A long-focus athermal lens suitable for outdoor shooting of distant targets

Abstract

The application relates to the fields of long-focus athermalization design of optical systems and precise manufacturing technology of optical elements, and particularly relates to a long-focus athermalization lens for outdoor shooting of long-distance targets, the athermalization lens comprising a moving lens barrel, an outer lens barrel, a first lens group, a diaphragm and a second lens group; the first lens group, the diaphragm and the second lens group are sequentially arranged and coaxially arranged in the outer lens barrel; the first lens group is composed of four lenses, and the four lenses are sequentially a first lens, a second lens, a third lens and a fourth lens; the second lens group is composed of three lenses, and the three lenses are sequentially a fifth lens, a sixth lens and a seventh lens; the fifth lens and the sixth lens are arranged in the moving lens barrel, the moving lens barrel is arranged in the outer lens barrel and is in sliding connection with the outer lens barrel; and the sliding range of the moving lens barrel is between the diaphragm and the seventh lens. The lens provided by the application can adapt to severe outdoor scenes such as severe cold and high temperature, can meet the wide-range observation requirement from near (10 m) to far, and has high overall cost performance.

Description

Technical Field

[0001] This application relates to the field of thermally insulated design of optical systems and precision manufacturing technology of optical components, specifically to a thermally insulated (-40℃~80℃) telephoto (200mm) lens for outdoor shooting of distant targets. Background Technology

[0002] Telephoto lenses, with their long focal length and narrow field of view, enable high-magnification imaging of distant targets, finding wide application in outdoor surveillance, ecological observation, long-range photography, drone reconnaissance, border security, and industrial inspection. As image sensor resolution continues to improve and application environments become increasingly complex, telephoto lenses not only need high resolution and low distortion optical performance, but also require higher standards in terms of lightweight design, environmental adaptability, and focus control.

[0003] In terms of optical materials and aberration correction, telephoto lenses often use aspherical lenses or special low-dispersion glass to correct aberrations such as spherical aberration, coma, and field curvature. Aspherical lenses are difficult to manufacture and inspect, and special optical glass is expensive, hindering the widespread adoption of these lenses in general industrial or consumer applications. While using only glass spherical lenses could reduce manufacturing difficulty and cost, it requires careful allocation of optical power, optimization of lens curvature, and air gaps to achieve high resolution and low distortion optical performance. Especially at high spatial frequencies, the MTF value at the image edge is often difficult to guarantee, resulting in a significant decrease in edge image quality.

[0004] To achieve sharp images from close distance to infinity, existing telephoto lenses typically require a focusing mechanism. However, traditional retractable focusing mechanisms are prone to drawing in dust and moisture during focusing and retraction, exhibiting poor sealing and moisture protection. This makes them ill-suited for harsh conditions such as rain, humidity, and temperature fluctuations. Over time, this can lead to lens mold growth or circuit corrosion, reducing long-term reliability. Furthermore, retractable focusing mechanisms require moving all front element elements during focusing, resulting in significant element movement and consequently poor focusing accuracy and slow focusing response, making it difficult to achieve high-precision autofocus with current autofocus systems. In addition, traditional retractable focusing mechanisms cause a change in the overall length of the lens during focusing, altering the lens's center of gravity with the focusing distance and affecting handheld or mechanically fixed stability.

[0005] Furthermore, due to their long focal lengths and large apertures, telephoto lenses are often quite heavy, making them unsuitable for handheld shooting or mounting on lightweight gimbals, drones, and other platforms. Therefore, achieving lightweight, low-cost, and easily controllable telephoto lenses while ensuring image quality, environmental adaptability, and focusing performance has become a key technical challenge in this field. Summary of the Invention

[0006] The purpose of this application is to provide a telephoto lens without thermal distortion for outdoor shooting of distant targets, which can combine the advantages of lightweight, low cost and easy control while ensuring image quality, environmental adaptability and focusing performance.

[0007] To achieve the above objectives, this application provides a telephoto lens without thermal distortion suitable for outdoor shooting of distant targets. The telephoto lens without thermal distortion includes a movable lens barrel, an outer lens barrel, a first lens group, an aperture stop, and a second lens group. From the object side to the image side, the first lens group, aperture stop, and second lens group are arranged sequentially and coaxially within the outer lens barrel. The first lens group consists of four lenses for aberration correction of incident light. From the object side to the image side, the four lenses are, in order, a first lens, a second lens, a third lens, and a fourth lens. The first lens is a positive lens, the second lens is a positive lens, the third lens is a negative lens, and the fourth lens is a positive lens. The aperture stop is used to limit the amount of incident light passing through. The second lens group consists of five lenses for residual aberration correction of light passing through the first lens group and the aperture stop. From the object side to the image side, the five lenses are, in order, sub-lens one, sub-lens two, a sixth lens, sub-lens three, and sub-lens four. The first sub-lens is a positive lens, the second sub-lens is a negative lens, and the first and second sub-lens are cemented together to form the fifth lens, which is also a negative lens; the sixth lens is a negative lens; the third sub-lens is a positive lens, the fourth sub-lens is a negative lens, and the third and fourth sub-lens are cemented together to form the seventh lens, which is also a positive lens; the total number of lenses used to construct the telephoto athermalized lens is nine; the second lens group consists of three lenses, used to correct residual aberrations in light passing through the first lens group and the aperture stop; from the object side to the image side, the three lenses are, in sequence, the fifth, sixth, and seventh lenses; the fifth lens is a negative lens, the sixth lens is a negative lens, and the seventh lens is a positive lens; wherein, the fifth and sixth lenses are arranged at a preset fixed distance within a movable lens barrel, which is located within an outer lens barrel and slidably connected to the outer lens barrel; the sliding range of the movable lens barrel is between the aperture stop and the seventh lens.

[0008] In this embodiment, the first lens is an asymmetric biconvex positive lens, with the side having a smaller radius of curvature facing the object side; the first lens is made of wear-resistant, high-temperature resistant, and heat-insulating glass material; the first lens is made of a medium refractive index, low dispersion material, and its refractive index Nd1 and Abbe number Vd1 satisfy the following constraints: 1.60≤Nd1<1.70; 50<Vd1<70.

[0009] In this embodiment, the second lens is a meniscus lens with its convex surface facing the object side and its concave surface facing the image side; the second lens is made of a low refractive index, low dispersion material, and its refractive index Nd2 and Abbe number Vd2 satisfy the following constraints: 1.40≤Nd2<1.50; 80≤Vd2.

[0010] In this embodiment, the third lens is a meniscus negative lens, with its convex surface facing the object side and its concave surface facing the image side; the third lens is made of a high refractive index and high dispersion material, and its refractive index Nd3 and Abbe number Vd3 satisfy the following constraints: 1.75<Nd3≤1.90; Vd3≤30.

[0011] In this embodiment, the fourth lens is an asymmetric biconvex positive lens, with the side having a smaller radius of curvature facing the object side; the fourth lens is made of a medium refractive index, low dispersion material, and its refractive index Nd4 and Abbe number Vd4 satisfy the following constraints: 1.60 < Nd4 < 1.70; 50 < Vd4 < 70.

[0012] In this embodiment, the fifth lens is a cemented doublet meniscus negative lens, with its convex surface facing the object side and its concave surface facing the image side. The fifth lens includes a first sub-lens and a second sub-lens, both made of high refractive index and high dispersion material. The refractive index Nd51 and Abbe number Vd51 of the first sub-lens satisfy the constraints: 1.90 ≤ Nd51 < 2.00; Vd51 < 20. The refractive index Nd52 and Abbe number Vd52 of the second sub-lens satisfy the constraints: 1.95 ≤ Nd51 < 2.00; Vd51 < 20. 52; Vd52 < 30; The sixth lens is a meniscus negative lens, with its convex surface facing the object side and its concave surface facing the image side. The sixth lens is made of a medium refractive index, low dispersion material. The refractive index Nd6 and Abbe number Vd6 of the sixth lens satisfy the constraints: 1.55 ≤ Nd6 < 1.68; 50 < Vd6 < 65; The movable lens barrel and the outer lens barrel form a linear guide sliding pair along the axial direction. The axial position of the outer lens barrel remains fixed, and the circumferential limit of the movable lens barrel restricts its rotational degree of freedom.

[0013] In this embodiment, the seventh lens is a cemented doublet meniscus lens, with its convex surface facing the object side and its concave surface facing the image side. The seventh lens includes sub-lens three and sub-lens four. Sub-lens three is made of a high-refractive-index, medium-dispersion material, and the refractive index Nd71 and Abbe number Vd71 of sub-lens three satisfy the constraints: 1.70 < Nd71 < 1.80; 44 < Vd71 ≤ 50. Sub-lens four is made of a medium-refractive-index, high-dispersion material, and the refractive index Nd72 and Abbe number Vd72 of sub-lens four satisfy the constraints: 1.60 < Nd72 < 1.70; 20 < Vd72 < 40. The incident angle of light rays exiting from the seventh lens to the image plane is less than 5°.

[0014] In this embodiment, the athermalization temperature range of the telephoto athermalization lens is -40℃ to 80℃; the fifth lens (5) and the seventh lens (7) are both cemented doublet lenses, the fifth lens (5) includes sub-lens one (51) and sub-lens two (52), and the seventh lens (7) includes sub-lens three (71) and sub-lens four (72); within the temperature range of -40℃ to 80℃, the coefficient of thermal expansion of the first lens (1) is 6.5*10. -6 The coefficient of thermal expansion of the second lens (2) is 12.7*10 mm / ℃. -6 The coefficient of thermal expansion of the third lens (3) is 8.4*10 mm / ℃. -6 The coefficient of thermal expansion of the fourth lens (4) is 8.0 mm / ℃. -6 mm / ℃, the coefficient of thermal expansion of sub-lens one (51) is 6.0*10 mm / ℃. -6 The coefficient of thermal expansion of sub-lens two (52) is 7.0 mm / ℃. -6 The coefficient of thermal expansion of the sixth lens (6) is 6.5 mm / ℃. -6 The coefficient of thermal expansion of sub-lens three (71) is 5.5*10 mm / ℃. -6 The coefficient of thermal expansion of sub-lens four (72) is 9.1*10 mm / ℃. -6 mm / ℃; the coefficient of thermal expansion of the aperture, the movable lens barrel, and the outer lens barrel is all 23.6*10 mm / ℃. -6 mm / ℃.

[0015] In this embodiment of the application, the F-number range of the telephoto non-thermalized lens is: 2 < F < 6.

[0016] In the embodiments of this application, the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens, and the seventh lens are all glass spherical lenses.

[0017] The solution provided in this application has at least the following beneficial effects:

[0018] 1) The telephoto anechoic lens provided in this application can achieve anechoicity over a wide temperature range based on optical passive anechoicity technology. It has strong environmental adaptability and its working temperature covers an ultra-wide temperature range of -40℃ to 80℃. No additional focusing compensation is required in high and low temperature environments. The internal optical structure of the lens can automatically offset the focal length drift and focus shift caused by thermal expansion and contraction. It can maintain clear and stable imaging in harsh outdoor scenarios such as extreme cold and high temperature.

[0019] 2) All seven lenses are made of glass spherical lenses, which have better thermal stability and anti-aging properties than plastic lenses. Compared with aspherical lenses, they are simpler to manufacture and cheaper. With the heat-free design, the optical performance degradation is extremely low during long-term outdoor service, resulting in a longer service life and lower maintenance costs.

[0020] 3) Equipped with an independent focusing group, it can accurately complete the focusing adjustment from close distance (10m) to long distance (object infinity). At a telephoto of 200mm, it can clearly image distant monitoring targets and also meet the needs of medium and close distance detail observation. The focusing travel is controllable and the positioning is accurate, and it is not easy to have focus drift or blurry focus.

[0021] Other features and advantages of the embodiments of this application will be described in detail in the following detailed description section. Attached Figure Description

[0022] The accompanying drawings are provided to further illustrate the embodiments of this application and form part of the specification. They are used together with the following detailed description to explain the embodiments of this application, but do not constitute a limitation on the embodiments of this application. In the drawings: Figure 1 The schematic diagram illustrates the structure and distribution of each lens element in a telephoto athermalized lens; Figure 2 This is the optical path diagram of the telephoto athermalized lens in this embodiment when the working distance is infinity. Figure 3 The MTF chart of the telephoto anechoic lens in this embodiment was measured at 20°C and at an infinite working distance. Figure 4 The MTF chart of the telephoto anechoic lens in this embodiment was measured at -40°C and at an infinite working distance. Figure 5 The MTF chart of the telephoto anechoic lens in this embodiment was measured at 80°C and at an infinite working distance. Figure 6 This is a positional chromatic aberration distribution diagram of the telephoto anechoic lens at infinity working distance in this embodiment; Figure 7 This is a distortion diagram measured at infinity working distance of the telephoto athermalized lens in this embodiment; Figure 8 This is a relative illumination map measured at infinity working distance of the telephoto athermal lens in this embodiment.

[0023] Explanation of reference numerals in the attached figures 1. First lens; 2. Second lens; 3. Third lens; 4. Fourth lens; 5. Fifth lens; 51. Sub-lens one; 52. Sub-lens two; 6. Sixth lens; 7. Seventh lens; 71. Sub-lens three; 72. Sub-lens four. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for illustration and explanation of the embodiments of this application and are not intended to limit the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0025] It should be noted that if the embodiments of this application involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0026] Furthermore, if the embodiments of this application involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, features defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed in this application.

[0027] Example 1

[0028] like Figure 1 As shown, this embodiment provides a telephoto lens without thermal distortion suitable for outdoor shooting of distant targets. The telephoto lens without thermal distortion includes a movable lens barrel, an outer lens barrel, a first lens group, an aperture stop, and a second lens group. The above structure of the lens is described in detail below: From the object side to the image side, the first mirror group, the aperture, and the second mirror group are arranged sequentially and coaxially inside the outer tube; during installation, it is necessary to ensure that the optical axis and the physical central axis of the tube are aligned and coincident as much as possible.

[0029] The first lens group consists of four lenses used to correct aberrations in the incident light. From the object side to the image side, the four lenses are, in order, lens 1, lens 2, lens 3, and lens 4. Lens 1 is a positive lens, lens 2 is a positive lens, lens 3 is a negative lens, and lens 4 is a positive lens. The first lens group is mainly used for light collection, supporting the principal focal length of the system, and performing primary aberration correction. As mentioned above, the first lens group mainly consists of positive power lenses, and the entire first lens group has positive power. This allows the large-diameter incident parallel beam to be compressed inward, reducing the originally large-diameter incident beam to a narrow beam before reaching the aperture stop. Based on this, a compact structure can be used to achieve a long focal length (i.e., a short-barrel long focal length structure), meeting the miniaturization design requirements of telephoto lenses.

[0030] Specifically, the first lens 1 is an asymmetric biconvex positive lens, with its side having a smaller radius of curvature facing the object side to collect incident light and provide positive optical power. The first lens 1 is made of a wear-resistant, high-temperature-resistant, and heat-insulating glass material (such as hard crown glass). Its wear-resistant and high-temperature-resistant properties allow it to be directly exposed to harsh environments, protecting the delicate optical glass behind it. Its heat-insulating properties also slow down the transmission of drastic external temperature changes to the lens interior, serving as the first line of defense for thermal stability. The first lens 1 is made of a medium refractive index, low dispersion material. For example, its refractive index Nd1 and Abbe number Vd1 satisfy the constraints: 1.60 ≤ Nd1 < 1.70; 50 < Vd1 < 70. As a positive lens, the use of a low-dispersion material in the first lens 1 can control chromatic aberration at its source. The medium refractive index combined with the asymmetric biconvex shape allows it to handle optical power with a relatively gentle curvature, which is beneficial for correcting spherical aberration.

[0031] The second lens 2 is a meniscus positive lens, with its convex surface facing the object side and its concave surface facing the image side; the third lens 3 is a meniscus negative lens, with its convex surface facing the object side and its concave surface facing the image side. For example, the refractive index Nd2 and Abbe number Vd2 of the second lens 2 satisfy the following constraints: 1.40 ≤ Nd2 < 1.50; 80 ≤ Vd2; the refractive index Nd3 and Abbe number Vd3 of the third lens 3 satisfy the constraints: 1.75 < Nd3 ≤ 1.90; Vd3 ≤ 30. From these constraints, it can be seen that the second lens 2 is made of a low-refractive-index, low-dispersion material (such as crown glass), which can be used for preliminary chromatic aberration correction; the third lens 3 is made of a high-refractive-index, high-dispersion material (such as flint), which is used to smooth the optical angle of incidence and bear a large contribution from spherical aberration. Meanwhile, the second lens 2 and the third lens 3 form an achromatic combination. The low dispersion of the second lens 2 (producing positive chromatic aberration) and the high dispersion of the third lens 3 (producing negative chromatic aberration) cancel each other out, effectively correcting axial chromatic aberration. In addition, the high refractive index of the third lens 3 effectively reduces the Petzval field curvature, helping to obtain a flat image plane. With one positive and one negative optical power, and one low and one high refractive index, they produce opposite spherical aberration and coma, which cancel each other out, effectively improving the beam quality passing through the first three lenses.

[0032] The aforementioned fourth lens 4 is an asymmetric biconvex positive lens, with its side having a smaller radius of curvature facing the object side. The refractive index Nd4 and Abbe number Vd4 of the fourth lens 4 satisfy the following constraints: 1.60 < Nd4 < 1.70; 50 < Vd4 < 70. As the last lens before the aperture stop, the fourth lens 4 is made of a medium refractive index, low dispersion material. Low dispersion materials typically also mean that their temperature coefficient of refractive index is extremely small. This ensures that the defocusing amount caused by the change in the refractive index of the material in the preceding lens group due to temperature is kept to a very low level, which is a prerequisite for the precise operation of the following lens group.

[0033] The aforementioned aperture stop is used to limit the amount of incident light passing through to the second lens group. The aperture size (i.e., F-number) can be changed by adjusting the aperture size of the aperture stop. In this embodiment, the adjustable range of the F-number is: 2 < F < 6.

[0034] The second lens group consists of three lenses: a fifth lens (5), a sixth lens (6), and a seventh lens (7). It is used to correct residual aberrations in light rays passing through the first lens group and the aperture stop. From the object side to the image side, the three lenses are arranged sequentially as follows: fifth lens 5, sixth lens 6, and seventh lens 7. Fifth lens 5 is a negative lens, sixth lens 6 is a negative lens, and seventh lens 7 is a positive lens. Fifth lens 5 and sixth lens 6 are positioned at a predetermined fixed interval within a movable lens barrel, which is located within an outer lens barrel and slidably connected to it. The sliding range of the movable lens barrel is between the aperture stop and the seventh lens 7. In the second lens group, the three lenses form a negative-negative-positive configuration, enabling a relay of optical power from the preceding lens group: the preceding (positive) lens group converges the image; the following lens group (negative-negative) extends the focal length and reduces the overall length; and the following (positive) lens group (fine-tuning) corrects the image field and controls the exit pupil. The fifth lens 5 and the sixth lens 6 constitute the focusing group of the system, providing a focusing range from infinity to 10 meters. The focusing group has a low light altitude in the optical path (close to the image plane, with small light altitude at the on-axis edge), and its movement contributes little to the overall focal length, placing it in a position insensitive to focal length. However, even a small movement can significantly change the image distance, meeting focusing requirements. In this embodiment, the focusing group is an internal focusing system, which prevents external dust and moisture from being drawn into the lens during focusing, meeting the lens's waterproof and moisture-proof outdoor requirements. Simultaneously, internal focusing does not change the lens length. When used in conjunction with the autofocus system for autofocus, the center of gravity remains locked near the camera body, preventing the camera's center of gravity from shifting due to focusing, resulting in more reliable stability. Furthermore, compared to external focusing, internal focusing only moves two internal lenses. The motor can drive it with very little current and extremely high speed, requiring less power and enabling rapid focusing response. The seventh lens 7 is used to balance the aberrations introduced by the focusing group and to smoothly guide light into the image plane for final imaging.

[0035] For example, the fifth lens 5 is a cemented doublet meniscus negative lens, with its convex surface facing the object side and its concave surface facing the image side. As the first lens behind the aperture stop, its cemented doublet structure is an active corrector for chromatic aberration. As a moving lens group, it can simultaneously change the convergence of different colors of light on and off-axis as it moves with the moving lens barrel.

[0036] Specifically, the fifth lens 5 includes sub-lens 1 51 and sub-lens 2 52. Sub-lens 1 51 is a biconvex positive lens with a refractive index Nd51 and Abbe number Vd51 satisfying the constraints: 1.90 ≤ Nd51 < 2.00; Vd51 < 20. Sub-lens 2 52 is a biconcave negative lens with a refractive index Nd52 and Abbe number Vd52 satisfying the constraints: 1.95 ≤ Nd52; Vd52 < 30. That is, both sub-lens 1 51 and sub-lens 2 52 are made of high-refractive-index, high-dispersion materials. The high refractive index allows for a gentler curvature of the meniscus negative lens, which helps reduce higher-order aberrations. The bonding of the two high-refractive-index materials efficiently achieves the negative optical power required for the telephoto structure. High-dispersion materials typically have a more pronounced negative refractive index temperature coefficient, meaning that as the temperature increases, the refractive index of the fifth lens 5 decreases, and its negative optical power weakens, which precisely offsets the focal shift caused by the expansion of the front positive lens and the lens barrel.

[0037] The sixth lens 6 is a meniscus negative lens, with its convex surface facing the object side and its concave surface facing the image side. The refractive index Nd6 and Abbe number Vd6 of the sixth lens 6 satisfy the constraints: 1.55≤Nd6<1.68; 50<Vd6<65; that is, the sixth lens 6 is made of a medium refractive index, low dispersion material. The sixth lens 6 itself provides negative optical power as a meniscus negative lens, and the use of a low dispersion material means that its contribution to chromatic aberration is small. At the same time, the sixth lens 6 plays a role in smoothing the beam transition between the preceding high refractive index negative lens and the following cemented doublet positive lens, avoiding large higher-order aberrations caused by abrupt changes in the light angle.

[0038] Preferably, the focusing curve of the aforementioned focusing group is linear, meaning that the displacement of the focusing group has a linear relationship with the reciprocal of the object distance (or the focusing ring rotation angle). For the lens to produce a sharp image, it must satisfy the Gaussian equation: In the formula, Indicates the lens focal length; Indicates object distance; The image distance is indicated by the focal length. When the focal length remains constant but the object distance changes, the image distance needs to be adjusted to match the object distance. As mentioned earlier, in this embodiment, the image distance can be changed by altering the position of the focusing group. When the focusing curve of the focusing group is linear, the focusing operation becomes simpler, the control more convenient, the focusing more precise, and the imaging effect better. Specifically, to ensure that the focusing curve is linear, in this embodiment, the moving lens barrel and the outer lens barrel form a linear guide sliding pair along the axial direction. The axial position of the outer lens barrel remains fixed, and the circumferential limit of the moving lens barrel restricts its rotational freedom. For example, the rotational motion can be converted to linear motion by relying on a focusing cam and a guide pin structure. The specific connection scheme is as follows: the focusing cam is circumferentially rotatable and axially limited, and is loosely fitted around the outer circumference of the outer lens barrel. The outer wall of the focusing cam is fixedly connected to the focusing ring, and the inner wall is provided with a spiral cam groove extending circumferentially. The axial position of the outer lens barrel is fixed, and multiple axial straight guide grooves parallel to the optical axis of the lens are opened on the barrel wall. Several guide pins are fixed on the outer wall of the movable lens barrel. The guide pins pass through the axial straight guide grooves from the inside to the outside and slide into the spiral cam grooves. The outer lens barrel restricts the circumferential rotational freedom of the movable lens barrel through the axial straight guide grooves, so that the movable lens barrel can only translate axially along the optical axis. When the rotating focusing ring drives the focusing cam to rotate around the optical axis, the spiral cam groove drives the guide pins to slide along the axial straight guide grooves, thereby driving the movable lens barrel to realize the focusing feed motion.

[0039] For example, in this embodiment, the seventh lens 7 is a cemented doublet meniscus lens, with its convex surface facing the object side and its concave surface facing the image side. The seventh lens 7 includes sub-lens three 71 and sub-lens four 72. Sub-lens three 71 is a biconvex positive lens, and its refractive index Nd71 and Abbe number Vd71 satisfy the constraints: 1.70 < Nd71 < 1.80; 44 < Vd71 ≤ 50. Sub-lens four 72 is a biconcave negative lens, and its refractive index Nd72 and Abbe number Vd72 satisfy the constraints: 1.60 < Nd72 < 1.70; 20 < Vd72 < 40. From the above constraints, it can be seen that sub-lens three 71 is made of a high refractive index, medium dispersion material, and its high refractive index is beneficial for flat field; sub-lens four 72 is made of a medium refractive index, high dispersion material, and its high dispersion is used to correct chromatic aberration and thermal aberration. As the last lens in the lens group, and located after the moving group, it must receive and process the changing light beams from the moving group. The design of the cemented doublet positive lens provides strong off-axis aberration correction capabilities (such as astigmatism, distortion, and chromatic aberration), balancing the aberrations introduced by the focusing moving group and ensuring excellent image quality at the image edges regardless of the moving group's position within the moving range. Simultaneously, the seventh lens element (7) allows light to smoothly enter the image plane, resulting in an incident angle of less than 5 degrees for the light rays exiting the image plane (i.e., the image-side principal ray angle (CRA)).

[0040] Example 2

[0041] The moving group in Embodiment 1 above is mainly used to achieve focusing, ensuring that the subject is clear and sharp, rather than to compensate for focus drift caused by temperature changes. The ability to achieve heat-free focusing relies primarily on the combination of internal and external optical structures and materials that can automatically offset focus drift and shift caused by thermal expansion and contraction.

[0042] For example, in this embodiment, the coefficient of thermal expansion (within the temperature range of -40℃ to 80℃) of the materials used in the structure such as the lens and outer lens barrel in Embodiment 1 and other basic parameters of each lens are listed for reference. The overall weight of the lens is approximately 919 grams.

[0043] For example, within a temperature range of -40℃ to 80℃, the coefficient of thermal expansion of the first lens 1 is 6.5*10. - 6 The coefficient of thermal expansion of the second lens 2 is 12.7*10 mm / ℃. -6 The coefficient of thermal expansion of the third lens 3 is 8.4*10 mm / ℃. -6 The coefficient of thermal expansion of the fourth lens 4 is 8.0*10 mm / ℃. -6 The coefficient of thermal expansion of the sub-lens 51 is 6.0 mm / ℃. -6 The coefficient of thermal expansion of the sub-lens 52 is 7.0*10 mm / ℃. -6 The coefficient of thermal expansion of the sixth lens (6) is 6.5*10 mm / ℃. -6 The coefficient of thermal expansion of the sub-lens 71 is 5.5*10 mm / ℃. -6 The coefficient of thermal expansion of the sub-lens 472 is 9.1*10 mm / ℃. -6 mm / ℃; the coefficient of thermal expansion of the aperture, the movable lens barrel, and the outer lens barrel is all 23.6*10 mm / ℃. -6 mm / ℃.

[0044] For example, the basic parameters of each lens element in the telephoto athermalized lens provided in this embodiment are shown in Table 1 below, where the units for radius of curvature and air gap are millimeters (mm). Note: 1) All radii of curvature (the larger the radius of curvature, the smaller the curvature), lens center thickness, and air gap are normalized values; 2) The positive and negative signs of the lens radius of curvature are uniformly consistent with the rules of geometric optics symbols.

[0045] Table 1 Mirror number radius of curvature Lens center thickness / air gap Refractive index Abbe number S1 101.685 2.5 1.6228 56.91 S2 -306.7 0.5 1.00 AIR S3 36.27 4.25 1.497 81.6 S4 175.895 0.53 1.00 AIR S5 INF 3.62 1.8467 23.79 S6 58.5975 19.2 1.00 AIR S7 65.855 2.95 1.6679 55.51 S8 -374.69 2 1.00 AIR S9 (Aperture) INF 3 1.00 AIR S10 95.93 3.965 1.94595 17.94 S11 -47.265 2.75 2.0007 25.43 S12 61.095 29.045 1.00 AIR S13 87.965 2.5 1.6228 56.91 S14 15.085 6.21 1.00 AIR S15 19.48 2.75 1.743 49.22 S16 -30.965 2.5 1.6889 31.16 S17 48.31 19.6 1.00 AIR

[0046] In Table 1, the lens surface numbers S1~S17 and Figure 1The numbers S1 to S17 correspond to the following. S9 represents the aperture stop. The value of "lens center thickness / air gap" corresponding to S1 indicates the interval between S1 and S2. In other words, the value of "lens center thickness / air gap" for each lens number represents the distance from the current lens to the next lens. This value may represent the lens center thickness or the air gap; you can check the specifics by comparing them. Figure 1 Please confirm with Table 1. The refractive index corresponding to S1 is the refractive index of the first lens 1. That is, the refractive index value corresponding to each lens number represents the refractive index of the medium (which may be a lens or air) between the current lens and the next lens. In the refractive index correspondence list, the value of 1.00 corresponds to the refractive index of air; correspondingly, the Abbe number corresponding to S1 is the Abbe number of the first lens 1. That is, the Abbe number value corresponding to each lens number represents the Abbe number of the medium (which may be a lens or air) between the current lens and the next lens. Note: Since air has almost no actual dispersion effect, Table 1 does not give specific values ​​for the Abbe number of air, and all are represented by "AIR".

[0047] Special Notes: 1) The lens center thickness / air gap value corresponding to the last mirror S17 represents the distance from mirror S17 to the image plane; 2) Since the fifth mirror 5 and the sixth mirror 6 belong to the moving group, the distance between the fourth mirror 4 and the fifth mirror 5 (data corresponding to S9) and the distance between the sixth mirror 6 and the seventh mirror 7 (data corresponding to S14) are not fixed. Figure 1 The data in the table represents the initial spacing values ​​under the default conditions.

[0048] Furthermore, in Embodiment 1, the first lens 1, the second lens 2, the third lens 3, the fourth lens 4, the fifth lens 5, the sixth lens 6, and the seventh lens 7 can all be glass spherical lenses to reduce manufacturing costs.

[0049] This embodiment also verifies the imaging effect of the aforementioned telephoto athermalized lens. Figure 2 The light path diagram when the lens is at infinity (the incident light rays are approximately parallel); Figure 3 The MTF chart is measured at 20°C and at an infinite working distance. Figure 4 The MTF chart is measured at -40℃ and at an infinite working distance. Figure 5 The MTF chart is measured at 80°C and at an infinite working distance. Figure 6 A positional chromatic aberration distribution diagram when the lens is at infinity working distance; Figure 7 The distortion diagram measured when the lens is at infinity working distance; Figure 8 This is a relative illumination map measured when the lens is at infinity working distance.

[0050] Figure 2In the image, lines of different colors represent the light paths of light of different wavelengths passing through the lens assembly. The blue line represents the reference light path (object-side incident field of view is 0°, parallel light incidence). The object-side incident field of view for the green, red, yellow, and magenta lines increases sequentially. Therefore, on the image side, the convergence points of the green, red, yellow, and magenta lines are arranged sequentially above the convergence point of the blue line. Figure 2 As can be seen, light of the same wavelength and the same field of view will converge to the same point on the image plane no matter where it enters the lens group, and the convergence points of light of different wavelengths are almost on the same plane (i.e., the image plane), indicating that the lens group of this application has good axial chromatic aberration correction capability.

[0051] Furthermore, Figure 6 The positional chromatic aberration distribution diagram shown can be used to further verify the lens's axial chromatic aberration correction capability. The horizontal axis represents focus shift (unit: μm), and the vertical axis represents wavelength (unit: μm). In this embodiment, the focus shift corresponding to each wavelength of light passing through the lens to achieve clear imaging was measured within a continuous wavelength range from 0.486µm (F light, blue) to 0.6563µm (C light, red). The maximum permissible focus shift under single-sided diffraction limit is 38.733μm (this value is determined based on the Rayleigh criterion), derived from... Figure 6 It can be seen that within the 0.486µm~0.6563µm band, the focal shift corresponding to most wavelengths (approximately 0.500µm~0.6563µm) is within the maximum allowable focal shift in the diffraction limit (38.733µm). Figure 2 This corroborates each other, demonstrating that the lens provided in this embodiment has good axial chromatic aberration correction capability over a wide wavelength range.

[0052] Figure 3 , Figure 4 and Figure 5The MTF chart shown is a multi-color composite white light MTF. The horizontal axis represents spatial frequency (Hz / mm), and the vertical axis represents the OTF modulus. The F-number is 4. The wavelength range used for MTF calculation is 0.4861μm to 0.6563μm, which is the standard correction band for lens chromatic aberration and includes the dominant sensitivity wavelength of the human eye at 0.587562μm (d light). The three MTF charts visually demonstrate the imaging reproduction capabilities of the telephoto anechoic lens at normal temperature (20℃) and extreme outdoor temperatures (-40℃, 80℃) at infinity. The different colored curves in the figure correspond to the MTF curves measured at different field-of-view positions on the image plane (sensor plane). The solid black line represents the theoretical upper limit of the performance of an ideal optical system (limited only by physical diffraction) in the meridional direction, and the dashed black line represents the theoretical upper limit of the performance of an ideal optical system (limited only by physical diffraction) in the sagittal direction (since it is an ideal state, the dashed black line (sagittal direction) coincides with the straight black line (meridian direction)). The distance from the center of the image plane to the field-of-view positions corresponding to the blue, green, red, yellow, and magenta curves gradually increases. Figure 3 For example, the solid green line curve corresponding to 5.75mm-Tangential represents the MTF curve measured along the meridian direction at a point 5.75mm outward from the center of the image plane, while the dashed green line curve corresponding to 5.75mm-Sagittal represents the MTF curve measured along the sagittal direction at the same point 5.75mm outward from the center of the image plane. Figure 3 , Figure 4 and Figure 5 As can be seen, the telephoto anechoic lens provided in this embodiment achieves an OTF value of over 0.9 at low frequencies (around 10 lp / mm) (reflecting overall contour contrast) and an OTF value of over 0.7 at high frequencies (around 50 lp / mm) (characterizing detail resolution) at temperatures of 20℃, -40℃, and 80℃, indicating that the lens possesses high-quality imaging output capabilities within a temperature range of -40℃ to 80℃. Furthermore, comparing the three MTF charts, in most cases, the T (meridian) and S (sagittal) curves for the same field of view (same color) at the three temperatures remain consistent, proving that the lens provided in this embodiment possesses excellent anechoic performance.

[0053] In this embodiment, Figure 7 This is a distortion graph of the lens, with the horizontal axis representing the distortion rate (%) and the vertical axis representing the image height value (unit: mm). The distortion rate is calculated using the formula: Distortion rate = [(actual image height - ideal image height) / ideal image height] × 100%; a positive value indicates pincushion distortion (image convex), while a negative value indicates barrel distortion (image concave). Figure 7In the image, the blue, green, and red curves correspond to the distortion curves for blue light (F-light 486.1nm), green light (d-light 587.6nm), and red light (C-light 656.3nm), respectively. The close alignment of these three curves indicates that the lens has no significant transverse chromatic aberration. Within the image height range of 0~11.5mm, the lens's maximum distortion rate is -0.100% (the green d-light curve represents the lens's primary imaging distortion; industry standards generally use green light as the benchmark for distortion), which is far less than the industrial testing standard for lenses (within ±1.5%), meeting the expected standards.

[0054] Relative illumination describes the degree of brightness decay from the center of the image to the edge of the field of view, reflecting the ratio of light intensity to the image surface of each field of view. Figure 8 The relative illumination diagram shown uses image height (mm) on the horizontal axis and relative illumination (%) on the vertical axis. Within the image height range of 0 to 11.5, the relative illumination remains close to 1. This indicates that the image brightness within this range is almost perfectly uniform, without any attenuation, ensuring uniform brightness from the center to the edges of the captured image. Furthermore, this relative illumination diagram was measured using commonly used d-light (0.587562μm) as the reference light. At different wavelengths, due to factors such as chromatic aberration, the relative illumination performance of the lens may vary slightly.

[0055] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0056] The above are merely embodiments of this application and are not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A telephoto lens without pyrolysis suitable for outdoor shooting of distant targets, characterized in that, The telephoto athermal lens includes a movable lens barrel, an outer lens barrel, a first lens group, an aperture stop, and a second lens group; from the object side to the image side, the first lens group, the aperture stop, and the second lens group are arranged sequentially and coaxially inside the outer lens barrel; The first lens group consists of four lenses, which are used to correct aberrations of the incident light. From the object side to the image side, the four lenses are the first lens (1), the second lens (2), the third lens (3), and the fourth lens (4) in sequence. Among them, the first lens (1) is a positive lens, the second lens (2) is a positive lens, the third lens (3) is a negative lens, and the fourth lens (4) is a positive lens. The aperture is used to limit the amount of incident light passing through; The second lens group consists of five lenses, used to correct residual aberrations in light rays passing through the first lens group and the aperture stop; from the object side to the image side, the five lenses are, in order, sub-lens one (51), sub-lens two (52), sixth lens (6), sub-lens three (71) and sub-lens four (72); sub-lens one (51) is a positive lens, sub-lens two (52) is a negative lens, sub-lens one (51) and sub-lens two (52) are cemented together to form the fifth lens (5), the fifth lens (5) is a negative lens; the sixth lens (6) is a negative lens; sub-lens three (71) is a positive lens, sub-lens four (72) is a negative lens, sub-lens three (71) and sub-lens four (72) are cemented together to form the seventh lens (7), the seventh lens (7) is a positive lens; The total number of lenses used to constitute the telephoto athermalized lens is nine; Among them, the fifth lens (5) and the sixth lens (6) are arranged in the movable lens tube at a preset fixed distance. The movable lens tube is arranged in the outer lens tube and is slidably connected to the outer lens tube. The sliding range of the movable lens tube is between the aperture stop and the seventh lens (7).

2. The telephoto lens without pyrolysis according to claim 1, characterized in that, The first lens (1) is an asymmetric biconvex positive lens, with the side with the smaller radius of curvature facing the object; the first lens (1) is made of wear-resistant, high-temperature resistant and heat-insulating glass material.

3. The telephoto non-heating lens according to claim 1, characterized in that, The second lens (2) is a meniscus lens, with its convex surface facing the object side and its concave surface facing the image side; the refractive index Nd2 and Abbe number Vd2 of the second lens (2) satisfy the following constraints: 1.40≤Nd2<1.50; 80≤Vd2.

4. The telephoto lens without pyrolysis according to claim 1, characterized in that, The third lens (3) is a meniscus negative lens, with its convex surface facing the object side and its concave surface facing the image side; the refractive index Nd3 and Abbe number Vd3 of the third lens (3) satisfy the following constraints: 1.75 < Nd3 ≤ 1.90; Vd3≤30.

5. The telephoto non-heating lens according to claim 1, characterized in that, The fourth lens (4) is an asymmetric biconvex positive lens, with its side having a smaller radius of curvature facing the object side; the refractive index Nd4 and Abbe number Vd4 of the fourth lens (4) satisfy the following constraints: 1.60 < Nd4 < 1.70; 50 < Vd4 < 70.

6. The telephoto non-heating lens according to claim 1, characterized in that, The fifth lens (5) is a cemented doublet meniscus negative lens, with its convex surface facing the object side and its concave surface facing the image side; the sixth lens (6) is a meniscus negative lens, with its convex surface facing the object side and its concave surface facing the image side; the movable lens barrel and the outer lens barrel form a linear guide sliding pair along the axial direction, the axial position of the outer lens barrel remains fixed, and the movable lens barrel is circumferentially limited to restrict the rotational degree of freedom.

7. The telephoto lens without thermal distortion according to claim 1, characterized in that, The seventh lens (7) is a cemented doublet meniscus lens, with its convex surface facing the object side and its concave surface facing the image side; the incident angle of the light rays emitted from the seventh lens (7) to the image surface is less than 5°.

8. The telephoto lens without pyrolysis according to claim 1, characterized in that, The athermal temperature range of the telephoto athermal lens is -40℃ to 80℃; the fifth lens (5) and the seventh lens (7) are both cemented doublet lenses, the fifth lens (5) includes sub-lens one (51) and sub-lens two (52), and the seventh lens (7) includes sub-lens three (71) and sub-lens four (72); within the temperature range of -40℃ to 80℃, the coefficient of thermal expansion of the first lens (1) is 6.5*10. -6 The coefficient of thermal expansion of the second lens (2) is 12.7*10 mm / ℃. -6 The coefficient of thermal expansion of the third lens (3) is 8.4*10 mm / ℃. -6 The coefficient of thermal expansion of the fourth lens (4) is 8.0 mm / ℃. -6 mm / ℃, the coefficient of thermal expansion of sub-lens one (51) is 6.0*10 mm / ℃. -6 The coefficient of thermal expansion of sub-lens two (52) is 7.0 mm / ℃. -6 The coefficient of thermal expansion of the sixth lens (6) is 6.5 mm / ℃. -6 The coefficient of thermal expansion of sub-lens three (71) is 5.5*10 mm / ℃. -6 The coefficient of thermal expansion of sub-lens four (72) is 9.1*10 mm / ℃. - 6 mm / ℃; the coefficient of thermal expansion of the aperture, the movable lens barrel, and the outer lens barrel is all 23.6*10 mm / ℃. -6 mm / ℃.

9. The telephoto lens without pyrolysis according to claim 1, characterized in that, The F-number range of the telephoto non-thermalized lens is: 2 < F < 6.

10. The telephoto lens without thermal distortion according to any one of claims 1 to 9, characterized in that, The first lens (1), the second lens (2), the third lens (3), the fourth lens (4), the fifth lens (5), the sixth lens (6) and the seventh lens (7) are all glass spherical lenses.

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