A fixed-focus lens

Abstract

An embodiment of the present invention discloses a fixed-focus lens. The fixed-focus lens includes a first lens with a negative optical power, a second lens with a negative optical power, a third lens with a positive optical power, a fourth lens with a positive optical power, a fifth lens with a positive optical power, a sixth lens with a negative optical power, and a seventh lens with a positive optical power, which are arranged in sequence from the object side to the image side along the optical axis; wherein the fourth lens is a glass aspherical lens; the first lens, the second lens, the third lens, the fifth lens, the sixth lens, and the seventh lens are all plastic aspherical lenses; the fixed-focus lens satisfies: IC / TTL > 0.4; where IC represents the image plane diameter of the fixed-focus lens, and TTL represents the overall optical length of the fixed-focus lens. The technical solution of the embodiment of the present invention can achieve the state that infrared imaging is not out of focus while visible light imaging is clear on the premise that the imaging target surface reaches 1 / 1.8 inches, and at the same time meet the 4K resolution requirement, which not only reduces the cost but also ensures the performance.

Description

Technical Field

[0001] Embodiments of the present invention relate to lens technology, and in particular to a fixed-focus lens. Background Art

[0002] The progress of technology has brought many conveniences to mankind. With the improvement of people's safety awareness, there are also higher requirements for security. The surveillance lens converts the target to be captured into an image signal and transmits it to the image processing and recognition system, saving accurate image information for places such as roads, shopping malls, and schools, and providing data for information collection and query.

[0003] With the development of communication industry technology and the gradual popularization of 5G, the video captured by the lens will not be limited by the transmission speed and bandwidth. Moreover, people's requirements for surveillance image quality are getting higher and higher. Thus, 4K (3840×2160) resolution surveillance cameras are gradually being accepted by people. Traditional 4K lenses usually use a large number of lenses, and there are problems such as large volume and high manufacturing cost. Summary of the Invention

[0004] Embodiments of the present invention provide a fixed-focus lens. The fixed-focus lens is small in volume. On the premise that the imaging target surface reaches 1 / 1.8 inch, it can achieve the state that the infrared imaging is not out of focus while the visible light imaging is clear, and at the same time meet the 4K resolution requirement, which not only reduces the cost but also ensures the performance.

[0005] Embodiments of the present invention provide a fixed-focus lens, including a first lens with negative optical power, a second lens with negative optical power, a third lens with positive optical power, a fourth lens with positive optical power, a fifth lens with positive optical power, a sixth lens with negative optical power, and a seventh lens with positive optical power, which are arranged in sequence from the object side to the image side along the optical axis;

[0006] Wherein the fourth lens is a glass aspherical lens;

[0007] The first lens, the second lens, the third lens, the fifth lens, the sixth lens, and the seventh lens are all plastic aspherical lenses;

[0008] The fixed-focus lens satisfies:

[0009] IC / TTL>0.4;

[0010] Wherein, IC represents the image plane diameter of the fixed-focus lens, and TTL represents the optical total length of the fixed-focus lens.

[0011] Optionally, the focal length of the first lens and the focal length of the fixed-focus lens satisfy:

[0012] 0.5<|f1 / f|<2;

[0013] Wherein, f1 represents the focal length of the first lens, and f represents the focal length of the fixed-focus lens.

[0014] Optionally, the focal length of the second lens and the focal length of the fixed-focus lens satisfy:

[0015] 2.0 < |f2 / f| < 5.5;

[0016] Wherein, f2 represents the focal length of the second lens, and f represents the focal length of the fixed-focus lens.

[0017] Optionally, the refractive index of the third lens is greater than 1.65.

[0018] Optionally, the focal length of the fourth lens and the focal length of the fixed-focus lens satisfy:

[0019] |f4 / f| > 2.0;

[0020] Wherein, f4 represents the focal length of the fourth lens, and f represents the focal length of the fixed-focus lens;

[0021] The Abbe number of the fourth lens is greater than 65.

[0022] Optionally, the focal length of the fifth lens and the focal length of the fixed-focus lens satisfy:

[0023] 1.5 < |f5 / f| < 3.5;

[0024] Wherein, f5 represents the focal length of the fifth lens, and f represents the focal length of the fixed-focus lens.

[0025] Optionally, the focal length of the sixth lens and the focal length of the fixed-focus lens satisfy:

[0026] |f6 / f| > 0.5;

[0027] Wherein, f6 represents the focal length of the sixth lens, and f represents the focal length of the fixed-focus lens;

[0028] The refractive index of the sixth lens is greater than 1.6.

[0029] Optionally, the focal length of the sixth lens and the focal length of the seventh lens satisfy:

[0030] 0.5 < |f6 / f7| < 2.0;

[0031] Wherein, f6 represents the focal length of the sixth lens, and f7 represents the focal length of the seventh lens.

[0032] Optionally, it further includes a diaphragm, which is disposed between the third lens and the fourth lens.

[0033] Optionally, the first lens is a meniscus lens, the second lens is a meniscus lens, the third lens is a biconvex lens, the fourth lens is a biconvex lens, the fifth lens is a biconcave lens, the sixth lens is a biconcave lens, and the seventh lens is a biconvex lens.

[0034] The fixed-focus lens provided by the embodiment of the present invention includes a first lens with a negative optical power, a second lens with a negative optical power, a third lens with a positive optical power, a fourth lens with a positive optical power, a fifth lens with a positive optical power, a sixth lens with a negative optical power, and a seventh lens with a positive optical power, which are arranged in sequence from the object side to the image side along the optical axis; wherein the fourth lens is a glass aspherical lens; the first lens, the second lens, the third lens, the fifth lens, the sixth lens, and the seventh lens are all plastic aspherical lenses; the fixed-focus lens satisfies: IC / TTL>0.4; wherein, IC represents the image plane diameter of the fixed-focus lens, and TTL represents the total optical length of the fixed-focus lens. By adopting an optical structure of a hybrid glass and plastic with six plastic aspherical lenses and one glass aspherical lens, the plastic aspherical lens has a small mass and low cost, and has good aberration correction ability; the middle fourth lens uses a glass aspherical lens, and the temperature deformation is small, which is beneficial to realizing infrared confocal at high and low temperatures. By setting IC / TTL>0.4, it is ensured that the lens has the characteristics of short length and large image plane. On the premise that the target surface reaches 1 / 1.8 inches, it can achieve clear visible light imaging and non-defocusing of infrared imaging, and at the same time meet the 4K resolution requirement, which not only reduces the cost but also ensures the performance. Description of the Drawings

[0035] Figure 1 is a schematic structural diagram of a fixed-focus lens provided by the embodiment of the present invention;

[0036] Figure 2 is a schematic diagram of the modulation transfer function MTF curve of the fixed-focus lens provided by the embodiment of the present invention under visible light;

[0037] Figure 3 is a schematic diagram of the MTF curve of the fixed-focus lens provided by the embodiment of the present invention under infrared light;

[0038] Figure 4 is a schematic diagram of the chromatic aberration curve of the fixed-focus lens provided by the embodiment of the present invention;

[0039] Figure 5 is a schematic diagram of the spherical aberration curve of the fixed-focus lens provided by the embodiment of the present invention. Detailed Embodiment

[0040] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It can be understood that the specific embodiments described herein are only for explaining the present invention, rather than limiting the present invention. Additionally, it should be noted that for the sake of description, only the parts related to the present invention are shown in the drawings, rather than all the structures.

[0041] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. It should be noted that the orientation terms such as "upper", "lower", "left", and "right" described in the embodiments of the present invention are described from the angles shown in the drawings, and should not be construed as limiting the embodiments of the present invention. In addition, in the context, it should also be understood that when it is mentioned that an element is formed "on" or "under" another element, it can not only be directly formed "on" or "under" another element, but also be indirectly formed "on" or "under" another element through an intermediate element. The terms "first", "second", etc. are only used for descriptive purposes, and do not indicate any order, quantity, or importance, but are only used to distinguish different components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0042] Figure 1 Shown is a schematic structural diagram of a fixed-focus lens provided by an embodiment of the present invention. Refer to Figure 1 , this fixed-focus lens includes a first lens 10 with a negative optical power, a second lens 20 with a negative optical power, a third lens 30 with a positive optical power, a fourth lens 40 with a positive optical power, a fifth lens 50 with a positive optical power, a sixth lens 60 with a negative optical power, and a seventh lens 70 with a positive optical power, which are arranged in sequence from the object side to the image side along the optical axis; wherein the fourth lens 40 is a glass aspherical lens; the first lens 10, the second lens 20, the third lens 30, the fifth lens 50, the sixth lens 60, and the seventh lens 70 are all plastic aspherical lenses; this fixed-focus lens satisfies: IC / TTL > 0.4; wherein, IC represents the image plane diameter of the fixed-focus lens, and TTL represents the overall optical length of the fixed-focus lens.

[0043] It can be understood that the optical power is equal to the difference between the converging degree of the image-side light beam and the converging degree of the object-side light beam, and it characterizes the ability of the optical system to deflect light rays. The larger the absolute value of the optical power, the stronger the bending ability of the light rays, and the smaller the absolute value of the optical power, the weaker the bending ability of the light rays. When the optical power is positive, the refraction of the light rays is convergent; when the optical power is negative, the refraction of the light rays is divergent. The optical power can be used to characterize a certain refracting surface of a lens (i.e., a surface of the lens), can be used to characterize a certain lens, or can be used to characterize a system formed by multiple lenses together (i.e., a lens group). In this embodiment, each lens can be fixed to a lens barrel ( Figure 1Inside (not shown in the figure), by reasonably distributing the optical power and shape of the lenses, for example, setting the first lens 10 and the second lens 20 with negative optical power, and the light-receiving surface of the first lens 10 is larger for receiving light rays to increase the field of view angle; by setting the fourth lens 40 at the middle position as a glass aspherical lens, the glass material has a small deformation with temperature change, which is beneficial to achieving confocal at high and low temperatures; the surfaces of all lenses are aspherical, which can effectively balance aberrations. Most of the lenses are plastic aspherical lenses, and the plastic lenses have low cost and are easy to mold, enabling the lens to achieve day-night confocal function in the visible and infrared bands, with the imaging target surface reaching 1 / 1.8 inches, which can match a 4K imaging chip and has the function of visible light and infrared confocal imaging.

[0044] In the technical solution of this embodiment, by adopting an optical structure of a combination of six plastic aspherical lenses and one glass aspherical lens, the plastic aspherical lenses have small mass and low cost, and have good aberration correction ability; the middle fourth lens adopts a glass aspherical lens with small temperature deformation, which is beneficial to achieving high and low temperature infrared confocal. By setting IC / TTL > 0.4, it is ensured that the lens has the characteristics of short length and large image surface. On the premise that the imaging target surface reaches 1 / 1.8 inches, it can achieve the state that the infrared imaging is not out of focus while the visible light imaging is clear, and at the same time meet the 4K resolution requirement, which not only reduces the cost but also ensures the performance.

[0045] On the basis of the above technical solution, optionally, continuing to refer to Figure 1 , the fixed-focus lens provided by the embodiment of the present invention further includes a diaphragm 80, which is disposed between the third lens 30 and the fourth lens 40. The diaphragm 80 can adjust the field of view size, block off-axis light rays, avoid the influence of off-axis light rays on the imaging quality, and improve the image quality.

[0046] Optionally, the first lens 10 is a meniscus lens, the second lens 20 is a meniscus lens, the third lens 30 is a biconvex lens, the fourth lens 40 is a biconvex lens, the fifth lens 50 is a biconcave lens, the sixth lens 60 is a biconcave lens, and the seventh lens 70 is a biconvex lens.

[0047] It can be understood that in specific implementation, the specific lens shape can be selected according to the design of the optical power. The above is only a specific example and does not limit the embodiments of the present invention.

[0048] Optionally, the focal length of the first lens 10 and the focal length of the fixed-focus lens satisfy:

[0049] 0.5 < |f1 / f| < 2;

[0050] wherein, f1 represents the focal length of the first lens 10, and f represents the focal length of the fixed-focus lens.

[0051] It can be understood that in this embodiment, the first lens 10 is a negative focal length lens. This setting is suitable for a lens with a large field of view angle. Designing 0.5 < |f1 / f| < 2 is beneficial for collecting the light entering the lens. In order to better converge the light, the radius of curvature of the surface of the first lens 10 on the image plane side is preferably relatively small. Optionally, in this embodiment, the radius of curvature of the surface of the first lens 10 on the image plane side is designed to be less than 4 mm.

[0052] Optionally, the focal length of the second lens 20 and the focal length of the fixed-focus lens satisfy:

[0053] 2.0 < |f2 / f| < 5.5;

[0054] wherein, f2 represents the focal length of the second lens 20, and f represents the focal length of the fixed-focus lens.

[0055] It can be understood that in this embodiment, the second lens 20 is a negative focal length lens. Designing 2.0 < |f2 / f| < 5.5 is beneficial for correcting the off-axis aberration and field curvature during the imaging process.

[0056] Optionally, the refractive index of the third lens 30 is greater than 1.65.

[0057] It can be understood that in this embodiment, the third lens 30 is a positive focal length lens. Designing the refractive index of the third lens 30 to be greater than 1.65 can reduce the incident angle of the light entering the next lens, thereby reducing the generation of higher-order aberrations during the imaging process and achieving the effect of reducing the sensitivity of the lens.

[0058] Optionally, the focal length of the fourth lens 40 and the focal length of the fixed-focus lens satisfy:

[0059] |f4 / f| > 2.0;

[0060] wherein, f4 represents the focal length of the fourth lens 40, and f represents the focal length of the fixed-focus lens; the Abbe number of the fourth lens 40 is greater than 65.

[0061] It can be understood that in this embodiment, the fourth lens 40 is a positive focal length lens. Designing |f4 / f| > 2.0 can effectively correct the axial chromatic aberration during the imaging process. In order to better achieve this effect, the fourth lens 40 is a glass lens with an Abbe number greater than 65.

[0062] Optionally, the focal length of the fifth lens 50 and the focal length of the fixed-focus lens satisfy:

[0063] 1.5 < |f5 / f| < 3.5;

[0064] wherein, f5 represents the focal length of the fifth lens 50, and f represents the focal length of the fixed-focus lens.

[0065] It can be understood that in this embodiment, the fifth lens 50 is a positive focal length lens, and the design is 1.5 < |f5 / f| < 3.5, which can effectively increase the aperture number F of the lens. In this embodiment, F can reach 1.6.

[0066] Optionally, the focal length of the sixth lens 60 and the focal length of the fixed-focus lens satisfy:

[0067] |f6 / f| > 0.5;

[0068] where f6 represents the focal length of the sixth lens 60, and f represents the focal length of the fixed-focus lens; the refractive index of the sixth lens 60 is greater than 1.6.

[0069] It can be understood that in this embodiment, the sixth lens 60 is a negative focal length lens, and the design is |f6 / f| > 0.5, and the refractive index is greater than 1.6, which can effectively correct the coma in the imaging process.

[0070] Optionally, the focal length of the sixth lens 60 and the focal length of the seventh lens 70 satisfy:

[0071] 0.5 < |f6 / f7| < 2.0;

[0072] where f6 represents the focal length of the sixth lens 60, and f7 represents the focal length of the seventh lens 70.

[0073] It can be understood that in this embodiment, the seventh lens 70 is a positive focal length lens, and the design is 0.5 < |f6 / f7| < 2.0. The cooperation of the sixth lens 60 and the seventh lens 70 can compensate for the high and low temperature effects of the lens.

[0074] Optionally, in an embodiment, the first lens 10 to the seventh lens 70 satisfy the following parameters:

[0075] Table 1 Parameters of each lens

[0076]

[0077]

[0078] where f1 to f7 represent the focal lengths of the first lens to the seventh lens, with the unit of mm, n1 to n7 represent the refractive indices of the first lens to the seventh lens, R1, R4, R7, R10, R12, R14, R16 respectively represent the curvature radii of the central surfaces of the first lens to the seventh lens facing the object side in sequence, and R2, R5, R8, R11, R13, R15, R17 respectively represent the curvature radii of the central surfaces of the first lens to the seventh lens facing the image side in sequence, with the unit of mm, and "-" indicates that the direction is negative.

[0079] Exemplarily, Table 2 shows the parameter design values of a specific embodiment of a fixed-focus lens provided by an embodiment of the present invention:

[0080] Table 2 Design values of lenses in the refractive lens group

[0081]

[0082]

[0083] Among them, surface serial numbers 3 and 6 represent virtual surfaces during lens design, surface serial number 1 represents the front surface of the first lens 10 close to the object side, and so on. PL indicates that the surface is a plane; R represents the spherical radius, positive indicates that the spherical center is close to the image side, and negative indicates that the spherical center is close to the object side; D represents the distance on the optical axis from the current surface to the next surface; nd represents the refractive index of the lens; k represents the conic coefficient of the aspheric surface.

[0084] Optionally, the surface shapes of the first lens 10 to the seventh lens 70 satisfy the formula:

[0085]

[0086] Among them, z represents the distance sag from the vertex of the aspheric surface when the aspheric surface is at a position with a height of y along the optical axis direction, r represents the curvature radius of the center of the surface shape, k represents the conic coefficient, and A, B, C, D, E, and F represent the high-order aspheric coefficients.

[0087] Table 3 shows the even-term coefficients of each aspheric surface in the above embodiment:

[0088] Table 3 Parameters of each aspheric surface

[0089]

[0090]

[0091] Among them, the surface serial numbers in Table 3 correspond to those in Table 2, and 6.0962283E-05 represents 6.0962283×10 -5 .

[0092] The fixed-focus lens provided by this embodiment can achieve a 4K pixel resolution both in the visible light and infrared states, and can obtain a clear image even in a low-illumination environment at night.

[0093] Exemplarily, Figure 2 shows a schematic diagram of the modulation transfer function MTF curve of the fixed-focus lens provided by an embodiment of the present invention under visible light, Figure 3 shows a schematic diagram of the MTF curve of the fixed-focus lens provided by an embodiment of the present invention under infrared light, Figure 4The figure shows a schematic diagram of the chromatic aberration curve of the fixed-focus lens provided by the embodiment of the present invention. Figure 5 The figure shows a schematic diagram of the spherical aberration curve of the fixed-focus lens provided by the embodiment of the present invention. Among them Figure 2 The shown MTF curve is obtained under the condition that the visible light wavelength is 436nm - 656nm. Figure 3 The shown MTF curve is obtained under the condition that the infrared light wavelength is 850nm. The fixed-focus lens provided by this embodiment meets the conditions of 4K resolution for both visible light and infrared light.

[0094] Note that the above is only the preferred embodiment of the present invention and the applied technical principles. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described here, and various obvious changes, re-adjustments and substitutions can be made by those skilled in the art without departing from the protection scope of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments. Without departing from the concept of the present invention, more other equivalent embodiments can be included, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A fixed-focus lens, characterized in that, It includes a first lens with a negative focal power, a second lens with a negative focal power, a third lens with a positive focal power, a fourth lens with a positive focal power, a fifth lens with a positive focal power, a sixth lens with a negative focal power, and a seventh lens with a positive focal power arranged in sequence from the object side to the image side along the optical axis; wherein the fourth lens is a glass aspherical lens; the first lens, the second lens, the third lens, the fifth lens, the sixth lens, and the seventh lens are all plastic aspherical lenses; the fixed-focus lens satisfies: IC / TTL > 0.4; wherein, IC represents the image plane diameter of the fixed-focus lens, and TTL represents the overall optical length of the fixed-focus lens; the focal length of the fifth lens and the focal length of the fixed-focus lens satisfy: 1.5 < |f5 / f| < 3.5; wherein, f5 represents the focal length of the fifth lens, and f represents the focal length of the fixed-focus lens; the first lens to the seventh lens are fixed in a lens barrel.

2. The fixed-focus lens according to claim 1, wherein the refractive index of the third lens is greater than 1.

65.

3. The fixed-focus lens according to claim 1, wherein, the focal length of the fourth lens and the focal length of the fixed-focus lens satisfy: |f4 / f| > 2.0; wherein, f4 represents the focal length of the fourth lens, and f represents the focal length of the fixed-focus lens; the Abbe number of the fourth lens is greater than 65.

4. The fixed-focus lens according to claim 1, characterized in that, the focal length of the sixth lens and the focal length of the fixed-focus lens satisfy: |f6 / f| > 0.5; wherein, f6 represents the focal length of the sixth lens, and f represents the focal length of the fixed-focus lens; the refractive index of the sixth lens is greater than 1.

6.

5. The fixed-focus lens according to claim 1, wherein the focal length of the sixth lens and the focal length of the seventh lens satisfy: 0.5 < |f6 / f7| < 2.0; wherein, f6 represents the focal length of the sixth lens, and f7 represents the focal length of the seventh lens.

6. The fixed-focus lens according to claim 1, wherein It further includes a diaphragm, which is arranged between the third lens and the fourth lens.

7. The fixed-focus lens according to any one of claims 1 to 6, characterized in that, the first lens is a meniscus lens, the second lens is a meniscus lens, the third lens is a biconvex lens, the fourth lens is a biconvex lens, the fifth lens is a biconvex lens, the sixth lens is a biconcave lens, and the seventh lens is a biconvex lens.

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