A long focal length lens

Abstract

The application discloses a long-focus lens, which is sequentially provided with a first lens, a second lens, an aperture diaphragm, a third lens, a fourth lens, a fifth lens, a sixth lens and a filter from an object side to an image side along an optical axis. By limiting the focal power and surface structure of each lens, the combination of glass-plastic hybrid lens groups, the combination of spherical surfaces and aspherical surfaces, and the accurate limitation of the refractive index, Abbe number and overall optical matching parameters of the lens, the technical problems of long-focus imaging difference, inconsistent double-waveband imaging, large volume and large aberration of a traditional household monitoring lens are solved, a miniaturized structure with an optical total length of less than or equal to 22.5 mm is realized, the long-focus lens has a large aperture of F#1.6 and a wide field of view of greater than or equal to 31.5 degrees under a 12 mm long-focus specification, can realize all-weather high-definition imaging in a visible light and near-infrared double-waveband, has excellent long-distance detail snapshot capability, is suitable for long-distance monitoring scenes of various smart home security terminals such as intelligent security cameras and visual doorbells, has good imaging quality, strong compatibility and controllable cost, and has wide mass production applicability.

Description

Technical Field

[0001] This invention relates to the field of optical lens technology, and more particularly to a telephoto optical lens with day and night confocal focus that can be used in smart home terminals. Background Technology

[0002] With the rapid iteration and upgrading of the smart home industry, visual sensing devices such as smart security cameras, video doorbells, smart peepholes, and home PTZ cameras have become core terminal devices for home security monitoring and intelligent human-computer interaction. These devices need to meet the requirements of 24 / 7 uninterrupted monitoring, which places stringent requirements on the comprehensive optical performance of the supporting imaging lenses.

[0003] In daytime visible light environments, lenses need to have high-definition imaging capabilities to accurately identify image details and meet the need for clear identification of people and objects. In low-light or no-light environments at night, existing security equipment generally uses 850nm or 940nm near-infrared supplementary lighting technology to achieve imaging. This requires lenses to be compatible with both visible light and near-infrared bands to ensure dual-band imaging clarity and avoid problems such as day-night imaging color difference, blurring, and resolution degradation.

[0004] Meanwhile, to meet the needs of long-distance home security monitoring and achieve functions such as remote personnel identification at unit doors, large-scale anomaly monitoring in courtyards, and full coverage of corridor depth, smart home security terminals have set higher standards for the telephoto imaging performance and long-distance detail capture capabilities of lenses. Traditional home monitoring lenses are mostly short-focal-length and wide-angle structures, which have the defects of short focal length, low magnification, and serious loss of long-distance imaging details, making them unsuitable for deep and long-distance monitoring scenarios. On the other hand, existing telephoto lenses are mostly all-glass lens structures, which have the problems of large size, heavy weight, high cost, poor aberration correction effect, and poor dual-band imaging consistency, making it difficult to meet the application requirements of miniaturized, high-imaging-quality, and wide-adaptability home security devices, which seriously restricts the scene adaptability and imaging performance upgrade of smart home security devices. Summary of the Invention

[0005] This invention provides a telephoto lens that employs a 6-element glass-plastic hybrid optical system structure. By optimizing the shape, power, and relative position of each lens element, a long focal length and day-night confocal lens design is achieved. This lens simultaneously meets the requirements of high resolution and small day-night focal plane offset, and is suitable for telephoto imaging in smart home application scenarios.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention provides a telephoto lens, defining the surface of the lens adjacent to the object plane as the object-side surface and the surface of the lens adjacent to the image plane as the image-side surface, arranged sequentially from the object-side to the image-side along the lens optical axis: The first lens has negative optical power, and its object side is convex and its image side is concave. The second lens has positive optical power, and its object side is convex and its image side is concave. Aperture stop; The third lens has positive optical power, and its object side is convex and its image side is either convex or concave. The fourth lens has a positive or negative optical power, and its object side is convex or concave, and its image side is convex or concave. The fifth lens has negative optical power, and its object side is concave and its image side is convex. The sixth lens has positive optical power, and its object side is convex and its image side is concave. Filter.

[0008] Furthermore, the first, third, and fourth lenses are glass lenses or plastic lenses; the second, fifth, and sixth lenses are all plastic lenses; the first, third, and fourth lenses are spherical or aspherical lenses; and the second, fifth, and sixth lenses are aspherical lenses. This invention employs a hybrid glass-plastic lens architecture, combining spherical and aspherical lenses, which can efficiently correct various optical aberrations and improve imaging uniformity while controlling the overall cost and weight of the lens.

[0009] Furthermore, the first lens, the second lens, the third lens, the fifth lens, and the sixth lens satisfy the following: -2.160≤Φ / Φ1≤-0.894, 1.807≤Φ / Φ2≤4.346, 0.468≤Φ / Φ3≤1.878 -0.962≤Φ / Φ5≤-0.725, 0.520≤Φ / Φ6≤1.016; Wherein, Φ represents the optical power of the lens, Φ1 represents the optical power of the first lens, Φ2 represents the optical power of the second lens, Φ3 represents the optical power of the third lens, Φ5 represents the optical power of the fifth lens, and Φ6 represents the optical power of the sixth lens. This invention achieves a rational allocation of optical power in the optical system by precisely defining the optical power ratio of each lens, effectively correcting optical aberrations such as spherical aberration, chromatic aberration, and coma, and ensuring image clarity in telephoto conditions.

[0010] Furthermore, the first lens, the second lens, the third lens, the fifth lens, and the sixth lens satisfy the following: 34.881≤Vd1≤65.241, 18.499≤Vd2≤85.335, 22.549≤Vd3≤98.110, 20.576≤Vd5≤26.368, 46.967≤Vd6≤62.159; Wherein, Vd1 is the Abbe number of the first lens, Vd2 is the Abbe number of the second lens, Vd3 is the Abbe number of the third lens, Vd5 is the Abbe number of the fifth lens, and Vd6 is the Abbe number of the sixth lens. This invention, by limiting the Abbe number range of each lens, can effectively suppress chromatic aberration in visible and near-infrared dual-band imaging, ensuring color consistency and detail clarity in day and night imaging.

[0011] Furthermore, the first lens, the second lens, the third lens, the fifth lens, and the sixth lens satisfy the following: 1.522≤Nd1≤1.841, 1.485≤Nd2≤1.671, 1.427≤Nd3≤1.704, 1.572≤Nd5≤1.683, 1.518≤Nd6≤1.614; Wherein, Nd1 is the refractive index of the first lens, Nd2 is the refractive index of the second lens, Nd3 is the refractive index of the third lens, Nd5 is the refractive index of the fifth lens, and Nd6 is the refractive index of the sixth lens. A reasonable refractive index ratio can optimize the light refraction path, reduce the overall loss of the optical system, and improve lens transmittance and image resolution.

[0012] Furthermore, the optical parameters of the lens of this invention meet the following requirements: total optical length (TTL) ≤ 22.5 mm; total focal length (EFL) ≤ 12 mm; and field of view (DFOV) ≥ 31.5°. These parameter settings enable miniaturized lens design while ensuring long-distance observation capabilities and sufficient monitoring coverage, adapting to the installation space limitations and scene monitoring needs of home security equipment.

[0013] Furthermore, the total optical length of the lens is TTL, and the total focal length of the lens is EFL, satisfying: 0.508 ≤ EFL / TTL ≤ 0.598. This ratio balances the lens's telephoto performance with its overall size, avoiding an excessively long focal length that results in a bulky lens, or an excessively small size that leads to a decline in telephoto imaging performance.

[0014] Furthermore, the total optical length of the lens is TTL, and the image plane diameter of the lens is IH, satisfying: 0.142≤IH / TTL≤0.176. This reasonable image plane adaptation ratio can match conventional security image sensors, ensuring uniformity of imaging across the entire field of view and avoiding edge imaging distortion and blurring issues.

[0015] Furthermore, the total optical length of the lens is TTL, and the optical back focal length of the lens is OBFL. The optical back focal length is the distance from the point on the image side of the sixth lens closest to the image plane to the image plane, satisfying: 0.281≤OBFL / TTL≤0.380. This parameter setting allows sufficient space for the installation of filters and sensors, while ensuring the stability of the optical path of the optical system and improving lens assembly compatibility and imaging stability.

[0016] Furthermore, the lens of this invention maintains a large relative aperture of F#1.6, which can effectively increase the amount of light transmitted through the lens, improve the imaging brightness in low-light environments at night, eliminate the problems of excessive noise and loss of detail in low-light environments, and achieve all-weather high-definition imaging.

[0017] Beneficial effects: 1. This invention adopts a six-element glass-plastic hybrid optical architecture, combined with a combination of spherical and aspherical lenses. Through precise matching of the curvature and optical power of multiple lenses, it can efficiently correct various optical aberrations such as spherical aberration, chromatic aberration, and coma, significantly improving the lens's imaging resolution and image uniformity. At the same time, compared with all-glass lenses, it effectively reduces lens weight and production costs, meeting the mass production needs of lightweight and low-cost smart home devices.

[0018] 2. By precisely limiting the range of values ​​for the optical power, Abbe number, and refractive index of each lens, this invention optimizes the optical path design of the optical system and can simultaneously adapt to imaging in the visible light band and the 850nm and 940nm near-infrared bands. It completely solves the problems of color difference and inconsistent clarity in day and night imaging of traditional lenses, and perfectly meets the needs of 24-hour all-weather monitoring of security equipment.

[0019] 3. This invention achieves a miniaturized telephoto design, with the total optical length controlled within 22.5mm and the total focal length ≤12mm. While ensuring the ability to capture details at long distances, it also takes into account a wide field of view coverage of ≥31.5°, which can meet the large-scale monitoring needs of home deep-seated scenes such as unit doors, courtyards, and corridors, and solves the defects of traditional telephoto lenses with too small field of view and limited monitoring range.

[0020] 4. This invention features a large relative aperture of F#1.6, ensuring ample light transmission and significantly improving imaging capabilities in low-light environments. High-definition imaging can be achieved in low-light scenes at night without the need for high-intensity supplemental lighting, reducing device power consumption. Simultaneously, through optimization of multiple optical parameters, it balances the four core performance aspects of lens size, focal length, field of view, and image quality, making it compatible with various smart home security visual terminal devices and applicable to a wide range of scenarios. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the optical structure of Embodiment 1 of the present invention; Figure 2 The MTF curves for visible light 0.435-0.656μm (200lp / mm) in Example 1 of the present invention are shown. Figure 3 This is the MTF curve of infrared 850μm (200lp / mm) of Embodiment 1 of the present invention; Figure 4 This is a schematic diagram of the optical structure of Embodiment 2 of the present invention; Figure 5 The MTF curves for visible light (0.435-0.656 μm, 200 lp / mm) in Example 2 of this invention are shown. Figure 6 This is the MTF curve of infrared 850μm (200lp / mm) of Embodiment 2 of the present invention; Figure 7 This is a schematic diagram of the optical structure of Embodiment 3 of the present invention; Figure 8 The MTF curve for visible light 0.435-0.656μm (200lp / mm) in Example 3 of the present invention is shown. Figure 9 This is the MTF curve of infrared 850μm (200lp / mm) of Example 3 of the present invention; Reference numerals: L1-first lens, L2-second lens, L3-third lens, L4-fourth lens, L5-fifth lens, L6-sixth lens, ST-aperture stop, G1-filter, S15-image plane. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. In this specification, the expressions "first," "second," "third," etc., are only used to distinguish one feature from another, and do not indicate any limitation on the features. The shape of a spherical or aspherical surface is not limited to the spherical or aspherical shapes shown in the drawings. The drawings are for illustrative purposes only and are not strictly drawn to scale.

[0023] In this invention, the paraxial region refers to the region near the optical axis. If the lens surface is convex and the location of the convexity is not defined, it means that the lens surface is convex at least in the paraxial region; if the lens surface is concave and the location of the concaveness is not defined, it means that the lens surface is concave at least in the paraxial region; if the lens surface is not defined as convex, concave, or flat, it means that the lens surface can be convex, concave, or flat. The surface of each lens closest to the object being photographed is called the object-side surface of the lens, and the surface of each lens closest to the imaging plane is called the image-side surface of the lens.

[0024] Unless otherwise specified, all terms used in this invention (including technical and scientific terms) shall have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. It should also be understood that terms (e.g., those defined in common dictionaries) shall be interpreted as having the same meaning as they have in the context of the relevant art and shall not be interpreted in an idealized or overly formal sense unless expressly so defined in this invention.

[0025] It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0026] This invention provides a telephoto lens. The surface of the lens adjacent to the object plane is the object-side surface, and the surface of the lens adjacent to the image plane is the image-side surface. Along the lens optical axis from the object side to the image side, a first lens L1, a second lens L2, an aperture stop ST, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, a filter G1, and an imaging surface S15 are arranged sequentially. The aperture stop ST is located between the second lens L2 and the third lens L3. The filter G1 is disposed on the image-side surface of the sixth lens L6, and the imaging surface S15 is disposed on the image-side surface of the filter G1. Wherein: The first lens L1 has negative optical power, and its object side is convex while its image side is concave. The second lens L2 has positive optical power, and its object side is convex while its image side is concave. The third lens L3 has positive optical power, its object side is convex, and its image side can be either convex or concave. The fourth lens L4 can have positive or negative optical power, and its object side can be convex or concave, and its image side can be convex or concave. The fifth lens L5 has negative optical power, with a concave object side and a convex image side. The sixth lens L6 has positive optical power, with a convex object side and a concave image side.

[0027] In the optical lens provided by this invention, the lens material can be either a glass lens or a plastic lens. When the lens material is plastic, the surface shape can be an aspherical lens. Aspherical lenses offer high design freedom, effectively reducing the number of lenses while correcting advanced aberrations and improving image quality. When the lens material is glass, it can correct axial chromatic aberration to support day and night confocal performance, while also exhibiting strong environmental stability and excellent weather resistance, effectively improving lens stability. Specifically, in some embodiments, the first lens L1, the third lens L3, and the fourth lens L4 can be either glass or plastic lenses; the second lens L2, the fifth lens L5, and the sixth lens L6 are all plastic lenses. This invention employs a glass-plastic hybrid structure, leveraging the complementary properties of the two materials to achieve an optimal balance between image quality, size, environmental reliability, and mass production cost.

[0028] In this invention, when the lens is an aspherical lens, the aspherical surface of the lens satisfies the following formula: , In the formula, Z is the sag of the lens along the optical axis, k is the conic coefficient of the quadratic surface, γ is the lens height, c is the lens curvature, and A, B, C, D, E, F, and G are the coefficients of the 4th, 6th, 8th, 10th, 12th, 14th, and 16th order terms of the aspherical polynomial.

[0029] The optical lens of the present invention will be specifically described below with reference to the above-described configuration.

[0030] The main element symbols in the specific embodiments of the present invention are explained in Table 1.

[0031] Table 1

[0032] The values ​​of each conditional expression in the specific embodiments of the present invention are shown in Table 2 below.

[0033] Table 2

[0034] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments.

[0035] Example 1 Reference Figure 1 As shown, Figure 1 This is a schematic diagram of the optical structure of Embodiment 1. In this embodiment, the total focal length of the lens is EFL=11.52 mm, the full field of view is DFOV=32°, the aperture value is F#=1.6, the total optical length of the lens is TTL=22.5 mm, and the optical back focal length of the lens is OBFL=6.32 mm.

[0036] In this embodiment, the lenses are arranged sequentially from the object side to the image side along the lens optical axis: The first lens L1 is a spherical glass lens with negative optical power, its object side is convex and its image side is concave. The second lens L2 is an aspherical plastic lens with positive optical power, its object side is convex and its image side is concave. Aperture stop ST; The third lens L3 is a spherical glass lens with positive optical power, and its object side is convex and its image side is convex. The fourth lens L4 is an aspherical plastic lens with negative optical power. Its object side is convex and its image side is concave. The fifth lens L5 is an aspherical plastic lens with negative optical power. Its object side is concave and its image side is convex. The sixth lens L6 is an aspherical plastic lens with positive optical power. Its object side is convex and its image side is concave. Filter G1 has both its object-side and image-side surfaces as planes. Imaging plane S15 is a plane.

[0037] In this embodiment, the radius of curvature (in mm), center thickness d (in mm), refractive index (ND), and Abbe constant (VD) of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5, and the sixth lens L6 are shown in Table 3.

[0038] Table 3

[0039] In Table 3, the radius of curvature represents the degree of curvature of the lens surface, with a positive value indicating that the surface bends toward the image plane and a negative value indicating that the surface bends toward the object plane; the thickness represents the central axial distance from the current surface to the next surface; the refractive index represents the ability of the current lens material to deflect light; and the Abbe number represents the dispersion characteristics of the current lens material.

[0040] In this embodiment, the aspherical surfaces of the second lens L2, the fourth lens L4, the fifth lens L5, and the sixth lens L6 can all be defined by the following equation for even-order aspherical surfaces: , In the formula, Z is the sag of the lens along the optical axis, k is the surface conic coefficient, γ is the lens height, c is the lens curvature, and A, B, C, D, E, F, G, H, and I are the coefficients of the 4th, 6th, 8th, 10th, 12th, 14th, 16th, 18th, and 20th order terms of the aspherical polynomial.

[0041] Table 4 gives the coefficients of the aspherical surfaces of each optical surface of the second lens L2, the fourth lens L4, the fifth lens L5, and the sixth lens L6.

[0042] Table 4

[0043] refer to Figure 2 The figure shows the MTF curves of the lens in this embodiment at different spatial frequencies and fields of view under visible light wavelengths of 0.435-0.656μm. The horizontal axis represents spatial frequency, and the vertical axis represents MTF value. As can be seen from the figure, at a spatial frequency of 120 lp / mm, the MTF value of the lens across the entire field of view is above 0.6. At a spatial frequency of 200 lp / mm, the MTF value at the center field of view is greater than 0.75. Within the range of 0–200 lp / mm, the MTF curve decreases uniformly and slowly from the center to the edge of the field of view, indicating that the optical lens has high imaging quality and good detail resolution at both low and high frequencies.

[0044] refer to Figure 3 The figure shows the MTF curves of the lens in this embodiment at different spatial frequencies and fields of view at an infrared wavelength of 0.85 μm. The horizontal axis represents the spatial frequency, and the vertical axis represents the MTF value. As can be seen from the figure, at a spatial frequency of 120 lp / mm, the MTF value of the lens across the entire field of view is above 0.65, and at a spatial frequency of 200 lp / mm, the MTF value is greater than 0.45. The MTF curve decreases slowly and smoothly from the center to the edge of the field of view, indicating that the optical lens maintains high imaging quality and stable imaging capability even at night.

[0045] Example 2 Reference Figure 4 As shown, Figure 4 This is a schematic diagram of the optical structure of Embodiment 2. In this embodiment, the total focal length of the lens is EFL=11.44 mm, the full field of view is DFOV=32°, the aperture value is F#=1.6, the total optical length of the lens is TTL=22.5 mm, and the optical back focal length of the lens system is OBFL=7.32 mm.

[0046] In this embodiment, the lenses are arranged sequentially from the object side to the image side along the lens optical axis: The first lens L1 is a spherical glass lens with negative optical power, its object side is convex and its image side is concave. The second lens L2 is an aspherical plastic lens with positive optical power, its object side is convex and its image side is concave. Aperture stop ST; The third lens L3 is an aspherical plastic lens with positive optical power. Its object side is convex and its image side is concave. The fourth lens L4 is a spherical glass lens with positive optical power. Its object side is convex and its image side is convex. The fifth lens L5 is an aspherical plastic lens with negative optical power. Its object side is concave and its image side is convex. The sixth lens L6 is an aspherical plastic lens with positive optical power. Its object side is convex and its image side is concave. Filter G1 has both its object-side and image-side surfaces as planes. Imaging plane S15 and imaging plane S19 are planes.

[0047] In this embodiment, the radius of curvature (in mm), center thickness d (in mm), refractive index (ND), and Abbe constant (VD) of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5, and the sixth lens L6 are shown in Table 5.

[0048] Table 5

[0049] In Table 5, the radius of curvature represents the degree of curvature of the lens surface, with a positive value indicating that the surface bends toward the image plane and a negative value indicating that the surface bends toward the object plane; the thickness represents the central axial distance from the current surface to the next surface; the refractive index represents the ability of the current lens material to deflect light; and the Abbe number represents the dispersion characteristics of the current lens material.

[0050] In this embodiment, the aspherical surfaces of the second lens L2, the third lens L3, the fifth lens L5, and the sixth lens L6 can all be defined by the following equation for even-order aspherical surfaces: , In the formula, Z is the sag of the lens along the optical axis, k is the surface conic coefficient, γ is the lens height, c is the lens curvature, and A, B, C, D, E, F, G, H, and I are the coefficients of the 4th, 6th, 8th, 10th, 12th, 14th, 16th, 18th, and 20th order terms of the aspherical polynomial.

[0051] Table 6 gives the coefficients of the aspherical surfaces of each optical surface of the second lens L2, the third lens L3, the fifth lens L5, and the sixth lens L6.

[0052] Table 6

[0053] refer to Figure 5The figure shows the MTF curves of the lens in this embodiment at different spatial frequencies and fields of view under visible light wavelengths of 0.435-0.656μm. The horizontal axis represents spatial frequency, and the vertical axis represents MTF value. As can be seen from the figure, at a spatial frequency of 120 lp / mm, the MTF value of the lens across the entire field of view is above 0.59. At a spatial frequency of 200 lp / mm, the MTF value at the center field of view is greater than 0.68. Within the range of 0–200 lp / mm, the MTF curve decreases uniformly and slowly from the center to the edge of the field of view, indicating that the optical lens has high imaging quality and good detail resolution at both low and high frequencies.

[0054] refer to Figure 6 The figure shows the MTF curves of the lens in this embodiment at different spatial frequencies and fields of view at an infrared wavelength of 0.85 μm. The horizontal axis represents the spatial frequency, and the vertical axis represents the MTF value. As can be seen from the figure, at a spatial frequency of 120 lp / mm, the MTF value of the lens across the entire field of view is above 0.55, and at a spatial frequency of 200 lp / mm, the MTF value is greater than 0.32. The MTF curve decreases slowly and smoothly from the center to the edge of the field of view, indicating that the optical lens maintains high imaging quality and stable imaging capability even at night.

[0055] Example 3 Reference Figure 7 As shown, Figure 7 This is a schematic diagram of the optical structure of Embodiment 3. In this embodiment, the total focal length of the lens is EFL=11.45 mm, the total field of view is DFOV=31.5°, the aperture value is F#=1.6, the total optical length of the lens is TTL=19.27 mm, and the optical back focal length of the lens system is OBFL=7.04 mm.

[0056] In this embodiment, the lenses are arranged sequentially from the object side to the image side along the lens optical axis: The first lens L1 is an aspherical plastic lens with negative optical power, its object side is convex and its image side is concave. The second lens L2 is an aspherical plastic lens with positive optical power, its object side is convex and its image side is concave. Aperture stop ST; The third lens L3 is a spherical glass lens with positive optical power, and its object side is convex and its image side is convex. The fourth lens L4 is a spherical glass lens with negative optical power. Its object side is concave and its image side is convex. The fifth lens L5 is an aspherical plastic lens with negative optical power. Its object side is concave and its image side is convex. The sixth lens L6 is an aspherical plastic lens with positive optical power. Its object side is convex and its image side is concave. Filter G1 has both its object-side and image-side surfaces as planes. Imaging plane S15 and imaging plane S19 are planes.

[0057] In this embodiment, the radius of curvature (in mm), center thickness d (in mm), refractive index (ND), and Abbe constant (VD) of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5, and the sixth lens L6 are shown in Table 7.

[0058] Table 7

[0059] In Table 7, the radius of curvature represents the degree of curvature of the lens surface, with a positive value indicating that the surface bends toward the image plane and a negative value indicating that the surface bends toward the object plane; the thickness represents the central axial distance from the current surface to the next surface; the refractive index represents the ability of the current lens material to deflect light; and the Abbe number represents the dispersion characteristics of the current lens material.

[0060] In this embodiment, the aspherical surfaces of the first lens L1, the second lens L2, the fifth lens L5, and the sixth lens L6 can all be defined by the following equation for even-order aspherical surfaces: , In the formula, Z is the sag of the lens along the optical axis, k is the surface conic coefficient, γ is the lens height, c is the lens curvature, and A, B, C, D, E, F, G, H, and I are the coefficients of the 4th, 6th, 8th, 10th, 12th, 14th, 16th, 18th, and 20th order terms of the aspherical polynomial.

[0061] Table 8 gives the coefficients of the aspherical surfaces of each optical surface of the first lens L1, the second lens L2, the fifth lens L5, and the sixth lens L6.

[0062] Table 8

[0063] refer to Figure 8The figure shows the MTF curves of the lens in this embodiment at different spatial frequencies and fields of view under visible light wavelengths of 0.435-0.656μm. The horizontal axis represents spatial frequency, and the vertical axis represents MTF value. As can be seen from the figure, at a spatial frequency of 120 lp / mm, the MTF value of the lens across the entire field of view is above 0.55. At a spatial frequency of 200 lp / mm, the MTF value at the center field of view is greater than 0.67. Within the range of 0–200 lp / mm, the MTF curve decreases uniformly and slowly from the center to the edge of the field of view, indicating that the optical lens has high imaging quality and good detail resolution at both low and high frequencies.

[0064] refer to Figure 9 The figure shows the MTF curves of the lens in this embodiment at different spatial frequencies and fields of view at an infrared wavelength of 0.85 μm. The horizontal axis represents the spatial frequency, and the vertical axis represents the MTF value. As can be seen from the figure, at a spatial frequency of 120 lp / mm, the MTF value of the lens across the entire field of view is above 0.52, and at a spatial frequency of 200 lp / mm, the MTF value is greater than 0.25. The MTF curve decreases slowly and smoothly from the center to the edge of the field of view, indicating that the optical lens maintains high imaging quality and stable imaging capability even at night.

[0065] The above description merely illustrates several embodiments of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and the present invention also intends to include these modifications and variations.

Claims

1. A telephoto lens, characterized in that: The surface of the lens adjacent to the object plane is defined as the object-side surface, and the surface of the lens adjacent to the image plane is defined as the image-side surface. These surfaces are arranged sequentially from the object-side to the image-side along the lens optical axis. The first lens has negative optical power, and its object side is convex and its image side is concave. The second lens has positive optical power, and its object side is convex and its image side is concave. The third lens has positive optical power, and its object side is convex and its image side is either convex or concave. The fourth lens has a positive or negative optical power, and its object side is convex or concave, and its image side is convex or concave. The fifth lens has negative optical power, and its object side is concave and its image side is convex. The sixth lens has positive optical power, and its object side is convex and its image side is concave. The total optical length of the lens is TTL, satisfying TTL≤22.5mm; The total focal length of the lens is EFL, which satisfies EFL≤12mm; The lens has a field of view (DFOV) of ≥31.5°.

2. A telephoto lens according to claim 1, characterized in that: The first lens, the third lens, and the fourth lens are glass lenses or plastic lenses, while the second lens, the fifth lens, and the sixth lens are all plastic lenses.

3. A telephoto lens according to claim 1, characterized in that: The first lens, the third lens, and the fourth lens are spherical or aspherical lenses, and the second lens, the fifth lens, and the sixth lens are aspherical lenses.

4. A telephoto lens according to claim 1, characterized in that: The first lens, the second lens, the third lens, the fifth lens, and the sixth lens satisfy the following: -2.160≤Φ / Φ1≤-0.894, 1.807≤Φ / Φ2≤4.346, 0.468≤Φ / Φ3≤1.878 -0.962≤Φ / Φ5≤-0.725, 0.520≤Φ / Φ6≤1.016; Wherein, Φ is the optical power of the lens, Φ1 is the optical power of the first lens, Φ2 is the optical power of the second lens, Φ3 is the optical power of the third lens, Φ5 is the optical power of the fifth lens, and Φ6 is the optical power of the sixth lens.

5. A telephoto lens according to claim 1, characterized in that: The first lens, the second lens, the third lens, the fifth lens, and the sixth lens satisfy the following: 34.881≤Vd1≤65.241, 18.499≤Vd2≤85.335, 22.549≤Vd3≤98.110, 20.576≤Vd5≤26.368, 46.967≤Vd6≤62.159; Wherein, Vd1 is the Abbe number of the first lens, Vd2 is the Abbe number of the second lens, Vd3 is the Abbe number of the third lens, Vd5 is the Abbe number of the fifth lens, and Vd6 is the Abbe number of the sixth lens.

6. A telephoto lens according to claim 1, characterized in that: The first lens, the second lens, the third lens, the fifth lens, and the sixth lens satisfy the following: 1.522≤Nd1≤1.841, 1.485≤Nd2≤1.671, 1.427≤Nd3≤1.704, 1.572≤Nd5≤1.683, 1.518≤Nd6≤1.614; Wherein, Nd1 is the refractive index of the first lens, Nd2 is the refractive index of the second lens, Nd3 is the refractive index of the third lens, Nd5 is the refractive index of the fifth lens, and Nd6 is the refractive index of the sixth lens.

7. A telephoto lens according to claim 1, characterized in that: The total optical length of the lens is TTL, and the total focal length of the lens is EFL, satisfying: 0.508≤EFL / TTL≤0.

598.

8. A telephoto lens according to claim 1, characterized in that: The total optical length of the lens is TTL, and the image plane diameter of the lens is IH, satisfying: 0.142≤IH / TTL≤0.

176.

9. A telephoto lens according to claim 1, characterized in that: The total optical length of the lens is TTL, and the optical back focal length of the lens is OBFL, satisfying: 0.281≤OBFL / TTL≤0.

380.

10. A telephoto lens according to any one of claims 1 to 9, characterized in that: Along the lens optical axis from the object side to the image side, the following are also provided: An aperture stop is disposed on the image side of the second lens; A filter is disposed on the image-side surface of the sixth lens.

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