A fixed focus lens

Abstract

The embodiment of the present invention discloses a fixed-focus lens. The fixed-focus lens includes a first lens with positive focal length, a second lens with positive focal length, a third lens with positive focal length, a fourth lens with negative focal length, a fifth lens with negative focal length, a sixth lens with positive focal length, and a seventh lens with positive focal length, which are arranged in sequence from the object side to the image side along the optical axis; wherein the fifth lens and the sixth lens are plastic aspherical lenses; the first lens, the second lens, the third lens, the fourth lens, and the seventh lens are all glass spherical lenses, and the third lens and the fourth lens constitute a cemented lens; the fixed-focus lens satisfies: f / TTL>0.45; f represents the focal length of the fixed-focus lens, and TTL represents the total optical length of the fixed-focus lens. The technical solution of the embodiment of the present invention has a focal length greater than or equal to 10 mm, and infrared imaging does not defocus when visible light imaging is clear, while meeting the 4K resolution requirement, which reduces costs and ensures performance.

Description

Technical Field

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

[0002] As people's safety awareness increases, various surveillance and security facilities are becoming more and more popular, and the requirements for surveillance environment and image quality are becoming higher and higher. The surveillance lens converts the captured target into an image signal and transmits it to the image processing and recognition system to save accurate image information for roads, shopping malls, schools and other places, and provide data for information collection and query.

[0003] With the development of communication industry technology and the gradual popularization of 5G, the video shot by the lens will not be limited by transmission speed and bandwidth. In addition, people have higher and higher requirements for monitoring image quality. Therefore, 4K (3840×2160) resolution surveillance cameras have gradually begun to be accepted by people. Because it is more difficult to correct chromatic aberration of telephoto lenses than ordinary lenses, telephoto lenses on the market generally use all-glass lenses to achieve the effect of achromatic aberration, which makes the lens larger in size and more expensive, making it difficult to be popularized in the market. Summary of the invention

[0004] An embodiment of the present invention provides a fixed-focus lens, which has the characteristics of short length and large focal length. The focal length is greater than or equal to 10 mm, and the infrared imaging is not out of focus while the visible light imaging is clear. At the same time, the 4K resolution requirement is met under an ambient temperature of -30°C to 80°C, which not only reduces the cost but also ensures the performance.

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

[0006] The fifth lens and the sixth lens are plastic aspherical lenses;

[0007] The first lens, the second lens, the third lens, the fourth lens and the seventh lens are all glass spherical lenses, and the third lens and the fourth lens form a cemented lens;

[0008] The fixed-focus lens meets the following requirements:

[0009] f / TTL>0.45;

[0010] Wherein, f represents the focal length of the fixed-focus lens, and TTL represents the total optical 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] 1.0<|f1 / f|<3.8;

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

[0014] The refractive index of the first lens is less than 1.6.

[0015] Optionally, the focal length of the second lens and the focal length of the fixed-focus lens satisfy:

[0016] 1.0<|f2 / f|<3.5;

[0017] Wherein, f2 represents the focal length of the second lens, and f represents the focal length of the fixed-focus lens.

[0018] Optionally, the focal length of the third lens and the focal length of the fourth lens satisfy:

[0019] 1.0<|f3 / f4|<2.5;

[0020] Wherein, f3 represents the focal length of the third lens, and f4 represents the focal length of the fourth lens.

[0021] Optionally, the Abbe number of the third lens and the Abbe number of the fourth lens satisfy:

[0022] |Vd3-Vd4|>30;

[0023] Wherein, Vd3 represents the Abbe number of the third lens, and Vd4 represents the Abbe number of the fourth lens.

[0024] Optionally, the focal length of the fifth lens and the focal length of the sixth lens satisfy:

[0025] 1.0<|f5 / f6|<2.5;

[0026] Wherein, f5 represents the focal length of the fifth lens, and f6 represents the focal length of the sixth lens.

[0027] Optionally, the focal length of the seventh lens and the focal length of the fixed-focus lens satisfy:

[0028] |f7 / f|>1.5;

[0029] Wherein, f7 represents the focal length of the seventh lens, and f represents the focal length of the fixed-focus lens.

[0030] Optionally, the focal length of the fixed-focus lens is greater than or equal to 10 mm.

[0031] Optionally, a stop is further included, which is arranged between the fourth lens and the fifth lens.

[0032] 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 biconcave lens, the fifth lens is a meniscus lens, the sixth lens is a meniscus lens, and the seventh lens is a meniscus lens.

[0033] The fixed-focus lens provided by an embodiment of the present invention comprises a first lens with positive focal power, a second lens with positive focal power, a third lens with positive focal power, a fourth lens with negative focal power, a fifth lens with negative focal power, a sixth lens with positive focal power and a seventh lens with positive focal power, which are arranged in sequence from the object side to the image side along the optical axis; wherein the fifth lens and the sixth lens are plastic aspherical lenses; the first lens, the second lens, the third lens, the fourth lens and the seventh lens are all glass spherical lenses, and the third lens and the fourth lens constitute a cemented lens; the fixed-focus lens satisfies: f / TTL>0.45; wherein f represents the focal length of the fixed-focus lens, and TTL represents the total optical length of the fixed-focus lens. By adopting a glass-plastic hybrid optical structure of five glass spherical lenses and two plastic aspherical lenses, the plastic aspherical lenses have a smaller mass and lower cost, and have good aberration correction capability; the glass spherical lenses are easy to process and have small temperature deformation, which is conducive to achieving high and low temperature infrared confocality. By designing the third lens and the fourth lens in the middle position to be glued together, the chromatic aberration is effectively balanced. By setting f / TTL>0.45, the lens is guaranteed to have the characteristics of short length and large focal length, with a focal length greater than or equal to 10mm, and infrared imaging is not out of focus when visible light imaging is clear. At the same time, the 4K resolution requirement is met at an ambient temperature of -30℃~80℃, which not only reduces costs but also ensures performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a structural schematic diagram of a fixed-focus lens provided by an embodiment of the present invention;

[0035] Figure 2 is a schematic diagram of a modulation transfer function MTF curve of a fixed-focus lens provided in an embodiment of the present invention under visible light;

[0036] Figure 3 is a schematic diagram of an MTF curve of a fixed-focus lens provided by an embodiment of the present invention under infrared light;

[0037] Figure 4 is a schematic diagram of a chromatic aberration curve of a fixed-focus lens provided by an embodiment of the present invention;

[0038] Figure 5 Schematic diagram of the spherical aberration curve of the fixed-focus lens provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0039] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0040] 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 directional words such as "upper", "lower", "left", "right" and the like described in the embodiments of the present invention are described at the angles shown in the accompanying drawings and should not be understood as limitations on the embodiments of the present invention. In addition, in the context, it is also necessary to understand 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 indirectly formed "on" or "under" another element through an intermediate element. The terms "first", "second" and the like 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 the specific circumstances.

[0041] Figure 1 FIG. 1 is a schematic diagram of the structure of a fixed-focus lens provided by an embodiment of the present invention. Figure 1 The fixed-focus lens comprises a first lens 10 with positive focal power, a second lens 20 with positive focal power, a third lens 30 with positive focal power, a fourth lens 40 with negative focal power, a fifth lens 50 with negative focal power, a sixth lens 60 with positive focal power and a seventh lens 70 with positive focal power, which are arranged in sequence from the object side to the image side along the optical axis; wherein the fifth lens 50 and the sixth lens 60 are plastic aspherical lenses; the first lens 10, the second lens 20, the third lens 30, the fourth lens 40 and the seventh lens 70 are all glass spherical lenses, and the third lens 30 and the fourth lens 40 form a cemented lens; the fixed-focus lens satisfies: f / TTL>0.45; wherein f represents the focal length of the fixed-focus lens, and TTL represents the total optical length of the fixed-focus lens.

[0042] It can be understood that the optical power is equal to the difference between the convergence of the image-side light beam and the convergence of the object-side light beam, and it characterizes the ability of the optical system to deflect light. The larger the absolute value of the optical power, the stronger the ability to bend light, and the smaller the absolute value of the optical power, the weaker the ability to bend light. When the optical power is a positive number, the refraction of light is convergent; when the optical power is a negative number, the refraction of light is divergent. The optical power can be used to characterize a certain refractive surface of a lens (i.e., a surface of a lens), can be used to characterize a certain lens, and can also be used to characterize a system formed by multiple lenses (i.e., a lens group). In this embodiment, each lens can be fixed to a lens barrel ( Figure 1 (not shown in the figure), by reasonably allocating the optical power and shape of the lens, for example, setting the first lens 10 and the second lens 20 with positive optical power, and the first lens 10 with a larger light receiving surface, which is used for receiving light and converging imaging light; by setting the intermediate third lens 30 and the fourth lens 40 as a cemented lens, the chromatic aberration during imaging can be effectively eliminated, and the surfaces of all glass lenses are spherical. Spherical lenses are easy to process, which can effectively reduce costs, and there are a large number of glass lenses. The deformation of glass materials changes with temperature, which is conducive to achieving high and low temperature confocality; the fifth lens 50 and the sixth lens 60 are both plastic aspherical lenses, which make full use of aspherical lenses to eliminate various aberrations, and plastic lenses are low in cost and easy to shape, so that the lens can achieve day and night confocality in the visible and infrared bands. Optionally, the focal length of the fixed-focus lens provided in this embodiment is greater than or equal to 10 mm, which can match a 4K imaging chip and has the function of achieving visible light and infrared confocality at an ambient temperature of -30°C to 80°C.

[0043] The technical solution of this embodiment adopts a glass-plastic hybrid optical structure of five glass spherical lenses and two plastic aspherical lenses. The plastic aspherical lenses have small mass and low cost and good aberration correction capability. The glass spherical lenses are easy to process and have small temperature deformation, which is conducive to achieving high and low temperature infrared confocality. The third lens and the fourth lens in the middle are designed to be glued together to effectively balance chromatic aberration. By setting f / TTL>0.45, the lens is short in length and large in focal length, with a focal length greater than or equal to 10mm. The infrared imaging is not out of focus when the visible light imaging is clear, and the 4K resolution requirement is met at an ambient temperature of -30℃ to 80℃, which reduces costs and ensures performance.

[0044] Based on the above technical solutions, continue to refer to Figure 1 The fixed focus lens provided in the embodiment of the present invention further includes an aperture 80, which is disposed between the fourth lens 40 and the fifth lens 50. The aperture 80 can adjust the field of view, block the far-axis light, prevent the far-axis light from affecting the imaging quality, and improve the image quality.

[0045] 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 biconcave lens, the fifth lens 50 is a meniscus lens, the sixth lens 60 is a meniscus lens, and the seventh lens 70 is a meniscus lens.

[0046] It can be understood that, in specific implementation, the specific lens shape can be selected according to the design of the optical focal length. The above is only a specific example and is not a limitation to the embodiments of the present invention.

[0047] Optionally, the focal length of the first lens 10 and the focal length of the fixed-focus lens satisfy:

[0048] 1.0<|f1 / f|<3.8;

[0049] Wherein, f1 represents the focal length of the first lens 10, and f represents the focal length of the fixed-focus lens; the refractive index of the first lens 10 is less than 1.6.

[0050] It can be understood that, in this embodiment, the first lens 10 is a lens with positive focal power, and is designed to be 1.0<|f1 / f|<3.8, which can be suitable for a telephoto lens. In order to better eliminate axial chromatic aberration, a lens material with a smaller refractive index is preferably used, and therefore the refractive index of the first lens 10 is designed to be less than 1.6.

[0051] Optionally, the focal length of the second lens 20 and the focal length of the fixed-focus lens satisfy:

[0052] 1.0<|f2 / f|<3.5;

[0053] Wherein, f2 represents the focal length of the second lens 20, and f represents the focal length of the fixed-focus lens.

[0054] It can be understood that, in this embodiment, the second lens 20 is a positive power lens, and is designed to be 1.0<|f2 / f|<3.5, which can effectively correct the spherical aberration and field curvature in the imaging process and improve the imaging performance of the fixed-focus lens.

[0055] Optionally, the focal length of the third lens 30 and the focal length of the fourth lens 40 satisfy:

[0056] 1.0<|f3 / f4|<2.5;

[0057] Wherein, f3 represents the focal length of the third lens 30 , and f4 represents the focal length of the fourth lens 40 .

[0058] It can be understood that, in this embodiment, the third lens 30 and the fourth lens 40 form a cemented lens, and the design 1.0<|f3 / f4|<2.5 can effectively eliminate chromatic aberration. Further, in order to better eliminate spherical aberration, the dispersion coefficient of such a cemented lens generally has a large contrast. Optionally, the Abbe number of the third lens 30 and the Abbe number of the fourth lens 40 satisfy:

[0059] |Vd3-Vd4|>30;

[0060] Wherein, Vd3 represents the Abbe number of the third lens, and Vd4 represents the Abbe number of the fourth lens.

[0061] Optionally, the focal length of the fifth lens 40 and the focal length of the sixth lens 60 satisfy:

[0062] 1.0<|f5 / f6|<2.5;

[0063] Wherein, f5 represents the focal length of the fifth lens 50 , and f6 represents the focal length of the sixth lens 60 .

[0064] It can be understood that, in this embodiment, the fifth lens 50 and the sixth lens 60 are a combination of a negative lens and a positive lens. When the focal lengths of the two lenses are different, the focal length of the lens group formed by them can be positive or negative. The design of 1.0<|f5 / f6|<2.5 can effectively eliminate the high and low temperature defocus of the lens.

[0065] Optionally, the focal length of the seventh lens 70 and the focal length of the fixed-focus lens satisfy:

[0066] |f7 / f|>1.5;

[0067] Wherein, f7 represents the focal length of the seventh lens 70, and f represents the focal length of the fixed-focus lens.

[0068] It can be understood that the seventh lens 70 is a positive focal length lens used to increase the light transmittance of the lens, and its focal length is preferably designed to be larger. In this embodiment, |f7 / f|>1.5 is designed, which can effectively increase the light transmittance of the lens and ensure the imaging performance of the lens.

[0069] Optionally, in one embodiment, the first lens 10 to the seventh lens 70 satisfy the following parameters:

[0070] Table 1 Lens parameters

[0071] f1＝31.6～35.9 n1＝1.48～1.68 R1＝14.1～15.6 R2＝72.5～83.4 f2＝18.3～21.5 n2＝1.75～2.15 R3＝16.3～17.9 R4＝60.7～63.6 f3＝9.6～12.1 n3＝1.48～1.68 R5＝5.2～7.9 R6＝-28.1～-30.5 f4＝-5.2～-6.1 n4＝1.68～1.92 R6＝-28.1～-30.5 R7＝4.53～6.02 f5＝-23.6～-24.8 n5＝1.56～1.76 R9＝-3.1～-4.8 R10＝-4.9～-5.6 f6＝15.4～16.9 n6＝1.48～1.68 R11＝-28.6～-32.1 R12＝-6.4～-7.2 f7＝23.6～24.8 n7＝1.48～1.68 R13＝5.2～6.1 R14＝7.3～8.3

[0072] Wherein, f1~f7 represent the focal lengths of the first to seventh lenses, and the unit is mm; n1~n7 represent the refractive indices of the first to seventh lenses; R1, R3, R5, R6, R9, R11, and R13 represent the curvature radii of the centers of the surfaces of the first to seventh lenses facing the object side, respectively; R2, R4, R6, R8, R10, R12, and R14 represent the curvature radii of the centers of the surfaces of the first to seventh lenses facing the image side, respectively; R6 corresponds to the bonding surface of the third lens and the fourth lens, and the unit is mm; and “-” represents the negative direction.

[0073] For example, Table 2 shows the parameter design values ​​of a specific embodiment of a fixed-focus lens provided by an embodiment of the present invention:

[0074] Table 2 A design value of the lens in the refractive lens group

[0075]

[0076]

[0077] Among them, surface number 1 represents the front surface of the first lens 10 close to the object side, and so on, 6 is the cemented surface, PL indicates that the surface is a plane; R represents the radius of the spherical surface, a positive value represents the center of the spherical surface close to the image side, and a negative value represents the center of the spherical surface close to the object side; D represents the distance from the current surface to the next surface on the optical axis; nd represents the refractive index of the lens; k represents the cone coefficient of the aspherical surface.

[0078] Optionally, the surface shapes of the first lens 10 to the seventh lens 70 satisfy the formula:

[0079]

[0080] Where z represents the distance vector height from the vertex of the aspheric surface when the aspheric surface is at a height of y along the optical axis. r represents the radius of curvature of the surface center, k represents the cone coefficient, and A, B, C, D, E, and F represent high-order aspheric coefficients.

[0081] Table 3 shows the even-order coefficients of various aspherical surfaces in the above embodiments:

[0082] Table 3 Aspheric surface parameters

[0083] Surface number 9 10 11 12 A 0.002294127 0.0020063342 -0.00027816448 -0.0032884116 B -0.00071232339 -0.00003560684 0.0003004728 0.00032388354 C -1.180629e-004 -6.4114385e-004 5.608263e-005 3.7000205e-006 D -5.5492541e-005 8.8624013e-005 -2.8286062e-006 1.2679609e-006 E 1.0911009e-006 -4.2285835e-006 -1.0550893e-007 1.5559292e-007 F 0 0 0 0

[0084] Among them, surface numbers 9 and 11 correspond to the front surfaces of the fifth lens 50 and the sixth lens 60 close to the object plane, and surface numbers 10 and 10 correspond to the back surfaces of the fifth lens 50 and the sixth lens 60 close to the image plane. -1.180629e-004 means -1.180629×10 -4 .

[0085] The fixed-focus lens provided in this embodiment can achieve a focal length greater than or equal to 10mm in visible light and infrared state, and can achieve 4K pixel resolution, so that clear images can be obtained even in low-light environments at night. At the same time, this design does not shift focus when used in an environment of -30℃ to 80℃.

[0086] Specifically, Figure 2 FIG. 1 is a schematic diagram of a modulation transfer function (MTF) curve of a fixed-focus lens provided in an embodiment of the present invention under visible light. Figure 3 FIG. 1 is a schematic diagram of an MTF curve of a fixed-focus lens under infrared light provided by an embodiment of the present invention, Figure 4 FIG. 1 is a schematic diagram of a chromatic aberration curve of a fixed-focus lens provided in an embodiment of the present invention. Figure 5 FIG. 1 is a schematic diagram of a spherical aberration curve of a fixed-focus lens provided by an embodiment of the present invention. Figure 2 The MTF curve shown is obtained under the condition of visible light wavelength of 436nm~656nm. Figure 3 The MTF curve shown is obtained under the condition that the infrared light wavelength is 850nm. The fixed-focus lens provided in this embodiment meets the 4K resolution condition for both visible light and infrared light.

[0087] Note that the above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the scope of protection 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, and may include more other equivalent embodiments without departing from the concept of the present invention, 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: The invention comprises a first lens with positive focal power, a second lens with positive focal power, a third lens with positive focal power, a fourth lens with negative focal power, a fifth lens with negative focal power, a sixth lens with positive focal power and a seventh lens with positive focal power, which are arranged in sequence from the object side to the image side along the optical axis; The fifth lens and the sixth lens are plastic aspherical lenses; The first lens, the second lens, the third lens, the fourth lens and the seventh lens are all glass spherical lenses, and the third lens and the fourth lens form a cemented lens; The fixed-focus lens meets the following requirements: f / TTL>0.45; Wherein, f represents the focal length of the fixed-focus lens, and TTL represents the total optical length of the fixed-focus lens; The focal length of the first lens and the focal length of the fixed-focus lens satisfy: 1.0<|f1 / f|<3.8; Wherein, f1 represents the focal length of the first lens, and f represents the focal length of the fixed-focus lens; The refractive index of the first lens is less than 1.6; The optical system further includes a stop disposed between the fourth lens and the fifth lens.

2. The fixed-focus lens according to claim 1, characterized in that: The focal length of the second lens and the focal length of the fixed-focus lens satisfy: 1.0<|f2 / f|<3.5; Wherein, f2 represents the focal length of the second lens, and f represents the focal length of the fixed-focus lens.

3. The fixed-focus lens according to claim 1, characterized in that: The focal length of the third lens and the focal length of the fourth lens satisfy: 1.0<|f3 / f4|<2.5; Wherein, f3 represents the focal length of the third lens, and f4 represents the focal length of the fourth lens.

4. The fixed-focus lens according to claim 3, characterized in that: The Abbe number of the third lens and the Abbe number of the fourth lens satisfy: |Vd3-Vd4|>30; Wherein, Vd3 represents the Abbe number of the third lens, and Vd4 represents the Abbe number of the fourth lens.

5. The fixed-focus lens according to claim 1, wherein: The focal length of the fifth lens and the focal length of the sixth lens satisfy: 1.0<|f5 / f6|<2.5; Wherein, f5 represents the focal length of the fifth lens, and f6 represents the focal length of the sixth lens.

6. The fixed-focus lens according to claim 1, wherein: The focal length of the seventh lens and the focal length of the fixed-focus lens satisfy: |f7 / f|>1.5; Wherein, f7 represents the focal length of the seventh lens, and f represents the focal length of the fixed-focus lens.

7. The fixed-focus lens according to claim 1, wherein: The focal length of the fixed-focus lens is greater than or equal to 10 mm.

8. The fixed-focus lens according to any one of claims 1 to 7, 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 biconcave lens, the fifth lens is a meniscus lens, the sixth lens is a meniscus lens, and the seventh lens is a meniscus lens.

Images