Prime lens

Abstract

The prime lens comprises a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens and an eighth lens which are sequentially arranged from an object side to an image side along an optical axis, the first lens has positive focal power, the second lens has positive focal power, the third lens has focal power, and the fourth lens has focal power. The fourth lens has focal power, the fifth lens has negative focal power, the sixth lens has positive focal power, the seventh lens has focal power, and the eighth lens has negative focal power. According to the prime lens provided by the embodiment of the utility model, the eight lenses are adopted, the focal power of each lens is reasonably distributed, and the surface types of part of the lenses are further set, so that a telephoto lens which has a longer shot distance under a large target surface, stable high and low temperature performance, a large aperture, small distortion and clear imaging is realized; and the use requirements under more conditions can be met.

Description

Technical Field

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

[0002] With the development of technology, more and more fixed-focus lenses are used in security monitoring, vehicle-mounted radar, smart home and other fields. These fields often place higher requirements on lens performance. Among them, the demands for stable high and low temperature performance, long-distance scene imaging, small distortion, large target area, large aperture and greater resolution support are increasing day by day. However, the existing fixed-focus lenses are difficult to meet the above requirements at the same time. Utility Model Content

[0003] The utility model provides a fixed-focus lens, so as to realize a fixed-focus lens which has stable high and low temperature performance, a longer shooting distance, a large target surface, a large aperture and high imaging performance.

[0004] The fixed-focus lens provided by the utility model comprises a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens and an eighth lens which are arranged in sequence from the object side to the image side along the optical axis;

[0005] The first lens has positive refractive power, its object side surface is convex, and its image side surface is concave;

[0006] The second lens has positive optical power;

[0007] The third lens has an optical power;

[0008] The fourth lens has optical power;

[0009] The fifth lens has negative optical power;

[0010] The sixth lens has positive refractive power, its object side surface is concave, and its image side surface is convex;

[0011] The seventh lens has optical power;

[0012] The eighth lens has negative optical power, its object side surface is concave, and its image side surface is concave;

[0013] The focal length of the fixed-focus lens is The optical power of the first lens is The optical power of the fourth lens is The optical power of the fifth lens is

[0014]

[0015]

[0016]

[0017] Optionally, the third lens and the fourth lens form a first cemented lens group.

[0018] Optionally, the fourth lens and the fifth lens form a second cemented lens group.

[0019] Optionally, the fixed-focus lens further includes a diaphragm;

[0020] The aperture stop is located in an optical path between the sixth lens and the seventh lens.

[0021] Optionally, the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens, the seventh lens and the eighth lens are all glass spherical lenses.

[0022] Optionally, the refractive index of the first lens is Nd1, and the Abbe number is Vd1; the refractive index of the second lens is Nd2, and the Abbe number is Vd2; the refractive index of the seventh lens is Nd7, and the Abbe number is Vd7;

[0023] 1.73≤Nd1≤1.94, 20.2≤Vd1≤35;

[0024] 1.61≤Nd2≤1.86,40.0≤Vd2≤60;

[0025] 1.57≤Nd7≤1.89, 41.5≤Vd7≤65.0.

[0026] Optionally, the back focus of the fixed-focus lens is BFL, and the total optical length of the fixed-focus lens is TTL;

[0027] 0.102≤BFL / TTL.

[0028] Optionally, the aperture of the first lens is Φ1, and the total optical length of the fixed-focus lens is TTL;

[0029] 0.305≤Φ1 / TTL≤0.347.

[0030] Optionally, the aperture of the third lens is Φ3, the aperture of the fourth lens is Φ4, the aperture of the fifth lens is Φ5, and the total optical length of the fixed-focus lens is TTL;

[0031] 0.603≤(Φ3+Φ4+Φ5) / TTL≤0.905.

[0032] Optionally, the fixed-focus lens further includes flat glass;

[0033] The flat glass is located on the image side of the eighth lens.

[0034] The fixed-focus lens provided by the embodiment of the utility model adopts eight lenses, and by reasonably allocating the focal power of each lens and further setting the surface shape of some lenses, the focal length of the fixed-focus lens reaches more than 20mm, which can meet the long-distance imaging requirements that cannot be achieved by the short focal length of conventional fixed-focus lenses. At the same time, the aperture number F / # is less than 2.2, the image plane size can reach 9.7mm, and a larger resolution can be supported, realizing a telephoto lens with a longer shooting distance, stable high and low temperature performance, large aperture, small distortion, and clear imaging under a large target surface, which can meet the use requirements in more situations.

[0035] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present utility model, nor are they intended to limit the scope of the present utility model. Other features of the present utility model will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0037] Figure 1 A schematic diagram of the structure of a fixed-focus lens provided in an embodiment of the utility model;

[0038] Figure 2 A schematic diagram of the structure of another fixed-focus lens provided in an embodiment of the utility model;

[0039] Figure 3 A schematic structural diagram of another fixed-focus lens provided in an embodiment of the utility model;

[0040] Figure 4 A light fan diagram of the fixed-focus lens provided in the first embodiment of the utility model;

[0041] Figure 5 A schematic diagram of field curvature and distortion of a fixed-focus lens provided in Embodiment 1 of the present utility model;

[0042] Figure 6 A vertical axis chromatic aberration curve diagram of the fixed-focus lens provided in Example 1 of the utility model;

[0043] Figure 7 A light fan diagram of a fixed-focus lens provided in Embodiment 2 of the present utility model;

[0044] Figure 8 A schematic diagram of field curvature and distortion of a fixed-focus lens provided in Embodiment 2 of the present utility model;

[0045] Fig. 9 A vertical axis chromatic aberration curve diagram of the fixed-focus lens provided in Example 2 of the utility model;

[0046] Fig.10 This is a light fan diagram of the fixed-focus lens provided in the third embodiment of the utility model;

[0047] Fig.11 A schematic diagram of field curvature and distortion of a fixed-focus lens provided in Embodiment 3 of the present utility model;

[0048] Fig.12 This is a vertical axis chromatic aberration curve diagram of the fixed-focus lens provided in Example 3 of the utility model. DETAILED DESCRIPTION

[0049] In order to enable those skilled in the art to better understand the solution of the utility model, the technical solution in the embodiment of the utility model will be clearly and completely described below in conjunction with the drawings in the embodiment of the utility model. Obviously, the described embodiment is only a part of the embodiment of the utility model, not all of the embodiments. Based on the embodiment of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the utility model.

[0050] It should be noted that the terms "first", "second", etc. in the specification and claims of the utility model and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the utility model described here can be implemented in an order other than those illustrated or described here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0051] Figure 1 A schematic diagram of the structure of a fixed-focus lens provided in an embodiment of the utility model is shown in FIG. Figure 1 As shown, the fixed-focus lens provided by the 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, which are arranged in sequence from the object side to the image side along the optical axis.

[0052] The first lens L1 has positive refractive power, its object-side surface is convex, and its image-side surface is concave.

[0053] The second lens L2 has positive refractive power.

[0054] The third lens L3 has optical power.

[0055] The fourth lens L4 has optical power.

[0056] The fifth lens L5 has negative refractive power.

[0057] The sixth lens L6 has positive refractive power, its object-side surface is concave, and its image-side surface is convex.

[0058] The seventh lens L7 has optical power.

[0059] The eighth lens L8 has negative refractive power, its object-side surface is concave, and its image-side surface is concave.

[0060] The focal length of a fixed-focus lens is The optical power of the first lens L1 is The optical power of the fourth lens L4 is The optical power of the fifth lens L5 is in:

[0061]

[0062] Specifically, the focal length is equal to the difference between the convergence of the image-side light beam and the convergence of the object-side light beam, and it characterizes the ability of the optical system to deflect light. The larger the absolute value of the focal length, the stronger the ability to bend light, and the smaller the absolute value of the focal length, the weaker the ability to bend light. When the focal length is a positive number, the refraction of light is convergent; when the focal length is a negative number, the refraction of light is divergent. The focal length can be used to characterize a refractive surface of a lens (i.e., a surface of a lens), can be used to characterize a lens, or can be used to characterize a system formed by multiple lenses (i.e., a lens group).

[0063] In the fixed-focus lens provided in this embodiment, each lens can be fixed to a lens barrel ( Figure 1 (not shown), but is not limited to this.

[0064] Among them, the first lens L1 and the second lens L2 both have positive optical power, which are used to control the light path entering the fixed-focus lens, adjust the incident angle of the fixed-focus lens, and are beneficial to correct the field curvature so that light at different distances can eventually converge on the same plane to form a clear image.

[0065] Furthermore, the object-side surface of the first lens L1 is convex, and the image-side surface is concave. By adjusting the curvatures of the object-side surface and the image-side surface of the first lens L1, the refraction path of the light can be more precisely controlled, which is beneficial for correcting aberrations.

[0066] The fifth lens L5 has negative optical power, which is used to ensure that light can pass through the aperture of the fixed-focus lens that is sufficiently large. At a large aperture, light can also be effectively transmitted, which is conducive to the realization of a large aperture lens (aperture number F / # is less than 2.2).

[0067] The sixth lens L6 has positive focal power, and the seventh lens L7 has optical focal power. The cooperation between the sixth lens L6 and the seventh lens L7 can ensure that the path of the light passing through the aperture is optimized, ensuring that the light can pass through the aperture smoothly, reducing light scattering or reflection caused by improper angles, and avoiding reflection and other stray light at the aperture position. At the same time, the aberration of the fixed-focus lens can be adjusted to a certain extent, ensuring the aberration balance of the lens and stable high and low temperature performance.

[0068] Among them, the object side surface of the sixth lens L6 is concave, and the image side surface is convex. By adjusting the curvatures of the object side surface and the image side surface of the sixth lens L6, while meeting the required positive focal power, the refraction path of the light can be more finely controlled to ensure the aberration balance of the lens and stable high and low temperature performance.

[0069] The eighth lens L8 has negative optical power, and its object side and image side are both concave, which can help adjust the light path so that the light is distributed more widely when it reaches the imaging sensor (target surface), thereby expanding the target surface size of the fixed-focus lens. At the same time, it can effectively increase the distance from the eighth lens L8 to the plane where the imaging sensor is located, ensuring that the fixed-focus lens has a sufficiently long back focus. The longer back focus can provide more installation space for the imaging sensor, making it easier to install large sensors. In addition, the eighth lens L8 can also smooth the light so that the light can be projected more evenly onto the target surface, achieving clear imaging.

[0070] Furthermore, the focal length of the fixed-focus lens is set Refractive power of the first lens L1 Refractive power of fourth lens L4 And the optical power of the fifth lens L5 satisfy By controlling the optical power of the entire fixed-focus lens to be distributed in a certain proportion, while ensuring the functions of the above-mentioned lenses, the balance of the incident angles of the front and rear lenses can be ensured to reduce the sensitivity of the lens, which is beneficial to reduce distortion, improve the stability of the fixed-focus lens, and enhance imaging quality.

[0071] In summary, the fixed-focus lens provided by the embodiment of the utility model adopts eight lenses, and by reasonably allocating the focal power of each lens and further setting the surface shape of some lenses, the focal length of the fixed-focus lens reaches more than 20mm, which can meet the long-distance imaging requirements that cannot be achieved by the short focal length of conventional fixed-focus lenses. At the same time, the aperture number F / # is less than 2.2, the image plane size can reach 9.7mm, and a larger resolution can be supported, realizing a telephoto lens with a longer shooting distance, stable high and low temperature performance, large aperture, small distortion, and clear imaging under a large target surface, which can meet the use requirements in more situations.

[0072] Figure 2 A schematic diagram of the structure of another fixed-focus lens provided in an embodiment of the utility model is shown in FIG. Figure 2 As shown, optionally, the third lens L3 and the fourth lens L4 form a first cemented lens group G1.

[0073] Specifically, Figure 2 As shown, by arranging the third lens L3 and the fourth lens L4 to form the first cemented lens group G1, the light can be further converged and the chromatic aberration of the front light can be corrected to the greatest extent. Under the premise of compact structure, the resolution can be improved, the optical performance such as distortion can be optimized, and the light loss caused by reflection between lenses can be reduced, the illumination can be increased, the image quality can be improved, and the clarity of the lens imaging can be improved.

[0074] In addition, the use of the first cemented lens group G1 can also reduce the assembly components between the third lens L3 and the fourth lens L4, simplify the assembly procedures in the lens manufacturing process, reduce costs, and improve the tolerance sensitivity problems such as tilt / eccentricity generated in the lens assembly process.

[0075] Figure 3 A structural schematic diagram of another fixed-focus lens provided in an embodiment of the utility model is shown as follows: Figure 3 As shown, optionally, the fourth lens L4 and the fifth lens L5 form a second cemented lens group G2.

[0076] Specifically, Figure 3 As shown, by setting the fourth lens L4 and the fifth lens L5 to form the second cemented lens group G2, the light can be further converged and the chromatic aberration of the front light can be corrected to the greatest extent. Under the premise of compact structure, the resolution can be improved, the optical performance such as distortion can be optimized, and the light loss caused by reflection between lenses can be reduced, the illumination can be increased, the image quality can be improved, and the clarity of the lens imaging can be improved.

[0077] In addition, the use of the second cemented lens group G2 can also reduce the assembly components between the fourth lens L4 and the fifth lens L5, simplify the assembly procedures in the lens manufacturing process, reduce costs, and improve the tolerance sensitivity problems such as tilt / eccentricity generated in the lens assembly process.

[0078] Continue to refer Figure 1-Figure 3 Optionally, the fixed-focus lens provided in the embodiment of the utility model further includes a stop STO, and the stop STO is located in the optical path between the sixth lens L6 and the seventh lens L7.

[0079] Among them, the aperture STO, as an element that limits the diameter of the light beam passing through the fixed-focus lens, can effectively control the amount of light reaching the imaging surface.

[0080] In this embodiment, the aperture STO is set in the optical path between the sixth lens L6 and the seventh lens L7, which can block stray light from entering the fixed-focus lens and improve the clarity and contrast of the image. At the same time, the aberration of the fixed-focus lens can be adjusted to a certain extent to ensure the aberration balance of the lens and stable high and low temperature performance.

[0081] It should be noted that, in other embodiments, the aperture STO may also be set at other positions, and the embodiments of the present utility model do not specifically limit this.

[0082] Optionally, 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 all glass spherical lenses.

[0083] Among them, since glass lenses have the advantages of a small thermal expansion coefficient and good stability, by setting all eight lenses to glass lenses, the high and low temperature performance can be balanced, making the fixed-focus lens less affected by temperature. When the ambient temperature of the fixed-focus lens changes greatly, it is beneficial to maintain the focal length of the fixed-focus lens stable.

[0084] At the same time, the spherical lens is characterized by a constant curvature from the center of the lens to the periphery of the lens. By setting all eight lenses as spherical lenses, the setting method of each lens can be kept simple, reducing the difficulty of lens production, thereby helping to reduce costs.

[0085] It should be noted that the material of the glass lens is various types of glass materials known to those skilled in the art, and the embodiments of the present utility model will not elaborate on this and will not limit this.

[0086] Optionally, the refractive index of the first lens L1 is Nd1, and the Abbe number is Vd1; the refractive index of the second lens L2 is Nd2, and the Abbe number is Vd2; the refractive index of the seventh lens L7 is Nd7, and the Abbe number is Vd7; wherein:

[0087] 1.73≤Nd1≤1.94, 20.2≤Vd1≤35;

[0088] 1.61≤Nd2≤1.86,40.0≤Vd2≤60;

[0089] 1.57≤Nd7≤1.89, 41.5≤Vd7≤65.0.

[0090] Among them, 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 the material's ability to refract light. Different materials have different refractive indices.

[0091] The Abbe constant is an index used to indicate the dispersion ability of a transparent medium. The more severe the dispersion of the medium, the smaller the Abbe constant; conversely, the milder the dispersion of the medium, the larger the Abbe constant.

[0092] In this embodiment, the first lens L1 and the seventh lens L7 are lenses with a relatively high refractive index, so that the first lens L1 and the seventh lens L7 can converge light more effectively, which helps to achieve a longer focal length or a larger aperture while keeping the fixed-focus lens compact, thereby improving the light capture capability of the lens and the imaging quality in low-light environments.

[0093] At the same time, the second lens L2 adopts a lens with a higher Abbe number, which can make the refractive index difference of the second lens L2 on light of different wavelengths smaller, thereby significantly reducing chromatic aberration and improving the color reproduction and clarity of the image.

[0094] By properly selecting and matching the refractive index and Abbe number of the first lens L1, the second lens L2 and the seventh lens L7, light can pass smoothly between the lenses, reducing unnecessary reflection and scattering, and achieving high-definition imaging. At the same time, it can also ensure that light of different wavelengths can be correctly converged to the same focus when passing through the entire fixed-focus lens, achieving the confocality of visible light and infrared light, so that the fixed-focus lens can maintain high-quality imaging effects under visible light during the day and infrared light at night, improving the day and night confocal shooting capabilities.

[0095] Optionally, the back focus of the fixed-focus lens provided in the embodiment of the utility model is BFL, and the total optical length of the fixed-focus lens is TTL, wherein 0.102≤BFL / TTL.

[0096] Among them, the back focus BFL of the fixed focus lens refers to the distance from the center of the optical axis of the image side of the eighth lens L8 to the image plane.

[0097] The total optical length TTL of a fixed-focus lens refers to the distance from the center of the optical axis of the object-side surface of the first lens L1 to the image plane.

[0098] In this embodiment, by reasonably selecting the back focus BFL and the total optical length TTL of the fixed-focus lens, the fixed-focus lens can meet the telephoto requirement while ensuring that structures such as the imaging sensor and the flat filter have sufficient installation space, thereby ensuring that the fixed-focus lens will not interfere with the base and the housing during installation, ensuring that the equipment process of the fixed-focus lens is relatively simple.

[0099] Optionally, the aperture of the first lens L1 is Φ1, and the total optical length of the fixed-focus lens is TTL, wherein 0.305≤Φ1 / TTL≤0.347.

[0100] The aperture Φ1 of the first lens L1 is the diameter of the first lens L1.

[0101] The total optical length TTL of a fixed-focus lens refers to the distance from the center of the optical axis of the object-side surface of the first lens L1 to the image plane.

[0102] In this embodiment, by setting the aperture Φ1 of the first lens L1 and the total optical length TTL of the fixed-focus lens to satisfy 0.305≤Φ1 / TTL≤0.347, the outer diameter of the fixed-focus lens can be effectively constrained, thereby effectively controlling the volume of the fixed-focus lens and making the fixed-focus lens more compact.

[0103] At the same time, the light entering the fixed-focus lens can be converged to maximize the field of view and the amount of light entering the lens. While the field of view can meet the imaging needs of a wider scene, it can also ensure the imaging quality in low-light environments and meet the needs of use under more stringent conditions.

[0104] Optionally, the aperture of the third lens L3 is Φ3, the aperture of the fourth lens L4 is Φ4, the aperture of the fifth lens L5 is Φ5, and the total optical length of the fixed-focus lens is TTL, wherein 0.603≤(Φ3+Φ4+Φ5) / TTL≤0.905.

[0105] The total optical length TTL of the fixed-focus lens refers to the distance from the center of the optical axis of the object-side surface of the first lens L1 to the image plane.

[0106] In this embodiment, by reasonably setting the aperture Φ3 of the third lens L3, the aperture Φ4 of the fourth lens L4, the aperture Φ5 of the fifth lens L5 and the total optical length TTL of the fixed-focus lens to satisfy 0.603≤(Φ3+Φ4+Φ5) / TTL≤0.905, the light rays converged at the front end can pass through each lens relatively smoothly, which helps to reduce the loss and scattering of light rays at the interface between lenses, ensures that more light rays can be efficiently transmitted to the rear end, and improves the brightness and clarity of the image. At the same time, it can also ensure that the light rays are evenly distributed in the fixed-focus lens, reduce the light distortion or energy loss that may be caused by improper lens size, and thus ensure the stability and high definition of the fixed-focus lens image.

[0107] Continue to refer Figure 1-Figure 3 Optionally, the highly fixed-focus lens provided in the embodiment of the utility model further includes a flat glass CG, and the flat glass CG is located on the image side of the eighth lens L8.

[0108] Among them, the flat glass CG can protect the photosensitive chip in the imaging sensor. The photosensitive chip is used to convert the light signal collected by the fixed-focus lens into an electrical signal, thereby ensuring the imaging effect of the fixed-focus lens.

[0109] Specific embodiments of the fixed-focus lens applicable to the above-mentioned embodiments are further described below with reference to the accompanying drawings.

[0110] Embodiment 1

[0111] Continue to refer Figure 1 The fixed-focus lens provided in Embodiment 1 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, which are arranged in sequence from the object side to the image side along the optical axis.

[0112] Aperture STO is located in the optical path between sixth lens L6 and seventh lens L7.

[0113] The plate glass CG is located on the image side surface of the eighth lens L8.

[0114] Table 1 describes in detail the surface type, curvature radius, thickness and material (refractive index / Abbe number) of each lens in the fixed-focus lens provided in Example 1 in a feasible implementation manner. The fixed-focus lens in Table 1 corresponds to Figure 1 Prime lens shown.

[0115] Table 1 Design values ​​of optical physical parameters of fixed focus lens

[0116]

[0117]

[0118] Among them, the surface numbers in Table 1 are numbered according to the surface order of each lens, for example, the surface number "S1" represents the object side of the first lens, the surface number "S2" represents the image side of the first lens, and so on; "OBJ" represents the object plane; "IMA" represents the image plane; "STO" represents the aperture of the fixed focus lens; the radius of curvature represents the curvature of the corresponding lens surface, a positive value represents that the surface is bent toward the object side, and the center of the circle is close to the image plane; a negative value represents that the surface is bent toward the image side, and the center of the circle is close to the object plane, where "infinite" means that the surface is a plane and the radius of curvature is infinite; the thickness represents the central axial distance from the current surface to the next surface, the refractive index represents the ability of the material between the current surface and the next surface to deflect light, and the space represents that the current position is air. The refractive index (Nd) refers to the ability of the material between the current surface and the next surface to deflect light, and the space represents that the current position is air, and the refractive index is 1; the Abbe number (Vd) refers to the dispersion characteristics of the material between the current surface and the next surface to light, and the space represents that the current position is air.

[0119] The focal length f of the fixed-focus lens provided in the first embodiment is 20.8 mm, and the F / # (ie, the aperture number) is 2.052.

[0120] Figure 4 The ray fan diagram of the fixed focus lens provided in the first embodiment of the utility model, wherein the ray fan diagram is one of the evaluation methods commonly used by optical designers. Figure 4 As shown. In a single figure, the horizontal axis is the normalized beam aperture, and the vertical axis is the vertical axis aberration. Ideally, each curve should completely coincide with the horizontal axis, and all light rays in the field of view are focused on the same point on the image plane; the vertical axis in a single image can also be expressed as the maximum dispersion range of the light beam on the ideal image plane. The light fan diagram can not only reflect the monochromatic aberration of different wavelengths, but also indicate the size of the vertical axis chromatic aberration. Figure 4 It can be seen that the fixed-focus lens is close to the horizontal axis at each wavelength in each field of view, indicating that the vertical axis aberration of each wavelength is well corrected. In addition, the curves of each color are not obviously scattered, indicating that the fixed-focus lens also has good correction for chromatic aberration, ensuring the imaging requirements of the fixed-focus lens for clear images in the full band.

[0121] Figure 5 This is a schematic diagram of the field curvature and distortion of the fixed-focus lens provided in the first embodiment of the utility model, as shown in FIG. Figure 5 As shown, in the left coordinate system, the horizontal coordinate system represents the size of the field curvature, the unit is mm; the vertical coordinate system represents the normalized image height, no unit; in the right coordinate system, the horizontal coordinate represents the size of the distortion (F-Tan(Theta)), the unit is %; the vertical coordinate represents the normalized image height, no unit; the maximum field of view is 13.465 degrees. Figure 5 It can be seen that the fixed-focus lens provided in this embodiment has a sagittal field curvature of 0.0236 mm and a meridional field curvature of 0.0379 mm from light with a wavelength of 0.436 μm to light with a wavelength of 0.850 μm, and the field curvature is effectively controlled, that is, when imaging, the difference between the image quality at the center and the image quality at the periphery is small; the maximum distortion of the fixed-focus lens is -1.4259%, and the absolute value of the distortion is within 2%. Therefore, the distortion of the fixed-focus lens is well corrected, the imaging distortion is small, and the requirement of low distortion is met.

[0122] Figure 6 This is a vertical axis chromatic aberration curve of the fixed focus lens provided in Example 1 of the utility model, where the vertical direction represents the normalized aperture, 0 represents the optical axis, and the vertical axis vertex represents the maximum pupil radius; the main wavelength uses 546.074nm, the horizontal direction represents the offset relative to the main wavelength, the unit is micron (μm), and the maximum field of view is 4.9 mm. Figure 6It can be seen that the vertical chromatic aberration of light of different wavelengths (0.436μm~0.850μm) is controlled within a reasonable range, indicating that the vertical chromatic aberration of the fixed-focus lens is well controlled and can meet the requirements of wide-spectrum applications in the full band.

[0123] Embodiment 2

[0124] Continue to refer Figure 2 The fixed-focus lens provided in Embodiment 2 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, which are arranged in sequence from the object side to the image side along the optical axis.

[0125] The third lens L3 and the fourth lens L4 constitute a first cemented lens group G1.

[0126] Aperture STO is located in the optical path between sixth lens L6 and seventh lens L7.

[0127] The plate glass CG is located on the image side surface of the eighth lens L8.

[0128] Table 2 describes in detail the surface type, curvature radius, thickness and material (refractive index / Abbe number) of each lens in the fixed-focus lens provided in Example 2 in a feasible implementation manner. The fixed-focus lens in Table 2 corresponds to Figure 2 Prime lens shown.

[0129] Table 2 Design values ​​of optical physical parameters of fixed focus lens

[0130]

[0131]

[0132] Among them, the surface numbers in Table 2 are numbered according to the surface order of each lens, for example, the surface number "S1" represents the object side of the first lens, the surface number "S2" represents the image side of the first lens, and so on; "OBJ" represents the object plane; "IMA" represents the image plane; "STO" represents the aperture of the fixed focus lens; the radius of curvature represents the curvature of the corresponding lens surface, a positive value represents that the surface is bent toward the object side, and the center of the circle is close to the image plane; a negative value represents that the surface is bent toward the image side, and the center of the circle is close to the object plane, where "infinite" means that the surface is a plane and the radius of curvature is infinite; the thickness represents the central axial distance from the current surface to the next surface, the refractive index represents the ability of the material between the current surface and the next surface to deflect light, and the blank represents that the current position is air. The refractive index (Nd) refers to the ability of the material between the current surface and the next surface to deflect light, and the blank represents that the current position is air, and the refractive index is 1; the Abbe number (Vd) refers to the dispersion characteristics of the material between the current surface and the next surface to light, and the blank represents that the current position is air.

[0133] The focal length f of the fixed-focus lens provided in the second embodiment is 26.186 mm, and the F / # (ie, the aperture number) is 2.048.

[0134] Figure 7 The light fan diagram of the fixed focus lens provided in the second embodiment of the present utility model, wherein the light fan diagram is one of the evaluation methods commonly used by optical designers. Figure 7 As shown. In a single figure, the horizontal axis is the normalized beam aperture, and the vertical axis is the vertical axis aberration. Ideally, each curve should completely coincide with the horizontal axis, and all light rays in the field of view are focused on the same point on the image plane; the vertical axis in a single image can also be expressed as the maximum dispersion range of the light beam on the ideal image plane. The light fan diagram can not only reflect the monochromatic aberration of different wavelengths, but also indicate the size of the vertical axis chromatic aberration. Figure 7 It can be seen that the fixed-focus lens is close to the horizontal axis at each wavelength in each field of view, indicating that the vertical axis aberration of each wavelength is well corrected. In addition, the curves of each color are not obviously scattered, indicating that the fixed-focus lens also has good correction for chromatic aberration, ensuring the imaging requirements of the fixed-focus lens for clear images in the full band.

[0135] Figure 8 This is a schematic diagram of the field curvature and distortion of the fixed-focus lens provided in the second embodiment of the present utility model, as shown in FIG. Figure 8 As shown, in the left coordinate system, the horizontal coordinate system represents the size of the field curvature, the unit is mm; the vertical coordinate system represents the normalized image height, no unit; in the right coordinate system, the horizontal coordinate represents the size of the distortion (F-Tan(Theta)), the unit is %; the vertical coordinate represents the normalized image height, no unit; the maximum field of view is 10.609 degrees. Figure 8 It can be seen that the fixed-focus lens provided in this embodiment has a sagittal field curvature of 0.0483 mm and a meridional field curvature of 0.1018 mm from a wavelength of 0.436 μm to a wavelength of 0.850 μm, and the field curvature is effectively controlled, that is, when imaging, the difference between the image quality at the center and the image quality at the periphery is small; the maximum distortion of the fixed-focus lens is 0.1798%, which is within 2%. Therefore, the distortion of the fixed-focus lens is well corrected, the imaging distortion is small, and the requirement of low distortion is met.

[0136] Fig. 9 This is a vertical axis chromatic aberration curve of the fixed focus lens provided in Example 2 of the utility model, where the vertical direction represents the normalized aperture, 0 represents the optical axis, and the vertical axis vertex represents the maximum pupil radius; the main wavelength uses 546.074nm, the horizontal direction represents the offset relative to the main wavelength, the unit is micron (μm), and the maximum field of view is 4.9 mm. Fig. 9It can be seen that the vertical chromatic aberration of light of different wavelengths (0.436μm~0.850μm) is controlled within a reasonable range, indicating that the vertical chromatic aberration of the fixed-focus lens is well controlled and can meet the requirements of wide-spectrum applications in the full band.

[0137] Embodiment 3

[0138] Continue to refer Figure 3 The fixed-focus lens provided in Embodiment 3 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, which are arranged in sequence from the object side to the image side along the optical axis.

[0139] The fourth lens L4 and the fifth lens L5 constitute a second cemented lens group G2.

[0140] Aperture STO is located in the optical path between sixth lens L6 and seventh lens L7.

[0141] The plate glass CG is located on the image side surface of the eighth lens L8.

[0142] Table 3 describes in detail the surface type, curvature radius, thickness and material (refractive index / Abbe number) of each lens in the fixed-focus lens provided in Example 3 in a feasible implementation manner. The fixed-focus lens in Table 3 corresponds to Figure 3 Prime lens shown.

[0143] Table 3 Design values ​​of optical physical parameters of fixed focus lens

[0144]

[0145]

[0146] Among them, the surface numbers in Table 3 are numbered according to the surface order of each lens, for example, the surface number "S1" represents the object side of the first lens, the surface number "S2" represents the image side of the first lens, and so on; "OBJ" represents the object plane; "IMA" represents the image plane; "STO" represents the aperture of the fixed focus lens; the radius of curvature represents the curvature of the corresponding lens surface, a positive value represents that the surface is bent toward the object side, and the center of the circle is close to the image plane; a negative value represents that the surface is bent toward the image side, and the center of the circle is close to the object plane, where "infinite" means that the surface is a plane and the radius of curvature is infinite; the thickness represents the central axial distance from the current surface to the next surface, the refractive index represents the ability of the material between the current surface and the next surface to deflect light, and the blank represents that the current position is air. The refractive index (Nd) refers to the ability of the material between the current surface and the next surface to deflect light, and the blank represents that the current position is air, and the refractive index is 1; the Abbe number (Vd) refers to the dispersion characteristics of the material between the current surface and the next surface to light, and the blank represents that the current position is air.

[0147] The focal length f of the fixed-focus lens provided in the third embodiment is 21.4, and the F / # (ie, the aperture number) is 2.17.

[0148] Fig.10 The light fan diagram of the fixed focus lens provided in the third embodiment of the present utility model is one of the evaluation methods commonly used by optical designers. Fig.10 As shown. In a single figure, the horizontal axis is the normalized beam aperture, and the vertical axis is the vertical axis aberration. Ideally, each curve should completely coincide with the horizontal axis, and all light rays in the field of view are focused on the same point on the image plane; the vertical axis in a single image can also be expressed as the maximum dispersion range of the light beam on the ideal image plane. The light fan diagram can not only reflect the monochromatic aberration of different wavelengths, but also indicate the size of the vertical axis chromatic aberration. Fig.10 It can be seen that the fixed-focus lens is close to the horizontal axis at each wavelength in each field of view, indicating that the vertical axis aberration of each wavelength is well corrected. In addition, the curves of each color are not obviously scattered, indicating that the fixed-focus lens also has good correction for chromatic aberration, ensuring the imaging requirements of the fixed-focus lens for clear images in the full band.

[0149] Fig.11 This is a schematic diagram of the field curvature and distortion of the fixed-focus lens provided in the third embodiment of the present utility model, as shown in FIG. Fig.11 As shown, in the left coordinate system, the horizontal coordinate system represents the size of the field curvature, the unit is mm; the vertical coordinate system represents the normalized image height, no unit; in the right coordinate system, the horizontal coordinate represents the size of the distortion (F-Tan(Theta)), the unit is %; the vertical coordinate represents the normalized image height, no unit; the maximum field of view is 12.915 degrees. Fig.11 It can be seen that the fixed-focus lens provided in this embodiment has a sagittal field curvature of 0.0242 mm and a meridional field curvature of 0.1089 mm from a wavelength of 0.436 μm to a wavelength of 0.850 μm, and the field curvature is effectively controlled, that is, when imaging, the difference between the image quality at the center and the image quality at the periphery is small; the maximum distortion of the fixed-focus lens is 0.1614%, which is within 2%. Therefore, the distortion of the fixed-focus lens is well corrected, the imaging distortion is small, and the requirement of low distortion is met.

[0150] Fig.12 This is a vertical axis chromatic aberration curve of the fixed focus lens provided in Example 3 of the utility model, where the vertical direction represents the normalization of the aperture, 0 represents the optical axis, and the vertical axis vertex represents the maximum pupil radius; the main wavelength uses 546.074nm, the horizontal direction represents the offset relative to the main wavelength, the unit is micron (μm), and the maximum field of view is 4.9 mm. Fig.12It can be seen that the vertical chromatic aberration of light of different wavelengths (0.436μm~0.850μm) is controlled within a reasonable range, indicating that the vertical chromatic aberration of the fixed-focus lens is well controlled and can meet the requirements of wide-spectrum applications in the full band.

[0151] In order to more clearly illustrate the above embodiments, Table 4 details the specific optical and physical parameters of each lens in the fixed-focus lens provided in Embodiments 1 to 3 of the present invention.

[0152] Table 4 Design values ​​of optical physical parameters of fixed focus lens

[0153]

[0154]

[0155] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps described in the present invention can be performed in parallel, sequentially or in different orders, as long as the desired results of the technical solution of the present invention can be achieved, and this document does not limit this.

[0156] The above specific implementations do not constitute a limitation on the protection scope of the present utility model. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present utility model shall be included in the protection scope of the present utility model.

Claims

1. A fixed-focus lens, characterized in that: comprising a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens and an eighth lens arranged in sequence from the object side to the image side along the optical axis; The first lens has positive refractive power, its object side surface is convex, and its image side surface is concave; The second lens has positive optical power; The third lens has an optical power; The fourth lens has optical power; The fifth lens has negative optical power; The sixth lens has positive refractive power, its object side surface is concave, and its image side surface is convex; The seventh lens has optical power; The eighth lens has negative optical power, its object side surface is concave, and its image side surface is concave; The focal length of the fixed-focus lens is The optical power of the first lens is The optical power of the fourth lens is The optical power of the fifth lens is 2. The fixed-focus lens according to claim 1, characterized in that: The third lens and the fourth lens form a first cemented lens group.

3. The fixed-focus lens according to claim 1, characterized in that: The fourth lens and the fifth lens form a second cemented lens group.

4. The fixed-focus lens according to claim 1, characterized in that: The fixed-focus lens further includes an aperture; The aperture stop is located in an optical path between the sixth lens and the seventh lens.

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

6. The fixed-focus lens according to claim 1, wherein: The refractive index of the first lens is Nd1, and the Abbe number is Vd1; the refractive index of the second lens is Nd2, and the Abbe number is Vd2; the refractive index of the seventh lens is Nd7, and the Abbe number is Vd7; 1.73≤Nd1≤1.94, 20.2≤Vd1≤35; 1.61≤Nd2≤1.86,40.0≤Vd2≤60; 1.57≤Nd7≤1.89, 41.5≤Vd7≤65.

0.

7. The fixed-focus lens according to claim 1, wherein: The back focus of the fixed-focus lens is BFL, and the total optical length of the fixed-focus lens is TTL; 0.102≤BFL / TTL.

8. The fixed-focus lens according to claim 1, wherein: The aperture of the first lens is Φ1, and the total optical length of the fixed-focus lens is TTL; 0.305≤Φ1 / TTL≤0.

347.

9. The fixed-focus lens according to claim 1, wherein: The aperture of the third lens is Φ3, the aperture of the fourth lens is Φ4, the aperture of the fifth lens is Φ5, and the total optical length of the fixed-focus lens is TTL; 0.603≤(Φ3+Φ4+Φ5) / TTL≤0.

905.

10. The fixed-focus lens according to claim 1, wherein: The fixed-focus lens also includes flat glass; The flat glass is located on the image side of the eighth lens.

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