging lens according to the above embodiment is applied to the imaging optical system of a camera built into a portable information device such as a smartphone, a mobile phone, or a personal digital assistant, or into a game console, a home appliance, or an automobile, it is possible to achieve both high functionality and miniaturization of the camera. [Industrial Applicability]

[0121] The present invention is applicable to imaging lenses incorporated into relatively small cameras built into portable information devices such as smartphones, medical devices, game consoles, home appliances, automobiles, and the like. [Explanation of symbols]

[0122] X optical axis ST aperture stop L1 First lens L2 Second lens L3 Third lens L4 4th lens L5 Fifth lens L6 6th lens L7 7th lens L8 8th lens IR filter IM image plane

Claims

1. An imaging lens that forms a subject image on an imaging element, the lens including the following elements in order from the object side to the image plane side: a first lens having a positive refractive power; a second lens having a negative refractive power; a third lens having a positive refractive power; a fourth lens having a negative refractive power; A fifth lens; a sixth lens having a negative refractive power; a seventh lens having a positive refractive power; and an eighth lens having a negative refractive power, the fifth lens has a surface on the image side that is convex on the paraxial direction; the sixth lens has an object-side surface that is paraxially concave; An imaging lens characterized by satisfying the following conditional expression: -50.0<f8 / f<-3.0 however, f: focal length of the entire lens system, f8: the focal length of the eighth lens, Let us assume that.

2. 2. The imaging lens according to claim 1, wherein the following condition is satisfied: -6.50<f4 / f3<-1.50 however, f3: the focal length of the third lens, f4: the focal length of the fourth lens, Let us assume that.

3. 2. The imaging lens according to claim 1, wherein the following condition is satisfied: -6.00<f56 / f<-1.00 however, f: focal length of the entire lens system, f56: a composite focal length of the fifth lens and the sixth lens, Let us assume that.

4. 2. The imaging lens according to claim 1, wherein the following condition is satisfied: 2.0<f7 / f<30.0 however, f: focal length of the entire lens system, f7: the focal length of the seventh lens, Let us assume that.

5. 2. The imaging lens according to claim 1, wherein the following condition is satisfied: -90.0<R4f / D34<-15.0 however, R4f: paraxial radius of curvature of the object side surface of the fourth lens, D34: the distance on the optical axis between the third lens and the fourth lens, Let us assume that.

6. 2. The imaging lens according to claim 1, wherein the following condition is satisfied: -2.00<R6f / f<-0.40 however, f: focal length of the entire lens system, R6f: paraxial radius of curvature of the object side surface of the sixth lens, Let us assume that.

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