Bifocal endoscope objective and endoscope

Abstract

A bifocal endoscope objective and endoscope, relating to the field of optical technology, includes a first lens with negative optical power, a second lens with positive optical power, a third lens with positive optical power and movable along the optical axis from the object side to the image side, a fourth lens with positive optical power, a fifth lens with negative optical power, and a sixth lens with negative optical power, arranged sequentially along the optical axis from the object side to the image side. The objective has a total optical length ≤ 6.8 mm and a full field of view ≥ 160°. The third lens is configured to change the air gap between the third lens and the second and fourth lenses by moving it along the optical axis to a first axial position or a second axial position, respectively corresponding to a long-distance observation mode and a short-distance observation mode, while maintaining a constant total optical length during the switching process. This objective achieves stable bifocal switching with a constant total optical length during the switching process in an extremely compact structure.

Description

Technical Field

[0001] This application relates to the field of optical technology, and more specifically, to a bifocal endoscope objective and an endoscope. Background Technology

[0002] Endoscopes are widely used in medical diagnosis and industrial inspection. As the core imaging component of an endoscope, the endoscope objective needs to achieve both a wide field of view and magnification of local details within a confined space. To balance long-distance searching and close-range fine examination, bifocal endoscope objectives have been developed.

[0003] Existing bifocal endoscope objectives typically employ multiple moving lens groups or complex structures such as aspherical / freeform surfaces to achieve bifocal switching, resulting in complex system structures, difficult assembly, and high costs. While some simplified solutions attempt to achieve bifocality by moving a single lens, they are often constrained by the conflicting limitations of total optical length and field of view. This makes it difficult to simultaneously guarantee imaging quality in bifocal mode under extreme constraints of ultra-short total optical length (≤7mm) and ultra-wide full field of view (≥160°). Furthermore, the total system length is prone to change during switching, affecting the sealing and operational stability of the endoscope tip.

[0004] Therefore, how to achieve stable switching of bifocal points under the constraints of extremely compact size (total optical length ≤ 6.8 mm, full field of view ≥ 160°) through a simplified single-lens moving structure, while keeping the total optical length of the objective lens unchanged, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this application is to provide a bifocal endoscope objective and endoscope that achieves stable bifocal switching and maintains the total optical length of the objective unchanged during the switching process, under an extremely compact structure with an optical total length ≤6.8mm and a full field of view ≥160°.

[0006] The embodiments of this application are implemented as follows: A first aspect of this application provides a bifocal endoscope objective, comprising a first lens with negative optical power, a second lens with positive optical power, a third lens with positive optical power and movable along the optical axis from the object side to the image side, a fourth lens with positive optical power, a fifth lens with negative optical power, and a sixth lens with negative optical power, arranged sequentially along the optical axis from the object side to the image side; the total optical length of the bifocal endoscope objective is less than or equal to 6.8 mm, and the full field of view is greater than or equal to 160°; the third lens is configured such that by moving along the optical axis to a first axial position or a second axial position, the air gap between the third lens and the second and fourth lenses is changed to correspond to a remote observation mode and a near observation mode, respectively, and the total optical length of the bifocal endoscope objective remains unchanged during the switching between the remote observation mode and the near observation mode. This bifocal endoscope objective achieves stable bifocal switching with the total optical length remaining unchanged during the switching process, all within an extremely compact structure with a total optical length ≤6.8mm and a full field of view ≥160°.

[0007] In one possible implementation, the first lens has a refractive index of 1.7-1.9 and an Abbe number of 35-45; the second lens has a refractive index of 1.8-2.0 and an Abbe number of 20-30; the third lens has a refractive index of 1.4-1.6 and an Abbe number of 60-80; the fourth lens has a refractive index of 1.6-1.8 and an Abbe number of 40-60; the fifth lens has a refractive index of 1.6-1.8 and an Abbe number of 20-35; and the sixth lens has a refractive index of 1.8-2.0 and an Abbe number of 15-30.

[0008] As one possible implementation, an aperture stop is also included, which is disposed between the third lens and the fourth lens.

[0009] In one possible implementation, the fourth lens is cemented to the fifth lens, the image-side surface of the fourth lens is convex, and the object-side surface of the fifth lens is concave; the effective focal length of the bifocal endoscope objective is 0.9mm~1.2mm.

[0010] As one possible implementation, the bifocal endoscope objective lens satisfies the following conditional expressions: 0.7 < |f / f1| < 0.9, 0.1 < |f / f2| < 0.3, 0.1 < |f / f3| < 0.3, 0.8 < |f / f45| < 1.0, 0.6 < |f / f6| < 0.8, where f is the effective focal length of the bifocal endoscope objective lens, f1 is the focal length of the first lens, f2 is the focal length of the second lens, f3 is the focal length of the third lens, f45 is the combined focal length of the fourth and fifth lenses, and f6 is the focal length of the sixth lens.

[0011] As one possible implementation, the bifocal endoscope objective also satisfies the following conditions: 3.8 < |f2 / f1| < 4.2, 3.5 < |f3 / f45| < 4.5, 0 < |f / (f1+f2+f3+f45+f6)| < 0.2.

[0012] As one possible implementation, the bifocal endoscope objective lens satisfies the following condition: |D2 / R2|≤1.8, where D2 is the aperture of the image-side surface of the first lens, and R2 is the radius of curvature of the image-side surface of the first lens.

[0013] As one possible implementation, the bifocal endoscope objective lens satisfies the following condition: 2.5≤TTL / (d1+d2+d3)≤4, where d1 is the core thickness of the first lens, d2 is the core thickness of the second lens, d3 is the core thickness of the third lens, and TTL is the total optical length of the bifocal endoscope objective lens.

[0014] As one possible implementation, the working distance range corresponding to the long-distance observation mode is 5mm~100mm, and the working distance range corresponding to the close-distance observation mode is 2mm~6mm.

[0015] A second aspect of this application provides an endoscope, including the aforementioned bifocal endoscope objective and an image sensor located on the mirror side of the bifocal endoscope objective. This bifocal endoscope objective, with an extremely compact structure of ≤6.8mm total optical length and ≥160° full field of view, achieves stable bifocal switching while maintaining a constant total optical length during switching.

[0016] The beneficial effects of the embodiments of this application include: The bifocal endoscope objective provided in this application achieves stable switching between bifocal modes under extremely compact structural constraints of an optical length ≤6.8mm and a full field of view ≥160°, through a simplified structure involving the movement of a single lens (i.e., the third lens). Compared to complex solutions involving the movement of multiple lens groups, this application requires only one miniature linear drive mechanism to drive the third lens in precise one-dimensional linear motion along the optical axis, significantly simplifying the mechanical structure, reducing assembly difficulty and cost, and perfectly fitting the confined space of the endoscope tip. Furthermore, the optical length of the objective remains unchanged during the switching between the two modes, ensuring that the dimensions and sealing structure of the endoscope tip are unaffected during mode switching, thus improving the system's reliability and operational stability. Simultaneously, through a reasonable combination of positive and negative optical powers and a compact lens layout, an ultra-wide field of view exceeding 160° is achieved with an ultra-short overall length, accommodating both long-distance, wide-range searches and close-range, fine-tuned examinations. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A schematic diagram of the structure of a bifocal endoscope objective lens provided in the embodiments of this application in the remote observation mode; Figure 2 A schematic diagram of the structure of a bifocal endoscope objective lens provided in the embodiments of this application in close-up observation mode; Figure 3 MTF curve of the bifocal endoscope objective lens in the long-distance observation mode provided in the embodiments of this application under visible light; Figure 4 A transverse chromatic aberration curve of a bifocal endoscope objective lens in the long-distance observation mode provided in this application embodiment under visible light; Figure 5 MTF curve of the bifocal endoscope objective lens in close-up observation mode provided in the embodiments of this application under visible light; Figure 6 A transverse chromatic aberration curve of a bifocal endoscope objective lens in close-up observation mode provided in this application embodiment under visible light; Figure 7 Field curvature diagram of the bifocal endoscope objective lens in the long-distance observation mode provided in the embodiments of this application under visible light.

[0019] Icons: 1-First lens; 2-Second lens; 3-Third lens; 4-Fourth lens; 5-Fifth lens; 6-Sixth lens; 7-Aperture stop; 8-Filter; 9-Protective glass. Detailed Implementation

[0020] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. The described embodiments are only some embodiments of this application, not all embodiments. Similar reference numerals and letters in the following drawings indicate similar items. Once an item is defined in one drawing, it does not need to be further defined in other drawings.

[0021] The terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product is in use. They are used only for the convenience of describing this application and should not be construed as limiting this application. The terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0022] Unless otherwise expressly specified and limited, the terms "set up," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to connections within two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0023] Please refer to the reference. Figures 1 to 7 This application provides a bifocal endoscope objective, comprising, arranged sequentially along the optical axis from the object side to the image side: a first lens 1 with negative optical power, a second lens 2 with positive optical power, a third lens 3 with positive optical power and movable along the optical axis, a fourth lens 4 with positive optical power, a fifth lens 5 with negative optical power, and a sixth lens 6 with negative optical power. The total optical length of this bifocal endoscope objective is less than or equal to 6.8 mm, and the full field of view is greater than or equal to 160°.

[0024] The third lens 3 is configured to change the air gap between the third lens 3 and the second lens 2 and the fourth lens 4 by moving it to the first axial position or the second axial position along the optical axis, so as to correspond to the long-distance observation mode and the short-distance observation mode respectively, and the total optical length of the bifocal endoscope objective remains unchanged during the switching between the long-distance observation mode and the short-distance observation mode.

[0025] It should be noted that, as Figure 1 and Figure 2As shown, along the optical axis from the object side to the image side, the arrangement of optical components follows the core logic of "wide-angle beam expansion - light convergence - focus switching - aberration correction". The first lens 1, as the first optical element on the object side, has negative optical power and can effectively diverge the incident light from the object side, expanding the system's field of view and laying the foundation for achieving a full field of view of over 160°. The second lens 2 has positive optical power and is used to converge the light rays diverged by the first lens 1, initially compressing the beam aperture and providing a suitable light angle for subsequent focus switching. The third lens 3, as the core motion component, has positive optical power and changes its air gap with the preceding and following lenses by precisely moving along the optical axis to a position on the first axis (i.e., closer to the second lens 2) or a position on the second axis (i.e., closer to the fourth lens 4). The fourth lens 4 has positive optical power, the fifth lens 5 has negative optical power, and the sixth lens 6 has negative optical power. As the rear-end imaging and correction components of the system, they are responsible for the final aberration correction and focusing of the light rays after focus switching.

[0026] For example, when observing distant targets within a range of 5mm to 100mm, the drive mechanism moves the third lens 3 to the first axial position (i.e., distant observation mode). This slight change in spacing alters the optical power distribution in the middle of the system, thereby compensating for the image plane adjustment required due to the significant increase in object distance, resulting in clear imaging of distant objects. When observing near targets within a range of 2mm to 6mm, the drive mechanism moves the third lens 3 to the second axial position (i.e., near observation mode). At this time, the optical path of the entire optical system is optimized, allowing near objects to be clearly imaged on the image plane. This single-lens movement process simultaneously achieves the switching of the system's focal length and adaptive compensation of the image plane, ensuring that the image plane accurately falls on the target surface of the image sensor in both modes. During the switching process, the overall focal length and the 160° ultra-wide-angle field of view of the system remain essentially unchanged, the half-image height is fixed at 1mm, and the total optical length remains strictly constant.

[0027] The bifocal endoscope objective provided in this application achieves stable switching between bifocal modes under extremely compact structural constraints of an optical length ≤6.8mm and a full field of view ≥160°, through a simplified structure involving the movement of a single lens (i.e., the third lens 3). Compared to complex solutions involving the movement of multiple lens groups, this application requires only one miniature linear drive mechanism to drive the third lens 3 to perform precise one-dimensional linear motion along the optical axis, significantly simplifying the mechanical structure, reducing assembly difficulty and cost, and perfectly fitting the confined space of the endoscope tip. Furthermore, the optical length of the objective remains unchanged during the switching between the two modes, ensuring that the external dimensions and sealing structure of the endoscope tip are unaffected during mode switching, thus improving the system's reliability and operational stability. Simultaneously, through a reasonable combination of positive and negative optical powers and a compact lens layout, an ultra-wide field of view exceeding 160° is achieved with an ultra-short overall length, balancing the dual needs of long-distance wide-range searching and close-range fine examination.

[0028] As one possible implementation, the first lens 1 has a refractive index of 1.7~1.9 and an Abbe number of 35~45; the second lens 2 has a refractive index of 1.8~2.0 and an Abbe number of 20~30; the third lens 3 has a refractive index of 1.4~1.6 and an Abbe number of 60~80; the fourth lens 4 has a refractive index of 1.6~1.8 and an Abbe number of 40~60; the fifth lens 5 has a refractive index of 1.6~1.8 and an Abbe number of 20~35; and the sixth lens 6 has a refractive index of 1.8~2.0 and an Abbe number of 15~30.

[0029] It should be noted that the above-mentioned ranges of refractive index and Abbe number are determined by comprehensively considering aberration correction, material cost, and manufacturing process optimization under extremely compact dimensions. Specifically, the first lens 1 uses a high refractive index, medium-high Abbe number material to achieve sufficient light divergence angle and control field curvature within a very short total length; the sixth lens 6 uses a high refractive index, low Abbe number material to correct Pittsvan field curvature and ensure a flat field of view; the third lens 3, as a moving lens, uses a low refractive index, high Abbe number material to minimize chromatic aberration changes during movement; the Abbe number difference between the fourth lens 4 and the fifth lens 5 is greater than 20, specifically used to correct axial chromatic aberration in bifocal mode, ensuring that transverse chromatic aberration is always suppressed within 2μm when switching from near to far view.

[0030] Specifically, the first lens 1 uses a material with a high refractive index and a medium-to-high Abbe number, enabling sufficient light divergence angle within a very short total length. The second lens 2 uses a material with a high refractive index and a low Abbe number, which facilitates rapid light convergence and correction of primary chromatic aberration. The third lens 3, acting as a movable lens, uses a material with a low refractive index and a high Abbe number, which reduces chromatic aberration fluctuations caused by angle changes during movement, ensuring color reproduction in bifocal mode. The fourth lens 4 uses a material with a medium-to-high refractive index and a relatively high Abbe number, used to provide the system's positive optical power and correct chromatic aberration. The fifth lens 5 uses a material with a medium-to-high refractive index and a relatively low Abbe number, and works in conjunction with the fourth lens 4 to effectively correct axial chromatic aberration. The sixth lens 6 uses a material with a high refractive index and a low Abbe number, which facilitates achieving the required negative optical power within a compact space, while also correcting the system's Pittswan field curvature to ensure a flat field of view.

[0031] As one possible implementation method, such as Figure 1 and Figure 2 As shown, the bifocal endoscope objective also includes an aperture stop 7, which is positioned between the third lens 3 and the fourth lens 4.

[0032] It should be noted that the optical structure before and after stop 7 is approximately symmetrically distributed about stop 7 (i.e., three lenses are provided before and after stop 7). This symmetrical arrangement of stop 7 is beneficial for correcting coma, astigmatism, and off-axis aberrations such as distortion of the objective lens. Especially for ultra-wide-angle objectives, it can significantly improve the consistency of imaging across the entire field of view and reduce image quality degradation at the edges of the field of view. At the same time, stop 7 is located between the third lens 3 and the fourth lens 4, which can effectively control the aperture of the light entering the rear imaging group, avoid stray light interference, and improve image contrast.

[0033] As one possible implementation method, such as Figure 1 and Figure 2 As shown, the bifocal endoscope objective also includes a filter 8, which is positioned between the aperture stop 7 and the fourth lens 4. The filter 8 is used to filter out interfering light such as infrared light in the object-side light, preventing stray light from affecting image quality and ensuring the color reproduction and clarity of the output image. The filter 8 is preferably an infrared cutoff filter.

[0034] As one possible implementation method, such as Figure 1 and Figure 2 As shown, the fourth lens 4 and the fifth lens 5 are cemented together to form a cemented lens. Specifically, the image-side surface of the fourth lens 4 is convex, and the object-side surface of the fifth lens 5 is concave. This cemented structure can effectively correct chromatic aberration and spherical aberration of the system, especially compensating for axial chromatic aberration and field curvature changes caused by the movement of the third lens 3, ensuring full-field imaging sharpness in both observation modes. At the same time, the cemented design reduces air gaps, further compressing the overall optical length, which is beneficial for achieving a compact structure with an overall optical length ≤6.8mm.

[0035] As one possible implementation, the effective focal length of the bifocal endoscope objective is 0.9mm to 1.2mm. This focal length range matches a full field of view of 160°, representing the optimal range that balances wide-angle coverage with the ability to magnify local details.

[0036] As one possible implementation, the bifocal endoscope objective lens satisfies the following conditional equations: 0.7 < |f / f1| < 0.9, 0.1 < |f / f2| < 0.3, 0.1 < |f / f3| < 0.3, 0.8 < |f / f45| < 1.0, 0.6 < |f / f6| < 0.8, where f is the effective focal length of the bifocal endoscope objective lens, f1 is the focal length of the first lens 1, f2 is the focal length of the second lens 2, f3 is the focal length of the third lens 3, f45 is the combined focal length of the fourth lens 4 and the fifth lens 5, and f6 is the focal length of the sixth lens 6.

[0037] It should be noted that the above conditions are the core design constraints for achieving the synergistic optimization of extremely compact size and ultra-wide-angle performance in this application. 0.7 < |f / f1| < 0.9 ensures that the first lens 1 has sufficiently strong negative optical power to expand the field of view, while avoiding distortion and astigmatism that are difficult to correct due to excessive optical power. 0.1 < |f / f2| < 0.3 rationally allocates the positive optical power of the second lens 2, enabling it to effectively converge light without excessively compressing the beam and overburdening subsequent lenses. 0.1 < |f / f3| < 0.3 allocates a moderate positive optical power to the third lens 3, allowing it to sensitively change the system focal length during movement while maintaining image plane stability and avoiding drastic aberration fluctuations caused by minor movements. 0.8 < |f / f45| < 1.0 indicates that the cemented group of the fourth lens 4 and the fifth lens 5 bears the main positive optical power of the system and is the core power unit for imaging. Its optical power is comparable to the effective focal length of the system, ensuring that light is efficiently converged to the image plane. 0.6 < |f / f6| < 0.8 indicates that the sixth lens 6 bears a strong negative optical power, used to balance the field curvature caused by the positive optical power of the front group, ensuring the edge imaging quality at ultra-wide angles.

[0038] As an implementation method, the bifocal endoscope objective also satisfies the following conditions: 3.8 < |f2 / f1| < 4.2, 3.5 < |f3 / f45| < 4.5, 0 < |f / (f1+f2+f3+f45+f6)| < 0.2.

[0039] It should be noted that the above conditional expressions further optimize the focal length ratio between key lenses or lens groups. 3.8 < |f2 / f1| < 4.2 constrains the optical power ratio of the front-end beam expander group (i.e., the first lens 1 and the second lens 2), ensuring that while achieving a 160° ultra-wide angle, the system has a reasonable backstop and low aberration sensitivity. 3.5 < |f3 / f45| < 4.5 ensures that the optical power of the movable third lens 3 matches the optical power of the main imaging group (i.e., the cemented group of the fourth lens 4 and the fifth lens 5), enabling the third lens 3 to achieve stable switching between two sharp focus states within a limited movement range (the total length remains unchanged during switching), avoiding situations where the total length cannot be controlled due to excessive movement or the switching is insensitive due to excessively short movement. 0 < |f / (f1+f2+f3+f45+f6)| < 0.2, controlling the ratio of the sum of the focal lengths of each lens to the effective focal length of the system, ensuring that the optical power distribution of the entire optical system is reasonable and the incident angle of light on the surface of each lens is gentle, thereby reducing tolerance sensitivity and improving the yield of mass production.

[0040] As one possible implementation, the bifocal endoscope objective lens satisfies the following condition: |D2 / R2|≤1.8, where D2 is the aperture of the image-side surface of the first lens 1, and R2 is the radius of curvature of the image-side surface of the first lens 1.

[0041] It should be noted that this conditional expression is used to optimize the curved shape of the first lens 1. Controlling |D2 / R2|≤1.8 can prevent the image side of the first lens 1 from being too curved, thereby reducing the high-order aberrations (especially distortion and astigmatism) of this surface. At the same time, it is beneficial to the processing and inspection of the lens, ensuring that the first lens 1 still has good process feasibility under the design of ultra-wide full field of view ≥160°.

[0042] As one possible implementation, the bifocal endoscope objective lens satisfies the following condition: 2.5≤TTL / (d1+d2+d3)≤4, where d1 is the core thickness of the first lens 1, d2 is the core thickness of the second lens 2, d3 is the core thickness of the third lens 3, and TTL is the total optical length of the bifocal endoscope objective lens.

[0043] It should be noted that this conditional expression is used to control the balance between the structural compactness of the optical system and the manufacturability of the lenses. If the ratio of TTL / (d1+d2+d3) is too small (<2.5), it means that the core thickness of the lens accounts for too large a proportion of the total optical length, leaving insufficient space for the air gap, which is not conducive to achieving bifocal switching. If the ratio of TTL / (d1+d2+d3) is too large (>4), it means that the lens is too thin, making it difficult to manufacture and resulting in poor structural strength. Controlling the ratio between 2.5 and 4 ensures that the third lens 3 has enough room to move to achieve bifocal switching, while also ensuring that each lens has a reasonable core thickness, which is convenient for manufacturing and assembly.

[0044] This application also provides an endoscope, including the aforementioned bifocal endoscope objective and an image sensor located on the image side of the bifocal endoscope objective. The bifocal endoscope objective may further include a protective glass 9, disposed between the sixth lens 6 and the image side, for protecting the image sensor and not participating in power distribution or aberration correction. This endoscope can be applied in medical diagnosis, industrial inspection, and other fields, and is particularly suitable for scenarios requiring simultaneous large-area searching and local detail magnification within confined spaces. Since the structure, working principle, and beneficial effects of the bifocal endoscope objective have been described in detail in the foregoing embodiments, they will not be repeated here.

[0045] This endoscope, employing the bifocal endoscope objective lens provided in this application, achieves stable switching between long-distance and short-distance observation modes within an extremely compact structure with a total optical length ≤6.8mm and a full field of view ≥160°. This is achieved by using only one drive mechanism to move the third lens 3 to either the first or second axial position, while maintaining a constant total optical length during switching. This completely solves the problem of the total length change affecting the tip seal in traditional solutions. Simultaneously, the single-lens moving structure significantly simplifies the mechanical structure of the endoscope tip, reduces its overall size, adapts to the needs of use in confined spaces, shortens assembly time, improves reliability, and reduces costs. The precise matching of the image sensor and the bifocal endoscope objective lens ensures clear imaging from the objective lens output, enabling wide-range searching in long-distance mode (5mm~100mm) and detailed local inspection in short-distance mode (2mm~6mm). This meets the requirements of medical diagnosis and industrial inspection for imaging accuracy and observation flexibility, improving the overall performance and user experience of the endoscope. Specific Implementation In this embodiment, all lenses are spherical glass lenses. The specific values ​​of the parameters of the object plane (surface 0), first lens 1 (surface 1-2), second lens 2 (surface 3-4), third lens 3 (surface 5-6), aperture 7 (surface 7), filter 8 (surface 8-9), fourth lens 4 (surface 10-11), fifth lens 5 (surface 11-12), sixth lens 6 (surface 13-14), protective glass 9 (surface 15-16), and image plane (surface 17) in the above-mentioned bifocal endoscope objective are shown in the table below.

[0047]

[0048] The table below shows the key optical parameters of the system in two observation modes. D0 is the object distance, D1 is the air gap between the second lens 2 and the third lens 3, D2 is the air gap between the third lens 3 and the aperture stop 7, FN0 is the F-number, FOV / 2 is the half-field angle, and half-image height (half the image height) is 1.0 mm. This data clearly demonstrates the effect of moving the third lens 3 on adjusting the system's imaging parameters, and the characteristic that the total optical length (TTL) remains constant during switching.

[0049]

[0050] In this embodiment, when the system is in long-distance observation mode, the third lens 3 is located at the first axial position, with D1=0.10mm, D2=0.76mm, and an object distance of 13.00mm. The half-field of view reaches 80.0° (i.e., the full field of view is 160°), satisfying the need for a wide-range search. When it is necessary to switch to close-range observation mode for fine examination of local details, the third lens 3 is driven to move along the optical axis to the image side to the second axial position. At this time, D1 increases to 0.43mm, D2 decreases to 0.43mm, the object distance switches to 3.30mm, the half-field of view remains at 80.0° (i.e., the full field of view is 160°), and the F-number is finely adjusted from 6.30 to 6.02. During the switching process, the half-image height remains at 1.0mm, and the total optical length TTL remains strictly unchanged (which can be verified by superimposing the air gap according to the lens parameter table), ensuring the stability of the external dimensions and sealing structure of the endoscope tip.

[0051] Experimental data show that the bifocal endoscope objective of this application successfully achieved an ultra-wide-angle design with a full field of view of 160° under the extremely compact constraint of an optical total length of ≤6.8mm. By switching the axial position of a single lens (i.e., the third lens 3), two clear imaging modes, namely long distance (13mm) and short distance (3.3mm), were stably obtained. In both modes, the half field of view remained at 80°, perfectly balancing the dual functions of long-distance search and close-range fine examination. The optical total length remained unchanged during the switching process, and the structure was simple and reliable.

[0052] The bifocal endoscope objective of this application exhibits excellent imaging quality in both modes. For example... Figure 3 As shown, in long-distance observation mode, the objective lens has a full-field MTF value greater than 0.1 at a spatial frequency of 200 lp / mm, indicating high resolution; Figure 4 As shown, the vertical color difference in this mode is less than 1μm, and the color reproduction is good. Figure 5 As shown, in close-up observation mode, the objective lens also maintains a full-field MTF value greater than 0.1 at a spatial frequency of 200 lp / mm; Figure 6 As shown, the vertical color difference in this mode is less than 2μm, which meets the stringent requirements for color reproduction in fine inspection.

[0053] The above are merely optional embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

[0054] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable way without contradiction. In order to avoid unnecessary repetition, this application will not describe the various possible combinations separately. At the same time, the various embodiments of this application can be combined with each other. As long as they do not violate the spirit of this application, they should also be regarded as the content disclosed in this application.

Claims

1. A bifocal endoscope objective, characterized in that, It includes a first lens with negative optical power, a second lens with positive optical power, a third lens with positive optical power that can move along the optical axis, a fourth lens with positive optical power, a fifth lens with negative optical power, and a sixth lens with negative optical power, arranged sequentially from the object side to the image side along the optical axis. The total optical length of the bifocal endoscope objective is less than or equal to 6.8 mm, and the full field of view is greater than or equal to 160°. The third lens is configured to change the air gap between the third lens and the second and fourth lenses by moving it to a first axial position or a second axial position along the optical axis, so as to correspond to the long-distance observation mode and the short-distance observation mode respectively, and the total optical length of the bifocal endoscope objective remains unchanged during the switching between the long-distance observation mode and the short-distance observation mode.

2. The bifocal endoscope objective lens according to claim 1, characterized in that, The first lens has a refractive index of 1.7-1.9 and an Abbe number of 35-45; the second lens has a refractive index of 1.8-2.0 and an Abbe number of 20-30; the third lens has a refractive index of 1.4-1.6 and an Abbe number of 60-80; the fourth lens has a refractive index of 1.6-1.8 and an Abbe number of 40-60; the fifth lens has a refractive index of 1.6-1.8 and an Abbe number of 20-35; and the sixth lens has a refractive index of 1.8-2.0 and an Abbe number of 15-30.

3. The bifocal endoscope objective lens according to claim 1, characterized in that, It also includes an aperture stop, which is disposed between the third lens and the fourth lens.

4. The bifocal endoscope objective lens according to claim 1, characterized in that, The fourth lens is cemented to the fifth lens, the image side of the fourth lens is convex, and the object side of the fifth lens is concave; the effective focal length of the bifocal endoscope objective is 0.9mm~1.2mm.

5. The bifocal endoscope objective lens according to claim 4, characterized in that, The bifocal endoscope objective satisfies the following conditions: 0.7 < |f / f1| < 0.9, 0.1 < |f / f2| < 0.3, 0.1 < |f / f3| < 0.3, 0.8 < |f / f45| < 1.0, 0.6 < |f / f6| < 0.8, where f is the effective focal length of the bifocal endoscope objective, f1 is the focal length of the first lens, f2 is the focal length of the second lens, f3 is the focal length of the third lens, f45 is the combined focal length of the fourth and fifth lenses, and f6 is the focal length of the sixth lens.

6. The bifocal endoscope objective lens according to claim 5, characterized in that, The bifocal endoscope objective also satisfies the following conditions: 3.8 < |f2 / f1| < 4.2, 3.5 < |f3 / f45| < 4.5, 0 < |f / (f1+f2+f3+f45+f6)| < 0.

2.

7. The bifocal endoscope objective lens according to claim 1, characterized in that, The bifocal endoscope objective lens satisfies the following condition: |D2 / R2|≤1.8, where D2 is the aperture of the image-side surface of the first lens, and R2 is the radius of curvature of the image-side surface of the first lens.

8. The bifocal endoscope objective lens according to claim 1, characterized in that, The bifocal endoscope objective lens satisfies the following condition: 2.5≤TTL / (d1+d2+d3)≤4, where d1 is the core thickness of the first lens, d2 is the core thickness of the second lens, d3 is the core thickness of the third lens, and TTL is the total optical length of the bifocal endoscope objective lens.

9. The bifocal endoscope objective lens according to claim 1, characterized in that, The working distance range corresponding to the long-distance observation mode is 5mm~100mm, and the working distance range corresponding to the close-distance observation mode is 2mm~6mm.

10. An endoscope, characterized in that, It includes the bifocal endoscope objective as described in any one of claims 1 to 9, and an image sensor located on the mirror side of the bifocal endoscope objective.

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