Endoscope imaging objective lens with focusing function and focusing method

Abstract

The present invention discloses a focusing method for an imaging objective lens, wherein a wedge prism group for focusing is added to the imaging objective lens, wherein the wedge prism group comprises two wedge prisms with the same wedge angle and parallel inclined surfaces, wherein the wedge angle α satisfies 60°≤α≤85°, and the two wedge prisms can move relative to each other along the inclined surface direction, thereby changing the distance that light passes through the wedge prism group and realizing continuous focusing of the optical path. The focusing method of the present invention is simple and easy to implement, and occupies little space, which is conducive to the miniaturization of the overall endoscope body.

Description

Technical Field

[0001] The present invention relates to the field of medical endoscopes, and in particular to an endoscope imaging objective lens with a focusing function and a focusing method. Background Art

[0002] The medical endoscope is a commonly used medical device. It enters the body through natural orifices or through small surgical incisions. When used, the endoscope is inserted into the organ being examined, allowing direct observation of changes in the affected area. The clearer the visualization of localized lesions during surgery, the easier it is for doctors to accurately diagnose the condition and perform the surgery. The quality of medical endoscope images directly determines the effectiveness of the endoscope and signals the advancement of endoscopic technology.

[0003] In recent years, the image quality of camera components has significantly improved, with HD, Full HD, and 4K camera systems being released one after another. Currently, most medical electronic endoscopes use fixed-focus lenses, such as those described in patents CN110651213A and CN101507596A. For fixed-focus lenses, the depth range (i.e., depth of field) that can be clearly observed is determined by the lens's aperture value (hereinafter referred to as "Fno"). A larger Fno value increases the depth of field, but this, in turn, reduces the image resolution. A larger Fno value reduces the amount of light entering the endoscope's camera system, resulting in a poorer image signal. To achieve high-definition image quality, the lens's Fno value must be further reduced. However, this reduction in Fno narrows the depth of field. Medical electronic endoscopes require both long-range observation to locate disease sites and close-up identification of pathological features and surgical procedures. Therefore, fixed-focus lenses cannot achieve both high-definition image quality and a large depth of field.

[0004] To address the conflict between high-resolution, high-definition image quality and a large depth of field, various focusing endoscope imaging lens designs have been proposed in recent years. Patent CN105717626A states that observation of both far and near points can be achieved by moving the position of lens group CE2. Patent CN105899994A states that observation of both far and near points can be achieved by moving the position of lens L3. However, in these and similar patents, observation of both far and near points is achieved by driving a group of lenses back and forth. In the process of driving the lens to move, a certain degree of clearance must be maintained between the moving and fixed components to ensure smooth lens movement. Therefore, as the focusing lens moves along the optical axis, it is prone to becoming eccentric relative to the optical axis. In particular, with the advancement of higher-pixel imaging components in recent years, image quality degradation caused by lens eccentricity errors has become more pronounced.

[0005] In order to further solve the problem of image quality degradation caused by the decentration of the lens of the endoscope focusing lens. Patent CN104054013A uses a set of arm components to switch a flat glass and a focusing lens with optical power to achieve focusing at different working distances. Although this patent partially solves the image quality degradation caused by the decentration of the focusing lens during the focusing process, if the optical axis of the focusing lens does not coincide with the optical axis of the objective lens during the insertion of the focusing lens, the problem of image quality degradation will still exist. Therefore, the focusing mechanism has extremely high requirements for mechanical precision. In addition, the switching device takes up a lot of space, which is not conducive to the miniaturization of the outer diameter of the endoscope head. Moreover, this design can only achieve focusing at two positions, the near point and the far point, and cannot achieve a continuous focusing process.

[0006] In summary, the current designs of endoscope objectives have the following problems. Fixed-focus lenses cannot simultaneously meet the requirements of high-quality images and a large depth of field for observation in current endoscopes. The current dual-focus imaging objective design has solved the requirements of large depth of field and high resolution to a certain extent, but there is a problem of image quality degradation caused by the eccentricity of optical elements due to the structural gap during focusing. The device for switching optical elements in the optical path of the arm component also has the problem of image quality degradation to a certain extent due to the misalignment between the center of the focusing lens and the center of the objective lens. The arm component structure occupies a large space, which is not conducive to the miniaturization of the endoscope. Moreover, the structure can only achieve focusing at two positions, the near point and the far point. There may be a problem that the observation depth of the near point and the far point cannot fully cover the depth of field range. Summary of the Invention

[0007] The main purpose of the present invention is to provide an endoscope imaging objective lens with a focusing function and a focusing method, which can meet the requirements of large depth of field and high resolution while being able to focus continuously.

[0008] The technical solution adopted in the present invention is:

[0009] Provided is a focusing method for an imaging objective lens. A wedge prism group for focusing is added to the imaging objective lens. The wedge prism group includes two wedge prisms with the same wedge angle and parallel inclined surfaces, wherein the wedge angle α satisfies 60°≤α≤85°. The two wedge prisms can move relative to each other along the inclined surface to change the distance that light passes through the wedge prism group, thereby achieving continuous focusing of the optical path.

[0010] Following the above technical solution, the wedge prism group is placed between the last lens of the imaging objective lens and the image sensor.

[0011] Following the above technical solution, the wedge prism group is placed between any two optical components in the imaging objective lens.

[0012] Following the above technical solution, one of the wedge-shaped prisms in the wedge-shaped prism group is fixed in position, and the other wedge-shaped prism can move along the oblique direction.

[0013] The present invention also provides an application of the above imaging objective lens focusing method, which is applied to an endoscope.

[0014] The present invention also provides an endoscope imaging objective lens, which is provided with a wedge prism group for focusing. The wedge prism group includes two wedge prisms with the same wedge angle and parallel inclined surfaces, wherein the wedge angle α satisfies 60°≤α≤85°, and the two wedge prisms can move relative to each other along the inclined surface direction.

[0015] Continuing with the above technical solution, the endoscope imaging objective lens also includes a plane lens L1 from the object side to the image side, a first lens group G1 with negative optical focal length, a double flat lens, a second lens group G2 with positive optical focal length, and a third lens group G3 with positive optical focal length. The wedge prism group is placed between the first lens group G1 and the second lens group G2, or between the second lens group G2 and the third lens group G3, or between the third lens group G3 and the image sensor.

[0016] Following the above technical solution, the first lens group G1 includes a meniscus lens L2 with negative optical power and a plano-concave lens L3 with negative optical power, and black light-absorbing materials are provided between the meniscus lens L2 and the plano-concave lens L3 and between the plano-concave lens L3 and the double plano lens.

[0017] Following the above technical solution, an aperture stop made of black light-shielding material is provided between the double flat lens and the second lens group G2.

[0018] The present invention achieves the following beneficial effects: by adding a wedge prism assembly for focusing within the imaging objective lens, the present invention achieves continuous focusing of the optical path by adjusting the distance light travels through the assembly by adjusting two wedge prisms within the assembly. Since no lens deviates from the optical axis during the focusing process, image quality degradation is avoided. The present invention's focusing method is simple and easy to implement, occupies little space, and facilitates the miniaturization of the entire endoscope body. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0020] FIG1( a ) is a diagram illustrating the focusing principle of an imaging objective lens according to an embodiment of the present invention when focusing at a near observation point;

[0021] FIG1( b ) is a diagram showing the focusing principle of the imaging objective lens according to an embodiment of the present invention when focusing at a far observation point;

[0022] Figure 2 1 is a schematic structural diagram of an imaging objective lens according to an embodiment of the present invention;

[0023] Figure 3 1 is a schematic structural diagram of an endoscope imaging objective lens according to an embodiment of the present invention;

[0024] Figure 4 is a schematic structural diagram of an endoscope imaging objective lens according to another embodiment of the present invention;

[0025] Figure 5 is the modulation degree of the imaging objective lens in one embodiment of the present invention;

[0026] Figure 6 Schematic diagram of the imaging object image field in one embodiment of the present invention. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0028] In the actual propagation process of light, the distance d that light travels through the flat glass with a refractive index of n is 0’ Equivalent to the propagation distance d0 of light in the air. The relationship between the two is d0 = d 0’ / n. As shown in Figure 1(a), when the imaging objective lens is focused at a near observation point, the distance between the image sensor CMOS and the last lens is L = d1 + d2 + d3, which is converted to the corresponding back focal length Lo = d1 + d3 + d2 / n2, where n2 is the refractive index of the flat glass; as shown in Figure 1(b), when the imaging objective lens is focused at a far observation point, the distance between the CMOS and the back surface of the last lens is L' = d1' + d3' + d2', and the corresponding back focal length is L O ' = d1' + d3' + d2' / n2, where n2 is the refractive index of the flat glass. It can be seen that by maintaining the physical distance L = L' constant, varying the thickness of the inserted flat glass allows focusing at different working distances of the imaging lens.

[0029] Based on the above focusing principle, Figure 2An embodiment provides a focusing method for an imaging objective lens, wherein the position of the imaging objective lens and the position of the image sensor remain fixed, and the imaging objective lens is provided with a focusing prism group within a back focus range, the prism group including two prisms, P1 and P2, with an air gap d between the two prisms. Prisms P1 and P2 are both wedge-shaped prisms, and the inclined surfaces of the two prisms are arranged adjacently and parallel to each other, and the two prisms can move relative to each other. The wedge angles of the two wedge-shaped prisms are consistent, and the wedge angle α satisfies 60°≤α≤85°. The wedge angle α is the angle between the wedge surface and the horizontal. If α is less than 60°, the light's exit angle on one wedge surface and the incident angle on the other wedge surface are both large. From an optical performance perspective, as the incident angle or exit angle increases at the interface between two media with different refractive indices, the reflected light at the interface between the two media will significantly increase. The reflected light that increases with the incident angle at the interface between the two media will cause a reduction in the transmitted light, affecting the brightness of the image. In addition, the reflected light will also form stray light, causing image degradation. If α>85°, to achieve the same focusing distance, the distance the wedge needs to move is too long, which is not conducive to the application of miniaturization of endoscopes.

[0030] In this embodiment, P1 is a moving prism, and P2 is a fixed prism. During focusing, by moving prism P1 along the X direction (more precisely, along the oblique surface), while maintaining the distance d between the two prisms constant, the thickness of prism P1 entering the optical path changes, thereby achieving objective lens focusing. In this embodiment of the present invention, 0.1mm < d < 2mm is preferred.

[0031] The wedge prism assembly can be placed between the last lens element of the imaging objective and the image sensor, making it easier to focus various objectives. The wedge prism assembly can also be placed between any two optical components in the imaging objective. Although the design is more complex, it can also achieve continuous focus.

[0032] In this embodiment, since the relative positions of the imaging objective lens assembly and the image sensor CMOS are fixed, adjusting prism P1 during focusing is equivalent to switching the thickness of the parallel plate glass. Since no lens deviates from the optical axis, image quality degradation is prevented. Precisely controlling the movement of P1 allows for continuous focusing at varying observation distances. This demonstrates the simplicity and ease of implementation of the present invention, the compact size of the endoscope, and its overall miniaturization.

[0033] The focusing method of the imaging objective lens can be applied to various endoscopes, such as electronic laparoscopes.

[0034] like Figure 3As shown, a wedge prism group for focusing is provided inside the endoscope imaging objective lens according to an embodiment of the present invention. The wedge prism group includes two wedge prisms P1 and P2 with the same wedge angle and parallel inclined surfaces. The wedge angle α satisfies 60° ≤ α ≤ 85°. The two wedge prisms can move relative to each other along the inclined surface direction, and the focusing function of the optical path is achieved through the relative movement of the two wedge prism groups. In the embodiment of the present invention, the thickness of the thinnest part of the wedge prism is greater than or equal to 0.4 mm.

[0035] As Figure 3 shown, the endoscope imaging objective lens further includes a plano-lens L1 from the object side to the image side, a first lens group G1 with a negative optical power, a double plano-lens L4, a second lens group G2 with a positive optical power, and a third lens group G3 with a positive optical power. The wedge prism group is placed between the first lens group G1 and the second lens group G2, or between the second lens group G2 and the third lens group G3, or between the third lens group G3 and the image sensor. As Figure 3 shown in the embodiment, the wedge prism group is placed between the third lens group G3 and the image sensor. Among them, the L1 lens is a sapphire protection window with high hardness and scratch resistance. G1 is a lens group with a negative optical power, and its main function is to reduce the projection angle of incident light with a high field angle onto the subsequent plano-lens L4, achieving a large field angle. L4 is a double plano-lens, and its main function is to replace the prism with a steering function in the optical path of the objective lens, realizing the material sharing of the 0-degree viewing direction objective lens and the 30-degree viewing direction objective lens except for the prism.

[0036] Among them, the first lens group G1 includes a meniscus lens L2 with a negative optical power and a plano-concave lens L3 with a negative optical power, and black light-absorbing materials are provided between the meniscus lens L2 and the plano-concave lens L3, and between the plano-concave lens L3 and the double plano-lens.

[0037] An aperture stop made of black light-shielding material is provided between the double plano-lens L4 and the second lens group G2.

[0038] The focal length of the entire imaging objective lens is f, and the image height corresponding to the imaging lens is h. The length d4 of the double plano-lens L4 satisfies 0.7 * f * h < d4 < 1.2 * f * h. The focal length f and the image height h are related to the parameters of the image sensor used in the endoscope. In the embodiment of the present invention: 2 mm < f < 2.5 mm, 1.2 mm < h < 1.8 mm.

[0039] As Figure 4 shown, the double plano-lens L4 can be converted into a 30-degree deflection prism with an equal optical path to achieve the conversion of the observation viewing angle. Through the deflection of the optical axis, objects outside the field of view directly in front of the endoscope body can be observed, improving the observation range.

[0040] The plano-lens L1 can be selected as a sapphire plano-lens, which has the characteristics of high hardness, scratch resistance, and good chemical stability.

[0041] The meniscus lens L2 has a negative optical power f2, the plano-concave lens L3 has a negative optical power f3, and the first lens group G1 composed of the meniscus lens L2 and the plano-concave lens L3 has a negative optical power f G1 Among them: 1.9<|f2 / f|<2.8; 2.5<|f3 / f|<3.2; 1.3<|f G1 / f|<1.5.

[0042] The second lens group G2 includes lens L5 and lens L6, which are glued together by optical glue. The second lens group G2 has a positive optical power f G2 , and 2.5<f G2 / f<3.0.

[0043] The third lens group G3 includes lenses L7, L8, and L9. L8 and L9 are glued together with optical glue. The third lens group G3 has a positive optical power f G3 , and 2.9<f G3 / f<3.2.

[0044] Black light-absorbing material J1 is set between the meniscus lens L2 and the plano-concave lens L3, and black light-absorbing material J2 is set between the plano-concave lens L3 and the biplanar lens L4. The arrangement of J1 and J2 achieves the purpose of eliminating stray light. An aperture stop (Stop) made of black light-shielding material is also set between the biplanar lens L4 and the second lens group G2. The aperture stop is a light hole that selects the light beam to pass through. The area outside the light hole is black. The aperture stop is a hole that limits the size of the incident light beam. The size of the aperture stop can improve the resolution, light transmission capacity and depth of field of the imaging lens. The aperture stop hole diameter in this patent ranges from 0.6mm to 1.3mm.

[0045] The lens structure and optical path of the objective lens for an endoscope in an embodiment of the present invention are shown in Figure 1(b). Table 1 shows the basic lens data of the objective lens for an endoscope in this embodiment. In the surface column of Table 1, the surface on the object side of the structural element is the first, and the number of the i-th (i=1, 2, 3, ...) surface increases in sequence as it approaches the image side. The R column represents the curvature radius of the i-th surface, and the d column represents the surface interval on the optical axis Z between the i-th surface and the i+1-th surface. In addition, the Nd column represents the refractive index related to the d-line (wavelength 587.6nm) of the j-th (j=1, 2, 3, ...) optical element closest to the object side as the first, and the j-th (j=1, 2, 3, ...) optical element increases in sequence as it approaches the image side. The νd column represents the Abbe number of the d-line reference of the j-th optical element. The sign of the radius of curvature is positive when the surface shape is convex toward the object side, and negative when it is convex toward the image side. The value at the bottom of the column for the surface spacing is the surface spacing between the surface closest to the image side and the image plane shown in the table on the optical axis Z. The basic lens data also includes the aperture stop.

[0046] Table 1: Basic lens data for endoscope objective lenses

[0047] surface R d Nd Vd 1 Infinity 1.0 1.7682 72.2372 2 Infinity 0.2 3 35.87 1.0 1.5639 60.7914 4 2.54 0.69 5 infinity 1.0 1.8348 42.7432 6 6.47 0.289 7 infinity 6.0 1.8348 42.7432 stop infinity 0.08 10 72.40 1.16 1.8041 46.5677 11 -8.06 1.0 1.7170 47.9202 12 -5.28 5.076 13 42.78 2.0 1.5639 60.7914 14 -5.41 0.083 15 7.11 1.82 1.4565 90.2697 16 -4.18 1.67 1.8467 23.787 17 -19.04 0.4 18 infinity 4.0 1.9108 35.2557 19 infinity 0.355 20 infinity 0.4 1.5168 64.2124 Image plane infinity 0.045

[0048] Table 2 shows, as data items, the focal length f' of the entire system, FNo., and the full angle of view 2ω (unit: degree).

[0049] Table 2: Lens parameters

[0050] f’ 2.3712 FNo 5.4 2ω 80°

[0051] In the above tables, degrees are used as the unit of angle and mm is used as the unit of length. However, other appropriate units may be used to enable the optical system to be used even when scaled up or scaled down.

[0052] like Figure 5 、 Figure 6 As shown, the endoscope of the present invention has excellent optical performance. The optical transfer function reaches 200 lp / mm at a modulation index of 0.3 within 70% of the field of view. The field curvature is less than 0.03mm, meeting the requirements of high-definition electronic laparoscopes.

[0053] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all such improvements and changes should fall within the scope of protection of the appended claims of the present invention.

Claims

1. An endoscope imaging objective lens, characterized in that: The endoscope imaging objective lens includes a plane lens L1 from the object side to the image side, a first lens group G1 with negative optical power, a double flat lens L4, a second lens group G2 with positive optical power, and a third lens group G3 with positive optical power; The endoscope imaging objective lens also includes a wedge prism group for focusing, which is placed between the first lens group G1 and the second lens group G2, or between the second lens group G2 and the third lens group G3, or between the third lens group G3 and the image sensor; Among them, the double plane lens L4 is used to replace the optical path of the prism with a steering function in the objective lens, so that the 0-degree viewing objective lens and the 30-degree viewing objective lens can share materials other than the prism; The wedge prism group comprises two wedge prisms with the same wedge angle and parallel inclined surfaces, wherein the wedge angle α satisfies 60°≤α≤85°, and the two wedge prisms can move relative to each other along the inclined surface direction; The length d4 of the biplanar lens L4 is 6 mm, and the refractive index is 1.8348; The refractive index of the plane lens L1 is 1.7682; The meniscus lens L2 has a negative focal power f2 and a refractive index of 1.5639; the plano-concave lens L3 has a negative focal power f3 and a refractive index of 1.8348; the first lens group G1 composed of the meniscus lens L2 and the plano-concave lens L3 has a negative focal power f G1 ; The second lens group G2 includes lens L5 and lens L6. The refractive index of lens L5 is 1.8041, and the refractive index of lens L6 is 1.7170. The two are glued together by optical glue. The second lens group G2 has a positive optical power f G2 ; The third lens group G3 includes lenses L7, L8, and L9. L8 and L9 are glued together by optical glue. The refractive index of lens L7 is 1.5639, the refractive index of L8 is 1.4565, and the refractive index of lens L9 is 1.8467. The third lens group G3 has a positive optical power f G3 .

2. The endoscope imaging objective lens according to claim 1, characterized in that: The first lens group G1 includes a meniscus lens L2 with negative optical power and a plano-concave lens L3 with negative optical power, and black light absorbing materials are disposed between the meniscus lens L2 and the plano-concave lens L3 and between the plano-concave lens L3 and the double plano lens.

3. The endoscope imaging objective lens according to claim 1, characterized in that: An aperture stop made of black light-shielding material is provided between the double flat lens and the second lens group G2.

4. The endoscope imaging objective lens according to claim 1, characterized in that: One of the wedge prisms in the wedge prism group is fixed in position, and the other wedge prism can move along the inclined surface direction.

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