Wide field of view elongated underwater imaging system for fishing in great depth wells

Abstract

The application discloses a wide-view field elongated underwater imaging system for fishing in a large-depth well, which comprises a flat pressure window, a first lens, a second lens, a third lens, a fourth lens, a first cemented lens, a second cemented lens, a fifth lens, a third cemented lens, a sixth lens, a filter and a seventh lens which are sequentially arranged from an object plane to an image plane along a light path. The wide-view field elongated underwater imaging system for fishing in a large-depth well has the characteristics of a long optical total length while ensuring a small optical aperture, so that the system can well adapt to a narrow and long environment in an oil well casing, form a good heat buffer, avoid camera failure caused by a high-temperature environment in the well, and has a large underwater view field and a large depth of field, effectively increases the imaging range of the system, and improves the efficiency of fishing operation in the well. The flat pressure window made of sapphire can bear a water depth pressure of more than 3000 meters.

Description

Technical Field

[0001] This invention relates to the field of underwater imaging technology, and more specifically to a wide-field-of-view, slender underwater imaging system for deep well salvage. Background Technology

[0002] With the continuous development of science and technology, underwater imaging systems are playing an increasingly important role in various fields. During offshore oil well operations, accidents can cause drill strings and other debris to fall into the well, collectively known as "fallen fish," which can significantly impact normal drilling. Timely retrieval is crucial to resuming normal operations. However, at great depths, retrieval often involves situations where the well is invisible and intangible. Imaging equipment can penetrate deep into the well to visualize the downhole conditions, ensuring a smooth and efficient retrieval process. Furthermore, regular maintenance of the drilling casing and screen is essential for ensuring normal production operations. High-quality imaging equipment helps quickly locate and pinpoint problems, facilitating well repair. Since the internal medium of offshore oil wells is water, an underwater imaging system is what we truly need during maintenance.

[0003] Offshore oil wells present unique downhole environments. Depths can reach thousands of meters, temperatures can exceed 100 degrees Celsius, and the casing diameter is extremely narrow. Therefore, underwater imaging systems need to achieve clear images with a large depth of field and wide field of view to improve observation efficiency and accuracy. However, a larger field of view often means a smaller depth of field, a larger optical aperture, and a smaller focal length. Furthermore, the system must be pressure-resistant and heat-resistant, and its structural dimensions must be adaptable to the narrow environment. This necessitates increasing the system length while reducing the aperture, presenting significant challenges and difficulties in system design and manufacturing. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a wide-field-of-view, slender underwater imaging system for deep well salvage, which solves the problem that existing underwater imaging systems are unable to achieve clear imaging under conditions of large depth of field, large field of view, and high pressure resistance, while also possessing the characteristics of small aperture, long overall length, and high temperature resistance.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a wide field of view slender underwater imaging system for deep well salvage, comprising a flat pressure-resistant window, a first lens, a second lens, a third lens, a fourth lens, a cemented lens one, a cemented lens two, a fifth lens, a cemented lens three, a sixth lens, a filter and a seventh lens arranged sequentially along the light rays from the object plane to the image plane.

[0006] The first lens is a biconcave lens with negative optical power.

[0007] The second lens mentioned above is a meniscus lens with a negative optical power, and its object side is concave.

[0008] The third lens mentioned above is a biconvex lens with a positive optical power.

[0009] The fourth lens mentioned above is a biconcave lens with a negative optical power.

[0010] The first cemented lens mentioned above is a doublet lens with a positive optical power.

[0011] The second cemented lens mentioned above is a doublet lens with a positive optical power.

[0012] The fifth lens mentioned above is a meniscus lens with a positive optical power.

[0013] The third cemented lens mentioned above is a doublet lens with a negative optical power.

[0014] The sixth lens mentioned above is a biconvex lens with a positive optical power.

[0015] The filter mentioned above is a flat mirror.

[0016] The seventh lens mentioned above is a biconvex lens with a positive optical power.

[0017] The system entrance pupil diameter EPD and the system focal length f satisfy: 0.22 < EPD / f < 0.35, where: the value range of f is 3.7 mm < f < 6.5 mm.

[0018] The total optical length of the system, that is, the distance TTL from the object side of the flat pressure-resistant window to the image plane and the size IMH of the image formed by the system on the camera chip satisfy: 11 < TTL / IMH < 17, where: the value range of TTL is 97 mm < TTL < 150 mm.

[0019] The present invention also has the following technical features:

[0020] The effective optical aperture DW1 of the object side of the flat pressure-resistant window and the distance T1 from the image side of the flat pressure-resistant window to the object side of the first lens on the optical axis satisfy: 5.2 < DW1 / T1 < 10.5.

[0021] The central thickness CT1 of the flat pressure-resistant window satisfies: 8 mm < CT1 < 12 mm.

[0022] An optical system aperture stop is also provided between the first cemented lens and the second cemented lens.

[0023] The central thickness CT1 of the first lens and the central thickness CT4 of the fourth lens satisfy: 0.11 < CT1 / CT4 < 0.3.

[0024] The radius of curvature R2 of the image-side surface of the first lens and the distance ET12 between the edges of the first lens and the second lens satisfy: 17.5 <R2 / ET12<35。

[0025] The radius of curvature R3 of the object-side surface of the second lens and the center thickness CT2 of the second lens satisfy: -1.3 <R3 / CT2<-0.8。

[0026] The focal length f3 of the third lens, the focal length f5 of the fifth lens, and the overall effective focal length f of the system satisfy: -0.05 <f / f3-f / f5<0.07。

[0027] The distance CT45 between the fourth lens and the cemented lens on the optical axis and the radius of curvature R8 of the image side surface of the fourth lens satisfy: 0.008 <CT45 / R8<0.015。

[0028] The distance ET89 between the edge of the cemented lens three and the edge of the sixth lens, and the radius of curvature R16 of the side surface of the cemented lens three, satisfy: 0.13 <ET89 / R16<0.16。

[0029] The effective optical aperture DA22 of the image-side surface of the seventh lens and the distance T2 from the image-side surface of the seventh lens to the imaging plane satisfy: 2.0 <DA22 / T2<3.3。

[0030] Compared with the prior art, the present invention has the following technical effects:

[0031] (I) The present invention provides a wide field of view slender underwater imaging system for deep well fishing. While ensuring a small optical aperture, it has the characteristic of a long optical length, which makes the system well adaptable to the narrow environment in the well casing, forming a good heat buffer and avoiding camera failure caused by the high temperature environment downhole. In addition, the system has a large underwater field of view and a large depth of field, which effectively increases the imaging range of the system and improves the efficiency of downhole fishing operations.

[0032] (II) The present invention provides a wide field of view slender underwater imaging system for deep well salvage. By using a sapphire flat pressure-resistant window, the system can withstand water pressure at depths of more than 3,000 meters.

[0033] (III) This invention uses multiple lens elements, including three sets of cemented lenses. Through the rational selection of lens materials, the rational allocation of lens power, center thickness, edge thickness, lens spacing, and the full optimization of different aberrations, the system has good imaging quality and is easy to manufacture and implement. Attached Figure Description

[0034] Figure 1 This is an optical path diagram of the wide field-of-view, slender underwater imaging system for deep well salvage according to the present invention.

[0035] Figure 2 The MTF curve of the wide field-of-view slender underwater imaging system for deep well salvage of the present invention is shown at an object distance of 300 mm.

[0036] Figure 3 The MTF curve of the wide field-of-view slender underwater imaging system for deep well fishing of the present invention is shown at an object distance of 500 mm.

[0037] Figure 4 The MTF curve of the wide field-of-view slender underwater imaging system for deep well salvage of the present invention is shown at an object distance of 1000 mm.

[0038] Figure 5 The field curvature and distortion curves of the wide field-of-view slender underwater imaging system for deep well retrieval of the present invention are shown at an object distance of 500 mm.

[0039] Figure 6 The axial chromatic aberration of the wide field-of-view slender underwater imaging system for deep well salvage of the present invention at an object distance of 500mm.

[0040] Figure 7 The vertical chromatic aberration curve of the wide field-of-view slender underwater imaging system for deep well salvage of the present invention at an object distance of 500 mm.

[0041] The meanings of the labels in the attached diagram are as follows:

[0042] E1 - Flat plate pressure-resistant window, L1 - First lens, L2 - Second lens, L3 - Third lens, L4 - Fourth lens, G1 - Cemented lens one, G2 - Cemented lens two, L5 - Fifth lens, G3 - Cemented lens two, L6 - Sixth lens, P1 - Filter, L7 - Seventh lens.

[0043] The specific content of the present invention will be further explained in detail below with reference to the embodiments. Detailed Implementation

[0044] Unless otherwise specified, all components in this invention are components known in the prior art.

[0045] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments. All equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0046] Example 1:

[0047] This embodiment presents a wide-field-of-view, slender underwater imaging system for deep well salvage operations, such as... Figure 1As shown, the array includes a flat pressure-resistant window E1, a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a cemented mirror G1, a cemented mirror G2, a fifth lens L5, a cemented mirror G3, a sixth lens L6, a filter P1, and a seventh lens L7, arranged sequentially along the light path from the object plane to the image plane.

[0048] The first lens L1 is a biconcave lens with negative optical power.

[0049] The second lens L2 is a meniscus lens with negative optical power and its object side is concave.

[0050] The third lens L3 is a biconvex lens with positive optical power.

[0051] The fourth lens L4 is a biconcave lens with negative optical power.

[0052] The cemented lens G1 is a cemented doublet lens with positive optical power.

[0053] The cemented lens G1 is a cemented doublet with positive optical power.

[0054] The fifth lens L5 is a meniscus lens with positive optical power.

[0055] The aforementioned cemented lens G3 is a cemented doublet lens with negative optical power.

[0056] The sixth lens L6 is a biconvex lens with positive optical power.

[0057] The filter P1 is a plane mirror.

[0058] The seventh lens L7 is a biconvex lens with positive optical power.

[0059] Except for filter P1, all lens surfaces are spherical, which effectively reduces the difficulty and cost of processing.

[0060] A biconcave lens is a lens that diverges a parallel incident beam of light outwards. It has a negative focal length and consists of two concave surfaces of equal curvature. It is commonly used for beam expansion, collimation, projection, and increasing the focal length of optical systems. Because of its negative focal length, a biconcave lens is suitable for diverging and converging beams; it is also called a diverging lens or a negative spherical lens. A biconcave lens can diverge a collimated beam to a virtual focal point and is typically used in Galilean beam expanders.

[0061] Meniscus Lenses are convex-concave lenses. This lens has a convex outer surface and a concave inner surface. If the convex curvature of the outer surface is greater than the concave curvature of the inner surface, the lens has a positive focal length and is used as a magnifying glass; if the concave curvature is large and the convex curvature is small, it is a negative meniscus lens, and the negative meniscus lens can be used to replace other negative lenses. Meniscus lenses are used to greatly reduce spherical aberration, and can obtain a smaller focal point and fewer aberrations than plano-convex lenses to improve the imaging quality. When used in combination with another lens, the positive meniscus lens can shorten the focal length, thereby increasing the numerical aperture (NA) of the system without introducing significant spherical aberration. When used to converge collimated light, the convex surface of the lens should face the light source.

[0062] Double Convex Lenses are composed of two convex surfaces with equal radii. They can focus light into a point and have a positive focal length. Due to the symmetrical shape on both sides, they are a more suitable single element for 1:1 imaging applications. They are commonly used in imaging relay systems and for imaging objects or focusing, collimating, and expanding beams at a finite conjugate distance. The characteristic of double convex lenses is that the larger the conjugate ratio, the greater the aberration generated. Double convex lenses are suitable for situations where the object and the image are on both sides of the lens, and the ratio of the image distance to the object distance (conjugate ratio) is between 0.2 and 5.

[0063] Glued lenses (achromatic lenses) are used to minimize or eliminate chromatic aberration. Their achromatic design also helps to minimize spherical aberration. Achromatic lenses are suitable for various applications such as fluorescence microscopes, image relays, detections, or spectroscopy. The manufacturing process of achromatic lenses includes gluing two elements together or mounting two elements in a housing. Compared with single-piece lenses, achromatic lenses can form smaller light spots.

[0064] The inner surface of the system flat pressure-resistant window E1 described in the present invention is coated with an anti-reflection film in the visible light band (400 - 700 nm), and the transmittance is greater than 99.3%, which is beneficial to improving the energy transmittance of the system and reducing the influence of stray light on imaging.

[0065] As a preference of this embodiment:

[0066] Furthermore, the system entrance pupil diameter EPD and the system focal length f satisfy: 0.22 < EPD / f < 0.35, where: the value range of f is 3.7 mm < f < 6.5 mm.

[0067] Satisfying the above relationship is beneficial to improving the imaging quality of the system, avoiding difficulties in installation caused by an overly large system aperture, while enhancing the light throughput of the system and increasing the system field of view and depth of field through the control of the focal length.

[0068] The total optical length of the system, i.e., the distance TTL from the object side of the flat pressure-resistant window E1 to the image plane and the size IMH of the image formed by the system on the camera chip, satisfy: 11 < TTL / IMH < 17, where: the value range of TTL is 97mm < TTL < 150mm.

[0069] Satisfying the above relational expression is beneficial to increasing the total length of the system, thereby buffering the heat transferred into the system at the flat pressure-resistant window E1, preventing the camera at the image plane of the system from being affected by high temperature, avoiding difficulties in installation caused by an overly large system aperture, and at the same time controlling the field of view range to avoid deterioration of the imaging effect due to an overly small image plane.

[0070] The effective optical aperture DW1 of the object side of the flat pressure-resistant window E1 and the distance T1 from the image side of the flat pressure-resistant window E1 to the object side of the first lens L1 on the optical axis satisfy: 5.2 < DW1 / T1 < 10.5.

[0071] Satisfying the above relational expression can make the aperture of the flat pressure-resistant window E1 within a reasonable range, and is also beneficial to enhancing the system's ability to collect large-field-of-view light beams.

[0072] The central thickness CT1 of the flat pressure-resistant window satisfies: 8mm < CT1 < 12mm.

[0073] Satisfying the above conditions enables the system to withstand the pressure of 3000 meters of water depth, reducing the overall size and weight of the system.

[0074] An optical system aperture stop is also provided between the cemented lens G1 and the cemented lens G2.

[0075] Satisfying the above conditions can effectively enhance the system's ability to control chromatic aberration, spherical aberration, and coma, improving the imaging quality.

[0076] The central thickness CT1 of the first lens and the central thickness CT4 of the fourth lens satisfy: 0.11 < CT1 / CT4 < 0.3.

[0077] Satisfying the above conditions is beneficial to controlling the sizes of each lens within a reasonable range, optimizing the deflection angles of light rays passing through each lens, and enhancing the imaging quality of the system.

[0078] The curvature radius R2 of the image side of the first lens L1 and the distance ET12 between the edge of the first lens L1 and the second lens L2 satisfy: 17.5 < R2 / ET12 < 35.

[0079] Satisfying the above conditions can prevent the edge distance between the first lens and the second lens from being too small, improve the processing manufacturability of the first lens, and at the same time reduce the maximum aperture of the lenses in the system.

[0080] The radius of curvature R3 of the object side surface of the second lens L2 and the center thickness CT2 of the second lens L2 satisfy: -1.3 <R3 / CT2<-0.8。

[0081] Meeting the above conditions helps reduce the difficulty of lens manufacturing, reduce system sensitivity, and improve the system's aberration correction capability.

[0082] The focal length f3 of the third lens L3, the focal length f5 of the fifth lens L5, and the overall effective focal length f of the system satisfy: -0.05 <f / f3-f / f5<0.07。

[0083] Meeting the above conditions can prevent the system's optical focal length from becoming too concentrated and keep the spacing between the lenses within a reasonable range.

[0084] The distance CT45 between the fourth lens L4 and the cemented lens G1 on the optical axis and the radius of curvature R8 of the image side surface of the fourth lens L4 satisfy: 0.008 <CT45 / R8<0.015。

[0085] Meeting the above conditions helps control the curvature of the image side of the fourth lens L4, improves the light-gathering ability, and allows for adjustment of the imaging position, thereby increasing the overall length of the system.

[0086] The edge spacing ET89 between the cemented lens 3G3 and the sixth lens L6, and the radius of curvature R16 of the image side surface of the cemented lens 3G3, satisfy: 0.13 <ET89 / R16<0.16。

[0087] Meeting the above conditions helps to enhance the system's ability to balance off-axis aberrations and reduce the difficulty of lens processing and assembly.

[0088] The effective optical aperture DA22 of the image-side surface of the seventh lens L7 and the distance T2 from the image-side surface of the seventh lens L7 to the imaging plane satisfy: 2.0 <DA22 / T2<3.3。

[0089] Satisfying the above relationship can effectively reduce the effective optical aperture of the lens, avoid excessive deflection of light on the seventh lens L7, improve the system's ability to converge light beams, and reduce the difficulty of camera assembly and adjustment.

[0090] Specific applications are as follows:

[0091] Downhole fishing of offshore oil wells is carried out in the well casing, which has a small diameter. As the fishing depth increases, the pressure increases and the temperature changes significantly, reaching up to 150℃. To meet these requirements, firstly, while ensuring imaging quality, the aperture of each lens must be controlled within a small range. On this basis, the overall length of the system is increased. When heat enters the system through the flat plate pressure-resistant window E1, the heat gradually weakens during the transfer process because the camera and its electronic components are located at the rear of the system, thus ensuring that the camera part of the system is not damaged by high temperature.

[0092] This system is designed for observation and salvage operations in offshore oil wells. Therefore, the first surface S0, i.e., the material medium, is seawater, and the well depth is required to be greater than 3000 meters. This means the system must be able to withstand underwater pressure exceeding 3000 meters. Therefore, the system is designed to withstand pressure of 35 MPa or higher. To achieve this performance, the L0 lens, which is in contact with seawater, uses a sapphire flat pressure-resistant window E1 to bear the pressure. The minimum required thickness is calculated using the following formula:

[0093] T g =0.5A(KfΔp / S) 1 / 2

[0094] In the above formula, A is the light transmission diameter of the flat pressure-resistant window E1, K is the support condition constant, which is taken as 0.75 under clamping conditions, f is empirically taken as 4, Δp is the pressure difference borne by the flat pressure-resistant window E1, and S is the typical value of the minimum fracture stress of the flat pressure-resistant window E1 material, which is taken as 300 MPa. In this system, the light transmission diameter of the flat pressure-resistant window E1 is 25 mm. It can be calculated that the minimum thickness of the flat pressure-resistant window E1 is 7.4 mm. For ease of processing, it is taken as 10 mm here.

[0095] This system design uses a sapphire-plated pressure-resistant window E1 for underwater system design. With a fixed image plane size, it optimizes and improves the underwater imaging field of view and reduces the minimum observation distance. On the other hand, it sets up multiple structures for the imaging object distance, and the system can have good imaging quality at 300mm, 500mm and 1000mm, increasing the system depth of field.

[0096] The following table shows the specific parameters of the wide-field-of-view, slender underwater imaging system for deep well salvage in this embodiment at an object distance of 500mm:

[0097] Table 1

[0098]

[0099]

[0100] In Table 1, the radius of curvature refers to the radius of curvature of each optical surface, the thickness refers to the thickness at the center of the lens or the thickness of the medium in front of and behind the lens, and the material used for the lens is characterized by the refractive index and the dispersion coefficient.

[0101] Except for the sapphire flat pressure-resistant window E1, all other lens materials use commercial glass materials from Chengdu Guangming. The surface curvature radius, lens thickness, and spacing of each lens are controlled within a reasonable range, which is beneficial to the manufacturing and processing of the lenses.

[0102] The use of three sets of cemented doublet lenses reduces chromatic aberration and on-axis spherical aberration in the system, while also helping to reduce the lateral size of the system.

[0103] The technical specifications of the wide-field-of-view, slender underwater imaging system for deep well salvage in this embodiment are shown in Table 2:

[0104] Table 2

[0105]

[0106]

[0107] In oil well casing, the presence of turbid fluid limits the effective imaging distance. To image a large area of ​​the sidewall within this short distance, the imaging system needs a large depth of field and field of view. This system has an effective imaging object distance of 300mm to 1000mm and a field of view greater than 68 degrees, increasing the imaging range and improving the system's observation and operational efficiency.

[0108] The optical system of this invention operates at the visible light wave end. The image plane uses a SONY IMX334 image sensor with a pixel size of 2 micrometers, a resolution of 3840*2160, and a diagonal size of 8.8mm. The final image plane completely covers the sensor target surface, and the resolution is better than 90lp / mm, enabling the system to acquire high-quality optical images that are easy to analyze on site.

[0109] The optical system's focal length is controlled within 6mm, and the F-number (aperture value) is controlled within 4. Except for the flat pressure-resistant window E1, the maximum lens diameter is less than 15mm, which improves the system's field of view, ensures the system's light transmission, and avoids the problem of the system being unable to be lowered into the well due to its excessive lateral size.

[0110] While ensuring a small lateral dimension, the total length of the optical system was optimized to over 110mm. By buffering and isolating heat in space, the normal operation of the image sensor in the high-temperature environment downhole was effectively guaranteed.

[0111] The MTF curve of the wide-field-of-view, slender underwater imaging system for deep well fishing of the present invention at an object distance of 300 mm is shown below. Figure 2As shown in the figure, the system contrast ratio reaches over 90 lp / mm, indicating good imaging resolution.

[0112] The MTF curve of the wide-field-of-view, slender underwater imaging system for deep well fishing of the present invention at an object distance of 500 mm is shown below. Figure 3 As shown in the figure, the system contrast ratio reaches over 90 lp / mm, indicating good imaging resolution.

[0113] The MTF curve of the wide-field-of-view, slender underwater imaging system for deep well fishing of the present invention at an object distance of 1000mm is shown below. Figure 4 As shown in the figure, the system contrast ratio reaches over 90 lp / mm, indicating good imaging resolution.

[0114] The field curvature and distortion curves of the wide-field-of-view, slender underwater imaging system for deep well fishing of the present invention at an object distance of 500 mm are shown below. Figure 5 As shown, the system field curvature has been corrected, and the optical distortion is reasonable and can meet the needs of downhole observation.

[0115] The axial and transverse chromatic aberration curves of the wide-field-of-view, slender underwater imaging system for deep well fishing of the present invention at an object distance of 500 mm are shown below. Figure 6 and Figure 7 As shown, the system's color difference is controlled within a small range, which can meet the imaging requirements of downhole retrieval.

[0116] The above technical solutions are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions conceived by those skilled in the art within the scope of the technology disclosed in the present invention without creative effort are covered within the scope of protection of the present invention.

Claims

1. A wide field of view, elongated, underwater imaging system for fishing in great depth wells, characterized in that, The system comprises, in sequence along the light path from the object plane to the image plane, a flat pressure window, a first lens, a second lens, a third lens, a fourth lens, a first cemented lens, a second cemented lens, a fifth lens, a third cemented lens, a sixth lens, a filter and a seventh lens. The first lens is a double-concave lens with negative focal power. The second lens is a meniscus lens with negative focal power, and the object side of the second lens is concave. The third lens is a double-convex lens with positive focal power. The fourth lens is a double-concave lens with negative focal power. The first cemented lens is a double-cemented lens with positive focal power. The second cemented lens is a double-cemented lens with positive focal power. The fifth lens is a meniscus lens with positive focal power. The third cemented lens is a double-cemented lens with negative focal power. The sixth lens is a double-convex lens with positive focal power. The filter is a flat mirror. The seventh lens is a double-convex lens with positive focal power. The system entrance pupil diameter EPD and the system focal length f satisfy 0.22<EPD / f<0.35, wherein the value range of f is 3.7mm<f<6.5mm. The system total track length TTL, which is the distance from the object side of the flat pressure window to the image plane, and the system image height IMH satisfy 11<TTL / IMH<17, wherein the value range of TTL is 97mm<TTL<150mm.

2. The wide field of view, elongated, underwater imaging system for fishing in great depth wells of claim 1, wherein, The effective optical aperture DW1 of the object side of the flat pressure window and the distance T1 from the image side of the flat pressure window to the object side of the first lens on the optical axis satisfy 5.2<DW1 / T1<10.

5. The central thickness CT1 of the flat pressure window satisfies 8mm<CT1<12mm.

3. The wide field of view, elongated, underwater imaging system for fishing in great depth wells of claim 1, wherein, An optical system aperture stop is further arranged between the first cemented lens and the second cemented lens. The central thickness CT1 of the first lens and the central thickness CT4 of the fourth lens satisfy 0.11<CT1 / CT4<0.

3.

4. The wide field of view, elongated, underwater imaging system for fishing in great depth wells of claim 1, wherein, The curvature radius R2 of the image side of the first lens and the distance ET12 between the edge of the first lens and the second lens satisfy 17.5<R2 / ET12<35. The curvature radius R3 of the object side of the second lens and the central thickness CT2 of the second lens satisfy -1.3<R3 / CT2<-0.

8.

5. The wide field of view, elongated, underwater imaging system for fishing in great depth wells of claim 1, wherein, The focal length f3 of the third lens, the focal length f5 of the fifth lens and the overall effective focal length f of the system satisfy -0.05<f / f3-f / f5<0.

07.

6. The wide field of view slim underwater imaging system for fishing in a large depth well according to claim 1, wherein the distance CT45 between the fourth lens and the first cemented lens on the optical axis and the curvature radius R8 of the image side of the fourth lens satisfy 0.008<CT45 / R8<0.

015. The distance ET89 between the edge of the third cemented lens and the sixth lens and the curvature radius R16 of the image side of the third cemented lens satisfy 0.13<ET89 / R16<0.

16. The effective optical aperture DA22 of the image side of the seventh lens and the distance T2 from the image side of the seventh lens to the image plane satisfy 2.0<DA22 / T2<3.3.

Images