Prime lens

Abstract

The invention discloses a prime lens. The prime lens comprises a first lens group, a second lens group and a third lens group, the first lens group comprises a first lens with negative focal power and a second lens with positive focal power which are sequentially arranged from the object plane to the image plane along the optical axis; the second lens group comprises a third lens with positive focal power, a fourth lens with positive focal power and a fifth lens with negative focal power which are sequentially arranged from the object plane to the image plane along the optical axis; the third lens group comprises a sixth lens with positive focal power and a seventh lens with negative focal power which are sequentially arranged from the object plane to the image plane along the optical axis; the focal power phi A of the first lens group, the focal power phi B of the second lens group, the focal power phi C of the third lens group and the focal power phi of the prime lens meet the condition that phi A / phi is larger than or equal to-0.475 and smaller than or equal to-0.395. -0.015 < = phi B / phi < = 0.025; 1.265 < = phi C / phi < = 1.315. By reasonably matching the focal power of the three lens groups and the focal power of the seven lenses, light can be transited among different lens groups at a smaller deflection angle, the aberration of the system can be effectively controlled, and the prime lens can realize an ultra-high-definition imaging effect.

Description

Technical Field

[0001] The present invention relates to the field of optical device technology, and in particular to a fixed-focus lens. Background Technology

[0002] As society continues to develop, the types of lenses have also become increasingly diverse. Medium to long telephoto lenses, capable of capturing objects at greater distances, are widely used in fields such as surveillance. With rising demands for image quality, and because small aperture lenses cannot adequately meet the needs of shooting in low-light environments, large apertures have become a trend in photographic lens products.

[0003] Currently, a range of large-aperture lenses are available on the market, but large-aperture medium-telephoto lenses are relatively rare; lenses that simultaneously offer both a large aperture and infrared confocal focal length are even rarer. Furthermore, large-aperture medium-telephoto lenses with infrared confocal focal length generally employ multiple spherical glass lenses, resulting in relatively high costs. Therefore, this patent provides a fixed-focus lens, specifically a medium-telephoto lens with a large aperture, infrared confocal focal length, low cost, and high resolution. Summary of the Invention

[0004] This invention provides a fixed-focus lens that achieves a lens design that balances large aperture, infrared confocal focus, low cost, and high resolution.

[0005] This invention provides a fixed-focus lens, comprising a first lens group, a second lens group, and a third lens group arranged sequentially along the optical axis from the object plane to the image plane;

[0006] The first lens group includes a first lens and a second lens arranged sequentially from the object plane to the image plane along the optical axis. The first lens is a negative power lens, and the second lens is a positive power lens.

[0007] The second lens group includes a third lens, a fourth lens, and a fifth lens arranged sequentially from the object plane to the image plane along the optical axis. The optical power of the third lens is positive, the optical power of the fourth lens is positive, and the optical power of the fifth lens is negative.

[0008] The third lens group includes a sixth lens and a seventh lens arranged sequentially from the object plane to the image plane along the optical axis. The optical power of the sixth lens is positive, and the optical power of the seventh lens is negative.

[0009] The optical power of the first lens group is The optical power of the second lens group is The optical power of the third lens group is: The optical power of the fixed-focus lens is:

[0010] in,

[0011] Optionally, the optical power of the first lens is The optical power of the second lens is The optical power of the third lens is The optical power of the fourth lens is: The optical power of the fifth lens is The optical power of the sixth lens is: The optical power of the seventh lens is

[0012] in,

[0013] Optionally, the first lens includes a first object-side surface near the object surface and a first image-side surface near the image surface, wherein the first object-side surface is convex and the first image-side surface is concave.

[0014] The second lens includes a second object-side surface near the object plane and a second image-side surface near the image plane. The second object-side surface is concave, and the second image-side surface is convex.

[0015] The third lens includes a third object-side surface near the object plane and a third image-side surface near the image plane. The third object-side surface is convex, and the third image-side surface is concave.

[0016] The fourth lens includes a fourth object-side surface near the object plane and a fourth image-side surface near the image plane. The fourth object-side surface is convex, and the fourth image-side surface is convex.

[0017] The fifth lens includes a fifth object-side surface near the object plane and a fifth image-side surface near the image plane. The fifth object-side surface is convex, and the fifth image-side surface is concave.

[0018] The sixth lens includes a sixth object-side surface near the object plane and a sixth image-side surface near the image plane. The sixth object-side surface is convex, and the sixth image-side surface is convex.

[0019] The seventh lens includes a seventh object-side surface near the object plane and a seventh image-side surface near the image plane. The seventh object-side surface is convex, and the seventh image-side surface is concave.

[0020] Optionally, the distance between the third lens and the fourth lens on the optical axis is d;

[0021] Where 0.01mm≤d≤0.25mm.

[0022] Optionally, the maximum effective diameter of the first lens is D1, the aperture of the fixed-focus lens is Fno, and the maximum image circle radius of the fixed-focus lens is Ymax;

[0023] Among them, 1.805≤D1 / (Fno*Ymax)≤1.925.

[0024] Optionally, the first lens, the second lens, the third lens, the fifth lens, the sixth lens, and the seventh lens are all plastic aspherical lenses, and the fourth lens is a glass spherical lens.

[0025] Optionally, the Abbe number of the fourth lens is VD4;

[0026] Among them, 65.52≤VD4≤98.16.

[0027] Optionally, the fixed-focus lens has an optical total length of TTL, an optical back focal length of BFL, and an effective focal length of F;

[0028] Wherein, 0.225≤BFL / TTL≤0.285, 3.485≤TTL / F≤3.605.

[0029] Optionally, the fixed-focus lens has an aperture of Fno, an infrared defocus amount of L, and a total optical length of TTL;

[0030] Wherein, Fno≤1.28, L≤10μm, TTL≤22.5mm.

[0031] Optionally, the fixed-focus lens further includes an aperture stop, which is disposed in the optical path between the second lens and the third lens.

[0032] The fixed-focus lens provided in this embodiment of the invention includes seven lenses in three lens groups. The reasonable setting of the number of lens groups and the number of lenses ensures a suitable overall length for the fixed-focus lens, which is beneficial for achieving miniaturized lens design. Furthermore, the optical power of the seven lenses is arranged in a negative-positive-positive-positive-negative-positive-negative pattern, and the optical power of the first lens group is... The optical power of the second lens group The optical power of the third lens group And the optical power of prime lenses satisfy By rationally combining the optical power of three lens groups and seven lenses, light can transition between different lens groups with a small deflection angle, effectively controlling system aberrations and enabling fixed-focus lenses to achieve ultra-high-definition imaging effects. This results in a fixed-focus lens with an imaging target surface that can match a 1 / 2.7-inch chip, an aperture no larger than 1.28, an infrared defocus (850nm) no larger than 10μm, a total optical length no larger than 22.5mm, and a resolution that can match an 8MP pixel chip.

[0033] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a schematic diagram of the structure of a fixed-focus lens provided in Embodiment 1 of the present invention;

[0036] Figure 2 This is a schematic diagram of the spherical aberration curve of a fixed-focus lens provided in Embodiment 1 of the present invention;

[0037] Figure 3 This is a schematic diagram of the light fan of a fixed-focus lens provided in Embodiment 1 of the present invention;

[0038] Figure 4 This is a schematic diagram of the field curvature distortion curve of a fixed-focus lens provided in Embodiment 1 of the present invention;

[0039] Figure 5 This is a schematic diagram of the structure of a fixed-focus lens provided in Embodiment 2 of the present invention;

[0040] Figure 6 This is a schematic diagram of the spherical aberration curve of a fixed-focus lens provided in Embodiment 2 of the present invention;

[0041] Figure 7 This is a schematic diagram of the light fan of a fixed-focus lens provided in Embodiment 2 of the present invention;

[0042] Figure 8 This is a schematic diagram of the field curvature distortion curve of a fixed-focus lens provided in Embodiment 2 of the present invention;

[0043] Figure 9 This is a schematic diagram of the structure of a fixed-focus lens provided in Embodiment 3 of the present invention;

[0044] Figure 10 This is a schematic diagram of the spherical aberration curve of a fixed-focus lens provided in Embodiment 3 of the present invention;

[0045] Figure 11 This is a schematic diagram of the light fan of a fixed-focus lens provided in Embodiment 3 of the present invention;

[0046] Figure 12 This is a schematic diagram of the field curvature distortion curve of a fixed-focus lens provided in Embodiment 3 of the present invention. Detailed Implementation

[0047] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0048] Example 1

[0049] Figure 1 This is a schematic diagram of the structure of a fixed-focus lens provided in Embodiment 1 of the present invention, as shown below. Figure 1 As shown, the fixed-focus lens provided in this embodiment of the invention includes a first lens group S1, a second lens group S2, and a third lens group S3 arranged sequentially along the optical axis from the object plane to the image plane. The first lens group S1 includes a first lens 101 and a second lens 102 arranged sequentially along the optical axis from the object plane to the image plane. The first lens 101 is a negative power lens, and the second lens 102 is a positive power lens. The second lens group S2 includes a third lens 103, a fourth lens 104, and a fifth lens 105 arranged sequentially along the optical axis from the object plane to the image plane. The third lens 103 has a positive power, the fourth lens 104 has a positive power, and the fifth lens 105 has a negative power. The third lens group S3 includes a sixth lens 106 and a seventh lens 107 arranged sequentially along the optical axis from the object plane to the image plane. The sixth lens 106 has a positive power, and the seventh lens 107 has a negative power. The power of the first lens group S1 is... The optical power of the second lens group S2 is: The optical power of the third lens group S3 is: The optical power of a fixed-focus lens is in,

[0050] like Figure 1As shown, the fixed-focus lens provided in this embodiment of the invention includes three lens groups with a total of seven lenses with optical power. The arrangement of seven lenses with optical power ensures that the number of lenses in the fixed-focus lens is reasonable. Too many lenses will result in a large lens size, and too few lenses will result in a large aberration due to a single lens bearing a large optical power. This ensures that the fixed-focus lens is miniaturized while ensuring small imaging aberrations and high imaging quality.

[0051] Furthermore, optical power is equal to the difference between the convergence of the beam at the image plane and the convergence of the beam at the object plane, characterizing the ability of an optical system to deflect light. The larger the absolute value of the optical power, the stronger the bending ability of light; the smaller the absolute value, the weaker the bending ability. When the optical power is positive, the refraction of light is converging; when the optical power is negative, the refraction of light is diverging. Optical power can be used to characterize a single refractive surface of a lens (i.e., a surface of the lens), a single lens, or a system formed by multiple lenses (i.e., a lens group). In this embodiment of the invention, the optical power of the first lens group S1 is negative, and the first lens group S1 includes a first lens 101 with negative optical power and a second lens 102 with positive optical power. The first lens 101, as the lens that first adjusts the incident light in the optical lens, has a negative optical power setting that ensures a larger aperture before the light enters the aperture stop, increasing the aperture of the optical lens and enabling the lens to still form a clear image under dim or dark conditions. The second lens 102 with positive optical power can promptly correct the large aberrations produced by the first lens 101, especially effectively correcting the edge aberrations of the optical lens, thereby improving the imaging resolution of the optical system. The second lens group S2 has either negative or positive optical power and includes a third lens 103 with positive optical power, a fourth lens 104 with positive optical power, and a fifth lens 105 with negative optical power. The third lens 103 and the fourth lens 104 with positive optical power can further promptly correct the large aberrations produced by the first lens 101 and effectively correct the edge aberrations of the optical lens, thereby improving the imaging resolution of the optical system. The fifth lens 105 is a negative optical power lens. Combined with the positive optical power settings of the third lens 103 and the fourth lens 104, the optical power of each subsequent lens in the optical path is different from that of the preceding lens, which is beneficial for aberration correction. Furthermore, by setting the first lens 101 as a negative optical power lens, the second lens 102 as a positive optical power lens, and the third lens 103 as a positive optical power lens, axial chromatic aberration can be corrected and a large aperture can be achieved, ensuring the overall large aperture performance of the fixed-focus lens. The optical power of the third lens group S3 is positive, and the third lens group S3 includes a sixth lens 106 with positive optical power and a seventh lens 107 with negative optical power. Combined with the negative optical power setting of the fifth lens 105, the optical power of each subsequent lens in the optical path is different from that of the preceding lens, further realizing the correction of aberrations.

[0052] Furthermore, the optical power of the first lens group The optical power of the second lens group The optical power of the third lens group And the optical power of prime lenses satisfy

[0053] The optical power of the first lens group S1, the second lens group S2, and the third lens group S3 in the fixed-focus lens has a reasonable distribution ratio, which allows light to pass between different lens groups with a small deflection angle, effectively controlling the introduction of system aberrations and facilitating the realization of ultra-high-definition imaging effects of the fixed-focus lens.

[0054] In summary, the fixed-focus lens provided in this embodiment of the invention, by reasonably setting the number of lens groups and the number of lenses, ensures a suitable overall length for the fixed-focus lens, which is beneficial for achieving miniaturized lens design. Furthermore, the optical power of the seven lenses is arranged in a negative-positive-positive-positive-negative-positive-negative pattern, and the optical power of the first lens group is... The optical power of the second lens group The optical power of the third lens group And the optical power of prime lenses satisfy

[0055] By rationally combining the optical power of three lens groups and seven lenses, light can transition between different lens groups with a small deflection angle, effectively controlling system aberrations and enabling fixed-focus lenses to achieve ultra-high-definition imaging effects. This results in a fixed-focus lens with an imaging target surface that can match a 1 / 2.7-inch chip, an aperture no larger than 1.28, an infrared defocus (850nm) no larger than 10μm, a total optical length no larger than 22.5mm, and a resolution that can match an 8MP pixel chip.

[0056] Further reference Figure 1 As shown, the fixed-focus lens of this embodiment may further include an aperture stop STO and a filter 108. The aperture stop STO is disposed in the optical path between the second lens 102 and the third lens 103, and the filter 108 is disposed in the optical path between the seventh lens 107 and the image plane. The aperture stop STO can adjust the propagation direction of the light beam, which is beneficial for improving image quality. Furthermore, in this fixed-focus lens, the aperture stop STO, disposed in the optical system, can limit the beam size and control the amount of light transmitted through the lens, thus facilitating a reduction in aperture value and achieving a large aperture. The filter 108 can filter out stray light, improving the imaging effect.

[0057] Furthermore, the optical lens provided in this embodiment of the invention may also include a protective glass and an imaging sensor. The protective glass may be disposed on the image-side of the filter, and the imaging sensor may be disposed on the image-side of the protective glass. The optical system is protected by the protective glass, and the image is acquired by the imaging sensor, thus enabling the optical system to perform its normal imaging function.

[0058] Based on the above embodiments, the optical power of the first lens 101 is: The optical power of the second lens 102 is The optical power of the third lens 103 is: The optical power of the fourth lens 104 is The optical power of the fifth lens 105 is The optical power of the sixth lens 106 is The optical power of the seventh lens 107 is in,

[0059] By properly setting the optical power values ​​of each lens or lens group, the direction of light can be effectively controlled, the field curvature and spherical aberration of the optical system can be reduced, the tolerance sensitivity of the fixed-focus lens can be reduced, and the image quality of the optical system can be improved.

[0060] Based on the above embodiments, the first lens 101 includes a first object-side surface near the object plane and a first image-side surface near the image plane, wherein the first object-side surface is convex and the first image-side surface is concave; the second lens 102 includes a second object-side surface near the object plane and a second image-side surface near the image plane, wherein the second object-side surface is concave and the second image-side surface is convex; the third lens 103 includes a third object-side surface near the object plane and a third image-side surface near the image plane, wherein the third object-side surface is convex and the third image-side surface is concave; and the fourth lens 104 includes a fourth object-side surface near the object plane. The fifth lens 105 includes a fifth object-side surface near the object plane and a fifth image-side surface near the image plane, both of which are convex. The fifth object-side surface is convex, and the fifth image-side surface is concave. The sixth lens 106 includes a sixth object-side surface near the object plane and a sixth image-side surface near the image plane, both of which are convex. The seventh lens 107 includes a seventh object-side surface near the object plane and a seventh image-side surface near the image plane, both of which are convex.

[0061] Specifically, the object-side surface of a lens can be understood as the surface of the lens closest to the object plane, and the image-side surface of a lens can be understood as the surface of the lens closest to the image plane.

[0062] The object-side surface of the first lens 101 is convex, and the image-side surface is concave. This can be understood as the object-side surface of the first lens 101 convex towards the object plane near the optical axis, while the image-side surface is concave towards the image plane near the optical axis. In other words, the first lens 101 is a lens with a convex-concave structure. Designing the object-side surface of the first lens as convex helps to converge light rays into the system as much as possible, while designing the image-side surface as concave allows light rays to enter the system at a smaller deflection angle, which is beneficial for achieving a larger aperture and smaller aberrations.

[0063] The object-side surface of the second lens 102 is concave, and the image-side surface is convex. This can be understood as the object-side surface of the second lens 102 being concave towards the object plane near the optical axis, and the image-side surface being convex towards the image plane near the optical axis. In other words, the second lens 102 is a lens with a concave-convex structure. This effectively controls the direction of light rays, reduces field curvature and spherical aberration in the optical system, and improves the image quality of the optical system.

[0064] The object-side surface of the third lens 103 is convex, and the image-side surface is concave. This can be understood as the object-side surface of the third lens 103 bulging towards the object plane near the optical axis, and the image-side surface concave towards the image plane near the optical axis; therefore, the third lens 103 is a lens with a convex-concave structure. Designing the third lens 103 as a convex-concave positive lens can effectively reduce aberrations caused by the aperture stop. The object-side surface of the fourth lens 104 is convex, and the image-side surface of the fourth lens 104 is also convex. This can be understood as the object-side surface of the fourth lens 104 bulging towards the object plane near the optical axis, and the image-side surface bulging towards the image plane near the optical axis; therefore, the fourth lens 104 is a biconvex lens. Compared to designing the third lens 103 as a biconvex positive power lens, this embodiment of the invention designs the third lens 103 as a meniscus positive power lens, maintaining a reasonable distance between the third lens 103 and the fourth lens 104 on the optical axis. Specifically, the distance between the third lens 103 and the fourth lens 104 on the optical axis is d; where 0.01mm ≤ d ≤ 0.25mm. Simultaneously, the image-side profile of the third lens 103 and the object-side profile of the fourth lens 104 are ensured to maintain a smooth, even spacing throughout the entire aperture range. By designing the third lens 103 as described above, on the one hand, light rays from each field of view can transition from the third lens 103 to the fourth lens 104 with a small light deflection angle throughout the entire aperture range, effectively reducing the introduction of system aberrations and thus improving the system's resolution; on the other hand, designing the third lens 103 as a meniscus positive power lens can effectively balance aberrations caused by the aperture stop and also correct the field curvature of the entire optical system through this meniscus lens.

[0065] The object-side surface of the fifth lens 105 is convex, and the image-side surface is concave. This can be understood as the object-side surface of the fifth lens 105 bulging towards the object plane near the optical axis, and the image-side surface concave towards the image plane near the optical axis. In other words, the fifth lens 105 is a lens with a convex-concave structure. Furthermore, the object-side surface of the fifth lens 105 exhibits a certain degree of curvature, which effectively controls the direction of light rays, shortens the overall optical length of the system, and makes the system structure more compact.

[0066] The object-side surface of the sixth lens 106 is convex, and the image-side surface is also convex. This can be understood as the object-side surface of the sixth lens 106 bulging towards the object plane near the optical axis, and the image-side surface bulging towards the image plane near the optical axis. In other words, the sixth lens 106 can be considered a biconvex lens. The fact that both surfaces of the sixth lens 106 are convex effectively controls the direction of light, allowing light to enter the seventh lens 107 with a smaller deflection angle, thus effectively reducing system tolerance sensitivity. Furthermore, the surface configuration of the fifth lens 105 and the sixth lens 106 ensures a small distance between them, which helps reduce the overall length of the optical system. Moreover, this surface configuration of the fifth lens 105 and the sixth lens 106, combined with their optical power setting, not only helps balance various aberrations caused by light passing through the aperture, thereby improving the image quality of the fixed-focus lens, but also facilitates a larger aperture, ensuring clear imaging even in low-light conditions, which is beneficial for meeting the all-weather monitoring requirements of surveillance equipment.

[0067] The object-side surface of the seventh lens 107 is convex, and the image-side surface is concave. This can be understood as the object-side surface of the seventh lens 107 convex towards the object plane near the optical axis, and the image-side surface concave towards the image plane near the optical axis. In other words, the seventh lens 107 is a lens with a convex-concave structure. Furthermore, the combination of the sixth lens 106 and the seventh lens 107 improves the smoothness of light transmission, reduces the probability of various aberrations, and lowers the tolerance sensitivity of the fixed-focus lens, thereby improving the assembly yield of the fixed-focus lens. It also compresses the light beam, thereby reducing the divergence angle of the principal ray to meet the CRA (principal angle) curve requirements of the image sensor located on the image plane, improving the matching degree with the image sensor.

[0068] By properly setting the concave and convex surfaces of each lens, it is possible to ensure that each lens modulates the light emission angle and reduce the spacing between adjacent lenses, which is beneficial for achieving a small-volume fixed-focus lens design.

[0069] Based on the above embodiments, the maximum effective diameter of the first lens 101 is D1, the aperture of the fixed-focus lens is Fno, and the maximum image radius of the fixed-focus lens is Ymax; wherein, 1.805≤D1 / (Fno*Ymax)≤1.925. By limiting the maximum image radius and aperture size of the optical imaging system, the effective optical diameter of the first lens 101 can be limited, thereby ensuring the miniaturization requirement of the optical system.

[0070] Based on the above embodiments, the first lens 101, the second lens 102, the third lens 103, the fifth lens 105, the sixth lens 106 and the seventh lens 107 are all plastic aspherical lenses, and the fourth lens 104 is a glass spherical lens.

[0071] Specifically, aspherical lenses are characterized by a continuous change in curvature from the center to the periphery, unlike spherical lenses which have a constant curvature from the center to the periphery. Aspherical lenses have better curvature radius characteristics, which improves distortion aberrations and astigmatism. The first lens 101, second lens 102, third lens 103, fifth lens 105, sixth lens 106, and seventh lens 107 are all plastic aspherical lenses. Using plastic aspherical lenses helps reduce the processing complexity of aspherical lenses, and the lower cost of aspherical lenses can reduce the cost of the optical system.

[0072] A key characteristic of spherical lenses is their constant curvature from the center to the periphery, ensuring a simple lens configuration. Furthermore, due to the low coefficient of thermal expansion and good stability of glass lenses, the fourth lens 104 is a glass spherical lens. The thermal properties of glass spherical lenses are more stable, ensuring good resolving power over a wide temperature range when handling higher optical powers. Moreover, the wider range of glass materials available allows for more flexible selection of refractive index and Abbe number, enabling better control over higher aberrations and chromatic aberration, thus meeting the needs of use under complex conditions.

[0073] Therefore, the fixed-focus lens provided in this embodiment of the invention can adopt a combination of glass spherical lenses and plastic aspherical lenses, which can effectively control the cost of the fixed-focus lens while ensuring its optical performance; at the same time, the lens materials have a mutual compensating effect, which can ensure normal use in high and low temperature environments.

[0074] Based on the above embodiment, the Abbe number of the fourth lens 104 is VD4; where 65.52≤VD4≤98.16.

[0075] Specifically, the Abbe number is an index used to represent the dispersion capability of a transparent medium. The more severe the dispersion of the medium, the smaller the Abbe number; conversely, the less severe the dispersion, the larger the Abbe number. The fourth lens 104, which uses glass, employs a low-dispersion material to optimize the purple fringing effect at the edges of objects, better reproducing the true scene. It also provides thermal compensation for the entire optical system, ensuring stable thermal drift at high and low temperatures and guaranteeing the required resolution at these conditions. Furthermore, it smooths out light transitions, reduces the tolerance sensitivity of the optical system, and improves the assembly yield.

[0076] Based on the above embodiments, the total optical length of the fixed-focus lens is TTL, the optical back focal length is BFL, and the effective focal length is F; wherein, 0.225≤BFL / TTL≤0.285, 3.485≤TTL / F≤3.605. This facilitates the horizontal miniaturization of the fixed-focus lens.

[0077] Based on the above embodiments, the fixed-focus lens has an aperture of Fno, an infrared defocusing amount of L, and a total optical length of TTL; wherein, Fno≤1.28, L≤10μm, and TTL≤22.5mm. This also refers to a fixed-focus lens with a large aperture, infrared confocal focus, and a small total optical length.

[0078] As a feasible implementation method, the parameters of each lens in the fixed-focus lens will be explained next.

[0079] Table 1. Optical design values ​​for a fixed-focus lens in Example 1.

[0080]

[0081] Table 2 Design values ​​of optical physical parameters for fixed-focus lenses

[0082]

[0083]

[0084] The surface numbers in Table 2 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 stop. The radius of curvature represents the curvature of the corresponding lens surface; 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 central axial distance between the current surface and the next surface. 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. k represents the conicity coefficient of the aspherical surface.

[0085] In this embodiment of the invention, the aspherical lens of the fixed-focus lens satisfies the following formula:

[0086]

[0087] Where Z is the axial distance from the vertex of the surface at a position perpendicular to the optical axis at a height of r along the optical axis; c represents the curvature at the vertex of the aspherical surface; A, B, C, D, E, F, and G are the fourth, sixth, eighth, tenth, twelfth, fourteenth, and sixteenth order aspherical coefficients of the corresponding aspherical surfaces.

[0088] Table 3 Aspherical coefficients of fixed-focus lenses

[0089]

[0090]

[0091] Wherein, 7.481311E-03 represents 7.481311 * 10 -3 All other parameters can be represented in this way.

[0092] This embodiment satisfies the following parameters:

[0093] Focal length: f = 6.28mm;

[0094] Aperture number: F# = 1.27;

[0095] Field of view: DFOV = 70°;

[0096] Total optical length: TTL = 22.47 mm.

[0097] Figure 2 This is a schematic diagram of the spherical aberration curve of a fixed-focus lens according to Embodiment 1 of the present invention. The vertical direction represents the normalized aperture, 0 indicates that 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). The different linear curves in the figure represent different wavelengths of system imaging (436nm, 486nm, 546nm, 588nm, 656nm, and 850nm, respectively), which are... Figure 2 It can be seen that the axial aberrations of different wavelengths are all controlled within the range of (-0.10mm, +0.10mm), 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.

[0098] Figure 3 This is a schematic diagram of the light fan of a fixed-focus lens according to Embodiment 1 of the present invention. The light fan diagram is one of the most commonly used evaluation methods in modern optical design. The horizontal axis represents the beam aperture, and the vertical axis represents the transverse aberration. The ideal curve is a straight line coinciding with the horizontal axis, indicating that all light rays are focused at the same point on the image plane. The interval corresponding to the vertical axis of the curve is the maximum dispersion range of the beam on the ideal image plane. The light fan diagram can reflect not only monochromatic aberrations of different wavelengths but also the magnitude of transverse chromatic aberration. Figure 3 It can be seen that the system closely approximates the horizontal axis at each wavelength (436nm, 486nm, 546nm, 588nm, 656nm and 850nm) in each field of view, indicating that the transverse aberration of each wavelength is well corrected. At the same time, there is no obvious dispersion of each wavelength, indicating that the chromatic aberration of the system is also well corrected, thus ensuring that the optical system can achieve the high-resolution imaging requirements.

[0099] Figure 4 This is a schematic diagram of the field curvature distortion curve of a fixed-focus lens according to Embodiment 1 of the present invention. In the coordinate system on the left side of the figure, the horizontal axis represents the magnitude of the field curvature in mm; the vertical axis represents the normalized image height, which has no unit. Figure 4 It can be seen that the lens provided in this embodiment effectively controls the field curvature from light with wavelengths from 436nm to 850nm, meaning that during imaging, the difference in image quality between the center and the periphery is small; in the coordinate system on the right, the horizontal axis represents the magnitude of distortion, expressed as a percentage; the vertical axis represents the normalized image height, which has no unit; from Figure 4 It can be seen that the maximum distortion of the lens provided in this embodiment is 21.4767%.

[0100] In summary, the fixed-focus lens provided in this embodiment of the invention adopts a 1G5P structure, with an optical power of negative-positive-positive-positive-negative-positive-negative. The optical power, shape, and position of each lens are reasonably arranged, realizing a low-cost and high-resolution day and night confocal fixed-focus lens design with a focal length of about 6.28mm, an imaging target surface that can be matched with a 1 / 2.7-inch chip, a total length of less than 22.5mm, and an aperture of 1.27.

[0101] Example 2

[0102] Figure 5 This is a schematic diagram of the structure of a fixed-focus lens provided in Embodiment 2 of the present invention, as shown below. Figure 5 As shown, the fixed-focus lens provided in Embodiment 2 of the present invention includes a first lens group S1, a second lens group S2, and a third lens group S3 arranged sequentially along the optical axis from the object plane to the image plane. The first lens group S1 includes a first lens 101 and a second lens 102 arranged sequentially along the optical axis from the object plane to the image plane. The first lens 101 is a negative power lens, and the second lens 102 is a positive power lens. The second lens group S2 includes a third lens 103, a fourth lens 104, and a fifth lens 105 arranged sequentially along the optical axis from the object plane to the image plane. The optical power of the third lens 103 is positive, the optical power of the fourth lens 104 is positive, and the optical power of the fifth lens 105 is negative. The third lens group S3 includes a sixth lens 106 and a seventh lens 107 arranged sequentially along the optical axis from the object plane to the image plane. The optical power of the sixth lens 106 is positive, and the optical power of the seventh lens 107 is negative. The optical power of the first lens group S1 is... The optical power of the second lens group S2 is: The optical power of the third lens group S3 is: The optical power of a fixed-focus lens is in,

[0103] Other parameters are the same as in Example 1, and will not be repeated here.

[0104] As another feasible implementation method, the specific parameters of the fixed-focus lens are explained below.

[0105] Table 4. Optical design values ​​for a fixed-focus lens in Example 2.

[0106]

[0107] Table 5 Design values ​​of optical physical parameters for fixed-focus lenses

[0108]

[0109]

[0110] The surface numbers in Table 5 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 stop. The radius of curvature represents the curvature of the corresponding lens surface; 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 central axial distance between the current surface and the next surface. 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. k represents the conicity coefficient of the aspherical surface.

[0111] In this embodiment of the invention, the aspherical lens of the fixed-focus lens satisfies the following formula:

[0112]

[0113] Where Z is the axial distance from the vertex of the surface at a position perpendicular to the optical axis at a height of r along the optical axis; c represents the curvature at the vertex of the aspherical surface; A, B, C, D, E, F, and G are the fourth, sixth, eighth, tenth, twelfth, fourteenth, and sixteenth order aspherical coefficients of the corresponding aspherical surfaces.

[0114] Table 6 Aspherical coefficients of fixed-focus lenses

[0115]

[0116] Where -4.573065E-03 represents -4.573065 * 10 -3 All other parameters can be represented in this way.

[0117] This embodiment satisfies the following parameters:

[0118] Focal length: f = 6.39mm;

[0119] Aperture number: F# = 1.28;

[0120] Field of view: DFOV = 70°;

[0121] Total optical length: TTL = 22.47 mm.

[0122] Figure 6 This is a schematic diagram of the spherical aberration curve of a fixed-focus lens provided in Embodiment 2 of the present invention. The vertical direction represents the normalized aperture, 0 indicates that 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). The different linear curves in the figure represent different wavelengths of system imaging (436nm, 486nm, 546nm, 588nm, 656nm, and 850nm, respectively), which are... Figure 6 It can be seen that the axial aberrations of different wavelengths are all controlled within the range of (-0.10mm, +0.10mm), 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.

[0123] Figure 7 This is a schematic diagram of the light fan of a fixed-focus lens according to Embodiment 2 of the present invention. The light fan diagram is one of the most commonly used evaluation methods in modern optical design. The horizontal axis represents the beam aperture, and the vertical axis represents the transverse aberration. The ideal curve is a straight line coinciding with the horizontal axis, indicating that all light rays are focused at the same point on the image plane. The interval corresponding to the vertical axis of the curve is the maximum dispersion range of the beam on the ideal image plane. The light fan diagram can reflect not only monochromatic aberrations of different wavelengths but also the magnitude of transverse chromatic aberration. Figure 7 It can be seen that the system closely approximates the horizontal axis at each wavelength (436nm, 486nm, 546nm, 588nm, 656nm and 850nm) in each field of view, indicating that the transverse aberration of each wavelength is well corrected. At the same time, there is no obvious dispersion of each wavelength, indicating that the chromatic aberration of the system is also well corrected, thus ensuring that the optical system can achieve the high-resolution imaging requirements.

[0124] Figure 8 This is a schematic diagram of the field curvature distortion curve of a fixed-focus lens according to Embodiment 2 of the present invention. In the coordinate system on the left side of the figure, the horizontal axis represents the magnitude of the field curvature in mm; the vertical axis represents the normalized image height, which has no unit. Figure 8 It can be seen that the lens provided in this embodiment effectively controls the field curvature from light with wavelengths from 436nm to 850nm, meaning that during imaging, the difference in image quality between the center and the periphery is small; in the coordinate system on the right, the horizontal axis represents the magnitude of distortion, expressed as a percentage; the vertical axis represents the normalized image height, which has no unit; from Figure 8 It can be seen that the maximum distortion of the lens provided in this embodiment is 23.3108%.

[0125] In summary, the fixed-focus lens provided in this embodiment of the invention adopts a 1G5P structure, with an optical power of negative-positive-positive-positive-negative-positive-negative. The optical power, shape, and position of each lens are reasonably arranged, realizing a low-cost and high-resolution day and night confocal fixed-focus lens design with a focal length of about 6.39mm, an imaging target surface that can be matched with a 1 / 2.7-inch chip, a total length of less than 22.5mm, and an aperture of 1.28.

[0126] Example 3

[0127] Figure 9 This is a schematic diagram of a fixed-focus lens at the optimal object distance according to Embodiment 3 of the present invention, as shown below. Figure 9 As shown, the fixed-focus lens provided in Embodiment 3 of the present invention includes a first lens group S1, a second lens group S2, and a third lens group S3 arranged sequentially along the optical axis from the object plane to the image plane. The first lens group S1 includes a first lens 101 and a second lens 102 arranged sequentially along the optical axis from the object plane to the image plane. The first lens 101 is a negative power lens, and the second lens 102 is a positive power lens. The second lens group S2 includes a third lens 103, a fourth lens 104, and a fifth lens 105 arranged sequentially along the optical axis from the object plane to the image plane. The optical power of the third lens 103 is positive, the optical power of the fourth lens 104 is positive, and the optical power of the fifth lens 105 is negative. The third lens group S3 includes a sixth lens 106 and a seventh lens 107 arranged sequentially along the optical axis from the object plane to the image plane. The optical power of the sixth lens 106 is positive, and the optical power of the seventh lens 107 is negative. The optical power of the first lens group S1 is... The optical power of the second lens group S2 is: The optical power of the third lens group S3 is: The optical power of a fixed-focus lens is in,

[0128] Other parameters are the same as in Example 1, and will not be repeated here.

[0129] As another feasible implementation method, the specific parameters of the fixed-focus lens are explained below.

[0130] Table 7. Optical design values ​​for a fixed-focus lens in Example 3.

[0131]

[0132]

[0133] Table 8 Design values ​​of optical physical parameters for fixed-focus lenses

[0134]

[0135] The surface numbers in Table 8 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 stop. The radius of curvature represents the curvature of the corresponding lens surface; 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 central axial distance between the current surface and the next surface. 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. k represents the conicity coefficient of the aspherical surface.

[0136] In this embodiment of the invention, the aspherical lens of the fixed-focus lens satisfies the following formula:

[0137]

[0138] Where Z is the axial distance from the vertex of the surface at a position perpendicular to the optical axis at a height of r along the optical axis; c represents the curvature at the vertex of the aspherical surface; A, B, C, D, E, F, and G are the fourth, sixth, eighth, tenth, twelfth, fourteenth, and sixteenth order aspherical coefficients of the corresponding aspherical surfaces.

[0139] Table 9 Aspherical coefficients of fixed-focus lenses

[0140]

[0141] Where -4.540365E-03 represents -4.540365 * 10 -3 All other parameters can be represented in this way.

[0142] This embodiment satisfies the following parameters:

[0143] Focal length: f = 6.30mm;

[0144] Aperture number: F# = 1.28;

[0145] Field of view: DFOV = 70°;

[0146] Total optical length: TTL = 22.35 mm.

[0147] Figure 10This is a schematic diagram of the spherical aberration curve of a fixed-focus lens provided in Embodiment 3 of the present invention. The vertical direction represents the normalized aperture, 0 indicates that 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). The different linear curves in the figure represent different wavelengths of system imaging (436nm, 486nm, 546nm, 588nm, 656nm, and 850nm, respectively), which are... Figure 10 It can be seen that the axial aberrations of different wavelengths are all controlled within the range of (-0.10mm, +0.10mm), 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.

[0148] Figure 11 This is a schematic diagram of the light fan of a fixed-focus lens according to Embodiment 3 of the present invention. The light fan diagram is one of the most commonly used evaluation methods in modern optical design. The horizontal axis represents the beam aperture, and the vertical axis represents the transverse aberration. The ideal curve is a straight line coinciding with the horizontal axis, indicating that all light rays are focused at the same point on the image plane. The interval corresponding to the vertical axis of the curve is the maximum dispersion range of the beam on the ideal image plane. The light fan diagram can reflect not only monochromatic aberrations of different wavelengths but also the magnitude of transverse chromatic aberration. Figure 11 It can be seen that the system closely approximates the horizontal axis at each wavelength (436nm, 486nm, 546nm, 588nm, 656nm and 850nm) in each field of view, indicating that the transverse aberration of each wavelength is well corrected. At the same time, there is no obvious dispersion of each wavelength, indicating that the chromatic aberration of the system is also well corrected, thus ensuring that the optical system can achieve the high-resolution imaging requirements.

[0149] Figure 12 This is a schematic diagram of the field curvature distortion curve of a fixed-focus lens provided in Embodiment 3 of the present invention. In the coordinate system on the left side of the figure, the horizontal axis represents the magnitude of the field curvature, in mm; the vertical axis represents the normalized image height, which has no unit; Figure 12 It can be seen that the lens provided in this embodiment effectively controls the field curvature from light with wavelengths from 436nm to 850nm, meaning that during imaging, the difference in image quality between the center and the periphery is small; in the coordinate system on the right, the horizontal axis represents the magnitude of distortion, expressed as a percentage; the vertical axis represents the normalized image height, which has no unit; from Figure 12 It can be seen that the maximum distortion of the lens provided in this embodiment is 21.7148%.

[0150] In summary, the fixed-focus lens provided in this embodiment of the invention adopts a 1G5P structure, with an optical power of negative-positive-positive-positive-negative-positive-negative. The optical power, shape, and position of each lens are reasonably arranged, realizing a low-cost and high-resolution day and night confocal fixed-focus lens design with a focal length of about 6.30mm, an imaging target surface that can be matched with a 1 / 2.7-inch chip, a total length of less than 22.5mm, and an aperture of 1.28.

[0151] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A fixed-focus lens, characterized in that, It includes a first lens group, a second lens group, and a third lens group arranged sequentially along the optical axis from the object plane to the image plane; The first lens group includes a first lens and a second lens arranged sequentially from the object plane to the image plane along the optical axis. The first lens is a negative power lens, and the second lens is a positive power lens. The second lens group includes a third lens, a fourth lens, and a fifth lens arranged sequentially from the object plane to the image plane along the optical axis. The optical power of the third lens is positive, the optical power of the fourth lens is positive, and the optical power of the fifth lens is negative. The third lens group includes a sixth lens and a seventh lens arranged sequentially from the object plane to the image plane along the optical axis. The optical power of the sixth lens is positive, and the optical power of the seventh lens is negative. The optical power of the first lens group is φ A The optical power of the second lens group is φ B The optical power of the third lens group is φ C The optical power of the fixed-focus lens is φ; Where -0.475≤φ A / φ≤-0.395;-0.015≤φ B / φ≤0.025;1.265≤φ C / φ≤1.

315.

2. The fixed-focus lens according to claim 1, characterized in that, The optical power of the first lens is φ1, the optical power of the second lens is φ2, the optical power of the third lens is φ3, the optical power of the fourth lens is φ4, the optical power of the fifth lens is φ5, the optical power of the sixth lens is φ6, and the optical power of the seventh lens is φ7. Among them, -0.815≤φ1 / φ≤-0.685, 0.145≤φ2 / φ≤0.255, 0.035≤φ3 / φ≤0.065, 0.585≤φ4 / φ≤0.725, -1.125≤φ5 / φ≤-0.905, 1.295≤φ6 / φ≤1.385, and -0.315≤φ7 / φ≤-0.

205.

3. The fixed-focus lens according to claim 1, characterized in that, The first lens includes a first object-side surface near the object plane and a first image-side surface near the image plane. The first object-side surface is convex, and the first image-side surface is concave. The second lens includes a second object-side surface near the object plane and a second image-side surface near the image plane. The second object-side surface is concave, and the second image-side surface is convex. The third lens includes a third object-side surface near the object plane and a third image-side surface near the image plane. The third object-side surface is convex, and the third image-side surface is concave. The fourth lens includes a fourth object-side surface near the object plane and a fourth image-side surface near the image plane. The fourth object-side surface is convex, and the fourth image-side surface is convex. The fifth lens includes a fifth object-side surface near the object plane and a fifth image-side surface near the image plane. The fifth object-side surface is convex, and the fifth image-side surface is concave. The sixth lens includes a sixth object-side surface near the object plane and a sixth image-side surface near the image plane. The sixth object-side surface is convex, and the sixth image-side surface is convex. The seventh lens includes a seventh object-side surface near the object plane and a seventh image-side surface near the image plane. The seventh object-side surface is convex, and the seventh image-side surface is concave.

4. The fixed-focus lens according to claim 3, characterized in that, The distance between the third lens and the fourth lens on the optical axis is d; Where 0.01mm≤d≤0.25mm.

5. The fixed-focus lens according to claim 1, characterized in that, The maximum effective diameter of the first lens is D1, the aperture of the fixed-focus lens is Fno, and the maximum image circle radius of the fixed-focus lens is Ymax; Among them, 1.805≤D1 / (Fno*Ymax)≤1.

925.

6. The fixed-focus lens according to claim 1, characterized in that, The first lens, the second lens, the third lens, the fifth lens, the sixth lens, and the seventh lens are all plastic aspherical lenses, and the fourth lens is a glass spherical lens.

7. The fixed-focus lens according to claim 6, characterized in that, The Abbe number of the fourth lens is VD4; Among them, 65.52≤VD4≤98.

16.

8. The fixed-focus lens according to claim 1, characterized in that, The fixed-focus lens has an optical total length of TTL, an optical back focal length of BFL, and an effective focal length of F. Wherein, 0.225≤BFL / TTL≤0.285, 3.485≤TTL / F≤3.

605.

9. The fixed-focus lens according to claim 1, characterized in that, The fixed-focus lens has an aperture of Fno, an infrared defocusing amount of L, and a total optical length of TTL. Wherein, Fno≤1.28, L≤10μm, TTL≤22.5mm.

10. The fixed-focus lens according to claim 1, characterized in that, The fixed-focus lens also includes an aperture stop, which is disposed in the optical path between the second lens and the third lens.

Images