Multi-view medical endoscope optical system and design method

Abstract

The application discloses a multi-view medical endoscope optical system and a design method, and aims to solve the problem of visual blind area of a single view of a traditional endoscope; the system first applies panoramic ring lens technology to a medical endoscope, realizes synchronous observation of front (0°-55°) and side (55°-85°) views through a folding light path design combining refraction and reflection, and the total view angle reaches 170°. The system is only coated with a reflective film on a reflecting surface, and a transmission surface is not coated with a film, so that light energy attenuation caused by half-transmission and half-reflection is avoided, and a weak light environment in a cavity is effectively adapted; the optical system is compact in structure, the total length is only 24.288 mm, the maximum aperture is 10 mm, a CMOS sensor with an image element size of 3 microns is matched, the front and side view MTF values are greater than 0.4 and 0.5 respectively, the spot diagram RMS radius is less than the Airy disk radius, and the imaging quality is excellent; in addition, the application also provides a three-stage design method including side channel design, front channel design and double-channel fusion optimization, multiple structure optimization is carried out by using ZEMAX software, and engineering feasibility and high-precision imaging are ensured, so that the risk of lesion omission is significantly reduced.

Description

Technical Field

[0001] This invention belongs to the field of optical lens design, specifically relating to a multi-field medical endoscope optical system and its design method. Background Technology

[0002] Endoscopes are widely used in small and medium-sized minimally invasive surgical procedures. However, the core field of view of mainstream medical endoscopes is concentrated on the axial front, with extremely limited lateral and circumferential fields of view. The only way to supplement the field of view is to rotate the endoscope and adjust the angle. It is impossible to simultaneously observe the front and the side walls of the cavity, resulting in a large number of blind spots and easy to miss lesions. This is the core pain point in the development of new endoscopes with large field of view and lateral imaging.

[0003] A similar domestic technology is a published patent entitled "A Blind Spot-Free Panoramic Ring-Swept Stereo Lens" (application number: CN202310674908.X). The patent's optical system includes a lens L1, a panoramic ring-swept lens L2, and a rear lens group G3 arranged sequentially along the optical path direction and coaxially. The object-side surface of L2 includes a front transmission surface R3 and a front reflection surface R4; the image-side surface includes a central transmission surface R5 and a polarizing, semi-reflective, semi-transparent surface R6 surrounding R5. L1, L2, and G3 constitute three channels. The field of view of the front channel is 0~a, with light rays passing sequentially through L1, R3, R5, and G3 to reach the image plane. The field of view of the panoramic channel is a~β, with light rays passing sequentially through R3 (transmission), R6 (reflection), R4 (reflection), R5 (transmission), and G3 to reach the image plane. The patent system is as follows: Figure 1 As shown.

[0004] Traditional medical endoscopes can only observe a single field of view in front and cannot observe the lateral field of view of the cavity. Moreover, the field of view is limited, with a maximum half field of view around the optical axis of about ±60°, resulting in a large blind spot.

[0005] While the aforementioned patented panoramic ring lens can observe the side field of view, its large lens diameter results in a large overall system size. Secondly, some surfaces require simultaneous reflection and transmission of light. This lens uses a polarization-filtering film coated on the lens to achieve transmission or reflection depending on the angle of light incidence. However, this polarization filtering method involves a semi-reflective, semi-transparent lens, leading to significant light energy loss and insufficient image brightness. Since medical endoscopes operate inside the body with limited ambient light, this system is only suitable for machine recognition, intelligent recognition, and autonomous driving scenarios, and cannot be applied to medical endoscopic examinations. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a multi-field medical endoscope optical system and design method, which can simultaneously observe lesions in the front and side fields of view within the cavity. With the folded optical path design that combines refraction and reflection, the axial dimension can be greatly shortened, the number of lenses is small, and the overall volume is small, so that a large field of view imaging can be achieved in the narrow installation space at the front end of the endoscope.

[0007] A multi-field medical endoscope optical system includes a front lens group (M1), a panoramic ring lens, and a rear lens group (M2) arranged sequentially along the optical path.

[0008] The central area of ​​the front surface of the panoramic ring lens is a second transmission surface (t4), and the outer area of ​​the front surface is provided with a second reflection surface (r3); the side of the panoramic ring lens is a first transmission surface (t1); the central area of ​​the rear surface is a third transmission surface (t5), and the outer area of ​​the rear surface is provided with a first reflection surface (r2).

[0009] The light rays from the side field of view enter sequentially through the transmission surface (t1), are reflected by the first reflection surface (r2), are reflected by the second reflection surface (r3), and exit through the third transmission surface (t5) to the subsequent lens group (M2).

[0010] The light rays in the forward field of view pass sequentially through the front lens group (M1), through the second transmission surface (t4) into the panoramic ring lens, and through the third transmission surface (t5) to the subsequent lens group (M2).

[0011] Preferably, the first reflective surface (r2) and the second reflective surface (r3) are coated with reflective films, while the second transmissive surface (t4) and the third transmissive surface (t5) are not coated with reflective films.

[0012] Preferably, the radius of curvature of the transmission surface (t4) is greater than 0, and the radius of curvature of the transmission surface (t5) is less than 0.

[0013] Preferably, at least one surface of the panoramic ring lens is an aspherical surface, the aspherical surface is an even-order aspherical surface, and the transmission surface (t1) and the transmission surface (t5) are even-order aspherical surfaces.

[0014] Preferably, the field of view of the front view is 0°-55°, the field of view of the side view is 55°-85°, and the total field of view of the system is 0°-±85°.

[0015] Preferably, the system operates in the visible light band, has an operating F-number of 3.8, the maximum aperture of the panoramic ring lens does not exceed 10mm, and the total length of the system does not exceed 24.288mm.

[0016] Preferably, the system focal length of the front field of view is 0.78 mm, and the system focal length of the side field of view is 0.95 mm.

[0017] Preferably, the front lens group includes six lenses, and the subsequent lens group includes fourteen lenses.

[0018] A design method for a multi-field medical endoscope optical system includes the following steps:

[0019] Step 1: Design the side field of view channel. The side field of view channel includes a panoramic ring lens and a subsequent lens group. The aperture stop is set between the panoramic ring lens and the subsequent lens group, and the image height of the inner ring of the image plane of the side field of view channel is greater than the maximum image height of the front field of view channel, and the focal length of the side field of view is greater than the focal length of the front field of view.

[0020] Step 2: Design the front field of view channel. Add a front lens group in front of the panoramic ring lens, fix the parameter values ​​of each lens in the side field of view channel, optimize only the front lens group, and control the front field of view aperture.

[0021] Step 3: Combine the front field of view channel and the side field of view channel into a dual-channel system. Use multiple structural optimization functions to optimize the front optical path and the side optical path simultaneously, and constrain the image planes of the two channels to not overlap.

[0022] Furthermore, the design method for the panoramic ring lens includes:

[0023] To be compatible with subsequent lens groups, the field curvature of the panoramic ring lens must be negative, meaning its Pittsvar sum must be constrained to negative values; let the curvature of the front surface containing the incident surface t4 and the second reflecting surface r3 be... The curvature of the rear surface where the exit surface t5 and the first reflecting surface r2 are located is The piezoresistive sum produced by the panoramic ring lens is:

[0024]

[0025] In the above formula, n represents the refractive index of the lens material, and J is the Lagrange constant;

[0026] As can be seen from the formula, it is necessary to ensure that ( The value is greater than zero; further considering that the front surface of the panoramic ring lens must have the function of compressing the ring-shaped ultra-large field of view beam, therefore, the following was chosen. and The range of values ​​for .

[0027] The present invention has the following beneficial effects:

[0028] This technology, which was first introduced into medical endoscopes from fields such as machine vision, intelligent recognition, and autonomous driving, solves the inherent defect of traditional endoscopes that can only observe a single field of view in front. It enables simultaneous observation of the front and side fields of view inside the cavity, effectively eliminating blind spots and reducing the risk of missing lesions.

[0029] The system's total field of view reaches 0°-±85° (170° in total), far exceeding the ±60° of traditional endoscopes, achieving ultra-wide field of view imaging. The anterior field of view covers 0°-55°, and the lateral field of view covers 55°-85°. The images from the two channels do not overlap on the image plane and are clearly divided, making it easy for doctors to obtain complete information from both the anterior and lateral walls simultaneously.

[0030] Unlike existing technologies that use a semi-transparent, semi-reflective film across the entire panoramic lens, resulting in light energy attenuation (the sum of transmission and reflection is less than 100%, with the remaining energy being absorbed and scattered), this invention only coats the reflective surface (r2, r3), leaving the transmission surface uncoated. The reflected and transmitted light paths are completely separated, with side rays undergoing total reflection through the total reflection film. Without the semi-transparent, semi-reflective beam-splitting structure, energy loss is extremely low, making it perfectly suited for the low-light working environment of human cavities where tissues absorb light strongly and natural illumination is low.

[0031] Balancing miniaturization with high image quality, the system employs a folded optical path design that combines refraction and reflection, significantly reducing axial dimensions. The total system length is only 24.288mm, and the maximum aperture is only 10mm, allowing for installation within the confined space at the front of the endoscope. It also features a small number of lenses: the panoramic ring lens has only 2-3 elements, the rear group has 14 elements, and the front group has 6 elements, resulting in a simple overall structure.

[0032] The panoramic ring lens uses even-order aspherical surfaces (t1, t5 surfaces), which, compared with traditional spherical systems, effectively correct aberrations such as spherical aberration and coma while compressing the size, ensuring that the center and edges of the image are clear in a large field of view.

[0033] By setting the radius of curvature of the transmission surface t4 to be greater than 0 and the radius of curvature of t5 to be less than 0, the field curvature of the panoramic ring lens is ensured to be negative, which is matched and compensated with the positive field curvature of the subsequent lens group, and the overall field curvature is reduced to zero, thus ensuring image quality.

[0034] Employing a CMOS sensor with a pixel size of 3μm (such as the OV9281), corresponding to a Nyquist frequency of 167 lp / mm: the forward field of view MTF > 0.4; the lateral field of view MTF > 0.5, both far exceeding the minimum requirements for human eye observation (MTF > 0.22). The RMS radius of the dot plot is smaller than the Airy disk radius (2.73μm), the imaging quality of the forward and lateral fields of view is balanced, and the overall imaging performance is good, meeting the high-precision diagnostic requirements of medical endoscopes.

[0035] A complete three-stage design methodology (side channel design → front channel design → dual-channel fusion optimization) is provided. In ZEMAX software, the two channels are simultaneously optimized through multiple structural optimizations, and the image plane images are precisely controlled to prevent overlap. It has good engineering feasibility and reproducibility. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the optical system of the patent "A panoramic ring-shaped stereo lens without blind spots";

[0037] Figure 2 This is a schematic diagram of a multi-field medical endoscope optical system according to the present invention;

[0038] Figure 3 The image distribution on the image plane of the optical system;

[0039] Figure 4 The structure of the side field-of-view optical system;

[0040] Figure 5 This is the structure of the forward field-of-view optical system;

[0041] Figure 6 This is the overall system architecture diagram;

[0042] Figure 7 The MTF plot for the front field of view channel;

[0043] Figure 8 MTF plot for the side field of view channel;

[0044] Figure 9 A diagram showing the points of view in front;

[0045] Figure 10 A diagram showing the points of view from the side. Detailed Implementation

[0046] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0047] The medical endoscope of the present invention comprises three parts: a front lens group, a panoramic ring lens, and a rear lens group.

[0048] The front lens group is used to receive light from the front field of view, which has a field of view range of 0°-55°.

[0049] The panoramic ring lens is positioned behind the front lens group to receive light from the side field of view and transmit light from the front field of view emitted by the front lens group. The field of view of the side field of view is 55°-85°.

[0050] The follow-up lens group is placed behind the panoramic ring lens to transmit the front field of view and side field of view rays emitted from the panoramic ring lens.

[0051] The medical endoscope of this invention operates in the visible light band and has an F-number of 3.8.

[0052] The working principle of this invention is as follows: Figure 2 As shown.

[0053] The front surface of the panoramic ring lens of the present invention has a central region of a transmission surface t4 and a reflective surface r3 on its outer region; the side surface of the panoramic ring lens has a transmission surface t1; the rear surface of the panoramic ring lens has a central region of a transmission surface t5 and a reflective surface r2 on its outer region.

[0054] For the side field of view, the light beam does not pass through the front lens group M1 and enters the optical system directly from the transmission surface t1 of the panoramic ring lens. Inside the panoramic ring lens, the light beam is reflected on the reflecting surface r2, then reflected again by the reflecting surface r3, and finally passes through the transmission surface t5 to leave the panoramic ring lens. It is then imaged onto the image plane by the subsequent lens group M2.

[0055] Reflective films are coated on the reflective surfaces r2 and r3.

[0056] For the forward field of view, the beam first passes through the front lens group M1 to compress the beam's aperture and angle of incidence, resulting in a smaller cross-sectional area for the forward beam reaching the panoramic ring lens. This allows it to enter the panoramic ring lens through the central region of the transmission surface t4. It then exits the panoramic ring lens through the transmission surface t5 and is imaged onto the image plane by the subsequent lens group M2.

[0057] The central area of ​​the last surface t5 of the panoramic ring lens transmits light, while the outer area reflects it. To achieve these two different functions on the same optical surface, a semi-transparent, semi-reflective coating can be applied to the entire area, or a reflective coating can be applied only to the outer area. Considering that a semi-transparent, semi-reflective coating would cause light loss and introduce stray light, the option of applying a reflective coating only to the outer area was chosen.

[0058] The semi-transparent, semi-reflective film applied across the entire surface of the panoramic ring lens in the aforementioned patent inevitably leads to light energy attenuation and loss. Light rays passing through the panoramic ring lens must pass through this semi-transparent, semi-reflective film, which must simultaneously perform reflection and transmission functions. Since the sum of transmission and reflection is less than 100%, the remaining energy is absorbed and scattered, resulting in reduced illumination at both ends of the light path. This leads to low image brightness. Medical endoscopes need to operate within human cavities, where the working environment is inherently confined, tissues absorb light strongly, and natural illumination is low. Therefore, the semi-transparent, semi-reflective film structure is unsuitable.

[0059] This invention coats a reflective film only on both sides of the end face of the panoramic ring lens, avoiding the semi-transparent and semi-reflective structure, adapting to the low-light environment of the endoscope, separating the reflected light from the transmitted light path, and the incident light from the side is totally reflected by the total reflection film, separating the reflection and transmission areas, eliminating the semi-transparent and semi-reflective beam splitting structure, and resulting in extremely low energy loss.

[0060] The panoramic ring lens of this invention uses an aspherical surface, which makes the panoramic ring lens lighter and thinner, reducing the overall weight of the panoramic ring lens and shortening the system size.

[0061] Traditional spherical lenses are prone to spherical aberrations (such as edge blurring and chromatic aberration) at the edges when light passes through them, leading to image distortion or loss of quality. Compressing the overall length of a full-size spherical lens inevitably sacrifices the aperture or imaging quality, resulting in a significant decrease in image quality. Furthermore, it is difficult to compress system size using a full-size spherical structure, making it impractical for medical endoscopes.

[0062] This invention employs an asymmetrical curvature design of aspherical lenses, allowing light from different positions to be focused more precisely onto the same plane. This effectively corrects aberrations such as spherical aberration and coma while compressing lens size. In particular, this large field-of-view system can significantly improve the sharpness of the center and edges of the image.

[0063] This invention provides a design method for the above system, and the overall optical design process is divided into three stages:

[0064] 1. Design the side field of view channel, including a panoramic ring lens and a subsequent lens group;

[0065] II. Design and integration of the forward field of view channel;

[0066] Third, the final joint optimization of the dual-channel panoramic ring lens system. This invention was designed using ZEMAX software.

[0067] Phase 1:

[0068] (1) Before designing the optical system, the position of the aperture stop and the focal length of the system should be considered first.

[0069] 1) Aperture position:

[0070] The aperture stop plays a crucial role in an optical system, directly impacting its image quality, overall size, and stray light suppression. This is especially true for complex optical systems like panoramic annular lenses, where light transmission is intricate. Therefore, the aperture stop's position must be determined before designing the panoramic annular optical system. The primary magnification chromatic aberration expression for a single refracting spherical surface is:

[0071]

[0072] The aperture angle of the object. For the image aperture angle, and and are the refractive indices of the two media, respectively. In the formula... and These are the dispersions of the image-side and object-side media, respectively. The angle of incidence of the principal ray. and These represent the chromatic aberrations on the image and object sides, respectively. The total chromatic aberration of the system is expressed as the sum of the chromatic aberrations of all individual spherical surfaces. To more easily suppress aberrations caused by the panoramic ring lens when optimizing the subsequent lens system, the design requires a smaller field of view of the subsequent lens system (i.e., the exit angle range of the panoramic ring lens). Therefore, it is more reasonable to place the aperture stop of the system between the panoramic ring lens and the rear lens group in the endoscope system of this invention.

[0073] 2) Focal length setting:

[0074] like Figure 3 For the image distribution on the image plane of the optical system, in order to distinguish the images of the front field of view and the side field of view on the image plane, the dark and light circular regions are the images of the front field of view and the side field of view, respectively. The radii of the two image regions are determined by the focal length and the field of view angle of the two fields of view. The image height and focal length between the two channels should satisfy the following formula:

[0075]

[0076] In the formula, , These are the system focal length values ​​for the panoramic imaging channel and the front field of view channel, respectively. , These are the maximum and minimum field of view for the panoramic imaging channel, respectively. This represents the maximum field of view of the forward field of view channel. This represents the maximum image height value of the forward field of view channel. , These represent the inner and outer ring image height values ​​on the image plane of the side field of view channel, respectively. Where, This indicates that the image height of the inner ring of the image plane of the lateral field of view channel of the endoscope must be greater than the maximum image height of the front field of view channel, so as to avoid the situation where the images of the two channels overlap on the image plane.

[0077]

[0078] This is caused by the difference between the two focal points. In this design, the minimum field of view in the side field of view and the maximum field of view in the front field of view are equal, i.e. and They are equal, both at 55°. Therefore, the following condition must be met: Greater than 0, requires > This means that the focal length of the side field of view is greater than the focal length of the front field of view. By selecting a focal length of 0.78mm for the front field of view and 0.95mm for the side field of view, the light rays from the two fields of view will not overlap on the image plane.

[0079] (2) Side field of view channel design

[0080] Since this optical system is designed for medical endoscopic imaging, the requirement is to minimize the number of lenses in subsequent lens groups while achieving image quality. Traditional spherical lenses are simple to manufacture and assemble. However, due to the limited parameters of spherical lenses and the constraints on the number of lenses in this design, the degrees of freedom for optimization are insufficient. Therefore, this design considers incorporating some aspherical structures to provide more optimization variables to correct aberrations and simplify the overall system structure. We set the t1 and t5 surfaces of the panoramic lens as even-order aspherical surfaces.

[0081] Aspherical surfaces satisfy the following equations:

[0082] The relationship between the even-order aspherical conic coefficients and their various orders for a side-view panoramic ring lens is as follows:

[0083]

[0084] In the formula: z is the distance vector from the vertex of the aspherical surface along the optical axis at a height of h. C = 1 / r; r represents the radius of curvature of the vertex of the aspherical surface, k is the conic coefficient, and A, B, C, and D are higher-order aspherical coefficients.

[0085] Table 1. Conic coefficients and parameters of even-order aspherical surfaces used.

[0086] surface Conic coefficient A B C D t1 0 0.021 5.17E-03 5.584E-04 5.466E-05 t5 0 0.011 2.508E-03 5.670E-05 2.208E-04

[0087] Furthermore, the manufacturing of subsequent lens groups requires precise control of glass and air thickness. Operands such as CTGT and ETGT are used in the optimization function to constrain the center and edge thicknesses, ensuring proper light propagation within acceptable transmission and reflection areas. Simultaneously, considering the special working environment of medical endoscopes, the maximum aperture of the panoramic ring lens is controlled to not exceed 10mm using MXSD operands.

[0088] like Figure 4 Table 2 shows the structural diagram of the side field-of-view optical system. The specific structural parameters of the panoramic ring lens group and the rear lens group M2 are shown in Table 2. The surface numbers and optical element characteristics in Table 2 are arranged from top to bottom according to the transmission order of the side field-of-view light.

[0089] Table 2. Specific structural parameters of the panoramic ring lens and rear lens group M2

[0090] Surface serial number Surface type radius of curvature thickness Material Effective half-caliber 1 Standard sphere 14.360 7.628 K8 7.364 2 even aspherical surface 6.404 6.690 MIRROR 2.458 3 Standard sphere 6802.590 6.690 MIRROR 1.631 4 even aspherical surface 6.404 1.134 0.812 5. Aperture Standard sphere unlimited 0.097 0.518 6 Standard sphere 2.462 0.396 QF50GTI 0.531 7 Standard sphere 2.950 0.038 0.637 8 Standard sphere 7.562 2.758 HTK9 0.680 9 Standard sphere 3.140 0.191 SF5 1.058 10 Standard sphere 9.960 0.477 1.107 11 Standard sphere 177.948 0.311 BAK11 1.206 12 Standard sphere 7.143 0.573 1.229 13 Standard sphere 34.201 1.080 HZK3A 1.286 14 Standard sphere 4.000 0.191 ZF13 1.317 15 Standard sphere 11.983 0.038 1.341 16 Standard sphere 4.257 1.063 HZK21 1.353 17 Standard sphere 49.443 0.940 1.263 18 Standard sphere 4.222 2.007 HLAK52 1.145 19 Standard sphere 4.358 0.038 1.210 20 Standard sphere 4.424 0.265 HZLAF73 1.152 21 Standard sphere 6.968 0.240 1.109

[0091] It should be noted that in the design of this invention, the radius of curvature of the transmission surface t4 (same as R4 in the aforementioned patent, with a radius of curvature greater than 0) is greater than 0, and the radius of curvature of the transmission surface t5 (same as R5 in the aforementioned patent, with a radius of curvature greater than 0) is less than 0. The specific design process is as follows:

[0092] Multi-field medical endoscopes have a field of view of 0° to ±85°. For such ultra-large field-of-view imaging optical systems, the Pittsvar field curvature P is an important parameter for measuring image quality. To obtain good image quality, the Pittsvar field curvature of the optical system must be zero, i.e.:

[0093]

[0094] Generally, if the Pittsvar field curvature of the rear lens group is greater than zero, then the Pittsvar sum of the panoramic ring lens must be less than zero. The Pittsvar sum of an optical system can be estimated by the following formula:

[0095]

[0096] Where: J is the Lagrange daily quantity. and These are the refractive indices before and after the i-th face, respectively. Let be the curvature of the i-th surface. For the reflecting surface, take . . This represents the arithmetic mean of the refractive indices of the media on both sides of the i-th refractive surface.

[0097] To ensure compatibility with subsequent lens groups, the field curvature of the panoramic ring lens must be negative, meaning its Pittsvar and constraint must be negative. This requires the system to pre-configure the panoramic ring lens as a two-sided structure. For the ring field of view, the curvature of the front surface containing the incident surface t4 and the second reflecting surface r3 is... The curvature of the rear surface where the exit surface t5 and the first reflecting surface r2 are located is Therefore, according to the formula, the Pittsvar sum produced by the panoramic loop lens is:

[0098]

[0099] In the above formula, n represents the refractive index of the lens material.

[0100] As can be seen from the formula, as long as ( If the value is greater than zero, then the conditions of Pittsvar and less than zero are met for a panoramic ring-shaped lens. Simultaneously, considering that the first surface of the panoramic ring-shaped lens must have the function of compressing the ring-shaped ultra-large field-of-view beam, the following is selected... >0, If <0, then the shape of the panoramic ring lens of the present invention is as follows: Figure 2As shown.

[0101] The lens structure in the aforementioned patented solution causes field curvature imbalance, a sharp increase in coma, severe image plane curvature, and poor image quality. The lens structure used in this invention, compared to the aforementioned patented lens structure, can ensure (…). The condition that the value is greater than zero is always true, thus providing the necessary field curvature correction for the entire imaging system. This is the premise that this structure can guarantee good imaging quality of the entire optics and is suitable for systems with high imaging quality requirements, such as medical endoscopes.

[0102] Phase Two: Design of the Forward Field of View Passage

[0103] Next, the parameter values ​​of each lens in the previously designed side field of view channel were fixed, and the field of view range of the incident light was set to 0-55°. A front correction lens group structure was added in front of the panoramic ring lens.

[0104] The beam in the forward field of view must be refracted through the central light-transmitting area of ​​the panoramic ring lens, but the forward half-field of view reaches 55°. Therefore, the incident aperture and incident angle of the beam in the forward field of view must be compressed. Simultaneously, the front lens group also undertakes the task of correcting optical system aberrations. A reverse telephoto optical structure is used and stitched together with the already designed ring observation structure. During the optimization of the forward observation structure, the panoramic ring lens and subsequent lens group must remain unchanged; only the front lens group is optimized. MXSD operands are used to control the forward field of view aperture. The forward field of view observation structure is as follows: Figure 5 As shown.

[0105] The specific structural parameters of the front lens group M1 in the final embodiment of the present invention are shown in Table 3. The surface numbers and optical element characteristics in Table 3 are arranged from top to bottom according to the transmission order of the light rays in the front field of view.

[0106] Table 3 Specific structural parameters of the front lens group M1

[0107] Surface serial number Surface type radius of curvature thickness Material Effective half-caliber 1 Standard sphere 12.139 1.713 F1 5.000 2 Standard sphere 23.125 0.918 4.085 3 Standard sphere 30.033 1.000 HLAK52 2.228 4 Standard sphere 1.861 0.846 1.219 5 Standard sphere 3.106 0.996 HLAK52 1.093 6 Standard sphere 4.415 0.284 0.929

[0108] Phase 3: Dual-channel fusion design

[0109] Finally, the optical designs of the two channels were combined into a single system, and the parameters of all optical components in the entire system were optimized to ensure that the overall structure of the optical system was reasonable and that it had imaging quality that met the usage requirements.

[0110] By combining the two observation structures described above, the multi-structure optimization function of ZEMAX software is used to simultaneously optimize the forward and side field-of-view optical paths, ensuring good imaging quality for both the side and forward fields of view. Additional constraints are applied to the image surface. The relative radial position of the two images is strictly controlled using operands such as REAY to ensure sufficient distance to prevent overlap.

[0111] The final system architecture diagram is shown below. Figure 6 This is a schematic diagram of the final overall system structure. The maximum aperture R of the system lens is 7.371 mm, and the total system length L is 24.288 mm.

[0112] Furthermore, the medical endoscope described in this invention can use a CMOS sensor of model OV9281 with a pixel size a of 3 micrometers as the detector.

[0113] The cutoff frequency N of the optical system is:

[0114]

[0115] MTF (Modulation Transfer Function) is an important indicator of lens performance. Generally, in lens design, an MTF > 0.22 is considered sufficient for human visual perception. Figure 7 This is the MTF plot for the front field of view channel. Figure 8 The MTF plots for the side fields of view show that the MTF for the front field of view at 167 lp / mm is greater than 0.4, and the MTF for the side fields of view at 167 lp / mm is greater than 0.5, indicating good imaging quality for both the front and side fields of view.

[0116] Dot plots evaluate the performance of an optical system by quantifying the spot size and energy concentration. Figure 9 , 10 The diagrams show the front and side fields of view, respectively. The Airy disk radius of the side-view structure is 2.73 μm, while that of the front-view structure is 2.727 μm. The RMS radius of both structures is smaller than the Airy disk radius, indicating balanced imaging quality across the side and front-view optical paths and good overall imaging performance.

[0117] In summary, the above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A multi-field medical endoscope optical system, characterized in that, It includes a front lens group (M1), a panoramic ring lens, and a rear lens group (M2) arranged sequentially along the optical path. The central area of ​​the front surface of the panoramic ring lens is a second transmission surface (t4), and the outer area of ​​the front surface is provided with a second reflection surface (r3); the side of the panoramic ring lens is a first transmission surface (t1); the central area of ​​the rear surface is a third transmission surface (t5), and the outer area of ​​the rear surface is provided with a first reflection surface (r2). The light rays from the side field of view enter sequentially through the transmission surface (t1), are reflected by the first reflection surface (r2), are reflected by the second reflection surface (r3), and exit through the third transmission surface (t5) to the subsequent lens group (M2). The light rays in the forward field of view pass sequentially through the front lens group (M1), through the second transmission surface (t4) into the panoramic ring lens, and through the third transmission surface (t5) to the subsequent lens group (M2).

2. The multi-field medical endoscope optical system according to claim 1, characterized in that, The first reflective surface (r2) and the second reflective surface (r3) are coated with reflective films, while the second transmissive surface (t4) and the third transmissive surface (t5) are not coated with reflective films.

3. The multi-field medical endoscope optical system according to claim 1, characterized in that, The radius of curvature of the transmission surface (t4) is greater than 0, and the radius of curvature of the transmission surface (t5) is less than 0.

4. The multi-field medical endoscope optical system according to claim 1, characterized in that, At least one surface of the panoramic ring lens is an aspherical surface, the aspherical surface is an even-order aspherical surface, and the transmission surface (t1) and the transmission surface (t5) are even-order aspherical surfaces.

5. The multi-field medical endoscope optical system according to claim 1, characterized in that, The field of view of the front view is 0°-55°, the field of view of the side view is 55°-85°, and the total field of view of the system is 0°-±85°.

6. The multi-field medical endoscope optical system according to claim 1, characterized in that, The system operates in the visible light band with an F-number of 3.

8. The maximum aperture of the panoramic ring lens does not exceed 10mm, and the total length of the system does not exceed 24.288mm.

7. The multi-field medical endoscope optical system according to claim 1, characterized in that, The system focal length of the front field of view is 0.78 mm, and the system focal length of the side field of view is 0.95 mm.

8. The multi-field medical endoscope optical system according to claim 1, characterized in that, The front lens group includes six lenses, and the rear lens group includes fourteen lenses.

9. A design method for a multi-field medical endoscope optical system, characterized in that, Includes the following steps: Step 1: Design the side field of view channel. The side field of view channel includes a panoramic ring lens and a subsequent lens group. The aperture stop is set between the panoramic ring lens and the subsequent lens group, and the image height of the inner ring of the image plane of the side field of view channel is greater than the maximum image height of the front field of view channel, and the focal length of the side field of view is greater than the focal length of the front field of view. Step 2: Design the front field of view channel. Add a front lens group in front of the panoramic ring lens, fix the parameter values ​​of each lens in the side field of view channel, optimize only the front lens group, and control the front field of view aperture. Step 3: Combine the front field of view channel and the side field of view channel into a dual-channel system. Use multiple structural optimization functions to optimize the front optical path and the side optical path simultaneously, and constrain the image planes of the two channels to not overlap.

10. The design method of the multi-field medical endoscope optical system according to claim 9, characterized in that, The design method for the panoramic ring lens includes: To be compatible with subsequent lens groups, the field curvature of the panoramic ring lens must be negative, meaning its Pittsvar sum must be constrained to negative values; let the curvature of the front surface containing the incident surface t4 and the second reflecting surface r3 be... The curvature of the rear surface where the exit surface t5 and the first reflecting surface r2 are located is The piezoresistive sum produced by the panoramic ring lens is: ； In the above formula, n represents the refractive index of the lens material, and J is the Lagrange constant; As can be seen from the formula, it is necessary to ensure that ( The value is greater than zero; further considering that the front surface of the panoramic ring lens must have the function of compressing the ring-shaped ultra-large field of view beam, therefore, the following was chosen. and The range of values ​​for .

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