Wide-angle endoscope lens

Abstract

The application discloses a wide-angle endoscope lens, which comprises, in sequence from the object side to the image side, a protective window sheet, a first lens, a second lens, a third lens, a diaphragm, a fourth lens, a fifth lens, a protective glass sheet and an image sensor, wherein the first lens, the second lens and the fifth lens have negative focal lengths, and the third lens and the fourth lens have positive focal lengths; the object side surface of the protective window sheet and the first lens is a plane, so that the protective window sheet is convenient to assemble, and the sealing and assembly difficulty of the lens is reduced; the combination of the first lens and the second lens with negative focal lengths is beneficial to collect large field of view light, reduce the light aperture of the lens, reduce the size of the lens, and reserve sufficient non-photosensitive areas for the sealing of the lens, so that the endoscope lens has the characteristics of extremely low cost, few lenses, large depth of field and super wide angle while ensuring the image definition of the endoscope lens.

Description

Technical Field

[0001] This invention relates to the field of endoscopy technology, and in particular to a wide-angle endoscopy lens. Background Technology

[0002] The advent of minimally invasive surgery allows patients to undergo surgical treatment through small or even no incisions, offering advantages such as less pain and faster recovery. Endoscopes play a crucial role in minimally invasive surgical applications. The surgical field, depth of field, clarity, color reproduction, product stability, and operating costs of an endoscope are all closely related to the lens. The design of the endoscope lens influences the structural and electronic design of the accompanying components, making it a key factor in determining the success of an endoscope product.

[0003] Currently, endoscope lenses on the market are generally composed of multiple glass lenses. Small-sized glass lenses are prone to problems such as surface asymmetry, excessive thinness or thickness, and small aperture, leading to higher manufacturing difficulty and costs. In contrast, lenses made from resin lenses do not have these problems. However, resin lenses are mostly high-order aspherical surfaces, which are sensitive to tolerances, especially at the edges of the field of view, resulting in generally less than ideal image quality. Furthermore, the space at the tip of an endoscope is very compact, and the adhesive bonding area between the window and the tip is very small, making it difficult to guarantee a proper seal. According to the depth-of-field formula and Gaussian formula in geometric optics, fixed-focus lenses have a very small depth of field when shooting close-up objects. Directly increasing the depth of field will increase the size of the Airy disk due to diffraction, leading to reduced image sharpness. Therefore, improving the depth of field and sharpness of endoscopes while manufacturing small-sized lenses at low cost is of great significance. Summary of the Invention

[0004] This invention provides a wide-angle endoscope lens that can manufacture small-sized endoscope lenses at extremely low cost while ensuring image clarity and improving the depth of field of the endoscope.

[0005] To achieve the above effects, the technical solution of the present invention is as follows:

[0006] A wide-angle endoscope lens, comprising, from the object side to the image side, a first lens, a second lens, a third lens, an aperture stop, a fourth lens, and a fifth lens, wherein the first lens, the second lens, and the fifth lens have negative optical power, and the third lens and the fourth lens have positive optical power; the aperture stop is closely attached to the object side of the fourth lens.

[0007] The object-side surface of the first lens is either flat or convex, and the image-side surface is concave; the image-side surface of the second lens is concave; the object-side surface of the third lens is convex; both the object-side surface and the image-side surface of the fourth lens are convex; and both the object-side surface and the image-side surface of the fifth lens are concave.

[0008] In the above scheme, the first and second lenses are responsible for collecting light from a large field of view. The use of two negative power lenses helps reduce the lens aperture, decrease lens size, and provides sufficient adhesive area for sealing. Behind the aperture stop S, at least one positive power lens and one negative power lens are allocated, with the positive and negative power lenses separated to better correct the field curvature of the endoscope lens. The aperture stop is attached to the object side of the fourth lens to limit the beam aperture.

[0009] Furthermore, the refractive index n1 of the first lens and the refractive index n2 of the third lens, and the refractive index n3 of the fourth lens and the refractive index n4 of the fifth lens satisfy the following relationship:

[0010] 0.08 < |n1-n2| < 0.25

[0011] 0.08 < |n3-n4| < 0.25.

[0012] In the above scheme, the refractive indices of the first lens and the third lens, as well as the fourth lens and the fifth lens, are limited respectively, which helps to reduce the overall chromatic aberration of the endoscope lens and reduce the size of the blur spot.

[0013] Furthermore, the aperture D1 and curvature C1 of the object-side surface of the third lens, and the aperture D2 and curvature C2 of the image-side surface, satisfy the following relationship:

[0014] |D1C1-D2C2|≥0.25.

[0015] In the above scheme, limiting the aperture and curvature of the third lens improves the manufacturability of the wide-angle endoscope lens.

[0016] Furthermore, the depth of field δ of the endoscope lens satisfies the following relationship:

[0017]

[0018] Where Z is the allowable blur diameter, p is the distance from the object to the entrance pupil, a is the entrance pupil radius, and f is the focal length of the endoscope lens. Reducing the focal length of the endoscope lens helps to improve the depth of field.

[0019] Furthermore, the focal length f of the combination of the fourth and fifth lenses... 56 Compared to the total focal length f of the lens, it satisfies the following relationship:

[0020] 1 <f 56 / f<2.

[0021] Furthermore, the second to fifth lenses are all resin lenses, while the first lens is a glass lens or a resin lens.

[0022] In the above scheme, at least four of the lenses are resin lenses, which can significantly reduce lens processing costs.

[0023] Furthermore, at least one surface of the resin lens is aspherical, and the surface shape x of the aspherical surface is described as follows:

[0024]

[0025] in h It is the height of any point on the aspherical surface from the optical axis. c It is the vertex curvature. k It is the cone constant, A i Is it an aspherical first i Order coefficient.

[0026] Furthermore, the fifth lens has an image sensor for acquiring light signals on the side facing the image plane.

[0027] In the above solution, the plane of the object-side surface of the protective window and the plane of the object-side surface of the first lens are fitted together. Setting the protective window as a plane increases the contact area between the protective window and the first lens, resulting in good sealing.

[0028] Furthermore, the object-side surfaces of the first lens and the image sensor are respectively provided with a protective window and a protective glass sheet; the object-side surface and the image-side surface of the protective window and the protective glass sheet are both planar.

[0029] Furthermore, the first lens protective glass has a Mohs hardness >8 and is made of Al2O3 glass material. This enhances the endoscope lens's scratch resistance.

[0030] Compared with the prior art, the beneficial effects of the technical solution of the present invention are:

[0031] This invention relates to an endoscope lens composed of five lenses with non-zero optical power. The object-side surfaces of the protective window and the first lens are flat, facilitating assembly of the protective window and reducing the difficulty of sealing and assembling the lens. The combination of the first and second lenses, both negative optical power lenses, helps to collect light from a wide field of view, focusing the beam of a wide-angle lens, reducing the lens aperture, decreasing the lens size, and reserving sufficient non-photosensitive area for sealing. The fourth and fifth lenses bear the main optical power, reducing the focal length of the endoscope lens to increase the depth of field. The endoscope lens uses 4-5 resin lenses, greatly reducing the manufacturing cost. While ensuring image clarity, it features low cost, easy processing, large depth of field, and ultra-wide angle, making it practically valuable. Attached Figure Description

[0032] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the invention. To better illustrate this embodiment, some components in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0033] Figure 1 This is a schematic diagram of the endoscope lens structure provided in an embodiment of the present invention;

[0034] Figure 2 This is a schematic diagram of the MTF curves of the endoscope lens of the present invention under different viewing angles;

[0035] Figure 3 This is a schematic diagram of the diffusion spot and Airy spot of the endoscope lens of the present invention at a working distance of 15mm;

[0036] Figure 4 This is a schematic diagram of the diffusion spot and Airy spot of the endoscope lens of the present invention at a distance of 5mm;

[0037] Figure 5 This is a schematic diagram of the diffusion spot and Airy spot of the endoscope lens of the present invention at an object distance of 100mm; Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] Before introducing the embodiments of this application, the relevant terms involved in the embodiments of this application are first explained as follows:

[0040] Optical power: equal to the difference between the convergence of the image-side beam and the convergence of the object-side beam, it characterizes the ability of an optical system to deflect light rays.

[0041] Entrance pupil: An optical term that corresponds to the aperture stop, which actually affects the incident light energy and resolution. It is the image formed in the object space of the optical system by the aperture stop through the preceding optical group, and is simply called the entrance pupil.

[0042] Principal point: The intersection of the principal line of sight and the perspective plane, or the intersection of a pair of conjugate planes (i.e., principal planes) with the optical axis of the optical system.

[0043] Field curvature, also known as "image field curvature," occurs when a lens exhibits field curvature. The intersection of the entire beam does not coincide with the ideal image point. Although a clear image point can be obtained at each specific point, the entire image plane is curved. This makes it impossible to see the entire image plane clearly during microscopic examination, causing difficulties for observation and photography.

[0044] An aperture stop is a physical object in an optical system that limits the beam of light. It can be the edge of a lens, a frame, or a specially designed perforated screen. Its function can be twofold: to limit the beam of light or to limit the size of the field of view (imaging range).

[0045] OTF: Optical transfer function.

[0046] MTF: Modulation Transfer Function, is a relatively scientific method for analyzing the resolution of a lens.

[0047] Spatial frequency: refers to the number of grating cycles of the brightness and darkness of an image or stimulus pattern in sinusoidal modulation per degree of visual angle, with the unit being period (lp) / mm.

[0048] Airy disk: When a point light source is imaged through a diffraction-limited lens, the light spot formed at the focal point due to diffraction. It has a bright circular spot in the center, surrounded by a set of concentric rings of weaker light and dark. The central bright spot, bounded by the first dark ring, is called the Airy disk.

[0049] Diffusion spot: The intensity distribution of the diffracted image formed on different cross sections in front of and behind the image after a point light source (i.e., a star point) passes through an optical system is called the diffusion spot. The energy distribution of the diffusion spot can very sensitively reflect optical aberrations and defects. Therefore, quantitatively measuring the diffusion spot parameters is an important means of controlling the imaging quality of an optical system.

[0050] Example 1

[0051] For easier understanding, please refer to Figure 1 The present invention provides an embodiment of a wide-angle endoscope lens, which includes, from the object side to the image side, the following components in sequence: a first lens 2, a second lens 3, a third lens 4, an aperture stop S, a fourth lens 5, a fifth lens 6, and an image sensor 8 for acquiring incident light signals. The first lens 2, the second lens 3, and the fifth lens 6 have negative optical power, and the third lens 4 and the fourth lens 5 have positive optical power. The aperture stop is in close contact with the object side of the fourth lens 5, and the distance between the two is 0.

[0052] The object-side surface of the first lens 2 is either flat or convex, and the image-side surface is concave; the image-side surface of the second lens 3 is concave; the object-side surface of the third lens 4 is convex; both the object-side surface and the image-side surface of the fourth lens 5 are convex; and both the object-side surface and the image-side surface of the fifth lens 6 are concave.

[0053] Specifically, the object-side surfaces of the first lens 2 and the image sensor 8 are respectively provided with a protective window 1 and a protective glass sheet 7; the object-side and image-side surfaces of the protective window 1 and the protective glass sheet 7 are both planar, the protective window 1 has a Mohs hardness >8 and is made of Al2O3 glass material. The planar surface of the object-side surface of the protective window 1 is fitted to the planar surface of the object-side surface of the first lens 2.

[0054] It should be noted that the object-side surfaces of the protective window 1 and the first lens 2 are flat, which facilitates the assembly of the protective window 1, reduces the processing cycle of the endoscope lens, and lowers the difficulty of sealing and assembling the lens, making the sealing of the protective window 1 and the first lens 2 simpler. The first lens 2 and the second lens 3 are responsible for collecting light from a large field of view, the third lens 4 is used to balance the aberrations introduced by the first lens 2 and the second lens 3, the aperture S is responsible for absorbing stray light and reducing aberrations in the off-axis field of view, the fourth lens 5 bears the main optical power of the endoscope lens, and the fifth lens 6 is responsible for correcting field curvature. Light from the object side passes through the protective glass 7 in front of the image sensor 8 and is incident on the photosensitive chip of the image sensor 8, where photoelectric conversion occurs to obtain the image-side image, which is displayed on the endoscope's display screen. The image sensor 8 uses a small-sized CMOS image sensor.

[0055] The combination of two negative-power lenses, first lens 2 and second lens 3, is beneficial for collecting light from a wide field of view, reducing the aperture of the lenses, shrinking the lens size, and reserving sufficient non-photosensitive area, making the lens easier to seal. To reduce the impact of manufacturing errors, the incident and exit angles of light are controlled within 30° during the design phase. The slight bending of light helps improve the lens's tolerance resistance. Combined with tolerance analysis, the difference between the endoscope lens design value and the actual product is small, with good consistency and insensitivity to tolerance.

[0056] Specifically, the refractive index n1 of the first lens 2 and the refractive index n2 of the third lens 4, and the refractive index n3 of the fourth lens 5 and the refractive index n4 of the fifth lens 6 satisfy the following relationship:

[0057] 0.08 < |n1-n2| < 0.25

[0058] 0.08 < |n3-n4| < 0.25.

[0059] In the above scheme, the range of n1-n2 limits the refractive index of the plano-concave lens material. If |n1-n2| is less than 0.08, it will be detrimental to the correction of chromatic aberration in the endoscope lens and reduce image sharpness. If |n1-n2| is greater than 0.25, it will greatly increase the material cost of the resin lens. The effect of the range of n3-n4 is limited in the same way as above, and will not be repeated here.

[0060] Specifically, the aperture D1 and curvature C1 of the object side of the third lens 4, and the aperture D2 and curvature C2 of the image side, are constrained by the following relationship to ensure its manufacturability.

[0061] |D1C1-D2C2|≥0.25.

[0062] Specifically, the depth of field δ of the endoscope lens satisfies the following relationship:

[0063]

[0064] Where Z is the allowable blur diameter, p is the distance from the object to the entrance pupil, a is the entrance pupil radius, and f is the focal length of the endoscope lens. By combining negative, negative, and positive lens groups before the aperture stop, the principal point of the lens group is moved as close to the image side as possible. By limiting the focal length range of the fourth lens 5 and the fifth lens 6, they are made to bear the main optical power of the optical system, reducing the system's focal length f, thereby increasing the depth of field δ of the optical system. Therefore, the focal length f of the combination of the fourth lens 5 and the fifth lens 6 is... 56 Compared to the lens's total focal length f, the following range is limited:

[0065] 1 <f 56 / f<2.

[0066] Specifically, the second lens 3 to the fifth lens 6 are all resin lenses, and the first lens 2 can be a resin lens or a glass lens. At least one surface of the resin lens is aspherical, and the surface shape x of the aspherical surface is described as follows:

[0067]

[0068] in h It is the height of any point on the aspherical surface from the optical axis. c It is the vertex curvature. k It is the cone constant, A i Is it an aspherical first i Order coefficient.

[0069] The endoscope lens of this invention consists of five lenses with non-zero optical power, featuring a large depth of field, small size, low cost, short processing cycle, simple sealing, compact structure, and miniaturization, and has a field of view of over 140°. The positive and negative lenses behind the aperture are in a separate state to better correct field curvature.

[0070] Example 2

[0071] Specifically, based on Example 1, the solution will be described in conjunction with specific embodiments to further demonstrate its technical effects. Specifically:

[0072] like Figure 1 The optical lens, from the object-side OBJ to the image-side image sensor photosensitive surface DET, sequentially includes: a protective window 1, a first lens 2, a second lens 3, a third lens 4, an aperture stop S, a fourth lens 5, a fifth lens 6, a CMOS protective window 7, and an image sensor 8 for acquiring incident light signals. The first lens 2, the second lens 3, and the fifth lens 6 have negative optical power, while the third lens 4 and the fourth lens 5 have positive optical power. The object-side distance between the aperture stop and the fourth lens 5 is 0.

[0073] The object-side surface S1 of the protective window 1 is flat, and the image-side surface S2 is flat. The object-side surface S3 of the first lens 2 is flat or convex, and the image-side surface S4 is concave. The object-side surface S5 of the second lens 3 is concave, and the image-side surface S6 is concave. The object-side surface S7 of the third lens 4 is convex, and the image-side surface S8 is concave. The object-side surface S10 and the image-side surface S11 of the fourth lens 5 are both convex. The object-side surface S12 and the image-side surface S13 of the fifth lens 6 are both concave.

[0074] Specifically, the object-side surfaces of the first lens 2 and the image sensor 8 are respectively provided with a protective window 1 and a protective glass sheet 7; the object-side surface S14 and the image-side surface S15 of the protective glass sheet 7 are both planar, and the photosensitive surface DET of the image sensor is planar. The protective window 1 has a Mohs hardness >8 and is made of Al2O3 glass material. The image-side surface S2 of the protective window 1 and the object-side surface S3 of the first lens 2 are attached together.

[0075] Table 1 below shows the basic parameters of the optical lens of Example 2, where the units for radius of curvature, thickness / distance, and focal length are all millimeters (mm).

[0076] Table 1 Basic Parameters of Optical Lenses

[0077]

[0078] In this example, the total effective focal length f of the optical lens is 1.061 mm, the total length (i.e., the distance from surface S1 to the photosensitive surface DET of the image sensor on the optical axis) TTL of the optical lens is 7.46 mm, the maximum effective radius of the optical lens is 1.88 mm, the F-number of the optical lens is 6.47, the maximum field of view (FOV) of the optical lens is 140.0°, and the entrance pupil diameter (ENPD) of the optical lens is 0.175 mm.

[0079] Table 2 shows the higher-order coefficients A4, A6, A8, A10, and A12 that can be used for each mirror in the aspherical surfaces S4~S8 and S10~S13 in Example 2. The surface shape of each aspherical surface can be defined by the aspherical surface shape formula given in Example 1 above.

[0080] Table 2. Coefficients of higher-order terms for each mirror in aspherical surfaces S4~S8 and S10~S13

[0081]

[0082] Figure 2 , Figure 3 , Figure 4 , Figure 5 The results are simulation results of the endoscope lens performance. Figure 3 , Figure 4 , Figure 5 The number in the upper right corner represents the wavelength of the light, in μm; the circle in the figure represents the Airy disk in the current state, and the set of points represents the diffuse disk in the current state; the image plane in the figure refers to the image plane height.

[0083] from Figure 2 The modulation transfer function (MTF) curves show that the transfer function for each field of view has reached the diffraction limit, resulting in excellent imaging performance. At a spatial frequency of 120 lp / mm, the MTF is >0.2 across the entire field of view depth, and within a 100° field of view (i.e., ... Figure 2 The MTF of the curve with a mid-field angle ≤ 50° reaches above 0.32, which is close to the diffraction state.

[0084] like Figure 3 As shown in the dot plot, at a working optical distance of 15mm, the Airy disk radius is much larger than the blur disk radius, the aberrations of the endoscope lens are well balanced, the difference in blur disk distribution at different wavelengths is small, the lens chromatic aberration is small, and the imaging quality is good.

[0085] Figure 4 This is a spectrogram of light spots at an object distance of 5 mm. Figure 5 The image shows a spot pattern at a 100mm object distance. It can be seen that at close range (5mm) and distant range (100mm), the geometric radius of the diffuse spot is close to the radius of the Airy disk. The root mean square radius of the diffuse spot is smaller than the radius of the Airy disk. Considering the influence of lens manufacturing tolerances, the root mean square radius of the diffuse spot in the actual manufactured endoscope lens is comparable to the radius of the Airy disk, exhibiting good matching degree. This allows the lens to have a depth of field of 5-100mm and good image sharpness.

[0086] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A wide-angle endoscope lens characterized by, From the object side to the image side, the wide-angle endoscope lens successively comprises a first lens (2), a second lens (3), a third lens (4), a diaphragm S, a fourth lens (5) and a fifth lens (6), wherein the first lens (2), the second lens (3) and the fifth lens (6) have negative refractive powers, and the third lens (4) and the fourth lens (5) have positive refractive powers; the diaphragm is tightly attached to the object side surface of the fourth lens (5); The lens number of the wide-angle endoscope lens is five; The object side surface of the first lens (2) is a plane or a convex surface, and the image side surface is a concave surface; the image side surface of the second lens (3) is a concave surface; the object side surface of the third lens (4) is a convex surface; the object side surface and the image side surface of the fourth lens (5) are both convex surfaces; and the object side surface and the image side surface of the fifth lens (6) are both concave surfaces; The refractive index n1 of the first lens (2), the refractive index n2 of the third lens (4), the refractive index n3 of the fourth lens (5) and the refractive index n4 of the fifth lens (6) satisfy the following relationships: 0.08<|n1-n2|<0.25 0.08<|n3-n4|<0.25; The aperture D1 of the object side surface of the third lens (4) and the curvature C1, and the aperture D2 of the image side surface and the curvature C2 satisfy the following relationship: |D1C1-D2C2|≥0.25; The focal length f of the fourth lens (5), fifth lens (6) combination 56 , compared to the total focal length f of the lens, satisfies the following relationship: 1 < f 56 / f < 2.

2. The wide-angle endoscope lens of claim 1, wherein, The fourth lens (5) and the fifth lens (6) are in a separated state.

3. The wide-angle endoscope lens of claim 2, wherein, The second lens (3) to the fifth lens (6) are all resin lenses, and the first lens (2) is a glass lens or a resin lens.

4. The wide-angle endoscope lens of claim 3, wherein, At least one surface of the resin lens is an aspheric surface, and the surface type x of the aspheric surface is expressed as: wherein, h is the height of any point on the asphere from the optical axis, c is the vertex curvature, k is the conic constant, A i is the asphere's ith order coefficient.

5. The wide-angle endoscope lens of claim 4, wherein, The fifth lens (6) is provided with an image sensor (8) for collecting incident light signals on the side facing the image surface.

6. The wide-angle endoscope lens of claim 5, wherein, The object side surface of the first lens (2) and the image sensor (8) are respectively provided with a protective window sheet (1) and a protective glass sheet (7); and the object side surface and the image side surface of the protective window sheet (1) and the protective glass sheet (7) are both planes.

7. The wide-angle endoscope lens of claim 6, wherein, The Mohs hardness of the protective window sheet (1) is greater than 8, and the protective window sheet (1) is made of Al2O3 glass material.

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