An ultra-wide-angle lens

Abstract

The present invention provides an ultra-wide-angle lens, which sequentially includes a first lens, a second lens, a diaphragm, a third lens and a fourth lens from the object side to the image side along the optical axis. The first lens, the second lens, the diaphragm, the third lens and the fourth lens are coaxially arranged in sequence from the object side to the image side. Among them, the first lens and the fourth lens have negative optical powers, and the second lens and the third lens have positive optical powers. For this ultra-wide-angle lens, by centrally arranging the diaphragm and optimizing the lens structure, the optical powers of the lenses in the lens structure are distributed as negative, positive, positive, negative, effectively reducing the off-axis aberration, improving the relative illumination of the edge field of view of the ultra-wide-angle lens and the imaging quality. With the use of 4 plastic aspherical lenses and a lens design with 1.5 < TTL / 2Y < 2.5, the manufacturing difficulty and the unit cost are reduced, while the optical performance is improved.

Description

Technical Field

[0001] The present invention relates to the field of lens technology, and in particular to an ultra-wide-angle lens that can be used for in vivo diagnosis and treatment of patients and provide high-quality imaging for a corresponding endoscope system. Background Art

[0002] Endoscope is an effective tool for clinical diagnosis. It enters the body through the natural channels or surgical incisions of the human body. It can be directly peeked by simply aiming the front lens at the corresponding part. It has a wide range of applications in the examination of organ lesions in the body and minimally invasive surgery. Most traditional endoscopic devices are reusable, that is, they are put back into use after cleaning and disinfection after the patient has completed the examination. The lenses of reusable endoscopes are mostly made of glass, which can achieve very excellent optical performance indicators and provide doctors with high-definition diagnostic images. At the same time, this small-sized lens also has the disadvantages of high processing difficulty and high cost. However, after years of development, reusable endoscopes have always been unable to get rid of the risk of cross-infection. Due to the complex structure of reusable endoscopes and the use of special materials, it is very difficult to disinfect and sterilize them; and because of their high price, most hospitals purchase limited quantities, which often cannot meet the clinical diagnosis and treatment needs of patients, so there will be safety hazards such as too short disinfection time. For example, a disposable electronic endoscope is disclosed in the Chinese utility model patent with publication number CN202120621824.6. Its core advantage is that it can effectively reduce the risk of cross infection and is low in price.

[0003] Disposable electronic endoscopes need to take into account optical performance while controlling costs. For example, when doctors perform bronchial examinations, they will encounter some narrow tissue channels, which makes it impossible to control the shooting angle by bending the end of the endoscope. This places high demands on the mechanical and optical performance of the lens itself. When the resolution is sufficient, a larger field of view can provide a larger observation field of view and reduce blind spots, making it easier for doctors to find lesions. Endoscope products generally use ultra-wide-angle lenses to increase the observation range. Existing ultra-wide-angle lenses generally use specific structures to compensate for aberrations during the design process. Increasing the number of lenses or using aspherical lenses can also improve image quality, but the lens structure is complex and the mechanical aperture is large.

[0004] However, the existing wide-angle lenses are not conducive to the miniaturization of head-end components. In addition, there are problems such as edge field aberrations that are difficult to eliminate, low relative illumination, dark corners and poor image quality around the image surface. Disposable endoscope lenses are difficult to control costs while ensuring image quality.

[0005] In summary, there is an urgent need for an ultra-wide-angle lens that can ensure imaging quality and reduce production costs. Summary of the invention

[0006] Based on this, the present invention provides an ultra-wide-angle lens to solve the technical problems mentioned in the above background technology.

[0007] According to one object of the present invention, the present invention provides a cooling structure, comprising:

[0008] The optical axis includes a first lens, a second lens, a stop, a third lens and a fourth lens from the object side to the image side, wherein the first lens, the second lens, the stop, the third lens, the fourth lens and the filter are coaxially arranged in sequence from the object side to the image side, wherein the first lens and the fourth lens have negative optical power, the second lens and the third lens have positive optical power, the first lens, the second lens, the third lens and the fourth lens are all made of plastic, and at least one surface of the first lens, the second lens, the third lens and the fourth lens is aspherical, and the stop is arranged at the center of the entire ultra-wide-angle lens;

[0009] The ratio of the total optical length TTL of the ultra-wide-angle lens to the total imaging height 2Y of the main ray corresponding to the maximum field of view of the ultra-wide-angle lens on the image plane meets the condition: 1.5 <TTL / 2Y<2.5。

[0010] Preferably, the front and rear surfaces of the first lens are both concave, the concave surface of the second lens faces the image side, the front and rear surfaces of the third lens are both convex, and the concave surface of the fourth lens faces the object side.

[0011] Preferably, the ultra-wide-angle lens further includes:

[0012] A filter, the filter is located between the fourth lens and the image plane, and the filter is an infrared cutoff filter;

[0013] A protective glass is located on a side of the first lens facing the object, and a hydrophobic film is coated on a flat surface of the protective glass on the object side.

[0014] Preferably, the protective glass, the first lens, the second lens, the aperture, the third lens, the fourth lens and the filter are coaxially arranged in sequence from the object side to the image side;

[0015] The protective glass includes two flat surfaces, namely the first flat surface and the second flat surface, the first lens includes the first aspheric surface and the second aspheric surface, the second lens includes the third aspheric surface and the fourth aspheric surface, the third lens includes the fifth aspheric surface and the sixth aspheric surface, the fourth lens includes the seventh aspheric surface and the eighth aspheric surface, the filter includes two flat surfaces, namely the third flat surface and the fourth flat surface, the first flat surface, the second flat surface, the first aspheric surface, the second aspheric surface, the third aspheric surface, the fourth aspheric surface, the aperture, the fifth aspheric surface, the sixth aspheric surface, the seventh aspheric surface, the eighth aspheric surface, the third flat surface and the fourth flat surface are coaxially arranged in sequence from the object side to the image side.

[0016] Preferably, the refractive index of the first lens and the third lens are both 1.51-1.71, and the Abbe number is both 39-49. The refractive index of the second lens and the fourth lens are both 1.59-1.79, and the Abbe number is both 27-37.

[0017] Preferably, the refractive index of the protective glass is 1.60-1.80, and the Abbe number is 71-81; the refractive index of the filter is 1.48-1.68, and the Abbe number is 55-65.

[0018] Preferably, the absolute value of the ratio of the focal length of the first lens to the focal length of the ultra-wide-angle lens is 0.49 to 2.39;

[0019] The absolute value of the ratio of the focal length of the second lens to the focal length of the ultra-wide-angle lens is 2.81 to 4.53;

[0020] The absolute value of the ratio of the focal length of the third lens to the focal length of the ultra wide-angle lens is 0.68 to 2.52;

[0021] An absolute value of a ratio of a focal length of the fourth lens element to a focal length of the ultra-wide-angle lens element is 1.33 to 3.26.

[0022] Preferably, the absolute value of the radius of curvature of the object-side surface of the second lens is smaller than the absolute value of the radius of curvature of the image-side surface, and the absolute value of the radius of curvature of the object-side surface of the third lens is larger than the absolute value of the radius of curvature of the image-side surface.

[0023] Preferably, the aspheric surface shapes of the first lens, the second lens, the third lens and the fourth lens conform to the following calculation formula:

[0024]

[0025] Among them, Y is the projection height of the light on the surface; R is the radius of curvature of the surface centered at its intersection with the optical axis; k is the cone coefficient, A4, A6, A8, A 10 , A 12is the high-order aspheric coefficient; X is the perpendicular length from the point on the aspheric surface at a distance Y from the optical axis to the optical axis.

[0026] Preferably, the F-number of the ultra-wide-angle lens is 4, and the full field of view angle is 140 degrees.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] For this ultra-wide-angle lens, by setting the aperture in the center and optimizing the lens structure, the optical power distribution of the lenses in the lens structure is negative, positive, positive, negative, effectively reducing the off-axis aberration, improving the relative illumination of the edge field of view of the ultra-wide-angle lens and the imaging quality. The use of 4 plastic aspheric lenses and the lens design of 1.5 < TTL / 2Y < 2.5 improve the optical performance while reducing the manufacturing difficulty and the unit cost.

[0029] The present invention will be further described below in conjunction with the accompanying drawings and embodiments. Description of the Drawings

[0030] Figure 1 is a schematic diagram of an ultra-wide-angle lens according to the present invention;

[0031] Figure 2 is a schematic diagram of the field curvature curve of an ultra-wide-angle lens according to the present invention;

[0032] Figure 3 is a schematic diagram of the optical distortion curve of an ultra-wide-angle lens according to the present invention;

[0033] Figure 4 is a schematic diagram of the MTF curve of an ultra-wide-angle lens according to the present invention;

[0034] Figure 5 is a relative illumination curve diagram of an ultra-wide-angle lens according to the present invention.

[0035] In the figure: 10, the first lens; 11, the first aspheric surface; 12, the second aspheric surface; 20, the second lens; 21, the third aspheric surface; 22, the fourth aspheric surface; 30, the third lens; 31, the fifth aspheric surface; 32, the sixth aspheric surface; 40, the fourth lens; 41, the seventh aspheric surface; 42, the eighth aspheric surface; 50, the protective glass; 51, the first flat surface; 52, the second flat surface; 60, the aperture; 70, the filter; 71, the third flat surface; 72, the fourth flat surface; 80, the image plane. Detailed Embodiments

[0036] The following description is used to elaborate on the present invention so that those skilled in the art can implement the present invention. The preferred embodiments in the following description are only examples, and other obvious variations can be conceived by those skilled in the art. The basic principles defined in the following description of the present invention can be applied to other implementation schemes, variant schemes, improvement schemes, equivalent schemes, and other technical schemes without departing from the spirit and scope of the present invention.

[0037] To ensure imaging quality and reduce production costs, the present invention provides the following embodiments.

[0038] See Figure 1 , a super wide-angle lens provided by the present invention includes:

[0039] Along the optical axis from the object side to the image plane 80 side, it includes a first lens 10, a second lens 20, a diaphragm 60, a third lens 30, a fourth lens 40, and a filter 70 in sequence. The first lens 10, the second lens 20, the diaphragm 60, the third lens 30, and the fourth lens 40 are coaxially arranged in sequence from the object side to the image side. Among them, the first lens 10 and the fourth lens 40 have negative optical powers, the second lens 20 and the third lens 30 have positive optical powers. The first lens 10, the second lens 20, the third lens 30, and the fourth lens 40 are all made of plastic material. At least one surface of the first lens 10, the second lens 20, the third lens 30, and the fourth lens 40 is aspherical. The diaphragm 60 is arranged at the central position of the whole super wide-angle lens;

[0040] The ratio of the total optical length TTL of the super wide-angle lens to the full height 2Y of the chief ray corresponding to the maximum field of view angle of the super wide-angle lens on the image plane 80 satisfies the condition: 1.5 < TTL / 2Y < 2.5.

[0041] Through the above limitations, the diaphragm 60 is centrally arranged and the lens structure is optimized. The distribution of the optical powers of the lenses in the lens structure is negative, positive, positive, negative, effectively reducing the off-axis aberration, improving the relative illumination of the edge field of view of the super wide-angle lens and the imaging quality. The use of 4 plastic aspherical lenses and the lens design of 1.5 < TTL / 2Y < 2.5 improve the optical performance while reducing the manufacturing difficulty and the unit cost.

[0042] Specifically, continue to refer to Figure 1 , this embodiment provides a super wide-angle lens. Along the optical axis from the object side to the image side, where the image side is the image plane 80 in the figure, it is in sequence a protective glass 50, a first lens 10, a second lens 20, a diaphragm 60, a third lens 30, a fourth lens 40, and a filter 70.

[0043] The protective glass 50 is located on the side of the first lens 10 facing the object, and the protective glass 50 includes two flat surfaces, namely a first flat surface 51 and a second flat surface 52. Preferably, the flat surface of the protective glass 50 on the object side is coated with a hydrophobic film;

[0044] The optical focal length of the first lens 10 is negative. The first lens 10 is an aspheric lens. At least one side of the first lens 10 is an aspheric surface. In this embodiment, the first lens 10 includes a first aspheric surface 11 and a second aspheric surface 12, that is, the first lens 10 is a lens with concave front and rear surfaces.

[0045] The optical focal length of the second lens 20 is positive. The second lens 20 is a lens with a concave surface facing the image side. The second lens 20 is an aspherical lens. At least one surface of the second lens 20 is an aspherical surface. In the present embodiment, the second lens 20 includes a third aspherical surface 21 and a fourth aspherical surface 22.

[0046] The third lens 30 has a positive optical power. The third lens 30 is a lens with convex front and rear surfaces. The third lens 30 has at least one aspherical surface. In the present embodiment, the third lens 30 includes a fifth aspherical surface 31 and a sixth aspherical surface 32 .

[0047] The fourth lens 40 has a negative optical power. The fourth lens 40 is a lens with a concave surface facing the object side. The fourth lens 40 has at least one aspherical surface. In this embodiment, the fourth lens 40 includes a seventh aspherical surface 41 and an eighth aspherical surface 42 .

[0048] The filter 70 includes two flat surfaces, namely a third flat surface 71 and a fourth flat surface 72 . The filter 70 is located between the fourth lens 40 and the image plane 80 .

[0049] The protective glass 50, the first lens 10, the second lens 20, the aperture 60, the third lens 30, the fourth lens 40 and the filter 70 are coaxially arranged in sequence from the object side to the image side. Specifically, the first flat surface 51, the second flat surface 52, the first aspheric surface 11, the second aspheric surface 12, the third aspheric surface 21, the fourth aspheric surface 22, the aperture 60, the fifth aspheric surface 31, the sixth aspheric surface 32, the seventh aspheric surface 41, the eighth aspheric surface 42, the third flat surface 71 and the fourth flat surface 72 are coaxially arranged in sequence from the object side to the image side.

[0050] The first lens 10, the second lens 20, the third lens 30 and the fourth lens 40 are all even-order aspheric lenses. The first aspheric surface 11 and the second aspheric surface 12 of the first lens 10 are both even-order aspheric surfaces, the third aspheric surface 21 and the fourth aspheric surface 22 of the second lens 20 are both even-order aspheric surfaces, the fifth aspheric surface 31 and the sixth aspheric surface 32 of the third lens 30 are both even-order aspheric surfaces, and the seventh aspheric surface 41 and the eighth aspheric surface 42 of the fourth lens 40 are both even-order aspheric surfaces.

[0051] Furthermore, the filter 70 is an infrared cut-off filter 70. The filter 70 can block infrared light and only allow visible light to pass, thereby eliminating the interference of infrared light, and then obtaining a clearer and more accurate image, improving the accuracy of diagnosis and the success rate of treatment. In addition, the infrared cut-off filter 70 has other functions, for example, it can protect the endoscope lens from thermal damage, prevent infrared radiation from damaging the equipment, and at the same time, it can also reduce image noise and improve the stability of the imaging system.

[0052] In this embodiment, the refractive index of the first lens 10 and the third lens 30 are both 1.51-1.71, and the Abbe number is both 39-49. The refractive index of the second lens 20 and the fourth lens 40 are both 1.59-1.79, and the Abbe number is both 27-37.

[0053] The protective glass 50 has a refractive index of 1.60-1.80 and an Abbe number of 71-81.

[0054] The refractive index of the filter 70 is 1.48-1.68, and the Abbe number is 55-65.

[0055] In this embodiment, the absolute value of the ratio of the focal length of the first lens 10 to the focal length of the ultra wide-angle lens is 0.49-2.39; the absolute value of the ratio of the focal length of the second lens 20 to the focal length of the ultra wide-angle lens is 2.81-4.53; the absolute value of the ratio of the focal length of the third lens 30 to the focal length of the ultra wide-angle lens is 0.68-2.52; the absolute value of the ratio of the focal length of the fourth lens 40 to the focal length of the ultra wide-angle lens is 1.33-3.26.

[0056] Further, the absolute value of the radius of curvature of the object-side surface of the second lens 20 is smaller than the absolute value of the radius of curvature of the image-side surface, and the absolute value of the radius of curvature of the object-side surface of the third lens 30 is greater than the absolute value of the radius of curvature of the image-side surface. In this embodiment, the radius of curvature of the first flat surface 51 is ∞, and the thickness is 0.23mm. The radius of curvature of the second flat surface 52 is ∞, and the thickness is 0.10mm. The radius of curvature of the first aspheric surface 11 is -6.03mm, and the thickness is 0.11mm. The radius of curvature of the second aspheric surface 12 is 0.34mm, and the thickness is 0.32mm. The radius of curvature of the third aspheric surface 21 is 1.41mm, and the thickness is 0.61mm. The radius of curvature of the fourth aspheric surface 22 is 2.95mm, and the thickness is 0.018mm. The radius of curvature of the aperture 60 is ∞, and the thickness is 0.06mm. The fifth aspheric surface 31 has a radius of curvature of 0.68 mm and a thickness of 0.52 mm. The sixth aspheric surface 32 has a radius of curvature of -0.31 mm and a thickness of 0.10 mm. The seventh aspheric surface 41 has a radius of curvature of -0.39 mm and a thickness of 0.54 mm. The eighth aspheric surface 42 has a radius of curvature of -1.18 mm and a thickness of 0.47 mm. The third flat surface 71 has a radius of curvature of ∞ and a thickness of 0.40 mm. The fourth flat surface 72 has a radius of curvature of ∞ and a thickness of 0.05 mm. The structural parameters of the ultra-wide-angle lens are specifically shown in the following table:

[0057]

[0058]

[0059] The aspherical surface shape of the ultra-wide-angle lens conforms to the following calculation formula:

[0060]

[0061] Among them, Y is the projection height of the light on the surface; R is the radius of curvature of the surface centered at its intersection with the optical axis; k is the cone coefficient, A4, A6, A8, A 10 , A 12 is the high-order aspheric coefficient; X is the length of the perpendicular line between the point on the aspheric surface at a distance Y from the optical axis and the optical axis. The various aspheric coefficients in this embodiment are shown in the following table:

[0062] k <![CDATA[A4]]> <![CDATA[A6]]> <![CDATA[A8]]> <![CDATA[A 10 ]]> <![CDATA[A 12 ]]> The first aspheric surface 35.969 0.376 -0.972 1.293 -0.822 0.169 Second aspheric surface -1.245 -2.013 31.949 -202.142 707.706 -1146.015 The third aspheric surface 0.459 -1.546 12.866 -95.479 346.859 -562.872 Fourth aspheric surface 50.000 -2.419 259.949 -2.053E+04 8.124E+05 -1.200E+07 Fifth aspheric surface 3.358 -2.481 6.423 -442.715 6688.610 -4.587E+04 The sixth aspheric surface -3.677 -2.339 5.678 -39.860 -262.667 3181.353 Seventh aspheric surface -5.206 2.642 -75.743 627.916 -3787.400 9678.044 The eighth aspheric surface -22.154 1.772 -9.400 22.646 -29.528 17.258

[0063] In this embodiment, through the above parameter settings, large-aperture ultra-wide-angle imaging with an F-number of 4 and a full field of view of 140 degrees for the ultra-wide-angle lens is achieved. It should be noted that the aperture range of ultra-wide-angle lenses is usually between F2.8 and F16. For wide-angle lenses, the smaller the aperture value, the greater the amount of light entering. Therefore, lenses with smaller F-values usually have a greater amount of light entering and are suitable for shooting under relatively dim light conditions. An ultra-wide-angle lens with an F-number of 4 can obtain clearer photos under dim conditions.

[0064] In addition, the optical total length of the ultra-wide-angle lens and the full height of the image satisfy the following condition: 1.5 < TTL / 2Y < 2.5; where TTL represents the optical total length of the ultra-wide-angle lens; 2Y represents the full height of the image formed by the chief ray corresponding to the maximum field of view angle of the ultra-wide-angle lens on the image plane. In this embodiment, the TTL (optical total length) of the ultra-wide-angle lens is 3.57 mm, the focal length is 0.64 mm, and the maximum diameter of the lens is 1.8 mm.

[0065] See Figure 2 , from the field curvature curve graph of the ultra-wide-angle lens, it can be seen that the maximum absolute value of the field curvature of the ultra-wide-angle lens is at most 0.04 mm. Continuing to refer to Figure 3 , it can be seen that the maximum absolute value of the distortion of the ultra-wide-angle lens is 40%, and the distortion curve of the edge field of view changes relatively smoothly.

[0066] See Figure 4 , Figure 4 is the MTF curve graph (Modulation Transfer Funtion) of the ultra-wide-angle lens. MTF is used to characterize the attenuation degree of the contrast of the sine intensity distribution function at different frequencies after passing through the optical system. The horizontal axis of this MTF curve graph represents the spatial frequency, with the unit of lp / mm; the vertical axis is the modulation degree of the optical transfer function, representing the attenuation degree of the contrast at each spatial frequency. The topmost straight line (diffraction limit) is the MTF curve under the ideal condition where only diffraction occurs and the influence of aberration is not considered when light passes through the optical system for imaging. This MTF curve graph respectively shows the MTF curves at field of view angles of 0°, 10°, 20°, 30°, 40°, 50°, 60°, and 70°. It can be seen that the MTF curves at field of view angles of 0° and 10° are basically close to the diffraction limit. At a field of view angle of 60°, the modulation degree at a spatial frequency of 200 lp / mm is approximately 0.2, and it slightly decreases at a field of view angle of 70°. Generally speaking, the ultra-wide-angle lens in this embodiment has good resolution and resolving power.

[0067] See Figure 5 , Figure 5It is the relative illumination curve of the ultra-wide-angle lens. From this figure, it can be seen that the relative illumination of the ultra-wide-angle lens is greater than 0.5 within the full field of view angle range, and the relative illumination curve changes gently, indicating that the image brightness uniformity of the image formed by the ultra-wide-angle lens is good, avoiding the problem of vignetting in the edge field of view.

[0068] In summary, the ultra-wide-angle lens provided by the present invention includes a protective glass, a first lens, a second lens, a diaphragm, a third lens, a fourth lens, and a filter along the optical axis from the object side to the image side. The first lens has a negative focal power and is a lens with both front and rear surfaces being concave; the second lens has a positive focal power and is a lens with the concave surface facing the image side; the third lens has a positive focal power and is a lens with both front and rear surfaces being convex; the fourth lens has a negative focal power and is a lens with the concave surface facing the object side. At least one surface of the first lens, the second lens, the third lens, and the fourth lens is an aspherical surface, and the first lens, the second lens, the diaphragm, the third lens, the fourth lens, and the filter are coaxially arranged in sequence from the object side to the image side. The following conditions are satisfied for the optical total length and the imaging full height of the ultra-wide-angle lens of the present invention: 1.5 < TTL / 2Y < 2.5; where TTL represents the optical total length of the ultra-wide-angle lens; 2Y represents the imaging full height of the chief ray corresponding to the maximum field of view angle of the ultra-wide-angle lens on the image plane.

[0069] The advantages of the present invention are as follows:

[0070] (1) Aiming at the problem that it is difficult to design a large field of view, large aperture, and small size lens using all plastic materials or glass-plastic materials for traditional ultra-wide-angle lenses, the present invention adopts 4 plastic aspherical lenses to achieve a lens design that exceeds the current imaging performance, with an F number of 4, a full field of view angle of 140 degrees, and 1.5 < TTL / 2Y < 2.5. While reducing the manufacturing difficulty and the unit cost, the optical performance is improved.

[0071] (2) For the ultra-wide-angle lens proposed by the present invention, by setting the diaphragm in the middle and optimizing the lens structure, the off-axis aberration is effectively reduced, and the relative illumination and the imaging quality of the ultra-wide-angle lens are improved.

[0072] The above embodiments are only used to illustrate the technical idea and characteristics of the present invention, and the purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. The scope of the patent adoption of the present invention cannot be limited only by this embodiment, that is, any equivalent changes or modifications made according to the spirit disclosed by the present invention still fall within the scope of the patent of the present invention.

Claims

1. An ultra-wide-angle lens, characterized in that: The ultra-wide-angle lens has four lenses with optical power, and includes a first lens (10), a second lens (20), an aperture (60), a third lens (30) and a fourth lens (40) in sequence along the optical axis and from the object side to the image plane (80); the first lens (10), the second lens (20), the aperture (60), the third lens (30) and the fourth lens (40) are coaxially arranged in sequence from the object side to the image side; the first lens (10) and the fourth lens (40) have negative optical power, the second lens (20) and the third lens (30) have positive optical power, the first lens (10), the second lens (20), the third lens (30) and the fourth lens (40) are all made of plastic; at least one surface of the first lens (10), the second lens (20), the third lens (30) and the fourth lens (40) is aspherical; the aperture (60) is arranged at the center of the ultra-wide-angle lens as a whole; The ratio of the total optical length TTL of the ultra-wide-angle lens to the total imaging height 2Y of the main ray corresponding to the maximum field angle of the ultra-wide-angle lens on the image plane (80) satisfies the condition: 1.5 <TTL / 2Y<2.5; The first lens (10) has front and rear surfaces that are both concave; the second lens (20) includes a third aspheric surface (21) and a fourth aspheric surface (22); the third aspheric surface (21) faces the object side, the fourth aspheric surface (22) faces the image side, the fourth aspheric surface (22) is a concave surface, and the third aspheric surface (21) is a convex surface; the third lens (30) has front and rear surfaces that are both convex; the fourth lens (40) includes a seventh aspheric surface (41) and an eighth aspheric surface (42); the seventh aspheric surface (41) faces the object side, the eighth aspheric surface (42) faces the image side, the seventh aspheric surface (41) is a concave surface, and the eighth aspheric surface (42) is a convex surface; The aspheric surface shapes of the first lens (10), the second lens (20), the third lens (30) and the fourth lens (40) conform to the following calculation formula: Among them, Y is the projection height of the light on the surface; R is the radius of curvature of the surface centered at its intersection with the optical axis; k is the cone coefficient, A4, A6, A8, A10, A12 are high-order aspheric coefficients; X is the length of the perpendicular line from the point on the aspheric surface at a distance Y from the optical axis to the optical axis; The ultra-wide-angle lens has an F number of 4 and a full field of view of 140 degrees; The refractive index of the first lens (10) and the third lens (30) are both 1.51 to 1.71, and the Abbe number is both 39 to 49; the refractive index of the second lens (20) and the fourth lens (40) are both 1.59 to 1.79, and the Abbe number is both 27 to 37; It also includes a protective glass (50), the protective glass (50) being located on the side of the first lens (10) facing the object, the protective glass (50) being coated with a hydrophobic film on the flat surface on the object side, the refractive index of the protective glass (50) being 1.60 to 1.80, and the Abbe number being 71 to 81; The optical filter (70) is also included. The optical filter (70) is located between the fourth lens (40) and the image plane (80). The optical filter (70) is an infrared cutoff filter (70). The refractive index of the optical filter (70) is 1.48 to 1.68, and the Abbe number is 55 to 65.

2. The ultra-wide-angle lens according to claim 1, characterized in that: The protective glass (50), the first lens (10), the second lens (20), the aperture (60), the third lens (30), the fourth lens (40), and the filter (70) are coaxially arranged in sequence from the object side to the image side; The protective glass (50) comprises two flat surfaces, namely a first flat surface (51) and a second flat surface (52); the first lens (10) comprises a first aspheric surface (11) and a second aspheric surface (12); the second lens (20) comprises a third aspheric surface (21) and a fourth aspheric surface (22); the third lens (30) comprises a fifth aspheric surface (31) and a sixth aspheric surface (32); the fourth lens (40) comprises a seventh aspheric surface (41) and an eighth aspheric surface (42); the filter (70) comprises two flat surfaces, namely a third flat surface (71) and a fourth flat surface (72), wherein the first flat surface (51), the second flat surface (52), the first aspheric surface (11), the second aspheric surface (12), the third aspheric surface (21), the fourth aspheric surface (22), the aperture (60), the fifth aspheric surface (31), the sixth aspheric surface (32), the seventh aspheric surface (41), the eighth aspheric surface (42), the third flat surface (71) and the fourth flat surface (72) are coaxially arranged in sequence from the object side to the image side.

3. The ultra-wide-angle lens according to claim 1, characterized in that: The absolute value of the ratio of the focal length of the first lens (10) to the focal length of the ultra-wide-angle lens is 0.49 to 2.39; The absolute value of the ratio of the focal length of the second lens (20) to the focal length of the ultra-wide-angle lens is 2.81 to 4.53; The absolute value of the ratio of the focal length of the third lens (30) to the focal length of the ultra-wide-angle lens is 0.68 to 2.52; The absolute value of the ratio of the focal length of the fourth lens (40) to the focal length of the ultra-wide-angle lens is 1.33 to 3.

26.

4. The ultra-wide-angle lens according to claim 1, characterized in that: The absolute value of the curvature radius of the object-side surface of the second lens (20) is smaller than the absolute value of the curvature radius of its image-side surface, and the absolute value of the curvature radius of the object-side surface of the third lens (30) is larger than the absolute value of the curvature radius of its image-side surface.

Images