A front wide-angle lens for underwater use

Abstract

The present invention discloses a front wide-angle lens for underwater use, comprising a first lens, a second lens, a third lens and a fourth lens, wherein the first lens and the second lens are negative lenses, the third lens and the fourth lens are positive lenses, and the effective aperture ranges of the first lens, the second lens, the third lens and the fourth lens are 110-115mm, 80-85mm, 70-75mm and 57-62mm, respectively. In addition to isolating external water and resisting external water pressure, the first lens has the functions of expanding the shooting angle of view and correcting chromatic aberration. The first lens also replaces two lenses in the prior art, reduces the height of the front wide-angle lens, and reduces the weight and production cost. When used underwater, the front wide-angle lens can be directly adapted to a camera with a maximum viewing angle of 84 degrees, widening the viewing angle to 130 degrees; it reduces the need for the underwater photographer in the prior art to adjust the viewing angle of the zoom lens to reduce it to eliminate black corners and other extra repeated operations.

Description

Technical Field

[0001] The present invention relates to the field of optical imaging technology, and is applied to underwater recording and shooting environments, and specifically to a front wide-angle lens that can provide a wider field of view and improve optical imaging quality (for example, reduce optical problems such as chromatic aberration and deformation) when used with a digital camera. The front wide-angle lens can be replaced underwater. Background Art

[0002] Portable digital cameras are the first choice for many photography enthusiasts because of their compact size, portability, and high cost-effectiveness. In recent years, with the rapid development of electronic technology and image processing technology, portable digital cameras have made a qualitative leap in focusing speed and image quality, and can now compete with professional micro-single cameras or SLR cameras. Therefore, bringing portable digital cameras into underwater photography has become a hobby for many underwater photographers.

[0003] When using a portable digital camera for underwater photography, it is usually installed in a special waterproof housing to avoid direct contact with water or seawater. The waterproof housing is made of plastic or aluminum alloy, and its strength is enough to withstand water pressure; the front end is provided with a lens barrel to protect the lens. The front end of the lens barrel is provided with a flat glass window or a hemispherical transparent cover, and the two are sealed by a sealing ring. The camera and lens installed in the waterproof housing capture underwater images through the flat glass window or hemispherical transparent cover, the water or seawater outside.

[0004] Because water absorbs light, the light underwater will be significantly weakened as the depth increases; moreover, in nature, there are also a large number of tiny impurities in the water, and visibility is relatively low. When using natural light to shoot underwater, you can only take clear pictures within a limited depth by zooming in. Usually, photographers will also use flashlights or flashlights as the main or auxiliary light source for underwater photography. For the same reason, their light can only illuminate the subject at a relatively close distance. Therefore, many photographers will use ultra-wide-angle lenses to shoot large sea creatures and fish schools at close range. However, the widest-angle zoom end of a general portable digital camera has a viewing angle of only 75-84 degrees, which is far from meeting the requirements of underwater photographers.

[0005] On the other hand, due to the optical properties of water or seawater, the camera will produce additional chromatic aberration and other problems when imaging underwater, that is, the image will have color distortion and color stripes. In addition, due to the refraction of water or seawater (refractive index 1.33-1.34), the original viewing angle of the camera lens will also be narrowed after entering the water through the air in the waterproof shell. For example, the combined viewing angle of the lens barrel and the camera using a flat glass window is about two-thirds of the original viewing angle. Another commonly used method is to use a hemispherical transparent cover lens barrel, and through precise measurement, make its center close to the position of the lens entrance pupil; using the principle that when light is emitted from one transparent medium to another transparent medium, the forward direction generally does not change, to maximize the restoration of the lens's own viewing angle.

[0006] In summary, when using existing portable digital cameras to shoot underwater, there is generally a problem of insufficient viewing angle; and due to the optical properties of water or seawater, there will be relatively large chromatic aberration problems when the main image passes through this medium, and the image quality is much lower than that of photos taken above water.

[0007] In order to solve the problem of insufficient viewing angle and chromatic aberration in underwater shooting, one solution is to install a front wide-angle lens at the front end of the lens barrel of the waterproof housing. The lens assembly in the front wide-angle lens can expand the viewing angle and correct chromatic aberration. Figure 1 As shown, in general, the first lens of the existing front wide-angle lens ( Figure 1 The leftmost lens in the figure is a hemispherical lens with uniform thickness, which may be made of glass or plastic. This hemispherical lens, in addition to isolating external water or seawater and resisting external water pressure, has no effect on increasing the shooting angle. The design mainly relies on the second and third lenses to increase the shooting angle. The third to fifth lenses use different optical materials to correct various chromatic aberration problems.

[0008] Although the existing front wide-angle lens has the ability to expand the shooting angle of view and correct chromatic aberration, the product is tall and heavy, and the cost is high; moreover, the existing underwater front wide-angle lens is mainly suitable for widening the maximum angle of view of the wide-angle end of the camera lens from 75 degrees to about 130 degrees.

[0009] In recent years, with the development of portable digital cameras, the widest angle of view has increased from 75 degrees to 84 degrees, making it easier to shoot wider scenes. Since the existing underwater wide-angle lens is suitable for a camera angle of 75 degrees, when the camera angle is greater than 75 degrees, black corners will appear in all four corners. Therefore, with the existing underwater wide-angle lens, underwater photographers need to manually zoom in and adjust the angle of view of the camera zoom lens every time they use it, so as to narrow it down to eliminate black corners, which is very cumbersome and inconvenient. Summary of the invention

[0010] The purpose of the present invention is to provide a front wide-angle lens for underwater use, which is used to solve the problems of insufficient viewing angle and chromatic aberration of the camera when shooting underwater, and at the same time to solve the problems of large height, weight and high cost of the existing front wide-angle lens, and to solve the problems of cumbersome operation of the existing underwater front wide-angle lens to adapt to cameras with a viewing angle of up to 84 degrees.

[0011] In one embodiment, a front wide-angle lens for underwater use is provided, comprising:

[0012] The outer shell is a cylindrical structure, and the outer shell has a connection end, and the connection end of the outer shell is provided with a physical structure port for rotating and quickly disassembling the camera waterproof housing;

[0013] And a lens assembly, the lens assembly includes a first lens, a second lens, a third lens and a fourth lens coaxially installed in the shell in sequence, the first lens and the second lens are negative lenses, the third lens and the fourth lens are positive lenses, the effective aperture range of the first lens is 110-115mm, the effective aperture range of the second lens is 80-85mm, the effective aperture range of the third lens is 70-75mm, and the effective aperture range of the fourth lens is 57-62mm; the first lens is far away from the connecting end of the shell, the fourth lens is close to the connecting end of the shell, the first lens and the fourth lens are respectively sealed and connected to the shell, the first lens, the fourth lens and the shell enclose a sealed accommodating cavity, and the second lens and the third lens are located in the accommodating cavity.

[0014] In one embodiment, the incident surface of the first lens is convex, and the exit surface is concave; the incident surface and the exit surface of the second lens are both concave, and the incident surface and the exit surface of the third lens are both convex; the incident surface of the fourth lens is convex, and the exit surface is concave.

[0015] In one embodiment, the Abbe number of the first lens is 62-66, the Abbe number of the second lens is 25-35, the Abbe number of the third lens is 44-48, and the Abbe number of the fourth lens is 24-28.

[0016] In one embodiment, the refractive index of the first lens is 1.4-1.6, the refractive index of the second lens is 1.8-2.0, the refractive index of the third lens is 1.5-1.7, and the refractive index of the fourth lens is 1.7-1.9.

[0017] In one embodiment, a broadband anti-reflection coating is applied to the surfaces of the first lens, the second lens, the third lens and the fourth lens.

[0018] In one embodiment, a radially extending annular seat is provided on the inner wall of the shell, and the surface of the first lens facing the second lens includes a concave surface in the middle and an annular plane located around the concave surface, and the annular plane of the first lens is installed on the annular seat.

[0019] In one embodiment, the accommodating cavity of the housing is expanded to form a buoyancy cavity, and the buoyancy cavity generates buoyancy underwater to offset the weight of the front wide-angle lens itself.

[0020] In one embodiment, the physical structure port of the housing is provided with a snap-fit ​​device for connecting to a quick-release interface.

[0021] In one embodiment, the physical structure port of the housing is provided with a water inlet channel for introducing water into between the fourth lens and the flat glass of the camera waterproof housing.

[0022] According to the front wide-angle lens used underwater in the above embodiment, the first lens adopts a negative lens structure. In addition to being able to isolate external water or seawater and resist external water pressure, it also cooperates with the three lenses behind it to form an image, and has the functions of increasing the shooting angle and correcting various chromatic aberrations. The first lens 21 with optical characteristics has the functions of waterproofing, correcting chromatic aberration and expanding the angle of view. It replaces the two lenses in the prior art, reduces the length of the front wide-angle lens in the optical axis direction, thereby reducing the height of the front wide-angle lens, and reducing the number of lenses also reduces the weight and production cost; in addition, the four lenses of this front wide-angle lens adopt an effective aperture within a specific range, which can achieve the widening of the camera's 84-degree angle of view to 130 degrees underwater. As a result, when this front wide-angle lens is adapted to a camera with a maximum angle of view of 84 degrees, it is not necessary to manually zoom every time, and the camera's zoom lens angle of view is narrowed to about 75 degrees, which greatly reduces the additional operations during use. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the structure of a lens of a front widening lens in the prior art;

[0024] Figure 2 An axial cross-sectional view of a front wide-angle lens in use in an embodiment;

[0025] Figure 3 It is an exploded schematic diagram of the disassembly and assembly of the front wide-angle lens in one embodiment;

[0026] Figure 4 It is an exploded schematic diagram of the disassembly and assembly of the front wide-angle lens in one embodiment;

[0027] Figure 5 is a light path diagram of a lens assembly in one embodiment;

[0028] Figure 6This is a color chart of the underwater image of the Panasonic LX100II with a hemispherical transparent cover lens barrel and analyzed using ImatestSFRplus;

[0029] Figure 7 A color chart of an underwater image of a Panasonic LX100II with a front wide-angle lens in one embodiment and analyzed using Imatest SFRplus;

[0030] Among them, 100-front wide-angle lens, 200-quick release interface, 300-camera, 10-housing, 11-lens hood, 12-buckle, 13-accommodating cavity, 14-annular seat, 15-buoyancy cavity, 20-lens assembly, 21-first lens, 22-second lens, 23-third lens, 24-fourth lens, 400-camera waterproof housing, 401-flat glass. DETAILED DESCRIPTION

[0031] The present invention is further described in detail below by specific embodiments in conjunction with the accompanying drawings. Wherein similar elements in different embodiments adopt associated similar element numbers. In the following embodiments, many detailed descriptions are for making the present application better understood. However, those skilled in the art can easily recognize that some features can be omitted in different situations, or can be replaced by other elements, materials, methods. In some cases, some operations related to the present application are not shown or described in the specification, this is to avoid the core part of the present application being overwhelmed by too much description, and for those skilled in the art, it is not necessary to describe these related operations in detail, and they can fully understand the related operations according to the description in the specification and the general technical knowledge in the art.

[0032] In addition, the features, operations or characteristics described in the specification can be combined in any appropriate manner to form various implementations. At the same time, the steps or actions in the method description can also be interchanged or adjusted in a manner that is obvious to those skilled in the art. Therefore, the various sequences in the specification and the drawings are only for the purpose of clearly describing a certain embodiment and are not meant to be a required sequence, unless otherwise specified that a certain sequence must be followed.

[0033] The serial numbers assigned to the components herein, such as "first", "second", etc., are only used to distinguish the objects described and do not have any order or technical meaning. The "connection" and "coupling" mentioned in this application include direct and indirect connections (couplings) unless otherwise specified. For the convenience of description, in this embodiment, the end facing the object side is the front end, and the end facing the imaging side is the back end.

[0034] The present embodiment discloses a front wide-angle lens for underwater use, which is mainly used by diving enthusiasts to bring into the water, especially for shooting in the sea. The front wide-angle lens can be installed at the front end of the lens barrel of a camera waterproof housing through a quick release interface, and the camera is located in the camera waterproof housing. The front wide-angle lens has the functions of expanding the viewing angle and correcting the absolute error, and assists the land camera to shoot high-quality images underwater. At the same time, the front wide-angle lens has the advantages of small height, light weight and low cost.

[0035] The embodiment relates to a front wide-angle lens for underwater use, and its optical design is suitable for a portable digital camera with a widest angle of view of 84 degrees. Therefore, when using this product, even if the camera's angle of view reaches 84 degrees, it is not necessary to manually zoom every time, and the camera's zoom lens angle of view is narrowed to about 75 degrees, which greatly reduces the extra operations during use.

[0036] like Figure 2 As shown, the front wide-angle lens 100 of this embodiment mainly includes a housing 10 and a lens assembly 20. The housing 10 is made of a waterproof material, such as an aluminum alloy. The housing 10 is a cylindrical structure, and the housing 10 has a through hole that runs through the entire housing. A light shield 11 is installed at the front end of the housing 10. The light shield 11 is composed of four trapezoidal light shielding sheets, which are used to eliminate reflections and stray light, and improve the clarity and color reproduction of the image. The light shield 11 can be installed at the front end of the housing 10 by snapping, and the light shield 11 can also be an integrated structure with the housing 10. The rear end of the housing 10 is a connection end, and the connection end of the housing 10 has a physical structure port for rotating and quickly connecting with a quick release interface 200 (a quick release interface device for underwater installation of a conversion lens in patent document CN206710779U), and the quick release interface 200 is connected to the lens barrel of the camera waterproof housing 400. The camera 300 (such as a portable digital camera) is installed in the camera waterproof housing 400, and the lens of the camera 300 is located in the lens barrel of the camera waterproof housing 400. The housing 10 can be quickly disassembled and assembled with the camera waterproof housing 400 through the quick release interface 200, which is convenient for underwater replacement and use. Among them, the quick release interface 200 and the lens barrel of the camera waterproof housing 400 can also be an integrated structure.

[0037] like Figure 3 and Figure 4As shown, in order to realize the rapid disassembly and assembly of the front wide-angle lens 100, the physical structure port of the housing 10 is provided with buckles 12, and there are three buckles 12, and the three buckles 12 are evenly distributed on the outer circumference of the physical structure port of the housing 10. The three buckles 12 are adapted to the card slots on the quick release interface 200, and the housing 10 can be quickly disassembled and assembled with the quick release interface 200 by rotating, and the quick release interface 200 is connected to the lens barrel of the camera waterproof housing 400 through a thread. The provision of the buckles 12 enables the front wide-angle lens 100 to be quickly disassembled and assembled with the camera waterproof housing 400 underwater, and is extremely convenient to use.

[0038] like Figure 2 As shown, in this embodiment, the lens assembly 20 includes a first lens 21, a second lens 22, a third lens 23 and a fourth lens 24. The first lens 21 to the fourth lens 24 are sequentially installed in the housing 10, and the four lenses are aligned and assembled on the same optical axis. The first lens 21 is located at the front end, and the fourth lens 24 is located at the rear end, that is, the first lens 21 is far away from the connection end of the housing 10, and the fourth lens 24 is close to the connection end of the housing 10. Among them, the first lens 21 and the fourth lens 24 are respectively sealed and connected to the housing 10, and the first lens 21 and the fourth lens 24 are respectively sealed and connected to the housing 10 through a sealing member, for example, the first lens 21 and the fourth lens 24 are respectively sealed and connected to the housing 10 through a sealing ring, so that the first lens 21, the fourth lens 24 and the housing 10 enclose a sealed accommodating chamber 13, the second lens 22 and the third lens 23 are located in the accommodating chamber 13, and a corresponding limiting structure is provided in the accommodating chamber 13 for fixing the second lens 22 and the third lens 23, for example, the limiting structure is an annular seat or a cylinder, Figure 2 The limiting structure is not shown in FIG.

[0039] The first lens 21 is a meniscus-shaped negative lens, the incident surface of the first lens 21 is a convex surface, and the exit surface is a concave surface. The first lens 21 is mainly used to expand the viewing angle. The second lens 22 is a negative lens, and the incident surface and the exit surface of the second lens 22 are both concave surfaces. The second lens 22 is used to smooth the light path and make the turning gentler to avoid high-order aberrations. The third lens 23 is a positive lens, and the incident surface and the exit surface of the third lens 23 are convex surfaces, which are used to converge light. The fourth lens 24 is a positive lens, and the incident surface of the fourth lens 24 is a convex surface, and the exit surface is a concave surface. The fourth lens 24 is also a meniscus-shaped lens. The fourth lens 24 is used to reduce the focal length, reduce spherical aberration, and cooperate with the third lens 23 to increase the numerical aperture of the system.

[0040] The first lens 21 is a large negative lens with a front convex spherical radius of 80-85mm, a rear concave spherical radius of 50-55mm, and a medium thickness of 5-6mm, replacing the first and second lenses in the past. Its specially designed geometric shape, in addition to being able to isolate external water or seawater and resist external water pressure, also cooperates with the three lenses behind it to increase the shooting angle and correct various chromatic aberrations. Compared with the previous hemispherical design, the first lens 21 protrudes less forward, reducing the overall height of the product. The first lens 21 with optical properties has the functions of waterproofing, correcting chromatic aberration and expanding the angle of view. It replaces the previous two lenses, reduces the height of the front wide-angle lens 100 (the length in the optical axis direction), and reduces the weight and production cost of the product.

[0041] like Figure 5 As shown, the first lens 21, the second lens 22, the third lens 23 and the fourth lens 24 form a lens assembly 20 with the functions of correcting chromatic aberration and expanding viewing angle. Among them, the effective aperture (diameter) range of the first lens 21 is 110-115mm, the effective aperture range of the second lens 22 is 80-85mm, the effective aperture range of the third lens 23 is 70-75mm, and the effective aperture range of the fourth lens 24 is 57-62mm. The first lens 21, the second lens 22, the third lens 23 and the fourth lens 24 coincide with the optical axis of the camera 300 to form a wide-angle objective lens, which can obtain a larger optical viewing angle and capture a larger picture, so that the front wide-angle lens 100 can adapt to a camera with a maximum viewing angle of 84 degrees, and widen the widest angle end viewing angle of the camera from 84° to 130°.

[0042] In order to better widen the viewing angle and correct chromatic aberration, the first lens 21 is made of crown glass with an Abbe number of 62 to 66 and a refractive index of 1.4 to 1.6; the second lens 22 is made of heavy lanthanum flint glass with an Abbe number of 25 to 35 and a refractive index of 1.8 to 2.0, and the second lens 22 has the characteristics of high refractive index and large dispersion; the third lens 23 is made of light flint glass with an Abbe number of 44 to 48 and a refractive index of 1.5 to 1.7; the fourth lens 24 is made of heavy flint glass with an Abbe number of 24 to 28 and a refractive index of 1.7 to 1.9.

[0043] In this embodiment, in order to better fix the first lens 21, a radially extending annular seat 14 is provided on the inner wall of the housing 10, and the surface of the first lens 21 facing the second lens 22 includes a concave surface in the middle and an annular plane located around the concave surface, wherein the concave surface is the exit surface of the first lens 21, and the annular plane is the fixed installation surface of the first lens 21. The annular plane of the first lens 21 is fitted on the annular seat 14 of the housing 10, and the first lens 21 is sealed and connected to the housing 10 through an O-ring. The annular seat 14 and the first lens 21 block the front end of the housing 10, and the annular seat 14 plays a role of limiting and water isolation.

[0044] In this embodiment, the accommodating cavity 13 of the housing 10 is radially expanded to form a buoyancy cavity 15. The accommodating cavity 13 and the buoyancy cavity 15 are an integrated cavity. The buoyancy cavity 15 will increase the buoyancy generated by the entire front wide-angle lens 100 in the water. Preferably, the buoyancy cavity 15 has a volume of a preset size, so that the buoyancy of the front wide-angle lens 100 in the water is approximately equal to its own weight, so that the front wide-angle lens 100 will not increase the burden of the photographer underwater, and the shooting is more stable. Specifically, due to the different densities of fresh water and seawater, the front wide-angle lens 100 can also be divided into a freshwater-applicable version and a seawater-applicable version. The sizes of the buoyancy cavities 15 of the freshwater-applicable version and the seawater-applicable version are slightly different, so that the buoyancy of the freshwater-applicable version and the seawater-applicable version in fresh water and seawater, respectively, is equal to its own weight; in actual experience, the difference in buoyancy in fresh water and seawater is not obvious, and a universal housing 10 can also be used.

[0045] In this embodiment, a water inlet channel is provided on the physical structure port of the housing 10, and the water inlet channel is a notch or a through hole, and the water inlet channel is used to introduce water between the fourth lens 24 and the flat glass 401 in the front end lens barrel of the camera waterproof housing 400. To this end, the optical characteristics of the lens assembly 20 of this embodiment take the water between the fourth lens 24 and the flat glass 401 into consideration, and the lens assembly 20 simultaneously eliminates the chromatic aberration and reduced viewing angle caused by the water between the fourth lens 24 and the flat glass 401. This structure allows the front wide-angle lens 100 and the quick-release interface 200 to be directly disassembled and replaced underwater without considering the sealing problem between the two, which greatly facilitates the rapid replacement of the front lens during underwater photography.

[0046] In this embodiment, a multi-layer broadband anti-reflection coating is plated on the incident surface and the exit surface of the first lens 21, the second lens 22, the third lens 23 and the fourth lens 24 to reduce the reflection problem and thus improve the imaging quality. In one embodiment, the optical parameters of the four lenses of the lens assembly 20 are shown in Table 1 below:

[0047] Table 1

[0048]

[0049]

[0050] In the above table, surface numbers 1 to 9 are respectively the incident surface and the exit surface of the first lens 21, the incident surface and the exit surface of the second lens 22, the incident surface and the exit surface of the third lens 23, the incident surface and the exit surface of the fourth lens 24, and the flat glass 401 at the front end of the lens barrel of the camera waterproof housing 400. The thickness, refractive index and Abbe number in the same column of surface number 1 represent the thickness, refractive index and Abbe number of the first lens 21 on the optical axis; the thickness in the same column of surface number 2 represents the spacing on the optical axis between the first lens 21 and the second lens 22; the thickness, refractive index and Abbe number in the same column of surface number 3 represent the thickness, refractive index and Abbe number of the second lens 22 on the optical axis; the thickness in the same column of surface number 4 represents the spacing on the optical axis between the second lens 22 and the third lens 23; the thickness, refractive index and Abbe number in the same column of surface number 5 represent the thickness, refractive index and Abbe number of the third lens 23 on the optical axis. Refractive index and Abbe number; the thickness in the same column of surface sequence 6 represents the distance on the optical axis between the third lens 23 and the fourth lens 24; the thickness, refractive index and Abbe number in the same column of surface sequence 7 represent the thickness, refractive index and Abbe number on the optical axis of the fourth lens 24; the thickness in the same column of surface sequence 8 represents the distance on the optical axis between the fourth lens 24 and the flat glass 401 at the front end of the lens barrel of the camera waterproof housing 400; the thickness, refractive index and Abbe number in the same column of surface sequence 9 represent the thickness, refractive index and Abbe number on the optical axis of the flat glass 401 of the lens barrel of the camera waterproof housing 400.

[0051] The front wide-angle lens for underwater use provided by this embodiment has four lenses installed in the housing 10, of which two lenses located at the optical front end are positive lenses and two lenses located at the optical rear end are negative lenses, so that the lens assembly 20 can correct the chromatic aberration caused by underwater shooting, thereby improving the imaging quality; in addition, the four lenses form a wide-angle objective lens, which expands the optical viewing angle and can assist the camera 300 in shooting a wider range of images underwater. The front wide-angle lens of the lens assembly 20 with the above optical parameters, when used with a portable digital camera underwater, can widen the viewing angle of the widest angle end from 84° to 130°. It can be seen that the front wide-angle lens can widen the field of view of the camera and obtain a larger shooting picture.

[0052] Figure 6 This is a chromatic aberration chart of the Panasonic LX100II with a hemispherical transparent cover lens barrel taken underwater and analyzed using Imatest SFRplus. The combined viewing angle is approximately 84 degrees.

[0053] The analysis position is the lower left corner #4, CA (area) = 4.95 pixels = 0.212% of center-ROI dist.

[0054] Figure 7Underwater image of a Panasonic LX100II with a front wide-angle lens in one embodiment and a color difference chart analyzed using Imatest SFRplus, with a combined viewing angle of 130 degrees.

[0055] The analysis position is the lower left corner #4, CA (area) = 0.388 pixels = 0.03% of center-ROI dist.

[0056] CA (area): Chromatic aberration area in pixels. Chromatic aberration index, representing the pixel values ​​used in the chromatic aberration channel from the highest to the lowest area; the larger the value, the more serious the chromatic aberration.

[0057] CA (area) as a percentage of the distance from the image center to the ROI.: Another better color difference indicator represents the percentage of pixels from the analysis position color difference to the distance from the image center to this position. Usually, the color difference of the imaging system increases proportionally from the center to the edge.

[0058] Calculation formula:

[0059] CA(%)=100%*CA(pixels) / (distance in pixels from the image center to the ROI)

[0060] To judge the severity of color difference, please refer to the public standards of imatest, as shown in the following table:

[0061] Severity of chromatic aberration

[0062]

[0063] The above related content is quoted from http: / / www.imatest.com / docs / sfr_chromatic / .

[0064] We can see that when the Panasonic LX100II is paired with an ordinary hemispherical transparent cover, the overall image chromatic aberration is in the range of over 0.15, which is quite serious; in 100% mode, it is very obvious. When the Panasonic LX100II is paired with the lens assembly 20 of the present optical parameters, even when the viewing angle is widened to 130 degrees, the overall image chromatic aberration is still in the range of 0-0.04, which can be ignored; in 100% mode, it is not visible. Therefore, the present front wide-angle lens can eliminate the chromatic aberration caused by water or seawater, and obtain high-quality images under a wide viewing angle.

[0065] It should be noted that the scope of application of the front wide-angle lens used underwater includes but is not limited to portable digital cameras, and is also suitable for other types of digital cameras. For example, when used with a mirrorless or SLR camera with a lens of a specific viewing angle for underwater photography, it can also play a role in widening the viewing angle and eliminating chromatic aberration.

[0066] The above description is only a preferred embodiment of the present application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in the present application is not limited to the technical solution formed by a specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the inventive concept. For example, the above features are replaced with (but not limited to) technical features with similar functions disclosed in the present application.

Claims

1. A front wide-angle lens for underwater use, characterized in that: include: The outer shell is a cylindrical structure, and the outer shell has a connection end, and the connection end of the outer shell is provided with a physical structure port for rotating and quickly disassembling the camera waterproof housing; And a lens assembly, the lens assembly consists of a first lens, a second lens, a third lens and a fourth lens coaxially installed in the shell in sequence, the first lens and the second lens are negative lenses, the third lens and the fourth lens are positive lenses, the effective aperture range of the first lens is 110-115mm, the effective aperture range of the second lens is 80-85mm, the effective aperture range of the third lens is 70-75mm, and the effective aperture range of the fourth lens is 57-62mm; the first lens is far away from the connecting end of the shell, the fourth lens is close to the connecting end of the shell, the first lens and the fourth lens are respectively sealed and connected to the shell, the first lens, the fourth lens and the shell enclose a sealed accommodating cavity, and the second lens and the third lens are located in the accommodating cavity.

2. The front wide-angle lens for underwater use as claimed in claim 1, characterized in that: The incident surface of the first lens is convex, and the exit surface is concave; the incident surface and the exit surface of the second lens are both concave, the incident surface and the exit surface of the third lens are both convex; the incident surface of the fourth lens is convex, and the exit surface is concave.

3. The underwater front wide-angle lens as claimed in claim 2, characterized in that: The Abbe number of the first lens is 62-66, the Abbe number of the second lens is 25-35, the Abbe number of the third lens is 44-48, and the Abbe number of the fourth lens is 24-28.

4. The underwater front wide-angle lens as claimed in claim 2, characterized in that: The refractive index of the first lens is 1.4 to 1.6, the refractive index of the second lens is 1.8 to 2.0, the refractive index of the third lens is 1.5 to 1.7, and the refractive index of the fourth lens is 1.7 to 1.

9.

5. The underwater front wide-angle lens as claimed in claim 1, characterized in that: Broadband anti-reflection coatings are applied to surfaces of the first lens, the second lens, the third lens and the fourth lens.

6. The underwater front wide-angle lens according to any one of claims 1 to 5, characterized in that: A radially extending annular seat is provided on the inner wall of the shell. The surface of the first lens facing the second lens includes a concave surface in the middle and an annular plane located around the concave surface. The annular plane of the first lens is installed on the annular seat.

7. The underwater front wide-angle lens according to any one of claims 1 to 5, characterized in that: The accommodating cavity of the shell is expanded to form a buoyancy cavity, and the buoyancy cavity generates buoyancy underwater to offset the weight of the front wide-angle lens itself.

8. The underwater front wide-angle lens according to any one of claims 1 to 5, characterized in that: The physical structure port of the shell is provided with a snap-fit ​​device for connecting with the quick-release interface.

9. The underwater front wide-angle lens as claimed in claim 8, characterized in that: The physical structure port of the housing is provided with a water inlet channel for introducing water into between the fourth lens and the flat glass of the camera waterproof housing.

Images