A fixed-focus lens

Abstract

The present invention discloses a fixed-focus lens, which 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 arranged in sequence from the object plane to the image plane along the optical axis; the first lens has a negative optical power, the second lens has a negative optical power, the third lens has a positive optical power, the fourth lens has a positive optical power, the fifth lens has a negative optical power, the sixth lens has a positive optical power, the seventh lens has a positive optical power or a negative optical power, and the eighth lens has a negative optical power; the second lens, the seventh lens and the eighth lens are all plastic aspherical lenses, the third lens, the fourth lens, the fifth lens and the sixth lens are all glass spherical lenses, and the first lens is a glass spherical lens or a plastic aspherical lens. The fixed-focus lens provided by the present invention improves the image quality while reducing the lens volume and cost when monitoring an object with a relatively far object distance and low ambient brightness.

Description

Technical Field

[0001] The embodiments of the present invention relate to the technical field of optical devices, and particularly to a fixed-focus lens. Background Art

[0002] With the progress of technology, higher requirements are put forward for various performance aspects of lenses in the security industry. Generally, in an environment where the object to be photographed is far away, an ordinary camera can only use a long-focus fixed-focus lens with a small aperture or a zoom long-focus lens with a large aperture. When monitoring an object with a far object distance and low environmental brightness, using a long-focus fixed-focus lens for photographing will result in problems such as insufficient photographing brightness, a lot of photo noise, and very poor image quality; using a zoom long-focus lens for photographing will have problems such as a very large volume of the camera and a very high cost of the lens. Summary of the Invention

[0003] The present invention provides a fixed-focus lens to improve the image quality while reducing the volume and cost of the lens when monitoring an object with a far object distance and low environmental brightness.

[0004] The embodiments of the present invention provide a fixed-focus lens, which 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 arranged in sequence along the optical axis from the object plane to the image plane;

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

[0006] The second lens, the seventh lens, and the eighth lens are all plastic aspherical lenses, the third lens, the fourth lens, the fifth lens, and the sixth lens are all glass spherical lenses, and the first lens is a glass spherical lens or a plastic aspherical lens.

[0007] Optionally, the fourth lens, the fifth lens, and the sixth lens form a triple cemented lens.

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

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

[0010] The object side surface of the third lens is convex, and the image side surface of the third lens is convex;

[0011] The object side surface of the fourth lens is convex;

[0012] The object side of the fifth lens is concave, and the image side of the fifth lens is concave;

[0013] The object side of the sixth lens is convex, and the image side of the sixth lens is convex or concave;

[0014] The object side of the seventh lens is convex or concave, and the image side of the seventh lens is convex;

[0015] The object side of the eighth lens is convex, and the image side of the eighth lens is concave.

[0016] Optionally, the focal power of the fixed-focus lens is The focal power of the first lens is The focal power of the second lens is The focal power of the third lens is Wherein,

[0017] Optionally, the focal power of the first lens is The thickness of the first lens is D1, wherein,

[0018] Optionally, the refractive index of the first lens is Nd1, the refractive index of the second lens is Nd2, and the refractive index of the third lens is Nd3, wherein, Nd1 > 1.5, 1.5 ≤ Nd2 ≤ 1.7, Nd3 > 1.4.

[0019] Optionally, the refractive index of the seventh lens is Nd7, and the refractive index of the eighth lens is Nd8, wherein, |Nd7 - Nd8| < 0.2.

[0020] Optionally, the dispersion coefficient of the fourth lens is Vd4, the dispersion coefficient of the fifth lens is Vd5, and the dispersion coefficient of the sixth lens is Vd6, wherein, |Vd4 - Vd5| > 10, |Vd6 - Vd5| > 10.

[0021] Optionally, the aperture number F of the fixed-focus lens satisfies F < 1.11.

[0022] Optionally, the fixed-focus lens further includes a diaphragm;

[0023] The diaphragm is located in the optical path between the third lens and the fourth lens.

[0024] The fixed-focus lens provided by the embodiment of the present invention ensures that, under the premise of a small aperture number, the fixed-focus lens meets the requirement of a large light transmission amount by reasonably setting the number of lenses in the fixed-focus lens, the optical power of each lens, and the material of each lens, so as to realize the monitoring requirements under the conditions of a long object distance and low ambient brightness; at the same time, the total optical path length is short, thereby ensuring that the overall volume of the lens is small. By adopting a mixed combination of glass lenses and plastic lenses, the optical performance of the fixed-focus lens is ensured while effectively controlling the cost of the fixed-focus lens. Description of the Drawings

[0025] Figure 1 It is a schematic structural diagram of the fixed-focus lens provided by Embodiment 1 of the present invention;

[0026] Figure 2 It is an axial aberration curve graph provided by Embodiment 1 of the present invention;

[0027] Figure 3 It is a field curvature curve graph provided by Embodiment 1 of the present invention;

[0028] Figure 4 It is a distortion curve graph provided by Embodiment 1 of the present invention;

[0029] Figure 5 It is a chromatic aberration curve graph provided by Embodiment 1 of the present invention;

[0030] Figure 6 It is a schematic structural diagram of the fixed-focus lens provided by Embodiment 2 of the present invention;

[0031] Figure 7 It is an axial aberration curve graph provided by Embodiment 2 of the present invention;

[0032] Figure 8 It is a field curvature curve graph provided by Embodiment 2 of the present invention;

[0033] Figure 9 It is a distortion curve graph provided by Embodiment 2 of the present invention;

[0034] Figure 10 It is a chromatic aberration curve graph provided by Embodiment 2 of the present invention;

[0035] Figure 11 It is a schematic structural diagram of the fixed-focus lens provided by Embodiment 3 of the present invention;

[0036] Figure 12 It is an axial aberration curve graph provided by Embodiment 3 of the present invention;

[0037] Figure 13 It is a field curvature curve graph provided by Embodiment 3 of the present invention;

[0038] Figure 14 It is a distortion curve graph provided by Embodiment 3 of the present invention;

[0039] Figure 15 This is the chromatic aberration curve graph provided by Embodiment 3 of the present invention. Detailed implementation manners

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

[0041] Embodiment 1

[0042] Figure 1 This is a schematic structural diagram of a fixed-focus lens provided by Embodiment 1 of the present invention. As Figure 1 shown, the fixed-focus lens provided by Embodiment 1 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 arranged in sequence along the optical axis from the object plane to the image plane. The first lens 110 has a negative optical power, the second lens 120 has a negative optical power, the third lens 130 has a positive optical power, the fourth lens 140 has a positive optical power, the fifth lens 150 has a negative optical power, the sixth lens 160 has a positive optical power, the seventh lens 170 has a positive optical power or a negative optical power, and the eighth lens 180 has a negative optical power. The second lens 120, the seventh lens 170, and the eighth lens 180 are all plastic aspherical lenses, the third lens 130, the fourth lens 140, the fifth lens 150, and the sixth lens 160 are all glass spherical lenses, and the first lens 110 is a glass spherical lens or a plastic aspherical lens.

[0043] Exemplarily, 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 rays. The greater the absolute value of the optical power, the stronger the bending ability of the light rays, and the smaller the absolute value of the optical power, the weaker the bending ability of the light rays. When the optical power is positive, the refraction of the light rays is convergent; when the optical power is negative, the refraction of the light rays is divergent. The optical power can be used to characterize a certain refracting surface of a lens (i.e., a surface of the lens), can be used to characterize a certain lens, or can be used to characterize a system formed by multiple lenses together (i.e., a lens group).

[0044] In the fixed-focus lens provided in this embodiment, each lens can be fixed to a lens barrel ( Figure 1Inside (not shown in the figure), by setting the first lens 110 to have a negative optical power, it is used to compress the light incident aperture; the second lens 120 has a negative optical power and is used to correct the field curvature; the third lens 130 has a positive optical power and is used to correct spherical aberration; the fourth lens 140 has a positive optical power, the fifth lens 150 has a negative optical power, and the sixth lens 160 has a positive optical power, which is used to correct primary chromatic aberration and higher-order chromatic aberration; the seventh lens 170 has a positive optical power or a negative optical power, and the eighth lens 180 has a negative optical power, which is used to correct high and low temperatures and increase the lens aperture from the design.

[0045] By reasonably distributing the optical powers of each lens, while the spherical aberration and field curvature of the imaging system are small, the image quality of the on-axis and off-axis fields is ensured. Through the optical system composed of the above lenses, the total optical path length is short, thereby ensuring that the overall volume of the lens is small.

[0046] Furthermore, the second lens 120, the seventh lens 170, and the eighth lens 180 are all plastic aspherical lenses, the third lens 130, the fourth lens 140, the fifth lens 150, and the sixth lens 160 are all glass spherical lenses, and the first lens 110 is a glass spherical lens or a plastic aspherical lens. Among them, the material of the plastic aspherical lens can be various plastics known to those skilled in the art, and the material of the glass spherical lens is various types of glass known to those skilled in the art. The embodiments of the present invention do not elaborate or limit this.

[0047] Since the cost of the lens made of plastic material is much lower than that of the lens made of glass material, in the fixed-focus lens provided by the embodiments of the present invention, a mixed combination of glass lenses and plastic lenses is adopted, which can effectively control the cost of the fixed-focus lens while ensuring the optical performance of the fixed-focus lens.

[0048] In summary, by reasonably setting the number of lenses, the optical power of each lens, and the material of each lens in the fixed-focus lens, it is ensured that the fixed-focus lens meets the requirements of a large light transmission amount under the premise of a small aperture number, realizes the monitoring requirements under the conditions of a long object distance and a low environmental brightness; at the same time, it is ensured that the resolving power of the fixed-focus lens meets the imaging requirements when used in an environment of -40 to 80 °C, ensures the imaging ability of the lens in a night environment, and realizes the consistency of the image quality under different conditions.

[0049] As a feasible implementation manner, as Figure 1 shown, the fourth lens 140, the fifth lens 150, and the sixth lens 160 form a triple cemented lens.

[0050] Among them, by using a triple cemented lens, the air gap between the fourth lens 140, the fifth lens 150, and the sixth lens 160 can be effectively reduced, thereby reducing the overall length of the lens. In addition, the cemented lens can be used to minimize or eliminate chromatic aberration, so that various aberrations of the fixed-focus lens can be fully corrected. On the premise of a compact structure, the resolution can be improved, and optical performances such as distortion can be optimized; and the light loss caused by reflection between lenses can be reduced, the illuminance can be increased, thereby improving the image quality and enhancing the clarity of the lens imaging. In addition, the use of the cemented lens can also reduce the assembly components between two lenses, simplify the assembly procedure in the lens manufacturing process, reduce costs, and reduce the tolerance sensitivity problems such as tilt / eccentricity generated during the assembly process of the lens unit.

[0051] It should be noted that the fourth lens 140, the fifth lens 150, and the sixth lens 160 can form a triple cemented lens by bearing against each other through a spacer ring, and the process is relatively simple; in other embodiments, the fourth lens 140, the fifth lens 150, and the sixth lens 160 can also be bonded together with glue to form a triple cemented lens, and the embodiments of the present invention do not limit this.

[0052] As a feasible implementation manner, as Figure 1 shown, the object side of the first lens 110 is convex, and the image side of the first lens 110 is concave; the object side of the second lens 120 is concave, and the image side of the second lens 120 is convex; the object side of the third lens 130 is convex, and the image side of the third lens 130 is convex; the object side of the fourth lens 140 is convex; the object side of the fifth lens 150 is concave, and the image side of the fifth lens 150 is concave; the object side of the sixth lens 160 is convex, and the image side of the sixth lens 160 is convex or concave; the object side of the seventh lens 170 is convex or concave, and the image side of the seventh lens 170 is convex; the object side of the eighth lens 180 is convex, and the image side of the eighth lens 180 is concave.

[0053] Among them, by reasonably setting the surface types of each lens, while ensuring that the optical power of each lens meets the optical power requirements in the above embodiments, the structure of the entire fixed-focus lens can also be ensured to be compact, and the lens integration can be improved.

[0054] As a feasible implementation manner, the optical power of the fixed-focus lens provided in the embodiments of the present invention is The optical power of the first lens 110 is The optical power of the second lens 120 is The optical power of the third lens 130 is Among them,

[0055] Specifically, the optical power of the first lens 110 satisfies To better compress the light incident aperture. The optical power of the second lens 120 satisfies To better correct the field curvature. The optical power of the third lens 130 satisfies To better correct the spherical aberration.

[0056] In this embodiment, by reasonably distributing the focal lengths of the respective lenses, while the spherical aberration and field curvature of the imaging system are small, the image quality of the on-axis and off-axis fields of view is improved.

[0057] As a feasible implementation manner, the optical power of the first lens 110 is The thickness of the first lens 110 is D1, where

[0058] Wherein, by setting the optical power of the first lens 110 and the thickness D1 of the first lens 110 satisfy It helps to reasonably control the light incident aperture of the fixed-focus lens, thereby achieving a better imaging effect.

[0059] As a feasible implementation manner, the refractive index of the first lens 110 is Nd1, the refractive index of the second lens 120 is Nd2, and the refractive index of the third lens 130 is Nd3, where Nd1 > 1.5, 1.5 ≤ Nd2 ≤ 1.7, Nd3 > 1.4.

[0060] Wherein, the refractive index is the ratio of the speed of light in vacuum to the speed of light in the medium, mainly used to describe the refractive ability of the material to light, and the refractive indices of different materials are different.

[0061] In this embodiment, by matching the refractive indices of the respective lenses in the fixed-focus lens, it is beneficial to achieve the miniaturized design of the fixed-focus lens; at the same time, it is also beneficial to achieve a higher pixel resolution and a larger aperture.

[0062] As a feasible implementation manner, the refractive index of the seventh lens 170 is Nd7, and the refractive index of the eighth lens 180 is Nd8, where |Nd7 - Nd8| < 0.2.

[0063] Wherein, by matching the refractive indices of the seventh lens 170 and the eighth lens 180, it is beneficial to better correct the high and low temperature aberration and further increase the lens aperture.

[0064] As a feasible implementation manner, the dispersion coefficient of the fourth lens 140 is Vd4, the dispersion coefficient of the fifth lens 150 is Vd5, and the dispersion coefficient of the sixth lens 160 is Vd6, where |Vd4 - Vd5| > 10, |Vd6 - Vd5| > 10.

[0065] Among them, the dispersion coefficient is an important index to measure the imaging quality of the lens, usually represented by the Abbe number, so the dispersion coefficient is also called the Abbe number. The Abbe number is an index used to represent the dispersion ability of a transparent medium. The more severe the medium dispersion is, the smaller the Abbe number; conversely, the milder the medium dispersion is, the larger the Abbe number.

[0066] In this embodiment, by matching and setting the Abbe numbers of the lenses in the fixed-focus lens, it is beneficial to realize the miniaturized design of the fixed-focus lens; at the same time, it is also beneficial to achieve a higher pixel resolution and a larger aperture.

[0067] As a feasible implementation manner, the aperture number F of the fixed-focus lens provided by the embodiment of the present invention satisfies F < 1.11.

[0068] Among them, the fixed-focus lens provided by the embodiment of the present invention is a large-aperture fixed-focus lens, and the aperture number F is less than 1.11, meeting the requirement of a super-large light transmission amount and being applicable to the monitoring requirements under low illumination conditions.

[0069] As a feasible implementation manner, as Figure 1 shown, the fixed-focus lens provided by the embodiment of the present invention further includes a diaphragm 190, and the diaphragm 190 is located in the optical path between the third lens 130 and the fourth lens 140.

[0070] Among them, by setting the diaphragm 190 in the optical path between the third lens 130 and the fourth lens 140, the propagation direction of the light beam can be adjusted, and the incident angle of the light can be adjusted, which is beneficial to improving the imaging quality.

[0071] As a feasible implementation manner, as Figure 1 shown, the fixed-focus lens provided by the embodiment of the present invention further includes a filter 200, and the filter 200 is arranged on the image side of the eighth lens 180.

[0072] Among them, by arranging the filter 200 on the image side of the eighth lens 180 to filter out unnecessary stray light, the image quality of the fixed-focus lens can be improved. For example, by filtering out infrared light during the day through the filter 200, the imaging quality of the fixed-focus lens can be improved.

[0073] Exemplarily, Table 1, in a feasible implementation manner, details the specific setting parameters of each lens in the fixed-focus lens provided in the first embodiment of the present invention, and the fixed-focus lens in Table 1 corresponds to Figure 1 the described fixed-focus lens.

[0074] Table 1 A design value of the optical parameters of the fixed-focus lens

[0075]

[0076]

[0077] Among them, the surface numbers in Table 1 are numbered according to the surface order of each lens. For example, "S1" represents the object side surface of the first lens 110, "S2" represents the image side surface of the first lens 110, and so on; "STO" represents the aperture stop 190; "IMA" represents the image plane; the radius of curvature represents the degree of curvature of the lens surface, a positive value represents that the surface is curved towards the image plane side, and a negative value represents that the surface is curved towards the object plane side; "PL" represents that the surface is a plane and the radius of curvature is infinite; the thickness represents the central axial distance from the current surface to the next surface; the refractive index represents the ability of the material between the current surface and the next surface to deflect light, and a space represents that the current position is air and the refractive index is 1; the K value represents the numerical value of the best fitting conic coefficient of the aspheric surface; the units of the radius of curvature and the thickness are both millimeters (mm).

[0078] The aspheric conic coefficient can be defined by the following aspheric surface shape equation z, but is not limited to the following representation methods:

[0079]

[0080] Among them, z is the axial sagittal height in the Z direction of the aspheric surface; r is the height of the aspheric surface; c is the curvature of the fitting spherical surface, numerically the reciprocal of the radius of curvature; k is the fitting conic coefficient; A - F are the coefficients of the 4th, 6th, 8th, 10th, 12th, and 14th order terms of the aspheric polynomial. Among them, the units of z and r are both mm.

[0081] Exemplarily, Table 2 details the aspheric coefficients of each lens in Embodiment 1 of the present invention in a feasible implementation manner.

[0082] A design value of the aspheric coefficient in the fixed - focus lens in Table 2

[0083] S1 S2 S3 S4 S12 S13 S14 S15 A4 -2.89871E-07 2.28985E-07 -2.22416E-04 -4.79493E-05 7.15741E-04 -1.18411E-03 -5.81443E-03 -8.27807E-04 A6 -9.45016E-09 8.06532E-09 1.60667E-05 7.70738E-06 -8.02179E-05 1.17828E-04 1.83112E-04 -4.50551E-06 A8 -3.43469E-10 3.55224E-10 -1.09148E-06 -3.40885E-07 7.19540E-06 -6.04035E-06 -7.90219E-06 -4.93320E-06 A10 -1.22710E-11 1.65977E-11 2.54468E-08 7.45485E-09 -3.90198E-07 1.61114E-07 3.47201E-08 2.11523E-07 A12 -4.20950E-13 7.90075E-13 2.19739E-10 1.73261E-11 1.04205E-08 -3.58641E-09 2.77375E-09 -1.70283E-09 A14 -9.57296E-12 -1.03022E-12 -1.39825E-10 3.22712E-11 -1.62519E-11 -2.92333E-11

[0084] Among them, - 2.89871E - 07 indicates that the coefficient A4 of the 4th order term of the surface numbered S1 is - 2.89871×10 -7 , and so on.

[0085] Furthermore,[[]] Figure 2 is the axial aberration curve graph provided in Embodiment 1 of the present invention. As Figure 2 shown, the aberrations of this fixed - focus lens at different wavelengths (0.436μm, 0.487μm, 0.546μm, 0.587μm, and 0.656μm) are all within 0.06mm, and the curves at different wavelengths are relatively concentrated, indicating that the axial aberration of this fixed - focus lens is very small. Thus, it can be known that the fixed - focus lens provided in the embodiment of the present invention can correct aberrations well.

[0086] Figure 3 is the field curvature curve graph provided in Embodiment 1 of the present invention. AsFigure 3 As shown, the horizontal coordinate represents the magnitude of the field curvature, with the unit of mm; the vertical coordinate represents the normalized image height, without a unit; where T represents the meridian and S represents the sagittal; from Figure 3 it can be seen that for the fixed-focus lens provided in this embodiment, from the light with a wavelength of 436 nm to the light with a wavelength of 656 nm, the field curvature is effectively controlled, that is, when imaging, the image quality difference between the center and the periphery is small.

[0087] Figure 4 The following is the distortion curve graph provided by Embodiment 1 of the present invention. As Figure 4 shown, the horizontal coordinate represents the magnitude of the distortion, with the unit of %; the vertical coordinate represents the normalized image height, without a unit; from Figure 4 it can be seen that the distortion of the fixed-focus lens provided by the embodiment of the present invention is well corrected, and the imaging distortion is small, meeting the requirement of low distortion.

[0088] Figure 5 The following is the chromatic aberration curve graph provided by Embodiment 1 of the present invention. As Figure 5 shown, the vertical direction represents the normalization of the field angle, 0 represents on the optical axis, and the vertex in the vertical direction represents the maximum field radius; the horizontal direction is the offset amount in the meridian range with 0.546 μm as the reference, with the unit of micrometer (μm). The numbers on the curve in the figure represent the wavelength represented by the curve, with the unit of micrometer (μm). From Figure 5 it can be seen that the lateral chromatic aberration can be controlled within the range of (-6 μm, 4 μm).

[0089] Embodiment 2

[0090] Figure 6 The following is the structural schematic diagram of the fixed-focus lens provided by Embodiment 2 of the present invention. As Figure 6 shown, the fixed-focus lens provided by Embodiment 2 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 arranged in sequence along the optical axis from the object plane to the image plane. Among them, the aperture stop 190 is arranged in the optical path between the third lens 130 and the fourth lens 140. Table 3 shows the specific setting parameters of each lens in the fixed-focus lens provided by Embodiment 2.

[0091] Table 3 A design value of the optical parameters of the fixed-focus lens

[0092] Plane number Radius of curvature Thickness Refractive index K value S1 6.23 2.83 1.54 -0.95 S2 3.72 3.65 -1.03 S3 -8.88 1.14 1.63 -4.83 S4 -11.90 0.34 -4.98 S5 22.21 2.25 1.74 S6 -16.77 0.04 STO PL 3.41 S8 17.08 2.60 1.49 S9 -11.33 0.78 1.64 S10 6.72 1.88 1.74 S11 16.51 0.11 S12 18.36 5.04 1.54 4.30 S13 -5.47 0.05 -8.99 S14 5.94 1.50 1.63 -2.15 S15 3.41 2.31 -4.13 S16 PL 0.92 1.52 S17 PL 1.63 IMA PL

[0093] Among them, the surface numbers in Table 3 are numbered according to the surface order of each lens. For example, "S1" represents the object side surface of the first lens 110, "S2" represents the image side surface of the first lens 110, and so on; "STO" represents the aperture stop 190; "IMA" represents the image plane; the radius of curvature represents the degree of curvature of the lens surface. A positive value represents that the surface bends towards the image plane side, and a negative value represents that the surface bends towards the object plane side; "PL" represents that the surface is a plane and the radius of curvature is infinity; the thickness represents the central axial distance from the current surface to the next surface; the refractive index represents the ability of the material between the current surface and the next surface to deflect light, and a space represents that the current position is air and the refractive index is 1; the K value represents the numerical value of the best-fit conic coefficient of the aspheric surface; the units of the radius of curvature and the thickness are both millimeters (mm).

[0094] The aspheric conic coefficient can be defined by the following aspheric surface shape equation z, but is not limited to the following representation methods:

[0095]

[0096] Among them, z is the axial sagittal height in the Z direction of the aspheric surface; r is the height of the aspheric surface; c is the curvature of the fitted spherical surface, which is numerically the reciprocal of the radius of curvature; k is the fitted conic coefficient; A - F are the coefficients of the 4th, 6th, 8th, 10th, 12th, and 14th order terms of the aspheric polynomial. Among them, the units of z and r are both mm.

[0097] Exemplarily, Table 4 details the aspheric coefficients of each lens in the second embodiment of the present invention in a feasible implementation manner.

[0098] A design value of the aspheric coefficient in the fixed-focus lens in Table 4

[0099] S1 S2 S3 S4 S12 S13 S14 S15 A4 -2.88420E-04 -9.29666E-05 -6.07171E-05 3.31207E-04 8.84279E-04 -1.13758E-04 -8.24422E-04 -3.63988E-04 A6 -1.34467E-05 -3.84773E-05 -5.96847E-06 -7.47557E-06 -9.04370E-06 2.98547E-05 -2.03617E-05 6.43304E-05 A8 1.22190E-07 5.52040E-07 9.19241E-08 1.47505E-07 -1.37813E-07 -1.89514E-06 1.50293E-06 -9.56387E-06 A10 4.62758E-09 3.05438E-08 -2.78074E-09 3.87865E-09 6.75095E-09 5.25452E-08 -3.10674E-07 1.96757E-07 A12 -1.15696E-10 -1.04763E-09 1.24354E-09 1.98518E-10 1.74168E-10 -6.13133E-10 1.04352E-08 3.41364E-09 A14 9.12681E-13 1.92763E-11 -4.02937E-11 -1.33261E-11 0.00000E+00 0.00000E+00 0.00000E+00 0.00000E+00

[0100] Among them, -2.88420E - 04 indicates that the coefficient A4 of the 4th order term of the surface numbered S1 is -2.88420×10 -4 , and so on.

[0101] Furthermore, Figure 7 is the axial aberration curve graph provided by the second embodiment of the present invention. As Figure 7 shown, the aberrations of this fixed-focus lens at different wavelengths (0.436 μm, 0.487 μm, 0.546 μm, 0.587 μm, and 0.656 μm) are all within 0.16 mm, and the curves at different wavelengths are relatively concentrated, indicating that the axial aberration of this fixed-focus lens is very small. Thus, it can be known that the fixed-focus lens provided by the embodiment of the present invention can correct aberrations well.

[0102] Figure 8 is the field curvature curve graph provided by the second embodiment of the present invention. AsFigure 8 As shown, the horizontal coordinate represents the magnitude of the field curvature, with the unit of mm; the vertical coordinate represents the normalized image height, without unit; where T represents the meridian and S represents the sagittal; from Figure 8 it can be seen that for the fixed-focus lens provided in this embodiment, from the light with a wavelength of 436 nm to the light with a wavelength of 656 nm, the field curvature is effectively controlled, that is, when imaging, the difference in image quality between the center and the periphery is small.

[0103] Figure 9 It is the distortion curve graph provided by the second embodiment of the present invention. As Figure 9 shown, the horizontal coordinate represents the magnitude of the distortion, with the unit of %; the vertical coordinate represents the normalized image height, without unit; from Figure 9 it can be seen that the distortion of the fixed-focus lens provided by the embodiment of the present invention is well corrected, the imaging distortion is small, and the requirement of low distortion is satisfied.

[0104] Figure 10 It is the chromatic aberration curve graph provided by the second embodiment of the present invention. As Figure 10 shown, the vertical direction represents the normalization of the field angle, 0 represents on the optical axis, and the vertex in the vertical direction represents the maximum field radius; the horizontal direction is the offset amount in the meridian range with 0.546 μm as the reference, with the unit of micrometer (μm). The numbers on the curve in the figure represent the wavelength represented by the curve, with the unit of micrometer (μm). From Figure 10 it can be seen that the lateral chromatic aberration can be controlled within the range of (-1 μm, 3 μm).

[0105] Embodiment 3

[0106] Figure 11 It is the structural schematic diagram of the fixed-focus lens provided by the third embodiment of the present invention. As Figure 11 shown, the fixed-focus lens provided by the third 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 that are sequentially arranged along the optical axis from the object plane to the image plane. Among them, the aperture stop 190 is arranged in the optical path between the third lens 130 and the fourth lens 140. Table 5 shows the specific setting parameters of each lens in the fixed-focus lens provided by Embodiment 3.

[0107] Table 5 A design value of the optical parameters of the fixed-focus lens

[0108]

[0109]

[0110] Among them, the surface numbers in Table 5 are numbered according to the surface order of each lens. For example, "S1" represents the object side surface of the first lens 110, "S2" represents the image side surface of the first lens 110, and so on; "STO" represents the aperture stop 190; "IMA" represents the image plane; the radius of curvature represents the degree of curvature of the lens surface. A positive value represents that the surface is bent towards the image plane side, and a negative value represents that the surface is bent towards the object plane side; "PL" represents that the surface is a plane and the radius of curvature is infinite; the thickness represents the central axial distance from the current surface to the next surface; the refractive index represents the ability of the material between the current surface and the next surface to deflect light, and a space represents that the current position is air and the refractive index is 1; the K value represents the numerical value of the best-fit conic coefficient of the aspherical surface; the units of the radius of curvature and the thickness are both millimeters (mm).

[0111] The aspherical conic coefficient can be defined by the following aspherical surface shape equation z, but is not limited to the following representation methods:

[0112]

[0113] Among them, z is the axial sagittal height in the Z direction of the aspherical surface; r is the height of the aspherical surface; c is the curvature of the fitted spherical surface, which is numerically the reciprocal of the radius of curvature; k is the fitted conic coefficient; A - F are the coefficients of the 4th, 6th, 8th, 10th, 12th, and 14th order terms of the aspherical polynomial. Among them, the units of z and r are both mm.

[0114] Exemplarily, Table 6 details the aspherical coefficients of each lens in Embodiment 3 of the present invention in a feasible implementation manner.

[0115] A design value of the aspherical coefficient in the fixed-focus lens in Table 6

[0116] S1 S2 S3 S4 S12 S13 S14 S15 A4 -5.34891E-04 -2.06465E-04 -9.07182E-05 1.16056E-04 1.65281E-03 -1.14112E-04 -4.92048E-03 -2.05291E-03 A6 -1.62233E-05 -3.11181E-05 -9.59780E-06 -4.41906E-06 -6.03377E-05 7.65326E-06 -3.51444E-05 -8.57804E-05 A8 3.09266E-07 5.11846E-07 -4.39443E-07 -6.63023E-08 9.65862E-07 -1.57591E-06 -1.86780E-06 -1.75748E-06 A10 4.37994E-09 1.69216E-08 -2.77238E-08 -6.66634E-09 -3.51460E-09 6.96529E-08 -3.17725E-07 3.15814E-07 A12 -1.24840E-10 -1.38224E-09 7.72347E-10 8.79135E-11 -6.95942E-10 -5.46774E-09 2.04753E-08 -8.33910E-09 A14 2.83108E-12 4.92555E-11 -6.23640E-12 5.00446E-12 -8.85040E-11 7.59505E-11 -4.97462E-10 2.43036E-11

[0117] Among them, -5.34891E-04 indicates that the coefficient A4 of the 4th order term of the surface numbered S1 is -5.34891×10 -4 , and so on.

[0118] Furthermore, Figure 12 is the axial aberration curve diagram provided by Embodiment 3 of the present invention. As Figure 12 shown, the aberrations of this fixed-focus lens at different wavelengths (0.436μm, 0.487μm, 0.546μm, 0.587μm, and 0.656μm) are all within 0.02mm, and the curves at different wavelengths are relatively concentrated, indicating that the axial aberration of this fixed-focus lens is very small. Thus, it can be known that the fixed-focus lens provided by the embodiment of the present invention can correct aberrations well.

[0119] Figure 13 is the field curvature curve diagram provided by Embodiment 3 of the present invention. AsFigure 13 As shown, the horizontal coordinate represents the magnitude of the field curvature, with the unit of mm; the vertical coordinate represents the normalized image height, without a unit; where T represents the meridian and S represents the sagittal; from Figure 13 it can be seen that for the fixed-focus lens provided in this embodiment, from the light with a wavelength of 436 nm to the light with a wavelength of 656 nm, the field curvature is effectively controlled, that is, during imaging, the difference in image quality between the center and the periphery is small.

[0120] Figure 14 It is the distortion curve graph provided by the third embodiment of the present invention. As Figure 14 shown, the horizontal coordinate represents the magnitude of the distortion, with the unit of %; the vertical coordinate represents the normalized image height, without a unit; from Figure 14 it can be seen that the distortion of the fixed-focus lens provided by the embodiment of the present invention is well corrected, and the imaging distortion is small, meeting the requirement of low distortion.

[0121] Figure 15 It is the chromatic aberration curve graph provided by the third embodiment of the present invention. As Figure 15 shown, the vertical direction represents the normalization of the field of view angle, 0 represents on the optical axis, and the vertex in the vertical direction represents the maximum field of view radius; the horizontal direction is the offset amount in the meridian range with 0.546 μm as the reference, with the unit of micrometer (μm). The numbers on the curve in the figure represent the wavelength represented by this curve, with the unit of micrometer (μm). From Figure 10 it can be seen that the lateral chromatic aberration can be controlled within the range of (-3 μm, 5 μm).

[0122] For the fixed-focus lens provided by the embodiment of the present invention, by reasonably setting the number of lenses, the materials, optical powers, refractive indices, and Abbe numbers of each lens in the fixed-focus lens, it meets the condition of aperture F ≤ 1.11, and can be maximally matched with a 1 / 1.8″ ultra-large target surface sensing chip. At the same time, it has the advantages of a large target surface and high pixels, and the total length of the lens is less than 31 mm. By using a combination method of glass lenses and plastic lenses, it realizes the characteristics of low cost and high performance, can meet the use conditions of -40°C - 80°C, and realizes a fixed-focus lens that can be used with a day-night full-color camera.

[0123] Note that the above is only the preferred embodiment of the present invention and the applied technical principles. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described here. Various obvious changes, re-adjustments, mutual combinations, and substitutions can be made by those skilled in the art without departing from the protection scope of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments. Without departing from the concept of the present invention, it can also include more other equivalent embodiments, 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 arranged in sequence along the optical axis from the object plane to the image plane; the first lens has a negative optical power, the second lens has a negative optical power, the third lens has a positive optical power, the fourth lens has a positive optical power, the fifth lens has a negative optical power, the sixth lens has a positive optical power, the seventh lens has a positive or negative optical power, and the eighth lens has a negative optical power; the second lens, the seventh lens, and the eighth lens are all plastic aspherical lenses, the third lens, the fourth lens, the fifth lens, and the sixth lens are all glass spherical lenses, and the first lens is a glass spherical lens or a plastic aspherical lens; the fourth lens, the fifth lens, and the sixth lens form a triple cemented lens; the object side surface of the first lens is convex, and the image side surface of the first lens is concave; the object side surface of the second lens is concave, and the image side surface of the second lens is convex; the object side surface of the third lens is convex, and the image side surface of the third lens is convex; the object side surface of the fourth lens is convex; the object side surface of the fifth lens is concave, and the image side surface of the fifth lens is concave; the object side surface of the sixth lens is convex, and the image side surface of the sixth lens is convex or concave; the object side surface of the seventh lens is convex or concave, and the image side surface of the seventh lens is convex; the object side surface of the eighth lens is convex, and the image side surface of the eighth lens is concave.

2. The fixed-focus lens according to claim 1, characterized in that The optical power of the fixed-focus lens is , the optical power of the first lens is 1, the optical power of the second lens is 2, the optical power of the third lens is 3, where 0.5 ≤ | / 1| ≤ 5; | / 2| ≥ 1; 3 ≤ 0.

1.

3. The fixed-focus lens according to claim 1, characterized in that The optical power of the first lens is 1, and the thickness of the first lens is D1, where |D1 / 1| ≥ 8.

4. The fixed-focus lens according to claim 1, characterized in that the refractive index of the first lens is Nd1, the refractive index of the second lens is Nd2, and the refractive index of the third lens is Nd3, where Nd1 > 1.5, 1.5 ≤ Nd2 ≤ 1.7, and Nd3 > 1.

4.

5. The fixed-focus lens according to claim 1, characterized in that the refractive index of the seventh lens is Nd7, and the refractive index of the eighth lens is Nd8, where |Nd7 - Nd8| < 0.

2.

6. The fixed-focus lens according to claim 1, characterized in that the Abbe number of the fourth lens is Vd4, the Abbe number of the fifth lens is Vd5, and the Abbe number of the sixth lens is Vd6, where |Vd4 - Vd5| > 10 and |Vd6 - Vd5| > 10.

7. The fixed-focus lens according to claim 1, characterized in that the f-number F of the fixed-focus lens satisfies F < 1.

11.

8. The fixed-focus lens according to claim 1, characterized in that the fixed-focus lens further includes a diaphragm; the diaphragm is located in the optical path between the third lens and the fourth lens.

Images