Coaxial turn-back optical lens
By using a coaxial folding optical lens design, the problems of excessive total length and narrow spectral range of traditional telephoto lenses are solved, achieving a reduction in the number of lenses and high light transmission performance, thus improving the imaging effect of commercial satellite remote sensing systems.
Patent Information
- Application Number
- CN202511228425.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-29
- Publication Date
- 2025-11-07
AI Technical Summary
Traditional telephoto lenses suffer from excessive length and narrow spectral range, resulting in large footprints and poor imaging quality in commercial satellite remote sensing systems.
It adopts a coaxial folding optical lens design, including a concave mirror, a convex mirror, a meniscus negative lens, a biconvex positive lens, a meniscus positive lens, and a biconcave negative lens. By rationally allocating optical power and selecting materials, it optimizes lens aberrations and achieves compactness and hyperspectral performance.
It achieves a reduction in the number of lenses and a compact optical lens, possessing high light transmission performance and good imaging capabilities, and can provide high-resolution images over a wide spectral range, thereby improving target detection capabilities.
Smart Images
Figure CN120908983A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to optical lens, in particular to a coaxial return optical lens. BACKGROUND
[0002] Long-focus lens is a typical optical lens configuration. When a clear image of a distant object is needed, a long-focus lens is selected to obtain a high-resolution image due to the large object distance. However, the traditional transmissive long-focus lens has the problems of too long total length and narrow spectral range, which limits its application.
[0003] In commercial satellite remote sensing systems, the space for the load is limited, and high image quality and wide spectrum are required during use. The use of traditional transmissive long-focus lenses will result in large space occupation and poor imaging effect. SUMMARY
[0004] The purpose of the present application is to solve the problems of too long total length and narrow spectral range of the traditional transmissive long-focus lens, and to provide a coaxial return optical lens.
[0005] In order to achieve the above purpose, the present application adopts the following technical solutions:
[0006] A coaxial return optical lens, characterized in that: comprising a concave mirror L1, a convex mirror L2, a meniscus negative lens L3, a biconvex positive lens L4, a meniscus positive lens L5 and a biconcave negative lens L6 arranged along the incident light propagation direction from the object plane to the image plane IMA in sequence along the optical axis.
[0007] The reflecting surface of the concave mirror L1 is a parabolic surface with a conic constant k=-1; the reflecting surface of the convex mirror L2 is a parabolic surface with a conic constant k=-1; the entrance surface of the meniscus negative lens L3 is convex, and the exit surface is concave; the entrance surface of the biconvex positive lens L4 is convex, and the exit surface is convex; the entrance surface of the meniscus positive lens L5 is convex, and the exit surface is concave; the entrance surface of the biconcave negative lens L6 is concave, and the exit surface is concave; the exit surface of the meniscus negative lens L3 is cemented with the entrance surface of the biconvex positive lens L4.
[0008] The focal length f1 of the concave mirror L1, the focal length f2 of the convex mirror L2, the focal length f3 of the meniscus negative lens L3, the focal length f4 of the lenticular positive lens L4, the focal length f5 of the meniscus positive lens L5, and the focal length f6 of the biconcave negative lens L6, respectively, and the focal length f of the overall structure composed of the concave mirror L1, the convex mirror L2, the meniscus negative lens L3, the lenticular positive lens L4, the meniscus positive lens L5, and the biconcave negative lens L6 satisfy the following relationships: -0.27 < f1 / f < -0.22, 2.63 < f2 / f < 2.71, -2.61 < f3 / f < -2.54, 0.51 < f4 / f < 0.62, 0.19 < f5 / f < 0.23, and -0.05 < f6 / f < -0.04.
[0009] Further, the meniscus negative lens L3 adopts an optical glass material with 1.73 ≤ nd ≤ 1.77 and 50 ≤ vd ≤ 52;
[0010] The lenticular positive lens L4 adopts an optical glass material with 1.49 ≤ nd ≤ 1.52 and 80 ≤ vd ≤ 82;
[0011] The meniscus positive lens L5 adopts an optical glass material with 1.81 ≤ nd ≤ 1.85 and 42 ≤ vd ≤ 44;
[0012] The biconcave negative lens L6 adopts an optical glass material with 1.67 ≤ nd ≤ 1.71 and 52 ≤ vd ≤ 54;
[0013] Wherein, nd represents the refractive index, and vd represents the Abbe number.
[0014] Further, the meniscus negative lens L3 adopts H-LAK3 material with nd = 1.75 and vd = 50.95; the lenticular positive lens L4 adopts H-FK61 material with nd = 1.50 and vd = 81.61; the meniscus positive lens L5 adopts H-ZLAF55C material with nd = 1.83 and vd = 42.71; and the biconcave negative lens L6 adopts H-LAK6 material with nd = 1.69 and vd = 53.3.
[0015] Further, the reflecting surface of the convex mirror L2 is provided with a stop STO, and the surface curvature radius of the stop STO is infinite, for limiting the light beam.
[0016] Further,
[0017] The distance between the reflecting surface S1 of the concave mirror L1 and the reflecting surface S2 of the convex mirror L2, the distance between the reflecting surface S2 of the convex mirror L2 and the incident surface S3 of the meniscus negative lens L3, the distance between the exit surface S5 of the biconvex positive lens L4 and the incident surface S6 of the meniscus positive lens L5, the distance between the exit surface S7 of the meniscus positive lens L5 and the incident surface S8 of the biconcave negative lens L6, and the distance between the exit surface S9 of the biconcave negative lens L6 and the image plane IMA are respectively: -170.42 to -167.04 mm, 157.14 to 160.32 mm, 107.79 to 109.97 mm, 2.78 to 2.84 mm, 22.93 to 23.39 mm;
[0018] The thicknesses of the meniscus negative lens L3, the biconvex positive lens L4, the meniscus positive lens L5 and the biconcave negative lens L6 are respectively: 1.98 to 2.02 mm, 11.12 to 11.34 mm, 14.85 to 15.15 mm, 14.85 to 15.15 mm.
[0019] Further, the distance between the reflecting surface S1 of the concave mirror L1 and the reflecting surface S2 of the convex mirror L2, the distance between the reflecting surface S2 of the convex mirror L2 and the incident surface S3 of the meniscus negative lens L3, the distance between the exit surface S5 of the biconvex positive lens L4 and the incident surface S6 of the meniscus positive lens L5, the distance between the exit surface S7 of the meniscus positive lens L5 and the incident surface S8 of the biconcave negative lens L6, and the distance between the exit surface S9 of the biconcave negative lens L6 and the image plane IMA are respectively: -168.73 mm, 158.73 mm, 108.88 mm, 2.81 mm, 23.16 mm;
[0020] The thicknesses of the meniscus negative lens L3, the biconvex positive lens L4, the meniscus positive lens L5 and the biconcave negative lens L6 are respectively: 2.00 mm, 11.23 mm, 15.00 mm, 15.00 mm.
[0021] Further, the radius of curvature of the reflecting surface of the concave mirror L1 is -464.53 to -454.35 mm;
[0022] The radius of curvature of the reflecting surface of the convex mirror L2 is -135.18 to -132.50 mm;
[0023] The radius of curvature of the incident surface of the meniscus negative lens L3 is 306.22 to 312.40 mm, and the radius of curvature of the exit surface and the radius of curvature of the incident surface of the biconvex positive lens L4 are all 81.11 to 82.75 mm;
[0024] The radius of curvature of the exit surface of the biconvex positive lens L4 is -103.94 to -101.88 mm;
[0025] The incident surface radius of curvature of the meniscus positive lens L5 is 40.76mm-41.58mm, and the exit surface radius of curvature is 45.37mm-46.29mm;
[0026] The incident surface radius of curvature of the biconcave negative lens L6 is -112.09mm--109.87mm, and the exit surface radius of curvature is 39.67mm-40.47mm.
[0027] Further, the reflection surface radius of curvature of the concave mirror L1 is -458.94mm;
[0028] The reflection surface radius of curvature of the convex mirror L2 is -133.84mm;
[0029] The incident surface radius of curvature of the meniscus negative lens L3 is 309.31mm, and the exit surface radius of curvature and the incident surface radius of curvature of the biconvex positive lens L4 are both 81.93mm;
[0030] The exit surface radius of curvature of the biconvex positive lens L4 is -102.91mm;
[0031] The incident surface radius of curvature of the meniscus positive lens L5 is 41.17mm, and the exit surface radius of curvature is 45.83mm;
[0032] The incident surface radius of curvature of the biconcave negative lens L6 is -110.98mm, and the exit surface radius of curvature is 40.07mm.
[0033] Further, the F number of the overall structure composed of the concave mirror L1, the convex mirror L2, the meniscus negative lens L3, the biconvex positive lens L4, the meniscus positive lens L5 and the biconcave negative lens L6 is ≤5.
[0034] Further, the F number of the overall structure composed of the concave mirror L1, the convex mirror L2, the meniscus negative lens L3, the biconvex positive lens L4, the meniscus positive lens L5 and the biconcave negative lens L6 is 4.9.
[0035] The beneficial effects of the present application are as follows:
[0036] (1) The coaxial folding optical lens provided by the present application is composed of 6 optical elements (including mirrors and lenses), the number of lenses is reduced, the optical power of each element is reasonably distributed, and the ratio relationship of f1, f2, f3, f4, f5 and f6 is set respectively, so that the lens aberration is optimized, the optical lens has low distortion performance, and the market competitiveness is improved.
[0037] (2) The coaxial folded return optical lens can be used for a target surface with a diameter of 26.36 mm (1920*1920, pixel size 9.7 μm), can realize high light transmission performance with F number ≤ 5, and has a field of view angle of ± 0.8°, has good imaging function at a resolution of 40 lp / mm, and greatly improves the target detection capability.
[0038] (3) The coaxial folded return optical lens can realize collaborative correction of chromatic aberration and spherical aberration by accurately matching optical materials with different dispersion characteristics, further reduces distortion by combining with front aperture design and compact optical path layout, has good practicability, and has outstanding market competitive advantage. BRIEF DESCRIPTION OF DRAWINGS
[0039] Figure 1 It is a structure schematic view of an embodiment of the coaxial folded return optical lens;
[0040] Figure 2 It is a modulation transfer function diagram in the embodiment of the coaxial folded return optical lens;
[0041] Figure 3 It is a point spread diagram in the embodiment of the coaxial folded return optical lens;
[0042] Figure 4 It is a field curvature diagram in the embodiment of the coaxial folded return optical lens;
[0043] Figure 5 It is a distortion diagram in the embodiment of the coaxial folded return optical lens;
[0044] Figure 6 It is a ray aberration curve diagram of the embodiment of the coaxial folded return optical lens in the range of 0-0.398°;
[0045] Figure 7 It is a ray aberration curve diagram of the embodiment of the coaxial folded return optical lens in the range of 0.569-0.801°. DETAILED DESCRIPTION
[0046] The technical solutions of the present application will be described clearly and completely in combination with embodiments. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.
[0047] The embodiment provides a coaxial folded return optical lens, as shown in Figure 1As shown, the optical lens comprises a concave mirror L1, a convex mirror L2, a meniscus negative lens L3, a biconvex positive lens L4, a meniscus positive lens L5 and a biconcave negative lens L6 arranged along the direction of the incident light propagation from the object plane to the image plane IMA.
[0048] The focal length of the concave mirror L1 is f1, the reflecting surface S1 is a parabolic surface, the conic constant k is -1, and the curvature radius of the reflecting surface S1 is -464.53mm to -454.35mm.
[0049] The focal length of the convex mirror L2 is f2, the reflecting surface S2 is a parabolic surface, the conic constant k is -1, and the curvature radius of the reflecting surface S2 is -135.18mm to -132.50mm.
[0050] The reflecting surface of the convex mirror L2 is provided with a stop STO, and the surface curvature radius of the stop STO is infinite.
[0051] The stop STO is used for limiting the light beam, can reduce the generation of the optical lens astigmatism, and improve the image quality. In the embodiment, the stop STO is arranged at the front end of the whole optical lens, can reduce the number of lenses, make the overall structure more compact, and can better inhibit the stray light and improve the signal-to-noise ratio. The front stop reduces the temperature gradient influence of the subsequent optical elements, and enhances the system thermal stability.
[0052] The concave mirror L1 and the convex mirror L2 can realize the light path folding and compact the overall structure.
[0053] The focal length of the meniscus negative lens L3 is f3, the incident surface S3 is a convex surface with a curvature radius of 306.22mm to 312.40mm, the exit surface is a concave surface with a curvature radius of 81.11mm to 82.75mm, and an optical glass material with 1.73≤nd≤1.77, 50≤vd≤52 is adopted.
[0054] The focal length of the biconvex positive lens L4 is f4, the incident surface is a convex surface with a curvature radius of 81.11mm to 82.75mm, the exit surface S5 is a convex surface with a curvature radius of -103.94mm to -101.88mm, and an optical glass material with 1.49≤nd≤1.52, 80≤vd≤82 is adopted.
[0055] The exit surface of the meniscus negative lens L3 and the incident surface of the biconvex positive lens L4 are cemented to form a cemented surface S4.
[0056] The focal length of the meniscus positive lens L5 is f5, the incident surface S6 is a convex surface with a curvature radius of 40.76mm to 41.58mm, the exit surface S7 is a concave surface with a curvature radius of 45.37mm to 46.29mm, and an optical glass material with 1.81≤nd≤1.85, 42≤vd≤44 is adopted.
[0057] The focal length f6 of the double-concave negative lens L6, the incident surface S8 is concave with a radius of curvature of -112.09mm to -109.87mm, and the exit surface S9 is concave with a radius of curvature of 39.67mm to 40.47mm, and the optical glass material with 1.67≤nd≤1.71, 52≤vd≤54 is adopted.
[0058] In the above, nd represents the refractive index, and vd represents the Abbe number.
[0059] In the embodiment, the distance between the reflecting surface S1 of the concave mirror L1 and the reflecting surface S2 of the convex mirror L2, the distance between the reflecting surface S2 of the convex mirror L2 and the incident surface S3 of the meniscus negative lens L3, the distance between the exit surface S5 of the double-convex positive lens L4 and the incident surface S6 of the meniscus positive lens L5, the distance between the exit surface S7 of the meniscus positive lens L5 and the incident surface S8 of the double-concave negative lens L6, and the distance between the exit surface S9 of the double-concave negative lens L6 and the image plane IMA are respectively -170.42 to -167.04mm, 157.14 to 160.32mm, 107.79 to 109.97mm, 2.78 to 2.84mm, and 22.93 to 23.39mm; and the thicknesses of the meniscus negative lens L3, the double-convex positive lens L4, the meniscus positive lens L5 and the double-concave negative lens L6 are respectively 1.98 to 2.02mm, 11.12 to 11.34mm, 14.85 to 15.15mm, and 14.85 to 15.15mm.
[0060] The focal lengths of the concave mirror L1, the convex mirror L2, the meniscus negative lens L3, the double-convex positive lens L4, the meniscus positive lens L5 and the double-concave negative lens L6 satisfy the following relationships with the focal length f of the overall structure composed of the concave mirror L1, the convex mirror L2, the meniscus negative lens L3, the double-convex positive lens L4, the meniscus positive lens L5 and the double-concave negative lens L6: -0.27<f1 / f<-0.22, 2.63<f2 / f<2.71, -2.61<f3 / f<-2.54, 0.51<f4 / f<0.62, 0.19<f5 / f<0.23, and -0.05<f6 / f<-0.04.
[0061] The F number of the overall structure composed of the concave mirror L1, the convex mirror L2, the meniscus negative lens L3, the double-convex positive lens L4, the meniscus positive lens L5 and the double-concave negative lens L6 is ≤5.
[0062] The performance of the coaxial folding optical lens provided in the embodiment is tested, and the specific parameters selected are as follows:
[0063] f=931, f1=-229.5, f2=2485.0, f3=-2399.6, f4=528.6, f5=197.1, and f6=-40.8.
[0064] The meniscus negative lens L3 is made of H-LAK3 material with nd=1.75 and vd=50.95; the biconvex positive lens L4 is made of H-FK61 material with nd=1.50 and vd=81.61; the meniscus positive lens L5 is made of H-ZLAF55C material with nd=1.83 and vd=42.71; and the biconcave negative lens L6 is made of H-LAK6 material with nd=1.69 and vd=53.3.
[0065] The F number of the overall structure of the concave mirror L1, the convex mirror L2, the meniscus negative lens L3, the biconvex positive lens L4, the meniscus positive lens L5 and the biconcave negative lens L6 is 4.9.
[0066] The surface curvature radius of each mirror and lens, the interval between the adjacent surfaces of the entrance surface to the image surface IMA of the concave mirror L1 along the light path propagation direction, and the material of each lens are shown in Table 1:
[0067] Table 1
[0068]
[0069] The technical indexes achieved are as follows:
[0070] (1) Focal length: EFFL=931mm
[0071] (2) Relative aperture: 1 / 4.9
[0072] (3) Field of view angle: ±0.8°
[0073] (4) Image element size: 9.7μm
[0074] (5) Imaging circle diameter greater than Φ26.1mm
[0075] (6) Working waveband: 400nm-1000nm
[0076] (7) Optical total length TTL≤496mm, optical back aperture≥23mm
[0077] (8) Optical distortion≤1%
[0078] (9) Obstruction ratio: 30%.
[0079] The image quality of the coaxial return optical lens with the above parameters is evaluated:
[0080] Figure 2 is the modulation transfer function curve diagram of the embodiment of the present application, and Figure 2 It can be seen that the MTF at the full field of view 40lp / mm is greater than 0.4, and the image quality is good, which can meet the production requirements.
[0081] Figure 3 is a spot diagram of an embodiment of the present application, wherein Figure 3 It can be seen that the full field spot diagram RMS radius < 25 μm, and the geometric radius < 100 μm.
[0082] Figure 4 is a field curvature diagram of an embodiment of the present application, wherein Figure 4 It can be seen that the field curvature < 0.5 mm, the astigmatism < 0.5 mm, and the image surface is flat.
[0083] Figure 5 is a distortion diagram of an embodiment of the present application, wherein Figure 5 It can be seen that the full field distortion < 1%, which meets the requirements of industrial production.
[0084] Figure 6 and Figure 7 is a ray aberration curve diagram of an embodiment of the present application in the range of 0-0.398° and 0.569-0.801°, wherein Figure 6 and Figure 7 It can be seen that the ray aberration curve is smooth, without obvious edge lifting, and the image quality is good.
[0085] The above is merely a specific embodiment of the present application, and the effect of the relevant specific embodiment and the related comparative example is compared, but the protection scope of the present application is not limited thereto, any change or replacement within the technical scope disclosed by the present application should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.
Claims
1. A coaxial fold mirror, characterized by: The concave mirror L1, the convex mirror L2, the meniscus negative lens L3, the lenticular positive lens L4, the meniscus positive lens L5 and the biconcave negative lens L6 are arranged along the direction of incident light propagation. The reflecting surface of the concave mirror L1 is a parabolic surface with a conic constant k=-1; the reflecting surface of the convex mirror L2 is a parabolic surface with a conic constant k=-1; the entrance surface of the meniscus negative lens L3 is a convex surface, and the exit surface is a concave surface; the entrance surface of the lenticular positive lens L4 is a convex surface, and the exit surface is a convex surface; the entrance surface of the meniscus positive lens L5 is a convex surface, and the exit surface is a concave surface; the entrance surface of the biconcave negative lens L6 is a concave surface, and the exit surface is a concave surface; the exit surface of the meniscus negative lens L3 is cemented with the entrance surface of the lenticular positive lens L4. The focal length f1 of the concave mirror L1, the focal length f2 of the convex mirror L2, the focal length f3 of the meniscus negative lens L3, the focal length f4 of the lenticular positive lens L4, the focal length f5 of the meniscus positive lens L5 and the focal length f6 of the biconcave negative lens L6 satisfy the following relationship with the focal length f of the overall structure composed of the concave mirror L1, the convex mirror L2, the meniscus negative lens L3, the lenticular positive lens L4, the meniscus positive lens L5 and the biconcave negative lens L6: -0.27<f1 / f<-0.22, 2.63<f2 / f<2.71, -2.61<f3 / f<-2.54, 0.51<f4 / f<0.62, 0.19<f5 / f<0.23, -0.05<f6 / f<-0.
04.
2. The coaxial folding optical lens according to claim 1, wherein: The meniscus negative lens L3 is made of optical glass material with 1.73≤nd≤1.77 and 50≤vd≤52; The lenticular positive lens L4 is made of optical glass material with 1.49≤nd≤1.52 and 80≤vd≤82; The meniscus positive lens L5 is made of optical glass material with 1.81≤nd≤1.85 and 42≤vd≤44; The biconcave negative lens L6 is made of optical glass material with 1.67≤nd≤1.71 and 52≤vd≤54; Wherein, nd represents the refractive index, and vd represents the Abbe number.
3. The coaxial retro-reflection optical lens according to claim 1, wherein: The meniscus negative lens L3 is made of H-LAK3 material with nd=1.75 and vd=50.95; the lenticular positive lens L4 is made of H-FK61 material with nd=1.50 and vd=81.61; the meniscus positive lens L5 is made of H-ZLAF55C material with nd=1.83 and vd=42.71; and the biconcave negative lens L6 is made of H-LAK6 material with nd=1.69 and vd=53.
3.
4. The coaxial retro-reflection optical lens according to claim 1, wherein: The reflecting surface of the convex mirror L2 is provided with a stop STO, and the surface curvature radius of the stop STO is infinite, which is used for limiting the light beam.
5. The coaxial retro-reflection optical lens according to claim 1, wherein: The distance between the reflecting surface S1 of the concave mirror L1 and the reflecting surface S2 of the convex mirror L2, the distance between the reflecting surface S2 of the convex mirror L2 and the incident surface S3 of the meniscus negative lens L3, the distance between the exit surface S5 of the biconvex positive lens L4 and the incident surface S6 of the meniscus positive lens L5, the distance between the exit surface S7 of the meniscus positive lens L5 and the incident surface S8 of the biconcave negative lens L6, and the distance between the exit surface S9 of the biconcave negative lens L6 and the image plane IMA are respectively: -170.42 to -167.04 mm, 157.14 to 160.32 mm, 107.79 to 109.97 mm, 2.78 to 2.84 mm, 22.93 to 23.39 mm; The thicknesses of the meniscus negative lens L3, the biconvex positive lens L4, the meniscus positive lens L5 and the biconcave negative lens L6 are respectively: 1.98 to 2.02 mm, 11.12 to 11.34 mm, 14.85 to 15.15 mm, 14.85 to 15.15 mm.
6. The coaxial fold mirror of claim 3, wherein: The distance between the reflecting surface S1 of the concave mirror L1 and the reflecting surface S2 of the convex mirror L2, the distance between the reflecting surface S2 of the convex mirror L2 and the incident surface S3 of the meniscus negative lens L3, the distance between the exit surface S5 of the biconvex positive lens L4 and the incident surface S6 of the meniscus positive lens L5, the distance between the exit surface S7 of the meniscus positive lens L5 and the incident surface S8 of the biconcave negative lens L6, and the distance between the exit surface S9 of the biconcave negative lens L6 and the image plane IMA are respectively: -168.73 mm, 158.73 mm, 108.88 mm, 2.81 mm, 23.16 mm; The thicknesses of the meniscus negative lens L3, the biconvex positive lens L4, the meniscus positive lens L5 and the biconcave negative lens L6 are respectively: 2.00 mm, 11.23 mm, 15.00 mm, 15.00 mm.
7. The coaxial retro-reflection optical lens according to claim 1, wherein: The radius of curvature of the reflecting surface of the concave mirror L1 is -464.53 to -454.35 mm; The radius of curvature of the reflecting surface of the convex mirror L2 is -135.18 to -132.50 mm; The radius of curvature of the incident surface of the meniscus negative lens L3 is 306.22 to 312.40 mm, and the radius of curvature of the exit surface and the radius of curvature of the incident surface of the biconvex positive lens L4 are all 81.11 to 82.75 mm; The radius of curvature of the exit surface of the biconvex positive lens L4 is -103.94 to -101.88 mm; The radius of curvature of the incident surface of the meniscus positive lens L5 is 40.76 to 41.58 mm, and the radius of curvature of the exit surface is 45.37 to 46.29 mm; The radius of curvature of the incident surface of the biconcave negative lens L6 is -112.09 to -109.87 mm, and the radius of curvature of the exit surface is 39.67 to 40.47 mm.
8. The coaxial retro-reflection optical lens according to claim 6, wherein: The radius of curvature of the reflecting surface of the concave mirror L1 is -458.94 mm; The radius of curvature of the reflecting surface of the convex mirror L2 is -133.84 mm; The incident surface radius of curvature of the meniscus negative lens L3 is 309.31 mm, the exit surface radius of curvature and the incident surface radius of curvature of the biconvex positive lens L4 are 81.93 mm; The exit surface radius of curvature of the biconvex positive lens L4 is -102.91 mm; The incident surface radius of curvature of the meniscus positive lens L5 is 41.17 mm, and the exit surface radius of curvature is 45.83 mm; The incident surface radius of curvature of the biconcave negative lens L6 is -110.98 mm, and the exit surface radius of curvature is 40.07 mm.
9. The coaxial return optical lens according to any one of claims 1-8, wherein: The F number of the overall structure of the concave mirror L1, the convex mirror L2, the meniscus negative lens L3, the biconvex positive lens L4, the meniscus positive lens L5 and the biconcave negative lens L6 is ≤5.
10. The coaxial retro-reflection optical lens of claim 8, wherein: The F number of the overall structure of the concave mirror L1, the convex mirror L2, the meniscus negative lens L3, the biconvex positive lens L4, the meniscus positive lens L5 and the biconcave negative lens L6 is 4.9.