Endoscope optical system

Abstract

The invention discloses an endoscope optical system which is composed of a first lens, a steering prism, a diaphragm, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens and a beam splitter prism from an object plane to an image plane, the focal power of the first lens is negative, the object side is a convex surface, and the image side is a concave surface; the focal power of the second lens is positive, the object side is a plane, and the image side is a convex surface; the object side of the third lens is a convex surface, the focal power of the fourth lens is opposite to that of the third lens, and the image side is a convex surface; the focal power of the fifth lens is positive, and the image side of the fifth lens is a convex surface; the focal power of the sixth lens is negative, the object side is a concave surface, and the image side is a concave surface; the focal power of the seventh lens is positive, the object side is a convex surface, and the image side is a convex surface; the object space numerical aperture NA of the endoscope optical system is more than 0.001 and less than 0.006, and the endoscope optical system has the advantages that lens combinations with different surface shapes and focal powers are used, and the depth of field and the axial resolution capability of an endoscope are improved by reducing the object space numerical aperture.

Description

Technical Field

[0001] The present invention relates to an optical system, and in particular to an endoscope optical system. Background Art

[0002] Endoscopes are widely used in the medical field. With the development of medical devices and related technologies, the performance requirements for endoscopes have also increased. After entering the human body, the endoscope needs to image tissues within a large working range. The Chinese utility model patent with the publication number CN218383456U provides an endoscope objective zoom optical system, which adjusts the lens group to adapt to objects with different object distances while maintaining good imaging quality. However, the presence of the moving mechanism reduces the reliability and service life of the endoscope and increases the manufacturing cost.

[0003] To improve the comprehensiveness and accuracy of diagnosis, steering prisms and beam-splitting prisms are provided in the endoscope to provide a more convenient user experience for doctors. The steering prism and the beam-splitting prism are usually composed of multiple prisms combined together. After the light is reflected multiple times therein and deflected for output, on the one hand, the transmission angle of the light beam is changed, and on the other hand, images formed by various lights with different properties, such as white light, fluorescence, polarized light, etc., can be obtained, improving the accuracy of the final image. This has an impact on the light energy utilization rate and also has high precision requirements for the prism angles. The US invention patent with the patent number US11805983B2 provides a light path deflection prism, which realizes the light path deflection through the combination of special-shaped prisms and mirror coatings, and can improve the light transmittance. However, the special-shaped prisms increase the manufacturing cost and the assembly difficulty. The Chinese invention patent application with the publication number CN114176485A uses a beam splitter to obtain white light and polarized light, providing a clearer image in a fuzzy environment. However, in order to make the images of each light beam match well, the length of the beam splitter is increased to compensate for the optical path, resulting in a larger volume at the rear end of the lens and affecting the actual use. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an endoscope optical system that can improve the depth of field and axial resolution ability.

[0005] The technical solution adopted by the present invention to solve the above technical problems is as follows: An endoscope optical system is composed of a first lens, a turning prism, a diaphragm, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, and a beam splitter prism from the object plane to the image plane. The optical power of the first lens is negative, the object side is convex, and the image side is concave; the optical power of the second lens is positive, the object side is flat, and the image side is convex; the object side of the third lens is convex, the optical power of the fourth lens is opposite to that of the third lens, and the image side is convex; the optical power of the fifth lens is positive, and the image side is convex; the optical power of the sixth lens is negative, the object side is concave, and the image side is concave; the optical power of the seventh lens is positive, the object side is convex, and the image side is convex; the object-side numerical aperture NA of the endoscope optical system satisfies: 0.001 < NA < 0.006.

[0006] Compared with the prior art, the advantages of the present invention are that a combination of lenses with different surface shapes and optical powers is used, and by reducing the object-side numerical aperture, the depth of field and axial resolution ability of the endoscope are improved. At the same time, a turning prism and a beam splitter prism are used to realize the turning and splitting functions of all-field light rays, improve the light energy utilization rate, and image with light beams of various properties such as white light, fluorescence, and polarized light, so as to improve the imaging performance of the endoscope while maintaining a small volume.

[0007] Preferably, both surfaces of the first lens are aspherical. Selecting aspherical surfaces can further improve the imaging quality of the lens and reduce the aberration in the imaging system.

[0008] Preferably, the third lens and the fourth lens form a doublet lens, and the fifth lens, the sixth lens, and the seventh lens form a triplet lens. The doublet lens and the triplet lens can balance the chromatic aberration during the propagation of broadband light, achieve the correction of chromatic aberration and aberration on and off the axis, and reduce the lens sensitivity.

[0009] Preferably, the focal length f of the endoscope optical system, the focal length f L1 of the first lens, the focal length f L2 of the second lens, the focal length f 34 of the doublet lens, and the focal length f 567 of the triplet lens respectively satisfy: -0.8 < f L1 / f < -0.7, 1.5 < f L2 / f < 1.7, 3.2 < f 34 / f < 3.5, -900000 < f 567 / f < -9000. The focal length of the triplet lens is relatively large, close to that of a flat glass, which can maintain the imaging height and adjust the light angle.

[0010] Preferably, define the refractive index of the material of the first lens as Nd L1 , the refractive index of the material of the second lens as Nd L2 , the refractive index of the material of the third lens as Nd L3 , the refractive index of the material of the fourth lens as Nd L4 , the refractive index of the material of the fifth lens as Nd L5 , the refractive index of the material of the sixth lens as Nd L6 , the refractive index of the material of the seventh lens as Nd L7 , respectively satisfying: 1.9 < Nd L1 < 2.1, 1.6 < Nd L2 < 1.8, 0.15 < |Nd L3 - Nd L4 | < 0.25, 0.15 < |Nd L5 - Nd L6 | < 0.25, 0.15 < |Nd L6 - Nd L7 | < 0.25.

[0011] Preferably, the steering prism is provided with a steering incident surface, a first reflecting surface, a second reflecting surface and a steering exit surface. The steering exit surface is located between the first reflecting surface and the second reflecting surface and is perpendicular to the optical axis of the endoscope optical system. Light is incident perpendicularly on the steering incident surface and enters the first reflecting surface at a first incident angle. It is reflected by the first reflecting surface and enters the second reflecting surface at a second incident angle, and then is reflected by the second reflecting surface to the steering exit surface and exits perpendicularly. Define the steering angle of the steering prism as θ, the included angle between the steering incident surface and the second reflecting surface as θ1, the included angle between the second reflecting surface and the first reflecting surface as θ2, and the included angle between the first reflecting surface and the optical axis of the endoscope optical system as θ3. They respectively satisfy the following relationships: θ = 30°, θ2 = θ / 2, θ1 + θ2 + θ3 + θ = 90°, 6° < θ3 < 16°. By adjusting the shape of the steering prism to achieve a 30° light steering function and controlling the deflection degree of light inside the steering prism, light energy loss caused by light exiting the steering prism can be avoided, and at the same time, the volume of the steering prism can be controlled.

[0012] Preferably, the steering prism is a single prism, and the included angle θ3 between the first reflecting surface and the optical axis of the endoscope optical system is 15°. Controlling the turning length of light in the steering prism and coordinating with the field of view angle of the optical system can ensure that the optical path difference of light between the edge field of view and the central field of view in the steering prism is small and symmetric, reducing the impact on the imaging quality.

[0013] Preferably, the turning prism is composed of a first sub - prism and a second sub - prism glued together. The turning incident surface is the object side surface of the first sub - prism. The first reflecting surface is in contact with air. The second reflecting surface is the glued surface between the first sub - prism and the second sub - prism. The turning exit surface is the image side surface of the second sub - prism. The included angle θ3 between the first reflecting surface and the optical axis of the endoscope optical system is θ3 = 7° or θ3 = 10°.

[0014] Preferably, the first reflecting surface is coated with a reflective film. Define the refractive index of the first sub - prism as Nd G01 , and the refractive index of the second sub - prism as Nd G02 . The second incident angle is θ5, satisfying: Nd G01 ≤Nd G02 *sinθ5. The reflection function of the first reflecting surface is realized by coating the reflective film, while the reflection function of the second reflecting surface is realized by the refractive index difference between the first sub - prism and the second sub - prism, so that the light is totally reflected at the second reflecting surface, which can reduce the coating cost.

[0015] Preferably, define the refractive index of the first sub - prism as Nd G01 , and the refractive index of the second sub - prism as Nd G02 . The second incident angle is θ5, satisfying: Nd G01 ≤Nd G02 *sin(θ5 - 8°). This structure can not only reduce the coating cost, but also enable the light in the entire field of view to be totally reflected at the second reflecting surface, reducing the light energy loss.

[0016] Preferably, the beam - splitting prism is composed of multiple beam - splitting prisms made of the same material and glued together. The glued surface of each beam - splitting prism is the beam - splitting surface. The light emerging from the seventh lens enters from the beam - splitting incident surface of the beam - splitting prism and is split into light of different properties on different beam - splitting surfaces and then exits from the beam - splitting exit surfaces of different beam - splitting prisms in the beam - splitting prism.

[0017] Preferably, the beam splitting prism is formed by gluing a first sub - prism, a second sub - prism, and a third sub - prism made of the same material. The object side of the first sub - prism is the beam splitting incident surface of the beam splitting prism. The gluing surface between the first sub - prism and the second sub - prism is the first beam splitting surface. Define the image side of the first sub - prism as the first beam splitting exit surface. The gluing surface between the second sub - prism and the third sub - prism is the second beam splitting surface. The image side of the second sub - prism is the second beam splitting exit surface. The image side of the third sub - prism is the third beam splitting exit surface. Define the angle between the beam splitting incident surface of the beam splitting prism and the first beam splitting surface as θ61, and the angle between the first beam splitting surface and the second beam splitting surface as θ71, which respectively satisfy: 25° < θ61 < 35°, 35° < θ71 < 45°; Define the first - stage length of the light ray in the first sub - prism as d11, the first - stage length in the second sub - prism as d21, and the first - stage length in the third sub - prism as d31, which respectively satisfy: 0.7mm < d11 < 0.9mm, 0.9mm < d21 < 1.1mm, 3.7mm < d11 + d21 + d31 < 3.9mm.

[0018] Preferably, the beam splitting prism is formed by gluing a first sub - prism and a second sub - prism made of the same material. The object side of the first sub - prism is the beam splitting incident surface of the beam splitting prism. Define the gluing surface between the first sub - prism and the second sub - prism as the first beam splitting surface. The image side of the first sub - prism is the first beam splitting exit surface. The image side of the second sub - prism is the second beam splitting exit surface. The angle between the beam splitting incident surface of the beam splitting prism and the first beam splitting surface is θ62 = 45°. Define the first - stage length of the light ray in the first sub - prism as d12, the second - stage length as d22, and the length of the light ray in the second sub - prism as d32, which respectively satisfy: 2.1mm < d12 < 2.3mm, 1.5mm < d22 < 1.7mm, 1.5mm < d32 < 1.7mm. Description of the Drawings

[0019] Figure 1 is a schematic structural diagram of the endoscopic optical system according to the embodiment and Example 1 of the present invention; Figure 2 is a schematic structural diagram of the endoscopic optical system of the present invention when the turning prism is a single prism; Figure 3 is a schematic structural diagram of the endoscopic optical system of the present invention when the turning prism is a double prism; Figure 4 is a schematic structural diagram of the endoscopic optical system of the present invention when the turning prism is a triple prism; Figure 5 is a schematic structural diagram of the endoscopic optical system of the present invention when the beam splitting prism is a triple prism; Figure 6 Schematic structural diagram of the beam splitting prism of the endoscope optical system of the present invention, which is a two-prism structure; Figure 7 Transfer function curve graph at an object distance of 50 mm in the first example of the present invention; Figure 8 Transfer function curve graph at an object distance of 35 mm in the first example of the present invention; Figure 9 Transfer function curve graph at an object distance of 125 mm in the first example of the present invention; Figure 10 Schematic structural diagram of the endoscope optical system in the second example of the present invention; Figure 11 Transfer function curve graph at an object distance of 50 mm in the second example of the present invention; Figure 12 Transfer function curve graph at an object distance of 35 mm in the second example of the present invention; Figure 13 Transfer function curve graph at an object distance of 125 mm in the second example of the present invention; Figure 14 Schematic diagram of the four-eye endoscope optical system in the first example of the present invention; Figure 15 Schematic diagram of the two-eye endoscope optical system in the first example of the present invention.

[0020] Explanation of reference numerals in the drawings: L1, the first lens; G, the turning prism; G01, the first sub-prism; G02, the second sub-prism; G03, the third sub-prism; STO, the aperture stop; L2, the second lens; L3, the third lens; L4, the fourth lens; L5, the fifth lens; L6, the sixth lens; L7, the seventh lens; P, the beam splitting prism; P01, the first beam splitting prism; P02, the second beam splitting prism; P03, the third beam splitting prism; IMA, the image plane; IMA1, the first image plane; IMA2, the second image plane; IMA3, the third image plane; GS1, the first protective glass; GS2, the second protective glass; S1, the turning incident surface; S2, the first reflecting surface; S3, the second reflecting surface; S4, the turning exit surface; S5, the beam splitting incident surface; Figure 5 Explanation of reference numerals in the drawings: S61, the first beam splitting surface; S71, the first beam splitting exit surface; S81, the second beam splitting surface; S91, the second beam splitting exit surface; S101, the third beam splitting exit surface; Figure 6 Explanation of reference numerals in the drawings: S62, the first beam splitting surface; S72, the first beam splitting exit surface; S92, the second beam splitting exit surface. Detailed implementation manners

[0021] The present invention will be further described in detail below in conjunction with the embodiments and the accompanying drawings.

[0022] The exemplary embodiments of the present invention will be specifically described below in conjunction with the accompanying drawings. The accompanying drawings are for reference and illustration only and do not limit the scope of protection of the present invention.

[0023] Embodiment: In the accompanying drawings, for the sake of clarity, the thickness, dimensions and shape of the lens have been slightly exaggerated. The drawings are only schematic and not drawn to an exact scale.

[0024] In an exemplary embodiment, in order to improve the imaging quality of the lens and reduce the aberration in the imaging system, the aspherical lens surface profile satisfies the following equation: .

[0025] Wherein, y represents the radial coordinate value of the lens perpendicular to the optical axis of the endoscopic optical system, is the sagittal height of the aspherical lens from the vertex along the optical axis of the endoscopic optical system at a height of y , c =1 / R, where R represents the radius of curvature corresponding to the center of the aspherical lens surface profile, k represents the conic coefficient, and the parameters B , C are the coefficients of the 4th and 6th order terms of the high-order aspherical polynomial, respectively.

[0026] The endoscopic optical system operates in the wavelength band of 0.486um to 1um, where the central wavelength is 0.587um and the fluorescence is in the wavelength band of 0.82um to 1um.

[0027] An endoscopic optical system, as Figure 1 shown, consists of a first lens L1, a turning prism G, a diaphragm STO, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, a seventh lens L7 and a beam splitting prism P from the object plane to the image plane IMA. First protective glass GS1 and second protective glass GS2 are respectively arranged at both ends of the endoscopic optical system to play a protective role.

[0028] It is possible to consider placing a filter or coating a filter film layer in the endoscopic optical system to filter out stray light. To save costs, one filter can be set; and to increase the cut-off depth and improve the image quality, two filters can also be set. Usually, the filter can be placed between the diaphragm STO and the third lens L3 or between the fourth lens L4 and the image plane IMA. The filter film layer can be set on the image side of the fourth lens L4 or the object side of the fifth lens L5 or the object side of the beam splitter prism P. Usually, the numerical value of the radius of curvature of the image side of the fourth lens L4 and the numerical value of the radius of curvature of the object side of the fifth lens L5 are set to be relatively large, and the object side of the beam splitter prism P is set to be a plane, so that the filtering effect is better when coating the filter film layer.

[0029] The object-side numerical aperture NA of the endoscopic optical system satisfies: 0.001 < NA < 0.006, and the distance between the object plane and the object side of the first lens L1 is the object distance d, which satisfies: 30 mm ≤ d ≤ 125 mm. More preferably, d = 50 mm. Controlling the object-side numerical aperture NA of the endoscopic optical system within a small range can obtain a larger depth-of-field range, improve the axial resolution ability of the endoscope, and provide doctors with more comprehensive and detailed information on the internal tissues of the human body.

[0030] The optical power of the first lens L1 is negative, the object side is convex, and the image side is concave. The focal length f of the endoscopic optical system and the focal length f L1 of the first lens L1 satisfy: -0.8 < f L1 / f < -0.7. Defining the refractive index of the material of the first lens L1 as Nd L1 satisfies: 1.9 < Nd L1 < 2.1. Selecting a high-refractive-index material can effectively collect light and reduce aberration.

[0031] The optical power of the second lens L2 is positive, the object side is flat, and the image side is convex. The focal length f L2 of the second lens L2 satisfies: 1.5 < f L2 / f < 1.7. Defining the refractive index of the material of the second lens L2 as Nd L2 satisfies: 1.6 < Nd L2 < 1.8. Selecting a relatively high-refractive-index material can effectively converge light and reduce aberration.

[0032] The object side of the third lens L3 is convex, the optical power of the fourth lens L4 is opposite to that of the third lens L3, the image side is convex, and the third lens L3 and the fourth lens L4 form a doublet lens. The focal length f 34 of the doublet lens formed by the third lens L3 and the fourth lens L4 satisfies: 3.2 < f 34 / f < 3.5, which can converge light and control the imaging height. Defining the refractive index of the material of the third lens L3 as Nd L3, the refractive index of the material of the fourth lens L4 is Nd L4 , satisfying: 0.15 < |Nd L3 - Nd L4 | < 0.25. By using a doublet lens to balance the chromatic aberration during the propagation of broadband light, it is possible to correct the chromatic aberration and spherical aberration on and off the axis, and reduce the lens sensitivity.

[0033] The optical power of the fifth lens L5 is positive, and the image side is convex. The optical power of the sixth lens L6 is negative, the object side is concave, and the image side is concave. The optical power of the seventh lens L7 is positive, the object side is convex, and the image side is convex. The fifth lens L5, the sixth lens L6, and the seventh lens L7 form a triplet lens. The focal length f 567 of the triplet lens satisfies: -900000 < f 567 / f < -9000. The focal length f 567 of the triplet lens is relatively large, close to a flat glass, which can maintain the imaging height and adjust the light angle. Define the refractive index of the material of the fifth lens L5 as Nd L5 , the refractive index of the material of the sixth lens L6 as Nd L6 , and the refractive index of the material of the seventh lens L7 as Nd L7 , which respectively satisfy: 0.15 < |Nd L5 - Nd L6 | < 0.25, 0.15 < |Nd L6 - Nd L7 | < 0.25. By using a triplet lens to balance the chromatic aberration during the propagation of broadband light, it is possible to correct the chromatic aberration and spherical aberration on and off the axis, and reduce the lens sensitivity.

[0034] The turning prism G can be composed of three sub - prisms or two sub - prisms, or it can be a single prism.

[0035] Figure 2 The turning prism G shown is a single prism. Light enters from the turning incident surface S1, is reflected successively from the first reflection surface S2 and the second reflection surface S3, and finally exits from the turning exit surface S4, realizing the turning of light. The reflection functions of the first reflection surface S2 and the second reflection surface S3 are achieved by coating a reflective film, so that the light in the full field of view is reflected by the turning prism G, which can reduce the light energy loss.

[0036] From Figure 2It can be seen that the steering angle of the steering prism G is θ, the angle between the steering incident surface S1 and the second reflection surface S3 is θ1, the angle between the second reflection surface S3 and the first reflection surface S2 is θ2, the angle between the first reflection surface S2 and the optical axis of the endoscope optical system is θ3, the incident angle of the light reaching the first reflection surface S2 is θ4, and the incident angle of the light reaching the second reflection surface S3 is θ5, satisfying: θ=30°, θ2=θ / 2, θ1+θ2+θ3+θ=90°, 6°<θ3<16°, and the 30° light steering function is achieved by adjusting the shape of the steering prism G, and the degree of deflection of the light inside the steering prism G is controlled to avoid the light energy loss caused by the light exiting the steering prism G, and the volume of the steering prism G can be controlled at the same time. The best solution is θ3=15°, which can control the turning length of the light in the turning prism G. Combined with the field of view angle of the optical system, it can ensure that the optical path difference between the light in the edge field of view and the light in the center field of view in the turning prism G is small and symmetrical, thereby reducing the impact on the imaging quality.

[0037] Figure 3 The steering prism G shown is composed of a first sub-prism G01 and a second sub-prism G02 glued together. The object side of the first sub-prism G01 is the steering incident surface S1, and the contact surface of the second sub-prism G02 with the air is the first reflection surface S2. The reflection function of the first reflection surface S2 is achieved by coating a reflection film. The contact surface between the first sub-prism G01 and the second sub-prism G02 is the second reflection surface S3. The reflection function of the second reflection surface S3 is achieved by the refractive index difference between the first sub-prism G01 and the second sub-prism G02, which can reduce the coating cost. The image side of the second sub-prism G02 is the steering exit surface S4. The light is incident from the steering incident surface S1, reflected from the first reflection surface S2 and the second reflection surface S3 in turn, and finally emitted from the steering exit surface S4 to achieve the steering of the light.

[0038] from Figure 3As can be seen, the turning angle of the turning prism G is θ, the angle between the turning incident surface S1 and the second reflection surface S3 is θ1, the angle between the second reflection surface S3 and the first reflection surface S2 is θ2, the angle between the first reflection surface S2 and the optical axis of the endoscope optical system is θ3, the incident angle of the light ray reaching the first reflection surface S2 is θ4, and the incident angle of the light ray reaching the second reflection surface S3 is θ5, which respectively satisfy: θ = 30°, θ2 = θ / 2, θ1 + θ2 + θ3 + θ = 90°, 6° < θ3 < 16°. By adjusting the shape of the sub - prism, the 30° light ray turning function is realized, and the deflection degree of the light ray inside the turning prism G is controlled to avoid the sub - prism blocking the light ray, and at the same time, the volume of the turning prism G can be controlled. θ3 = 7° or θ3 = 10° can be selected, so that the turning length of the light ray in the turning prism G can be controlled, and combined with the field - of - view angle of the optical system, it is ensured that the optical path difference of the light rays in the edge field of view and the central field of view in the turning prism G is small and symmetric, reducing the influence on the imaging quality. In this structure, the refractive index Nd of the first sub - prism G01 G01 and the refractive index Nd of the second sub - prism G02 G02 can be selected to satisfy: Nd G01 ≤Nd G02 ×sinθ5, so that the light ray is totally reflected on the second reflection surface S3. A better choice is to satisfy: Nd G01 ≤Nd G02 ×sin(θ5 - 8°). Such a choice can make the light rays in the entire field of view be totally reflected on the second reflection surface S3, which can reduce the light energy loss and at the same time reduce the coating cost.

[0039] Figure 4 The turning prism G shown is composed of a first sub - prism G01, a second sub - prism G02 and a third sub - prism G03 glued together.

[0040] The beam - splitting prism P can be composed of three or two sub - prisms.

[0041] Figure 5 The beam - splitting prism P shown is composed of a first sub - prism P01, a second sub - prism P02 and a third sub - prism P03 glued together. The materials of the three sub - prisms are the same. Therefore, when the beam - splitting function is not used, it can be regarded as a prism, reducing the pressure on the design of the endoscope optical system.

[0042] A film with different properties is set on each gluing surface. After passing through each gluing surface, light is divided into two groups of reflected and refracted light. Eventually, information of different channels provided by light with different properties, such as white light, fluorescence, and polarized light, can be collected, improving the accuracy of the final imaging. White light is the conventionally used wavelength band, providing a true image of the surface layer of human internal tissues for doctors; fluorescence provides an image of the tissues below the surface layer, providing precise positioning for the treatment of diseases to reduce the surgical risk; while the image formed by polarized light can shield the reflected light brought by metal objects such as medical devices and the scattered light brought by media such as normal saline or biological tissues, providing a clearer image.

[0043] The object side surface of the first splitting prism P01 is the splitting incident surface S5 of the splitting prism P. Define the gluing surface of the first splitting prism P01 and the second splitting prism P02 as the first splitting surface S61, the image side surface of the first splitting prism P01 as the first splitting exit surface S71, the gluing surface of the second splitting prism P02 and the third splitting prism P03 as the second splitting surface S81, the image side surface of the second splitting prism P02 as the second splitting exit surface S91, and the image side surface of the third splitting prism P03 as the third splitting exit surface S101.

[0044] It can be seen from Figure 5 that the included angle between the splitting incident surface S5 of the splitting prism P and the first splitting surface S61 is θ61, and the included angle between the first splitting surface S61 and the second splitting surface S81 is θ71, which respectively satisfy: 25° < θ61 < 35°, 35° < θ71 < 45°. Controlling the angles of each splitting prism can control the light path. Combining with the field of view angle of the optical system, it can ensure that the light in each field of view and each wavelength band is not blocked by the prism surface. Define the first segment length of light in the first splitting prism P01 as d11, the first segment length of light in the second splitting prism P02 as d21, and the first segment length of light in the third splitting prism P03 as d31, which respectively satisfy: 0.7mm < d11 < 0.9mm, 0.9mm < d21 < 1.1mm, 3.7mm < d11 + d21 + d31 < 3.9mm. By controlling the sizes of each splitting prism, the optical path of light in each wavelength band can be made the same, without generating additional aberrations, meeting the requirements of the imaging focal lengths of different lights; at the same time, the volume and mass of the lens can be controlled. Meeting the above formulas, the direction of light can be controlled by controlling the shapes of each splitting prism, making the light exit heights of each splitting prism close, so that the imaging pictures of each splitting prism match the detector, ensuring the imaging quality of each field of view.

[0045] After the light enters the beam splitter prism P, it is reflected and refracted to produce light beams of different properties. The white light beam is emitted from the first beam splitter prism P01 and imaged on the first image plane IMA1, the fluorescent light beam is emitted from the second beam splitter prism P02 and imaged on the second image plane IMA2, and the polarized light beam is emitted from the third beam splitter prism P03 and imaged on the third image plane IMA3. Different detectors are used to receive these three signals, and high-quality color images can be obtained through subsequent fusion processing. When the imaging focal planes of the three light beams overlap in the same endoscopic optical system, the optical paths of the three light beams in the respective prisms from which they emerge are the same. When the imaging focal planes of the three light beams do not overlap in the same endoscopic optical system, the positions of the three beam splitter exit surfaces can be slightly moved so that the optical paths of the three light beams in the respective prisms from which they emerge are different, to compensate for the uneven imaging focal planes.

[0046] Figure 6 The beam splitter prism P shown is formed by gluing a first beam splitter prism P01 and a second beam splitter prism P02 together. The two beam splitters are made of the same material, so when the beam splitting function is not used, they can be regarded as one prism, reducing the pressure on the design of the endoscope optical system.

[0047] The object side surface of the first splitter prism P01 is the splitter incident surface S5 of the splitter prism P, the bonding surface of the first splitter prism P01 and the second splitter prism P02 is defined as the first splitter surface S62, the image side surface of the first splitter prism P01 is the first splitter exit surface S72, and the image side surface of the second splitter prism P02 is the second splitter exit surface S92.

[0048] from Figure 6 It can be seen that the angle between the beam splitting incident surface S5 of the beam splitting prism P and the first beam splitting surface S62 is θ62=45°, and the length of the first section of the light in the first prism P01 is defined as d12, the length of the second section is d22, and the length in the second prism P02 is d32, which respectively satisfy: 2.1mm<d12<2.3mm, 1.5mm<d22<1.7mm, 1.5mm<d32<1.7mm, so that the imaging focal length requirements of different light rays can be met, and the field of view angle of the optical system and the volume and quality of the lens can be controlled by controlling the size of each prism.

[0049] After entering the beam splitter prism P, the light is reflected and refracted, and two types of light beams appear, which can be a combination of white light and fluorescent light, a combination of white light and polarized light, or a combination of fluorescent light and polarized light. The first type of light beam in the above beam combination is emitted from the first beam splitter prism P01 and imaged on the first image plane IMA1, and the second type of light beam is emitted from the second beam splitter prism P02 and imaged on the second image plane IMA2. They are received by different detectors and finally fused in the later stage to obtain a high-quality color image.

[0050] When the imaging focal planes of two light beams overlap under the same endoscope optical system, their optical paths in the respective beam splitting prisms where they emerge are the same. When the imaging focal planes of the two light beams do not overlap under the same endoscope optical system, the positions of the two beam splitting exit surfaces can be slightly moved so that their optical paths in the respective beam splitting prisms where they emerge are different, to compensate for the misalignment of the imaging focal planes.

[0051] After the light enters the beam splitting prism P, reflection and refraction occur, and only the reflected light can be used to achieve the basic imaging function.

[0052] By combining two sets of endoscope optical systems, a four-eye or binocular endoscope optical system can be formed to obtain a stereoscopic image to match the visual habit of the human eye. The four-eye endoscope optical system is as Figure 14 shown. By placing the receiving detectors for the two sets of reflected light in the middle or on both sides of the endoscope optical system, clearer images can be obtained while controlling the volume. The binocular endoscope optical system is as Figure 15 shown. By placing the receiving detectors for the two sets of reflected light in the middle or on both sides of the endoscope optical system, the situation where the volume of the binocular endoscope optical system is too large due to the too large volume of the detector can be avoided.

[0053] The following makes a specific description of two examples in conjunction with the accompanying drawings.

[0054] Example 1: As Figure 1 shown, the endoscope optical system sequentially consists of a first lens L1, a turning prism G, a stop STO, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, a seventh lens L7, and a beam splitting prism P from the object plane to the image plane IMA. First protective glass GS1 and second protective glass GS2 are respectively arranged at both ends of the endoscope optical system. In this Example 1, the optical power of the third lens L3 is negative, the object side is convex, and the image side is concave. The optical power of the fourth lens L4 is positive, the object side is convex, and the image side is convex. The optical power of the fifth lens L5 is positive, the object side is flat, and the image side is convex.

[0055] The main optical structure parameters of the endoscope optical system in Example 1 are shown in Table 1: Table 1

[0056] The aspheric parameters of the endoscope optical system in Example 1 are shown in Table 2: Table 2

[0057] Figure 7 、 Figure 8 、 Figure 9 And Table 3 shows the imaging performance of the endoscope optical system in Example 1. In the figure, the meridian and sagittal lines of 0° coincide.

[0058] As Figure 7 shown, for the endoscopic optical system of Example 1, when the medium object distance is 50 mm, the MTF value of the 0° central field of view is greater than 0.4, and the MTF value of the 42.8° peripheral field of view is greater than 0.3; As Figure 8 shown, for the endoscopic optical system of Example 1, when the near object distance is 35 mm, the MTF value of the 0° central field of view is greater than 0.3, and the MTF value of the 42.8° peripheral field of view is greater than 0.25; As Figure 9 shown, for the endoscopic optical system of Example 1, when the far object distance is 125 mm, the MTF value of the 0° central field of view is greater than 0.2, and the MTF value of the 42.8° peripheral field of view is greater than 0.2; The performance parameters of the endoscopic optical system of Example 1 are shown in Table 3: Table 3

[0059] As shown in Table 3, for the endoscopic optical system of Example 1, the field curvature is small at three object distances, the radius RMS of the imaging blur spot is small, and the relative illumination within the entire field of view is greater than 84%. The endoscopic optical system of Example 1 has a good imaging effect within a relatively large object distance range, and has a large depth of field and axial resolution ability.

[0060] Example 2: As Figure 10 shown, the endoscopic optical system is successively composed of a first lens L1, a turning prism G, a stop STO, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, a seventh lens L7, and a beam splitting prism P from the object plane to the image plane IMA. At both ends of the endoscopic optical system, a first protective glass GS1 and a second protective glass GS2 are respectively provided. In this Example 2, the optical power of the third lens L3 is positive, the object side is convex, and the image side is convex; the optical power of the fourth lens L4 is negative, the object side is concave, and the image side is convex; the optical power of the fifth lens L5 is positive, the object side is concave, and the image side is convex.

[0061] The main optical structure parameters of the endoscopic optical system of Example 2 are shown in Table 4: Table 4

[0062] The aspheric parameters of the endoscopic optical system of Example 2 are shown in Table 5: Table 5

[0063] Figure 11 , Figure 12 , Figure 13Table 6 shows the imaging performance of the endoscope optical system of Example 2. In the figure, the meridian line and the sagittal line of 0° coincide.

[0064] As Figure 11 shown, for the endoscope optical system of Example 2 at a medium object distance of 50 mm, the MTF value of the 0° central field of view is greater than 0.4, and the MTF value of the 42.8° peripheral field of view is greater than 0.3; As Figure 12 shown, for the endoscope optical system of Example 2 at a near object distance of 35 mm, the MTF value of the 0° central field of view is greater than 0.3, and the MTF value of the 42.8° peripheral field of view is greater than 0.29; As Figure 13 shown, for the endoscope optical system of Example 2 at a far object distance of 125 mm, the MTF value of the 0° central field of view is greater than 0.2, and the MTF value of the 42.8° peripheral field of view is greater than 0.25; compared with Example 1, the imaging resolution is slightly improved; The main performance parameters of the endoscope optical system of Example 2 are shown in Table 6: Table 6

[0065] As shown in Table 6, the endoscope optical system of Example 2 has a smaller field curvature, a smaller radius RMS of the imaging blur spot, and a relative illuminance greater than 91% within the entire field of view, showing an improvement compared with the endoscope optical system of Example 1.

[0066] The endoscope optical system of Example 2 has a better imaging effect within a relatively large object distance range, with a larger depth of field and axial resolution ability.

[0067] The individual examples shown above are only for the present invention and cannot limit the scope of the patent protection of the present invention. Equivalent changes made according to the scope of the patent application of the present invention still fall within the scope covered by the present invention.

Claims

1. An endoscope optical system, characterized in that From the object plane to the image plane, it consists of a first lens, a turning prism, a diaphragm, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, and a beam splitter prism. The optical power of the first lens is negative, the object side is convex, and the image side is concave; the optical power of the second lens is positive, the object side is flat, and the image side is convex; the object side of the third lens is convex, the optical power of the fourth lens is opposite to that of the third lens, and the image side is convex; the optical power of the fifth lens is positive, and the image side is convex; the optical power of the sixth lens is negative, the object side is concave, and the image side is concave; the optical power of the seventh lens is positive, the object side is convex, and the image side is convex; the object space numerical aperture NA of the endoscope optical system satisfies: 0.001 < NA < 0.

006.

2. The endoscope optical system according to claim 1, characterized in that Both surfaces of the first lens are aspherical surfaces.

3. The endoscope optical system according to claim 1, characterized in that The third lens and the fourth lens form a doublet lens, and the fifth lens, the sixth lens, and the seventh lens form a triplet lens.

4. An endoscopic optical system according to claim 3, wherein The focal length f of the endoscopic optical system described above, the focal length f L1 of the first lens described above, the focal length f L2 of the second lens described above, the focal length f 34 of the doublet lens described above, the focal length f 567 of the triplet lens described above respectively satisfy: -0.8 < f L1 / f < -0.7, 1.5 < f L2 / f < 1.7, 3.2 < f 34 / f < 3.5, -900000 < f 567 / f < -9000.

5. An endoscopic optical system according to claim 1, characterized in that Define the refractive index of the material of the first lens as Nd L1 and the refractive index of the material of the second lens as Nd L2 and the refractive index of the material of the third lens as Nd L3 and the refractive index of the material of the fourth lens as Nd L4 and the refractive index of the material of the fifth lens as Nd L5 and the refractive index of the material of the sixth lens as Nd L6 and the refractive index of the material of the seventh lens as Nd L7 , which respectively satisfy: 1.9 < Nd L1 < 2.1, 1.6 < Nd L2 < 1.8, 0.15 < |Nd L3 - Nd L4 | < 0.25, 0.15 < |Nd L5 - Nd L6 | < 0.25, 0.15 < |Nd L6 - Nd L7 | < 0.

25.

6. An endoscopic optical system according to claim 1, characterized in that The turning prism is provided with a turning incident surface, a first reflecting surface, a second reflecting surface, and a turning exit surface. The turning exit surface is located between the first reflecting surface and the second reflecting surface and is perpendicular to the optical axis of the endoscope optical system. The light ray is perpendicularly incident on the turning incident surface and is incident on the first reflecting surface at a first incident angle, reflected by the first reflecting surface and incident on the second reflecting surface at a second incident angle, and then reflected by the second reflecting surface to the turning exit surface and then perpendicularly exits. Define the turning angle of the turning prism as θ, the included angle between the turning incident surface and the second reflecting surface as θ1, the included angle between the second reflecting surface and the first reflecting surface as θ2, and the included angle between the first reflecting surface and the optical axis of the endoscope optical system as θ3, which respectively satisfy the following relationships: θ = 30°, θ2 = θ / 2, θ1 + θ2 + θ3 + θ = 90°, 6° < θ3 < 16°.

7. An endoscopic optical system according to claim 6, characterized in that The turning prism is a single prism, and the included angle θ3 between the first reflecting surface and the optical axis of the endoscope optical system is 15°.

8. The endoscope optical system according to claim 6, characterized in that The turning prism is composed of a first sub - prism and a second sub - prism glued together. The turning incident surface is the object side surface of the first sub - prism, the first reflecting surface is in contact with air, the second reflecting surface is the glued surface between the first sub - prism and the second sub - prism, the turning exit surface is the image side surface of the second sub - prism, and the included angle θ3 between the first reflecting surface and the optical axis of the endoscope optical system is 7° or θ3 = 10°.

9. The endoscopic optical system according to claim 8, characterized in that The first reflecting surface is coated with a reflective film, and the refractive index of the first sub-prism is defined as Nd G01 , and the refractive index of the second sub-prism is Nd G02 , and the second incident angle is θ5, satisfying: Nd G01 ≤Nd G02 ×sinθ5.

10. An endoscope optical system according to claim 8, characterized in that Define the refractive index of the first sub - prism as Nd G01 , and the refractive index of the second sub - prism as Nd G02 , and the second incident angle is θ5, satisfying: Nd G01 ≤Nd G02 ×sin(θ5 - 8°).

11. An endoscopic optical system according to claim 1, wherein The beam splitter prism is composed of multiple prisms of the same material glued together. The glued surface of each prism is a beam splitting surface. The light ray emerging from the seventh lens is incident on the beam splitting incident surface of the beam splitter prism and is split into light rays of different properties on different beam splitting surfaces and then exits from the beam splitting exit surfaces of different prisms in the beam splitter prism.

12. An endoscopic optical system according to claim 11, wherein The described beam splitting prism is glued together by three first prisms, second prisms, and third prisms made of the same material. The object side of the first prism is the beam splitting incident surface of the beam splitting prism. Define the gluing surface between the first prism and the second prism as the first beam splitting surface, the image side of the first prism as the first beam splitting exit surface, the gluing surface between the second prism and the third prism as the second beam splitting surface, the image side of the second prism as the second beam splitting exit surface, and the image side of the third prism as the third beam splitting exit surface. Define the angle between the beam splitting incident surface of the beam splitting prism and the first beam splitting surface as θ61, and the angle between the first beam splitting surface and the second beam splitting surface as θ71, which respectively satisfy: 25° < θ61 < 35°, 35° < θ71 < 45°; Define the first segment length of the light in the first prism as d11, the first segment length in the second prism as d21, and the first segment length in the third prism as d31, which respectively satisfy: 0.7mm < d11 < 0.9mm, 0.9mm < d21 < 1.1mm, 3.7mm < d11 + d21 + d31 < 3.9mm.

13. An endoscopic optical system according to claim 11, wherein The described beam splitting prism is glued together by a first prism and a second prism made of the same material. The object side of the first prism is the beam splitting incident surface of the beam splitting prism. Define the gluing surface between the first prism and the second prism as the first beam splitting surface, the image side of the first prism as the first beam splitting exit surface, the image side of the second prism as the second beam splitting exit surface, and the angle between the beam splitting incident surface of the beam splitting prism and the first beam splitting surface as θ62 = 45°. Define the first segment length of the light in the first prism as d12, the second segment length as d22, and the length of the light in the second prism as d32, which respectively satisfy: 2.1mm < d12 < 2.3mm, 1.5mm < d22 < 1.7mm, 1.5mm < d32 < 1.7mm.

Images