Dual-band achromatic tube lens system

Abstract

The invention provides a dual-band achromatic tube lens system, which relates to the technical field of optical imaging and sequentially comprises an aperture diaphragm, a front beam splitter prism A, a front lens group G1 with positive focal power, a middle lens group G2 with negative focal power, a rear lens group G3 with positive focal power and a rear beam splitter prism B from an object space to an image space along an optical axis. Wherein the front lens group G1 with the positive focal power, the middle lens group G2 with the negative focal power and the rear lens group G3 with the positive focal power form a tube lens structure, the front lens group G1 with the positive focal power, the middle lens group G2 with the negative focal power and the rear lens group G3 with the positive focal power are arranged, and the rear lens group G3 is sequentially provided with a doublet lens G3a and a biconvex lens G3b from the object space to the image space. According to the technical scheme, the lens system is used for cooperatively controlling the axial chromatic aberration and the diaphragm aberration, high-resolution imaging is finally achieved, meanwhile, the lens system adopts the two wavebands with the working wavebands of 532 nm and 639 nm, the influence of the chromatic aberration on the imaging system can be eliminated by adopting the two wavebands with the working wavebands of 532 nm and 639 nm, and the working effect of the lens system is better.

Description

Technical Field

[0001] The present invention relates to the technical field of optical imaging, and in particular to a dual-band achromatic tube lens system. Background Art

[0002] In scientific research such as optical experiments and spectral analysis, the tube mirror system can be used to build high-precision optical systems that meet strict requirements for light collection, spectrometry, and imaging quality, helping researchers obtain accurate data.

[0003] Among them, in laser scanning imaging, spectral analysis and multi-channel optical detection systems, the tube lens system, as the core imaging component, must simultaneously meet stringent requirements such as high light flux, low aberration, compactness and spectral compatibility.

[0004] In the existing technology, although Japanese Nikon patent JP10142509A uses a fewer lens structures, when the object and image sides are simultaneously configured with a dichroic prism, the dispersion characteristics of the prism material produce a strong coupling effect with the optical system, which will lead to a series of problems such as chromatic aberration multiplication, which is not conducive to the application of tube lenses in optical imaging.

[0005] In view of this, how to provide a tube lens system that can reduce imaging chromatic aberration is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0006] (1) Technical problems solved

[0007] In view of the shortcomings of the existing technology, the present invention provides a dual-band achromatic tube lens system, which solves the problem that the dispersion characteristics of the prism material in the current tube lens system produce a strong coupling effect with the optical system, resulting in chromatic aberration multiplication.

[0008] (2) Technical solution

[0009] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0010] In the present invention, the dual-band achromatic tube lens system includes, along the optical axis from the object side to the image side, an aperture stop, a front dichroic prism A, a front lens group G1 with positive focal power, a middle lens group G2 with negative focal power, a rear lens group G3 with positive focal power, and a rear dichroic prism B.

[0011] Among them, the front lens group G1 with positive focal power, the middle lens group G2 with negative focal power and the rear lens group G3 with positive focal power constitute a tube lens structure;

[0012] The front lens group G1 is configured as a doublet lens G1a from the object side to the image side, responsible for correcting chromatic aberration and optimizing spherical aberration;

[0013] The middle lens group G2 is configured as a negative power concave lens G2a from the object side to the image side, which is responsible for performing preliminary correction of field curvature and distortion and coordinating the optical properties of the front and rear lens groups;

[0014] The rear lens group G3 is sequentially provided with a doublet lens G3a and a biconvex lens G3b from the object side to the image side, and is responsible for collaboratively controlling axial chromatic aberration and aperture aberration;

[0015] The tube lens system adopts a dual-band working band of 532nm and 639nm.

[0016] Furthermore, the total length of the tube lens structure does not exceed 50 mm.

[0017] Furthermore, the entire focal length F1 of the tube lens system is 60 mm, and the image space F number is 5;

[0018] The focal lengths allocated to the front lens group G1, the middle lens group G2, and the rear lens group G3 satisfy the following conditional formula: 10<F(G1)<50, -10<F(G2)<-50, 10<F(G3)<50;

[0019] The following conditions are met at the same time: 1.0<|F(G1) / F(G2)|<3.0, 0.1<|F(G3) / F1|<0.9;

[0020] Wherein, F(G1): focal length of front lens group G1; F(G2): focal length of middle lens group G2; F(G3): focal length of rear lens group G3; F1: focal length of the entire optical system at infinity.

[0021] Furthermore, the thickness of the doublet lens G1a is 9.5 mm ± 1.0 mm;

[0022] The thickness of the negative power concave lens G2a is 3.5 mm ± 1.0 mm;

[0023] The thickness of the doublet lens G3a is 10.5 mm ± 1.0 mm; the thickness of the biconvex lens G3b is 3.5 mm ± 1.0 mm;

[0024] The thickness of the front beam splitter prism A and the rear beam splitter prism B is 25 mm ± 5 mm.

[0025] Furthermore, the optical distance between the doublet lens G1a and the negative power concave lens G2a is 6.0 mm ± 1.0 mm;

[0026] The optical distance between the negative power concave lens G2a and the doublet lens G3a is 2.5 mm ± 1.0 mm;

[0027] The optical distance between the doublet lens G3a and the double convex lens G3b is 1.0 mm ± 1.0 mm.

[0028] Furthermore, the curvature radii of the front and rear surfaces of the doublet lens G1a are 20 mm ± 15 mm, 30 mm ± 15 mm, and 70 mm ± 15 mm, respectively;

[0029] The front and rear surface curvature radii of the negative power concave lens G2a are -70 mm ± 15 mm and 20 mm ± 15 mm respectively;

[0030] The three surface curvature radii of the doublet lens G3a are -150mm±15mm, -30mm±15mm and -80mm±15mm respectively;

[0031] The curvature radii of the front and rear surfaces of the biconvex lens G3b are 30 mm ± 15 mm and -1040 mm ± 15 mm respectively.

[0032] Furthermore, the refractive index Nd1 and the dispersion coefficient Vd1, the refractive index Nd2 and the dispersion coefficient Vd2 of the doublet lens G1a satisfy the condition: 1.4<Nd1<1.5;

[0033] 60<Vd1<75;

[0034] 1.8<Nd2<1.9;

[0035] 30<Vd2<45;

[0036] The refractive index Nd3 and the dispersion coefficient Vd3 of the negative power concave lens G2a satisfy the conditions 1.7<Nd3<1.8, 20<Vd3<35;

[0037] The refractive index Nd4 and the dispersion coefficient Vd4, the refractive index Nd5 and the dispersion coefficient Vd5 of the doublet lens G3a satisfy the condition: 1.7<Nd4<1.8;

[0038] 45<Vd4<60;

[0039] 1.6<Nd5<1.7;

[0040] 20<Vd5<35;

[0041] The refractive index Nd6 and the dispersion coefficient Vd6 of the biconvex lens G3b satisfy the following conditions: 1.8<Nd6<1.9;

[0042] 40<Vd6<55.

[0043] Furthermore, the full-field MTF of the tube lens system is close to the diffraction limit, and the field curvature is less than 0.03 mm.

[0044] Furthermore, the telecentricity of the tube lens system is <0.1 ° .

[0045] Furthermore, the aperture stop is arranged between the object plane and the front beam splitter prism A.

[0046] (3) Beneficial effects

[0047] The present invention provides a dual-band achromatic tube lens system. Compared with the prior art, it has the following advantages:

[0048] By setting up three lens groups, namely the front lens group G1 with positive focal power, the middle lens group G2 with negative focal power, and the rear lens group G3 with positive focal power, and setting the rear lens group G3 as a double-cemented lens G3a and a double convex lens G3b from the object side to the image side, it is responsible for collaboratively controlling axial chromatic aberration and aperture aberration, and ultimately achieving high-resolution imaging. At the same time, the tube lens system adopts a dual-band working band of 532nm and 639nm. The use of a dual-band working band of 532nm and 639nm can eliminate the influence of chromatic aberration on the imaging system, making the tube lens system work better. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order 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 use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0050] Figure 1 This is a schematic diagram of the structure of a dual-band achromatic tube lens system;

[0051] Figure 2 is a modulation transfer function curve diagram in an embodiment of a dual-band achromatic tube lens system;

[0052] Figure 3 is a graph of field curvature in an embodiment of a dual-band achromatic tube lens system;

[0053] Figure 4 A diagram showing incident angle vs. image height in an embodiment of a dual-band achromatic tube lens system;

[0054] Figure 5 Graph showing distortion in an embodiment of a dual-band achromatic tube lens system. DETAILED DESCRIPTION

[0055] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0056] The embodiment of the present application provides a dual-band achromatic tube lens system, which solves the problem that the dispersion characteristics of the prism material in the current tube lens system produce a strong coupling effect with the optical system, resulting in multiplication of chromatic aberration, and realizes high-resolution imaging of the tube lens system.

[0057] In order to better understand the above technical solution, the above technical solution will be described in detail below with reference to the accompanying drawings and specific implementation methods.

[0058] like Figure 1 As shown, a dual-band achromatic tube lens system includes, along the optical axis from the object side to the image side, an aperture stop, a front dichroic prism A, a front lens group G1 with positive focal power, a middle lens group G2 with negative focal power, a rear lens group G3 with positive focal power, and a rear dichroic prism B;

[0059] Among them, the front lens group G1 with positive focal power, the middle lens group G2 with negative focal power and the rear lens group G3 with positive focal power constitute a tube lens structure;

[0060] The front lens group G1 is configured as a doublet lens G1a from the object side to the image side, which is responsible for correcting chromatic aberration and optimizing spherical aberration, laying the foundation for initial optical power and image quality;

[0061] The middle lens group G2 is configured as a negative power concave lens G2a from the object side to the image side, which is responsible for performing preliminary correction of field curvature and distortion and coordinating the optical properties of the front and rear lens groups;

[0062] The rear lens group G3 is sequentially configured as a doublet lens G3a and a biconvex lens G3b from the object side to the image side, responsible for collaboratively controlling axial chromatic aberration and aperture aberration, ultimately achieving high-resolution imaging;

[0063] The tube lens system adopts a dual working band of 532nm and 639nm. The dual working band of 532nm and 639nm can eliminate the influence of chromatic aberration on the imaging system, so that the working effect of the tube lens system is better.

[0064] It should be noted that the total length of the tube mirror structure does not exceed 50mm, which can greatly expand the application field of the product. Its compact performance can meet the needs of a wide range of conditions.

[0065] The optical distance between the front beam splitter prism A and the rear beam splitter prism B and the tube lens structure is not less than 5mm, which increases the application capability of the tube lens and facilitates its use in multiple scenarios with the beam splitter prism.

[0066] Specifically, the aperture stop is arranged between the object plane and the front beam splitter prism A, which helps to balance the focal power distribution of each lens group, thereby optimizing aberration correction to avoid vignetting or uneven illumination on the image plane caused by pupil shift;

[0067] The entire focal length F1 of the tube lens system is 60 mm, and the image space F number is 5;

[0068] The focal lengths allocated to the front lens group G1, the middle lens group G2, and the rear lens group G3 satisfy the following conditional formula: 10 < F(G1) < 50;

[0069] -10<F(G2)<-50;

[0070] 10<F(G3)<50;

[0071] The following conditions are met at the same time: 1.0<|F(G1) / F(G2)|<3.0;

[0072] 0.1<|F(G3) / F1|<0.9

[0073] Wherein, F(G1): focal length of front lens group G1; F(G2): focal length of middle lens group G2; F(G3): focal length of rear lens group G3; F1: focal length of the entire optical system at infinity.

[0074] According to the above-mentioned power distribution method, a +-+ structure is satisfied, and the focal lengths of the lens groups are not much different, resulting in an initial low-stress lens structure with uniform power distribution and a flat surface shape.

[0075] Setting the image space F-number to 5 achieves high light flux, improving the optical system's ability to collect and process light, meeting imaging requirements in complex environments and suitable for scenes with high light throughput requirements.

[0076] It can also achieve full-field near-diffraction-limited imaging at a large aperture of F-number 5 in the image space, and simultaneously solve the technical contradictions of dual-band chromatic aberration, field curvature balance and ultra-short total length.

[0077] Specifically, the thickness of the doublet lens G1a is 9.5mm±1.0mm; the thickness of the negative power concave lens G2a is 3.5mm±1.0mm; the thickness of the doublet lens G3a is 10.5mm±1.0mm; the thickness of the biconvex lens G3b is 3.5mm±1.0mm; and the thickness of the front beam splitter prism A and the rear beam splitter prism B is 25mm±5mm. Through the precise design of the doublet lens G1a, the negative power concave lens G2a, the doublet lens G3a, and the biconvex lens G3b, the system is compact and lightweight while meeting imaging quality requirements, improving overall performance.

[0078] The optical spacing between the doublet lens G1a and the negative power concave lens G2a is 6.0mm±1.0mm; the optical spacing between the negative power concave lens G2a and the doublet lens G3a is 2.5mm±1.0mm; and the optical spacing between the doublet lens G3a and the biconvex lens G3b is 1.0mm±1.0mm. The optical spacing of the present invention can simplify the system structure, reduce the number of lenses and the processing difficulty, and lower production costs.

[0079] The three surface curvature radii of the doublet lens G1a are 20mm±15mm, 30mm±15mm, and 70mm±15mm, respectively. The front and rear surface curvature radii of the negative power concave lens G2a are -70mm±15mm and 20mm±15mm, respectively. The three surface curvature radii of the doublet lens G3a are -150mm±15mm, -30mm±15mm, and -80mm±15mm, respectively. The front and rear surface curvature radii of the biconvex lens G3b are 30mm±15mm and -1040mm±15mm, respectively.

[0080] The above settings can ensure that the surfaces will not be too curved or undulated, making it easy to form and helping to improve production yield.

[0081] The refractive index Nd1 and the dispersion coefficient Vd1, the refractive index Nd2 and the dispersion coefficient Vd2 of the doublet lens G1a meet the conditions: 1.4<Nd1<1.5, 60<Vd1<75, 1.8<Nd2<1.9, 30<Vd2<45; the refractive index Nd3 and the dispersion coefficient Vd3 of the negative power concave lens G2a meet the conditions 1.7<Nd3<1.8, 20<Vd3<35; the refractive index Nd1 of the doublet lens G3a meets the conditions 1.7<Nd3<1.8, 20<Vd3<35. 4 and the dispersion coefficient Vd4, the refractive index Nd5 and the dispersion coefficient Vd5 meet the conditions: 1.7<Nd4<1.8, 45<Vd4<60, 1.6<Nd5<1.7, 20<Vd5<35; the refractive index Nd6 and the dispersion coefficient Vd6 of the biconvex lens G3b meet the conditions: 1.8<Nd6<1.9, 40<Vd6<55; the correct selection and combination of lens group materials is conducive to eliminating the aberration of the system and improving the image quality of the system;

[0082] The full-field MTF of the tube lens system is close to the diffraction limit, the field curvature is <0.03mm, and the telecentricity is <0.1 ° ;

[0083] In a specific application process, the present invention uses a total of four lenses, and the system maintains a symmetrical structure. A beam splitter prism can be placed on the object side and the image side respectively, while maintaining high image quality.

[0084] The present invention is suitable for laser confocal microscopy, multispectral analysis systems, and industrial optical inspection equipment. Through an innovative lens group structure, precise parameter configuration, and the rational use of a beam splitter prism, it solves the problems of small aperture, large size, and difficulty in balancing multi-band aberrations in traditional tube lenses. It has the advantages of high resolution, low dispersion, and compactness.

[0085] Example:

[0086] Each optical element (surface) of this embodiment meets the conditions of Table 1 (surface data):

[0087] Table 1

[0088]

[0089]

[0090] in:

[0091] R (mm): radius of curvature of each surface;

[0092] D (mm): the distance between lenses and the thickness of the lenses;

[0093] Nd: refractive index of each glass at d line;

[0094] Vd: Abbe number of glass;

[0095] In this embodiment, the working band of the tube lens system is a dual band of 532nm and 639nm. Six fields of view (half image height 0-6.6mm) are set based on the actual image height. The field of view uses the actual image height as an indicator, and six field numbers are selected respectively, with half image heights of 0, 2mm, 3.3mm, 4.6mm, 5.5mmm, and 6.6mm. The image field diameter reaches Φ13.2mm, and a dual-band light source of 532nm and 639nm is used to eliminate chromatic aberration. The effective focal length is 60mm, the image space F number is 5.0, the rear working distance is 25mm, and the total length of the tube lens structure, that is, the total length of the front lens group G1, the middle lens group G2, and the rear lens group G3 is less than 50mm.

[0096] in, Figure 2-Figure 5 Graphs showing various image quality analyses of the large-aperture tube lens system of this embodiment;

[0097] Figure 2 is a modulation transfer function curve diagram of the large aperture tube lens system in this embodiment, Figure 2 The results show that the modulation transfer function values ​​of the main field MTF at a frequency of 200lp / mm are better than 0.25, and the modulation transfer function values ​​of the edge field MTF at a frequency of 200lp / mm are better than 0.15;

[0098] Figure 3 This is a field curvature curve diagram of the large-aperture tube lens system in this embodiment. The maximum optical field curvature of the entire field of view is less than 0.003mm. The optical power distribution and curvature design of the lens group are optimized to effectively balance the field curvature, ensure a flat image surface, and uniform imaging in each field of view (half-image height 0, 2mm, 3.3mm, 4.6mm, 5.5mm, 6.6mm), avoiding blur at the edge of the field of view.

[0099] Figure 4 This is a graph of the incident angle vs. image height of the tube lens system in this embodiment. The telecentricity is less than 0.1°, indicating good performance.

[0100] The image plane has excellent telecentricity: the image plane chief ray is parallel to the optical axis, eliminating the influence of object distance changes on imaging magnification. It is particularly suitable for application scenarios sensitive to the object-image relationship, such as precision measurement and visual inspection, and improves the stability of measurement and imaging.

[0101] Figure 5 This is a distortion curve diagram of the large-aperture tube lens system in this embodiment. The maximum optical distortion of the entire field of view is better than 0.7161%. All indicators are better than the design requirements, and the image quality is stable.

[0102] In summary, compared with the existing technology, the present invention has the following beneficial effects:

[0103] 1. The present invention utilizes a dual-band light source of 532nm and 639nm, combined with the characteristics of lens materials to correct chromatic aberration in a targeted manner, effectively improving the color reproduction and accuracy of imaging, and avoiding the impact of color deviation on imaging quality.

[0104] 2. The present invention adds dichroic prisms to both the object and image sides, especially the image side: the object side dichroic prism can introduce multiple light paths, and the image side dichroic prism is combined with the image side telecentric design to accurately control the outgoing light path, while enhancing the splitting function, improving the accuracy and stability of light path control, and expanding the application in the fields of spectral analysis, optical signal separation and precision measurement.

[0105] 3. The total length of the tube lens structure of the present invention, that is, the total length of the front lens group G1, the middle lens group G2, and the rear lens group G3, is controlled within 50 mm: by precisely calculating the lens thickness and spacing and adopting a compact design, the space occupancy is greatly reduced, which facilitates integration with other optical components or systems and is suitable for space-constrained equipment.

[0106] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply the existence of any such actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or device comprising the element.

[0107] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A dual-band achromatic tube lens system, characterized in that: Along the optical axis, from the object side to the image side, it includes an aperture stop, a front dichroic prism A, a front lens group G1 with positive focal power, a middle lens group G2 with negative focal power, a rear lens group G3 with positive focal power, and a rear dichroic prism B. Among them, the front lens group G1 with positive focal power, the middle lens group G2 with negative focal power and the rear lens group G3 with positive focal power constitute a tube lens structure; The front lens group G1 is configured as a doublet lens G1a from the object side to the image side, responsible for correcting chromatic aberration and optimizing spherical aberration; The middle lens group G2 is configured as a negative power concave lens G2a from the object side to the image side, which is responsible for performing preliminary correction of field curvature and distortion and coordinating the optical properties of the front and rear lens groups; The rear lens group G3 is sequentially provided with a doublet lens G3a and a biconvex lens G3b from the object side to the image side, and is responsible for collaboratively controlling axial chromatic aberration and aperture aberration; The tube lens system adopts a dual-band working band of 532nm and 639nm.

2. The dual-band achromatic tube lens system according to claim 1, wherein: The total length of the tube lens structure does not exceed 50 mm.

3. The dual-band achromatic tube lens system according to claim 1, characterized in that: The entire focal length F1 of the tube lens system is 60 mm, and the image space F number is 5; The focal lengths allocated to the front lens group G1, the middle lens group G2, and the rear lens group G3 satisfy the following conditional formula: 10<F(G1)<50, -10<F(G2)<-50, 10<F(G3)<50; The following conditions are met at the same time: 1.0<|F(G1) / F(G2)|<3.0, 0.1<|F(G3) / F1|<0.9; Wherein, F(G1): focal length of front lens group G1; F(G2): focal length of middle lens group G2; F(G3): focal length of rear lens group G3; F1: focal length of the entire optical system at infinity.

4. The dual-band achromatic tube lens system according to claim 1, wherein: The thickness of the doublet lens G1a is 9.5 mm ± 1.0 mm; The thickness of the negative power concave lens G2a is 3.5 mm ± 1.0 mm; The thickness of the doublet lens G3a is 10.5 mm ± 1.0 mm; The thickness of the biconvex lens G3b is 3.5 mm ± 1.0 mm; The thickness of the front beam splitter prism A and the rear beam splitter prism B is 25 mm ± 5 mm.

5. The dual-band achromatic tube lens system according to claim 1, wherein: The optical distance between the doublet lens G1a and the negative power concave lens G2a is 6.0 mm ± 1.0 mm; The optical distance between the negative power concave lens G2a and the doublet lens G3a is 2.5 mm ± 1.0 mm; The optical distance between the doublet lens G3a and the double convex lens G3b is 1.0 mm ± 1.0 mm.

6. The dual-band achromatic tube lens system according to claim 1, characterized in that: The three surface curvature radii of the doublet lens G1a are 20 mm ± 15 mm, 30 mm ± 15 mm, and 70 mm ± 15 mm respectively; The front and rear surface curvature radii of the negative power concave lens G2a are -70 mm ± 15 mm and 20 mm ± 15 mm respectively; The three surface curvature radii of the doublet lens G3a are -150 mm ± 15 mm, -30 mm ± 15 mm, and -80 mm ± 15 mm, respectively; The curvature radii of the front and rear surfaces of the biconvex lens G3b are 30 mm ± 15 mm and -1040 mm ± 15 mm respectively.

7. The dual-band achromatic tube lens system according to claim 1, wherein: The refractive index Nd1 and the dispersion coefficient Vd1, the refractive index Nd2 and the dispersion coefficient Vd2 of the doublet lens G1a satisfy the condition: 1.4<Nd1<1.5; 60<Vd1<75; 1.8<Nd2<1.9; 30<Vd2<45; The refractive index Nd3 and the dispersion coefficient Vd3 of the negative power concave lens G2a satisfy the condition 1.7<Nd3<1.8; 20<Vd3<35; The refractive index Nd4, the dispersion coefficient Vd4, the refractive index Nd5 and the dispersion coefficient Vd5 of the doublet lens G3a satisfy the following conditions: 1.7<Nd4<1.8; 45<Vd4<60; 1.6<Nd5<1.7; 20<Vd5<35; The refractive index Nd6 and the dispersion coefficient Vd6 of the biconvex lens G3b satisfy the following conditions: 1.8<Nd6<1.9; 40<Vd6<55.

8. The dual-band achromatic tube lens system according to claim 1, wherein: The full-field MTF of the tube lens system is close to the diffraction limit, and the field curvature is less than 0.03 mm.

9. The dual-band achromatic tube lens system according to claim 1, wherein: The telecentricity of the tube lens system is <0.1°.

10. The dual-band achromatic tube lens system according to claim 1, wherein: The aperture stop is arranged between the object plane and the front beam splitter prism A.

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