Prime lens

Abstract

The prime lens comprises a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens and an eighth lens which are sequentially arranged from an object plane to an image plane along an optical axis, the first lens is a negative-focal-power biconcave lens, the second lens is a negative-focal-power concave-convex lens, the third lens is a positive-focal-power convex-concave lens, the fourth lens is a positive-focal-power lens, the image side face of the fourth lens is a convex face, the fifth lens is a positive-focal-power biconvex lens, the sixth lens is a negative-focal-power biconcave lens, and the seventh lens is a positive-focal-power biconvex lens. And the eighth lens is a convex-concave lens with negative focal power. According to the technical scheme, the prime lens comprises eight lenses, and the focal power and the surface type of each lens are reasonably distributed, so that the imaging quality of the optical system is improved, the prime lens is ensured to have a good imaging effect, the relative illumination between an edge image and a center image can be improved, and the imaging quality of the optical system is improved. And the imaging requirement of the security lens is met.

Description

Technical Field

[0001] The embodiment of the utility model relates to the technical field of optical devices, and in particular to a fixed-focus lens. Background Art

[0002] As the mainstream product in the security industry, fixed-focus lenses are very popular in the market. The 1 / 1.8” chip is becoming more and more widely used, and the requirements for the size, aperture and use environment of the lenses that match it are becoming more and more stringent. At present, the mainstream 1 / 1.8” optical lens on the market has a small aperture, which is not conducive to the use and promotion of the product. Utility Model Content

[0003] The utility model provides a fixed-focus lens, which can match a maximum of 1 / 1.8″ sensor chip, and its comprehensive performance meets the use requirements of general security monitoring equipment.

[0004] The embodiment of the utility model provides a fixed-focus lens, comprising a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens and an eighth lens arranged in sequence from an object plane to an image plane along an optical axis;

[0005] The first lens is a negative power lens, the second lens is a negative power lens, the third lens is a positive power lens, the fourth lens is a positive power lens, the fifth lens is a positive power lens, the sixth lens is a negative power lens, the seventh lens is a positive power lens, and the eighth lens is a negative power lens;

[0006] The object side surface of the first lens is concave, and the image side surface is concave; the object side surface of the second lens is concave, and the image side surface is convex; the object side surface of the third lens is convex, and the image side surface is concave; the image side surface of the fourth lens is convex; the object side surface of the fifth lens is convex, and the image side surface is convex; the object side surface of the sixth lens is concave, and the image side surface is concave; the object side surface of the seventh lens is convex, and the image side surface is convex; the object side surface of the eighth lens is convex, and the image side surface is concave.

[0007] Optionally, the effective focal length F1 of the first lens, the effective focal length F2 of the second lens and the effective focal length F of the fixed-focus lens respectively satisfy the following corresponding relationship:

[0008] -1.89≤F1 / F≤-1.55; -2.96≤F2 / F≤-2.41.

[0009] Optionally, the effective focal length F34 of the combination of the third lens and the fourth lens and the effective focal length F of the fixed-focus lens satisfy the following corresponding relationship:

[0010] 1.70≤F34 / F≤1.95.

[0011] Optionally, the effective focal length F567 of the combination of the fifth lens, the sixth lens and the seventh lens and the effective focal length F of the fixed-focus lens satisfy the following corresponding relationship:

[0012] 1.44≤F567 / F≤2.07.

[0013] Optionally, the effective focal length F6 of the sixth lens, the effective focal length F8 of the eighth lens and the effective focal length F of the fixed-focus lens respectively satisfy the following corresponding relationship:

[0014] -1.97≤F6 / F≤11.42;-10.17≤F8 / F≤-4.89.

[0015] Optionally, the total optical length TTL of the fixed-focus lens and the half-image height H of the lens satisfy the following corresponding relationship:

[0016] 4.75≤TTL / H≤4.90;

[0017] The total optical length TTL of the fixed focus lens and the center distance BFL from the center of the image side surface of the eighth lens to the image plane IMA satisfy the following corresponding relationship:

[0018] 4.66≤TTL / BFL≤4.74.

[0019] Optionally, the core thickness D5 of the fifth lens, the core thickness D6 of the sixth lens, and the core thickness D7 of the seventh lens satisfy the following corresponding relationship with the total optical length TTL of the fixed-focus lens:

[0020] 3.49≤TTL / (D5+D6+D7)≤3.71.

[0021] Optionally, the incident angle θ of the light at the edge of the central field of view of the fixed-focus lens on the image plane satisfies the following corresponding relationship:

[0022] 27.33°≤θ≤27.65°.

[0023] Optionally, the fourth lens is a glass spherical lens, and the first lens, the second lens, the third lens, the fifth lens, the sixth lens, the seventh lens and the eighth lens are all plastic aspherical lenses.

[0024] Optionally, the fixed-focus lens further includes an aperture and a filter;

[0025] The aperture is arranged in the optical path between the second lens and the third lens;

[0026] The filter is arranged in the optical path between the eighth lens and the image plane.

[0027] The fixed-focus lens provided by the embodiment of the utility model is provided with eight lenses, and the optical powers of the first lens to the eighth lens are respectively set to be negative optical power, negative optical power, positive optical power, positive optical power, positive optical power, negative optical power, positive optical power and negative optical power, and at the same time, the first lens is a double concave lens, the second lens is a concave-convex lens, the third lens is a convex-concave lens, the image side surface of the fourth lens is a convex surface, the fifth lens is a double convex lens, the sixth lens is a double concave lens, the seventh lens is a double convex lens and the eighth lens is a convex-concave lens. Through the coordination of the optical power and the surface shape of each lens, it is beneficial to improve the imaging quality of the optical system, ensure that the fixed-focus lens has a good imaging effect, and can improve the relative illumination between the edge image and the center image, so as to meet the imaging requirements of the security lens.

[0028] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present utility model, nor are they intended to limit the scope of the present utility model. Other features of the present utility model will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0030] Figure 1 This is a structural schematic diagram of a fixed-focus lens provided in Embodiment 1 of the present utility model;

[0031] Figure 2 This is a schematic diagram of an axial aberration curve of a fixed-focus lens provided in Embodiment 1 of the present utility model;

[0032] Figure 3 This is a schematic diagram of a light fan of a fixed-focus lens provided in Embodiment 1 of the utility model;

[0033] Figure 4 This is a schematic diagram of vertical axis chromatic aberration of a fixed-focus lens provided in Embodiment 1 of the present utility model;

[0034] Figure 5 This is a structural schematic diagram of a fixed-focus lens provided in Embodiment 2 of the present utility model;

[0035] Figure 6 This is a schematic diagram of an axial aberration curve of a fixed-focus lens provided in Embodiment 2 of the present utility model;

[0036] Figure 7This is a schematic diagram of a light fan of a fixed-focus lens provided in Embodiment 2 of the present utility model;

[0037] Figure 8 This is a schematic diagram of vertical axis chromatic aberration of a fixed-focus lens provided in Embodiment 2 of the present utility model;

[0038] Fig. 9 This is a schematic structural diagram of a fixed-focus lens provided in Embodiment 3 of the present utility model;

[0039] Fig.10 This is a schematic diagram of an axial aberration curve of a fixed-focus lens provided in Embodiment 3 of the present utility model;

[0040] Fig.11 This is a schematic diagram of a light fan of a fixed-focus lens provided in Embodiment 3 of the present utility model;

[0041] Fig.12 This is a schematic diagram of vertical axis chromatic aberration of a fixed-focus lens provided in Embodiment 3 of the present utility model. DETAILED DESCRIPTION

[0042] In order to enable those skilled in the art to better understand the solution of the utility model, the technical solution in the embodiment of the utility model will be clearly and completely described below in conjunction with the drawings in the embodiment of the utility model. Obviously, the described embodiment is only a part of the embodiment of the utility model, not all of the embodiments. Based on the embodiment of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the utility model.

[0043] Embodiment 1

[0044] Figure 1 is a schematic diagram of the structure of a fixed-focus lens provided in the first embodiment of the utility model, such as Figure 1As shown, the fixed-focus lens provided in the first embodiment of the present invention includes a first lens 110, a second lens 120, a third lens 130, a fourth lens 140, a fifth lens 150, a sixth lens 160, a seventh lens 170 and an eighth lens 180 which are arranged in sequence from the object plane to the image plane along the optical axis, wherein the first lens 110 is a negative power lens, the second lens 120 is a negative power lens, the third lens 130 is a positive power lens, the fourth lens 140 is a positive power lens, the fifth lens 150 is a positive power lens, the sixth lens 160 is a negative power lens, and the seventh lens 180 is a positive power lens. 170 is a positive power lens, and the eighth lens 180 is a negative power lens; and the object side surface of the first lens 110 is concave, and the image side surface is concave; the object side surface of the second lens 120 is concave, and the image side surface is convex; the object side surface of the third lens 130 is convex, and the image side surface is concave; the image side surface of the fourth lens 140 is convex; the object side surface of the fifth lens 150 is convex, and the image side surface is convex; the object side surface of the sixth lens 160 is concave, and the image side surface is concave; the object side surface of the seventh lens 170 is convex, and the image side surface is convex; the object side surface of the eighth lens 180 is convex, and the image side surface is concave.

[0045] Specifically, further, the focal length is equal to the difference between the convergence of the image-side beam and the convergence of the object-side beam, which characterizes the ability of the optical system to deflect light. The larger the absolute value of the focal length, the stronger the bending ability of the light, and the smaller the absolute value of the focal length, the weaker the bending ability of the light. When the focal length is a positive number, the refraction of the light is convergent; when the focal length is a negative number, the refraction of the light is divergent. The focal length 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). Setting the first lens 110 and the second lens 120 as negative focal length lenses can ensure that the first lens 110 and the second lens 120 can effectively deflect large-angle incident light, thereby effectively increasing the field of view of the fixed-focus lens, and ensuring that the optical system can have wide-angle or even ultra-wide-angle characteristics. And setting the first lens 110 and the second lens 120 as negative focal length lenses can quickly expand the light aperture and increase the aperture of the lens. The third lens 130, the fourth lens 140 and the fifth lens 150 are set as positive power lenses, so that the third lens 130, the fourth lens 140 and the fifth lens 150 can timely correct the large aberrations generated by the first lens 110 and the second lens 120, especially the edge aberrations of the optical system can be significantly corrected, thereby improving the imaging resolution of the optical system. Further setting the sixth lens 160 as a negative power lens, the seventh lens 170 as a positive power lens and the eighth lens 180 as a negative power lens can ensure the aberration balance and high and low temperature performance stability of the lens while eliminating the high-order aberrations of the lens as much as possible, and at the same time can control the target surface (size) and improve the image quality of the lens to meet the use requirements in more situations.

[0046] Further, the object side of the lens can be understood as the surface of the lens close to the object plane, and the image side of the lens can be understood as the surface of the lens close to the image plane. Specifically, the object side of the first lens 110 is a concave surface, and the image side is a concave surface, which can be understood as the object side of the first lens 110 is concave toward the object plane at the near optical axis position, and the image side is concave toward the image plane at the near optical axis position, that is, the first lens 110 is a lens with a double concave structure. The object side of the second lens 120 is a concave surface, and the image side is a convex surface, which can be understood as the object side of the second lens 120 is concave toward the object plane at the near optical axis position, and the image side is convex toward the image plane at the near optical axis position, that is, the second lens 120 is a lens with a concave-convex structure. The object side of the third lens 130 is a convex surface, and the image side is a concave surface, which can be understood as the object side of the third lens 130 is convex toward the object plane at the near optical axis position, and the image side is concave toward the image plane at the near optical axis position, that is, the third lens 130 is a lens with a convex-concave structure. The image side surface of the fourth lens 140 is a convex surface, which can be understood as the image side surface of the fourth lens 140 is convex toward the image plane at the near optical axis position. The object surface of the fifth lens 150 is a convex surface, and the image side surface is a convex surface, which can be understood as the object side surface of the fifth lens 150 is convex toward the object plane at the near optical axis position, and the image side surface is convex toward the image plane at the near optical axis position, that is, the fifth lens 150 is a lens with a double convex structure. The object surface of the sixth lens 160 is a concave surface, and the image side surface is a concave surface, which can be understood as the object side surface of the sixth lens 160 is concave toward the object plane at the near optical axis position, and the image side surface is concave toward the image plane at the near optical axis position, that is, the sixth lens 160 is a lens with a double concave structure. The object side surface of the seventh lens 170 is a convex surface, and the image side surface is a convex surface, which can be understood as the object side surface of the seventh lens 170 is convex toward the object plane at the near optical axis position, and the image side surface is convex toward the image plane at the near optical axis position, that is, the seventh lens 170 is a lens with a double convex structure. The object side surface of the eighth lens 180 is convex, and the image side surface is concave. It can be understood that the object side surface of the eighth lens 180 is convex toward the object surface at the near optical axis position, and the image side surface is concave toward the image surface at the near optical axis position, that is, the eighth lens 180 is a lens with a convex-concave structure. By reasonably setting the surface shape of each lens, it can be ensured that the edge light trend is smoother, the relative illumination between the edge image and the center image is improved, and the imaging effect is improved. The relative illumination between the edge image and the center image in the embodiment of the utility model can reach 40%, ensuring good consistency of imaging brightness.

[0047] In summary, the technical solution in the embodiment of the utility model is to set a fixed-focus lens including eight lenses, and to combine the optical focal length and surface shape of each lens, specifically, to set the first lens to be a negative focal length biconcave lens, the second lens to be a negative focal length concave-convex lens, the third lens to be a positive focal length convex-concave lens, the fourth lens to be a positive focal length lens and the image side surface to be convex, the fifth lens to be a positive focal length biconvex lens, the sixth lens to be a negative focal length biconcave lens, the seventh lens to be a positive focal length biconvex lens, and the eighth lens to be a negative focal length convex-concave lens, so as to ensure that the imaging quality of the optical system is improved, ensure that the fixed-focus lens has a good imaging effect, and can improve the relative illumination between the edge image and the center image, so as to meet the imaging requirements of the security lens.

[0048] On the basis of the above-mentioned embodiments, the fixed-focus lens provided by the embodiments of the utility model may include at least one glass spherical lens with positive optical power. The use of glass lenses with positive optical power can greatly reduce the pressure of plastic aspherical lenses on optical power. In addition, compared with plastic aspherical lenses, the thermal properties of glass spherical lenses are more stable, and when bearing more optical power, the lens can be guaranteed to have good resolution capabilities within a wider temperature range (-40°C to 80°C). In addition, compared with plastic aspherical lenses, the range of glass materials available is wider, and the choice of refractive index and Abbe number is relatively free. To a certain extent, the high-order aberrations and chromatic aberrations of the lens can be controlled to meet the use requirements under complex conditions.

[0049] Furthermore, the fixed-focus lens provided by the embodiment of the utility model may also include at least one plastic aspherical lens. The characteristic of the aspherical lens is that the curvature changes continuously from the center of the lens to the periphery of the lens. Unlike the spherical lens with a constant curvature from the center of the lens to the periphery of the lens, the aspherical lens has a better curvature radius characteristic, and has the advantages of improving distortion aberration and improving astigmatism aberration. After adopting the aspherical lens, the aberration occurring during imaging can be eliminated as much as possible, thereby improving the imaging quality of the lens. On this basis, the aspherical lens can be a plastic aspherical lens, which is conducive to reducing the processing technology of the aspherical lens, and the cost of the aspherical lens is low. In the fixed-focus lens provided by the embodiment of the utility model, a glass spherical lens and a plastic aspherical lens can be mixed and matched, so that the cost of the fixed-focus lens can be effectively controlled while ensuring the optical performance of the fixed-focus lens; at the same time, the materials of each lens have a mutual compensation effect, which can ensure that it can still be used normally in high and low temperature environments.

[0050] As an optional implementation, the fourth lens 140 can be set as a glass spherical lens, and the first lens 110, the second lens 120, the third lens 130, the fifth lens 150, the sixth lens 160, the seventh lens 170 and the eighth lens 180 are all plastic aspherical lenses. By setting a glass-plastic hybrid fixed-focus lens, the cost of the fixed-focus lens can be effectively controlled while ensuring the optical performance of the fixed-focus lens.

[0051] On the basis of the above embodiment, the effective focal length F1 of the first lens 110 and the effective focal length F2 of the second lens 120 respectively satisfy the following corresponding relationship with the effective focal length F of the fixed focus lens: -1.89≤F1 / F≤-1.55; -2.96≤F2 / F≤-2.41. By controlling the ratio of the focal length F1 of the first lens 110 to the effective focal length F of the fixed focus lens, and the ratio of the focal length F2 of the second lens 120 to the effective focal length F of the fixed focus lens, the angle of the light entering the lens can be controlled; combined with the negative optical power of the first lens 110 and the second lens 120, the diameter of the light entering the aperture can be expanded as much as possible, thereby achieving the purpose of controlling the field of view angle and improving the imaging brightness.

[0052] On the basis of the above embodiment, the effective focal length F34 of the combination of the third lens 130 and the fourth lens 140 and the effective focal length F of the fixed-focus lens satisfy the following corresponding relationship: 1.70≤F34 / F≤1.95. By controlling the ratio of the effective focal length F34 of the combination of the third lens 130 and the fourth lens 140 to the effective focal length F of the fixed-focus lens, the higher-order aberrations of the lens can be optimized to a certain extent to prevent the image quality at the rear end of the lens from being affected. In addition, by controlling the light deflection angle through the third lens 130 and the fourth lens 140, the light deflection angle can be slowed down, which can improve the production yield to a certain extent.

[0053] Based on the above embodiment, the effective focal length F567 of the combination of the fifth lens 150, the sixth lens 160 and the seventh lens 170 and the effective focal length F of the fixed focus lens satisfy the following corresponding relationship: 1.44≤F567 / F≤2.07. The fifth lens 150, the sixth lens 160 and the seventh lens 170 share the focal length, so as to avoid a certain lens from bearing too much focal length, and to avoid the high-order aberration caused by the lens to the greatest extent, thereby improving the imaging quality of the lens.

[0054] Based on the above embodiment, the effective focal length F6 of the sixth lens 160 and the effective focal length F8 of the eighth lens 180 respectively satisfy the following corresponding relationship with the effective focal length F of the fixed focus lens: -1.97≤F6 / F≤11.42; -10.17≤F8 / F≤-4.89. The sixth lens 160 provides a certain positive distortion for the lens, which can be well corrected by cooperating with the negative distortion provided by the eighth lens 108 to improve the imaging quality of the lens.

[0055] On the basis of the above embodiment, the total optical length TTL of the fixed-focus lens and the half image height H of the lens satisfy the following corresponding relationship: 4.75≤TTL / H≤4.90. By controlling the ratio of the lens image height and the total length of the lens, the volume of the lens can be well controlled, which is conducive to realizing a small-volume fixed-focus lens. Further, the total optical length TTL of the fixed-focus lens and the center distance BFL from the center of the image side surface of the eighth lens 180 to the image plane IMA satisfy the following corresponding relationship: 4.66≤TTL / BFL≤4.74. The center distance from the center of the image side surface of the eighth lens 180 to the image plane IMA can be understood as the back focus of the lens. By controlling the ratio of the total length of the lens and the back focus of the lens, the assembly yield can be improved and the cost can be reduced.

[0056] Based on the above embodiment, the core thickness D5 of the fifth lens 150, the core thickness D6 of the sixth lens 160, and the core thickness D7 of the seventh lens 170 and the total optical length TTL of the fixed focus lens satisfy the following corresponding relationship: 3.49≤TTL / (D5+D6+D7)≤3.71. By controlling the core thickness of the fifth lens 150, the sixth lens 160, and the seventh lens 170, the lens can have good processability, and the interval between the lenses can be minimized to the greatest extent while reducing the sensitivity, thereby meeting the use requirements of miniaturization of the lens.

[0057] On the basis of the above-mentioned embodiment, the incident angle θ of the edge light of the central field of view of the fixed-focus lens on the image plane satisfies the following corresponding relationship: 27.33°≤θ≤27.65°. By reasonably controlling the incident angle of the edge light of the central field of view, the fixed-focus lens can be controlled to have a larger aperture, ensuring the amount of light entering the fixed-focus lens, and further ensuring the imaging effect of the fixed-focus lens. Optionally, the aperture number F# of the fixed-focus lens provided in the embodiment of the utility model can satisfy F#≤1.085.

[0058] Based on the above embodiment, the fixed-focus lens further includes an aperture (not shown in the figure) and a filter 190; the aperture is arranged in the light path between the second lens 120 and the third lens 130; the filter 190 is arranged in the light path between the eighth lens 180 and the image plane.

[0059] Specifically, by setting an aperture, the propagation direction of the light beam can be adjusted, which is beneficial to improving the imaging quality. And the aperture in the fixed-focus lens can be located in the optical path between the second lens 120 and the third lens 130. The aperture is located in the middle of the fixed-focus lens to ensure that the front and rear apertures of the fixed-focus lens are minimized. Furthermore, the filter 190 is set in the optical path between the eighth lens 180 and the image plane. The filter 190 can filter out stray spectra to ensure imaging quality. Furthermore, the fixed-focus lens can also include flat glass to protect the lens and the image sensor.

[0060] As a feasible implementation method, specific parameters of the fixed-focus lens are described below.

[0061] Table 1 Optical design values ​​of the fixed focus lens in Example 1

[0062] Scope of protection Example 1 Lower limit Upper limit F1 / F -1.88 -1.89 -1.55 F2 / F -2.42 -2.96 -2.41 F34 / F 1.94 1.70 1.95 F567 / F 1.45 1.44 2.07 F6 / F -1.43 -1.97 -1.42 F8 / F -4.9 -10.17 -4.89 TTL / (D5+D6+D7) 3.50 3.49 3.71 TTL / H 4.75 4.75 4.90 TTL / BFL 4.73 4.66 4.74 θ 27.62 27.33 27.65

[0063] In the present invention, the aspherical lens of the fixed-focus lens satisfies the following formula:

[0064]

[0065] Where Z is the axial distance from the surface at a height r perpendicular to the optical axis to the vertex of the surface along the optical axis; c represents the curvature at the vertex of the aspheric surface; a 4 、a 6 、a 8 、a 10 、a 12 、a 14 and a 16 are the high-order aspheric coefficients of the fourth, sixth, eighth, tenth, twelfth, fourteenth and sixteenth order corresponding to the aspheric surface, a i r i The combination becomes the high-order terms corresponding to the aspherical surface.

[0066] Table 2 Design values ​​of optical physical parameters of a fixed-focus lens

[0067]

[0068]

[0069] In the above Table 2, the surface numbers are numbered according to the order of the surfaces of each lens. "1" represents the object surface of the first lens, "2" represents the image surface of the first lens, and so on. "STO" represents the aperture of the lens. The radius of curvature represents the degree of curvature of the lens surface. A positive value represents that the surface is bent toward the image side, and a negative value represents that the surface is bent toward the object side. "INF" represents that the surface is a plane and the radius of curvature is infinite. Thickness represents the central axial distance from the current surface to the next surface. nd represents the refractive index, which represents the ability of the material between the current surface and the next surface to deflect light. The space represents that the current position is air, and the refractive index is 1. vd represents the Abbe constant, which represents the dispersion characteristics of the material between the current surface and the next surface to light.

[0070] Table 3 Design value of aspheric cone coefficient in a fixed focus lens

[0071]

[0072]

[0073] Among them, "1.75301729592E-03" means 1.75301729592*10 -3 The remaining coefficients are expressed in this way.

[0074] Furthermore, Figure 2 This is a schematic diagram of the axial aberration curve of a fixed-focus lens provided in Example 1 of the utility model, specifically a schematic diagram of the axial aberration curve when the pupil radius is 1.8113mm. The vertical direction represents the normalization of the aperture, 0 represents the optical axis, and the vertical vertex represents the maximum pupil radius; the main wavelength uses 546.074nm, and the horizontal direction represents the offset relative to the ideal focus, in millimeters (mm). The different linear curves in the figure represent different wavelengths of system imaging (0.436μm, 0.486μm, 0.546μm, 0.588μm and 0.656μm), as shown by Figure 2 It can be seen that the axial aberrations of normalized apertures of different wavelengths from 0 to 1.0 are all controlled within a reasonable range, indicating that the axial chromatic aberration of the fixed-focus lens is well controlled and meets the basic requirements for clear imaging in the visible light range.

[0075] Figure 3 Schematic diagram of a ray fan of a fixed-focus lens provided in the first embodiment of the present invention. The ray fan diagram is one of the evaluation methods commonly used by optical designers. Figure 3 As shown. In a single figure, the horizontal axis is the normalized beam aperture, and the vertical axis is the vertical axis aberration. Ideally, each curve should completely coincide with the horizontal axis, and all light rays in the field of view are focused on the same point on the image plane; the vertical axis in a single image can also be expressed as the maximum dispersion range of the light beam on the ideal image plane. The light fan diagram can not only reflect the monochromatic aberration of different wavelengths, but also indicate the size of the vertical axis chromatic aberration. Figure 3 It can be seen that the fixed-focus lens is close to the horizontal axis at each wavelength (0.436μm, 0.486μm, 0.546μm, 0.588μm and 0.656μm) in each field of view, indicating that the vertical axis aberration of each wavelength is well corrected. In addition, the curves of each color are not obviously scattered, indicating that the fixed-focus lens also has good correction for chromatic aberration, ensuring the imaging requirements of this fixed-focus lens for clear images in the visible light band.

[0076] Figure 4 This is a schematic diagram of vertical axis chromatic aberration of a fixed focus lens provided in Example 1 of the utility model. The vertical direction represents the normalized aperture, 0 represents the optical axis, and the vertical vertex represents the maximum pupil radius. The main wavelength uses 546.074nm, and the horizontal direction represents the offset relative to the main wavelength in micrometers (μm). Figure 4It can be seen that the vertical chromatic aberration of different wavelengths (0.436μm, 0.486μm, 0.546μm, 0.588μm and 0.656μm) is controlled within a reasonable range, indicating that the vertical chromatic aberration of the fixed-focus lens is well controlled and can meet the application requirements of clear imaging in the visible light range.

[0077] In summary, the fixed-focus lens provided in the first embodiment of the present invention can match a maximum of 1 / 1.8″ sensor chip by reasonably setting the number of lenses, the focal power, surface shape, focal length, back focus, total optical length, radius of curvature, refractive index and Abbe number of different lenses, and meet the requirements of small size and large aperture. The comprehensive performance meets the use requirements of general sensors for security monitoring.

[0078] Embodiment 2

[0079] Figure 5 Schematic diagram of the structure of a fixed-focus lens provided in the second embodiment of the present utility model. Figure 5 As shown, the fixed-focus lens provided in the first embodiment of the present invention includes a first lens 110, a second lens 120, a third lens 130, a fourth lens 140, a fifth lens 150, a sixth lens 160, a seventh lens 170 and an eighth lens 180 which are arranged in sequence from the object plane to the image plane along the optical axis, wherein the first lens 110 is a negative power lens, the second lens 120 is a negative power lens, the third lens 130 is a positive power lens, the fourth lens 140 is a positive power lens, the fifth lens 150 is a positive power lens, the sixth lens 160 is a negative power lens, and the seventh lens 180 is a positive power lens. 170 is a positive power lens, and the eighth lens 180 is a negative power lens; and the object side surface of the first lens 110 is concave, and the image side surface is concave; the object side surface of the second lens 120 is concave, and the image side surface is convex; the object side surface of the third lens 130 is convex, and the image side surface is concave; the image side surface of the fourth lens 140 is convex; the object side surface of the fifth lens 150 is convex, and the image side surface is convex; the object side surface of the sixth lens 160 is concave, and the image side surface is concave; the object side surface of the seventh lens 170 is convex, and the image side surface is convex; the object side surface of the eighth lens 180 is convex, and the image side surface is concave.

[0080] The configuration of the above-mentioned lens is the same as that in the first embodiment, and will not be described in detail here.

[0081] As another feasible implementation, specific parameters in the fixed-focus lens are described below.

[0082] Table 4 Optical design values ​​of the fixed focus lens in Example 2

[0083] Scope of protection Example 2 Lower limit Upper limit F1 / F -1.70 -1.89 -1.55 F2 / F -2.89 -2.96 -2.41 F34 / F 1.71 1.70 1.95 F567 / F 2.06 1.44 2.07 F6 / F -1.96 -1.97 -1.42 F8 / F -6.81 -10.17 -4.89 TTL / (D5+D6+D7) 3.70 3.49 3.71 TTL / H 4.90 4.75 4.90 TTL / BFL 4.67 4.66 4.74 θ 27.64 27.33 27.65

[0084] In the present invention, the aspherical lens of the fixed-focus lens satisfies the following formula:

[0085]

[0086] Where Z is the axial distance from the surface at a height r perpendicular to the optical axis to the vertex of the surface along the optical axis; c represents the curvature at the vertex of the aspheric surface; a 4 、a 6 、a 8 、a 10 、a 12 、a 14 and a 16 are the high-order aspheric coefficients of the fourth, sixth, eighth, tenth, twelfth, fourteenth and sixteenth order corresponding to the aspheric surface, a i r i The combination becomes the high-order terms corresponding to the aspherical surface.

[0087] Table 5 Design values ​​of optical physical parameters of a fixed-focus lens

[0088] Surface number Surface type Curvature radius (mm) Thickness(mm) Materials (n.d.) Material (vd) 1 Aspheric -48.181 0.907 1.629 40.52 2 Aspheric 4.709 2.451 3 Aspheric -2.840 0.730 1.500 81.49 4 Aspheric (STO) -6.092 0.028 5 Aspheric 6.771 2.847 1.640 23.50 6 Aspheric 18.363 0.069 7 Standard surface 75.271 3.072 1.760 57.26 8 Standard surface -7.294 0.045 9 Aspheric 5.879 2.008 1.553 63.00 10 Aspheric -125.343 0.242 11 Aspheric -6.492 0.902 1.661 20.38 12 Aspheric 27.668 0.089 13 Aspheric 11.064 3.061 1.535 55.71 14 Aspheric -4.643 0.028 15 Aspheric 8.830 0.922 1.661 20.38 16 Aspheric 5.683 0.428 17 Standard surface unlimited 0.700 1.517 64.20 18 Standard surface unlimited 3.610 19 IMA unlimited -

[0089] In the above Table 2, the surface numbers are numbered according to the order of the surfaces of each lens. "1" represents the object surface of the first lens, "2" represents the image surface of the first lens, and so on. "STO" represents the aperture of the lens. The radius of curvature represents the degree of curvature of the lens surface. A positive value represents that the surface is bent toward the object side, and a negative value represents that the surface is bent toward the image side. "INF" represents that the surface is a plane and the radius of curvature is infinite. Thickness represents the central axial distance from the current surface to the next surface. nd represents the refractive index, which represents the ability of the material between the current surface and the next surface to deflect light. The space represents that the current position is air, and the refractive index is 1. vd represents the Abbe constant, which represents the dispersion characteristics of the material between the current surface and the next surface to light.

[0090] Table 6 Design value of aspheric cone coefficient in a fixed focus lens

[0091]

[0092] "2.023915755807E-03" means 2.023915755807*10 -3 The remaining coefficients are expressed in this way.

[0093] Furthermore, Figure 6This is a schematic diagram of the axial aberration curve of a fixed-focus lens provided in Example 2 of the present invention, specifically, a schematic diagram of the axial aberration curve when the pupil radius is 1.7756mm. The vertical direction represents the normalization of the aperture, 0 represents the optical axis, and the vertical vertex represents the maximum pupil radius; the main wavelength uses 546.074nm, and the horizontal direction represents the offset relative to the ideal focus, in millimeters (mm). The different linear curves in the figure represent different wavelengths of system imaging (0.436μm, 0.486μm, 0.546μm, 0.588μm and 0.656μm), as shown in FIG. Figure 6 It can be seen that the axial aberrations of normalized apertures of different wavelengths from 0 to 1.0 are all controlled within a reasonable range, indicating that the axial chromatic aberration of the fixed-focus lens is well controlled and meets the basic requirements for clear imaging in the visible light range.

[0094] Figure 7 This is a schematic diagram of a ray fan of a fixed-focus lens provided in the second embodiment of the present utility model. The ray fan diagram is one of the evaluation methods commonly used by optical designers. Figure 7 As shown. In a single figure, the horizontal axis is the normalized beam aperture, and the vertical axis is the vertical axis aberration. Ideally, each curve should completely coincide with the horizontal axis, and all light rays in the field of view are focused on the same point on the image plane; the vertical axis in a single image can also be expressed as the maximum dispersion range of the light beam on the ideal image plane. The light fan diagram can not only reflect the monochromatic aberration of different wavelengths, but also indicate the size of the vertical axis chromatic aberration. Figure 7 It can be seen that the fixed-focus lens is close to the horizontal axis at each wavelength (0.436μm, 0.486μm, 0.546μm, 0.588μm and 0.656μm) in each field of view, indicating that the vertical axis aberration of each wavelength is well corrected. In addition, the curves of each color are not obviously scattered, indicating that the fixed-focus lens also has good correction for chromatic aberration, ensuring the imaging requirements of this fixed-focus lens for clear images in the visible light band.

[0095] Figure 8 This is a schematic diagram of vertical axis chromatic aberration of a fixed focus lens provided in Example 2 of the utility model. The vertical direction represents the normalized aperture, 0 represents the optical axis, and the vertical vertex represents the maximum pupil radius. The main wavelength uses 546.074nm, and the horizontal direction represents the offset relative to the main wavelength in micrometers (μm). Figure 8 It can be seen that the vertical chromatic aberration of different wavelengths (0.436μm, 0.486μm, 0.546μm, 0.588μm and 0.656μm) is controlled within a reasonable range, indicating that the vertical chromatic aberration of the fixed-focus lens is well controlled and can meet the application requirements of clear imaging in the visible light range.

[0096] In summary, the fixed-focus lens provided in the second embodiment of the present invention can match a maximum of 1 / 1.8″ sensor chip by reasonably setting the number of lenses, the focal length, surface shape, focal length, back focus, total optical length, radius of curvature, refractive index and Abbe number of different lenses, and meet the requirements of small size and large aperture. The comprehensive performance meets the use requirements of general sensors for security monitoring.

[0097] Embodiment 3

[0098] Fig. 9 Schematic diagram of the structure of a fixed-focus lens provided in Embodiment 3 of the present utility model. Fig. 9 As shown, the fixed-focus lens provided in the third embodiment of the present invention comprises a first lens 110, a second lens 120, a third lens 130, a fourth lens 140, a fifth lens 150, a sixth lens 160, a seventh lens 170 and an eighth lens 180 which are arranged in sequence from the object plane to the image plane along the optical axis, wherein the first lens 110 is a negative power lens, the second lens 120 is a negative power lens, the third lens 130 is a positive power lens, the fourth lens 140 is a positive power lens, the fifth lens 150 is a positive power lens, the sixth lens 160 is a negative power lens, the seventh lens 180 is a positive power lens, 170 is a positive power lens, and the eighth lens 180 is a negative power lens; and the object side surface of the first lens 110 is concave, and the image side surface is concave; the object side surface of the second lens 120 is concave, and the image side surface is convex; the object side surface of the third lens 130 is convex, and the image side surface is concave; the image side surface of the fourth lens 140 is convex; the object side surface of the fifth lens 150 is convex, and the image side surface is convex; the object side surface of the sixth lens 160 is concave, and the image side surface is concave; the object side surface of the seventh lens 170 is convex, and the image side surface is convex; the object side surface of the eighth lens 180 is convex, and the image side surface is concave.

[0099] The configuration of the above-mentioned lens is the same as that in the first embodiment, and will not be described in detail here.

[0100] As another feasible implementation, specific parameters in the fixed-focus lens are described below.

[0101] Table 7 Optical design values ​​of the fixed focus lens in Example 3

[0102]

[0103]

[0104] In the present invention, the aspherical lens of the fixed-focus lens satisfies the following formula:

[0105]

[0106] Where Z is the axial distance from the surface at a height r perpendicular to the optical axis to the vertex of the surface along the optical axis; c represents the curvature at the vertex of the aspheric surface; a 4 、a 6 、a 8 、a 10 、a 12 、a 14 and a 16 are the high-order aspheric coefficients of the fourth, sixth, eighth, tenth, twelfth, fourteenth and sixteenth order corresponding to the aspheric surface, a i r i The combination becomes the high-order terms corresponding to the aspherical surface.

[0107] Table 8 Design values ​​of optical physical parameters of a fixed-focus lens

[0108]

[0109]

[0110] In the above Table 8, the surface numbers are numbered according to the order of the surfaces of each lens. "1" represents the object surface of the first lens, "2" represents the image surface of the first lens, and so on. "STO" represents the aperture of the lens. The radius of curvature represents the degree of curvature of the lens surface. A positive value represents that the surface is bent toward the object side, and a negative value represents that the surface is bent toward the image side. "INF" represents that the surface is a plane and the radius of curvature is infinite. Thickness represents the central axial distance from the current surface to the next surface. nd represents the refractive index, which represents the ability of the material between the current surface and the next surface to deflect light. The space represents that the current position is air, and the refractive index is 1. vd represents the Abbe constant, which represents the dispersion characteristics of the material between the current surface and the next surface to light.

[0111] Table 9 Design value of aspheric cone coefficient in a fixed focus lens

[0112]

[0113]

[0114] "-8.07520775237E-04" means -8.07520775237*10 -4 The remaining coefficients are expressed in this way.

[0115] Furthermore, Fig.10This is a schematic diagram of the axial aberration curve of a fixed-focus lens provided in Example 3 of the present invention, specifically, a schematic diagram of the axial aberration curve when the pupil radius is 1.6738mm. The vertical direction represents the normalization of the aperture, 0 represents the optical axis, and the vertical vertex represents the maximum pupil radius; the main wavelength uses 546.074nm, and the horizontal direction represents the offset relative to the ideal focus, in millimeters (mm). The different linear curves in the figure represent different wavelengths of system imaging (0.436μm, 0.486μm, 0.546μm, 0.588μm and 0.656μm), as shown by Fig.10 It can be seen that the axial aberrations of normalized apertures of different wavelengths from 0 to 1.0 are all controlled within a reasonable range, indicating that the axial chromatic aberration of the fixed-focus lens is well controlled and meets the basic requirements for clear imaging in the visible light range.

[0116] Fig.11 This is a schematic diagram of a ray fan of a fixed-focus lens provided in the third embodiment of the present utility model. The ray fan diagram is one of the evaluation methods commonly used by optical designers. Fig.11 As shown. In a single figure, the horizontal axis is the normalized beam aperture, and the vertical axis is the vertical axis aberration. Ideally, each curve should completely coincide with the horizontal axis, and all light rays in the field of view are focused on the same point on the image plane; the vertical axis in a single image can also be expressed as the maximum dispersion range of the light beam on the ideal image plane. The light fan diagram can not only reflect the monochromatic aberration of different wavelengths, but also indicate the size of the vertical axis chromatic aberration. Fig.11 It can be seen that the fixed-focus lens is close to the horizontal axis at each wavelength (0.436μm, 0.486μm, 0.546μm, 0.588μm and 0.656μm) in each field of view, indicating that the vertical axis aberration of each wavelength is well corrected. In addition, the curves of each color are not obviously scattered, indicating that the fixed-focus lens also has good correction for chromatic aberration, ensuring the imaging requirements of this fixed-focus lens for clear images in the visible light band.

[0117] Fig.12 This is a schematic diagram of vertical axis chromatic aberration of a fixed focus lens provided in Example 3 of the utility model. The vertical direction represents the normalized aperture, 0 represents the optical axis, and the vertical vertex represents the maximum pupil radius. The main wavelength uses 546.074nm, and the horizontal direction represents the offset relative to the main wavelength in micrometers (μm). Fig.12 It can be seen that the vertical chromatic aberration of different wavelengths (0.436μm, 0.486μm, 0.546μm, 0.588μm and 0.656μm) is controlled within a reasonable range, indicating that the vertical chromatic aberration of the fixed-focus lens is well controlled and can meet the application requirements of clear imaging in the visible light range.

[0118] In summary, the fixed-focus lens provided in the third embodiment of the present invention can match a maximum of 1 / 1.8″ sensor chip by reasonably setting the number of lenses, the focal length, surface shape, focal length, back focus, total optical length, radius of curvature, refractive index and Abbe number of different lenses, and meet the requirements of small size and large aperture. The comprehensive performance meets the use requirements of general sensors for security monitoring.

[0119] The above specific implementations do not constitute a limitation on the protection scope of the present utility model. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present utility model shall be included in the protection scope of the present utility model.

Claims

1. A fixed-focus lens, characterized in that: It includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens and an eighth lens which are arranged in sequence from the object plane to the image plane along the optical axis; The first lens is a negative power lens, the second lens is a negative power lens, the third lens is a positive power lens, the fourth lens is a positive power lens, the fifth lens is a positive power lens, the sixth lens is a negative power lens, the seventh lens is a positive power lens, and the eighth lens is a negative power lens; The object side surface of the first lens is concave, and the image side surface is concave; the object side surface of the second lens is concave, and the image side surface is convex; the object side surface of the third lens is convex, and the image side surface is concave; the image side surface of the fourth lens is convex; the object side surface of the fifth lens is convex, and the image side surface is convex; the object side surface of the sixth lens is concave, and the image side surface is concave; the object side surface of the seventh lens is convex, and the image side surface is convex; the object side surface of the eighth lens is convex, and the image side surface is concave.

2. The fixed-focus lens according to claim 1, characterized in that: The effective focal length F1 of the first lens and the effective focal length F2 of the second lens respectively satisfy the following corresponding relationship with the effective focal length F of the fixed-focus lens: -1.89≤F1 / F≤-1.55; -2.96≤F2 / F≤-2.

41.

3. The fixed-focus lens according to claim 1, characterized in that: The effective focal length F34 of the combination of the third lens and the fourth lens and the effective focal length F of the fixed-focus lens satisfy the following corresponding relationship: 1.70≤F34 / F≤1.

95.

4. The fixed-focus lens according to claim 1, characterized in that: The effective focal length F567 of the combination of the fifth lens, the sixth lens and the seventh lens and the effective focal length F of the fixed focus lens satisfy the following corresponding relationship: 1.44≤F567 / F≤2.

07.

5. The fixed-focus lens according to claim 1, wherein: The effective focal length F6 of the sixth lens and the effective focal length F8 of the eighth lens respectively satisfy the following corresponding relationship with the effective focal length F of the fixed focus lens: -1.97≤F6 / F≤11.42;-10.17≤F8 / F≤-4.

89.

6. The fixed-focus lens according to claim 1, wherein: The total optical length TTL of the fixed-focus lens and the half-image height H of the lens satisfy the following corresponding relationship: 4.75≤TTL / H≤4.90; The total optical length TTL of the fixed focus lens and the center distance BFL from the center of the image side surface of the eighth lens to the image plane IMA satisfy the following corresponding relationship: 4.66≤TTL / BFL≤4.

74.

7. The fixed-focus lens according to claim 1, wherein: The core thickness D5 of the fifth lens, the core thickness D6 of the sixth lens, and the core thickness D7 of the seventh lens satisfy the following corresponding relationship with the total optical length TTL of the fixed focus lens: 3.49≤TTL / (D5+D6+D7)≤3.

71.

8. The fixed-focus lens according to claim 1, wherein: The incident angle θ of the edge light of the central field of view of the fixed-focus lens on the image plane satisfies the following corresponding relationship: 27.33°≤θ≤27.65°.

9. The fixed-focus lens according to claim 1, wherein: The fourth lens is a glass spherical lens, and the first lens, the second lens, the third lens, the fifth lens, the sixth lens, the seventh lens and the eighth lens are all plastic aspherical lenses.

10. The fixed-focus lens according to claim 1, wherein: The fixed-focus lens also includes an aperture and a filter; The aperture is arranged in the optical path between the second lens and the third lens; The filter is arranged in the optical path between the eighth lens and the image plane.

Images