Imaging lens

Abstract

The present invention relates to an imaging lens, comprising a first lens group (G1) with positive focal power, an aperture, a second lens group (G2) with positive focal power, and a third lens group (G3) with positive or negative focal power, arranged sequentially from the object side to the image side. The third lens group (G3) is a fixed group, and the first lens group (G1) and the second lens group (G2) form a focusing group that can move along the optical axis. The imaging lens of the present invention is arranged according to the above definitions and can achieve the characteristics of large aperture, high resolution, low distortion, uniform image quality, large depth of field, good color reproduction, and high contrast.

Description

Technical Field

[0001] The present invention relates to the field of optical devices, and in particular to an imaging lens. Background Art

[0002] Machine vision refers to the use of machines to replace human eyes for measurement and judgment. The captured target is converted into an image signal, which is transmitted to a dedicated image processing system to obtain the morphological information of the captured target. According to the pixel distribution, brightness, color and other information, it is converted into a digital signal; the image system performs various operations on these signals to extract the target's features, such as position, size, appearance, etc., and then outputs the results according to preset conditions to realize automatic recognition, judgment, measurement and other functions.

[0003] Therefore, imaging systems used in machine vision have very high requirements for pixel resolution, image uniformity, distortion, brightness, and color reproduction. However, the machine vision lenses currently available on the market have low optical magnification, small imaging frames, large distortion, uneven image clarity, and a narrow working object distance range. Although these machine vision lenses have a wide range of imaging, they lack detailed imaging, have a low dynamic range, and lack excellent color and contrast.

[0004] As the use of machine vision becomes more and more extensive, the requirements for machine vision imaging systems are becoming higher and higher. The machine vision lenses currently on the market are increasingly unable to meet market demand, especially in some high-precision high-tech fields with high imaging quality requirements. Summary of the Invention

[0005] The object of the present invention is to solve the above problems and provide an imaging lens with large aperture, high resolution, low distortion, uniform image quality, large depth of field, good color reproduction and high contrast.

[0006] To achieve the objectives of the present invention, the present invention provides an imaging lens, comprising a first lens group with positive focal power, an aperture, a second lens group with positive focal power, and a third lens group with positive or negative focal power, arranged in sequence from the object side to the image side. The third lens group is a fixed group, and the first lens group and the second lens group constitute a focusing group that is movable along the optical axis.

[0007] According to one aspect of the present invention, the first lens group includes at least two positive power lenses and one negative power lens, and the lens closest to the object side in the first lens group is a positive power lens, and the lens closest to the image side is a negative power lens.

[0008] According to one aspect of the present invention, along the direction from the object side to the image side, the lens closest to the object side in the first lens group is a biconvex lens, a convex-concave lens or a convex-planar lens.

[0009] According to one aspect of the present invention, the first lens group includes a doublet lens, and along the object side to image side direction, the doublet lens is composed of a positive power lens and a negative power lens.

[0010] According to one aspect of the present invention, the refractive index of the positive power lens in the doublet lens in the first lens group is ND, and the Abbe number is VD, which satisfies the following: 60≤VD≤96, 1.43≤ND≤1.65.

[0011] According to one aspect of the present invention, the second lens group includes at least two positive power lenses and one negative power lens, and the lens closest to the object side in the second lens group is a negative power lens, and the lens closest to the image side is a positive power lens.

[0012] According to one aspect of the present invention, along the direction from the object side to the image side, the lens closest to the image side in the second lens group is a biconvex lens, a meniscus lens or a plano-convex lens.

[0013] According to one aspect of the present invention, the second lens group includes a doublet lens, and along the object side to image side direction, the doublet lens is composed of a negative power lens and a positive power lens.

[0014] According to one aspect of the present invention, the third lens group includes at least one positive power lens and one negative power lens. Along the object side to the image side, the two lenses close to the object side in the third lens group are arranged in the order of positive power lens and negative power lens, or in the order of negative power lens and positive power lens.

[0015] According to one aspect of the present invention, the positive power lens in the third lens group is a biconvex lens, a convex-concave lens or a convex-planar lens, and the negative power lens is a biconcave lens, a convex-concave lens or a convex-concave lens.

[0016] According to one aspect of the present invention, the focal length of the focusing group consisting of the first lens group, the aperture and the second lens group is fm, and the focal length of the imaging lens is f, which satisfies the relationship: 1.0≤fm / f≤1.5.

[0017] According to one aspect of the present invention, the focal length of the third lens group is fg3, and the focal length of the imaging lens is f, which satisfies: 3.5≤|fg3 / f|≤8.5.

[0018] According to one aspect of the present invention, the total optical length of the imaging lens is TTL, and the focal length of the imaging lens is f, which satisfies 1.35≤TTL / f≤1.75.

[0019] The imaging lens of the present invention uses a first lens group with positive optical power, a second lens group with positive optical power, and a third lens group with positive or negative optical power, so that the imaging system has smaller distortion and smaller dispersion.

[0020] The imaging lens of the present invention has a first lens group comprising at least two positive-power lenses and one negative-power lens. The lens closest to the object side of the first lens group has a positive power, while the lens closest to the image side has a negative power. This arrangement, through the combination of positive and negative powers, facilitates correction of spherical aberration, astigmatism, and distortion within the first lens group, facilitating the realization of a wide aperture while also reducing sensitivity to tolerances within the lens group.

[0021] The imaging lens of the present invention includes a doublet in the first lens group. The doublet is composed of a positive and negative optical power lens in the object-to-image direction. This arrangement allows the doublet to be combined with appropriate optical powers to correct distortion, coma, and lateral chromatic aberration in the optical system, thereby ensuring near-diffraction-limited image quality and image plane consistency.

[0022] In the imaging lens of the present invention, the refractive index (ND) and Abbe number (VD) of the positive-power lens in the doublet of the first lens group satisfy the following conditions: 60 ≤ VD ≤ 96, and 1.43 ≤ ND ≤ 1.65. By properly matching these conditions, the lens can effectively correct chromatic aberration of the imaging system and improve image quality. Furthermore, the lens significantly contributes to maintaining image stability in the imaging system under normal temperature conditions.

[0023] The imaging lens of the present invention comprises a doublet in the second lens group. The doublet, along the object-to-image direction, is composed of a negative and positive power lens. The use of the doublet, combined with appropriate optical powers and in conjunction with the first lens group, facilitates correction of spherical aberration, astigmatism, coma, and distortion within the focusing lens group. This also reduces the proportion of aberration correction burden placed on the first lens group, further reducing the tolerance sensitivity of the active lens group, thereby significantly ensuring excellent image consistency within the optical system. This overall enhances the imaging quality of the optical system.

[0024] The imaging lens of the present invention satisfies the relationship: 1.0≤fm / f≤1.5, so that the optical system can quickly collect incident light, reduce field curvature and astigmatism, and achieve and maintain small distortion.

[0025] The imaging lens of the present invention satisfies the following condition: 3.5≤|fg3 / f|≤8.5. By rationally matching the positive and negative focal powers and focal power sizes of the first and second lens groups, the aberration correction burden ratio between the first and second lens groups of the optical system can be balanced, thereby facilitating guaranteed focusing performance and better ensuring that the imaging system achieves high image quality requirements close to the diffraction limit.

[0026] The imaging lens of the present invention is configured according to the above-mentioned limitations, and can achieve the characteristics of large aperture, high resolution, low distortion, uniform image quality, large depth of field, good color reproduction, and high contrast. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematically showing the structure of an imaging lens according to Embodiment 1 of the present invention;

[0028] Figure 2 Schematically showing an MTF diagram of the imaging lens according to Example 1 of the present invention when focusing at the optimal working object distance;

[0029] Figure 3 Schematically showing an MTF defocus diagram of the imaging lens at an optimal working object distance and low temperature according to Example 1 of the present invention;

[0030] Figure 4 Schematically showing an MTF defocus diagram of the imaging lens at an optimal working object distance and high temperature according to Example 1 of the present invention;

[0031] Figure 5 Schematic diagram showing the optical distortion of the imaging lens according to Example 1 of the present invention;

[0032] Figure 6 Schematically showing the structure of an imaging lens according to Embodiment 2 of the present invention;

[0033] Figure 7 Schematically showing an MTF diagram of an imaging lens according to Example 2 of the present invention when focusing at an optimal working object distance;

[0034] Figure 8 Schematically showing an MTF defocus diagram of an imaging lens at an optimal working object distance and low temperature according to Example 2 of the present invention;

[0035] Figure 9 Schematically showing an MTF defocus diagram of an imaging lens at an optimal working object distance and a high temperature state according to Example 2 of the present invention;

[0036] Figure 10 Schematic diagram showing the optical distortion of the imaging lens according to Example 2 of the present invention;

[0037] Figure 11Schematically showing the structure of an imaging lens according to Embodiment 3 of the present invention;

[0038] Figure 12 Schematically showing an MTF diagram of the imaging lens according to Example 3 of the present invention when focusing at the optimal working object distance;

[0039] Figure 13 Schematically showing an MTF defocus diagram of an imaging lens at an optimal working object distance and low temperature according to Example 3 of the present invention;

[0040] Figure 14 Schematically showing an MTF defocus diagram of an imaging lens at an optimal working object distance and a high temperature state according to Example 3 of the present invention;

[0041] Figure 15 Schematic diagram showing the optical distortion of the imaging lens according to Example 3 of the present invention;

[0042] Figure 16 Schematically showing the structure of an imaging lens according to Embodiment 4 of the present invention;

[0043] Figure 17 Schematically showing an MTF diagram of an imaging lens according to Example 4 of the present invention when focusing at an optimal working object distance;

[0044] Figure 18 Schematically showing an MTF defocus diagram of an imaging lens at an optimal working object distance and low temperature according to Example 4 of the present invention;

[0045] Figure 19 Schematically showing an MTF defocus diagram of an imaging lens at an optimal working object distance and a high temperature state according to Example 4 of the present invention;

[0046] Figure 20 Schematic diagram showing the optical distortion of the imaging lens according to Example 4 of the present invention;

[0047] Figure 21 Schematically showing the structure of an imaging lens according to Embodiment 5 of the present invention;

[0048] Figure 22 Schematically showing an MTF diagram of the imaging lens according to Example 5 of the present invention when focusing at the optimal working object distance;

[0049] Figure 23 Schematically showing an MTF defocus diagram of an imaging lens at an optimal working object distance and low temperature according to Example 5 of the present invention;

[0050] Figure 24 Schematically showing an MTF defocus diagram of an imaging lens at an optimal working object distance and a high temperature state according to Example 5 of the present invention;

[0051] Figure 25 The optical distortion diagram of the imaging lens according to Example 5 of the present invention is schematically shown. DETAILED DESCRIPTION

[0052] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be derived from these drawings without inventive effort.

[0053] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. The embodiments cannot be described one by one here, but the embodiments of the present invention are not limited to the following embodiments.

[0054] Reference Figure 1 As shown, the present invention provides an imaging lens, comprising a first lens group G1 with positive focal power, an aperture, a second lens group G2 with positive focal power, and a third lens group G3 with positive or negative focal power, arranged sequentially from the object side to the image side. The third lens group G3 is a fixed group, while the first lens group G1, the aperture, and the second lens group G2 form a focusing group that can move along the optical axis when imaging from an object at infinity to an object at close range. The imaging lens of the present invention utilizes a first lens group G1 with positive focal power, a second lens group G2 with positive focal power, and a third lens group G3 with positive or negative focal power, resulting in an imaging system with reduced distortion and less chromatic aberration.

[0055] In the present invention, the first lens group G1 includes at least two positive power lenses and one negative power lens, and the lens closest to the object side in the first lens group G1 is a positive power lens, and the lens closest to the image side is a negative power lens.

[0056] Such an arrangement, through the use of a combination of positive and negative optical powers, is conducive to correcting spherical aberration, astigmatism and distortion within the first lens group G1, is conducive to achieving a large aperture, and can also reduce the tolerance sensitivity within the group.

[0057] According to one embodiment of the present invention, along the object side to image side direction, the lens closest to the object side in the first lens group G1 is a biconvex lens, a convex-concave lens or a convex-planar lens.

[0058] In the present invention, the first lens group G1 includes a doublet lens. The doublet is composed of a positive and a negative optical power lens, viewed from the object side to the image side. This arrangement allows the doublet lens to be matched with appropriate optical powers, effectively correcting distortion, coma, and lateral chromatic aberration in the optical system, thereby ensuring near-diffraction-limited image quality and image plane consistency.

[0059] In this invention, the refractive index ND and Abbe number VD of the positive-power lens in the doublet of the first lens group G1 satisfy the following conditions: 60 ≤ VD ≤ 96, and 1.43 ≤ ND ≤ 1.65. Meeting these conditions and properly matching the optical power and Abbe number effectively corrects chromatic aberration in the imaging system, improving image quality. Furthermore, this lens significantly contributes to maintaining image stability in the imaging system under normal temperature conditions.

[0060] In the present invention, the second lens group G2 includes at least two positive power lenses and one negative power lens, and the lens closest to the object side in the second lens group G2 is a negative power lens, and the lens closest to the image side is a positive power lens. Along the object side to the image side, the lens closest to the image side in the second lens group G2 is a biconvex lens, a concave-convex lens, or a plano-convex lens. The second lens group G2 includes a doublet lens, and along the object side to the image side, the doublet lens is a combination of a negative power lens and a positive power lens. The use of the doublet lens, with appropriate optical power, cooperates with the first lens group, which is conducive to correcting spherical aberration, astigmatism, coma and distortion within the focusing lens group. At the same time, reducing the proportion of the aberration correction burden of the first lens group G1 can better reduce the tolerance sensitivity of the active group, thereby greatly ensuring that the optical system has good image surface consistency. Comprehensively improve the imaging quality of the optical system.

[0061] In the present invention, the third lens group G3 includes at least one positive power lens and one negative power lens. From the object side to the image side, the two lenses closer to the object side of the third lens group G3 are arranged in the order of positive power lens, negative power lens, or negative power lens, then positive power lens. The positive power lens in the third lens group G3 can be a biconvex lens, a convexo-concave lens, or a convex-planar lens, and the negative power lens can be a biconcave lens, a convexo-concave lens, or a convexo-concave lens.

[0062] The imaging lens of the present invention is provided with the first lens group G1, the second lens group G2, and the third lens group G3 according to the above-mentioned definition, so that the imaging system of the imaging lens of the present invention forms a Gaussian structure, which can effectively correct distortion, converge light, eliminate vignetting, and reduce spherical aberration.

[0063] In the present invention, the focal length of the focusing group consisting of the first lens group G1, the aperture stop, and the second lens group G2 is fm, and the focal length of the imaging lens is f, satisfying the relationship: 1.0 ≤ fm / f ≤ 1.5. Within this relationship, the optical system is able to quickly collect incident light, minimize field curvature and astigmatism, and achieve and maintain minimal distortion.

[0064] In the present invention, the focal length of the third lens group G3 is fg3, and the focal length of the imaging lens is f, satisfying the following relationship: 3.5 ≤ |fg3 / f| ≤ 8.5. Meeting this relationship allows for a balanced aberration correction ratio between the first and second lens groups G1 and G2 in the optical system by properly matching the positive and negative focal powers and their respective focal powers, thereby ensuring optimal focusing performance and better ensuring that the imaging system achieves high image quality requirements close to the diffraction limit.

[0065] In addition, in the present invention, the total optical length of the imaging lens is TTL, the focal length of the imaging lens is f, and 1.35≤TTL / f≤1.75 is satisfied.

[0066] In summary, the imaging lens of the present invention is configured according to the above limitations, and can achieve the characteristics of large aperture, high resolution, low distortion, uniform image quality, large depth of field, good color reproduction, and high contrast.

[0067] Five groups of specific implementations are given below based on the above-mentioned configuration of the present invention to specifically illustrate the imaging lens according to the present invention.

[0068] The data of the five implementation methods are as shown in Table 1 below:

[0069]

[0070]

[0071] Table 1

[0072] Implementation method one:

[0073] Figure 1 FIG. 1 is a diagram schematically showing the structure of an imaging lens according to a first embodiment of the present invention.

[0074] In the first embodiment, the total length of the optical system TTL=42.9 mm, the system focal length f=25.1 mm, the system imaging object distance range 0.15 m to inf, the system frame Y=12 mm, and the F number FNO=3.1.

[0075] Table 2 below lists the relevant parameters of each lens of this embodiment, including surface type, radius of curvature, thickness, refractive index of the material, and Abbe number:

[0076] Surface number Surface type R-value thickness Refractive index Abbe number sur1 standard 20.54 2.35 1.85 52.35 sur2 standard 52.41 0.5 sur3 standard 8.45 2.95 1.6 68.0 sur4 standard 25.71 1.2 1.58 46.17 sur5 standard 6.88 5.57 Stop standard infinity 3.15 Sur7 standard -8.84 0.8 1.68 33.85 Sur8 standard -45.37 2.5 1.76 50.35 Sur9 standard -8.34 0.3 Sur10 standard 75.35 1.7 1.76 50.35 sur11 standard -45.65 3.13 sur12 standard 30.22 1.6 1.68 35.85 sur13 standard 18.34 0.5 sur14 standard 25.73 3.5 1.64 60.4 sur15 standard 95.37 13.1 Image plane φI standard infinity -

[0077] Table 2

[0078] Combine Figure 1As shown, in this embodiment, the first lens group G1 includes three lenses (L1-L3), of which lenses L2 and L3 form a doublet. The second lens group G2 includes three lenses (L4-L6), of which lenses L4 and L5 form a doublet. The third lens group G3 includes two lenses (L7 and L8).

[0079] Figure 2-5 Schematic diagrams illustrate the MTF graph at optimal working object distance, the MTF through-focus graph at low temperature, the MTF through-focus graph at high temperature, and the optical distortion graph of the imaging lens according to Example 1 of the present invention. As can be seen from the accompanying figures, the imaging lens obtained according to Example 1 of the present invention achieves the characteristics of large aperture, high resolution, low distortion, uniform image quality, large depth of field, excellent color reproduction, and high contrast.

[0080] Implementation method 2:

[0081] Figure 6 FIG. 1 is a diagram schematically showing the structure of an imaging lens according to a second embodiment of the present invention.

[0082] In the second embodiment, the total length of the optical system TTL=43.5 mm, the system focal length f=26.4 mm, the system imaging object distance range 0.15 m to inf, the system frame Y=12.5 mm, and the F number FNO=2.5.

[0083] Table 3 below lists the relevant parameters of each lens of this embodiment, including surface type, radius of curvature, thickness, refractive index of the material, and Abbe number:

[0084] Surface number Surface type R-value thickness Refractive index Abbe number sur1 standard 22.5 2.45 1.78 60.23 sur2 standard 64.2 0.15 sur3 standard 10.73 3.56 1.55 75.0 sur4 standard -54.07 2.0 1.58 49.2 sur5 standard 8.83 2.38 Stop standard infinity 4.80 Sur7 standard -10.24 1.2 1.65 33.84 Sur8 standard 43.81 3.88 1.79 47.52 Sur9 standard -12.91 0.15 Sur10 standard infinity 2.2 1.65 50.12 sur11 standard -26.12 2.61 sur12 standard 108.75 2.0 1.72 49.61 sur13 standard 15.68 1.13 sur14 standard 20.51 4.9 1.80 46.57 sur15 standard infinity 9.6 Image plane φI standard infinity -

[0085] Table 3

[0086] Combine Figure 6 As shown, in this embodiment, the first lens group G1 includes three lenses (L1-L3), of which lenses L2 and L3 form a doublet. The second lens group G2 includes three lenses (L4-L6), of which lenses L4 and L5 form a doublet. The third lens group G3 includes two lenses (L7 and L8).

[0087] Figure 7-10 Schematic diagrams illustrate the MTF diagram at optimal working object distance, the MTF through-focus diagram at low temperature, the MTF through-focus diagram at high temperature, and the optical distortion diagram of the imaging lens according to Example 2 of the present invention. As can be seen from the accompanying figures, the imaging lens obtained according to Example 2 of the present invention achieves the characteristics of large aperture, high resolution, low distortion, uniform image quality, large depth of field, excellent color reproduction, and high contrast.

[0088] Implementation method three:

[0089] Figure 11 FIG. 1 is a diagram schematically showing the structure of an imaging lens according to a third embodiment of the present invention.

[0090] In the third embodiment, the total length of the optical system TTL=53.00 mm, the system focal length f=33.5 mm, the system imaging object distance range 0.15 m to inf, the system frame Y=11.5 mm, and the F number FNO=2.6.

[0091] Table 4 below lists the relevant parameters of each lens of this embodiment, including surface type, curvature radius, thickness, refractive index of the material, and Abbe number:

[0092] Surface number Surface type R-value thickness Refractive index Abbe number sur1 standard 35.02 4.2 1.85 37.5 sur2 standard 165.14 0.2 sur3 standard 18.2 4.1 1.50 80.2 sur4 standard infinity 3.85 1.70 35.15 sur5 standard 13.5 4.89 Stop standard infinity 4.5 Sur7 standard -15.75 2.54 1.62 36.35 Sur8 standard 96.57 2.35 1.76 53.34 Sur9 standard -25.26 0.2 Sur10 standard 79.25 3.82 1.90 40.2 Sur11 standard -82.35 5.45 Sur12 standard 45.47 3.62 1.78 50.61 sur13 standard -45.28 2.08 sur14 standard -35.03 1.1 1.62 45.35 sur15 standard 38.13 10.3 Image plane φI standard infinity -

[0093] Table 4

[0094] Combine Figure 11 As shown, in this embodiment, the first lens group G1 includes three lenses (L1-L3), of which lenses L2 and L3 form a doublet. The second lens group G2 includes three lenses (L4-L6), of which lenses L4 and L5 form a doublet. The third lens group G3 includes two lenses (L7 and L8).

[0095] Figure 12-15 Schematic diagrams illustrate the MTF graph at optimal working object distance, the MTF through-focus graph at low temperature, the MTF through-focus graph at high temperature, and the optical distortion graph for an imaging lens according to Example 3 of the present invention. As can be seen from the accompanying figures, the imaging lens obtained according to Example 3 of the present invention achieves the characteristics of a large aperture, high resolution, low distortion, uniform image quality, a large depth of field, excellent color reproduction, and high contrast.

[0096] Implementation method four:

[0097] Figure 16 FIG. 1 is a diagram schematically showing the structure of an imaging lens according to a fourth embodiment of the present invention.

[0098] In the fourth embodiment, the total length of the optical system TTL=49.1 mm, the system focal length f=35.1 mm, the system imaging object distance range 0.15 m to inf, the system frame Y=12 mm, and the F number FNO=2.8.

[0099] Table 5 below lists the relevant parameters of each lens of this embodiment, including surface type, curvature radius, thickness, refractive index of the material, and Abbe number:

[0100] Surface number Surface type R-value thickness Refractive index Abbe number sur1 standard 27.5 2.12 1.85 43.5 sur2 standard -80.2 0.2 sur3 standard 14.035 3.7 1.43 96.0 sur4 standard infinity 3.0 1.85 35.4 sur5 standard 10.08 3.5 Stop standard infinity 3.6 Sur7 standard -15.2 1.45 1.70 31.25 Sur8 standard -30.1 1.90 1.78 45.21 Sur9 standard -14.2 0.21 Sur10 standard 35.7 1.78 1.75 50.34 Sur11 standard -402.2 6.85 sur12 standard -153.06 1.5 1.82 30.1 sur13 standard -21.1 3.78 sur14 standard -25.8 1.2 1.78 23.5 sur15 standard -300.5 13.4 Image plane φI standard infinity -

[0101] Table 5

[0102] Combine Figure 16As shown, in this embodiment, the first lens group G1 includes three lenses (L1-L3), of which lenses L2 and L3 form a doublet. The second lens group G2 includes three lenses (L4-L6), of which lenses L4 and L5 form a doublet. The third lens group G3 includes two lenses (L7 and L8).

[0103] Figure 17-20 Schematic diagrams illustrate the MTF graph at optimal working object distance, the MTF through-focus graph at low temperature, the MTF through-focus graph at high temperature, and the optical distortion graph of the imaging lens according to Example 4 of the present invention. As can be seen from the accompanying figures, the imaging lens obtained according to Example 4 of the present invention achieves the characteristics of large aperture, high resolution, low distortion, uniform image quality, large depth of field, excellent color reproduction, and high contrast.

[0104] Implementation method five:

[0105] Figure 21 FIG. 1 is a diagram schematically showing the structure of an imaging lens according to a fifth embodiment of the present invention.

[0106] In the fifth embodiment, the total length of the optical system TTL=47.83 mm, the system focal length f=30.6 mm, the system imaging object distance range 0.15 m to inf, the system frame Y=11.6 mm, and the F number FNO=2.5.

[0107] Table 6 below lists the relevant parameters of each lens of this embodiment, including surface type, radius of curvature, thickness, refractive index of the material, and Abbe number:

[0108] Surface number Surface type R-value thickness Refractive index Abbe number sur1 standard 25.6 2.14 1.75 42.5 sur2 standard 75.33 0.18 sur3 standard 12.03 3.5 1.55 68.0 sur4 standard 20.12 2.0 1.67 40.2 sur5 standard 11.0 3.1 Stop standard infinity 3.25 Sur7 standard -13.97 1.32 1.69 37.5 Sur8 standard -32.61 1.85 1.75 42.5 Sur9 standard -14.47 1.1 Sur10 standard 436.1 1.5 1.78 42.5 sur11 standard -34.5 7.5 sur12 standard -195.06 2.2 1.85 25.1 sur13 standard -35.78 4.0 sur14 standard -24.65 1.2 1.81 23.7 sur15 standard infinity 13 Image plane φI standard infinity -

[0109] Table 6

[0110] Combine Figure 21 As shown, in this embodiment, the first lens group G1 includes three lenses (L1-L3), of which lenses L2 and L3 form a doublet. The second lens group G2 includes three lenses (L4-L6), of which lenses L4 and L5 form a doublet. The third lens group G3 includes two lenses (L7 and L8).

[0111] Figure 22-25 Schematic diagrams illustrate the MTF graph at optimal working object distance, the MTF through-focus graph at low temperature, the MTF through-focus graph at high temperature, and the optical distortion graph for the imaging lens according to Example 5 of the present invention. As can be seen from the accompanying figures, the imaging lens obtained according to Example 5 of the present invention achieves the characteristics of a large aperture, high resolution, low distortion, uniform image quality, a large depth of field, excellent color reproduction, and high contrast.

[0112] The above description is merely one embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. An imaging lens, characterized in that: The invention comprises a first lens group (G1) with positive focal power, an aperture, a second lens group (G2) with positive focal power, and a third lens group (G3) with positive focal power or negative focal power, which are arranged in sequence from the object side to the image side, totaling three lens groups. The third lens group (G3) is a fixed group, and the first lens group (G1) and the second lens group (G2) form a focusing group that can move along the optical axis. The first lens group (G1) includes a first lens (L1) with positive refractive power, a second lens (L2) with positive refractive power, and a third lens (L3) with negative refractive power, a total of three lenses; The second lens group (G2) includes a fourth lens (L4) with negative optical power, a fifth lens (L5) with positive optical power, and a sixth lens (L6) with positive optical power, a total of three lenses; The third lens group (G3) includes a seventh lens (L7) having positive refractive power and an eighth lens (L8) having negative refractive power, or a seventh lens (L7) having negative optical power and an eighth lens (L8) having positive optical power, a total of two lenses; The focal length of the focusing group composed of the first lens group (G1), the aperture and the second lens group (G2) is fm, and the focal length of the imaging lens is f, which satisfies the relationship: 1.28≤fm / f≤1.5; The focal length of the third lens group (G3) is fg3, and the focal length of the imaging lens is f, which satisfies: 4.2≤|fg3 / f|≤6.

8.

2. The imaging lens according to claim 1, wherein: Along the object side to the image side, the lens closest to the object side in the first lens group (G1) is a biconvex lens, a convex-concave lens or a convex-planar lens.

3. The imaging lens according to claim 2, wherein: The second lens (L2) and the third lens (L3) form a doublet lens.

4. The imaging lens according to claim 3, wherein: The refractive index of the second lens (L2) is ND, and the Abbe number is VD, which satisfies: 60≤VD≤96, 1.43≤ND≤1.

65.

5. The imaging lens according to claim 1, wherein: Along the direction from the object side to the image side, the lens closest to the image side in the second lens group (G2) is a biconvex lens, a meniscus lens or a plano-convex lens.

6. The imaging lens according to claim 5, wherein: The fourth lens (L4) and the fifth lens (L5) form a doublet lens.

7. The imaging lens according to claim 1, wherein: The positive power lens in the third lens group (G3) is a biconvex lens, a convex-concave lens or a convex-planar lens, and the negative power lens in the third lens group (G3) is a biconcave lens, a convex-convex lens or a convex-concave lens.

8. The imaging lens according to claim 1, wherein: The total optical length of the imaging lens is TTL, and the focal length of the imaging lens is f, which satisfies 1.35≤TTL / f≤1.64.

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