fixed focus lens

Abstract

The utility model discloses a fixed focus lens, including first lens, second lens, third lens, fourth lens, fifth lens, sixth lens, seventh lens and eighth lens that arrange in proper order from object plane to image plane along the optical axis, first lens has negative focal power, second lens has negative focal power, third lens has positive focal power, fourth lens has positive focal power, fifth lens has negative focal power, sixth lens has positive focal power, seventh lens has negative focal power, eighth lens has positive focal power, and third lens is glass spherical surface lens, first lens, second lens, fourth lens, fifth lens, sixth lens, seventh lens and eighth lens are all plastic aspherical surface lens. The fixed focus lens provided by the utility model embodiment has realized the design of long focus lens that can give consideration to imaging requirement, compact structure and low cost, and the fixed focus lens can match the chip of 1 / 1.8" target surface at most, and meets the requirement of small size, large aperture and low cost.

Description

Technical Field

[0001] This utility model relates to the field of optical technology, and in particular to a fixed-focus lens. Background Technology

[0002] With the increasing popularity of security monitoring facilities, monitoring equipment has higher and higher requirements for the monitoring environment and image quality, and needs to provide monitoring images with higher resolution and greater light transmission.

[0003] In some situations, surveillance requires long-distance video feeds. Currently, standard 4mm lenses cannot effectively focus on distant subjects, resulting in significant image distortion, low ambient light, and blurry images. While 7mm lenses typically have a smaller aperture (F#=2.0), using a large aperture like F#=1.0 fails to balance image quality requirements with a compact, low-cost design. Utility Model Content

[0004] This invention provides a fixed-focus lens that can achieve a combination of long focal length, high definition, small size, low cost, and large aperture.

[0005] According to one aspect of the present invention, a fixed-focus lens is provided, comprising a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, and an eighth lens arranged sequentially along the optical axis from the object plane to the image plane.

[0006] The first lens has negative optical power, and its object side is convex while its image side is concave.

[0007] The second lens has negative optical power, with its object side being concave and its image side being convex.

[0008] The third lens has positive optical power and its image-side surface is convex.

[0009] The fourth lens has positive optical power and its object side is convex.

[0010] The fifth lens has negative optical power and its image-side surface is concave.

[0011] The sixth lens has positive optical power, and its object side is convex, and its image side is convex.

[0012] The seventh lens has negative optical power, and its object side is concave while its image side is convex.

[0013] The eighth lens has positive optical power, and its object side is convex and its image side is concave.

[0014] The third lens is a glass spherical lens; the first lens, the second lens, the fourth lens, the fifth lens, the sixth lens, the seventh lens, and the eighth lens are all plastic aspherical lenses.

[0015] Optionally, the focal length of the fixed-focus lens is f, and the aperture number of the fixed-focus lens is F#;

[0016] 5.07 <f / F#<8.26。

[0017] Optionally, the total optical length of the fixed-focus lens is TTL, and the focal length of the fixed-focus lens is f;

[0018] 2.49 <TTL / f<4.16。

[0019] Optionally, the focal length of the fixed-focus lens is f, and the vertical height of the intersection point of the principal ray of the maximum field of view of the fixed-focus lens and the image plane is H;

[0020] 0.511 <H / f<0.826。

[0021] Optionally, the refractive index of the third lens is Nd3, and the Abbe number of the third lens is Vd3;

[0022] 1.77 <Nd3<2.00;

[0023] 28.3 <Vd3<49.61。

[0024] Optionally, the center thickness of the third lens is CT3, and the edge thickness of the third lens is ET3;

[0025] 1.25 <CT3 / ET3<2.07。

[0026] Optionally, the optical power of the first lens is Φ1, and the optical power of the second lens is Φ2;

[0027] -0.09 < Φ1 + Φ2 < -0.03.

[0028] Optionally, the optical power of the third lens is Φ3, the optical power of the fourth lens is Φ4, and the optical power of the fixed-focus lens is Φ;

[0029] 0.99 < (Φ3 + Φ4) / Φ < 1.38;

[0030] 0.28 < Φ3 / Φ < 0.56;

[0031] 0.71 < Φ4 / Φ < 0.82.

[0032] Optionally, the optical power of the fifth lens is Φ5, the optical power of the sixth lens is Φ6, the optical power of the seventh lens is Φ7, and the optical power of the fixed-focus lens is Φ.

[0033] -0.94 < Φ5 / Φ < -0.66;

[0034] 0.69 < Φ6 / Φ < 0.94;

[0035] -0.17 < Φ7 / Φ < -0.02.

[0036] Optionally, the optical power of the eighth lens is Φ8, and the optical power of the fixed-focus lens is Φ;

[0037] 0.007 < Φ8 / Φ < 0.06.

[0038] Optionally, the optical back focal length of the fixed-focus lens is BFL, and the total optical length of the fixed-focus lens is TTL;

[0039] 0.11 <BFL / TTL<0.18。

[0040] Optionally, the fixed-focus lens may also include an aperture stop;

[0041] The aperture stop is located in the optical path between the third lens and the fourth lens; or, the aperture stop is located in the optical path between the second lens and the third lens; or, the aperture stop is located in the optical path between the first lens and the second lens.

[0042] The fixed-focus lens provided in this embodiment of the utility model adopts eight lenses. By reasonably allocating the optical power, surface shape and material of each lens, a long-focus lens design that can meet imaging requirements, has a compact structure and low cost is achieved. This fixed-focus lens can be matched with an imaging chip with a target surface of up to 1 / 1.8″, which meets the requirements of small size, large aperture and low cost. Its comprehensive performance can meet the usage requirements of general security monitoring sensors.

[0043] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of this utility model, nor is it intended to limit the scope of this utility model. Other features of this utility model will become readily apparent from the following description. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of this utility model, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 A schematic diagram of the structure of a fixed-focus lens provided in an embodiment of this utility model;

[0046] Figure 2 This is a schematic diagram of another fixed-focus lens provided in an embodiment of the present utility model;

[0047] Figure 3 A schematic diagram of the structure of another fixed-focus lens provided in this embodiment of the utility model;

[0048] Figure 4 A spherical aberration curve of a fixed-focus lens provided in Embodiment 1 of this utility model;

[0049] Figure 5 Field curvature distortion diagram of a fixed-focus lens provided in Embodiment 1 of this utility model;

[0050] Figure 6 The ray fan diagram of the fixed-focus lens provided in Embodiment 1 of this utility model;

[0051] Figure 7 This is a spherical aberration curve of a fixed-focus lens provided in Embodiment 2 of this utility model;

[0052] Figure 8 The field curvature distortion diagram of the fixed-focus lens provided in Embodiment 2 of this utility model;

[0053] Figure 9 This is a ray fan diagram of a fixed-focus lens provided in Embodiment 2 of this utility model;

[0054] Figure 10 The spherical aberration curve of the fixed-focus lens provided in Embodiment 3 of this utility model;

[0055] Figure 11 The field curvature distortion diagram of the fixed-focus lens provided in Embodiment 3 of this utility model;

[0056] Figure 12 This is a ray fan diagram of a fixed-focus lens provided in Embodiment 3 of this utility model. Detailed Implementation

[0057] 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. 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 protection scope of the present invention.

[0058] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this utility model are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the utility model described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0059] Figure 1 This is a schematic diagram of the structure of a fixed-focus lens provided in an embodiment of the present invention. Figure 2 This is a schematic diagram of another fixed-focus lens provided in an embodiment of the present invention. Figure 3 A schematic diagram of another fixed-focus lens provided in this embodiment of the present invention is shown below. Figures 1-3 As shown, the fixed-focus lens provided in this embodiment of the present invention includes a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, a seventh lens L7, and an eighth lens L8 arranged sequentially along the optical axis from the object plane to the image plane.

[0060] The first lens L1 has negative optical power, with its object side being convex and its image side being concave.

[0061] The second lens L2 has negative optical power, with its object side being concave and its image side being convex.

[0062] The third lens L3 has positive optical power, and its image-side surface is convex.

[0063] The fourth lens L4 has positive optical power and its object side is convex.

[0064] The fifth lens L5 has negative optical power and its image-side surface is concave.

[0065] The sixth lens L6 has positive optical power, and its object side and image side are both convex.

[0066] The seventh lens L7 has negative optical power, with its object side being concave and its image side being convex.

[0067] The eighth lens L8 has positive optical power, with a convex object side and a concave image side.

[0068] The third lens L3 is a glass spherical lens, while the first lens L1, the second lens L2, the fourth lens L4, the fifth lens L5, the sixth lens L6, the seventh lens L7, and the eighth lens L8 are all plastic aspherical lenses.

[0069] 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 ability of an optical system to deflect light rays. The larger the absolute value of the optical power, the stronger the bending ability of light rays; the smaller the absolute value, the weaker the bending ability. When the optical power is positive, the refraction of light rays is converging; when the optical power is negative, the refraction of light rays is diverging. Optical power can be used to characterize a single refractive surface of a lens (i.e., one surface of the lens), a single lens, or a system formed by multiple lenses (i.e., a lens group).

[0070] In the lens provided in this embodiment, each lens can be fixed to a lens barrel. Figure 1 (Not shown in the text) but not limited to this.

[0071] The first lens L1 has negative optical power, which can be used to control the angle of incidence of the optical system of the fixed-focus lens and reduce optical distortion. At the same time, the light divergence at the front of the fixed-focus lens allows more light to enter the subsequent lenses at a greater angle.

[0072] The second lens L2 has negative optical power, which can share the negative optical power at the front of the fixed-focus lens. This helps to avoid excessive light refraction caused by the excessive concentration of optical power in the first lens L1. It can also correct off-axis aberrations and optimize the overall image quality.

[0073] The third lens L3 has positive optical power, which can focus the light that has been diverged by the first two negative optical power lenses (first lens L1 and second lens L2), thereby improving the light-gathering ability of the entire fixed-focus lens, especially in low-light environments where it can capture more light.

[0074] The fourth lens, L4, has positive optical power and is used to further focus light, improving the light-gathering ability of the fixed-focus lens.

[0075] The fifth lens L5 has negative optical power, the sixth lens L6 has positive optical power, the seventh lens L7 has negative optical power, and the eighth lens L8 has positive optical power. This facilitates a smooth transition of light and improves the image quality of the fixed-focus lens.

[0076] Among them, the seventh lens L7, with negative optical power, can concentrate light rays, reduce the height of light rays, correct higher spherical aberrations, balance various aberrations, and ensure the imaging quality of light rays in all bands.

[0077] In this embodiment, the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5, the sixth lens L6, the seventh lens L7, and the eighth lens L8 are configured with a negative-negative-positive-positive-negative-positive-negative-positive optical power combination. This allows for a reasonable allocation of the optical power of each lens, enabling light to propagate smoothly within the fixed-focus lens and preventing excessive bending of light on any lens surface. This effectively corrects aberrations and ensures sufficiently good image quality. It can be paired with 5MP / 4K, 1 / 1.8-inch imaging chips, making it widely applicable.

[0078] At the same time, the shape of the lens affects the direction of light propagation, determines how light bends when passing through the lens, and thus affects the lens's maximum aperture and light transmission, as well as the quality and characteristics of the image.

[0079] In this embodiment, the surface shapes of each lens are further rationally matched. While meeting the optical power requirements, imaging requirements and structural compactness of each lens, the path of light passing through the entire lens is also made smoother, reducing unnecessary reflection and absorption and improving image quality.

[0080] Furthermore, the fixed-focus lens adopts a design that combines one spherical glass lens and seven aspherical plastic lenses.

[0081] Among them, the third lens L3 is a glass spherical lens. Compared with plastic, glass has a lower coefficient of thermal expansion, which makes the shape of the third lens L3 more stable when facing changes in ambient temperature. This reduces the impact of high and low temperatures on the image quality of the fixed-focus lens, avoids the fixed-focus lens from being out of focus in different environments, and achieves the characteristic of not being out of focus from -40℃ to 80℃.

[0082] Meanwhile, glass has a higher refractive index than plastic, which can effectively focus the light after it has been adjusted by the first two negative power lenses, especially improving light collection efficiency and enhancing image clarity in low-light environments.

[0083] In addition, spherical lenses have a mature manufacturing process and relatively low cost, making them suitable for critical locations requiring high stability. The spherical design of the third lens L3 helps reduce lens costs, and when used in conjunction with other aspherical lenses, it can further optimize the overall aberration correction effect.

[0084] Furthermore, the first lens L1, the second lens L2, the fourth lens L4, the fifth lens L5, the sixth lens L6, the seventh lens L7, and the eighth lens L8 are all plastic aspherical lenses. Compared to glass, plastic materials have lower processing costs, and plastic lenses are lighter, which helps to achieve miniaturization and lightweight design of the lenses.

[0085] Meanwhile, an aspherical lens can effectively correct high-order aberrations such as spherical aberration and coma, significantly improving the imaging quality. Therefore, an aspherical lens can achieve complex optical functions with a smaller number of lenses, thereby reducing the overall length and volume of the lens.

[0086] In addition, plastic lenses can be easily manufactured into complex aspherical shapes through injection molding, simplifying the manufacturing process and further reducing costs.

[0087] It should be noted that the material of the glass lens is various types of glass known to those skilled in the art, and the material of the plastic lens is various types of plastics known to those skilled in the art. The embodiments of the present invention will not elaborate or limit this.

[0088] In summary, the fixed-focus lens provided by the embodiments of the present invention uses eight lenses. By reasonably distributing the optical power, surface shape, and material of each lens, the design of a long-focus lens that can balance imaging requirements, has a compact structure, and low cost is achieved. The fixed-focus lens can be maximally matched with an imaging chip with a 1 / 1.8″ target surface, meeting the requirements of small volume, large aperture, and low cost. The comprehensive performance can meet the usage requirements of general sensors for security monitoring.

[0089] As a feasible implementation manner, the focal length of the fixed-focus lens is f, and the f-number of the fixed-focus lens is F#, where 5.07 < f / F# < 8.26.

[0090] Among them, when the focal length f increases, the lens can capture farther targets and magnify distant objects for display; when the f-number F# is smaller, the entrance pupil diameter of the lens is larger, and more light can be collected. In this embodiment, by setting 5.07 < f / F# < 8.26, the focal length f of the fixed-focus lens is relatively large, and the f-number F# is relatively small. At this time, the fixed-focus lens achieves a balance between long-distance monitoring and light collection ability, that is, it ensures a large actual shooting distance and avoids light loss caused by too large a focal length, ensuring that the aperture is small enough to provide sufficient light collection ability, and can form a clear image in a relatively dark environment, suitable for low-light, long-distance all-weather monitoring.

[0091] As a feasible implementation manner, the overall optical length of the fixed-focus lens is TTL, and the focal length of the fixed-focus lens is f, where 2.49 < TTL / f < 4.16.

[0092] Among them, the overall length TTL of the fixed-focus lens refers to the distance from the optical axis center of the object side of the first lens L1 to the image plane.

[0093] In this embodiment, by restricting the ratio between the overall optical length TTL and the focal length f of the fixed-focus lens, the volume of the fixed-focus lens can be effectively reduced on the premise of ensuring the long-focus characteristics and large-aperture performance, thereby meeting the requirements of a compact structure and miniaturization.

[0094] As a feasible implementation method, the focal length of the fixed-focus lens is f, and the vertical height of the intersection point of the principal ray of the maximum field of view of the fixed-focus lens and the image plane is H, 0.511. <H / f<0.826。

[0095] In this context, the vertical height H of the intersection point between the principal ray of the maximum field of view and the image plane of a fixed-focus lens can be understood as the distance from the optical axis to the point of incidence of the principal ray on the image plane in the direction of the maximum field of view.

[0096] In this embodiment, by constraining the ratio between the vertical height H of the intersection point of the principal ray of the maximum field of view of the fixed-focus lens and the image plane and the focal length f, the field of view of the fixed-focus lens can be controlled within a certain angular range to balance the coverage of the monitoring scene and the imaging details, thus meeting the usage requirements.

[0097] As a possible implementation method, such as Figures 1-3 As shown, the fixed-focus lens also includes an aperture stop STO, which is located in the optical path between the third lens L3 and the fourth lens L4; or, the aperture stop STO is located in the optical path between the second lens L2 and the third lens L3; or, the aperture stop STO is located in the optical path between the first lens L1 and the second lens L2.

[0098] The aperture stop (STO) is a component in an optical system used to limit the diameter of the light beam passing through the lens.

[0099] In this embodiment, by setting the aperture stop STO in front of the fourth lens L4, the distribution of light entering the rear lens group can be effectively controlled, which facilitates subsequent aberration correction.

[0100] For example, such as Figures 1-3 As shown, the aperture stop STO is positioned in the optical path between the third lens L3 and the fourth lens L4. At this point, the first two negative power lenses (the first lens L1 and the second lens L2) plus the positive power third lens L3 have completed the initial light divergence and convergence operations, and the light entering the aperture stop STO has been effectively adjusted. Positioning the aperture stop STO in this location helps to rationally control the angle at which light enters the fourth lens L4, making it more suitable for the requirements of subsequent optical components and the image sensor, reducing edge distortion and improving overall image quality.

[0101] As a feasible implementation, the refractive index of the third lens L3 is Nd3, and the Abbe number of the third lens L3 is Vd3; 1.77 <Nd3<2.00;28.3<Vd3<49.61。

[0102] The refractive index is the ratio of the speed of light in a vacuum to the speed of light in the medium. It is mainly used to describe a material's ability to refract light, and different materials have different refractive indices. The higher the refractive index, the stronger the material's ability to bend light.

[0103] The Abbe number is an index used to represent the dispersion ability of a transparent medium. The more severe the dispersion of the medium, the smaller the Abbe number; conversely, the less severe the dispersion of the medium, the larger the Abbe number.

[0104] In this embodiment, the third lens L3 is made of glass, which, compared to plastic, has a higher refractive index (Nd3), a lower coefficient of thermal expansion, and better environmental stability. This allows the third lens L3 to maintain stable imaging quality over a wide temperature range (e.g., -40°C to 80°C), thereby reducing the impact of high and low temperatures on the imaging quality of the fixed-focus lens and avoiding the defocusing phenomenon caused by temperature changes in different environments.

[0105] The third lens L3 uses a higher refractive index to focus the light beam in front of the aperture stop STO, which can reduce chromatic aberration and other aberrations while ensuring sufficient focusing capability. At the same time, by limiting the Abbe number Vd3 of the third lens L3 to a reasonable range, other optical performance can be balanced while effectively correcting chromatic aberration.

[0106] As one feasible implementation, the center thickness of the third lens L3 is CT3, and the edge thickness of the third lens L3 is ET3; 1.25 <CT3 / ET3<2.07。

[0107] By constraining the ratio of the center thickness CT3 to the edge thickness ET3 of the third lens L3, the thickness-to-thickness ratio of the third lens L3 is ensured. This not only helps maintain the structural stability of the third lens L3 but also simplifies the manufacturing process and reduces costs. Furthermore, an appropriate thickness-to-thickness ratio ensures that the deformation of the third lens L3 is minimized at different temperatures, thereby maintaining good optical performance.

[0108] As a feasible implementation, the optical power of the first lens L1 is Φ1, and the optical power of the second lens L2 is Φ2; -0.09 < Φ1 + Φ2 < -0.03.

[0109] Among them, the first lens L1, as the first optical element after the light enters the lens, has negative optical power characteristics that can effectively control the angle at which the main ray enters the subsequent optical system and reduce optical distortion.

[0110] The second lens L2 further optimizes the light path transmitted from the first lens L1, which can correct off-axis aberrations and improve the sharpness of image edges.

[0111] In this embodiment, by combining the optical power of the first lens L1 and the second lens L2, the propagation path of light gradually diverges before entering the aperture STO, thereby ensuring that the aperture of light is maximized before entering the aperture STO, increasing the amount of light entering the aperture STO position, enabling the fixed-focus lens to form a clear image under dim conditions, and expanding the applicable environment of the lens.

[0112] As a feasible implementation, the optical power of the third lens L3 is Φ3, the optical power of the fourth lens L4 is Φ4, and the optical power of the fixed-focus lens is Φ; 0.99<(Φ3+Φ4) / Φ<1.38; 0.28<Φ3 / Φ<0.56; 0.71<Φ4 / Φ<0.82.

[0113] By constraining the proportion of the optical power provided by the third lens L3 and the fourth lens L4 to the total optical power of the fixed-focus lens, the proportion of the optical power of the third lens L3 in the entire fixed-focus lens, and the proportion of the optical power of the fourth lens L4 in the entire fixed-focus lens, it can be ensured that light is effectively focused when it passes through the third lens L3 and the aperture STO and enters the fourth lens L4. This avoids leaving too much converging task to the rear lens group and prevents the rear lens group from being under too much pressure during the correction of chromatic aberration, aberration, and CRA, which could introduce overly complex shapes or aspherical coefficients and result in shapes that are difficult to process.

[0114] As one feasible implementation, the optical power of the fifth lens L5 is Φ5, the optical power of the sixth lens L6 is Φ6, the optical power of the seventh lens L7 is Φ7, and the optical power of the fixed-focus lens is Φ.

[0115] -0.94<Φ5 / Φ<-0.66; 0.69<Φ6 / Φ<0.94; -0.17<Φ7 / Φ<-0.02.

[0116] Among them, the fifth lens L5, the sixth lens L6 and the seventh lens L7 adopt the above-mentioned optical power ratio, which can make the light pass through the entire optical system more smoothly and avoid abrupt changes that may cause other problems such as ghosting or serious advanced aberrations.

[0117] As a feasible implementation, the optical power of the eighth lens L8 is Φ8, and the optical power of the fixed-focus lens is Φ; 0.007<Φ8 / Φ<0.06.

[0118] In this process, the light passes through the fifth lens L5, the sixth lens L6, and the seventh lens L7 to eliminate the advanced aberrations and residual spherical aberrations that were not eliminated at the front end. Combined with the eighth lens L8, which is a plastic aspherical lens, and with the optical power ratio of the eighth lens L8 limited, the remaining advanced aberrations can be eliminated to the greatest extent.

[0119] Meanwhile, the reasonable combination of the optical power of the seventh lens L7 and the eighth lens L8 can also keep the angle of the principal ray within a suitable range, so that the height of the intersection point between the principal ray of the maximum field of view and the image plane can be adjusted at the end of the optical system, which can be adapted to a variety of imaging chips and help save lens costs.

[0120] As one feasible implementation, the optical back focal length of the fixed-focus lens is BFL, and the total optical length of the fixed-focus lens is TTL; 0.11 <BFL / TTL<0.18。

[0121] In this context, the optical back focal length (BFL) of a fixed-focus lens refers to the distance from the center of the optical axis on the image side of the eighth lens (L8) to the image plane.

[0122] In this embodiment, by reasonably limiting the ratio of the optical back focal length (BFL) to the total optical length (TTL) of the lens, a longer back focal length is achieved while compressing the total length of the lens. This ensures that the imaging chip and filter have sufficient installation space, facilitating module assembly.

[0123] As a possible implementation method, such as Figures 1-3 As shown, the fixed-focus lens provided in this embodiment of the utility model also includes a filter CG. The filter CG is located on the image side of the eighth lens L8, which can protect the imaging chip, prevent dust and contamination, and thus ensure the imaging effect of the lens.

[0124] In some cases, the CG filter can also be used to correct specific aberrations or filter out unwanted light, but this embodiment of the present invention does not specifically limit this.

[0125] It should be noted that the fixed-focus lens provided in this utility model embodiment can achieve efficient aberration correction and meet the usage requirements such as compact structure by reasonably allocating parameters such as the material, optical power, center thickness of each lens and on-axis spacing between each lens. It does not require the use of cemented lenses, which simplifies the manufacturing process and further reduces the cost of the lens.

[0126] The following describes in further detail, with reference to the accompanying drawings, specific embodiments of a fixed-focus lens applicable to the above-described embodiments.

[0127] Example 1

[0128] Continue to refer to Figure 1 The fixed-focus lens provided in Embodiment 1 of this utility model includes a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, a seventh lens L7, and an eighth lens L8 arranged sequentially along the optical axis from the object plane to the image plane.

[0129] The aperture stop STO is located in the optical path between the third lens L3 and the fourth lens L4; the filter CG is located on the image side of the eighth lens L8.

[0130] Table 1 details the surface shape, radius of curvature, thickness, refractive index, Abbe number, half-aperture, and k-value of each lens in the fixed-focus lens provided in Embodiment 1, according to a feasible implementation method. The fixed-focus lenses in Table 1 correspond to... Figure 1 The fixed-focus lens shown.

[0131] Table 1 Design values ​​of optical physical parameters for fixed-focus lenses

[0132]

[0133]

[0134] In Table 1, the surface numbers are assigned according to the surface sequence of each lens. "1" represents the object-side surface of the first lens, "2" represents the image-side surface of the first lens, and so on. "STO" represents the aperture of a fixed-focus lens. The radius of curvature represents the curvature of the lens surface in millimeters (mm). A positive value indicates that the surface bends towards the image plane, and a negative value indicates that the surface bends towards the object plane. "INF" indicates that the surface is flat and the radius of curvature is infinite. The thickness represents the axial distance between the current surface and the next surface in millimeters (mm). The refractive index represents the ability of the material between the current surface and the next surface to deflect light. A blank space indicates that the current position is air and the refractive index is 1. The Abbe number represents the dispersion characteristics of the material between the current surface and the next surface. A blank space indicates that the current position is air. The half-aperture represents the effective diameter of the lens. The k-value represents the magnitude of the conic coefficient of the aspherical surface. "IMA" represents the image plane of a fixed-focus lens.

[0135] In this embodiment, the aspherical conic coefficient of the aspherical lens in the fixed-focus lens can be defined by the following aspherical formula, but is not limited to the following representation:

[0136]

[0137] 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 AG are the coefficients of the 4th, 6th, 8th, 10th, 12th, 14th, and 16th order terms of the aspherical polynomial, respectively.

[0138] For example, Table 2 details the aspherical coefficients of each lens in this embodiment one of feasible implementations.

[0139] Table 2 Design values ​​of aspherical coefficients for each lens in a fixed-focus lens.

[0140]

[0141]

[0142] The fixed-focus lens provided in Example 1 has an optical total length (TTL) of 22.39 mm, a focal length (f) of 7.7 mm, and an f / # of 1.088.

[0143] Figure 4 This is a spherical aberration curve diagram of a fixed-focus lens provided in Embodiment 1 of this utility model. In the diagram, the vertical direction represents the normalized aperture, 0 indicates it is on the optical axis, and the vertical vertex represents the maximum pupil radius; the horizontal direction represents the offset relative to the ideal focus, in millimeters (mm); different linear curves in the diagram represent different wavelengths of the image formed by the fixed-focus lens. Figure 4 It can be seen that the axial aberrations of different wavelengths (0.436μm, 0.486μm, 0.546μm, 0.588μm and 0.656μm) at normalized apertures of 0.3 to 1.0 are all controlled within the range of (-0.03mm, +0.03mm), indicating that the spherical aberration of this fixed-focus lens is well controlled at each wavelength, which can meet the requirements of wide-spectrum applications.

[0144] Figure 5 This is a field curvature distortion diagram of a fixed-focus lens provided in Embodiment 1 of this utility model. In the coordinate system on the left side of the diagram, the horizontal axis represents the magnitude of the field curvature in mm; the vertical axis represents the normalized image height, which has no unit. In the coordinate system on the right side of the diagram, the horizontal axis represents the magnitude of the distortion (F-Tan(Theta)) in %; the vertical axis represents the normalized image height, which has no unit. Figure 5 As can be seen, the fixed-focus lens provided in this embodiment effectively controls field curvature under the condition of incident light wavelength of 436nm to 656nm. That is, during imaging, the difference between the central image quality and the peripheral image quality is small, and the entire shooting can produce a more uniform image quality structure, meeting a wider range of usage needs; at the same time, Figure 5 The maximum field of view is 36.344 degrees, and its distortion has been well corrected.

[0145] Figure 6 This is a ray fan plot of a fixed-focus lens provided in Embodiment 1 of this utility model. In a single plot, the horizontal axis represents the normalized beam aperture, and the vertical axis represents the transverse aberration. Ideally, each curve should completely coincide with the horizontal axis, at which point all light rays in the field of view are focused at the same point on the image plane. The vertical axis in a single image can also represent the maximum dispersion range of the beam on the ideal image plane. The ray fan plot can reflect not only monochromatic aberrations of different wavelengths but also the magnitude of transverse chromatic aberration. Figure 6It can be seen that the fixed-focus lens closely approximates the horizontal axis at all wavelengths in all fields of view, indicating that the transverse aberrations at each wavelength are well corrected. In addition, the curves of each color do not show obvious dispersion, indicating that the fixed-focus lens also has good correction for chromatic aberration, meeting the imaging requirements of sharp images across the entire wavelength range.

[0146] Example 2

[0147] Continue to refer to Figure 2 The fixed-focus lens provided in Embodiment 2 of this utility model includes a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, a seventh lens L7, and an eighth lens L8 arranged sequentially along the optical axis from the object plane to the image plane.

[0148] The aperture stop STO is located in the optical path between the third lens L3 and the fourth lens L4; the filter CG is located on the image side of the eighth lens L8.

[0149] Table 3 details the surface shape, radius of curvature, thickness, refractive index, Abbe number, half-aperture, and k-value of each lens in the fixed-focus lens provided in Embodiment 2, according to a feasible implementation method. The fixed-focus lenses in Table 3 correspond to... Figure 2 The fixed-focus lens shown.

[0150] Table 3 Design values ​​of optical physical parameters for fixed-focus lenses

[0151]

[0152]

[0153] In Table 3, the surface numbers are assigned according to the surface sequence of each lens. "1" represents the object-side surface of the first lens, "2" represents the image-side surface of the first lens, and so on. "STO" represents the aperture of a fixed-focus lens. The radius of curvature represents the curvature of the lens surface in millimeters (mm). A positive value indicates that the surface bends towards the image plane, and a negative value indicates that the surface bends towards the object plane. "INF" indicates that the surface is flat and the radius of curvature is infinite. The thickness represents the axial distance between the current surface and the next surface in millimeters (mm). The refractive index represents the ability of the material between the current surface and the next surface to deflect light. A blank space indicates that the current position is air and the refractive index is 1. The Abbe number represents the dispersion characteristics of the material between the current surface and the next surface. A blank space indicates that the current position is air. Half-aperture represents the effective diameter of the lens. The k-value represents the magnitude of the conic coefficient of the aspherical surface. "IMA" represents the image plane of a fixed-focus lens.

[0154] In this embodiment, the aspherical conic coefficient of the aspherical lens in a fixed-focus lens can be defined by the following aspherical formula, but is not limited to the following representation:

[0155]

[0156] 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 AG are the coefficients of the 4th, 6th, 8th, 10th, 12th, 14th, and 16th order terms of the aspherical polynomial, respectively.

[0157] For example, Table 4 details the aspherical coefficients of each lens in this embodiment two according to a feasible implementation.

[0158] Table 4. Design values ​​of aspherical coefficients for various lenses in fixed-focus lenses.

[0159]

[0160]

[0161] The fixed-focus lens provided in Example 2 has an optical total length (TTL) of 22.41 mm, a focal length (f) of 8.99, and an f / # of 1.089.

[0162] Figure 7 This is a spherical aberration curve diagram of a fixed-focus lens provided in Embodiment 2 of this utility model. In the diagram, the vertical direction represents the normalized aperture, 0 indicates it is on the optical axis, and the vertical vertex represents the maximum pupil radius; the horizontal direction represents the offset relative to the ideal focus, in millimeters (mm); different linear curves in the diagram represent different wavelengths of the image formed by the fixed-focus lens. Figure 7 It can be seen that the axial aberrations of different wavelengths (0.436μm, 0.487μm, 0.546μm, 0.587μm and 0.656μm) at normalized apertures of 0.3 to 1.0 are all controlled within the range of (-0.01mm, +0.04mm), indicating that the spherical aberration of this fixed-focus lens is well controlled at each wavelength, which can meet the requirements of wide-spectrum applications.

[0163] Figure 8 This is a field curvature distortion diagram of a fixed-focus lens provided in Embodiment 2 of this utility model. In the coordinate system on the left side of the diagram, the horizontal axis represents the magnitude of the field curvature in mm; the vertical axis represents the normalized image height, which has no unit. In the coordinate system on the right side of the diagram, the horizontal axis represents the magnitude of the distortion (F-Tan(Theta)) in %; the vertical axis represents the normalized image height, which has no unit. Figure 8 As can be seen, the fixed-focus lens provided in this embodiment effectively controls field curvature under the condition of incident light wavelength of 436nm to 656nm. That is, during imaging, the difference between the central image quality and the peripheral image quality is small, and the entire shooting can produce a more uniform image quality structure, meeting a wider range of usage needs; at the same time, Figure 8 The maximum field of view is 29.709 degrees, and its distortion has been well corrected.

[0164] Figure 9 This is a ray fan plot of a fixed-focus lens provided in Embodiment 2 of this utility model. In a single plot, the horizontal axis represents the normalized beam aperture, and the vertical axis represents the transverse aberration. Ideally, each curve should completely coincide with the horizontal axis, at which point all light rays in the field of view are focused at the same point on the image plane. The vertical axis in a single image can also represent the maximum dispersion range of the beam on the ideal image plane. The ray fan plot can not only reflect monochromatic aberrations of different wavelengths but also the magnitude of transverse chromatic aberration. Figure 9 It can be seen that the fixed-focus lens closely approximates the horizontal axis at all wavelengths in all fields of view, indicating that the transverse aberrations at each wavelength are well corrected. In addition, the curves of each color do not show obvious dispersion, indicating that the fixed-focus lens also has good correction for chromatic aberration, meeting the imaging requirements of sharp images across the entire wavelength range.

[0165] Example 3

[0166] Continue to refer to Figure 3 The fixed-focus lens provided in Embodiment 3 of this utility model includes a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, a seventh lens L7, and an eighth lens L8 arranged sequentially along the optical axis from the object plane to the image plane.

[0167] The aperture stop STO is located in the optical path between the third lens L3 and the fourth lens L4; the filter CG is located on the image side of the eighth lens L8.

[0168] Table 5 details the surface shape, radius of curvature, thickness, refractive index, Abbe number, half-aperture, and k-value of each lens in the fixed-focus lens provided in Embodiment 3, according to a feasible implementation method. The fixed-focus lenses in Table 5 correspond to... Figure 3 The fixed-focus lens shown.

[0169] Table 5 Design values ​​of optical physical parameters for fixed-focus lenses

[0170]

[0171]

[0172] In Table 5, the surface numbers are assigned according to the surface sequence of each lens. "1" represents the object-side surface of the first lens, "2" represents the image-side surface of the first lens, and so on. "STO" represents the aperture of a fixed-focus lens. The radius of curvature represents the curvature of the lens surface in millimeters (mm). A positive value indicates that the surface bends towards the image plane, and a negative value indicates that the surface bends towards the object plane. "INF" indicates that the surface is flat and the radius of curvature is infinite. The thickness represents the axial distance between the current surface and the next surface in millimeters (mm). The refractive index represents the ability of the material between the current surface and the next surface to deflect light. A blank space indicates that the current position is air and the refractive index is 1. The Abbe number represents the dispersion characteristics of the material between the current surface and the next surface. A blank space indicates that the current position is air. The half-aperture represents the effective diameter of the lens. The k-value represents the magnitude of the conic coefficient of the aspherical surface. "IMA" represents the image plane of a fixed-focus lens.

[0173] In this embodiment, the aspherical conic coefficient of the aspherical lens in a fixed-focus lens can be defined by the following aspherical formula, but is not limited to the following representation:

[0174]

[0175] 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 AG are the coefficients of the 4th, 6th, 8th, 10th, 12th, 14th, and 16th order terms of the aspherical polynomial, respectively.

[0176] For example, Table 6 details the aspherical coefficients of each lens in this embodiment three according to a feasible implementation.

[0177] Table 6. Design values ​​of aspherical coefficients for various lenses in fixed-focus lenses.

[0178]

[0179]

[0180] The fixed-focus lens provided in Example 3 has an optical total length (TTL) of 23.16 mm, a focal length (f) of 4.502, and an f / # of 1.014.

[0181] Figure 10 This is a spherical aberration curve diagram of a fixed-focus lens provided in Embodiment 3 of this utility model. In the diagram, the vertical direction represents the normalized aperture, 0 indicates it is on the optical axis, and the vertical vertex represents the maximum pupil radius; the horizontal direction represents the offset relative to the ideal focus, in millimeters (mm); different linear curves in the diagram represent different wavelengths of the image formed by the fixed-focus lens. Figure 10It can be seen that the axial aberrations of different wavelengths (0.436μm, 0.486μm, 0.546μm, 0.588μm and 0.656μm) at normalized apertures of 0.3 to 1.0 are all controlled within the range of (-0.01mm, +0.04mm), indicating that the spherical aberration of this fixed-focus lens is well controlled at each wavelength, which can meet the requirements of wide-spectrum applications.

[0182] Figure 11 This is a field curvature distortion diagram of a fixed-focus lens provided in Embodiment 3 of this utility model. In the coordinate system on the left side of the diagram, the horizontal axis represents the magnitude of the field curvature in mm; the vertical axis represents the normalized image height, which has no unit. In the coordinate system on the right side of the diagram, the horizontal axis represents the magnitude of the distortion (F-Tan(Theta)) in %; the vertical axis represents the normalized image height, which has no unit. Figure 11 As can be seen, the fixed-focus lens provided in this embodiment effectively controls field curvature under the condition of incident light wavelength of 436nm to 656nm. That is, during imaging, the difference between the central image quality and the peripheral image quality is small, and the entire shooting can produce a more uniform image quality structure, meeting a wider range of usage needs; at the same time, Figure 11 The maximum field of view is 47.931 degrees, and its distortion has been well corrected.

[0183] Figure 12 This is a ray fan plot of a fixed-focus lens provided in Embodiment 3 of this utility model. In a single plot, the horizontal axis represents the normalized beam aperture, and the vertical axis represents the transverse aberration. Ideally, each curve should completely coincide with the horizontal axis, at which point all light rays in the field of view are focused at the same point on the image plane. The vertical axis in a single image can also represent the maximum dispersion range of the beam on the ideal image plane. The ray fan plot can not only reflect monochromatic aberrations of different wavelengths but also the magnitude of transverse chromatic aberration. Figure 12 It can be seen that the fixed-focus lens closely approximates the horizontal axis at all wavelengths in all fields of view, indicating that the transverse aberrations at each wavelength are well corrected. In addition, the curves of each color do not show obvious dispersion, indicating that the fixed-focus lens also has good correction for chromatic aberration, meeting the imaging requirements of sharp images across the entire wavelength range.

[0184] To provide a clearer explanation of the above embodiments, Table 7 details the specific optical physical parameters of each lens in the fixed-focus lens provided in embodiments one to three of this utility model.

[0185] Table 7 Design values ​​of optical physical parameters for fixed-focus lenses

[0186] Example 1 Example 2 Example 3 f / F# 7.07 8.26 5.07 H / f 0.597 0.511 0.826 Nd3 1.95 1.77 2 Vd3 32.3 49.6 28.3 CT3 / ET3 2.07 1.68 1.25 Φ1+Φ2 -0.075 -0.03 -0.09 (Φ3+Φ4) / Φ 1.38 0.99 1.13 Φ3 / Φ 0.56 0.28 0.42 Φ4 / Φ 0.82 0.71 0.71 Φ5 / Φ -0.94 -0.88 -0.66 Φ6 / Φ 0.83 0.94 0.69 Φ7 / Φ -0.17 -0.02 -0.09 Φ8 / Φ 0.06 0.007 0.007 BFL / TTL 0.18 0.17 0.11 TTL / f 2.91 2.49 4.16

[0187] The specific embodiments described above do not constitute a limitation on the scope of protection of this utility model. 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 utility model should be included within the scope of protection of this utility model.

Claims

1. A fixed-focus lens, characterized in that, It includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, and an eighth lens arranged sequentially along the optical axis from the object plane to the image plane; The first lens has negative optical power, and its object side is convex while its image side is concave. The second lens has negative optical power, with its object side being concave and its image side being convex. The third lens has positive optical power and its image-side surface is convex. The fourth lens has positive optical power and its object side is convex. The fifth lens has negative optical power and its image-side surface is concave. The sixth lens has positive optical power, and its object side is convex, and its image side is convex. The seventh lens has negative optical power, and its object side is concave while its image side is convex. The eighth lens has positive optical power, and its object side is convex and its image side is concave. The third lens is a glass spherical lens; the first lens, the second lens, the fourth lens, the fifth lens, the sixth lens, the seventh lens, and the eighth lens are all plastic aspherical lenses.

2. The fixed-focus lens according to claim 1, characterized in that, The focal length of the fixed-focus lens is f, and the aperture number of the fixed-focus lens is F#; 5.07 <f / F#<8.26。 3. The fixed-focus lens according to claim 1, characterized in that, The total optical length of the fixed-focus lens is TTL, and the focal length of the fixed-focus lens is f; 2.49 <TTL / f<4.16。 4. The fixed-focus lens according to claim 1, characterized in that, The focal length of the fixed-focus lens is f, and the vertical height of the intersection point of the principal ray of the maximum field of view of the fixed-focus lens and the image plane is H; 0.511 <H / f<0.826。 5. The fixed-focus lens according to claim 1, characterized in that, The refractive index of the third lens is Nd3, and the Abbe number of the third lens is Vd3; 1.77 <Nd3<2.00; 28.3 <Vd3<49.61。 6. The fixed-focus lens according to claim 1, characterized in that, The center thickness of the third lens is CT3, and the edge thickness of the third lens is ET3; 1.25 <CT3 / ET3<2.07。 7. The fixed-focus lens according to claim 1, characterized in that, The optical power of the first lens is Φ1, and the optical power of the second lens is Φ2; -0.09 < Φ1 + Φ2 < -0.

03.

8. The fixed-focus lens according to claim 1, characterized in that, The optical power of the third lens is Φ3, the optical power of the fourth lens is Φ4, and the optical power of the fixed-focus lens is Φ; 0.99 < (Φ3 + Φ4) / Φ < 1.38; 0.28 < Φ3 / Φ < 0.56; 0.71 < Φ4 / Φ < 0.

82.

9. The fixed-focus lens according to claim 1, characterized in that, The optical power of the fifth lens is Φ5, the optical power of the sixth lens is Φ6, the optical power of the seventh lens is Φ7, and the optical power of the fixed-focus lens is Φ. -0.94 < Φ5 / Φ < -0.66; 0.69 < Φ6 / Φ < 0.94; -0.17 < Φ7 / Φ < -0.

02.

10. The fixed-focus lens according to claim 1, characterized in that, The optical power of the eighth lens is Φ8, and the optical power of the fixed-focus lens is Φ. 0.007 < Φ8 / Φ < 0.

06.

11. The fixed-focus lens according to claim 1, characterized in that, The optical back focal length of the fixed-focus lens is BFL, and the total optical length of the fixed-focus lens is TTL. 0.11 <BFL / TTL<0.18。 12. The fixed-focus lens according to claim 1, characterized in that, The fixed-focus lens also includes an aperture stop; The aperture stop is located in the optical path between the third lens and the fourth lens; or, the aperture stop is located in the optical path between the second lens and the third lens; or, the aperture stop is located in the optical path between the first lens and the second lens.

Images