A fixed focus lens

Abstract

The present invention proposes a fixed-focus lens, which relates to the technical field of lenses. The fixed-focus 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 arranged in sequence from the object side to the image side along the optical axis. Among them, the first lens, the second lens, the third lens, the seventh lens and the eighth lens are plastic aspherical lenses, and the fourth lens, the fifth lens and the sixth lens are glass spherical lenses. Through the above-mentioned fixed-focus lens structure, a low-cost fixed-focus lens that can take into account both imaging requirements and compact structure is realized. The fixed-focus lens can match a maximum of 1 / 1.8″ sensor chip, meet the requirements of small size, large aperture and clear imaging in the infrared band, and the comprehensive performance meets the use requirements of general sensors for security monitoring.

Description

Technical Field

[0001] The present invention relates to the technical field of lenses, 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. Summary of the invention

[0003] The embodiment of the present invention provides a fixed-focus lens to realize a low-cost fixed-focus lens that takes into account both imaging requirements and compact structure. The fixed-focus lens can match a sensor chip of up to 1 / 1.8″, meets the requirements of small size, large aperture and clear imaging in the infrared band, and the comprehensive performance meets the use requirements of general sensors for security monitoring.

[0004] In a first aspect, the present invention 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 the object side to the image side along an optical axis;

[0005] The first lens, the second lens, the third lens, the seventh lens and the eighth lens are plastic aspherical lenses, and the fourth lens, the fifth lens and the sixth lens are glass spherical lenses.

[0006] Optionally, the first lens, the second lens and the fifth lens have negative optical power;

[0007] The third lens, the fourth lens and the sixth lens have positive refractive power.

[0008] Optionally, the object-side surface of the first lens is convex toward the object side, and the image-side surface of the first lens is concave toward the image side;

[0009] The object-side surface of the second lens is concave toward the object side, and the image-side surface of the second lens is convex toward the image side;

[0010] The third lens, the fourth lens and the sixth lens are biconvex lenses;

[0011] The object-side surface of the fifth lens element is convex toward the object side, and the image-side surface of the fifth lens element is concave toward the image side;

[0012] The object-side surface of the seventh lens element is concave toward the object side, and the image-side surface of the seventh lens element is convex toward the image side;

[0013] The object-side surface of the eighth lens is convex toward the object side.

[0014] Optionally, the refractive index of the fourth lens is Nd4, the Abbe number of the fourth lens is Vd4, the refractive index of the fifth lens is Nd5, the Abbe number of the fifth lens is Vd5, the refractive index of the sixth lens is Nd6, and the Abbe number of the sixth lens is Vd6, satisfying:

[0015] 1.43≤Nd4≤1.6,65≤Vd4≤96;

[0016] 1.5≤Nd5≤1.9,22≤Vd5≤77;

[0017] 1.43≤Nd6≤1.6, 63≤Vd6≤96.

[0018] Optionally, the focal power of the first lens is Φ1, and the focal power of the second lens is Φ2, satisfying:

[0019] -0.19≤(Φ1+Φ2)≤-0.15.

[0020] Optionally, the focal power of the third lens is Φ3, the focal power of the fourth lens is Φ4, and the focal power of the fixed-focus lens is Φ, satisfying:

[0021] 0.58≤(Φ3+Φ4) / Φ≤0.69.

[0022] Optionally, the focal power of the fifth lens is Φ5, the focal power of the sixth lens is Φ6, the combined focal power of the fifth lens and the sixth lens is Φ56, and the focal power of the fixed-focus lens is Φ, which satisfies:

[0023] 0.33≤Φ56 / Φ≤0.51, -1.05≤Φ5 / Φ56≤0.7, 1.18≤Φ6 / Φ56≤1.95.

[0024] Optionally, the focal power of the seventh lens is Φ7, the focal power of the eighth lens is Φ8, and the focal power of the fixed-focus lens is Φ, satisfying:

[0025] -0.114≤(Φ7+Φ8) / Φ≤0.03.

[0026] Optionally, the aperture number of the fixed focus lens is F / #, satisfying:

[0027] 1.014≤F / #≤1.082.

[0028] Optionally, the vertical height of the intersection of the principal ray of the maximum field of view and the image plane is H, and the focal length of the fixed-focus lens is f, satisfying:

[0029] 0.86≤H / f≤1.07.

[0030] The fixed-focus lens provided by the technical solution of the present invention includes 8 lenses. Among them, the first lens, the second lens, the third lens, the seventh lens and the eighth lens are plastic aspherical lenses, and the fourth lens, the fifth lens and the sixth lens are glass spherical lenses. By optimizing the focal length matching and relative position of each lens, a low-cost fixed-focus lens that can take into account both imaging requirements and compact structure is finally realized. The fixed-focus lens can match a maximum of 1 / 1.8″ sensor chip, meeting the requirements of small size, large aperture and clear imaging in the infrared band, and its comprehensive performance meets the use requirements of general sensors for security monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. 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.

[0032] Figure 1 A schematic structural diagram of a fixed-focus lens provided in Embodiment 1 of the present invention;

[0033] Figure 2 A schematic diagram of a spherical aberration curve provided in Embodiment 1 of the present invention;

[0034] Figure 3 A schematic diagram of a field curvature curve provided in Embodiment 1 of the present invention;

[0035] Figure 4 A schematic diagram of a distortion curve provided in Embodiment 1 of the present invention;

[0036] Figure 5 A schematic diagram of a light fan provided in Embodiment 1 of the present invention;

[0037] Figure 6 A schematic structural diagram of a fixed-focus lens provided in Embodiment 2 of the present invention;

[0038] Figure 7 A schematic diagram of a spherical aberration curve provided in Embodiment 2 of the present invention;

[0039] Figure 8 A schematic diagram of a field curvature curve provided in Embodiment 2 of the present invention;

[0040] Fig. 9 A schematic diagram of a distortion curve provided in Embodiment 2 of the present invention;

[0041] Fig.10 A schematic diagram of a light fan provided in Embodiment 2 of the present invention;

[0042] Fig.11 A schematic structural diagram of a fixed-focus lens provided in Embodiment 3 of the present invention;

[0043] Fig.12 A schematic diagram of a spherical aberration curve provided in Embodiment 3 of the present invention;

[0044] Fig.13 A schematic diagram of a field curvature curve provided in Embodiment 3 of the present invention;

[0045] Fig.14 A schematic diagram of a distortion curve provided in Embodiment 3 of the present invention;

[0046] Fig.15 A schematic diagram of a light fan provided in Embodiment 3 of the present invention. DETAILED DESCRIPTION

[0047] 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.

[0048] Embodiment 1

[0049] Figure 1 This is a schematic diagram of the structure of a fixed-focus lens provided in Embodiment 1 of the present invention, referring to Figure 1 As shown, the fixed focus lens includes a first lens 1, a second lens 2, a third lens 3, a fourth lens 4, a fifth lens 5, a sixth lens 6, a seventh lens 7 and an eighth lens 8 which are arranged in sequence from the object side to the image side along the optical axis. The first lens 1, the second lens 2, the third lens 3, the seventh lens 7 and the eighth lens 8 are plastic aspherical lenses, and the fourth lens 4, the fifth lens 5 and the sixth lens 6 are glass spherical lenses.

[0050] The fixed-focus lens provided in the embodiment of the present invention includes 8 lenses. Among them, the 8 lenses are a mixed combination of 3 glass lenses and 5 aspherical plastic lenses, which can better realize aberration correction, ensure sufficiently good image quality, and have high imaging resolution. In addition, the fixed-focus lens can be matched with 5MP / 4K and 1 / 1.8-inch chips, and has a wide range of applications. In addition, the fourth lens 4, the fifth lens 5, and the sixth lens 6 use glass lenses to enable the fixed-focus lens to have good resolution in a relatively wide temperature range, and the glass lenses have a good effect on the chromatic aberration correction of the fixed-focus lens. Therefore, through the mutual cooperation of the fourth lens 4, the fifth lens 5, and the sixth lens 6, the correction ability of the fixed-focus lens for infrared wavelengths can be greatly improved, infrared confocality can be achieved, and more usage scenarios can be met, and on the other hand, the cost of the fixed-focus lens can be saved. The combination of the fifth lens 5 and the sixth lens 6 into a cemented lens group can also control the chromatic aberration of the fixed-focus lens to the greatest extent, ensure the imaging quality during night infrared, and expand the application range of the fixed-focus lens.

[0051] For example, reference Figure 1 The fixed focus lens further includes an aperture 9 and a filter 10. The aperture 9 is located between the second lens 2 and the third lens 3. The filter 10 is located on a side of the eighth lens 8 away from the seventh lens 7.

[0052] Optionally, the first lens 1, the second lens 2 and the fifth lens 5 have negative optical power, and the third lens 3, the fourth lens 4 and the sixth lens 6 have positive optical power.

[0053] Optionally, the object side surface of the first lens 1 is convex toward the object side, and the image side surface of the first lens 1 is concave toward the image side, and the first lens 1 is a convex-concave lens. The object side surface of the second lens 2 is concave toward the object side, and the image side surface of the second lens 2 is convex toward the image side, and the second lens 2 is a concave-convex lens. The third lens 3, the fourth lens 4 and the sixth lens 6 are double convex lenses. The object side surface of the fifth lens 5 is convex toward the object side, and the image side surface of the fifth lens 5 is concave toward the image side, and the fifth lens 5 is a convex-concave lens. The object side surface of the seventh lens 7 is concave toward the object side, and the image side surface of the seventh lens 7 is convex toward the image side, and the seventh lens 7 is a concave-convex lens. The object side surface of the eighth lens 8 is convex toward the object side.

[0054] Thus, the first lens 1 is a plastic aspheric lens with convex-concave negative focal power, the second lens 2 is a plastic aspheric lens with concave-convex negative focal power, the third lens 3 is a plastic aspheric lens with biconvex positive focal power, the fourth lens 4 is a glass spheric lens with biconvex positive focal power, the fifth lens 5 is a glass spheric lens with convex-concave negative focal power, the sixth lens 6 is a glass spheric lens with biconvex positive focal power, the seventh lens 7 is a concave-convex plastic aspheric lens, and the eighth lens 8 is a convex plastic aspheric lens on the object side surface. By optimizing the focal power matching and relative position of each lens element, a low-cost fixed-focus lens that can take into account both imaging requirements and compact structure is finally realized.

[0055] Optionally, the refractive index of the fourth lens 4 is Nd4, the Abbe number of the fourth lens 4 is Vd4, the refractive index of the fifth lens 5 is Nd5, the Abbe number of the fifth lens 5 is Vd5, the refractive index of the sixth lens 6 is Nd6, and the Abbe number of the sixth lens 6 is Vd6, which satisfies: 1.43≤Nd4≤1.6, 65≤Vd4≤96; 1.5≤Nd5≤1.9, 22≤Vd5≤77; 1.43≤Nd6≤1.6, 63≤Vd6≤96. Therefore, the use of a material with a high Abbe number for the fourth lens 4 can ensure that the chromatic aberration of the light is well corrected when passing through, and prevent excessive chromatic aberration and high-order aberration from being generated on the rear side of the fixed-focus lens, thereby affecting the image quality.

[0056] Optionally, the focal power of the first lens 1 is Φ1, and the focal power of the second lens 2 is Φ2, which satisfies: -0.19≤(Φ1+Φ2)≤-0.15. Therefore, the combination of the focal powers of the first lens 1 and the second lens 2 can ensure that the diameter of the light is expanded as much as possible before entering the aperture 9, increase the amount of light entering the aperture 9 position of the fixed-focus lens, enable the fixed-focus lens to still form a clear image in dim or dark conditions, and expand the applicable environment of the fixed-focus lens.

[0057] Optionally, the focal power of the third lens 3 is Φ3, the focal power of the fourth lens 4 is Φ4, and the focal power of the fixed-focus lens is Φ, which satisfies: 0.58≤(Φ3+Φ4) / Φ≤0.69. Therefore, when light passes through the aperture 9 and enters the third lens 3 and the fourth lens 4, the focal power of the third lens 3 and the fourth lens 4 can converge the light within this range, thereby preventing the rear lens from having a difficult-to-process shape due to excessive pressure during the process of correcting chromatic aberration, aberration and CRA.

[0058] Optionally, the optical power of the fifth lens 5 is Φ5, the optical power of the sixth lens 6 is Φ6, the combined optical power of the fifth lens 5 and the sixth lens 6 is Φ56, and the optical power of the fixed-focus lens is Φ, satisfying: 0.33 ≤ Φ56 / Φ ≤ 0.51, -1.05 ≤ Φ5 / Φ56 ≤ 0.7, 1.18 ≤ Φ6 / Φ56 ≤ 1.95. Thus, by using this optical power ratio, light can pass through the entire fixed-focus lens smoothly, avoiding sudden changes that may cause other problems such as ghost images or severe higher-order aberrations. In addition, the fifth lens 5 with negative optical power can adjust the angle of the light emerging from the fourth lens 4 and also has a certain effect on correcting aberrations.

[0059] Optionally, the optical power of the seventh lens 7 is Φ7, the optical power of the eighth lens 8 is Φ8, and the optical power of the fixed-focus lens is Φ, satisfying: -0.114 ≤ (Φ7 + Φ8) / Φ ≤ 0.03. Thus, the seventh lens 7 is a plastic aspherical lens. After the fifth lens 5 and the sixth lens 6 eliminate a certain amount of chromatic aberration, the aspherical seventh lens 7 can eliminate the higher-order aberrations and residual spherical aberration that were not eliminated at the front end. When paired with the eighth lens 8, which is also an aspherical lens, it can eliminate the remaining higher-order aberrations to the greatest extent. At the same time, the reasonable combination of the seventh lens 7 and the eighth lens 8 can also keep the chief ray angle within a suitable range, and can also adjust the height of the intersection of the chief ray of the maximum field of view and the image plane at the end of the fixed-focus lens to adapt to various chips, saving lens costs on the other hand.

[0060] Optionally, the f-number of the fixed-focus lens is F / #, satisfying: 1.014 ≤ F / # ≤ 1.082. Thus, the smaller the f-number of the fixed-focus lens, the stronger the light-gathering effect, and clear images can be formed in a darker environment, which can be used in special environments such as low-light and all-weather monitoring.

[0061] Optionally, the vertical height of the intersection of the chief ray of the maximum field of view and the image plane is H, and the focal length of the fixed-focus lens is f, satisfying: 0.86 ≤ H / f ≤ 1.07. Thus, by restricting the focal length of the fixed-focus lens and the vertical height of the intersection of the chief ray of the maximum field of view and the image plane, the field of view angle of the fixed-focus lens can be controlled within a certain range to meet the usage requirements.

[0062] Exemplarily, the distance from the vertex of the last optical surface of the fixed-focus lens to the image plane IMA is BFL, and the total system length of the fixed-focus lens is TTL: 0.08 < BFL / TTL < 0.155. Thus, it is beneficial to compress the total length of the fixed-focus lens while ensuring sufficient installation space for the imaging sensor and the filter 10.

[0063] Exemplarily, by reasonably allocating optical parameters such as the material, optical power, center thickness, and axial spacing between the first lens 1, the second lens 2, the third lens 3, the fourth lens 4, the fifth lens 5, the sixth lens 6, the seventh lens 7, and the eighth lens 8, the fixed-focus lens can achieve excellent imaging, compact structure, and low cost.

[0064] Table 1 A design value of the fixed focus lens in Example 1

[0065]

[0066] Table 2 A design value of the fixed focus lens in Example 1

[0067]

[0068]

[0069] Table 1 and Table 2 show a design value of the fixed-focus lens in Example 1, and the specific value can be adjusted according to product requirements and is not a limitation of the embodiment of the present invention. The fixed-focus lens shown in Table 1 and Table 2 can be Figure 1 As shown in . A lens generally includes two surfaces, each of which is a refractive surface. The surface numbers in Table 2 are numbered according to the surfaces of each lens. Among them, the surface number "S1" represents the front surface of the first lens 1 (i.e., the object side), the surface number "S2" represents the back surface of the first lens 1 (i.e., the image side), and so on, which will not be repeated here. It should be noted that "STO" in the "Surface Number" column represents the plane where the aperture 9 is located. "IMA" in the "Surface Number" column represents the image surface of the fixed focus lens. The radius of curvature represents the degree of curvature of the lens surface. A positive radius of curvature value indicates that the center of curvature is on the side of the surface close to the image side, that is, a positive value represents that the surface is bent toward the image surface IMA side; a negative radius of curvature value represents that the center of curvature is on the side of the surface away from the image surface IMA, that is, a negative value represents that the surface is bent toward the object side. "INF" in the "Radius of Curvature" column represents that the surface is a plane and the radius of curvature is infinite. The value in the "Thickness" column represents the central axial distance from the current surface to the next surface. The "Refractive Index" column indicates the refractive index of the medium between the current surface and the next surface, representing the ability of the material between the current surface and the next surface to deflect light. The blank in the "Refractive Index" column is the refractive index of air, which is 1. The Abbe number represents the dispersion characteristics of the material between the current surface and the next surface to light, and the blank represents that the current position is air. The value in the "Half-Aperture" column represents half of the aperture of the current surface. The K value represents the numerical value of the aspheric cone coefficient.

[0070] Optionally, the surface of the aspheric lens satisfies the formula:

[0071]

[0072] Among them, z is the axial vector height of the surface in the Z direction, r is the height of the aspherical surface, that is, z is the distance vector height from the vertex of the aspherical surface when the aspherical surface is at a height of r along the optical axis; c is the curvature of the fitted sphere, numerically c is the inverse of the radius of curvature, c = 1 / R, R represents the paraxial curvature radius of the mirror; k is the cone coefficient, A, B, C, D, E, F, G are the aspherical coefficients, specifically, A, B, C, D, E, F, G are the 4th, 6th, 8th, 10th, 12th, 14th and 16th order coefficients of the aspherical polynomial, respectively.

[0073] Table 3 A design value of the aspheric coefficient of the lens in the fixed focus lens in Example 1

[0074]

[0075] Table 3 shows a design value of the aspheric coefficient of the lens in the fixed-focus lens in Example 1. The specific value can be adjusted according to product requirements and is not a limitation of the embodiment of the present invention. The fixed-focus lens shown in Table 3 can be Figure 1 The meaning of the column "surface number" in Table 3 is consistent with that of the column "surface number" in Table 1. "E" in each embodiment of the present invention represents an index with base 10.

[0076] For example, in the first embodiment, the focal length f of the fixed-focus lens is 4.34273 mm, and the F / # (ie, the aperture number) is 1.0537.

[0077] Figure 2 A schematic diagram of a spherical aberration curve provided in Example 1 of the present invention, with reference to Figure 2 As shown in the figure, the vertical direction represents the normalization of the aperture, 0 represents the optical axis, and the vertical vertex represents the maximum pupil radius. 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 imaging, which are represented by Figure 2 It can be seen that the axial aberration of normalized apertures of different wavelengths of 0.3 to 1.0 is controlled within the range of (-0.04mm, +0.02mm), indicating that the spherical aberration of the fixed-focus lens at each wavelength is well controlled; it can meet the needs of wide-spectrum applications; in addition, at the pupil position of 0.5-0.9, there is no obvious chromatic aberration between visible light and infrared light, and the infrared defocus is about 8.2um, which meets the basic needs of clear night imaging.

[0078] Figure 3 A schematic diagram of a field curvature curve provided in Embodiment 1 of the present invention, Figure 4 A schematic diagram of a distortion curve provided in the first embodiment of the present invention, referring to Figure 3 and Figure 4 As shown, Figure 3 In the coordinate system in , the horizontal coordinate represents the field curvature of this fixed-focus lens, in mm; the vertical coordinate represents the normalized image height, without unit; T represents the meridian direction, and S represents the sagittal direction. Figure 3 It can be seen that the wavelength of incident light of the fixed-focus lens is 436nm~850nm. Under this wavelength condition, the field curvature of the fixed-focus lens can be effectively controlled, that is, when the fixed-focus lens is imaging, the difference between the central image quality and the peripheral image quality is small, and the entire shooting can present a relatively uniform image quality structure, meeting a wider range of usage needs.

[0079] Figure 5 A schematic diagram of a light fan provided in the first embodiment of the present invention, referring to Figure 5 As shown, 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 IMA. The vertical axis can also be expressed as the maximum dispersion range of the light beam on the ideal image plane IMA. 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 5 It can be seen that the fixed-focus lens is close to the horizontal axis at each wavelength in each field of view, indicating that the vertical axis aberration of each wavelength is well corrected. In addition, the curves corresponding to each color wavelength 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 full band.

[0080] Embodiment 2

[0081] The same points as those in the first embodiment are not repeated here.

[0082] Table 4: Design values ​​of the fixed focus lens in Example 2

[0083]

[0084] Table 5 A design value of the fixed focus lens in Example 2

[0085]

[0086]

[0087] Table 4 and Table 5 show a design value of the fixed-focus lens in Example 2, and the specific value can be adjusted according to product requirements and is not a limitation of the embodiment of the present invention. The fixed-focus lens shown in Table 4 and Table 5 can be Figure 6 as shown in .

[0088] Table 6 A design value of the aspheric coefficient of the lens in the fixed focus lens in Example 2

[0089]

[0090] Table 6 shows a design value of the aspheric coefficient of the lens in the fixed-focus lens in Example 2. The specific value can be adjusted according to product requirements and is not a limitation of the embodiment of the present invention. The fixed-focus lens shown in Table 6 can be Figure 6 as shown in .

[0091] For example, in the second embodiment, the focal length f of the fixed-focus lens is 5.245 mm, and the F / # (ie, the aperture number) is 1.082.

[0092] Figure 7 A schematic diagram of a spherical aberration curve provided in the second embodiment of the present invention, referring to Figure 7 As shown, the axial aberration of the normalized aperture at different wavelengths of 0.3 to 1.0 is controlled within the range of (-0.01mm, +0.03mm), indicating that the spherical aberration of the fixed-focus lens at each wavelength is well controlled; it can meet the needs of wide-spectrum applications; in addition, at the pupil position of 0.5-0.9, there is no obvious chromatic aberration between visible light and infrared light, and the infrared defocus is about 7.2um, which meets the basic needs of clear imaging at night.

[0093] Figure 8 A schematic diagram of a field curvature curve provided in the second embodiment of the present invention, Fig. 9 A schematic diagram of a distortion curve provided in the second embodiment of the present invention, referring to Figure 8 and Fig. 9 As shown, when the wavelength of incident light is 436nm~850nm, the field curvature of the fixed-focus lens can be effectively controlled, that is, when the fixed-focus lens is imaging, the difference between the central image quality and the peripheral image quality is small, and the entire shooting can present a relatively uniform image quality structure, meeting a wider range of usage needs.

[0094] Fig.10 A schematic diagram of a light fan provided by the second embodiment of the present invention, referring to Fig.10 As shown in the figure, the fixed-focus lens is close to the horizontal axis at each wavelength in each field of view, indicating that the vertical axis aberration of each wavelength is well corrected. In addition, the curves corresponding to each color wavelength are not obviously scattered, indicating that this fixed-focus lens also has good correction for chromatic aberration, ensuring the imaging requirements of this fixed-focus lens for clear images in the full band.

[0095] Embodiment 3

[0096] The same points as those in the first embodiment are not repeated here.

[0097] Table 7 A design value of the fixed focus lens in Example 3

[0098]

[0099] Table 8 A design value of the fixed focus lens in Example 3

[0100]

[0101] Table 7 and Table 8 show a design value of the fixed-focus lens in Example 3, and the specific value can be adjusted according to product requirements and is not a limitation of the embodiment of the present invention. The fixed-focus lens shown in Table 7 and Table 8 can be Fig.11 as shown in .

[0102] Table 9 A design value of the aspheric coefficient of the lens in the fixed focus lens in Example 3

[0103]

[0104] Table 9 shows a design value of the aspheric coefficient of the lens in the fixed-focus lens in Example 3. The specific value can be adjusted according to product requirements and is not a limitation of the embodiment of the present invention. The fixed-focus lens shown in Table 9 can be Fig.11 as shown in .

[0105] For example, in the third embodiment, the focal length f of the fixed-focus lens is 4.502 mm, and the F / # (ie, the aperture number) is 1.014.

[0106] Fig.12 A schematic diagram of a spherical aberration curve provided in Example 3 of the present invention, with reference to Fig.12 As shown, the axial aberration of the entire normalized aperture at different wavelengths of 0.3 to 1.0 is controlled within the range of (-0.02mm, +0.07mm), indicating that the spherical aberration of the fixed-focus lens at each wavelength is well controlled; it can meet the needs of wide-spectrum applications; in addition, at the pupil position of 0.5-0.9, there is no obvious chromatic aberration between visible light and infrared light, and the infrared defocus is about 3.1um, which meets the basic needs of clear night imaging.

[0107] Fig.13 A schematic diagram of a field curvature curve provided in Embodiment 3 of the present invention, Fig.14 A schematic diagram of a distortion curve provided in the third embodiment of the present invention, referring to Fig.13 and Fig.14 As shown, the incident light wavelength of the fixed-focus lens provided is 436nm~850nm. Under this wavelength condition, the field curvature of the fixed-focus lens can be effectively controlled, that is, when the fixed-focus lens is imaging, the difference between the central image quality and the peripheral image quality is small, and the entire shooting can present a relatively uniform image quality structure, meeting a wider range of usage requirements.

[0108] Fig.15 A schematic diagram of a light fan provided by Embodiment 3 of the present invention, referring to Fig.15As shown in the figure, the fixed-focus lens is close to the horizontal axis at each wavelength in each field of view, indicating that the vertical axis aberration of each wavelength is well corrected. In addition, the curves corresponding to the wavelengths of each color are not obviously scattered, indicating that this fixed-focus lens also has good correction for chromatic aberration, ensuring the imaging requirements of this fixed-focus lens for clear images in the full band.

[0109] 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, combinations 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: 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 side to the image side along the optical axis; The first lens, the second lens, the third lens, the seventh lens and the eighth lens are plastic aspherical lenses, and the fourth lens, the fifth lens and the sixth lens are glass spherical lenses; The focal power of the third lens is Φ3, the focal power of the fourth lens is Φ4, and the focal power of the fixed-focus lens is Φ, which satisfies: 0.58≤(Φ3+Φ4) / Φ≤0.69; The first lens, the second lens, the fifth lens and the seventh lens have negative optical power; The third lens, the fourth lens, the sixth lens and the eighth lens have positive refractive power; The optical components with optical power in the fixed-focus lens are only the first lens to the eighth lens.

2. The fixed-focus lens according to claim 1, characterized in that: The object-side surface of the first lens is convex toward the object side, and the image-side surface of the first lens is concave toward the image side; The object-side surface of the second lens is concave toward the object side, and the image-side surface of the second lens is convex toward the image side; The third lens, the fourth lens and the sixth lens are biconvex lenses; The object-side surface of the fifth lens is convex toward the object side, and the image-side surface of the fifth lens is concave toward the image side; The object-side surface of the seventh lens is concave toward the object side, and the image-side surface of the seventh lens is convex toward the image side; An object-side surface of the eighth lens is convex toward the object side.

3. The fixed-focus lens according to claim 1, characterized in that: The refractive index of the fourth lens is Nd4, the Abbe number of the fourth lens is Vd4, the refractive index of the fifth lens is Nd5, the Abbe number of the fifth lens is Vd5, the refractive index of the sixth lens is Nd6, and the Abbe number of the sixth lens is Vd6, satisfying: 1.43≤Nd4≤1.6,65≤Vd4≤96; 1.5≤Nd5≤1.9,22≤Vd5≤77; 1.43≤Nd6≤1.6, 63≤Vd6≤96.

4. The fixed-focus lens according to claim 1, wherein: The focal power of the first lens is Φ1, and the focal power of the second lens is Φ2, satisfying: -0.19≤(Φ1+Φ2)≤-0.

15.

5. The fixed-focus lens according to claim 1, wherein: The focal power of the fifth lens is Φ5, the focal power of the sixth lens is Φ6, the combined focal power of the fifth lens and the sixth lens is Φ56, and the focal power of the fixed focus lens is Φ, which satisfies: 0.33≤Φ56 / Φ≤0.51, -1.05≤Φ5 / Φ56≤0.7, 1.18≤Φ6 / Φ56≤1.

95.

6. The fixed-focus lens according to claim 1, wherein: The focal power of the seventh lens is Φ7, the focal power of the eighth lens is Φ8, and the focal power of the fixed-focus lens is Φ, which satisfies: -0.114≤(Φ7+Φ8) / Φ≤0.

03.

7. The fixed-focus lens according to claim 1, wherein: The aperture number of the fixed focus lens is F / #, which satisfies: 1.014≤F / #≤1.082。 8. The fixed-focus lens according to claim 1, wherein: The vertical height of the intersection of the principal ray of the maximum field of view and the image plane is H, and the focal length of the fixed-focus lens is f, which satisfies: 0.86≤H / f≤1.07.

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