A fixed focus lens

Abstract

The embodiment of the application discloses a fixed focus lens, which 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 along an optical axis from an object plane to an image plane; the first lens is a negative focal length lens, the second lens is a negative focal length plastic aspheric lens, the third lens is a positive focal length plastic aspheric lens, the fourth lens is a positive focal length glass lens, the fifth lens is a positive focal length plastic aspheric lens, the sixth lens is a negative focal length plastic aspheric lens, the seventh lens is a positive focal length plastic aspheric lens, and the eighth lens is a positive focal length plastic aspheric lens. By adopting the technical scheme, the fixed focus lens comprises eight lenses, the focal lengths and surface shapes of the lenses are reasonably distributed, the design of the fixed focus lens with excellent comprehensive performance which takes into account imaging requirements and compact structure is finally realized, and the comprehensive performance meets the use requirements of a general sensor of security monitoring.

Description

A fixed-focus lens 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 increasing popularity of security monitoring devices, users' requirements for the monitoring environment and images are getting higher and higher, and it is necessary to meet monitoring images with larger pixels and larger light fluxes. Currently, image sensor manufacturers have launched large-format low-light image sensors with a format of 1 / 1.8", which have better light-receiving capabilities. Therefore, it is necessary to develop a 1 / 1.8" lens with F1.0 for use under corresponding ultra-low light conditions. Summary of the Invention

[0003] The present invention provides a fixed-focus lens, which can be maximally matched with a 1 / 1.8″ sensor chip, and its comprehensive performance meets the usage requirements of general security monitoring devices.

[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; the number of lenses with optical power in the fixed-focus lens is eight;

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

[0006] -0.73 < Φ1 / Φ < -0.43, -0.42 < (Φ2 + Φ3) / Φ < -0.19, 0.31 ≤ Φ4 / Φ ≤ 0.52, 0.32 ≤ (Φ5 + Φ6 + Φ7) / Φ ≤ 0.57, 0.01 ≤ Φ8 / Φ ≤ 0.10, 0.14 < BFL / TTL < 0.24; where, Φ1 is the optical power of the first lens, Φ2 is the optical power of the second lens, Φ3 is the optical power of the third lens, Φ4 is the optical power of the fourth lens, Φ5 is the optical power of the fifth lens, Φ6 is the optical power of the sixth lens, Φ7 is the optical power of the seventh lens, Φ8 is the optical power of the eighth lens, Φ is the optical power of the fixed-focus lens, BFL is the distance from the vertex of the image side of the eighth lens to the image plane, and TTL is the total optical length of the fixed-focus lens.

[0007] Optionally, the first lens is a glass spherical lens, or the first lens is a plastic aspherical lens;

[0008] The fourth lens is a glass spherical lens, or the fourth lens is a glass aspherical lens.

[0009] Optionally, the third lens is a meniscus lens.

[0010] Optionally, the object-side surface of the fifth lens is convex, and the image-side surface of the fifth lens is convex.

[0011] The object-side surface of the sixth lens is concave, and the image-side surface of the sixth lens is also concave.

[0012] The object-side surface of the seventh lens is convex, and the image-side surface of the seventh lens is also convex.

[0013] Optionally, the eighth lens is a meniscus lens.

[0014] Optionally, the fifth lens and the sixth lens are cemented together.

[0015] Optionally, the fixed-focus lens may also include an aperture stop and a filter;

[0016] The aperture stop is disposed in the optical path between the fourth lens and the fifth lens;

[0017] The filter is disposed in the optical path between the eighth lens and the image plane.

[0018] The fixed-focus lens provided in this embodiment of the invention comprises eight lenses. The optical powers of the first to eighth lenses are respectively negative, negative, positive, positive, positive, negative, positive, and positive. The second, third, fifth, sixth, seventh, and eighth lenses are all plastic aspherical lenses, and the fourth lens is a glass spherical lens. By reasonably setting the optical powers and material surface shapes of each lens, the imaging quality of the optical system is improved, ensuring that the fixed-focus lens has good imaging performance and meeting the imaging requirements of security lenses.

[0019] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 is a schematic diagram of a fixed-focus lens provided in Embodiment 1 of the present invention;

[0022] Figure 2 is a schematic diagram of the spherical aberration curve of a fixed-focus lens provided in Embodiment 1 of the present invention;

[0023] Figure 3 is a schematic diagram of the field curvature distortion curve of a fixed-focus lens provided in Embodiment 1 of the present invention;

[0024] Figure 4 is a schematic diagram of a fixed-focus lens provided in Embodiment 2 of the present invention;

[0025] Figure 5 is a schematic diagram of the spherical aberration curve of a fixed-focus lens provided in Embodiment 2 of the present invention;

[0026] Figure 6 is a schematic diagram of the field curvature distortion curve of a fixed-focus lens provided in Embodiment 2 of the present invention;

[0027] Figure 7 is a structural schematic diagram of a fixed-focus lens provided in Embodiment 3 of the present invention;

[0028] Figure 8 is a schematic diagram of the spherical aberration curve of a fixed-focus lens provided in Embodiment 3 of the present invention;

[0029] Figure 9 is a schematic diagram of the field curvature distortion curve of a fixed-focus lens provided in Embodiment 3 of the present invention;

[0030] Figure 10 is a structural schematic diagram of a fixed-focus lens provided in Embodiment 4 of the present invention;

[0031] Figure 11 is a schematic diagram of the spherical aberration curve of a fixed-focus lens provided in Embodiment 4 of the present invention;

[0032] Figure 12 is a schematic diagram of the field curvature distortion curve of a fixed-focus lens provided in Embodiment 4 of the present invention. Detailed Implementation

[0033] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0034] Example 1

[0035] Figure 1 is a schematic diagram of an optimal object distance lens provided in Embodiment 1 of the present invention. As shown in Figure 1, the fixed-focus lens provided in 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 sequentially along the optical axis from the object plane to the image plane. Among them, the first lens 110 is a negative power lens, the second lens 120 is a negative power plastic aspherical lens, the third lens 130 is a positive power plastic aspherical lens, the fourth lens 140 is a positive power glass lens, the fifth lens 150 is a positive power plastic aspherical lens, the sixth lens 160 is a negative power plastic aspherical lens, the seventh lens 170 is a positive power plastic aspherical lens, and the eighth lens 180 is a positive power plastic aspherical lens.

[0036] Specifically, optical power is equal to the difference between the convergence of the image-side beam and the convergence of the object-side beam; it characterizes the optical system's ability to deflect light. The larger the absolute value of the optical power, the stronger the bending ability of light; the smaller the absolute value, the weaker the bending ability. When the optical power is positive, the refraction of light is converging; when the optical power is negative, the refraction of light is diverging. Optical power can be used to characterize a single refractive surface of a lens (i.e., a surface of the lens), a single lens, or a system formed by multiple lenses (i.e., a lens group). Setting the first lens 110 and the second lens 120 as negative optical power lenses ensures that they 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 possesses wide-angle or even ultra-wide-angle characteristics. Furthermore, setting the first lens 110 as a negative optical power lens helps control the entrance pupil position to be at a reasonable level, thereby reducing the lens's front aperture. By configuring the third lens 130, fourth lens 140, and fifth lens 150 as positive power lenses, the third lens 130 and fourth lens 140 can promptly correct the larger aberrations produced by the first lens 110 and second lens 120, especially effectively correcting the edge aberrations of the optical system, thereby improving the imaging resolution of the optical system. Further configuring the fifth lens 150 as a positive power lens, the sixth lens 160 as a negative power lens, and the seventh lens 170 as a positive power lens also helps to eliminate aberrations, including field curvature, coma, and astigmatism, further improving the imaging resolution of the optical system. Finally, configuring the eighth lens 180 as a positive power lens allows for timely correction of the final image on the image plane, particularly effectively correcting the edge aberrations of the optical system, thereby improving the imaging effect. Furthermore, the fourth lens 140 is a positive focal length glass lens, and the lenses on both sides are plastic aspherical lenses. This arrangement in the middle of the fixed focal length lens helps to achieve the large aperture characteristics of the fixed focal length lens, ensuring that more light enters the fixed focal length lens and improving the imaging effect of the fixed focal length lens.

[0037] Furthermore, aspherical lenses are characterized by a continuous change in curvature from the center to the periphery, unlike spherical lenses which have a constant curvature from the center to the periphery. Aspherical lenses possess superior curvature radius characteristics, offering advantages in improving distortion and astigmatism. Using aspherical lenses can minimize aberrations that occur during image formation, thereby enhancing the lens's image quality. For example, the second lens 120, third lens 130, fifth lens 150, sixth lens 160, seventh lens 170, and eighth lens 180 are all plastic aspherical lenses, used to correct off-axis point aberrations, optimize optical performance such as distortion and CRA, and improve image quality. Moreover, aspherical lenses can be made of plastic, which simplifies the manufacturing process and reduces the cost.

[0038] Glass lenses are characterized by their good stability. Furthermore, since the cost of plastic aspherical lenses is much lower than that of glass lenses, the fixed-focus lens provided in this embodiment of the invention adopts a combination of glass lenses and plastic aspherical lenses. This allows for effective cost control while ensuring the optical performance of the fixed-focus lens. At the same time, the various lens materials have a mutual compensating effect, ensuring normal operation even in high and low temperature environments.

[0039] In summary, the fixed-focus lens provided in this embodiment of the invention comprises eight lenses, with the first to eighth lenses having optical powers of negative, negative, positive, positive, positive, negative, positive, and positive respectively. Furthermore, the second, third, fifth, sixth, seventh, and eighth lenses are all plastic aspherical lenses, and the fourth lens is a glass lens. By rationally setting the optical powers and material properties of each lens, the imaging quality of the optical system is improved, ensuring the fixed-focus lens has excellent imaging performance and meeting the imaging requirements of security lenses.

[0040] Based on the above embodiments, the first lens 110 is a glass spherical lens; or, the first lens 110 is a plastic aspherical lens; the fourth lens 140 is a glass spherical lens; or, the fourth lens is a glass aspherical lens.

[0041] Specifically, a spherical lens is characterized by a constant curvature from its center to its periphery, ensuring a simple lens configuration. When both the first lens 110 and the fourth lens 140 are glass spherical lenses, the fixed-focus lens comprises two glass spherical lenses and six plastic aspherical lenses. Alternatively, when both lenses are glass spherical lenses, the fixed-focus lens comprises two glass lenses, six plastic lenses, one spherical lens, and seven aspherical lenses. Another option is to use a plastic aspherical lens as the first lens and a glass spherical lens as the fourth lens 140, resulting in one glass spherical lens and seven plastic aspherical lenses. Finally, when both lenses are plastic aspherical lenses as the first lens and a glass aspherical lens as the fourth lens 140, the fixed-focus lens comprises one glass lens, seven plastic lenses, and eight aspherical lenses. This provides multiple feasible configuration options for the fixed-focus lens, offering flexibility in its design.

[0042] Based on the above embodiment, -0.73 < Φ1 / Φ < -0.43, where Φ1 is the optical power of the first lens and Φ is the optical power of the fixed-focus lens. When the optical power of the first lens 110 and the optical power of the fixed-focus lens meet this range limit, the incident angle of light in the optical system can be effectively controlled, which is beneficial to the realization of a large field of view.

[0043] Based on the above embodiment, -0.42 < (Φ2 + Φ3) / Φ < -0.19, where Φ2 is the optical power of the second lens 120, Φ3 is the optical power of the third lens 130, and Φ is the optical power of the fixed-focus lens; furthermore, the third lens 130 includes a meniscus lens. When the optical powers of the second lens 120 and the third lens 130 satisfy this range limitation, and the third lens 130 is a meniscus lens, it is beneficial to further reduce the system's deflection angle, thereby reducing the system's tolerance sensitivity and improving the system's manufacturability.

[0044] Based on the above embodiment, 0.31≤Φ4 / Φ≤0.52, where Φ4 is the optical power of the fourth lens 140 and Φ is the optical power of the fixed-focus lens. When the optical power of the fourth lens 140 and the optical power of the fixed-focus lens meet this range limit, it is beneficial to reduce the light from the preceding system and allow it to enter the following system.

[0045] Based on the above embodiment, 0.32≤(Φ5+Φ6+Φ7) / Φ≤0.57, where Φ5 is the optical power of the fifth lens 150, Φ6 is the optical power of the sixth lens 160, Φ7 is the optical power of the seventh lens 170, and Φ is the optical power of the fixed-focus lens; furthermore, the object-side surface of the fifth lens 150 is convex, and the image-side surface of the fifth lens 150 is convex; the object-side surface of the sixth lens 160 is concave, and the image-side surface of the sixth lens 160 is concave; the object-side surface of the seventh lens 170 is convex, and the image-side surface of the seventh lens 170 is convex.

[0046] Specifically, the object-side surface of the fifth lens 150 is convex, and the image-side surface is also convex; that is, the object-side surface of the fifth lens 150 bulges towards the object plane, and the image-side surface bulges towards the image plane, making the fifth lens 150 a biconvex lens. The object-side surface of the sixth lens 160 is concave, and the image-side surface is also concave; that is, the object-side surface of the sixth lens 160 is recessed towards the object plane, and the image-side surface bulges towards the image plane, making the sixth lens 160 a biconcave lens. The object-side surface of the seventh lens 170 is convex, and the image-side surface is also convex; that is, the object-side surface of the seventh lens 170 bulges towards the object plane, and the image-side surface bulges towards the image plane, making the seventh lens 170 a biconvex lens. By setting the optical power of the fifth lens 150, the sixth lens 160, and the seventh lens 170 within this range, and by setting the surface shapes of the fifth lens 150, the sixth lens 160, and the seventh lens 170 to meet the above constraints, it can be shown that the positive and negative optical power distribution in this fixed-focus lens is reasonable, which is beneficial for the correction of system aberrations.

[0047] Furthermore, the fifth lens 150 and the sixth lens 160 are cemented together.

[0048] Specifically, the cemented configuration of the fifth lens 150 and the sixth lens 160, forming a cemented lens, can be understood as the image-side surface of the fifth lens 150 being cemented to the object-side surface of the sixth lens 160. Cemented lenses can be used to minimize or eliminate chromatic aberration. In fixed-focus lenses, the use of cemented lenses can improve image quality, reduce light energy reflection loss, and thus enhance the sharpness of the lens image. Furthermore, the use of cemented lenses can simplify the assembly process in lens manufacturing, improving equipment efficiency. For example, by introducing a cemented lens composed of the fifth lens 150 and the sixth lens 160, it is possible to help eliminate the effects of chromatic aberration and reduce tolerance sensitivity; at the same time, the cemented lens can also balance the overall chromatic aberration of the optical system. The cementation of the lenses eliminates the air gap between the two lenses, making the overall optical system compact and meeting the requirements of system miniaturization. Moreover, the cementation of the lenses reduces tolerance sensitivity issues such as tilting / eccentricity that occur during the assembly of lens units. Furthermore, the fifth lens 150 and the sixth lens 160 can be supported by a gasket or glued together. This embodiment of the invention does not limit the specific arrangement of the glued lenses.

[0049] Based on the above embodiment, 0.01≤Φ8 / Φ≤0.10, where Φ8 is the optical power of the eighth lens 180 and Φ is the optical power of the fixed-focus lens; and the eighth lens 180 includes a meniscus lens. By setting the optical power of the eighth lens 180 within this range, and by setting the surface shape of the eighth lens 180 to meet the above limitations, it can be shown that the positive and negative optical power distribution in the fixed-focus lens is reasonable, which is beneficial to the correction of system aberrations.

[0050] Based on the above embodiments, 0.14 < BFL / TTL < 0.24, where BFL is the distance from the image-side vertex of the eighth lens 180 to the image plane, and TTL is the overall optical length of the fixed-focus lens. The distance from the image-side vertex of the eighth lens 180 to the image plane can be understood as the back focal length of the fixed-focus lens. By setting the ratio between the back focal length and the overall optical length in the fixed-focus lens within this range, it is beneficial to compress the overall lens length, reduce the volume of the system, and at the same time ensure that there is sufficient installation space for the imaging sensor and the flat filter.

[0051] Based on the above embodiments, the fixed-focus lens further includes an aperture 190 and a filter 200; the aperture 190 is disposed in the optical path between the fourth lens 140 and the fifth lens 150; the filter 200 is disposed in the optical path between the eighth lens 180 and the image plane.

[0052] Specifically, by setting the aperture 190, the propagation direction of the light beam can be adjusted, which is beneficial to improving the imaging quality. And the aperture 190 in this fixed-focus lens can be located in the optical path between the fourth lens 140 and the fifth lens 150. The aperture 190 being located in the middle of the fixed-focus lens can ensure that the front and rear apertures of the fixed-focus lens are minimized. Further, the filter 200 is disposed in the optical path between the eighth lens 180 and the image plane, and the filter 200 can filter out stray spectra to ensure the imaging quality. Further, the fixed-focus lens may further include a flat glass, which serves to protect the lens and the image sensor.

[0053] As a feasible implementation manner, next, the parameters of each lens in the fixed-focus lens will be described.

[0054] Table 1 An optical design value of the fixed-focus lens in Embodiment 1

[0055]

[0056] Table 2 Design values of a fixed-focus lens

[0057]

[0058] In Table 2 above, the surface numbers are assigned according to the surface sequence of each lens. "S1" represents the object-side surface of the first lens, "S2" represents the image-side surface of the first lens, and so on. "STO" represents the aperture stop of the lens. The radius of curvature represents the degree of curvature of the lens surface; a positive value indicates that the surface bends towards the object plane, and a negative value indicates that the surface bends towards the image plane. "Infinity" indicates that the surface is flat and the radius of curvature is infinite. Thickness represents the central axial distance between the current surface and the next surface. Refractive index represents the ability of the material between the current surface and the next surface to deflect light. Abbe constant represents the dispersion characteristics of the material between the current surface and the next surface. Half-aperture indicates half the aperture size of the current surface. The k-value represents the magnitude of the conic coefficient of the aspherical surface.

[0059] Table 3. Design values ​​of aspherical conic coefficient in a fixed-focus lens

[0060]

[0061] "5.446013E-04" indicates All other coefficients are represented in this way.

[0062] The conicity coefficients of aspherical surfaces can be defined using the following aspherical formulas, but are not limited to the following representations:

[0063]

[0064] Where z is the axial sagitta in the Z direction of the aspherical surface; r is the height of the aspherical surface; c is the curvature of the fitted sphere, which is numerically the reciprocal of the radius of curvature R; k is the conic coefficient; AF are the 4th, 6th, 8th, 10th, 12th and 14th order coefficients of the aspherical polynomial.

[0065] The optical system in this embodiment achieves the following technical specifications:

[0066] Focal length: f=3.90mm

[0067] Aperture: F#=1.08

[0068] Furthermore, Figure 2 is a schematic diagram of the spherical aberration curve of a fixed-focus lens provided in Embodiment 1 of the present invention, specifically a schematic diagram of the spherical aberration curve with an aperture radius of 1.8199 mm. The vertical direction represents the normalization of the aperture, 0 indicates that it is on the optical axis, and the vertical vertex represents the maximum aperture 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 system imaging (0.436 μm, 0.486 μm, 0.546 μm, 0.588 μm, and 0.656 μm). As can be seen from Figure 2, the axial aberrations of different wavelengths are all controlled within the range of (-0.05 mm, +0.05 mm), indicating that the spherical aberration of the fixed-focus lens is well controlled at each wavelength, which can meet the requirements of wide-spectrum applications.

[0069] Figure 3 is a schematic diagram of the field curvature distortion curve of a fixed-focus lens provided in Embodiment 1 of the present invention. In the left coordinate system of the figure, the horizontal axis represents the magnitude of the field curvature in mm; the vertical axis represents the normalized image height, which has no unit. As can be seen from Figure 3, the lens provided in this embodiment effectively controls the field curvature from light with wavelengths from 436nm to 656nm, that is, during imaging, the difference between the image quality in the center and the image quality at the periphery is small; in the right coordinate system, the horizontal axis represents the magnitude of the distortion in %; the vertical axis represents the normalized image height, which has no unit.

[0070] In summary, the fixed-focus lens provided in Embodiment 1 of this invention, by reasonably setting parameters such as the optical power, surface shape, back focal length, total optical length, radius of curvature, refractive index, Abbe number, and maximum aperture of different lenses, ensures that the maximum aperture of the fixed-focus lens is 1.0, the total optical length is no more than 22.5mm, and it can be matched with a maximum 1 / 1.8″ sensor chip. Its comprehensive performance meets the requirements of general security monitoring sensors.

[0071] Example 2

[0072] Figure 4 is a schematic diagram of a fixed-focus lens provided in Embodiment 2 of the present invention. As shown in Figure 4, the fixed-focus lens provided in 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 sequentially along the optical axis from the object plane to the image plane. Among them, the first lens 110 is a negative power lens, the second lens 120 is a negative power plastic aspherical lens, the third lens 130 is a positive power plastic aspherical lens, the fourth lens 140 is a positive power glass lens, the fifth lens 150 is a positive power plastic aspherical lens, the sixth lens 160 is a negative power plastic aspherical lens, the seventh lens 170 is a positive power plastic aspherical lens, and the eighth lens 180 is a positive power plastic aspherical lens.

[0073] The lens setup is the same as in Embodiment 1, and will not be repeated here.

[0074] As another feasible implementation method, the specific parameters of the fixed-focus lens are described below. Table 4 shows an optical design value for the fixed-focus lens in Example 2.

[0075]

[0076] Table 5 Design values ​​for a fixed-focus lens

[0077]

[0078] In Table 5 above, the surface numbers are assigned according to the surface sequence of each lens. "S1" represents the object-side surface of the first lens, "S2" represents the image-side surface of the first lens, and so on. "STO" represents the aperture stop of the lens. The radius of curvature represents the degree of curvature of the lens surface; a positive value indicates that the surface bends towards the object plane, and a negative value indicates that the surface bends towards the image plane. "Infinity" indicates that the surface is flat and the radius of curvature is infinite. Thickness represents the central axial distance between the current surface and the next surface. Refractive index represents the ability of the material between the current surface and the next surface to deflect light. Abbe constant represents the dispersion characteristics of the material between the current surface and the next surface. Half-aperture indicates half the aperture size of the current surface. The k-value represents the magnitude of the conic coefficient of the aspherical surface.

[0079] Table 6 Design values ​​of aspherical conic coefficient in a fixed-focus lens

[0080]

[0081] "5.212070E-04" indicates All other coefficients are represented in this way.

[0082] The conicity coefficients of aspherical surfaces can be defined using the following aspherical formulas, but are not limited to the following representations:

[0083]

[0084] Where z is the axial sagitta in the Z direction of the aspherical surface; r is the height of the aspherical surface; c is the curvature of the fitted sphere, which is numerically the reciprocal of the radius of curvature; k is the coefficient of the fitted cone; and AF are the coefficients of the 4th, 6th, 8th, 10th, 12th, and 14th order terms of the aspherical polynomial.

[0085] The optical system in this embodiment achieves the following technical specifications:

[0086] Focal length: f=4.09mm

[0087] Aperture: F#=1.09

[0088] Furthermore, Figure 5 is a schematic diagram of the spherical aberration curve of a fixed-focus lens provided in Embodiment 2 of the present invention, specifically a schematic diagram of the spherical aberration curve with an aperture radius of 1.9079 mm. The vertical direction represents the normalization of the aperture, 0 indicates that it is on the optical axis, and the vertical vertex represents the maximum aperture 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 system imaging (0.436 μm, 0.486 μm, 0.546 μm, 0.588 μm, and 0.656 μm). As can be seen from Figure 5, the axial aberrations of different wavelengths are all controlled within the range of (-0.05 mm, +0.05 mm), indicating that the spherical aberration of the fixed-focus lens is well controlled at each wavelength, which can meet the requirements of wide-spectrum applications.

[0089] Figure 6 is a schematic diagram of the field curvature distortion curve of a fixed-focus lens provided in Embodiment 2 of the present invention. In the left coordinate system of the figure, the horizontal axis represents the magnitude of the field curvature in mm; the vertical axis represents the normalized image height, which has no unit. As can be seen from Figure 6, the lens provided in this embodiment effectively controls the field curvature from light with wavelengths from 436nm to 656nm, that is, during imaging, the difference between the image quality in the center and the image quality at the periphery is small; in the right coordinate system, the horizontal axis represents the magnitude of the distortion in %; the vertical axis represents the normalized image height, which has no unit.

[0090] In summary, the fixed-focus lens provided in Embodiment 2 of the present invention, by reasonably setting parameters such as the optical power, surface shape, back focal length, total optical length, radius of curvature, refractive index, Abbe number, and maximum aperture of different lenses, ensures that the maximum aperture of the fixed-focus lens is 1.0, the total optical length is no more than 22.5mm, and it can be matched with a maximum 1 / 1.8″ sensor chip. Its comprehensive performance meets the requirements of general security monitoring sensors.

[0091] Example 3

[0092] Figure 7 is a schematic diagram of a fixed-focus lens provided in Embodiment 3 of the present invention. As shown in Figure 7, the fixed-focus lens provided in Embodiment 3 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 sequentially along the optical axis from the object plane to the image plane. Among them, the first lens 110 is a negative power lens, the second lens 120 is a negative power plastic aspherical lens, the third lens 130 is a positive power plastic aspherical lens, the fourth lens 140 is a positive power glass lens, the fifth lens 150 is a positive power plastic aspherical lens, the sixth lens 160 is a negative power plastic aspherical lens, the seventh lens 170 is a positive power plastic aspherical lens, and the eighth lens 180 is a positive power plastic aspherical lens.

[0093] The lens setup is the same as in Embodiment 1, and will not be repeated here.

[0094] As another feasible implementation method, the specific parameters of the fixed-focus lens are explained below.

[0095] Table 7. Optical design values ​​for a fixed-focus lens in Example 3.

[0096]

[0097] Table 8 Design values ​​for a fixed-focus lens

[0098]

[0099] In Table 8 above, the surface numbers are assigned according to the surface sequence of each lens. "S1" represents the object-side surface of the first lens, "S2" represents the image-side surface of the first lens, and so on. "STO" represents the aperture stop of the lens. The radius of curvature represents the degree of curvature of the lens surface; a positive value indicates that the surface bends towards the object plane, and a negative value indicates that the surface bends towards the image plane. "Infinity" indicates that the surface is flat and the radius of curvature is infinite. Thickness represents the central axial distance between the current surface and the next surface. Refractive index represents the ability of the material between the current surface and the next surface to deflect light. Abbe constant represents the dispersion characteristics of the material between the current surface and the next surface. Half-aperture indicates half the aperture size of the current surface. The k-value represents the magnitude of the conicity coefficient of the aspherical surface.

[0100] Table 9 Design values ​​of aspherical conic coefficient in a fixed-focus lens

[0101]

[0102] "-5.379534E-03" indicates All other coefficients are represented in this way.

[0103] The conicity coefficients of aspherical surfaces can be defined using the following aspherical formulas, but are not limited to the following representations:

[0104]

[0105] Where z is the axial sagitta in the Z direction of the aspherical surface; r is the height of the aspherical surface; c is the curvature of the fitted sphere, which is numerically the reciprocal of the radius of curvature; k is the coefficient of the fitted cone; and AF are the coefficients of the 4th, 6th, 8th, 10th, 12th, and 14th order terms of the aspherical polynomial.

[0106] The optical system in this embodiment achieves the following technical specifications:

[0107] Focal length: f=4.01mm

[0108] Aperture: F#=1.08

[0109] Furthermore, Figure 8 is a schematic diagram of the spherical aberration curve of a fixed-focus lens provided in Embodiment 3 of the present invention, specifically a schematic diagram of the spherical aberration curve with an aperture radius of 1.8718 mm. The vertical direction represents the normalization of the aperture, 0 indicates that it is on the optical axis, and the vertical vertex represents the maximum aperture 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 system imaging (0.436 μm, 0.486 μm, 0.546 μm, 0.588 μm, and 0.656 μm). As can be seen from Figure 8, the axial aberrations of different wavelengths are all controlled within the range of (-0.05 mm, +0.05 mm), indicating that the spherical aberration of the fixed-focus lens is well controlled at each wavelength, which can meet the requirements of wide-spectrum applications.

[0110] Figure 9 is a schematic diagram of the field curvature distortion curve of a fixed-focus lens provided in Embodiment 3 of the present invention. In the coordinate system on the left side of the figure, the horizontal axis represents the magnitude of the field curvature in mm; the vertical axis represents the normalized image height, which has no unit. As can be seen from Figure 9, the lens provided in this embodiment effectively controls the field curvature from light with wavelengths from 436nm to 656nm, that is, during imaging, the difference between the image quality in the center and the image quality at the periphery is small; in the coordinate system on the right side, the horizontal axis represents the magnitude of the distortion in %; the vertical axis represents the normalized image height, which has no unit.

[0111] In summary, the fixed-focus lens provided in Embodiment 3 of the present invention, by reasonably setting parameters such as the optical power, surface shape, back focal length, total optical length, radius of curvature, refractive index, Abbe number, and maximum aperture of different lenses, ensures that the maximum aperture of the fixed-focus lens is 1.0, the total optical length is no more than 22.5mm, and it can be matched with a maximum 1 / 1.8″ sensor chip. Its comprehensive performance meets the requirements of general security monitoring sensors.

[0112] Example 4

[0113] Figure 10 is a schematic diagram of a fixed-focus lens provided in Embodiment 4 of the present invention. As shown in Figure 10, the fixed-focus lens provided in Embodiment 4 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 sequentially along the optical axis from the object plane to the image plane. Among them, the first lens 110 is a negative power lens, the second lens 120 is a negative power plastic aspherical lens, the third lens 130 is a positive power plastic aspherical lens, the fourth lens 140 is a positive power glass lens, the fifth lens 150 is a positive power plastic aspherical lens, the sixth lens 160 is a negative power plastic aspherical lens, the seventh lens 170 is a positive power plastic aspherical lens, and the eighth lens 180 is a positive power plastic aspherical lens.

[0114] The lens setup is the same as in Embodiment 1, and will not be repeated here.

[0115] As another feasible implementation method, the specific parameters of the fixed-focus lens are explained below.

[0116] Table 10. Optical design values ​​for a fixed-focus lens in Example 4.

[0117]

[0118] Table 11 Design values ​​for a fixed-focus lens

[0119]

[0120] In Table 11 above, the surface numbers are assigned according to the surface sequence of each lens. "S1" represents the object-side surface of the first lens, "S2" represents the image-side surface of the first lens, and so on. "STO" represents the aperture stop of the lens. The radius of curvature represents the degree of curvature of the lens surface; a positive value indicates that the surface bends towards the object plane, and a negative value indicates that the surface bends towards the image plane. "Infinity" indicates that the surface is flat and the radius of curvature is infinite. Thickness represents the central axial distance between the current surface and the next surface. Refractive index represents the ability of the material between the current surface and the next surface to deflect light. Abbe constant represents the dispersion characteristics of the material between the current surface and the next surface. Half-aperture indicates half the aperture size of the current surface. The k-value represents the magnitude of the conic coefficient of the aspherical surface.

[0121] Table 12 Design values ​​of aspherical conic coefficient in a fixed-focus lens

[0122]

[0123] "7.804806E-04" indicates All other coefficients are represented in this way.

[0124] The conicity coefficients of aspherical surfaces can be defined using the following aspherical formulas, but are not limited to the following representations:

[0125]

[0126] Where z is the axial sagitta in the Z direction of the aspherical surface; r is the height of the aspherical surface; c is the curvature of the fitted sphere, which is numerically the reciprocal of the radius of curvature; k is the coefficient of the fitted cone; and AF are the coefficients of the 4th, 6th, 8th, 10th, 12th, and 14th order terms of the aspherical polynomial.

[0127] The optical system in this embodiment achieves the following technical specifications:

[0128] Focal length: f=3.17mm

[0129] Aperture: F#=1.09

[0130] Furthermore, Figure 11 is a schematic diagram of the spherical aberration curve of a fixed-focus lens provided in Embodiment 4 of the present invention, specifically a schematic diagram of the spherical aberration curve with an aperture radius of 1.4778 mm. The vertical direction represents the normalization of the aperture, 0 indicates that it is on the optical axis, and the vertical vertex represents the maximum aperture 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 system imaging (0.436 μm, 0.486 μm, 0.546 μm, 0.588 μm, and 0.656 μm). As can be seen from Figure 11, the axial aberrations of different wavelengths are all controlled within the range of (-0.05 mm, +0.05 mm), indicating that the spherical aberration of the fixed-focus lens is well controlled at each wavelength, which can meet the requirements of wide-spectrum applications.

[0131] Figure 12 is a schematic diagram of the field curvature distortion curve of a fixed-focus lens provided in Embodiment 4 of the present invention. In the coordinate system on the left side of the figure, the horizontal axis represents the magnitude of the field curvature in mm; the vertical axis represents the normalized image height, which has no unit. As can be seen from Figure 12, the lens provided in this embodiment effectively controls the field curvature from light with wavelengths from 436 nm to 656 nm, that is, during imaging, the difference between the image quality in the center and the image quality at the periphery is small; in the coordinate system on the right side, the horizontal axis represents the magnitude of the distortion in %; the vertical axis represents the normalized image height, which has no unit.

[0132] In summary, the fixed-focus lens provided in Embodiment 4 of this invention, by reasonably setting parameters such as the optical power, surface shape, back focal length, total optical length, radius of curvature, refractive index, Abbe number, and maximum aperture of different lenses, ensures that the maximum aperture of the fixed-focus lens is 1.0, the total optical length is no more than 22.5mm, and it can be matched with a maximum 1 / 1.8″ sensor chip. Its comprehensive performance meets the requirements of general security monitoring sensors.

[0133] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

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 from the object plane to the image plane along the optical axis; the number of lenses with optical power in the fixed-focus lens is eight; the first lens is a lens with negative optical power, the second lens is a plastic aspherical lens with negative optical power, the third lens is a plastic aspherical lens with positive optical power, the fourth lens is a glass lens with positive optical power, the fifth lens is a plastic aspherical lens with positive optical power, the sixth lens is a plastic aspherical lens with negative optical power, the seventh lens is a plastic aspherical lens with positive optical power, and the eighth lens is a plastic aspherical lens with positive optical power; -0.73 < Φ1 / Φ < -0.43, -0.42 < (Φ2 + Φ3) / Φ < -0.19, 0.31 ≤ Φ4 / Φ ≤ 0.52, 0.32 ≤ (Φ5 + Φ6 + Φ7) / Φ ≤ 0.57, 0.01 ≤ Φ8 / Φ ≤ 0.10, 0.14 < BFL / TTL < 0.24; where, Φ1 is the optical power of the first lens, Φ2 is the optical power of the second lens, Φ3 is the optical power of the third lens, Φ4 is the optical power of the fourth lens, Φ5 is the optical power of the fifth lens, Φ6 is the optical power of the sixth lens, Φ7 is the optical power of the seventh lens, Φ8 is the optical power of the eighth lens, Φ is the optical power of the fixed-focus lens, BFL is the distance from the vertex of the image side of the eighth lens to the image plane, and TTL is the total optical length of the fixed-focus lens.

2. The fixed-focus lens according to claim 1, characterized in that, The first lens is a glass spherical lens, or the first lens is a plastic aspherical lens; the fourth lens is a glass spherical lens, or the fourth lens is a glass aspherical lens.

3. The fixed-focus lens according to claim 1, characterized in that, The third lens is a meniscus lens.

4. The fixed-focus lens according to claim 1, characterized in that, The object side of the fifth lens is convex, and the image side of the fifth lens is convex; the object side of the sixth lens is concave, and the image side of the sixth lens is concave; the object side of the seventh lens is convex, and the image side of the seventh lens is convex.

5. The fixed-focus lens according to claim 1, characterized in that, The eighth lens is a meniscus lens.

6. The fixed-focus lens according to claim 1, characterized in that, The fifth lens and the sixth lens are adhesively disposed.

7. The fixed-focus lens according to claim 1, characterized in that, The fixed-focus lens further includes an aperture stop and a filter; the aperture stop is disposed in the optical path between the fourth lens and the fifth lens; the filter is disposed in the optical path between the eighth lens and the image plane.

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