Integrated underwater imaging lens with lens group and window

Abstract

This application discloses an integrated underwater imaging lens with a lens assembly and window, relating to the field of optical design technology. The integrated underwater imaging lens comprises: a first lens, a meniscus lens with negative optical power, arranged sequentially from the object side to the image side, serving as a window to isolate water and air; a second lens with negative optical power; a third lens with positive optical power; a fourth lens with positive optical power; an aperture stop; a fifth lens with negative optical power; a sixth lens with positive optical power; and a seventh lens with positive optical power. The lens has a focal length of 10.5 mm, an F-number of 3, and a full field of view of 60°. This application achieves system miniaturization by integrating the optical window with the first lens, enabling it to both seal and participate in aberration correction. It uses only seven spherical lenses, achieving an MTF > 0.5@100lp / mm across the entire field of view, and possesses advantages such as excellent imaging quality, compact structure, and low manufacturing cost.

Description

Technical Field

[0001] This application relates to the field of optical design technology, and more specifically, to an underwater imaging lens that integrates a lens group and a window. Background Technology

[0002] With the development of underwater optical imaging applications, in recent years, the demand for deep-sea resource exploration, seabed target search, underwater environmental monitoring, and underwater recreational photography has exploded, placing higher and more comprehensive requirements on imaging systems in terms of resolution, field of view, depth of field, low-light performance, size and weight, cost control, and reliability.

[0003] Because water and air have different refractive indices, light refracts when it enters the lens from water, resulting in severe aberrations. Underwater optical imaging systems typically consist of three parts: a pressure-resistant window, an imaging lens assembly, and an image detector. The window must withstand external hydrostatic pressure while ensuring controllable aberrations at the seawater-air interface. Traditional separate window and lens assembly architectures are no longer sufficient to simultaneously meet these multi-dimensional requirements.

[0004] The ultra-short focal length underwater wide-angle monitoring lens proposed by Hu Feng et al. in "Advances in Lasers & Optoelectronics" 2023, 60(21):295-299 adopts a flat-pane window aspherical plastic lens group. This scheme uses a 10mm thick flat glass as a seawater barrier, and the optical power of the window and the lens group is completely decoupled. The advantages are simple structure and convenient assembly and adjustment. However, since the flat plate introduces a spherical aberration-coma coupling term that is approximately proportional to the cube of the incident angle for any field of view, the designer has to introduce two high-order aspherical plastic lenses in the rear group for compensation. Although the aspherical molding process is mature, the plastic surface has poor stability under deep-sea high and low temperature cycles (-2℃~+35℃) and low pressure resistance, and is only suitable for shallow water environments ≤20m. In addition, the thickness of the flat plate increases linearly with the working depth. When the designed diving depth reaches 1000m, the thickness needs to be ≥45mm, and the axial dimension and weight of the system deteriorate sharply.

[0005] Cao Yihui (Master's thesis, Xi'an University of Technology, 2013) and Wang Xuefeng (PhD dissertation, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, 2022) respectively disclosed a thick-walled hemispherical dome and a concentric, uniformly thick sapphire spherical cap window. This scheme utilizes the isotropic geometry of the spherical cap to convert external hydrostatic pressure into uniform thin-film stress, theoretically achieving the optimal pressure-to-weight ratio. However, the concentric, uniformly thick spherical cap is optically equivalent to a "meniscus negative lens," with its center of curvature located on the system's optical axis. This introduces negative spherical aberration at on-axis points and coma-astigmatism mixed terms proportional to the square of the field of view at off-axis points. To balance these aberrations, Wang Xuefeng's scheme additionally arranges six groups of ten zoom lenses behind the aperture stop, resulting in a system length >120mm and a lens weight >1.8kg, while still requiring the introduction of two higher-order aspherical surfaces. More importantly, the uniform thickness spherical cap must be made of sapphire with high elastic modulus (E≈400GPa) or oxynitride transparent ceramic, which has a high unit price and long processing cycle, resulting in high overall machine cost.

[0006] Therefore, there is an urgent need for an underwater imaging lens that integrates the lens group and the window to solve one of the aforementioned technical problems. Summary of the Invention

[0007] The purpose of this application is to provide an underwater imaging lens that integrates a lens group and a window, thereby solving at least one of the aforementioned technical problems. The specific solution is as follows: According to a specific embodiment of this application, this application provides an integrated underwater imaging lens with a lens assembly and a window, comprising the following components arranged sequentially along the optical path from the object side to the image side: The first lens is a meniscus lens with negative optical power; The second lens is a lens with negative optical power; The third lens is a lens with positive optical power; The fourth lens is a lens with positive optical power; Aperture; The fifth lens is a lens with negative optical power; The sixth lens is a lens with positive optical power; The seventh lens is a lens with positive optical power.

[0008] Furthermore, the air gap between the aperture stop and the fourth lens is 0.871 mm; the air gap between the aperture stop and the fifth lens is 1.310 mm.

[0009] Furthermore, the first lens is made of sapphire; the second, fourth, and sixth lenses are made of low-dispersion glass; and the third, fifth, and seventh lenses are made of high-refractive-index glass.

[0010] Furthermore, the low-dispersion glass is designated as H-FK61B; the high-refractive-index glass includes at least one of the following grades: H-ZLAF4LB, H-LAK2A, H-ZF52A, H-LAF53, and H-ZPK1A.

[0011] Furthermore, the focal length of the first lens and the focal length of the integrated underwater imaging lens (mirror group and window) satisfy the following condition: -50 < / f <0; The focal length of the second lens and the focal length of the integrated underwater imaging lens (lens group and window) satisfy the following condition: -8 < / f <-2; The focal length of the third lens and the focal length of the integrated underwater imaging lens (mirror group and window) satisfy the following relationship: 1 < / f <5; The focal length of the fourth lens and the focal length of the integrated underwater imaging lens (mirror group and window) satisfy the following relationship: 1 < / f <5; The focal length of the fifth lens and the focal length of the integrated underwater imaging lens (lens group and window) satisfy the following condition: -3.2 < / f <-0.6; The focal length of the sixth lens and the focal length of the integrated underwater imaging lens (lens group and window) satisfy the following condition: 0.8 < / f <4.2; The focal length of the seventh lens and the focal length of the integrated underwater imaging lens (mirror group and window) satisfy the following relationship: 1 < / f <6.

[0012] Furthermore, the integrated underwater imaging lens with lens group and window has a focal length of 10.5mm, an aperture of F / 3, and a full field of view of 60°.

[0013] Furthermore, The air gap between the first lens and the second lens is 7.817 mm; The air gap between the second lens and the third lens is 18.545 mm; The air gap between the third lens and the fourth lens is 3.461 mm; The air gap between the sixth lens and the seventh lens is 0.490 mm.

[0014] Furthermore, the seventh lens also includes a flat glass plate along its emission direction. The air gap between the flat glass plate and the seventh lens is 18.510 mm. The flat glass plate is made of D263TECO and has a thickness of 0.5 mm.

[0015] Furthermore, the optical transfer function of the integrated underwater imaging lens assembly and window satisfies: MTF>0.5@100lp / mm.

[0016] Furthermore, the first lens has an object-side radius of curvature of 525.162 mm, an image-side radius of curvature of 25.563 mm, and a center thickness of 10.0 mm; the second lens has an object-side radius of curvature of 45.729 mm, an image-side radius of curvature of 14.138 mm, and a center thickness of 2.6 mm.

[0017] Compared with the prior art, the above-described solutions of this application have at least the following beneficial effects: 1. This application provides an integrated underwater imaging lens with a lens assembly and window. By combining the traditionally separate sealed window with the first lens of the imaging system, it becomes a meniscus lens with negative optical power. This integrated lens assembly and window design directly reduces one independent optical element in terms of physical structure, laying the foundation for system miniaturization. Furthermore, this solution uses only seven spherical lenses and avoids complex processes such as aspherical or cemented lenses, greatly reducing the lens's processing difficulty, production cycle, and manufacturing cost, making the widespread application of high-performance underwater lenses possible.

[0018] 2. This application provides an integrated underwater imaging lens with a lens group and window, incorporating the window as an effective optical correction unit into the optical design. The negative optical power and meniscus shape of the first lens are specifically used to compensate for strong aberrations (such as negative spherical aberration and field curvature) generated when light enters the lens from water (a high refractive index medium). The specific optical power allocation of the front and rear lens groups in "negative-negative-positive-positive" and "negative-positive-positive" forms an effective aberration balancing system. This simplifies the structure while achieving high-resolution imaging with MTF>0.5@100 lp / mm across the entire field of view, effectively solving the image quality degradation problem caused by the additional aberrations introduced by the independent window in traditional underwater lenses. Attached Figure Description

[0019] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. It is obvious that the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. In the drawings: Figure 1 This is a schematic diagram of the structure of an underwater imaging lens integrating a lens assembly and a window, provided in an embodiment of the present invention. Figure 2 A graph of the optical transfer function in the 486.1nm-656.3nm band provided for embodiments of the present invention; Figure 3 An optical dot pattern provided for an embodiment of the present invention.

[0020] Explanation of reference numerals in the attached figures: First lens L1, second lens L2, third lens L3, fourth lens L4, aperture S10, fifth lens L5, sixth lens L6, seventh lens L7, flat glass L8, object side of first lens S1, image side of first lens S2, object side of second lens S3, image side of second lens S4, object side of third lens S5, image side of third lens S6, object side of fourth lens S7, image side of fourth lens S8, aperture S9, object side of fifth lens S10, image side of fifth lens S11, object side of sixth lens S12, image side of sixth lens S13, object side of seventh lens S14, image side of seventh lens S15, incident surface of flat glass S16, exit surface of flat glass S17, detection surface S18. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0022] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device. Without further limitation, an element defined by the phrase "comprising one" does not exclude the presence of other identical elements in the article or device that includes said element.

[0023] The optional embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0024] like Figure 1As shown in the specific embodiment of the present invention, the present invention provides an integrated underwater imaging lens with a lens group and a window, comprising eight optical elements arranged sequentially from the object side to the image side: a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, an aperture stop STO, a fifth lens L5, a sixth lens L6, a seventh lens L7, and a flat glass L8.

[0025] In this embodiment, the first lens L1, the second lens L2, and the third lens L3 constitute a front lens group with negative optical power, while the fourth lens L4, the fifth lens L5, the sixth lens L6, and the seventh lens L7 constitute a rear lens group with positive optical power. The negative optical power structure of the front lens group can bend light rays with a large field of view, allowing them to enter the system at a greater angle. This ensures a full field of view of 60° while providing space for the rear lens group to process the light. Simultaneously, the front lens group generates aberrations that cancel out those of the rear lens group. The rear lens group as a whole forms a quasi-telephoto lens group with positive optical power. The beam expanded by the front lens group is divergent, while the rear lens group converges the beam. The rear lens group finely corrects residual aberrations, especially higher-order aberrations, chromatic aberration, and astigmatism, after pre-correction by the front lens group, achieving high imaging quality.

[0026] The technical solution in this application embodiment achieves excellent image quality and sufficient back working distance by finely allocating the optical power of the front lens group and the rear lens group. This allows the lateral aberrations generated by the front and rear groups to cancel each other out, ultimately achieving a large field of view and short focal length while solving the technical problems of large size and difficult aberration correction in traditional underwater lenses.

[0027] As an optional implementation, the main parameters of an integrated underwater imaging lens with a lens group and window are shown in Table 1: Table 1. Main parameters of the integrated underwater imaging lens group and window. The first lens L1, serving as the front window of the integrated underwater imaging lens group and window, is a meniscus lens with negative optical power; in this example, it is a concave meniscus lens. The object-side surface S1 of the first lens is convex with a radius of curvature of 525.162 mm; the image-side surface S2 is concave with a radius of curvature of 25.563 mm; and the center thickness is 10.0 mm. It is made of sapphire or other optical materials with a refractive index range of 1.45-1.9, possessing both excellent optical performance and mechanical strength, capable of withstanding high-pressure underwater environments, and also serving a sealing and isolation function. The focal length of the first lens L1 is... The ratio of -50 to the system focal length f satisfies: / f<0. The first lens L1 compensates for the large negative spherical aberration and negative field curvature generated on the first surface when light enters the lens from the water, thus canceling out the main underwater aberrations at the source. The thickness of the first lens L1 can be selected according to the actual water depth, and this embodiment does not limit it.

[0028] The second lens, L2, is a lens with negative optical power, further enhancing the negative optical power of the front lens group. It utilizes a low-dispersion material to begin correcting axial chromatic aberration, preventing the first lens, L1, from bearing the entire negative optical power and introducing excessive higher-order aberrations. The object-side radius of curvature of the second lens, S3, is 45.729 mm, and the image-side radius of curvature, S4, is 14.138 mm. Its center thickness is 2.6 mm. The material used is low-dispersion glass H-FK61B, effectively correcting chromatic aberration. The focal length of the second lens, L2, is... The ratio of the system focal length f to the system focal length f satisfies: -8 < / f<-2.

[0029] The third lens, L3, is a lens with positive optical power. The object-side radius of curvature (S5) is 20.414 mm, the image-side radius of curvature (S6) is 51.495 mm, and the center thickness is 2.5 mm. It is made of high-refractive-index glass H-ZLAF4LB. The focal length of the third lens L3 is... The ratio of the system focal length f to the system focal length f satisfies: 1 < / f<5.

[0030] The fourth lens, L4, is a lens with positive optical power. Its object-side radius of curvature (S7) is 22.646 mm, its image-side radius of curvature (S8) is -76.339 mm, and its center thickness is 3.2 mm. It is made of H-LAK2A material. The focal length of the fourth lens L4 is... The ratio of the system focal length f to the system focal length f satisfies: 1 < / f<5.

[0031] The third lens L3 and the fourth lens L4 balance the excessive negative spherical aberration and negative field curvature generated by the first lens L1 and the second lens L2, and begin to converge the diverging beam towards the optical axis; the cancellation of positive and negative aberrations begins inside the front lens group to prevent the accumulation of a single type of aberration to an uncontrollable level, and prepares the beam to pass through the aperture stop STO and enter the rear lens group.

[0032] An aperture stop STO is disposed between the fourth lens L4 and the fifth lens L5. The air gap between the aperture stop STO and the image side surface S8 of the fourth lens is 0.871 mm, and the air gap between the aperture stop STO and the object side surface S10 of the fifth lens is 1.310 mm. In the embodiments of this application, when the aperture stop STO is regarded as a virtual surface, it is the aperture stop S9.

[0033] The fifth lens, L5, is a lens with negative optical power, precisely correcting astigmatism and field curvature. Utilizing its high dispersion characteristics, it works in conjunction with the preceding and following positive lenses to further correct chromatic aberration at magnification. The object-side radius of curvature (S10) of the fifth lens is -17.777 mm, the image-side radius of curvature (S11) is 23.166 mm, and the center thickness is 2.5 mm. It is made of high-refractive-index, high-dispersion glass H-ZF52A, and works in combination with the positive lenses to correct astigmatism and field curvature in the system. The focal length of the fifth lens L5 is... The ratio of the system focal length f to the system focal length f satisfies: -3.2 < / f<-0.6.

[0034] The sixth lens, L6, is a lens with positive optical power. The object-side radius of curvature (S12) is -234.369 mm, the image-side radius of curvature (S13) is -15.070 mm, and the center thickness is 2.5 mm. It is made of H-LAF53 material. The focal length of the sixth lens, L6, is... The ratio of the system focal length f to the system focal length f satisfies: 0.8 < / f<4.2.

[0035] The seventh lens, L7, is a lens with positive optical power. The object-side radius of curvature (S14) is 20.692 mm, the image-side radius of curvature (S15) is -216.075 mm, and the center thickness is 2.5 mm. It is made of H-ZPK1A material. The focal length of the seventh lens L7 is... The ratio of the system focal length f to the system focal length f satisfies: 1 < / f<6 range.

[0036] The sixth lens L6 and the seventh lens L7 provide the main positive optical power of the integrated underwater imaging lens group and window, complete the final beam convergence, and balance the remaining spherical aberration and coma of the system; together with the fifth lens L5, they complete the flattening of the entire image field and the final optimization of aberrations.

[0037] The flat glass L8 is positioned behind the seventh lens L7, with an air gap of 18.510mm between it and the image side S15 of the seventh lens. It is made of D263TECO material, 0.5mm thick, and serves to protect the imaging sensor.

[0038] In this embodiment, the integrated underwater imaging lens with mirror group and window has a focal length of f=10.5mm, an aperture of F / 3, and a full field of view of 60°. For example... Figure 2 As shown, the optical transfer function curves indicate that at a spatial frequency of 100 lp / mm, the MTF value is greater than 0.5 across the entire field of view, and greater than 0.7 in the central field of view, approaching the diffraction limit. Quantitative verification demonstrates that the resolution of the integrated underwater imaging lens and window group meets high-definition requirements, while maintaining high contrast at the edge fields of view. Figure 3The dot plots shown indicate that the RMS dot diameters for the 0, 0.5, 0.7, and 1.0 fields of view are all <2.2 µm, meaning that the RMS radius of the diffuse dot in each field of view is smaller than the pixel size, indicating good energy concentration and ensuring clear and sharp imaging. The underwater imaging lens with an integrated lens assembly and window designed according to the technical solution provided in this application has aberrations corrected to near the diffraction limit within a 60° field of view, achieving high-definition imaging without the need for an aspherical surface.

[0039] This application also provides device embodiments that follow the above embodiments. The interpretation of the same names is the same as that of the above embodiments, and they have the same technical effects as those of the above embodiments. They will not be described again here.

[0040] The basic lens structure and optical power distribution remain unchanged, but some parameters are adjusted: The material of the first lens L1 can be replaced with synthetic quartz to reduce costs while maintaining compressive strength; the air gap between the second lens L2 and the third lens L3 can be adjusted within the range of 15-20mm; the material of the fifth lens L5 can be other high dispersion glass such as H-ZF1, H-ZF3, etc.; the focal length ratio of each lens remains within the original range.

[0041] This application presents an integrated underwater imaging lens with a lens assembly and window. By designing the pressure-resistant window as a meniscus lens with strong negative optical power and integrating it as the first lens L1 into the optical system, it not only serves the physical function of isolating the water body but also becomes a key optical component for actively correcting underwater aberrations and forming an anti-telephoto structure. Based on this, by employing seven spherical single lenses and precisely arranging them according to a strict "negative-negative-positive-positive" and "negative-positive-positive" optical power sequence, combined with a strategic combination of low-dispersion and high-dispersion glass materials and key constraints on air gap and focal length ratio, a highly coordinated optical system with intrinsically balanced aberrations is constructed. The solution provided in this application ultimately achieves the following significant effects and advantages: In terms of optical performance, it achieves high-resolution imaging with MTF>0.5@100 lp / mm across the entire 60° field of view, and the image quality is uniform and close to the diffraction limit; in terms of structure, it achieves a significant reduction in the overall length of the system, completing the miniaturization and weight reduction of the lens; in terms of engineering and cost, it uses spherical lenses throughout, avoiding complex processes such as aspherical or cemented lenses, greatly reducing the processing difficulty and manufacturing cost; at the same time, the sapphire material and bridge arch structure used in the first lens L1 ensure the lens's excellent pressure resistance and environmental adaptability.

[0042] Finally, it should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems or apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple, and relevant parts can be referred to the method section.

[0043] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. An underwater imaging lens integrating a lens group and a window, characterized in that, Including the following sequentially arranged elements along the optical path from the object side to the image side: The first lens is a meniscus lens with negative optical power; The second lens is a lens with negative optical power; The third lens is a lens with positive optical power; The fourth lens is a lens with positive optical power; Aperture; The fifth lens is a lens with negative optical power; The sixth lens is a lens with positive optical power; The seventh lens is a lens with positive optical power.

2. The underwater imaging lens integrating lens group and window according to claim 1, characterized in that, The air gap between the aperture stop and the fourth lens is 0.871 mm; the air gap between the aperture stop and the fifth lens is 1.310 mm.

3. The underwater imaging lens integrating lens group and window according to claim 1, characterized in that, The first lens is made of sapphire; the second, fourth, and sixth lenses are made of low-dispersion glass; and the third, fifth, and seventh lenses are made of high-refractive-index glass.

4. The underwater imaging lens integrating lens group and window according to claim 3, characterized in that, The low-dispersion glass is designated as H-FK61B; the high-refractive-index glass includes at least one of the following grades: H-ZLAF4LB, H-LAK2A, H-ZF52A, H-LAF53, and H-ZPK1A.

5. The underwater imaging lens integrating lens group and window according to claim 1, characterized in that, The focal length of the first lens and the focal length of the integrated underwater imaging lens (lens group and window) satisfy the following condition: -50 < / f <0; The focal length of the second lens and the focal length of the integrated underwater imaging lens (lens group and window) satisfy the following condition: -8 < / f <-2; The focal length of the third lens and the focal length of the integrated underwater imaging lens (mirror group and window) satisfy the following relationship: 1 < / f <5; The focal length of the fourth lens and the focal length of the integrated underwater imaging lens (mirror group and window) satisfy the following relationship: 1 < / f <5; The focal length of the fifth lens and the focal length of the integrated underwater imaging lens (lens group and window) satisfy the following condition: -3.2 < / f <-0.6; The focal length of the sixth lens and the focal length of the integrated underwater imaging lens (lens group and window) satisfy the following condition: 0.8 < / f <4.2; The focal length of the seventh lens and the focal length of the integrated underwater imaging lens (mirror group and window) satisfy the following relationship: 1 < / f <6.

6. The underwater imaging lens integrating lens group and window according to claim 1, characterized in that, The integrated underwater imaging lens with lens group and window has a focal length of 10.5mm, an aperture of F / 3, and a full field of view of 60°.

7. The underwater imaging lens integrating lens group and window according to claim 1, characterized in that, The air gap between the first lens and the second lens is 7.817 mm; The air gap between the second lens and the third lens is 18.545 mm; The air gap between the third lens and the fourth lens is 3.461 mm; The air gap between the sixth lens and the seventh lens is 0.490 mm.

8. The underwater imaging lens integrating lens group and window according to claim 1, characterized in that, The seventh lens also includes a flat glass plate along its exit direction. The air gap between the flat glass plate and the seventh lens is 18.510 mm. The flat glass plate is made of D263TECO and has a thickness of 0.5 mm.

9. The underwater imaging lens integrating lens group and window according to claim 1, characterized in that, The optical transfer function of the integrated underwater imaging lens group and window satisfies: MTF>0.5@100lp / mm.

10. The underwater imaging lens integrating lens group and window according to claim 1, characterized in that, The first lens has an object-side radius of curvature of 525.162 mm, an image-side radius of curvature of 25.563 mm, and a center thickness of 10.0 mm; the second lens has an object-side radius of curvature of 45.729 mm, an image-side radius of curvature of 14.138 mm, and a center thickness of 2.6 mm.

Images