Underwater transmitted optical imaging system

Abstract

The present application relates to underwater optical imaging technology field, especially to a kind of underwater transmission optical imaging system, from the light beam of wet warehouse optical department zooms after in image sensor, imaging;Wet warehouse optical department includes the front Fresnel thin lens of positive refractive power and rear Fresnel thin lens, parallel light from underwater environment converges after the front Fresnel thin lens, and the convergent light is diffused again through the rear Fresnel thin lens, and is transmitted to dry warehouse optical department;Dry warehouse optical department includes front fixed lens and zoom lens group, the position of front fixed lens is fixed, and zoom lens group is linear differential type between front fixed lens and position fixed image sensor Move, the light beam from wet warehouse optical department converges in image sensor.The present application is based on the light-gathering increase of Fresnel thin lens, and the dry warehouse optical department of movable lens linear differential type movement is realized underwater large aperture high flux long distance detection.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of underwater optical imaging, and particularly relates to an underwater transmission optical imaging system. BACKGROUND

[0002] The existing underwater detection technology can be roughly divided into two categories according to the method principle of image acquisition. One is the traditional optical imaging / camera system, and the other is the advanced optical imaging detection system. The former relies on the optical design of the traditional imaging lens in the air, and is equipped with a sealed window and an underwater sealed structure shell. This is equivalent to a simple sealing improvement of the optical system in the air on land, and the cost is relatively low, but it may cause certain problems such as field of view reduction, image blur and poor light transmission. Gradually developed into special optical design for underwater environment, which is to directly replace the air medium in the traditional design with water body, and directly use the first lens as a cross-medium optical window. Although it has higher flexibility, it also brings certain problems such as high design and processing cost, poor adaptability to different refractive index water bodies, and difficulty in wide application. The advanced optical imaging and detection system relies on more advanced hardware structure devices or software algorithms, including laser range gating, structured light scanning, polarization imaging, multi-vision stereo imaging / panoramic imaging, and advanced spectral imaging. Although it can break through some fixed limitations in some specific application scenarios, it is still difficult to obtain universal application due to the complex and expensive device structure, complex imaging method, poor real-time performance and other problems. And in general, all kinds of underwater imaging devices at present are basically faced with the core bottleneck problems of unclear imaging, small imaging light flux and limited detection distance under the interference of complex underwater environment, especially the difference of refractive index of underwater medium and the absorption and scattering of water body.

[0003] The current situation of underwater optical imaging technology can be summarized as the limitation of cost and technology. In terms of cost, how to design a high-performance imaging system device with high cost performance and simple and reliable structure becomes a major problem. In terms of technology, it tends to develop in the direction of various high-end high-performance lasers, controllers, micro-nano elements, etc., and the further development and utilization of traditional imaging structure is slightly insufficient. SUMMARY

[0004] Therefore, the present application aims to provide an underwater transmission optical imaging system, which uses a Fresnel thin lens as a Kepler telescope magnification main mirror structure for light collection and reception, and combines a rear-end movable lens for linear differential movement of a zoom lens, to realize high-throughput connection transition under pupil matching, ensure that the large-aperture function is effective, and also make the zoom focusing flexible and considerate. The overall structure is simple, easy to assemble, and has high stability and reliability in underwater application.

[0005] To achieve the above object, the technical scheme of the present application is implemented as follows:

[0006] An underwater transmission optical imaging system comprises a wet bin optical unit, a dry bin optical unit and an image sensor, a light beam from the wet bin optical unit is zoomed through the dry bin optical unit and then imaged in the image sensor; the wet bin optical unit comprises a front Fresnel thin lens and a rear Fresnel thin lens with positive focal length, the front Fresnel thin lens and the rear Fresnel thin lens form a Kepler telescope structure, parallel light from an underwater environment is converged through the front Fresnel thin lens, the converged light is diffused through the rear Fresnel thin lens and then transmitted into the dry bin optical unit; the dry bin optical unit comprises a front fixed lens and a zoom lens group, the position of the front fixed lens is fixed, the zoom lens group moves linearly and differentially between the front fixed lens and the fixed-position image sensor, and the light beam from the wet bin optical unit is converged in the image sensor.

[0007] Further, the front Fresnel thin lens and the rear Fresnel thin lens are parabolic, one side of the two lenses is a plane and the other side is an equidistant threaded ring; the wet bin optical unit further comprises a wet bin sealed cabin, the front Fresnel thin lens and the rear Fresnel thin lens are arranged in the wet bin sealed cabin.

[0008] Further, the optical parameters of the front Fresnel thin lens and the rear Fresnel thin lens include the radius of curvature, the curvature, the quadratic coefficient of the even aspheric surface satisfied by the front Fresnel thin lens and the rear Fresnel thin lens, and the conic constant; the determination process of the optical parameters comprises:

[0009] The radius of curvature is determined by the following formula according to the focal length of the front Fresnel thin lens and the rear Fresnel thin lens:

[0010] R=(n-1)f;

[0011] Wherein, R represents the radius of curvature, f represents the focal length, and n represents the refractive index of the front Fresnel thin lens and the rear Fresnel thin lens; the curvature is the reciprocal of the radius of curvature;

[0012] The front Fresnel thin lens and the rear Fresnel thin lens satisfy the even aspheric surface of the following formula:

[0013] ;

[0014] Wherein, z represents the even aspheric surface, c represents the curvature, and k represents the conic constant;

[0015] The quadratic coefficient α1 is determined by the following formula:

[0016] ;

[0017] Analogously, the first term of the even-order aspheric surface is equal to the second term, and the conic constant k=-1 is obtained.

[0018] Further, the front Fresnel thin lens and the rear Fresnel thin lens are respectively provided with a plane cover plate on both sides; one of the plane cover plates is in direct contact with the plane side of the front Fresnel thin lens or the rear Fresnel thin lens, and an air gap is formed between the plane cover plate and the plane side, or the plane cover plate and the plane side are seamlessly connected through gluing; the other plane cover plate forms a complementary air gap with the equal-interval screw ring side of the front Fresnel thin lens or the rear Fresnel thin lens in the form of reverse threads, and the complementary air gap is filled with a refractive index matching liquid.

[0019] Further, the front fixed lens is a meniscus lens, the zoom lens group includes a first lens, a second lens and a third lens arranged in sequence along the optical path; the first lens moves between the front fixed lens and the second lens, and is used for variable magnification imaging; the second lens and the third lens move together between the first lens and the image sensor 1, and are used for focus compensation.

[0020] Further, the process of linear differential movement of the zoom lens group between the front fixed lens and the fixed-position image sensor includes that: the moving distance of the first lens and the moving distance of the second lens and the third lens together satisfy a linear relationship, and the moving amplitude of the first lens is much larger than the moving amplitude of the second lens and the third lens together; the moving direction of the first lens is opposite to the moving direction of the second lens and the third lens together.

[0021] Further, the dry chamber optical part further includes a waterproof window and a dry chamber sealed cabin, the front fixed lens and the zoom lens group are arranged in the dry chamber sealed cabin, the waterproof window is in the form of a flat plate and is arranged on the cabin wall of the dry chamber sealed cabin, and the aperture size of the window is the same as the aperture of the front Fresnel thin lens or the rear Fresnel thin lens.

[0022] Compared with the prior art, the application can achieve the following beneficial effects:

[0023] The underwater transmission optical imaging system comprises a wet bin part and a dry bin part. BRIEF DESCRIPTION OF DRAWINGS BRIEF DESCRIPTION OF DRAWINGS

[0024] The accompanying drawings, which form a part of the specification, are included to provide a further understanding of the application and are incorporated herein by reference. The embodiments of the present application, taken together with the accompanying drawings, serve to explain the present application, and do not constitute an improper limitation on the present application. In the drawings:

[0025] Figure 1 The structure schematic diagram of the underwater transmission optical imaging system according to the embodiment of the present application;

[0026] Figure 2 The structure schematic diagram of the wet bin optical part according to the embodiment of the present application;

[0027] Figure 3 The light ray tracing schematic diagram of the zoom lens group performing linear differential movement in the underwater transmission optical imaging system according to the embodiment of the present application;

[0028] Figure 4 The process schematic diagram of the zoom lens group performing linear differential movement according to the embodiment of the present application;

[0029] Figure 5 The light ray tracing schematic diagram of the underwater transmission optical imaging system in different short-focus field of view according to the embodiment of the present application;

[0030] Figure 6 The light ray tracing schematic diagram of the zoom lens performing imaging in different field of view according to the embodiment of the present application.

[0031] BRIEF DESCRIPTION OF DRAWINGS

[0032] 1, image sensor; 2, front Fresnel thin lens; 3, rear Fresnel thin lens; 4, transition wet tank water body; 5, rear end wet tank water body; 6, plane cover plate; 7, front fixed lens; 8, first lens; 9, second lens; 10, third lens; 11, waterproof window. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application will be further described in detail below in combination with the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and do not constitute a limitation on the present application.

[0034] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0035] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second" and the like are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features limited by "first", "second" and the like can explicitly or implicitly include one or more of the features. In the description of the present application, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0036] In the description of the present application, it should be noted that unless otherwise specified and limited, the terms "mounting", "connection", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood through specific circumstances.

[0037] The present application will be described in detail below with reference to the drawings and in combination with embodiments.

[0038] As Figure 1As shown, the underwater transmission optical imaging system described in this embodiment of the invention includes a wet chamber optics unit, a dry chamber optics unit, and an image sensor 1. A light beam from the wet chamber optics unit is zoomed by the dry chamber optics unit and then imaged in the image sensor 1. The wet chamber optics unit includes a front Fresnel lens 2 and a rear Fresnel lens 3 with positive optical power. The front Fresnel lens 2 and the rear Fresnel lens 3 form a Keplerian telescope structure. Parallel light from the underwater environment is converged by the front Fresnel lens 2, and the converged light is then diffused by the rear Fresnel lens 3 and transmitted into the dry chamber optics unit. The wet chamber optics unit also includes a wet chamber sealed chamber. The front Fresnel lens 2 and the rear Fresnel lens 3 are placed in the wet chamber sealed chamber. When ambient water enters the underwater transmission optical imaging system, the water in the wet chamber sealed chamber before the front Fresnel lens 2 forms the front water body (…). Figure 1 (Not shown in the diagram) The water between the front Fresnel thin lens 2 and the rear Fresnel thin lens 3 in the wet chamber forms the transition wet chamber water body 4, and the water between the rear Fresnel thin lens 3 and the subsequent dry chamber optical section in the wet chamber forms the rear wet chamber water body 5. These three water bodies do not need to be pre-filled. This invention combines the front Fresnel thin lens 2 and the rear Fresnel thin lens 3 into a Kepler telescope structure, making it easier to realize a high-magnification optical system.

[0039] The thread profile morphology of the front Fresnel thin lens 2 and the rear Fresnel thin lens 3 determines the various parameters of the Fresnel lens. Considering the wide range of practical applications and the characteristics of shelf products on the market, parabolic Fresnel thin lenses with positive optical power are easier to obtain and easier to implement Kepler structures. Therefore, in some embodiments, the front Fresnel thin lens 2 and the rear Fresnel thin lens 3 are preferably parabolic, that is, one side of the two lenses is a plane and the other side is a parabola. The principle structure of the wet chamber optics is as follows: Figure 2 As shown.

[0040] Furthermore, existing common Fresnel thin lens surface thread profile microstructure types include two types: equally spaced rings and equally deep rings. The former (equal ring spacing) is generally more prevalent in the market. Its manufacturing is relatively simple, suitable for large-scale injection molding production, and it is often processed into large-diameter structures. However, it also potentially suffers from large edge differences and low transmission and diffraction efficiency. Equal-depth thread structures, on the other hand, have each ring with equal depth. This generally requires higher processing precision, and the threaded rings become denser towards the lens edge, resulting in higher diffraction efficiency and more precise aberration control. In the structure of this invention, high throughput is its dominant advantage; therefore, minor aberration issues are not considered. Furthermore, to facilitate cost control in equipment setup, in some embodiments, equally spaced threaded rings are preferably used on one side of the front Fresnel thin lens 2 and the rear Fresnel thin lens 3.

[0041] In the optical design simulation software (Zemax), the calculation of the Fresnel thin lens can use the Fresnel object in the non-sequence mode (the equal spacing annulus and the equal depth annulus need to be set according to the actual situation), or use the "Fresnel surface", "extended Fresnel surface" and the like in the sequence mode. Considering the convenience of operation, the parameter calculation of the Fresnel thin lens is preferably carried out in the sequence mode, so that the general demand can be met, and the error is not easy to occur. In some embodiments, the setting process of the specific parameters of the Fresnel thin lens mainly involves the curvature radius, the curvature of the front Fresnel thin lens 2 and the rear Fresnel thin lens 3, the quadratic term coefficient of the even aspheric surface satisfied by the front Fresnel thin lens 2 and the rear Fresnel thin lens 3, and the conic constant. In the optical design simulation of the parabolic Fresnel lens, the conic constant k needs to be set, and the setting rule is as follows:

[0042] k=0 corresponds to a standard spherical surface;

[0043] k=-1 corresponds to a parabolic surface, including a parabolic reflector or a parabolic lens;

[0044] k>-1 corresponds to an ellipsoidal surface (k>0 is a flat ellipsoidal surface, -1<k<0 is a long ellipsoidal surface);

[0045] k<-1 corresponds to a hyperbolic surface.

[0046] The determination process of the optical parameters includes:

[0047] The front Fresnel thin lens 2 and the rear Fresnel thin lens 3 satisfy the even aspheric surface of the following formula:

[0048]

[0049] Wherein, z represents the even aspheric surface, c represents the curvature, which is the reciprocal of the curvature radius, and k represents the conic constant.

[0050] In the parameter setting process, if the "Fresnel surface" is selected, the curvature radius and the curvature parameters cannot be input, and the setting can be completed by setting the quadratic term coefficient α1. In this case, it is equivalent to the equal analogy of the first term and the second term α1r 2 in the even aspheric surface, at this time, the conic constant k=-1 is obtained, according to the setting rule of the conic constant k, it is also obtained that the front Fresnel thin lens 2 and the rear Fresnel thin lens 3 adopt a parabolic surface, at this time, it is obtained that:

[0051]

[0052] Further, the quadratic term coefficient α1=c / 2 is obtained.

[0053] ​​In the embodiment of the present application, the front Fresnel lens 2 and the rear Fresnel lens 3 are taken as examples of positive focal length Fresnel lens of acrylic material (refractive index n = 1.49) with focal length f = 260 mm, and the lens geometric calculation formula is as follows:

[0054] ;

[0055] Wherein, d represents the thickness of the front Fresnel lens 2 and the rear Fresnel lens 3, R1 and R2 respectively represent the radii of curvature of the front and rear surfaces of the front Fresnel lens 2 or the rear Fresnel lens 3. The lens thickness d is approximately close to 0, and the above formula is simplified as:

[0056] ;

[0057] Further, the curvature c is obtained as:

[0058] ;

[0059] Further, the quadratic coefficient α1 is obtained as:

[0060] ;

[0061] Further, the quadratic coefficient α1 is obtained as:

[0062] .

[0063] In the embodiment of the present application, the optical parameters of the front Fresnel lens 2 and the rear Fresnel lens 3 are consistent, that is, the aperture of the two lenses is 300 mm, the focal length is 250 mm, the thickness is 2-5 mm, and the thread spacing is 0.3-0.5 mm.

[0064] The effective application of the two Fresnel thin lenses under water cannot be achieved without the maintenance of the thread profile topography of the surface, and therefore, in some embodiments, a plane cover plate 6 is arranged on both sides of the front Fresnel thin lens 2 and the rear Fresnel thin lens 3. One of the plane cover plates 6 is in direct contact with the plane side of the front Fresnel thin lens 2 or the rear Fresnel thin lens 3, and a very thin layer of air gap is formed between the plane cover plate 6 and the plane side, or the plane cover plate 6 is seamlessly connected to the plane side through gluing. The other plane cover plate 6 forms a complementary air gap with the equal-interval thread ring side of the front Fresnel thin lens 2 or the rear Fresnel thin lens 3, and the formation of the complementary air gap ensures that the lens function of the Fresnel thin lens is not damaged under water, and the fine threads also provide a certain macro-scale uniform support for the plane cover plate, which cannot be achieved by traditional lenses when they are sealed under water. In addition, the arrangement of the plane cover plate 6 not only realizes waterproof sealing and ensures the normal operation of the front Fresnel thin lens 2 or the rear Fresnel thin lens 3 under water, but also provides mechanical support for the front Fresnel thin lens 2 or the rear Fresnel thin lens 3, avoiding the local deformation or damage of the front Fresnel thin lens 2 or the rear Fresnel thin lens 3 caused by water flow impact when they are applied under water.

[0065] In the embodiments of the present application, the plane cover plate 6 is preferably made of acrylic material with a thickness of 5mm-1cm, and in other embodiments, quartz glass material with high cost performance can also be used, but the problems of film plating and transmission rate of imaging optical band need to be considered, as well as the pollution and glass hydrogenation problems of long-time underwater application. In addition, the small space dense thread support of the air gap is also conducive to the application in deep-sea high-pressure environment, and the double-side offset of the plane cover plate 6 can greatly buffer the deep-sea high pressure. Furthermore, in order to further ensure the pressure resistance, the complementary air gap on the equal-interval thread ring side of the front Fresnel thin lens 2 or the rear Fresnel thin lens 3 is filled with a refractive index matching liquid in the embodiments of the present application to improve the pressure resistance, but the Fresnel thin lens focal length parameter change needs to be calculated according to the refractive index difference, and the distance between the two Fresnel thin lenses needs to be adjusted.

[0066] The dry bin optical part adopts a four-piece movable lens linear differential moving zoom lens structure, specifically including a front fixed lens 7 and a zoom lens group. The position of the front fixed lens 7 is fixed, and the zoom lens group moves linearly and differentially between the front fixed lens 7 and the fixed image sensor 1, and converges the light beam from the wet bin optical part in the image sensor 1. In some embodiments, the dry bin optical part further includes a dry bin sealed cabin, and the front fixed lens and the zoom lens group are arranged in the dry bin sealed cabin, and the dry bin sealed cabin is spliced with the wet bin sealed cabin. The imaging system provided by the present application can be repeatedly adapted to the mainstream 2 / 3 inch upper image sensor on the market, including mainstream color image sensors, black and white grayscale image sensors, polarization image sensors, etc., and can meet the needs of multiple types of underwater optical imaging detection.

[0067] In some embodiments, the front fixed lens 7 is a meniscus lens, and the zoom lens group comprises a first lens 8, a second lens 9 and a third lens 10 arranged in sequence along the optical path. In the present application, the linear differential movement is that the first lens 8 moves between the front fixed lens 7 and the second lens 9, and plays a role of variable magnification imaging, and the second lens 9 and the third lens 10 move together between the first lens 8 and the image sensor 1, and play a role of compensation for focusing. The moving distance of the first lens 8 and the moving distance of the second lens 9 and the third lens 10 together satisfy a linear relationship, and the moving amplitude of the first lens 8 is much larger than the moving amplitude of the second lens 9 and the third lens 10 together, and the moving direction of the first lens 8 is opposite to the moving direction of the second lens 9 and the third lens 10 together. The process of linear differential movement of the zoom lens group is as shown in Figure 3 and Figure 4 , wherein Figure 3 , (a) and (b) respectively show the position state of the zoom lens group at different times and the corresponding beam tracing, Figure 4 , it is shown that the first lens 8 moves away from the second lens 9 and the third lens 10, and the mechanical movement trajectory fully proves the simplicity and reliability of the mechanical displacement, but it needs to be explained that due to the limitation of the simulation software itself, Figure 4 , the movement of the second lens 9 and the third lens 10 is not obvious, but the second lens 9 and the third lens 10 are moving to the right. The zoom lens group can effectively compensate for focusing during zooming through such linear differential movement. Such zooming movement is simple and reliable, and the distance error is easy to control, and there is no complex movement amount drift problem.

[0068] In the embodiment of the present application, the meniscus lens is a common convex-concave shape, with an aperture of 50.8mm and a focal length of 200mm; the first lens 8 is a left-right symmetric double-concave lens, with a diameter of 50mm and a focal length of-50mm; the second lens 9 is an achromatic double cemented lens, with a common convex-concave cemented shape, a diameter of 35mm and a focal length of 80mm; and the third lens 10 is also an achromatic double cemented lens, with a common convex-concave cemented shape, a diameter of 25mm and a focal length of 40mm. In the embodiment of the present application, a non-cam displacement table is used to control the positions of the first lens 8, the second lens 9 and the third lens 10, which can further compress the cost of the device structure, and increase the system structure reliability and stability. In addition, in the embodiment of the present application, the second lens 9 and the third lens 10 are used as stops through their own size boundaries, and in other embodiments, a stop can be arranged between the second lens 9 and the third lens 10.

[0069] The ray tracing of the underwater transmission optical imaging system provided by the present application under different short-focus field rays is as shown in Figure 5 , Figure 5Figures (a)-(e) in the figure show the tracking of different fields of view with image heights of 1.12, 2.24, 3.36, 4.48, and 5.6 mm, respectively. It can be seen from Figure 5 Figures (a)-(e) in the figure show that the zoom lens group can converge light beams to the target surface of the image sensor 1 under different short-focus fields of view. It can be seen that the several fields of view can all be imaged on the target surface.

[0070] Compared with the existing zoom lens, the zoom lens group provided by the present application has a larger size and more self-light flux, and is more compatible with the front large-aperture Fresnel lens group part. The specific multi-field-of-view tracking imaging of different fields of view is shown in Figure 6 , wherein Figure 6 Figures (a) and (b) in the figure respectively show the imaging tracking of the zoom lens group part under multi-field-of-view zooming.

[0071] In some embodiments, the dry chamber optical part further comprises a waterproof window 11, which is a flat plate structure and is arranged on the cabin wall of the dry chamber sealed cabin. The waterproof window 11 can be made of acrylic, quartz glass, or sapphire material. For deep-sea pressure-resistant environments, acrylic and sapphire materials are mainly used. The thickness needs to be designed according to the working water depth, and the thickness design also considers the aperture size. The thickness-diameter ratio is often used as an empirical parameter for design. In the embodiments of the present application, the aperture size of the waterproof window 11 is the same as that of the front Fresnel thin lens 2 or the rear Fresnel thin lens 3.

[0072] It should be understood that the various forms of flow shown above can be used to reorder, add or delete steps. For example, the steps described in the present disclosure can be executed in parallel, sequentially or in different orders, as long as the desired results of the technical solutions of the present disclosure can be achieved, which are not limited herein.

[0073] The above specific embodiments do not constitute a limitation on the protection scope of the present application. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. An underwater transmitted-light optical imaging system, characterized by, The wet bin optical part, the dry bin optical part and the image sensor are included, the light beam from the wet bin optical part is zoomed through the dry bin optical part and then imaged in the image sensor; the wet bin optical part includes a front Fresnel thin lens and a rear Fresnel thin lens with positive focal length, the front Fresnel thin lens and the rear Fresnel thin lens form a Kepler telescope structure, parallel light from the underwater environment converges through the front Fresnel thin lens, the converged light diffuses through the rear Fresnel thin lens and then transmits to the dry bin optical part; The dry bin optical part includes a front fixed lens and a zoom lens group, the position of the front fixed lens is fixed, the zoom lens group moves linearly differentially between the front fixed lens and the fixed-position image sensor to converge the light beam from the wet bin optical part in the image sensor; The front Fresnel thin lens and the rear Fresnel thin lens are parabolic, one side of the two lenses is a plane and the other side is an equidistant threaded ring; the wet bin optical part further includes a wet bin sealed cabin, the front Fresnel thin lens and the rear Fresnel thin lens are arranged in the wet bin sealed cabin; A plane cover plate is arranged on each side of the front Fresnel thin lens and the rear Fresnel thin lens; one plane cover plate directly contacts one side of the plane of the front Fresnel thin lens or the rear Fresnel thin lens, and an air gap is formed between the plane cover plate and the plane side, or the plane cover plate is seamlessly connected with the plane side through gluing; the other plane cover plate and the equidistant threaded ring side of the front Fresnel thin lens or the rear Fresnel thin lens form a complementary air gap with an inverse thread topography, and a refractive index matching liquid is filled in the complementary air gap.

2. The underwater transmitted-light optical imaging system of claim 1, wherein, The optical parameters of the front Fresnel thin lens and the rear Fresnel thin lens include the curvature radius, the curvature, the quadratic coefficient of the even aspheric surface satisfied by the front Fresnel thin lens and the rear Fresnel thin lens, and the conic constant; The determination process of the optical parameters includes: The curvature radius is determined by the following formula according to the focal length of the front Fresnel thin lens and the rear Fresnel thin lens: R=(n-1)f; Wherein, R represents the curvature radius, f represents the focal length, and n represents the refractive index of the front Fresnel thin lens and the rear Fresnel thin lens; the curvature is the reciprocal of the curvature radius; The front Fresnel thin lens and the rear Fresnel thin lens satisfy the even aspheric surface of the following formula: ； Wherein, z represents the even aspheric surface, c represents the curvature, and k represents the conic constant; The quadratic coefficient α1 is determined by the following formula: ； The first term and the second term of the even aspheric surface are equal, and the conic constant k=-1 is obtained by analogy.

3. The underwater transmitted-light optical imaging system of claim 1, wherein, The front fixed lens is a meniscus lens, and the zoom lens group includes a first lens, a second lens and a third lens arranged in sequence along the optical path; The first lens moves between the front fixed lens and the second lens for variable magnification imaging; The second lens and the third lens move together between the first lens and the image sensor for focus compensation.

4. The underwater transmitted-light optical imaging system of claim 3, wherein, The process that the zoom lens group moves linearly differentially between the front fixed lens and the fixed-position image sensor includes: The moving distance of the first lens and the moving distance of the second lens and the third lens together satisfy a linear relationship, and the moving range of the first lens is much larger than the moving range of the second lens and the third lens together. The moving direction of the first lens is opposite to the moving direction of the second lens and the third lens together.

5. The underwater transmitted-light optical imaging system of claim 1, wherein, The dry chamber optical unit further comprises a waterproof window and a dry chamber sealed cabin, the front fixed lens and the zoom lens group are arranged in the dry chamber sealed cabin, the waterproof window is in a flat plate structure and arranged on the cabin wall of the dry chamber sealed cabin, and the aperture size of the window is the same as that of the front or rear Fresnel thin lens.

Images