Automatic focusing optical imaging system based on liquid lens

Abstract

The invention discloses an automatic focusing optical imaging system based on a liquid lens, which comprises a first lens group, a diaphragm, a second lens group, cover plate glass and a CMOS (Complementary Metal-Oxide-Semiconductor Transistor) photosensitive surface which are sequentially arranged from left to right along a light incidence direction, and is characterized in that the first lens group comprises a first lens, a second lens and a third lens, the first lens and the second lens have positive diopters, the object side is convex, and the image side is concave; the three lenses have negative diopter, concave object side and concave image side; the second lens group comprises a fourth lens, a fifth lens, a sixth lens, a liquid lens, a seventh lens and an eighth lens, and the fourth lens has positive diopter and is convex on the object side and convex on the image side; the five lenses have negative diopter, concave object side and convex image side; the six lenses have positive diopter and are convex on the object side and the image side; the seven lenses are positive in diopter, convex on the object side and convex on the image side; the eight lenses have negative diopter, concave object side and convex image side; the liquid lens comprises a first transparent surface layer, a first liquid area, an elastic film layer, a second liquid area and a second transparent surface layer. The optical system is wide in working wave band, large in view field, large in target surface, small in F number, capable of quickly and automatically focusing, free of noise, compact in structure and stable in imaging quality.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical systems, in particular to an automatic focusing optical imaging system based on a liquid lens. BACKGROUND

[0002] At present, camera automatic focusing is mainly through motor driving lens movement to adjust the optical interval between the lens and the camera chip, thereby compensating for the shift of the lens imaging focus caused by the working distance or the change of the environmental temperature. However, through the motor driving lens and lens group moving along the optical axis, the camera structure and assembly are relatively complex, which causes the increase of the camera volume and weight, and the inconvenience of use. At the same time, through the motor driving lens or lens group movement to realize focusing, the motor equipment needs to be controlled for a relatively long time, which causes the camera to be unable to effectively meet the application scenarios with high real-time requirements.

[0003] In recent years, a new type of optical element "liquid lens" based on the concept of biological bionics has been developed. Unlike the motor driving lens or lens group movement focusing, the liquid lens only needs to change its shape or refractive index through electric control method without moving any element in the camera system. The optical imaging lens with the liquid lens can realize self-focusing, which makes outstanding contributions to the miniaturization of the camera system and the rapid target capture.

[0004] However, in the past two years, the optical imaging lens with the liquid lens on the market has poor imaging quality, which limits the application field. Therefore, it is urgent to optimize the optical technology of the existing optical imaging lens with the liquid lens, and to design a small-sized optical imaging lens based on the liquid lens with a large relative aperture to solve the above technical problems. SUMMARY

[0005] The purpose of the present application is to overcome the problems of the existing technology that the optical imaging lens with the liquid lens has poor imaging quality and the application field is limited, and to provide an automatic focusing optical imaging system based on a liquid lens. The system has a wide working waveband, a large field of view, a large target surface and a small F number, can realize fast automatic focusing from 0.5m to infinity, has no noise, compact structure and more stable imaging quality.

[0006] In order to achieve the above purpose, the present application provides an automatic focusing optical imaging system based on a liquid lens, which comprises a first lens group with negative optical power, an aperture stop, a second lens group with positive optical power, a cover glass and a CMOS photosensitive surface arranged in sequence from left to right along the light incident direction, the first lens group and the second lens group constitute a reverse telephoto structure, and the first lens group is used for adjusting the object side light, and the second lens group is used for controlling the large relative aperture; wherein, The first lens group comprises, in order from the object side to the image side along the optical axis, a first lens, a second lens and a third lens, the first lens and the second lens have positive refractive power and the object side is a convex spherical surface and the image side is a concave spherical surface; the third lens has negative refractive power and the object side is a concave spherical surface and the image side is a concave spherical surface; The second lens group comprises, in order from left to right, a cemented lens formed by a fourth lens and a fifth lens, a sixth lens, a liquid lens, a seventh lens and an eighth lens, the fourth lens has positive refractive power and the object side is a convex spherical surface and the image side is a convex spherical surface; the fifth lens has negative refractive power and the object side is a concave spherical surface and the image side is a convex spherical surface; the sixth lens has positive refractive power and the object side is a convex spherical surface and the image side is a convex spherical surface; the seventh lens has positive refractive power and the object side is a convex spherical surface and the image side is a convex spherical surface; the eighth lens has negative refractive power and the object side is a concave spherical surface and the image side is a convex spherical surface; the liquid lens comprises, in order from the object side to the image side along the optical axis, a first transparent surface layer, a first liquid zone, an elastic film layer, a second liquid zone and a second transparent surface layer.

[0007] Preferably, the focal length of the optical imaging system is set according to formula (1) and formula (2) f , , (1) , (2) wherein, f 第一透镜组 is the combined focal length of the first lens to the third lens, f 第二透镜组 is the combined focal length of the cemented lens to the eighth lens.

[0008] Preferably, the liquid lens is set to be capable of: when the object distance is 500mm, the radius of curvature of the elastic film layer is adjusted to -15.5mm, the edge thickness of the first liquid zone is adjusted to 0.633mm, and the edge thickness of the second liquid zone is adjusted to 2.211mm; when the object distance is 1000mm, the radius of curvature of the elastic film layer is adjusted to -32.8mm, the edge thickness of the first liquid zone is adjusted to 1.249mm, and the edge thickness of the second liquid zone is adjusted to 1.594mm; when the object distance is 5000mm, the elastic film layer is adjusted to be flat, the edge thickness of the first liquid zone is adjusted to 1.79mm, and the edge thickness of the second liquid zone is adjusted to 1.053mm; when the object distance is 10000mm, the radius of curvature of the elastic film layer is adjusted to 280mm, the edge thickness of the first liquid zone is adjusted to 1.854mm, and the edge thickness of the second liquid zone is adjusted to 0.99mm; When the object distance is 25000mm, the curvature radius of the elastic film layer is adjusted to 143mm, the edge thickness of the first liquid zone is adjusted to 1.915mm, and the edge thickness of the second liquid zone is adjusted to 0.928mm; When the object distance is infinite, the curvature radius of the elastic film layer is adjusted to 119mm, the edge thickness of the first liquid zone is adjusted to 1.941mm, and the edge thickness of the second liquid zone is adjusted to 0.903mm.

[0009] Preferably, in the first lens group, The curvature radius of the object side surface of the first lens is 15-17.5mm, and the curvature radius of the image side surface is 27.5-30.5mm; The curvature radius of the object side surface of the second lens is 13.5-15.5mm, and the curvature radius of the image side surface is 46.8-50.5mm; The curvature radius of the object side surface of the third lens is -30.5-32.5mm, and the curvature radius of the image side surface is 11.8-13.5mm.

[0010] Preferably, in the first lens group, the air gap between the first lens and the second lens is 0.2mm, and the air gap between the second lens and the third lens is 0.98mm.

[0011] Preferably, in the cemented lens, the image side surface of the fourth lens is cemented with the object side surface of the fifth lens; wherein, The curvature radius of the object side surface of the fourth lens is 15.2-17.8mm, and the curvature radius of the image side surface is -16.5--14.5mm; The curvature radius of the object side surface of the fifth lens is -14.5--16.5mm, and the curvature radius of the image side surface is -38.5--35.5mm.

[0012] Preferably, in the second lens group, The curvature radius of the object side surface of the sixth lens is 41.5-43.5mm, and the curvature radius of the image side surface is -79.5--77.5mm; The curvature radius of the object side surface of the seventh lens is 85.2-87.5mm, and the curvature radius of the image side surface is -59.8--57.5mm; The curvature radius of the object side surface of the eighth lens is -9.5--8.2mm, and the curvature radius of the image side surface is -32.5--29.5mm.

[0013] Preferably, in the second lens group, the air gap between the cemented lens and the sixth lens is 1.02mm, the air gap between the sixth lens and the liquid lens is 0.25mm, the air gap between the liquid lens and the seventh lens is 0.21mm, and the air gap between the seventh lens and the eighth lens is 2.55mm.

[0014] Preferably, the diaphragm is located between the first lens group and the second lens group, and the air gap to the first lens group along the optical axis is 2.25mm, and the air gap to the second lens group along the optical axis is 0mm.

[0015] Preferably, the back focal length of the second lens group is 2.195mm, the distance from the second lens group to the cover glass is 1.012mm; the thickness of the cover glass is 0.55mm, and the air gap from the CMOS photosurface to the cover glass is 0.75mm.

[0016] Through the above technical solution, the first lens group is used for adjusting the object side light, so that the object side field of view angle meets the optical system field of view angle requirement; the second lens group is used for being responsible for large relative aperture control, the optical design solves the installation limitation of the short focal length lens in the compact space through reasonable distribution of optical components, and is an important solution of the large field of view optical system. Meanwhile, the optical imaging system of the application can quickly adjust the focal length by integrating the liquid lens, can adapt to objects with different working distances and depth of field requirements, and can significantly improve the accuracy and speed of imaging. And, through the design of the optical material, surface curvature, thickness of the first lens to the eighth lens and the air gap between the lenses, the transmission path of the light and the imaging quality are optimized, not only meeting the application scene and imaging clarity requirements, but also realizing the function of fast automatic focusing. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 A structure schematic diagram of the automatic focusing optical imaging system based on the liquid lens provided by the application is shown in the figure; Figure 2 A point array diagram of the automatic focusing optical imaging system based on the liquid lens provided by the application when the object distance is 500mm is shown in the figure; Figure 3 A point array diagram of the automatic focusing optical imaging system based on the liquid lens provided by the application when the object distance is 1000mm is shown in the figure; Figure 4 A point array diagram of the automatic focusing optical imaging system based on the liquid lens provided by the application when the object distance is 5000mm is shown in the figure; Figure 5 A point array diagram of the automatic focusing optical imaging system based on the liquid lens provided by the application when the object distance is 10000mm is shown in the figure; Figure 6 A point array diagram of the automatic focusing optical imaging system based on the liquid lens provided by the application when the object distance is 25000mm is shown in the figure; Figure 7 A point array diagram of the automatic focusing optical imaging system based on the liquid lens provided by the application when the object distance is infinity is shown in the figure; Figure 8A distortion curve diagram of the liquid lens-based automatic focusing optical imaging system provided by the application when the object distance is 500 mm; Figure 9 A distortion curve diagram of the liquid lens-based automatic focusing optical imaging system provided by the application when the object distance is 1000 mm; Figure 10 A distortion curve diagram of the liquid lens-based automatic focusing optical imaging system provided by the application when the object distance is 5000 mm; Figure 11 A distortion curve diagram of the liquid lens-based automatic focusing optical imaging system provided by the application when the object distance is 10000 mm; Figure 12 A distortion curve diagram of the liquid lens-based automatic focusing optical imaging system provided by the application when the object distance is 25000 mm; Figure 13 A distortion curve diagram of the liquid lens-based automatic focusing optical imaging system provided by the application when the object distance is infinite.

[0018] Explanation of reference signs 1-first lens group, 2-diaphragm, 3-second lens group, 4-liquid lens, 11-first lens, 12-second lens, 13-third lens, 34-fourth lens, 35-fifth lens, 36-sixth lens, 37-seventh lens, 38-eighth lens, 9-cover glass, 10-CMOS photosensitive surface. DETAILED DESCRIPTION

[0019] The specific embodiments of the application will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely intended to illustrate and explain the application, and are not intended to limit the application.

[0020] In the present application, the orientation words such as "left" and "right" contained in the terms only represent the orientation of the terms in the normal use state or the common name understood by those skilled in the art, and should not be regarded as a limitation of the terms, unless otherwise stated.

[0021] Reference Figure 1 The present application provides a liquid lens-based automatic focusing optical imaging system, which comprises, from left to right along the light incident direction, a first lens group 1 with negative optical power, a diaphragm 2, a second lens group 3 with positive optical power, a cover glass 9 and a CMOS photosensitive surface 10, the first lens group 1 and the second lens group 3 form a reverse telephoto structure, and the first lens group 1 is used to adjust the object side light, and the second lens group 3 is used to control the large relative aperture; wherein, The first lens group 1 includes, in order from the object side to the image side along the optical axis, a first lens 11, a second lens 12, and a third lens 13, the first lens 11 and the second lens 12 have positive refractive power and the object side is a convex spherical surface and the image side is a concave spherical surface; the third lens 13 has negative refractive power and the object side is a concave spherical surface and the image side is a concave spherical surface; The second lens group 3 includes, in order from left to right, a cemented lens formed by a fourth lens 34 and a fifth lens 35, a sixth lens 36, a liquid lens 4, a seventh lens 37, and an eighth lens 38, the fourth lens 34 has positive refractive power and the object side is a convex spherical surface and the image side is a convex spherical surface; the fifth lens 35 has negative refractive power and the object side is a concave spherical surface and the image side is a convex spherical surface; the sixth lens 36 has positive refractive power and the object side is a convex spherical surface and the image side is a convex spherical surface; the seventh lens 37 has positive refractive power and the object side is a convex spherical surface and the image side is a convex spherical surface; the eighth lens 38 has negative refractive power and the object side is a concave spherical surface and the image side is a convex spherical surface; the liquid lens 4 includes, in order from the object side to the image side along the optical axis, a first transparent surface layer, a first liquid region, an elastic film layer, a second liquid region, and a second transparent surface layer.

[0022] In the embodiment, the first lens group of the optical imaging system is used to adjust the object side light rays so that the object side field angle meets the optical system field angle requirement; the second lens group is used to be responsible for large relative aperture control, the optical design solves the installation limitation of the short focal length lens in the compact space through reasonable distribution of optical components, and is an important solution of the large field optical system.

[0023] In the embodiment, in order to make the refractive power distribution of the first lens group and the second lens group of the optical imaging system not only meet the needs of the large field optical system, but also be beneficial to realize small F number and large target surface imaging, preferably, the focal length of the optical imaging system should be set according to formula (1) and formula (2) f , , (1) , (2) wherein, f 第一透镜组 is the combined focal length of the first lens 11 to the third lens 13, f 第二透镜组 is the combined focal length of the cemented lens to the eighth lens 38.

[0024] In the embodiment, in order to be able to quickly adjust the focal length through the integrated liquid lens, adapt to objects with different working distances and depth of field requirements, and significantly improve the accuracy and speed of imaging, preferably, the liquid lens 4 is set to be able to adjust the focal length in the range of: When the object distance is 500 mm, the curvature radius of the elastic film layer is adjusted to -15.5 mm, the edge thickness of the first liquid zone is adjusted to 0.633 mm, and the edge thickness of the second liquid zone is adjusted to 2.211 mm; When the object distance is 1000 mm, the curvature radius of the elastic film layer is adjusted to -32.8 mm, the edge thickness of the first liquid zone is adjusted to 1.249 mm, and the edge thickness of the second liquid zone is adjusted to 1.594 mm; When the object distance is 5000 mm, the elastic film layer is adjusted to be flat, the edge thickness of the first liquid zone is adjusted to 1.79 mm, and the edge thickness of the second liquid zone is adjusted to 1.053 mm; When the object distance is 10000 mm, the curvature radius of the elastic film layer is adjusted to 280 mm, the edge thickness of the first liquid zone is adjusted to 1.854 mm, and the edge thickness of the second liquid zone is adjusted to 0.99 mm; When the object distance is 25000 mm, the curvature radius of the elastic film layer is adjusted to 143 mm, the edge thickness of the first liquid zone is adjusted to 1.915 mm, and the edge thickness of the second liquid zone is adjusted to 0.928 mm; When the object distance is infinity, the curvature radius of the elastic film layer is adjusted to 119 mm, the edge thickness of the first liquid zone is adjusted to 1.941 mm, and the edge thickness of the second liquid zone is adjusted to 0.903 mm.

[0025] In the present embodiment, in order to be able to design the optical materials, surface curvatures, thicknesses, and air gaps between the lenses of the first lens to the eighth lens, optimize the transmission path of light and the imaging quality, and at the same time meet the requirements of application scenarios and imaging clarity and the requirement of fast automatic focusing, preferably in the first lens group 1, The curvature radius of the object side surface of the first lens 11 is 15-17.5 mm, and the curvature radius of the image side surface is 27.5-30.5 mm; The curvature radius of the object side surface of the second lens 12 is 13.5-15.5 mm, and the curvature radius of the image side surface is 46.8-50.5 mm; The curvature radius of the object side surface of the third lens 13 is -30.5-32.5 mm, and the curvature radius of the image side surface is 11.8-13.5 mm.

[0026] Further, preferably in the first lens group 1, the air gap between the first lens 11 and the second lens 12 is 0.2 mm, and the air gap between the second lens 12 and the third lens 13 is 0.98 mm.

[0027] Similarly, preferably in the cemented lens, the image side surface of the fourth lens 34 is cemented with the object side surface of the fifth lens 35; wherein, The curvature radius of the object side surface of the fourth lens 34 is 15.2-17.8 mm, and the curvature radius of the image side surface is -16.5--14.5 mm; The curvature radius of the object side surface of the fifth lens 35 is -14.5--16.5 mm, and the curvature radius of the image side surface is -38.5--35.5 mm.

[0028] Further, preferably in the second lens group 3, The curvature radius of the object side surface of the sixth lens 36 is 41.5-43.5 mm, and the curvature radius of the image side surface is -79.5--77.5 mm; The curvature radius of the object side surface of the seventh lens 37 is 85.2-87.5 mm, and the curvature radius of the image side surface is -59.8--57.5 mm; The curvature radius of the object side surface of the eighth lens 38 is -9.5--8.2 mm, and the curvature radius of the image side surface is -32.5--29.5 mm.

[0029] Further, in the second lens group 3, the air gap between the cemented lens and the sixth lens 36 is 1.02 mm, the air gap between the sixth lens 36 and the liquid lens 4 is 0.25 mm, the air gap between the liquid lens 4 and the seventh lens 37 is 0.21 mm, and the air gap between the seventh lens 37 and the eighth lens 38 is 2.55 mm.

[0030] In the present embodiment, preferably, the diaphragm 2 is located between the first lens group 1 and the second lens group 3, and the air gap to the first lens group 1 along the optical axis is 2.25 mm, and the air gap to the second lens group 3 along the optical axis is 0 mm.

[0031] In the present embodiment, preferably, the back focal length of the second lens group 3 is 2.195 mm, the distance from the second lens group 3 to the cover glass 9 is 1.012 mm; the thickness of the cover glass 9 is 0.55 mm, and the air gap from the CMOS photosurface 10 to the cover glass 9 is 0.75 mm.

[0032] The following provides a specific embodiment to illustrate the liquid lens-based auto-focusing optical imaging system provided by the present application: First, the embodiment refers to the lens object side (or image side) refers to the specific area of the lens surface through which the imaging light passes. The determination of the concave and convex of the lens surface shape follows the conventional method in the field, that is, according to the sign of the curvature radius. The curvature radius is widely used in optical design software, such as ZEMAX software and CODE V software, which can be found in the software lens data table. Specifically, for the object side, when the curvature radius is positive, it is determined that the object side is a convex spherical surface; otherwise, it is determined that the object side is a concave spherical surface. Correspondingly, for the image side, when the curvature radius is positive, it is determined that the object side is a concave spherical surface; otherwise, it is determined that the object side is a convex spherical surface.

[0033] According to Figure 1 , an automatic focusing optical imaging system with large field of view, large target surface, small F number and liquid lens is provided. The negative lens group is in front and the positive lens group is in back to form a reverse telephoto structure, which is beneficial to realize a low-light night vision camera with large field of view, large relative aperture and large target surface. The liquid lens includes, along the optical axis from the object side to the image side, a first transparent surface layer, a first liquid zone, an elastic film layer, a second liquid zone and a second transparent surface layer. The liquid lens can have two placement positions, placed at the front end of the optical imaging system or embedded in the optical system. However, considering that if the camera is used for an airborne integrated helmet display system and embedded in the flight helmet, the camera must be compact and small in structure, and placing the optical imaging system at the front end will increase the volume of the camera, so the liquid lens is selected to be embedded in the system. Furthermore, in order to match the light aperture of the liquid lens and at the same time avoid introducing aberrations as much as possible, the liquid lens is embedded between the sixth lens and the seventh lens with positive refractive power in the middle of the light aperture which is small and changes relatively gently. At the same time, the working distance of the liquid lens with a refractive power of 0dpt is 5000mm, and the multiple structure operation number THIC is used to set multiple structures with different object distances, 500mm, 1000mm, 5000mm, 10000mm, 25000mm and Infinity (Infinity) 6 structures. The focal length of the liquid lens is controlled by the multiple structure operation number CRVT to control the different refractive powers of the liquid lens in different structures. Since the liquid lens can only achieve focusing effect and cannot be used to correct aberrations, when embedding the liquid lens, other aberrations are avoided as much as possible, but it is absolutely impossible to avoid aberrations. By properly adjusting the optical materials, surface curvature, thickness and lens spacing of the optical imaging system embedded with the liquid lens, aberration correction is achieved to realize clear imaging of the optical imaging system embedded with the liquid lens.

[0034] The embodiment requires the following optical performance indicators: 1. Working waveband: 585nm~950nm; 2. Field of view: not less than 40°×32°; 3. Relative aperture: 1:1.25; 4, Image sensor: adapt CMOS image sensor resolution 1280x1024, pixel size 9.7um; 5, Resolution: ≤1.32mrad@ambient illuminance 10 -3 lux; 6, Working temperature: -45℃~65℃; 7, Auto focus range: 0.5m to infinity.

[0035] In this embodiment, the optical element parameters are shown in Table One as follows: Table One

[0036] Wherein, the values of D1 and D2 of the liquid lens refer to Table Two (liquid lens parameters corresponding to different object distances): Table Two

[0037] The spot diagram of different working distances (500mm, 1000mm, 5000mm, 10000mm, 25000mm and infinity) in this embodiment is shown in Figures 2-7 As shown in the figure, the 0.7 field of view spot diagram RMS radius 9.6um is less than the selected CMOS chip pixel 9.7um, indicating that the optical imaging system has high imaging clarity.

[0038] The field curvature and distortion curve of different working distances (500mm, 1000mm, 5000mm, 10000mm, 25000mm and infinity) in this embodiment are shown in Figures 8-13 As shown in the figure, the optical imaging system distortion is less than 2%, indicating that the optical imaging system has small distortion; at the same time, the optical imaging system full field of view field curvature is less than 0.12mm, the system focal length is relatively small, and the focal depth is much larger than the field curvature, which will not affect the full field of view imaging clarity.

[0039] In summary, the optical imaging system provided by the application realizes the design of the 585nm-950nm wide working waveband, 40°x32° large field of view, 1.25 small F number, 9.7um pixel size 1280x1024 resolution large target, 0.5m to infinity auto focus micro-light night vision camera optical imaging system. From the spot diagram and field curvature and distortion curve of the object distance 500mm, 1000mm, 5000mm, 10000mm, 25000mm and infinity, it can be seen that the optical imaging system can realize the rapid auto focus function from 500mm to infinity, the time can reach millisecond level, the overall optical imaging system has no excessive noise, the structure is compact, and compared with the traditional overall moving focusing lens, it has more stable imaging quality, and has a wide application prospect in the fields of military and monitoring.

[0040] The preferred embodiments of the present application are described in detail above with reference to the accompanying drawings, but the present application is not limited thereto. Various simple modifications can be made to the technical solutions of the present application within the technical concept of the present application, including the combination of various specific technical features in any suitable manner. In order to avoid unnecessary repetition, the present application will not describe various possible combination manners again. However, these simple modifications and combinations should also be regarded as the disclosed content of the present application and belong to the protection scope of the present application.

Claims

1. An auto-focusing optical imaging system based on liquid lens, characterized in that, The optical imaging system comprises a first lens group (1) with negative focal length, an aperture (2), a second lens group (3) with positive focal length, a cover glass (9) and a CMOS photosurface (10) arranged in sequence from left to right along the light incident direction, the first lens group (1) and the second lens group (3) form a reversed telephoto structure, the first lens group (1) is used for adjusting the object side light, and the second lens group (3) is used for controlling the large relative aperture. The first lens group (1) comprises a first lens (11), a second lens (12) and a third lens (13) in sequence from the object side to the image side along the optical axis, the first lens (11) and the second lens (12) have positive refractive power, the object side surface is a convex spherical surface, and the image side surface is a concave spherical surface; the third lens (13) has negative refractive power, the object side surface is a concave spherical surface, and the image side surface is a concave spherical surface. The second lens group (3) comprises a cemented lens formed by a fourth lens (34) and a fifth lens (35) in sequence from left to right, a sixth lens (36), a liquid lens (4), a seventh lens (37) and an eighth lens (38), the fourth lens (34) has positive refractive power, the object side surface is a convex spherical surface, and the image side surface is a convex spherical surface; the fifth lens (35) has negative refractive power, the object side surface is a concave spherical surface, and the image side surface is a convex spherical surface; the sixth lens (36) has positive refractive power, the object side surface is a convex spherical surface, and the image side surface is a convex spherical surface; the seventh lens (37) has positive refractive power, the object side surface is a convex spherical surface, and the image side surface is a convex spherical surface; the eighth lens (38) has negative refractive power, the object side surface is a concave spherical surface, and the image side surface is a convex spherical surface; the liquid lens (4) comprises a first transparent surface layer, a first liquid zone, an elastic film layer, a second liquid zone and a second transparent surface layer in sequence from the object side surface to the image side surface along the optical axis.

2. The liquid lens based auto focus optical imaging system of claim 1, wherein, According to formula (1) and formula (2) to set the focal length of the optical imaging system f , ，（1） ，（2） wherein f 第一透镜组 is the combined focal length of the first lens (11) to the third lens (13), f 第二透镜组 is the combined focal length of the cemented lens to the eighth lens (38).

3. The liquid lens based auto focus optical imaging system of claim 1, wherein, The liquid lens (4) is arranged to be capable of: When the object distance is 500 mm, the curvature radius of the elastic film layer is adjusted to -15.5 mm, the edge thickness of the first liquid zone is adjusted to 0.633 mm, and the edge thickness of the second liquid zone is adjusted to 2.211 mm; When the object distance is 1000 mm, the curvature radius of the elastic film layer is adjusted to -32.8 mm, the edge thickness of the first liquid zone is adjusted to 1.249 mm, and the edge thickness of the second liquid zone is adjusted to 1.594 mm; When the object distance is 5000 mm, the elastic film layer is adjusted to be flat, the edge thickness of the first liquid zone is adjusted to 1.79 mm, and the edge thickness of the second liquid zone is adjusted to 1.053 mm; When the object distance is 10000 mm, the curvature radius of the elastic film layer is adjusted to 280 mm, the edge thickness of the first liquid zone is adjusted to 1.854 mm, and the edge thickness of the second liquid zone is adjusted to 0.99 mm; When the object distance is 25000 mm, the curvature radius of the elastic film layer is adjusted to 143 mm, the edge thickness of the first liquid zone is adjusted to 1.915 mm, and the edge thickness of the second liquid zone is adjusted to 0.928 mm; When the object distance is infinite, the radius of curvature of the elastic film layer is adjusted to 119 mm, the edge thickness of the first liquid zone is adjusted to 1.941 mm, and the edge thickness of the second liquid zone is adjusted to 0.903 mm.

4. The liquid lens based auto focus optical imaging system of claim 1, wherein, In the first lens group (1), The radius of curvature of the object side surface of the first lens (11) is 15-17.5 mm, and the radius of curvature of the image side surface is 27.5-30.5 mm. The radius of curvature of the object side surface of the second lens (12) is 13.5-15.5 mm, and the radius of curvature of the image side surface is 46.8-50.5 mm. The radius of curvature of the object side surface of the third lens (13) is -30.5-32.5 mm, and the radius of curvature of the image side surface is 11.8-13.5 mm.

5. The liquid lens based auto focus optical imaging system of claim 4, wherein, In the first lens group (1), the air gap between the first lens (11) and the second lens (12) is 0.2 mm, and the air gap between the second lens (12) and the third lens (13) is 0.98 mm.

6. The liquid lens based auto focus optical imaging system of claim 1, wherein, In the cemented lens, the image side surface of the fourth lens (34) is cemented with the object side surface of the fifth lens (35); wherein, The radius of curvature of the object side surface of the fourth lens (34) is 15.2-17.8 mm, and the radius of curvature of the image side surface is -16.5--14.5 mm. The radius of curvature of the object side surface of the fifth lens (35) is -14.5--16.5 mm, and the radius of curvature of the image side surface is -38.5--35.5 mm.

7. The liquid lens based auto focus optical imaging system of claim 1, wherein, In the second lens group (3), The radius of curvature of the object side surface of the sixth lens (36) is 41.5-43.5 mm, and the radius of curvature of the image side surface is -79.5--77.5 mm. The radius of curvature of the object side surface of the seventh lens (37) is 85.2-87.5 mm, and the radius of curvature of the image side surface is -59.8--57.5 mm. The radius of curvature of the object side surface of the eighth lens (38) is -9.5--8.2 mm, and the radius of curvature of the image side surface is -32.5--29.5 mm.

8. The liquid lens based auto focus optical imaging system of claim 7, wherein, In the second lens group (3), the air gap between the cemented lens and the sixth lens (36) is 1.02 mm, the air gap between the sixth lens (36) and the liquid lens (4) is 0.25 mm, the air gap between the liquid lens (4) and the seventh lens (37) is 0.21 mm, and the air gap between the seventh lens (37) and the eighth lens (38) is 2.55 mm.

9. The liquid lens based auto focus optical imaging system of claim 1, wherein, The diaphragm (2) is located between the first lens group (1) and the second lens group (3), and the air gap to the first lens group (1) along the optical axis is 2.25 mm, and the air gap to the second lens group (3) along the optical axis is 0 mm.

10. The liquid lens based auto focus optical imaging system of claim 1, wherein, The back focal length of the second lens group (3) is 2.195 mm, and the distance from the second lens group (3) to the cover glass (9) is 1.012 mm; the thickness of the cover glass (9) is 0.55 mm, and the air gap from the CMOS photosurface (10) to the cover glass (9) is 0.75 mm.

Images