Double telecentric optical lens

Abstract

The utility model provides a double telecentric optical lens. The double telecentric optical lens comprises a first lens, a second lens, a third lens, a fourth lens, a liquid lens, a fifth lens, a sixth lens, a seventh lens, an eighth lens and a ninth lens which are sequentially arranged from an object space to an image space along an optical axis, the first lens is a plano-convex lens or a biconvex lens with positive focal power, the second lens is a convex-concave lens with positive focal power, the third lens is a plano-concave lens or a biconcave lens with negative focal power, the fourth lens is a biconvex lens with positive focal power, the fifth lens is a biconcave lens with negative focal power, and the sixth lens is a concave-convex lens with positive focal power. The seventh lens is a biconcave lens with negative focal power, the eighth lens is a biconvex lens with positive focal power, and the ninth lens is a biconvex lens with positive focal power. The double telecentric optical lens provided by the embodiment of the utility model has the optical characteristics of high resolution, low distortion and the like, and also has a large depth of field.

Description

Technical Field

[0001] The utility model relates to the technical field of optical lenses, in particular to a double telecentric optical lens. Background Art

[0002] Bi-telecentric optical lenses are mainly used in the field of precision detection of machine vision systems. In precision optical detection systems, changes in the working distance of ordinary optical lenses will cause changes in magnification, which in turn affects the accuracy of measurement. Bi-telecentric optical lenses are mainly designed to correct the parallax of traditional industrial lenses. It can keep the image magnification unchanged within a certain object distance range, and will not affect the measurement accuracy due to changes in position height. This is a very important application for situations where the objects being measured are not on the same object plane. It is widely used in related machine vision detection fields. Although bi-telecentric optical lenses can correct the parallax problem of traditional industrial lenses, they can only produce clear images within a smaller object distance range. Once the depth of field range is exceeded, the image quality drops rapidly and cannot meet the application requirements of a large depth of field.

[0003] Bi-telecentric optical lenses have unique optical properties such as high resolution, ultra-low distortion, and unique parallel light design. With the development of society, the requirements for the application of bi-telecentric optical lenses are getting higher and higher. It is necessary to increase the depth of field of bi-telecentric optical lenses to further improve the accuracy and efficiency of precision detection of machine vision systems. In order to improve these optical properties, the structure of bi-telecentric optical lenses needs to be more complex and the design difficulty is greater, and the corresponding cost will also be greatly increased. Utility Model Content

[0004] The embodiment of the utility model provides a double telecentric optical lens, so as to realize the double telecentric optical lens having optical characteristics such as high resolution and low distortion while taking into account a large depth of field.

[0005] The embodiment of the utility model provides a double telecentric optical lens, comprising a first lens, a second lens, a third lens, a fourth lens, a liquid lens, a fifth lens, a sixth lens, a seventh lens, an eighth lens and a ninth lens arranged in sequence from the object side to the image side along the optical axis;

[0006] The first lens is a plano-convex lens or a biconvex lens with positive power, the second lens is a convex-concave lens with positive power, the third lens is a plano-concave lens or a biconcave lens with negative power, the fourth lens is a biconvex lens with positive power, the fifth lens is a biconcave lens with negative power, the sixth lens is a concave-convex lens with positive power, the seventh lens is a biconcave lens with negative power, the eighth lens is a biconvex lens with positive power, and the ninth lens is a biconvex lens with positive power;

[0007] Wherein, by adjusting the driving voltage or driving current of the liquid lens, the focusing position of the bi-telecentric optical lens can be adjusted.

[0008] Optionally, the object distance range of the bi-telecentric optical lens is D, the magnification of the bi-telecentric optical lens is M, and the focal length of the liquid lens is P, satisfying:

[0009] 110≤D≤160; 0.2≤M≤0.4; -5.3≤P≤4.7.

[0010] Optionally, the radius of curvature of the object-side surface of the first lens is R1, and the axial thickness of the first lens is D1, which satisfies:

[0011] 7≤R1 / D1≤11.8.

[0012] Optionally, the focal length of the first lens is f1, and the focal length of the second lens is f2, satisfying:

[0013] 0.57≤f1 / f2≤0.91.

[0014] Optionally, the radius of curvature of the object side surface of the second lens is R3, and the radius of curvature of the image side surface of the second lens is R4, satisfying: -2.1≤(R3+R4) / (R3-R4)≤-1.85;

[0015] The curvature radius of the object side surface of the fourth lens is R7, and the curvature radius of the image side surface of the fourth lens is R8, which satisfies:

[0016] 75≤(R7+R8) / (R7-R8)≤92.

[0017] Optionally, an axial thickness of the third lens is D5, and an axial distance from the image side surface of the third lens to the object side surface of the fourth lens is D6, satisfying: 8≤D6 / D5≤10.

[0018] Optionally, the focal length of the fifth lens is f5, and the focal length of the sixth lens is f6, satisfying:

[0019] -0.19≤f5 / f6≤-0.32.

[0020] Optionally, the radius of curvature of the object side surface of the fifth lens is R9, and the radius of curvature of the image side surface of the fifth lens is R10, satisfying: -11≤(R9+R10) / (R9-R10)≤-15;

[0021] The axial thickness of the sixth lens is D11, and the axial distance D12 from the image side surface of the sixth lens to the object side surface of the seventh lens satisfies: 0.095≤D12 / D11≤1.

[0022] Optionally, the focal length of the seventh lens is f7, the focal length of the eighth lens is f8, the on-axis thickness of the seventh lens is D13, and the on-axis thickness of the eighth lens is D14, satisfying:

[0023] -15≤f7 / f8≤-7.5; 0.32≤D13 / D14≤0.83.

[0024] Optionally, the axial distance from the image side surface of the eighth lens to the object side surface of the ninth lens is D15, and the total optical length of the bi-telecentric optical lens is TTL, which satisfies:

[0025] 0.32≤D15 / TTL≤0.83.

[0026] In an embodiment of the utility model, the focus position of the dual telecentric optical lens is adjusted in real time by controlling the driving voltage or driving current of the liquid lens, so as to achieve the purpose of fast focusing at different working distances. Since the liquid lens is used to achieve focusing, the lens does not shift during the focusing process, and the stability is better and the focusing speed is faster. By utilizing the combination of the liquid lens and the dual telecentric optical path, the variable compensation for different working distances is achieved through the variable of the focal length of the liquid lens, and the number and shape of the lenses located on both sides of the liquid lens and the spacing between the lenses are controlled, which at least includes the specific focal length and surface design of the first lens to the ninth lens, so as to achieve a dual telecentric optical lens with high resolution, low distortion and other optical characteristics while taking into account a large depth of field. The dual telecentric optical lens has a wider range of applications, and the overall hardware cost and work efficiency of the visual detection solution are significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a structural schematic diagram of a liquid lens provided by an embodiment of the utility model;

[0028] Figure 2 is a schematic structural diagram of a double telecentric optical lens in Embodiment 1;

[0029] Figure 3 is a schematic diagram of field curvature of the double telecentric optical lens in Example 1;

[0030] Figure 4 is a schematic diagram of distortion of the double telecentric optical lens in Example 1;

[0031] Figure 5 is an MTF curve diagram of the double telecentric optical lens in Example 1;

[0032] Figure 6 is a schematic diagram of the structure of the double telecentric optical lens in the second embodiment;

[0033] Figure 7is a schematic diagram of field curvature of the double telecentric optical lens in the second embodiment;

[0034] Figure 8 is a schematic diagram of distortion of the double telecentric optical lens in the second embodiment;

[0035] Fig. 9 is an MTF curve diagram of the bi-telecentric optical lens in Example 2;

[0036] Fig.10 is a schematic diagram of the structure of the double telecentric optical lens in Example 3;

[0037] Fig.11 is a schematic diagram of the field curvature of the double telecentric optical lens in Example 3;

[0038] Fig.12 is a schematic diagram of distortion of the double telecentric optical lens in Example 3;

[0039] Fig.13 It is the MTF curve diagram of the double telecentric optical lens in the third embodiment. DETAILED DESCRIPTION

[0040] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only the parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0041] Embodiment 1

[0042] Figure 1 is a schematic diagram of the structure of a liquid lens provided by an embodiment of the utility model, with reference to Figure 1 The liquid lens includes a first encapsulation glass GL1, a first liquid GL2, a second liquid GL3, and a second encapsulation glass GL4 which are arranged in sequence. The first liquid GL2 and the second liquid GL3 are located between the first encapsulation glass GL1 and the second encapsulation glass GL4. By adjusting the driving voltage or driving current of the liquid lens, the curvature of the interface between the first liquid GL2 and the second liquid GL3 changes, and the focus position of the double telecentric optical lens can be adjusted to achieve depth of field adjustment of the double telecentric optical lens.

[0043] As an example, the thickness of the first encapsulation glass GL1 can be 0.8 mm, the refractive index of the first encapsulation glass GL1 can be 1.5233, and the Abbe number of the first encapsulation glass GL1 can be 54.517. The thickness of the first liquid GL2 can be 1.89 mm, the refractive index of the first liquid GL2 can be 1.3960, and the Abbe number of the first liquid GL2 can be 59.036. The thickness of the second liquid GL3 can be 0.58 mm, the refractive index of the second liquid GL3 can be 1.4986, and the Abbe number of the second liquid GL3 can be 38.063. The thickness of the second encapsulation glass GL4 can be 0.55 mm, the refractive index of the second encapsulation glass GL4 can be 1.5233, and the Abbe number of the second encapsulation glass GL4 can be 54.517. It should be noted that the above values ​​can be flexibly adjusted as needed, and are not limited thereto.

[0044] Figure 2 is a schematic diagram of the structure of the double telecentric optical lens in Example 1, referring to Figure 2 The double telecentric optical lens includes 10 lenses, which are the first lens G1, the second lens G2, the third lens G3, the fourth lens G4, the liquid lens GL, the fifth lens G5, the sixth lens G6, the seventh lens G7, the eighth lens G8 and the ninth lens G9 arranged in sequence from the object side to the image side along the optical axis. Among them, the optical axis refers to the main optical axis of the double telecentric optical lens. The object side is also called the object side, and the image side is also called the image side.

[0045] The first lens G1 is a plano-convex lens with positive focal power, the object side surface of the first lens G1 is convex toward the object side, and the image side surface of the first lens G1 is a plane. In other embodiments, the first lens G1 can also be a biconvex lens with positive focal power. The second lens G2 is a convex-concave lens with positive focal power, the object side surface of the second lens G2 is convex toward the object side, and the image side surface of the second lens G2 is concave toward the image side. The third lens G3 is a plano-concave lens with negative focal power, the object side surface of the third lens G3 is a plane, and the image side surface of the third lens G3 is concave toward the image side. In other embodiments, the third lens G3 can also be a biconcave lens with negative focal power. The fourth lens G4 is a biconvex lens with positive focal power, the object side surface of the fourth lens G4 is convex toward the object side, and the image side surface of the fourth lens G4 is convex toward the image side. The fifth lens G5 is a biconcave lens with negative focal power, the object side surface of the fifth lens G5 is concave toward the object side, and the image side surface of the fifth lens G5 is concave toward the image side. The sixth lens G6 is a positive optical power meniscus lens, the object side surface of the sixth lens G6 is concave toward the object side, and the image side surface of the sixth lens G6 is convex toward the image side. The seventh lens G7 is a negative optical power biconcave lens, the object side surface of the seventh lens G7 is concave toward the object side, and the image side surface of the seventh lens G7 is concave toward the image side. The eighth lens G8 is a positive optical power biconvex lens, the object side surface of the eighth lens G8 is convex toward the object side, and the image side surface of the eighth lens G8 is convex toward the image side. The ninth lens G9 is a positive optical power biconvex lens. The object side surface of the ninth lens G9 is convex toward the object side, and the image side surface of the ninth lens G9 is convex toward the image side.

[0046] Optical power is used to characterize the refraction of an optical system to an incident parallel light beam. When the optical power is positive, the refraction is convergent, and when the optical power is negative, the refraction is divergent.

[0047] In the embodiment of the utility model, the focus position of the double telecentric optical lens is adjusted in real time by controlling the driving voltage or driving current of the liquid lens GL, so as to achieve the purpose of fast focusing at different working distances. Since the liquid lens GL is used to achieve focusing, the lens does not move during the focusing process, and the stability is better and the focusing speed is faster. By utilizing the combination of the liquid lens GL and the double telecentric optical path, the variable compensation for different working distances is achieved through the variable of the focal power of the liquid lens GL, and by controlling the number and shape of the lenses located on both sides of the liquid lens GL and the spacing between the lenses, which at least includes the specific focal power and surface design of the first lens G1 to the ninth lens G9, a double telecentric optical lens with optical characteristics such as high resolution and low distortion is achieved while taking into account a large depth of field. The double telecentric optical lens has a wider range of applications, and the overall hardware cost and work efficiency of the visual detection solution are significantly improved. The double telecentric optical lens of the embodiment of the utility model has a simple structure, adopts a double telecentric optical path design, has a high resolution, and can improve the detection accuracy and detection efficiency of the double telecentric optical lens.

[0048] Optionally, refer to Figure 2 , the object distance range of the double telecentric optical lens is D, the magnification of the double telecentric optical lens is M, and the focal length of the liquid lens GL is P, which satisfies: 110≤D≤160, 0.2≤M≤0.4, -5.3≤P≤4.7. The dynamic adjustment of the focal length range of the liquid lens GL is the key to achieving a large depth of field. In the embodiment of the utility model, the large depth of field range of the double telecentric optical lens is achieved by limiting the focal length of the liquid lens GL and the magnification of the double telecentric optical lens. And by limiting the object distance range of the double telecentric optical lens, the double telecentric effect is achieved on the basis of achieving a large depth of field range of the double telecentric optical lens.

[0049] Optionally, refer to Figure 2 , the radius of curvature of the object side surface of the first lens G1 is R1, and the axial thickness of the first lens G1 is D1, which satisfies: 7≤R1 / D1≤11.8. The first lens G1 is mainly used to collect light emitted from the object side. Through the reasonable distribution of the radius of curvature of the object side surface of the first lens G1 and the axial thickness of the first lens G1, the double telecentric optical lens has better imaging quality and lower sensitivity.

[0050] Optionally, refer to Figure 2 , the focal length of the first lens G1 is f1, and the focal length of the second lens G2 is f2, which satisfies: 0.57≤f1 / f2≤0.91. In the embodiment of the utility model, by limiting the focal length of the first lens G1 and the focal length of the second lens G2, the spherical aberration and the field curvature of the double telecentric optical lens are effectively balanced, thereby reducing aberrations and improving image quality.

[0051] Optionally, refer to Figure 2 , the radius of curvature of the object side surface of the second lens G2 is R3, and the radius of curvature of the image side surface of the second lens G2 is R4, which satisfies: -2.1≤(R3+R4) / (R3-R4)≤-1.85. The radius of curvature of the object side surface of the fourth lens G4 is R7, and the radius of curvature of the image side surface of the fourth lens G4 is R8, which satisfies: 75≤(R7+R8) / (R7-R8)≤92. The embodiment of the utility model can alleviate the degree of deflection of light passing through the lens, effectively reduce aberrations, and help improve the imaging quality of the double telecentric optical lens.

[0052] Optionally, refer to Figure 2 , the axial thickness of the third lens G3 is D5, and the axial distance from the image side of the third lens G3 to the object side of the fourth lens G4 is D6, which satisfies: 8≤D6 / D5≤10. Thus, the telecentricity of the double telecentric optical lens can be controlled, and the same magnification can be achieved under different object distance ranges, which is conducive to reducing the parallax of the final imaging.

[0053] Optionally, refer to Figure 2, the focal length of the fifth lens G5 is f5, and the focal length of the sixth lens G6 is f6, which satisfies: -0.19≤f5 / f6≤-0.32. The absolute value of the focal length of the sixth lens G6 is greater than the absolute value of the focal length of the fifth lens G5, and the sixth lens G6 has a larger divergence angle for light than the fifth lens G5.

[0054] Optionally, refer to Figure 2 The radius of curvature of the object side surface of the fifth lens G5 is R9, and the radius of curvature of the image side surface of the fifth lens G5 is R10, which satisfies: -11≤(R9+R10) / (R9-R10)≤-15. The axial thickness of the sixth lens G6 is D11, and the axial distance D12 from the image side surface of the sixth lens G6 to the object side surface of the seventh lens G7 satisfies: 0.095≤D12 / D11≤1.

[0055] Optionally, refer to Figure 2 , the focal length of the seventh lens G7 is f7, the focal length of the eighth lens G8 is f8, the axial thickness of the seventh lens G7 is D13, and the axial thickness of the eighth lens G8 is D14, satisfying: -15≤f7 / f8≤-7.5, 0.32≤D13 / D14≤0.83.

[0056] Optionally, refer to Figure 2 , the axial distance from the image side surface of the eighth lens G8 to the object side surface of the ninth lens G9 is D15, and the total optical length of the double telecentric optical lens is TTL, which satisfies: 0.32≤D15 / TTL≤0.83. Furthermore, through this constraint condition, the double telecentric optical lens is made more compact.

[0057] For example, reference Figure 2 , the seventh lens G7 and the eighth lens G8 form a cemented lens. The seventh lens G7 and the eighth lens G8 are cemented to form a cemented lens, which is beneficial to reduce the spherical aberration between the light of the near optical axis and the light of the far optical axis. Reduce the influence of dispersion on imaging, and can also effectively reduce the error that occurs when configuring the lens, improve imaging resolution, and thus improve imaging quality.

[0058] For example, reference Figure 2 A glass plate GF is provided between the ninth lens G9 and the image plane SI. The glass plate GF may be a glass cover plate or an optical filter.

[0059] Optionally, the bi-telecentric optical lens further includes an aperture ( Figure 2 The aperture is located between the liquid lens GL and the fifth lens G5. The aperture is mainly used to limit the light beam or the size of the imaging range, and has the ability to shape and optimize the light beam and improve the quality of the light beam.

[0060] Table 1 A design value of the double telecentric optical lens in Example 1

[0061]

[0062]

[0063] The double telecentric optical lens shown in Table 1 can be Figure 2 As shown in . A lens generally includes two surfaces, each of which is a refractive surface. The surface numbers in Table 1 are numbered according to the surfaces of each lens. Among them, surface number 1 is the object side surface of the first lens G1, and surface number 2 is the image side surface of the first lens G1. Surface number 3 is the object side surface of the second lens G2, and surface number 4 is the image side surface of the second lens G2. Surface number 5 is the object side surface of the third lens G3, and surface number 6 is the image side surface of the third lens G3. Surface number 7 is the object side surface of the fourth lens G4, and surface number 8 is the image side surface of the fourth lens G4. Surface number ST is the aperture. Surface number 9 is the object side surface of the fifth lens G5, and surface number 10 is the image side surface of the fifth lens G5. Surface number 11 is the object side surface of the sixth lens G6, and surface number 12 is the image side surface of the sixth lens G6. Surface number 13 is the object side surface of the seventh lens G7, surface number 14 is the image side surface of the seventh lens G7 or the object side surface of the eighth lens G8, and surface number 15 is the image side surface of the eighth lens G8. Surface number 16 is the object side surface of the ninth lens G9, and surface number 17 is the image side surface of the ninth lens G9. Surface number 18 is the object side surface of the glass plate GF, and surface number 19 is the image side surface of the glass plate GF.

[0064] The radius of curvature represents the degree of curvature of the lens surface. A positive radius of curvature value indicates that the center of curvature is on the side of the surface close to the image, and a negative radius of curvature value indicates that the center of curvature is on the side of the surface far from the image. The ∞ in the radius of curvature column is infinite (i.e., infinite), indicating that the surface is a plane. The unit of the radius of curvature is mm. The value in the thickness column indicates the axial distance from the current surface to the next surface. The unit of thickness is mm. The refractive index column indicates the refractive index of the medium between the current surface and the next surface. The Abbe number represents the dispersion characteristics of the material between the current surface and the next surface to light. The unit of focal length is mm.

[0065] Figure 3 is a schematic diagram of the field curvature of the double telecentric optical lens in Example 1, referring to Figure 3 , S is the field curvature in the sagittal direction, and T is the field curvature in the meridional direction.

[0066] Figure 5 is the MTF curve of the double telecentric optical lens in Example 1, referring to Figure 5 , in such Figure 5The MTF graph shown includes curves representing the performance of the diffraction limit, the central field of view (i.e., the central field of view), and the edge field of view (i.e., the maximum field of view T and the maximum field of view S), reflecting the high-performance optical characteristics of the bi-telecentric optical lens.

[0067] In Example 1, 110≤D≤160, M=0.3, -5.2≤P≤1.12, R1 / D1=11.75, f1 / f2=0.9, (R3+R4) / (R3-R4)=-1.86, D6 / D5=9.7, (R7+R8) / (R7-R8)=85.69, (R9+R10) / (R9-R10)=-14.83, f5 / f6=-0.19, f7 / f8=-15.47.

[0068] Embodiment 2

[0069] The similarities with the first embodiment are not repeated here. Figure 6 is a schematic diagram of the structure of the double telecentric optical lens in the second embodiment, referring to Figure 6 , the first lens G1 is a biconvex lens, and the third lens G3 is a biconcave lens.

[0070] Table 2 A design value of the double telecentric optical lens in Example 2

[0071]

[0072]

[0073] The double telecentric optical lens shown in Table 2 can be Figure 6 as shown in .

[0074] In Example 2, 110≤D≤160, M=0.2, -1.23≤P≤4.67, R1 / D1=7.29, f1 / f2=0.57, (R3+R4) / (R3-R4)=-2.09, D6 / D5=8.73, (R7+R8) / (R7-R8)=91.8, (R9+R10) / (R9-R10)=-11.5, f5 / f6=-0.22, f7 / f8=-9.33.

[0075] Embodiment 3

[0076] The similarities with the first and second embodiments are not repeated here.

[0077] Table 3 A design value of the double telecentric optical lens in Example 3

[0078]

[0079]

[0080] The double telecentric optical lens shown in Table 3 can be Fig.10 as shown in .

[0081] In Example 3, 110≤D≤160, M=0.4, -4≤P≤1.2, R1 / D1=8.99, f1 / f2=0.74, (R3+R4) / (R3-R4)=-1.95, D6 / D5=8.24, (R7+R8) / (R7-R8)=75.3,

[0082] (R9+R10) / (R9-R10)=-13.85, f5 / f6=-0.32, f7 / f8=-7.78.

[0083] Note that the above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments, combinations and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention is described in more detail through the above embodiments, the present invention is not limited to the above embodiments, and may include more other equivalent embodiments without departing from the concept of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A bi-telecentric optical lens, characterized in that: It includes a first lens, a second lens, a third lens, a fourth lens, a liquid lens, a fifth lens, a sixth lens, a seventh lens, an eighth lens and a ninth lens which are arranged in sequence from the object side to the image side along the optical axis; The first lens is a plano-convex lens or a biconvex lens with positive power, the second lens is a convex-concave lens with positive power, the third lens is a plano-concave lens or a biconcave lens with negative power, the fourth lens is a biconvex lens with positive power, the fifth lens is a biconcave lens with negative power, the sixth lens is a concave-convex lens with positive power, the seventh lens is a biconcave lens with negative power, the eighth lens is a biconvex lens with positive power, and the ninth lens is a biconvex lens with positive power; Wherein, by adjusting the driving voltage or driving current of the liquid lens, the focusing position of the bi-telecentric optical lens can be adjusted.

2. The bi-telecentric optical lens according to claim 1, characterized in that: The object distance range of the bi-telecentric optical lens is D, the magnification of the bi-telecentric optical lens is M, and the focal length of the liquid lens is P, which satisfies: 110≤D≤160; 0.2≤M≤0.4; -5.3≤P≤4.

7.

3. The bi-telecentric optical lens according to claim 1, characterized in that: The radius of curvature of the object side surface of the first lens is R1, and the axial thickness of the first lens is D1, which satisfies: 7≤R1 / D1≤11.

8.

4. The bi-telecentric optical lens according to claim 1, characterized in that: The focal length of the first lens is f1, and the focal length of the second lens is f2, satisfying: 0.57≤f1 / f2≤0.

91.

5. The bi-telecentric optical lens according to claim 4, characterized in that: The curvature radius of the object side surface of the second lens is R3, and the curvature radius of the image side surface of the second lens is R4, which satisfies: -2.1≤(R3+R4) / (R3-R4)≤-1.85; The curvature radius of the object side surface of the fourth lens is R7, and the curvature radius of the image side surface of the fourth lens is R8, which satisfies: 75≤(R7+R8) / (R7-R8)≤92.

6. The bi-telecentric optical lens according to claim 1, characterized in that: The axial thickness of the third lens is D5, and the axial distance from the image side surface of the third lens to the object side surface of the fourth lens is D6, which satisfies: 8≤D6 / D5≤10.

7. The bi-telecentric optical lens according to claim 1, characterized in that: The focal length of the fifth lens is f5, and the focal length of the sixth lens is f6, satisfying: -0.19≤f5 / f6≤-0.

32.

8. The bi-telecentric optical lens according to claim 7, characterized in that: The curvature radius of the object side surface of the fifth lens is R9, and the curvature radius of the image side surface of the fifth lens is R10, satisfying: -11≤(R9+R10) / (R9-R10)≤-15; The axial thickness of the sixth lens is D11, and the axial distance D12 from the image side surface of the sixth lens to the object side surface of the seventh lens satisfies: 0.095≤D12 / D11≤1.

9. The bi-telecentric optical lens according to claim 1, characterized in that: The focal length of the seventh lens is f7, the focal length of the eighth lens is f8, the axial thickness of the seventh lens is D13, and the axial thickness of the eighth lens is D14, satisfying: -15≤f7 / f8≤-7.5; 0.32≤D13 / D14≤0.

83.

10. The bi-telecentric optical lens according to claim 1, characterized in that: The axial distance from the image side surface of the eighth lens to the object side surface of the ninth lens is D15, and the total optical length of the bi-telecentric optical lens is TTL, which satisfies: 0.32≤D15 / TTL≤0.83.

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