Endoscope objective optical system

Abstract

The utility model provides a kind of endoscope objective optical system, it is related to optical lens technical field, the endoscope objective optical system includes from object side sequentially including diaphragm front group 1 of negative optical power, diaphragm STO, diaphragm rear group 2 of positive optical power, light splitting prism G2, diaphragm front group 1 includes protection glass P1, first lens L1 of negative optical power and view direction prism G1;Four lenses are used to constitute endoscope objective optical system, the optical performance and length of diaphragm front and rear lens are controlled, long back focus is realized while, effectively reduce objective volume, sufficient installation space is reserved for light splitting prism, third lens and fourth lens combination form double cemented lens, in combination with the refractive index, abbe number etc. Parameter design of each lens specific, can effectively correct chromatic aberration caused by wide spectral working band and aberration caused by reducing objective size, reduce the number of lenses, ensure that imaging is clear.

Description

Technical Field

[0001] This utility model relates to the field of optical lens technology, specifically an endoscope objective lens optical system. Background Technology

[0002] Endoscopes have a wide range of applications in the medical field. With the development of medical equipment and related technologies, the requirements for the imaging performance and structural dimensions of endoscopes have also increased. To achieve routine tissue observation and precise lesion identification, and improve the comprehensiveness and accuracy of diagnosis, the working wavelength of endoscopes can be extended to the near-infrared. A beam splitter is used to divide the beams into different wavelengths, and multiple sensors are used to detect the images formed by these beams. Algorithms are then used to fuse the images to obtain a multi-detailed image. The beam splitter is placed between the objective lens and the detector. The objective lens needs to have sufficient back focal length to ensure that the beams do not interfere with each other or are blocked by the reflective surface of the beam splitter. Simultaneously, when surgical robots are used with endoscopes, the endoscope's aperture needs to be sufficiently small to ensure that the image acquisition channel and instrument channel diameters are consistent, reducing the number and area of ​​incisions and improving the flexibility and precision of minimally invasive surgery. Furthermore, the chromatic aberration caused by the wide-spectrum working wavelength of the endoscope, as well as the aberrations caused by reducing the size of the objective lens and the number of lenses, also need to be corrected to obtain clear images.

[0003] The invention patent with patent application number CN201780041707.9 provides an objective lens optical system in which the front group of the aperture diverges the beam and the rear group of the aperture converges the beam. By controlling the ratio of the length to the focal length of each lens group, the length and aperture of the objective lens are reduced. However, the focal lengths of the positive single lens and the positive cemented lens in the rear group of the aperture are too close, and the beam gradually converges, resulting in a short back focal length, which does not leave enough space to place a beam splitter.

[0004] The invention patent with patent application number CN201880083484.7 provides an objective lens optical system that corrects aberrations and chromatic aberrations by controlling the material and focal length of key lenses, reduces the length of the objective lens, and takes into account the length of the back focal length by selecting an anti-telephoto structure. However, the overall focal length of the objective lens system is relatively small, and the increase in back focal length is limited.

[0005] The invention patent with patent application number 200710005250.4 uses a similar objective lens optical system to make the back focal length about 3 times the focal length, reserving enough length for configuring a beam splitter. However, the working wavelength of the objective lens system is visible light, and its aberration and chromatic aberration correction is completed in the visible light band, and the distortion is still relatively large, which is not conducive to the practical use of the objective lens. Utility Model Content

[0006] The purpose of this invention is to provide an endoscope objective optical system that addresses the problems in the prior art.

[0007] To achieve the above objectives, one embodiment of the present invention provides an endoscope objective optical system, which, from the object side, sequentially includes a front aperture group 1 with negative optical power, an aperture STO, a rear aperture group 2 with positive optical power, and a beam splitter G2. The front group of the aperture 1 includes a protective glass P1, a first lens L1 with negative optical power, and a viewing prism G1; The rear group 2 of the aperture includes a second lens L2 with positive optical power, a third lens L3 with positive optical power, and a fourth lens L4 with negative optical power. The third lens L3 and the fourth lens L4 are combined to form a cemented doublet with positive optical power. The relationship between the pre-aperture group 1 and the post-aperture group 2 satisfies the following condition: 2.9≤BFL / EFL≤3.2, 1.1≤fL2 / EFL≤1.4, 3.5≤s1 / imgH≤4.5; Where EFL is the focal length of the optical system, BFL is defined as the distance from the image side of the fourth lens to the image plane, fL2 is the focal length of the second lens L2, s1 is the length of the front group 1 of the aperture stop, and imgH is the maximum image height.

[0008] Preferably, the maximum height h of the 0.8 field ray on the image side of the fourth lens L4 satisfies: 0.11≤h / BFL≤0.13.

[0009] Preferably, the maximum height h' of the 0.64 field ray on the image side of the fourth lens L4 satisfies 0.10≤h' / BFL≤0.12.

[0010] Preferably, the image-side surface of the first lens L1 is concave; The object-side surface of the second lens L2 is convex, and the image-side surface is also convex. The object-side surface of the third lens L3 is concave, and the image-side surface is convex. The object side of the fourth lens L4 is concave, and the image side is convex.

[0011] Preferably, the refractive index ND1 of the first lens L1 satisfies: 1.7 ≤ ND1 ≤ 1.9; The refractive index ND2 of the second lens L2 satisfies: 1.7 ≤ ND4 ≤ 1.9; The refractive index ND4 of the fourth lens satisfies: 1.9≤ND4≤2.0.

[0012] Preferably, the Abbe number VD2 of the second lens L2 satisfies: 22≤VD2≤27; The Abbe number VD3 of the third lens L3 and the Abbe number VD4 of the fourth lens L4 satisfy: 35≤VD3-VD4≤57.

[0013] Preferably, the focal length fL1 of the first lens L1 satisfies: -0.65≤fL1 / EFL≤-0.68.

[0014] Preferably, the object-side radius of curvature R1 and the image-side radius of curvature R2 of the third lens L3 satisfy: 2.2≤R1 / R2≤3.6.

[0015] Preferably, the viewing prism G1 is a single prism or a combination of multiple sub-prisms, which deflects the light beam through surface reflection or transmission of the sub-prisms, and the deflection angle of the light beam is the viewing angle.

[0016] Preferably, the beam splitter G2 is a combination of one prism or multiple sub-prisms. The beam is separated into different wavelengths by surface reflection or transmission of the sub-prisms. The separated beams are imaged on different sensors and fused by an algorithm to form an image. The beam splitter G2 separates the beam into white light and near-infrared light.

[0017] Compared with the prior art, the beneficial effects of this utility model are: 1. The endoscope objective lens optical system is constructed using four lenses. By controlling the optical performance and length of the lenses before and after the aperture stop, a long back focal length is achieved while effectively reducing the size of the objective lens, leaving ample installation space for the beam splitter.

[0018] 2. The third and fourth lenses are combined to form a cemented doublet. The design incorporates the specific refractive index, Abbe number and other parameters of each lens, which can effectively correct chromatic aberration caused by the wide spectrum of working wavelengths and aberrations caused by reducing the size of the objective lens and the number of lenses, ensuring clear imaging. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the optical structure of Embodiment 1 of the present invention.

[0020] Figure 2 This is the field curve of Embodiment 1 of this utility model.

[0021] Figure 3 This is the distortion curve of Embodiment 1 of this utility model.

[0022] Figure 4 This is the vertical color difference curve of Embodiment 1 of this utility model.

[0023] Figure 5 This is a schematic diagram of the optical structure of Embodiment 2 of this utility model.

[0024] Figure 6 This is the field curve of Embodiment 2 of this utility model.

[0025] Figure 7 This is the distortion curve of Embodiment 2 of this utility model.

[0026] Figure 8 This is the vertical color difference curve of Embodiment 2 of this utility model.

[0027] Figure 9 This is a table of optical structure parameters for Embodiment 1 of this utility model.

[0028] Figure 10 This is a table of optical structure parameters for Embodiment 2 of this utility model.

[0029] Figure 11 The table shows the relevant performance parameters for Embodiment 1 and Embodiment 2 of this utility model.

[0030] In the diagram: 1. Front group of the aperture; P1. Protective glass; L1. First lens; G1. Viewing prism; 2. Rear group of the aperture; L2. Second lens; L3. Third lens; L4. Fourth lens; STO. Aperture stop; G2. Beam splitter. Detailed Implementation

[0031] The present invention will now be further described with reference to the accompanying drawings.

[0032] Example 1: As Figures 1 to 4 , Figure 9 and Figure 11 As shown, an endoscope objective optical system includes, from the object side, a front aperture group 1 with negative optical power, an aperture STO, a rear aperture group 2 with positive optical power, and a beam splitter G2. The front group 1 of the aperture includes a protective glass P1, a first lens L1 with negative optical power, and a viewing prism G1. The rear group 2 of the aperture includes a second lens L2 with positive optical power, a third lens L3 with positive optical power, and a fourth lens L4 with negative optical power. The third lens L3 and the fourth lens L4 are combined to form a cemented doublet with positive optical power.

[0033] The focal length EFL of the optical system and the back focal length BFL, the distance from the image side of the fourth lens L4 to the image plane IMA, satisfy 2.9 ≤ BFL / EFL ≤ 3.2. The beam splitter G2 is placed between the fourth lens L4 and the image plane IMA. Limiting this condition to the upper limit avoids an excessively long optical system that is impractical and reduces design complexity; limiting it to the lower limit provides sufficient space for the beam splitter G2, preventing insufficient optical path length for imaging and avoiding the disadvantage of using high-refractive-index materials to lengthen the optical path, which introduces aberrations and increases costs.

[0034] The focal length of the second lens L2 satisfies 1.1 ≤ fL2 / EFL ≤ 1.4. The optical power of the second lens L2 is positive, and it is the lens closest to the aperture stop STO in the rear group 2, converging light rays. Limiting this conditional expression to its upper limit helps improve the light-converging ability of the second lens L2, reduces the refractive force of the cemented doublet composed of the third lens L3 and the fourth lens L4, reduces the radial height of light rays exiting the fourth lens L4, and prevents light rays from being blocked by the reflecting surface of the beam splitter G2 when deflected. Limiting this conditional expression to its lower limit prevents the second lens L2 from excessively converging light rays, which could lead to aberrations.

[0035] The length s1 of the front group 1 of the aperture stop and the maximum image height imgH satisfy 3.5≤s1 / imgH≤4.5. The first lens L1 has a negative optical power and collects light. It usually has the largest aperture among lenses with optical power. The protective glass P1 is located on the object side of the first lens L1 and usually has the largest aperture in the entire endoscopic optical system. This condition restricts the condition from exceeding the upper limit. The length of the front group 1 of the aperture stop is limited by the maximum image height imgH, so that the incident pupil is close to the first lens L1. With a fixed field of view, the radial height of the light in the first lens L1 is reduced, thereby reducing the radial height of the light at the protective glass P1. This condition restricts the condition from exceeding the lower limit, leaving enough space for the viewing prism.

[0036] The maximum height h of the 0.8 field-of-view ray on the image side of the fourth lens L4 satisfies: 0.11≤h / BFL≤0.13. After exiting the image side of the fourth lens L4, the ray enters the beam splitter G2. A 1 field of view refers to a maximum image height of 1.3mm, and a 0.8 field of view refers to an image height of 1.04mm. This is because when the sensor size is 4:3, the maximum image height is taken diagonally, and the half-image height of the longer side is 1.04mm; if the sensor size is 16:9, the maximum image height is taken diagonally, and the half-image height of the longer side is 0.83mm, i.e., a 0.64 field of view. In this case, the maximum height h' of the 0.64 field-of-view ray on the image side of the fourth lens satisfies 0.10≤h' / BFL≤0.12. Limiting this condition to the upper limit reduces the aperture of the beam entering the beam splitter G2, preventing the beam from being blocked by the prism's reflecting surface. Limiting this condition to the lower limit prevents aberrations caused by excessively large ray angles.

[0037] The image side of the first lens L1 is concave. The focal length fL1 of the first lens L1 satisfies: -0.65≤fL1 / EFL≤-0.68. The refractive index ND1 of the first lens L1 satisfies: 1.7≤ND1≤1.9. The first lens collects light and has a large refractive force. Therefore, a high refractive index material is selected to avoid excessive surface curvature, which would lead to more aberrations.

[0038] The object side of the second lens L2 is convex, and the image side is also convex. The refractive index ND2 of the second lens L2 satisfies: 1.7≤ND2≤1.9, and the Abbe number VD2 of the second lens L2 satisfies: 22≤VD2≤27. Using a high refractive index and low Abbe number material reduces surface curvature, thereby reducing spherical aberration and transverse chromatic aberration.

[0039] The object-side surface of the third lens L3 is concave, and the image-side surface is convex. The radius of curvature R1 of the object-side surface and R2 of the image-side surface of the third lens L3 satisfy: 2.2 ≤ R1 / R2 ≤ 3.6. This controls the lens thickness. The object side of the fourth lens L4 is concave, and the image side is convex. The refractive index ND4 of the fourth lens satisfies: 1.9≤ND4≤2.0. High refractive index material is used to reduce surface curvature, and a meniscus shape is adopted to reduce field curvature.

[0040] The combination of the third lens L3 and the fourth lens L4 forms a cemented doublet with positive optical power. The Abbe number VD3 of the third lens L3 and the Abbe number VD4 of the fourth lens L4 satisfy: 35≤VD3-VD4≤57. Chromatic aberration is corrected by using the two lenses with larger Abbe number aberrations.

[0041] The viewing prism G1 is a combination of one prism or multiple sub-prisms. The beam is deflected by reflection or transmission through the surface of the sub-prism. The deflection angle of the beam is the viewing angle. By using different viewing angles, the user can observe a larger range.

[0042] The beam splitter G2 is a combination of one prism or multiple sub-prisms. It separates the light beam into different wavelengths through surface reflection or transmission of the sub-prisms. The separated light beams are imaged on different sensors and fused by an algorithm to form an image. The beam splitter G2 separates the light beam into white light and near-infrared light. White light imaging simulates the effect of observation by the naked eye, while near-infrared light imaging highlights lesions with specific markings, i.e., fluorescence imaging.

[0043] in Figure 2 This demonstrates that the sagittal field curvature of Example 1 is less than 0.1 mm, and the meridional field curvature is less than 0.01 mm. Figure 3 This demonstrates that the distortion in Example 1 is less than 20%. Figure 4 The example demonstrates that the visible light vertical axis chromatic aberration is less than 1µm and the near-infrared light vertical axis chromatic aberration is less than 4µm, with aberrations and chromatic aberrations corrected.

[0044] Example 2: Figures 5-8 , Figure 10 and Figure 11 Based on Example 1, the curvature radius and thickness of the first lens L1, the viewing prism G1, the second lens L2, the third lens L3, the fourth lens L4, the beam splitter G2, the aperture stop STO, and the filter are changed, thereby altering the refractive index and other properties. Figure 6The example shows that the sagittal field curvature is less than 0.1 mm and the meridional field curvature is less than 0.02 mm. Figure 7 This demonstrates that the distortion in Example 1 is less than 20%. Figure 8 The example demonstrates that the visible light vertical axis chromatic aberration is less than 1µm and the near-infrared light vertical axis chromatic aberration is less than 4µm, with aberrations and chromatic aberrations corrected.

[0045] It will be apparent to those skilled in the art that this invention is not limited to the details of the exemplary embodiments described above, and that it can be implemented in other specific forms without departing from the spirit or essential characteristics of this invention. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of this invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within this invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0046] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. An endoscope objective optical system characterized by comprising: Starting from the object side, the optical diaphragm includes, in sequence, front group 1 with negative optical power, diaphragm STO, rear group 2 with positive optical power, and beam splitter G2. The front group of the aperture 1 includes a protective glass P1, a first lens L1 with negative optical power, and a viewing prism G1; The rear group 2 of the aperture includes a second lens L2 with positive optical power, a third lens L3 with positive optical power, and a fourth lens L4 with negative optical power. The third lens L3 and the fourth lens L4 are combined to form a cemented doublet with positive optical power. The relationship between the pre-aperture group 1 and the post-aperture group 2 satisfies the following condition: 2.9≤BFL / EFL≤3.2, 1.1≤fL2 / EFL≤1.4, 3.5≤s1 / imgH≤4.5; Where EFL is the focal length of the optical system, BFL is defined as the distance from the image side of the fourth lens to the image plane, fL2 is the focal length of the second lens L2, s1 is the length of the front group 1 of the aperture stop, and imgH is the maximum image height.

2. An endoscope objective optical system according to claim 1, characterized by The maximum height h of the 0.8 field ray on the image side of the fourth lens L4 satisfies: 0.11≤h / BFL≤0.

13.

3. An endoscope objective optical system according to claim 2, characterized by The maximum height h' of the 0.64 field ray on the image side of the fourth lens L4 satisfies 0.10≤h' / BFL≤0.

12.

4. An endoscope objective optical system according to claim 3, characterized by The image-side surface of the first lens L1 is concave; The object-side surface of the second lens L2 is convex, and the image-side surface is also convex. The object-side surface of the third lens L3 is concave, and the image-side surface is convex. The object side of the fourth lens L4 is concave, and the image side is convex.

5. An endoscope objective optical system according to claim 4, characterized in that, The refractive index ND1 of the first lens L1 satisfies: 1.7 ≤ ND1 ≤ 1.9; The refractive index ND2 of the second lens L2 satisfies: 1.7 ≤ ND4 ≤ 1.9; The refractive index ND4 of the fourth lens satisfies: 1.9≤ND4≤2.

0.

6. An endoscope objective optical system according to claim 5, characterized in that, The Abbe number VD2 of the second lens L2 satisfies: 22≤VD2≤27; The Abbe number VD3 of the third lens L3 and the Abbe number VD4 of the fourth lens L4 satisfy: 35≤VD3-VD4≤57.

7. An endoscope objective optical system according to claim 6, characterized in that, The focal length fL1 of the first lens L1 satisfies: -0.65≤fL1 / EFL≤-0.

68.

8. An endoscope objective optical system according to claim 7, characterized in that, The object-side curvature radius R1 and the image-side curvature radius R2 of the third lens L3 satisfy: 2.2≤R1 / R2≤3.

6.

9. An endoscope objective optical system according to claim 8, characterized in that, The viewing prism G1 is a single prism or a combination of multiple sub-prisms. The beam is deflected by reflection or transmission through the surface of the sub-prisms, and the deflection angle of the beam is the viewing angle.

10. An endoscope objective optical system according to claim 9, characterized in that, The beam splitter G2 is a combination of one prism or multiple sub-prisms. It separates the light beam into different wavelengths through surface reflection or transmission of the sub-prisms. The separated light beams are imaged on different sensors and fused by an algorithm to form an image. The beam splitter G2 also separates the light beam into white light and near-infrared light.

Images