Optical system, image capturing module and endoscope

Abstract

The present application relates to an optical system, an image-taking module and an endoscope. The optical system comprises a first lens group with negative focal power and a second lens group with positive focal power, the first lens group comprises a first lens with negative focal power and a second lens with positive focal power, and the second lens group comprises a third lens with positive focal power, a fourth lens with positive focal power and a fifth lens with negative focal power; the optical system satisfies: 0.15≤IH / TTL≤0.2; IH is half of the image height corresponding to the maximum field angle of the optical system, and TTL is the distance on the optical axis from the object side of the first lens to the imaging surface of the optical system. The above optical system can balance the miniaturization design and the realization of high imaging quality, and can have a large depth of field.

Description

Technical Field

[0001] This invention relates to the field of endoscopy technology, and in particular to an optical system, an image acquisition module, and an endoscope. Background Technology

[0002] With the rapid development of medical equipment, endoscopes are increasingly widely used in the medical field, and the industry's requirements for their structure and imaging quality are also rising. Specifically, to minimize endoscopic damage to patients, the industry typically requires endoscopes to be miniaturized. Simultaneously, when using endoscopes for medical diagnosis, the ability to generate high-resolution images of lesions is usually required. However, current endoscopes often struggle to simultaneously achieve both miniaturization and high imaging quality. Summary of the Invention

[0003] Therefore, it is necessary to provide an optical system, an image acquisition module, and an endoscope to address the problem that current endoscopes often struggle to achieve both miniaturization and high imaging quality.

[0004] An optical system includes, along the optical axis from the object side to the image side, a first lens group having negative optical power and a second lens group having positive optical power. The first lens group includes, along the optical axis from the object side to the image side, a first lens having negative optical power and a second lens having positive optical power. The second lens group includes, along the optical axis from the object side to the image side, a third lens having positive optical power, a fourth lens having positive optical power, and a fifth lens having negative optical power.

[0005] And the optical system satisfies the following condition:

[0006] 0.15≤IH / TTL≤0.2;

[0007] Wherein, IH is half the image height corresponding to the maximum field of view of the optical system, and TTL is the distance on the optical axis from the object side of the first lens to the imaging surface of the optical system, that is, the total optical length of the optical system.

[0008] In the aforementioned optical system, the first lens group with negative optical power and the second lens group with positive optical power constitute a reverse telephoto structure, which helps to shorten the overall length of the optical system. Furthermore, the first lens group with negative optical power can effectively compensate for the aberrations produced by the second lens group with positive optical power, thereby improving the image quality of the optical system. Simultaneously, the second lens group with positive optical power can effectively bring the principal point of the optical system closer to the imaging plane, thus helping to shorten the focal length of the optical system, thereby increasing the depth of field and promoting miniaturization of the optical system. The first lens, with its negative optical power, helps to expand the field of view of the optical system. The second lens, with its positive optical power, helps to correct the aberrations produced by the first lens. The third and fourth lenses, with their positive optical power, help to shorten the overall length of the optical system and effectively share the positive optical power required by the optical system, thus helping to reduce the sensitivity of the optical system. The fifth lens, with its negative optical power, helps to correct the aberrations produced by the fourth lens and also helps to correct chromatic aberration in the optical system.

[0009] When the above conditions are met, the ratio of the half-image height to the total optical length of the optical system can be rationally configured. This is beneficial for matching the optical system with high-pixel photosensitive elements, thereby improving the imaging quality of the optical system. It also helps to shorten the total length of the optical system, thus achieving miniaturization. Below the lower limit of the above conditions, the half-image height of the optical system is too small, which is not conducive to matching high-pixel photosensitive elements, making it difficult to achieve high-pixel images. At the same time, the total length of the optical system is too long, making miniaturization difficult. Above the upper limit of the above conditions, the total length of the optical system is too short, resulting in an overly compact structure. This increases the sensitivity of the optical system's manufacturing process, leading to a decrease in production yield, difficulty in stable production, and increased manufacturing costs. Having the above optical power characteristics and satisfying the above conditions, the optical system can achieve both miniaturization and high imaging quality, and also possess a large depth of field.

[0010] In one embodiment,

[0011] The image-side surface of the first lens is concave near the optical axis;

[0012] The image-side surface of the second lens is convex near the optical axis;

[0013] The image-side surface of the third lens is convex near the optical axis;

[0014] The object side of the fourth lens is convex near the optical axis, and the image side is convex near the optical axis.

[0015] The object-side surface of the fifth lens is concave near the optical axis, and the image-side surface is also concave near the optical axis.

[0016] The concave surface of the first lens's image side, combined with its negative optical power, helps to expand the field of view of the optical system. The biconvex surface of the fourth lens effectively converges light rays, which helps to shorten the overall length of the optical system. The concave surface of the fifth lens's image side helps to shorten the back focal length of the optical system, thus helping to shorten the overall length of the optical system.

[0017] In one embodiment, the optical system satisfies the following condition:

[0018] 2ω≥130°;

[0019] Wherein, 2ω is the maximum field of view of the optical system. When the above condition is satisfied, the optical system has a wide-angle characteristic. When applied to endoscopic pathological examinations inside the body, it can achieve a large field of view, thereby reducing the risk of missed examinations.

[0020] In one embodiment, the optical system satisfies the following condition:

[0021] -1.6≤f1 / f≤-0.9;

[0022] Where f1 is the effective focal length of the first lens, and f is the effective focal length of the optical system. When the above condition is satisfied, the proportion of the negative optical power of the first lens in the optical system can be reasonably configured, which is beneficial for suppressing aberrations such as distortion, field curvature, and magnification chromatic aberration. This, in turn, helps the image-side lenses of the first lens to effectively correct the aberrations generated by the first lens, improving the imaging quality of the optical system. Below the lower limit of the above condition, the refractive power of the first lens is too weak, making it difficult to balance the negative optical power of the first lens group with the positive optical power of the second lens group. This results in increased inward curvature of the image plane, i.e., increased negative field curvature, making it difficult to obtain high-definition image quality. Furthermore, the image quality at different observation depths also deteriorates, i.e., the depth of field decreases. Above the upper limit of the above condition, image distortion increases, leading to excessive distortion when the optical system is applied to an endoscope, affecting the assessment of lesions.

[0023] In one embodiment, the optical system satisfies the following condition:

[0024] -1.1≤f1 / f4≤-0.45;

[0025] Where f1 is the effective focal length of the first lens and f4 is the effective focal length of the fourth lens. When the above condition is satisfied, the ratio of the effective focal lengths of the first and fourth lenses can be reasonably configured, which is beneficial for shortening the overall length of the optical system and achieving miniaturization. It also helps the fourth lens correct aberrations such as coma and field curvature in the optical system, improving the imaging quality. Furthermore, it prevents the optical power of the first lens from being too large, thus preventing excessive curvature of the first lens surface and reducing its tolerance sensitivity, which is beneficial for the processing and assembly of the first lens. When the upper limit of the above condition is exceeded, the optical power of the first lens is too small, which is not conducive to shortening the overall length of the optical system, making it difficult to meet the requirements of miniaturization. At the same time, the optical power of the fourth lens is too large, making it difficult to correct aberrations such as coma and field curvature, leading to image quality degradation. When the value is below the lower limit of the above conditional formula, the optical focal length of the first lens is too large, which causes the surface of the first lens to be excessively curved. This increases the processing and assembly sensitivity of the first lens, making it easy for image quality to deteriorate due to processing and assembly errors. At the same time, the optical focal length of the fourth lens is too small, making it difficult to effectively deflect light rays. This is not conducive to shortening the overall length of the optical system, thus failing to meet the requirements of miniaturization design.

[0026] In one embodiment, the optical system satisfies the following condition:

[0027] 0.2≤d1 / f≤0.75;

[0028] Where d1 is the thickness of the first lens along the optical axis, i.e., the center thickness of the first lens, and f is the effective focal length of the optical system. When the above condition is satisfied, the ratio of the center thickness of the first lens to the effective focal length of the optical system can be reasonably configured, which is beneficial for the processing and assembly of the first lens, and also for the miniaturization design of the optical system. If the thickness is below the lower limit of the above condition, the center thickness of the first lens is too small, making it prone to breakage during processing and assembly. If the thickness exceeds the upper limit of the above condition, the center thickness of the first lens is too large, leading to an increase in the incident height of light on the first lens, and also increasing the overall length of the optical system, which is detrimental to the realization of miniaturization design.

[0029] In one embodiment, the optical system satisfies the following condition:

[0030] 0.1≤(1 / FNO)*(f1 / f5)≤0.28;

[0031] Wherein, FNO is the aperture number of the optical system, f1 is the effective focal length of the first lens, and f5 is the effective focal length of the fifth lens. When the above conditions are met, the aperture number of the optical system and the effective focal lengths of the first and fifth lenses can be reasonably configured, enabling the first lens to effectively deflect light, which is beneficial for shortening the overall length of the optical system and achieving miniaturization. Simultaneously, it can effectively correct aberrations such as astigmatism and field curvature of the optical system, thereby improving the imaging quality. Furthermore, it is beneficial for the optical system to obtain sufficient light intake and increase the depth of field. When the upper limit of the above conditions is exceeded, the focal length of the first lens becomes too large, resulting in insufficient light deflection capability, which is detrimental to miniaturization. Simultaneously, the focal length of the fifth lens becomes too small, resulting in excessive astigmatism correction, leading to image quality degradation. Additionally, if the aperture number of the optical system is too small and the aperture is too large, it is difficult to effectively correct aberrations such as astigmatism and field curvature in a large field of view, resulting in image quality degradation and a smaller depth of field, which is detrimental to the application of the optical system in endoscopes. When the focal length is below the lower limit of the above conditional formula, the focal length of the first lens is too small, which can easily produce severe aberrations. The focal length of the fifth lens is too large, which makes it difficult to effectively correct aberrations such as astigmatism and field curvature, thus making it difficult to obtain a clear image. At the same time, the aperture number is too large, which leads to the light-transmitting aperture being too small, resulting in insufficient image brightness and hindering the improvement of image quality.

[0032] In one embodiment, the optical system further includes an aperture stop disposed between the first lens group and the second lens group. This centrally located aperture stop, combined with the reverse telephoto structure formed by the first lens group with negative optical power and the second lens group with positive optical power, facilitates the wide-angle and miniaturization of the optical system.

[0033] An image-capturing module includes a photosensitive element and an optical system as described in any of the above embodiments, wherein the photosensitive element is disposed on the image side of the optical system. Using the aforementioned optical system in the image-capturing module allows for both miniaturization and high image quality, while also providing a large depth of field, thus facilitating the application of the image-capturing module in endoscopes.

[0034] An endoscope includes a housing and the aforementioned image acquisition module, wherein the image acquisition module is disposed within the housing. By employing the aforementioned image acquisition module in the endoscope, the module achieves both miniaturization and high image quality, while also possessing a large depth of field. This allows the endoscope, when applied in the medical field, to minimize damage to patients and to generate high-resolution images of lesions, thereby improving diagnostic accuracy. Attached Figure Description

[0035] Figure 1 These are schematic diagrams of the optical system in some embodiments;

[0036] Figure 2 This is a schematic diagram of the optical system in the first embodiment;

[0037] Figure 3A This is a field curvature astigmatism curve of the optical system in the first embodiment;

[0038] Figure 3B This is a distortion curve diagram of the optical system in the first embodiment;

[0039] Figure 3C This is a diagram showing the chromatic aberration curve of the optical system in the first embodiment;

[0040] Figure 4 This is a schematic diagram of the optical system in the second embodiment;

[0041] Figure 5A This is a field curvature astigmatism curve of the optical system in the second embodiment;

[0042] Figure 5B This is a distortion curve diagram of the optical system in the second embodiment;

[0043] Figure 5C This is a diagram showing the chromatic aberration curve of the optical system in the second embodiment;

[0044] Figure 6 This is a schematic diagram of the optical system in the third embodiment;

[0045] Figure 7A This is a field curvature astigmatism curve of the optical system in the third embodiment;

[0046] Figure 7B This is a distortion curve diagram of the optical system in the third embodiment;

[0047] Figure 7C This is a diagram showing the chromatic aberration curve of the optical system in the third embodiment;

[0048] Figure 8 This is a schematic diagram of the imaging module in some embodiments. Detailed Implementation

[0049] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0050] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0051] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0052] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0053] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0054] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0055] Please see Figure 1 In some embodiments of this application, the optical system 100 includes, along the optical axis 110 from the object side to the image side, a first lens group G1 with negative optical power and a second lens group G2 with positive optical power. The first lens group G1 with negative optical power and the second lens group G2 with positive optical power constitute a reverse telephoto structure, which helps to shorten the overall length of the optical system 100. Furthermore, the first lens group G1 with negative optical power can effectively compensate for the aberrations produced by the second lens group G2 with positive optical power, thereby improving the imaging quality of the optical system 100. Simultaneously, the second lens group G2 with positive optical power can effectively bring the principal point of the optical system 100 closer to the imaging plane, thereby helping to shorten the focal length of the optical system 100, increasing the depth of field of the optical system 100, and promoting the miniaturization design of the optical system 100.

[0056] Specifically, the first lens group G1, along the optical axis 110 from the object side to the image side, includes a first lens L1 with negative optical power and a second lens L2 with positive optical power. The second lens group G2, along the optical axis 1100 from the object side to the image side, includes a third lens L3 with positive optical power, a fourth lens L4 with positive optical power, and a fifth lens L5 with negative optical power. The first lens L1 has negative optical power, which helps to expand the field of view of the optical system 100. The second lens L2 has positive optical power, which helps to correct the aberrations generated by the first lens L1. The third lens, L3, and the fourth lens L4 have positive optical power, which helps to shorten the overall length of the optical system 100 and effectively distributes the positive optical power required by the optical system 100, thus reducing the sensitivity of the optical system 100. The fifth lens L5 has negative optical power, which helps to correct the aberrations generated by the fourth lens L4 and also helps to correct the chromatic aberration of the optical system 100.

[0057] It is understood that the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, and the fifth lens L5 are coaxially arranged, and the common axis of all lenses in the optical system 100 is the optical axis 110 of the optical system 100. The optical system 100 also includes an image plane IMA located on the image side of the fifth lens L5. The image plane IMA is the imaging plane of the optical system 100. After the incident light is adjusted by the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, and the fifth lens L5, it can be imaged onto the image plane IMA.

[0058] Furthermore, in some embodiments, the image-side surface of the first lens L1 is concave near the optical axis 110, which, combined with the negative optical power of the first lens L1, helps to expand the field of view of the optical system 100. The image-side surface of the second lens L2 is convex near the optical axis 110, which helps to correct the aberrations caused by the concave surface of the image-side surface of the first lens L1. The image-side surface of the third lens L3 is convex near the optical axis 110, which helps to correct the astigmatism of the optical system 100. The object-side surface of the fourth lens L4 is convex near the optical axis 110, and the image-side surface is convex near the optical axis 110, which can effectively converge light rays and help to shorten the overall length of the optical system 100. The object-side surface of the fifth lens L5 is concave near the optical axis 110, which helps to balance the aberrations caused by the biconvex surface of the fourth lens L4, and also helps to correct the chromatic aberration of the optical system 100. The image-side surface of the fifth lens L5 is concave near the optical axis 110, which helps to shorten the back focal length of the optical system 100, thereby helping to shorten the overall length of the optical system 100.

[0059] In some embodiments, the optical system 100 is provided with an aperture stop S, which can be positioned between the first lens group G1 and the second lens group G2, that is, between the second lens L2 and the third lens L3. The centrally positioned aperture stop, combined with the anti-photograph structure formed by the first lens group G1 with negative optical power and the second lens group G2 with positive optical power, is beneficial for achieving a wide-angle and miniaturized optical system 100.

[0060] In some embodiments, the optical system 100 further includes a first protective glass CG1 and a second protective glass CG2. The first protective glass CG1 is disposed on the object side of the first lens L1, and the second protective glass CG2 is disposed on the image side of the fifth lens L5. When the optical system 100 is used for observation in an endoscope, it inevitably accumulates substances such as blood and mucus. The first protective glass CG1 protects the lenses within the optical system 100, preventing direct rinsing of the first lens L1 and thus avoiding damage or breakage when water is sprayed through the nozzle at the endoscope tip. The second protective glass CG2 protects the photosensitive element disposed at the image plane IMA of the optical system 100.

[0061] In some embodiments, the optical system 100 further includes a filter F, which may be disposed between the second lens L2 and the third lens L3, for example, between the second lens L2 and the aperture stop S, or on the image side of the fifth lens L5, for example, between the fifth lens L5 and the protective glass CG2. The filter F is used to filter out interfering light, preventing it from reaching the imaging surface of the optical system 100 and affecting normal imaging. Specifically, the filter F may be an infrared cut-off filter, used to block light in the near-infrared region that may be sensed by the photosensitive element.

[0062] In some embodiments, the object-side and image-side surfaces of each lens in the optical system 100 are aspherical, and the surface shapes of the object-side and image-side surfaces of each lens may differ near the optical axis 110 and around the circumference. The use of aspherical structures can improve the flexibility of lens design and effectively correct spherical aberration, thereby improving image quality. In other embodiments, the object-side and image-side surfaces of each lens in the optical system 100 may also be spherical, and the surface shapes of the object-side and image-side surfaces of each lens will be the same near the optical axis 110 and around the circumference. It should be noted that the above embodiments are merely examples of some embodiments of this application; in some embodiments, the surfaces of each lens in the optical system 100 can be any combination of aspherical or spherical surfaces.

[0063] In some embodiments, the lenses in the optical system 100 can be made of either glass or plastic. Using plastic lenses reduces the weight of the optical system 100 and lowers production costs, allowing for a slimmer and lighter design, especially considering the smaller size of the optical system 100. Using glass lenses, on the other hand, provides the optical system 100 with excellent optical performance and high temperature resistance. It should be noted that the lenses in the optical system 100 can also be made of any combination of glass and plastic, and do not necessarily have to be made entirely of either glass or plastic.

[0064] It is important to note that the first lens L1 does not necessarily mean that there is only one lens. In some embodiments, the first lens L1 may contain two or more lenses, which can form a cemented lens. The surface of the cemented lens closest to the object side can be considered the object-side surface of the first lens L1, and the surface closest to the image side can be considered the image-side surface of the first lens L1. Alternatively, the lenses in the first lens L1 may not form a cemented lens, but the distance between the lenses is relatively fixed. In this case, the object-side surface of the lens closest to the object side is the object-side surface of the first lens L1, and the image-side surface of the lens closest to the image side is the image-side surface of the first lens L1. In addition, in some embodiments, the number of lenses in the second lens L2, third lens L3, fourth lens L4, or fifth lens L5 may be greater than or equal to two, and any adjacent lenses may form a cemented lens or a non-cemented lens.

[0065] In some embodiments, the optical system 100 satisfies the condition: 0.15 ≤ IH / TTL ≤ 0.2; where IH is half the image height corresponding to the maximum field of view of the optical system 100, and TTL is the distance on the optical axis 110 from the object side of the first lens L1 to the imaging surface of the optical system 100, i.e., the total optical length of the optical system 100. Specifically, IH / TTL can be: 0.174, 0.175, 0.176, 0.177, 0.178, 0.179, 0.180, 0.181, 0.182, or 0.184. When the above condition is satisfied, the ratio of half image height to total optical length of the optical system 100 can be reasonably configured, which is beneficial for matching the optical system 100 with high-pixel photosensitive elements, thereby improving the imaging quality of the optical system 100. At the same time, it is also beneficial for shortening the total length of the optical system 100, thereby achieving miniaturization design. When the image height is below the lower limit of the above conditional expression, the half-image height of the optical system 100 is too small, which is not conducive to matching high-pixel photosensitive elements, making it difficult to achieve high-pixel images. At the same time, the overall length of the optical system 100 is too long, making it difficult to achieve miniaturization. When the image height exceeds the upper limit of the above conditional expression, the overall length of the optical system 100 is too short, and the structure is too compact, leading to increased sensitivity in the manufacturing process of the optical system 100. This results in a decrease in the production yield of the optical system 100, making stable production difficult and increasing production costs. By possessing the above optical power characteristics and satisfying the above conditional expression, the optical system 100 can achieve both miniaturization and high imaging quality, and can also have a large depth of field.

[0066] In some embodiments, the optical system 100 satisfies the condition: 0.16≤IH / TTL≤0.19; thereby further shortening the overall length of the optical system 100 and improving the imaging quality of the optical system 100.

[0067] In some embodiments, the optical system 100 satisfies the condition: 2ω ≥ 130°; where 2ω is the maximum field of view of the optical system 100. Specifically, 2ω can be: 142.6°, 142.7°, 142.9°, 143.0°, 143.2°, 143.3°, 143.5°, 143.6°, 143.8°, or 143.9°. When the above condition is satisfied, the optical system 100 has a wide-angle characteristic. When applied to endoscopic pathological examinations in vivo, it can achieve a large field of view, thereby reducing the risk of missed examinations.

[0068] In some embodiments, the optical system 100 satisfies the condition: 2ω≥140°; thereby further expanding the field of view of the optical system 100 and realizing a wide field of view observation.

[0069] It should be noted that in some embodiments, the optical system 100 can be matched with a photosensitive element having a rectangular photosensitive surface, and the imaging surface of the optical system 100 coincides with the photosensitive surface of the photosensitive element. In this case, the effective pixel area on the imaging surface of the optical system 100 has both a horizontal direction and a diagonal direction. Therefore, 2ω can be understood as the maximum field of view in the diagonal direction of the optical system 100, and IH can be understood as half the length of the effective pixel area in the diagonal direction on the imaging surface of the optical system 100.

[0070] In some embodiments, the optical system 100 satisfies the condition: -1.6 ≤ f1 / f ≤ -0.9; where f1 is the effective focal length of the first lens L1, and f is the effective focal length of the optical system 100. Specifically, f1 / f can be: -1.431, -1.425, -1.411, -1.308, -1.296, -1.255, -1.206, -1.164, -1.098, or -1.027. When the above condition is satisfied, the proportion of the negative optical power of the first lens L1 in the optical system 100 can be reasonably configured, which is beneficial to suppressing the generation of aberrations such as distortion, field curvature, and magnification chromatic aberration. This is beneficial to the effective correction of aberrations generated by the first lens L1 by the lens on the image side of the first lens L1, thereby improving the imaging quality of the optical system 100. Below the lower limit of the above conditional expression, the refractive power of the first lens L1 is too weak, making it difficult to balance the negative optical power of the first lens group G1 and the positive optical power of the second lens group G2. This results in increased inward curvature of the image plane IMA, i.e., increased negative field curvature, making it difficult to obtain high-resolution image quality. Moreover, the image quality at different observation depths also deteriorates, i.e., the depth of field decreases. Above the upper limit of the above conditional expression, image distortion increases, resulting in excessive distortion when the optical system 100 is applied to the endoscope, affecting the identification of lesions.

[0071] In some embodiments, the optical system 100 satisfies the condition: -1.5≤f1 / f≤-1.0; thereby further suppressing the generation of aberrations and improving the imaging quality of the optical system 100.

[0072] In some embodiments, the optical system 100 satisfies the condition: -1.1 ≤ f1 / f4 ≤ -0.45; where f1 is the effective focal length of the first lens L1 and f4 is the effective focal length of the fourth lens L4. Specifically, f1 / f4 can be: -0.961, -0.932, -0.887, -0.852, -0.764, -0.728, -0.674, -0.652, -0.611, or -0.579. When the above conditions are met, the ratio of the effective focal lengths of the first lens L1 and the fourth lens L4 can be reasonably configured, which is beneficial for shortening the overall length of the optical system 100 and achieving miniaturization. It also helps the fourth lens L4 correct aberrations such as coma and field curvature in the optical system 100, improving the imaging quality of the optical system 100. Furthermore, it prevents the optical power of the first lens L1 from being too large, thus preventing excessive curvature of the surface of the first lens L1 and reducing its tolerance sensitivity, which is beneficial for the processing and assembly of the first lens L1. When the upper limit of the above conditions is exceeded, the optical power of the first lens L1 becomes too small, which is not conducive to shortening the overall length of the optical system 100, making it difficult to meet the requirements of miniaturization. Simultaneously, the optical power of the fourth lens L4 becomes too large, making it difficult to correct aberrations such as coma and field curvature, leading to image quality degradation. When the value is below the lower limit of the above conditional formula, the optical focal length of the first lens L1 is too large, which causes the surface of the first lens L1 to be excessively curved. This increases the processing and assembly sensitivity of the first lens L1, making it easy for image quality to deteriorate due to processing and assembly errors. At the same time, the optical focal length of the fourth lens L4 is too small, making it difficult to effectively deflect light rays. This is not conducive to shortening the total length of the optical system 100, thus failing to meet the requirements of miniaturization design.

[0073] In some embodiments, the optical system 100 satisfies the condition: -1.0≤f1 / f4≤-0.5; thereby further shortening the overall length of the optical system 100 and improving the imaging quality of the optical system 100, while further reducing the tolerance sensitivity of the first lens L1.

[0074] In some embodiments, the optical system 100 satisfies the condition: 0.2 ≤ d1 / f ≤ 0.75; where d1 is the thickness of the first lens L1 on the optical axis 110, i.e., the center thickness of the first lens L1, and f is the effective focal length of the optical system 100. Specifically, d1 / f can be: 0.382, 0.399, 0.402, 0.423, 0.457, 0.496, 0.521, 0.555, 0.567, or 0.588. When the above condition is satisfied, the ratio of the center thickness of the first lens L1 to the effective focal length of the optical system 100 can be reasonably configured, which is beneficial to the processing and assembly of the first lens L1, and also beneficial to the miniaturization design of the optical system 100. When the value is lower than the lower limit of the above condition, the center thickness of the first lens L1 is too small, which makes the first lens L1 prone to breakage during processing and assembly. When the upper limit of the above conditional expression is exceeded, the center thickness of the first lens L1 becomes too large, which increases the incident height of light on the first lens L1 and also increases the total length of the optical system 100, which is not conducive to the realization of miniaturization design.

[0075] In some embodiments, the optical system 100 satisfies the condition: 0.3≤d1 / f≤0.65; thereby further improving the processing and assembly yield of the first lens L1 and shortening the overall length of the optical system 100.

[0076] In some embodiments, the optical system 100 satisfies the condition: 0.1 ≤ (1 / FNO)*(f1 / f5) ≤ 0.28; where FNO is the aperture number of the optical system 100, f1 is the effective focal length of the first lens L1, and f5 is the effective focal length of the fifth lens L5. Specifically, (1 / FNO)*(f1 / f5) can be: 0.170, 0.175, 0.179, 0.181, 0.184, 0.187, 0.190, 0.195, 0.197, or 0.202. When the above conditions are met, the aperture number of the optical system 100 and the effective focal lengths of the first lens L1 and the fifth lens L5 can be reasonably configured, so that the first lens L1 can effectively deflect light, which is beneficial to shortening the total length of the optical system 100 and realizing miniaturization design; at the same time, it can effectively correct aberrations such as astigmatism and field curvature of the optical system 100, thereby improving the imaging quality of the optical system 100; in addition, it is also beneficial for the optical system 100 to obtain sufficient light intake, and at the same time, it is beneficial to increase the depth of field of the optical system 100. When the upper limit of the above conditional expression is exceeded, the focal length of the first lens L1 is too large, resulting in insufficient light deflection capability, which is detrimental to miniaturization design. Simultaneously, the focal length of the fifth lens L5 is too small, resulting in excessive optical focal length and over-correction of astigmatism, leading to image quality degradation. Furthermore, the aperture number of the optical system 100 is too small, and the aperture is too large, making it difficult to effectively correct astigmatism, field curvature, and other aberrations in a large field of view, thus degrading image quality and reducing the depth of field, which is unfavorable for its application in endoscopes. When the lower limit of the above conditional expression is exceeded, the focal length of the first lens L1 is too small, easily producing severe aberrations. The focal length of the fifth lens L5 is too large, making it difficult to effectively correct astigmatism, field curvature, and other aberrations, resulting in difficulty obtaining a clear image. Simultaneously, the aperture number is too large, resulting in an insufficient light-transmitting aperture, leading to insufficient image brightness and hindering image quality improvement.

[0077] In some embodiments, the optical system 100 satisfies the condition: 0.1≤(1 / FNO)*(f1 / f5)≤0.28; thereby further shortening the total length of the optical system 100, improving the imaging quality of the optical system 100, and further increasing the depth of field of the optical system 100 while obtaining sufficient light intake.

[0078] The reference wavelength for the above effective focal length values ​​is 587.6nm.

[0079] Based on the descriptions of the above embodiments, more specific embodiments and accompanying drawings are provided below for detailed explanation.

[0080] First Embodiment

[0081] Please see Figure 2 , Figure 3A , Figure 3B and Figure 3C , Figure 2 The diagram below shows the structure of the optical system 100 in the first embodiment. The optical system 100 includes, from the object side to the image side, a first protective glass CG1, a first lens L1 with negative optical power, a second lens L2 with positive optical power, a filter F, an aperture S, a third lens L3 with positive optical power, a fourth lens L4 with positive optical power, a fifth lens L5 with negative optical power, and a second protective glass CG2.

[0082] The object-side surface and image-side surface of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, and the fifth lens L5 are all spherical.

[0083] The object-side surface of the first lens L1 is convex, and the image-side surface is concave.

[0084] The object-side surface of the second lens L2 is concave, and the image-side surface is convex.

[0085] The object side of the third lens L3 is concave, and the image side is convex.

[0086] The object-side surface of the fourth lens L4 is convex, and the image-side surface is also convex.

[0087] The object side of the fifth lens L5 is concave, and the image side is also concave.

[0088] Table 1 shows detailed parameters for each lens in the optical system of the first embodiment, including surface type, radius of curvature, thickness, refractive index, Abbe number, effective focal length f, total optical length TTL, maximum field of view 2ω, and effective aperture value FNO. The reference wavelength for the refractive index and Abbe number of each lens is 587.6 nm, which is the same in other embodiments. The image plane IMA in Table 1 can be understood as the imaging plane of the optical system 100. The elements from the object plane (not shown in the figure) to the image plane IMA are arranged sequentially from top to bottom according to the elements in Table 1. The first value in the "thickness" parameter column of the first lens L1 is the thickness of the first lens L1 on the optical axis 110, i.e., the distance d1 in the figure. The second value is the distance from the image side of the first lens L1 to the rear surface in the image side direction (the object side of the second lens L2) on the optical axis 110, i.e., d2 in the figure. The meanings of other values ​​in the thickness parameter column can be deduced from this.

[0089] It should be noted that in this embodiment and the following embodiments, the optical system 100 may also omit the filter F, the first protective glass CG1 and the second protective glass CG2, but in this case, the distance from the image side of the second lens L2 to the object side of the third lens L3 and the distance from the image side of the fifth lens L5 to the image plane IMA remains unchanged.

[0090] As can be seen from the data in Table 1, the optical system 100 has the characteristics of miniaturization, high resolution, and large depth of field.

[0091] Table 1

[0092]

[0093]

[0094] In addition, the numerical values ​​of each condition of the optical system 100 in the first embodiment are detailed in Table 4. The effects of each condition can be referred to the above description. The second and third embodiments can also be obtained from Table 4, and will not be described again later.

[0095] Figure 3A This is a field curvature astigmatism curve of the optical system 100 in the first embodiment, derived from... Figure 3A It can be seen that the sagittal field curvature and meridional field curvature of the optical system 100 are both small, with the sagittal field curvature being less than 0.003 mm. The field curvature and astigmatism of each field of view are well corrected, and the center and edge of the field of view have clear imaging, which is conducive to the optical system 100 obtaining a large depth of field effect.

[0096] Figure 3B This is a distortion curve diagram of the optical system 100 in the first embodiment, from... Figure 3B It can be seen that the maximum field-of-view distortion of the optical system 100 is less than 60%, the distortion within the effective observation field of view is less than 50%, the image distortion caused by the main beam is small, and the system has excellent imaging quality. The reference wavelength for the field curvature astigmatism curve and the distortion curve is 587.6 nm, and the same applies to other embodiments.

[0097] Figure 3C This is a chromatic aberration curve of the optical system 100 in the first embodiment, derived from... Figure 3C It can be seen that the maximum difference between the wavelengths of 656.3nm and 486.1nm is less than 2µm, and the transverse chromatic aberration of the optical system 100 is well corrected, resulting in good imaging quality.

[0098] Second Embodiment

[0099] Please see Figure 4 , Figure 5A , Figure 5B and Figure 5C , Figure 4 The diagram below illustrates the structure of the optical system 100 in the second embodiment. From the object side to the image side, the optical system 100 includes, in sequence, a first protective glass CG1, a first lens L1 with negative optical power, a second lens L2 with positive optical power, an aperture stop S, a third lens L3 with positive optical power, a fourth lens L4 with positive optical power, a fifth lens L5 with negative optical power, and a second protective glass CG2. The first protective glass CG1 is bonded to the first lens L1; for example, the image side of the first protective glass CG1 is bonded to the object side of the first lens L1 using high-temperature resistant adhesive.

[0100] Figure 5A This is a field curvature astigmatism curve of the optical system 100 in the second embodiment, derived from... Figure 5A It can be seen that the sagittal field curvature and meridional field curvature of the optical system 100 are both small, and the field curvature and astigmatism of each field of view are well corrected. The center and edge of the field of view have clear imaging, which is conducive to the optical system 100 obtaining a large depth of field effect.

[0101] Figure 5B This is a distortion curve diagram of the optical system 100 in the second embodiment, from... Figure 5B It can be seen that the maximum field of view distortion of the optical system 100 is less than 65%, the distortion within the effective observation field of view is less than 55%, the image distortion caused by the main beam is small, and the imaging quality of the system is excellent.

[0102] Figure 5C This is a chromatic aberration curve of the optical system 100 in the second embodiment, derived from... Figure 5C It can be seen that the maximum difference between the wavelengths of 656.3nm and 486.1nm is less than 2µm, and the transverse chromatic aberration of the optical system 100 is well corrected, resulting in good imaging quality.

[0103] The object-side surface and image-side surface of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, and the fifth lens L5 are all spherical.

[0104] The object-side surface of the first lens L1 is flat, and the image-side surface is concave.

[0105] The object-side surface of the second lens L2 is convex, and the image-side surface is also convex.

[0106] The object-side surface of the third lens L3 is a plane, and the image-side surface is a convex surface.

[0107] The object-side surface of the fourth lens L4 is convex, and the image-side surface is also convex.

[0108] The object side of the fifth lens L5 is concave, and the image side is also concave.

[0109] In addition, the parameters of the optical system 100 are given in Table 2, and the definitions of each parameter can be derived from the first embodiment, and will not be repeated here.

[0110] Table 2

[0111]

[0112] Third Embodiment

[0113] Please see Figure 6 , Figure 7A , Figure 7B and Figure 7C , Figure 6 This is a schematic diagram of the optical system 100 in the third embodiment. The optical system 100, from the object side to the image side, includes, in sequence, a first protective glass CG1, a first lens L1 with negative optical power, a second lens L2 with positive optical power, an aperture stop S, a third lens L3 with positive optical power, a fourth lens L4 with positive optical power, a fifth lens L5 with negative optical power, and a second protective glass CG2. The first protective glass CG1 is cemented to the first lens L1.

[0114] Figure 7A This is a field curvature astigmatism curve of the optical system 100 in the third embodiment, derived from... Figure 7A It can be seen that the sagittal field curvature and meridional field curvature of the optical system 100 are both small, and the field curvature and astigmatism of each field of view are well corrected. The center and edge of the field of view have clear imaging, which is conducive to the optical system 100 obtaining a large depth of field effect.

[0115] Figure 7B This is a distortion curve diagram of the optical system 100 in the third embodiment, from... Figure 7B It can be seen that the maximum field of view distortion of the optical system 100 is less than 65%, the distortion within the effective observation field of view is less than 55%, the image distortion caused by the main beam is small, and the imaging quality of the system is excellent.

[0116] Figure 7C This is a chromatic aberration curve of the optical system 100 in the third embodiment, derived from... Figure 7C It can be seen that the maximum difference between the wavelengths of 656.3nm and 486.1nm is less than 2µm, and the transverse chromatic aberration of the optical system 100 is well corrected, resulting in good imaging quality.

[0117] The object-side surface and image-side surface of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, and the fifth lens L5 are all spherical.

[0118] The object-side surface of the first lens L1 is flat, and the image-side surface is concave.

[0119] The object-side surface of the second lens L2 is convex, and the image-side surface is also convex.

[0120] The object-side surface of the third lens L3 is a plane, and the image-side surface is a convex surface.

[0121] The object-side surface of the fourth lens L4 is convex, and the image-side surface is also convex.

[0122] The object side of the fifth lens L5 is concave, and the image side is also concave.

[0123] In addition, the various parameters of the optical system 100 are given in Table 3, and the definitions of each parameter can be derived from the first embodiment, and will not be repeated here.

[0124] Table 3

[0125]

[0126] In addition, Table 4 shows the numerical values ​​of the conditional expressions satisfied by the first to third embodiments.

[0127] Table 4

[0128] 2ω(°) 140 143.8 143.8 f1 / f -1.431 -1.027 -1.045 f1 / f4 -0.961 -0.579 -0.631 d1 / f 0.382 0.588 0.570 IH / TTL 0.175 0.174 0.184 (1 / FNO)*(f1 / f5) 0.202 0.170 0.173

[0129] Please see Figure 8 In some embodiments, the optical system 100 can be assembled with the photosensitive element 210 to form an imaging module 200. In this case, the photosensitive surface of the photosensitive element 210 can be regarded as the image plane IMA of the optical system 100. Specifically, the photosensitive element 210 can be a charge-coupled device (CCD) or a complementary metal-oxide-semiconductor sensor (CMOS sensor). By using the above-described optical system 100 in the imaging module 200, it is possible to achieve both miniaturization and high image quality, while also possessing a large depth of field, thereby facilitating the application of the imaging module 200 in endoscopes.

[0130] In some embodiments, the image acquisition module 200 can be applied to an endoscope, such as in the objective lens of an endoscope. The endoscope includes a housing, and the image acquisition module 200 is disposed within the housing, which can be the tube of the endoscope objective lens. The endoscope can be used in the medical field, such as for medical diagnosis of patients. By employing the image acquisition module 200 in an endoscope, the module can achieve both miniaturization and high image quality, while also possessing a large depth of field. This allows the endoscope, when used in the medical field, to minimize damage to patients and to form high-resolution images of lesions, thereby improving diagnostic accuracy.

[0131] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0132] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. An optical system, characterized in that, The optical system comprises five lenses with optical power. The optical system includes, along the optical axis from the object side to the image side, a first lens group with negative optical power and a second lens group with positive optical power. The first lens group includes, along the optical axis from the object side to the image side, a first lens with negative optical power and a second lens with positive optical power. The second lens group includes, along the optical axis from the object side to the image side, a third lens with positive optical power, a fourth lens with positive optical power, and a fifth lens with negative optical power. And the optical system satisfies the following condition: 0.15≤IH / TTL≤0.2; -1.1≤f1 / f4≤-0.45; 2ω≥130°; Wherein, IH is half the image height corresponding to the maximum field of view of the optical system, TTL is the distance on the optical axis from the object side of the first lens to the imaging surface of the optical system, f1 is the effective focal length of the first lens, f4 is the effective focal length of the fourth lens, and 2ω is the maximum field of view of the optical system.

2. The optical system according to claim 1, characterized in that, The following conditions must be met: 0.16≤IH / TTL≤0.

19.

3. The optical system according to claim 1, characterized in that, The following conditions must be met: -1.6≤f1 / f≤-0.9; Where f1 is the effective focal length of the first lens, and f is the effective focal length of the optical system.

4. The optical system according to claim 1, characterized in that, The image-side surface of the first lens is concave near the optical axis, the image-side surface of the second lens is convex near the optical axis, the image-side surface of the third lens is convex near the optical axis, the object-side surface of the fourth lens is convex near the optical axis, and the image-side surface of the fifth lens is concave near the optical axis.

5. The optical system according to claim 1, characterized in that, The following conditions must be met: 0.2≤d1 / f≤0.75; Where d1 is the thickness of the first lens on the optical axis, and f is the effective focal length of the optical system.

6. The optical system according to claim 1, characterized in that, The following conditions must be met: 0.1≤(1 / FNO)*(f1 / f5)≤0.28; Wherein, FNO is the aperture number of the optical system, f1 is the effective focal length of the first lens, and f5 is the effective focal length of the fifth lens.

7. The optical system according to claim 1, characterized in that, It also includes an aperture stop, which is disposed between the first lens group and the second lens group.

8. An image acquisition module, characterized in that, It includes a photosensitive element and an optical system as described in any one of claims 1-7, wherein the photosensitive element is disposed on the image side of the optical system.

9. An endoscope, characterized in that, It includes a housing and the imaging module as described in claim 8, wherein the imaging module is disposed in the housing.

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