A continuous zoom infrared lens, lens module

Abstract

The application belongs to the field of infrared optical technology and discloses a continuous zooming infrared lens and a lens module. The lens comprises a first lens, a second lens, a third lens, a fourth lens and a fifth lens which are arranged along an optical axis from an object side to an image side. The first lens is a convex meniscus positive lens, the second lens is a double-concave lens, the third lens is a double-convex lens, the fourth lens is a convex meniscus negative lens and the fifth lens is a double-convex lens. The continuous zooming of the infrared lens is realized by driving the second lens and the third lens to move along the same optical axis. The application can continuously and adjustably change between wide and narrow fields of view, the focal length can be continuously changed, the continuous zooming with a large zoom ratio can be realized, there are only five lenses with optical power in the overall structure, the structure is relatively simple, the image quality is excellent and the target surface is large.

Description

Technical Field

[0001] This technology belongs to the field of infrared optical technology, and specifically relates to a continuous zoom infrared lens and lens module. Background Technology

[0002] Infrared lenses are widely used in military and security fields due to their advantages such as clear imaging in adverse weather conditions and all-day operation. Compared with fixed-focus and range-shift lenses, continuous zoom infrared lenses can capture targets in a wide field of view and then adjust to a narrow field of view to aim and track them after detection. Furthermore, during focal length and field of view transitions, they can maintain the continuity of the image of the observed target on the detector surface. This is beneficial for searching and tracking high-speed moving targets and solves the defect of range-shift zoom lenses that are prone to losing high-speed targets when switching fields of view.

[0003] However, changes in ambient temperature can alter the refractive index and surface curvature of infrared lenses, leading to blurred images and target loss in fields such as infrared guidance and tracking. To eliminate the degradation in image quality caused by temperature changes, compensation techniques are typically employed to maintain good image quality over a wide temperature range; this technique is known as athermalization. Currently, athermalization techniques are mainly categorized into optical athermalization, active mechanical athermalization, and passive mechanical athermalization. Optical and passive athermalization techniques generally require more lenses, resulting in more complex systems and larger volumes.

[0004] To improve the ability of infrared devices to detect and identify targets, it is often desirable for infrared lenses to have a longer focal length. However, when using long-focal-length imaging, it is difficult to simultaneously meet the requirements for athermalization and image quality, making it difficult to obtain high-quality optical imaging. Furthermore, existing common long-wave infrared zoom systems generally have relatively small zoom ratios (e.g., below 5x), and most of them use small-area camera modules, resulting in relatively low resolution (e.g., 640×480, 25μm). Summary of the Invention

[0005] To address the above problems, one objective of this invention is to provide a continuous zoom infrared lens, the specific technical solution of which is as follows:

[0006] A continuous zoom infrared lens includes a first lens, a second lens, a third lens, a fourth lens, and a fifth lens arranged sequentially along the optical axis from the object side to the image side; the first lens is a meniscus positive lens with its convex surface facing the object side, the second lens is a biconcave lens, the third lens is a biconvex lens, the fourth lens is a meniscus negative lens with its convex surface facing the image side, and the fifth lens is a biconvex lens; continuous zoom of the infrared lens is achieved by driving the second and third lenses to move along the same optical axis.

[0007] Furthermore, the first lens, second lens, third lens, fourth lens, and fifth lens are all made of germanium single crystal.

[0008] Furthermore, the object-side surfaces of the fourth lens and the fifth lens are aspherical and satisfy the aspherical formula:

[0009]

[0010] Where Z is the distance vector from the vertex of the aspherical surface at a height r along the optical axis; c = 1 / R; R is the paraxial curvature fitting radius of the mirror; k is the conic coefficient; A, B, C, D, and E are higher-order aspherical coefficients.

[0011] Furthermore, the object-side surface of the second lens and the image-side surface of the third lens are binary surfaces, satisfying the aspherical formula and the equation for the binary surface in Zemax: M(B1ρ) 2 +B2ρ 4 +B3ρ 6 ); where M is the diffraction order, B1, B2, and B3 are the binary surface phase coefficients, and ρ is the normalized radius.

[0012] Furthermore, an aperture is provided on the object side of the fourth lens.

[0013] Furthermore, the infrared lens operates in the 8μm~12μm wavelength range and has a focal length of 30~300mm.

[0014] Furthermore, the center thickness of the first lens is 16.093 mm, the object-side radius of curvature is 323.577 mm, and the image-side radius of curvature is 525.066 mm; the center thickness of the second lens is 4.5 mm, the object-side radius of curvature is -421.303 mm, and the image-side radius of curvature is 300.398 mm; the center thickness of the third lens is 9.75 mm, the object-side radius of curvature is 560.838 mm, and the image-side radius of curvature is -421.137 mm; the center thickness of the fourth lens is 3.75 mm, the object-side radius of curvature is -127.290 mm, and the image-side radius of curvature is -176.103 mm; and the center thickness of the fifth lens is 4.5 mm, the object-side radius of curvature is 557.872 mm, and the image-side radius of curvature is -385.298 mm.

[0015] Furthermore, the air gap between the first lens and the second lens is 151.178 mm to 40.185 mm; the air gap between the second lens and the third lens is 10.539 mm to 186.646 mm; the air gap between the third lens and the fourth lens is 76.189 mm to 11.075 mm; and the air gap between the fourth lens and the fifth lens is 66.464 mm.

[0016] Another object of the present invention is to provide a lens module, including the above-mentioned continuous zoom infrared lens and a detector, wherein the detector has 1280×1024 pixels and a pixel size of 12μm.

[0017] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects:

[0018] (1) It can be continuously and adjustable between wide and narrow fields of view, and the focal length can be continuously changed without any sudden change points, which can effectively avoid the system from getting stuck during zooming.

[0019] (2) During zooming, the second and third lenses are adjusted to move coaxially; the overall structure has only 5 lenses with optical power, and the structure is relatively simple.

[0020] (3) It can achieve continuous zoom with a large zoom ratio, such as 10x zoom ratio (30 to 300mm).

[0021] (4) Excellent image quality and large target area, such as a resolution of 1280×1024, 12μm, horizontal field of view 2.93°~28.7°; vertical field of view: 2.35°~23.15°. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a diagram of the lens composition of the continuous zoom infrared lens in Example 1.

[0024] Figure 2 This is the optical path diagram of the continuous zoom infrared lens in Example 1.

[0025] Figure 3 This is a dot plot of the continuous zoom infrared lens in Example 1 at a focal length of 30mm.

[0026] Figure 4The MTF diagram of the continuous zoom infrared lens in Example 1 at a focal length of 30mm is shown.

[0027] Figure 5 This is a dot plot of the continuous zoom infrared lens in Example 1 at a focal length of 300mm.

[0028] Figure 6 The MTF diagram of the continuous zoom infrared lens in Example 1 at a focal length of 300mm is shown.

[0029] Reference numerals: 1. First lens; 2. Second lens; 3. Third lens; 4. Fourth lens; 5. Fifth lens; 6. Protective window; 7. Detector image plane. Detailed Implementation

[0030] 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. It should be noted that the terms "first" and "second" are used only for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features.

[0031] like Figure 1 As shown, a continuous zoom infrared lens includes a first lens 1, a second lens 2, a third lens 3, a fourth lens 4, and a fifth lens 5 arranged coaxially from the object side to the image side.

[0032] The first lens 1 is a meniscus positive lens with its convex surface facing the object side; the second lens 2 is a biconcave lens; the third lens 3 is a biconvex lens; the fourth lens 4 is a meniscus negative lens with its convex surface facing the image side; and the fifth lens 5 is a biconvex lens.

[0033] In this design, continuous zoom of the infrared lens is achieved by moving the second lens 2 and the third lens 3 along the same optical axis. For example, when it is necessary to adjust the focal length of the lens from the telephoto end to the short focal length end, the second lens 2 should be moved away from the image plane, while the third lens 3 should be moved closer to the image plane.

[0034] like Figure 2 As shown, in the specific optical path transmission, the light emitted by the object is converged by the first lens 1 and then reaches the second lens 2. After being diverged by the second lens 2, it reaches the third lens 3. After being converged by the third lens 3, it reaches the fourth lens 4. After being diverged by the fourth lens 4, it reaches the fifth lens 5. After being converged by the fifth lens 5, it passes through the protective window 6 and is imaged on the detector image plane 7.

[0035] In a specific implementation, the first lens 1, the second lens 2, the third lens 3, the fourth lens 4, and the fifth lens 5 are all made of germanium single crystal.

[0036] In one specific implementation, the object-side surface S7 of the fourth lens 4 and the object-side surface S9 of the fifth lens 5 are aspherical surfaces, and satisfy the aspherical surface formula:

[0037]

[0038] Where Z is the distance vector from the vertex of the aspherical surface at a height r along the optical axis; c = 1 / R; R is the paraxial curvature fitting radius of the mirror; k is the conic coefficient; A, B, C, D, and E are higher-order aspherical coefficients.

[0039] The object-side surface S3 of the second lens 2 and the image-side surface S6 of the third lens 3 are binary surfaces, satisfying the above aspherical surface formula and the expression equation for binary surfaces in Zemax: M(B1ρ 2 +B2ρ 4 +B3ρ 6 ); where M is the diffraction order, B1, B2, and B3 are the binary surface phase coefficients, and ρ is the normalized radius.

[0040] Example 1

[0041] The following explanation uses a specific infrared lens as an example. The first lens 1 has a center thickness of 16.093 mm, an object-side radius of curvature of 323.577 mm, and an image-side radius of curvature of 525.066 mm; the second lens 2 has a center thickness of 4.5 mm, an object-side radius of curvature of -421.303 mm, and an image-side radius of curvature of 300.398 mm; the third lens 3 has a center thickness of 9.75 mm, an object-side radius of curvature of 560.838 mm, and an image-side radius of curvature of -421.137 mm; the fourth lens 4 has a center thickness of 3.75 mm, an object-side radius of curvature of -127.290 mm, and an image-side radius of curvature of -176.103 mm; and the fifth lens 5 has a center thickness of 4.5 mm, an object-side radius of curvature of 557.872 mm, and an image-side radius of curvature of -385.298 mm.

[0042] The air gap between the first lens 1 and the second lens 2 is adjustable, the air gap between the second lens 2 and the third lens 3 is adjustable, and the air gap between the third lens 3 and the fourth lens 4 is adjustable. During zooming, the second lens 2 and the third lens 3 move between the first lens 1 and the fourth lens 4. As shown in Table 1, when the system focal length is 300mm, the air gap between the first lens 1 and the second lens 2 is 151.178mm, the air gap between the second lens 2 and the third lens 3 is 10.539mm, and the air gap between the third lens 3 and the fourth lens 4 is 76.189mm; when the focal length is 165mm, the air gap between the first lens 1 and the second lens 2 is 133.193mm, the air gap between the second lens 2 and the third lens 3 is 51.463mm, and the air gap between the third lens 3 and the fourth lens 4 is 53.249mm; when the focal length is 30mm, the air gap between the first lens 1 and the second lens 2 is 40.18mm, the air gap between the second lens 2 and the third lens 3 is 186.646mm, and the air gap between the third lens 3 and the fourth lens 4 is 11.075mm.

[0043] It is understandable that the side of a lens where light rays enter is the object-side side, and the side where light rays exit is the image-side side. For example, for the first lens 1, S1 is the object-side side, and S2 is the image-side side. Other lenses will not be described in detail here. The parameters of each component are shown in Table 1.

[0044] Table 1 Parameters of each component

[0045]

[0046] The aspherical data of the object surface S7 of the fourth lens 4 and the object surface S9 of the fifth lens 5 are shown in Table 2 (in scientific notation).

[0047] Table 2 Aspherical data of the lens

[0048]

[0049] As shown in Tables 3 and 4, the object-side surface S3 of the second lens 2 and the image-side surface S6 of the third lens 3 are binary surfaces, satisfying the above aspherical surface formula and the expression equation for binary surfaces in Zemax: M(B1ρ 2 +B2ρ 4 +B3ρ 6 ); where M is the diffraction order, the diffraction order is 1, B1, B2, B3 are the binary surface phase coefficients, and ρ is the normalized radius.

[0050] Table 3. Aspherical data of lenses (II)

[0051]

[0052] Table 4. Two-dimensional surface data of the lens

[0053]

[0054] The infrared lens in this embodiment achieves the following specifications:

[0055] Operating wavelength: 8μm~12μm;

[0056] Focal length: f′=30~300mm;

[0057] Resolution: 1280×1024, 12μm;

[0058] F-number: 1.4;

[0059] Horizontal field of view: 2.93°~28.7°;

[0060] Vertical field of view: 2.35°~23.15°.

[0061] The lens in this embodiment can be used in a lens module, which includes the above-mentioned continuous zoom infrared lens and a detector. The detector has 1280×1024 pixels and a pixel size of 12μm.

[0062] Figure 3 , Figure 4 The images show the dot plot and MTF chart of the lens at a focal length of 30mm. Figure 5 , Figure 6 The images show a dot plot and an MTF (Mean Transformer Factor) plot for the lens at a focal length of 300mm. In the MTF plot, the horizontal axis represents different spatial frequencies, and the vertical axis represents modulation. All fields of view represent the MTF curves in the meridional plane. It can be seen that the MTF is close to the diffraction limit, the root mean square diameter of the spot of confusion is smaller than the Airy disk diameter, and the image quality is good.

[0063] Obviously, the above embodiments are merely examples to clearly illustrate the technical solutions of the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the claims of the present invention.

Claims

1. A continuous zoom infrared lens, characterized in that, The system includes a first lens, a second lens, a third lens, a fourth lens, and a fifth lens arranged sequentially along the optical axis from the object side to the image side. The first lens is a meniscus positive lens with its convex surface facing the object side, the second lens is a biconcave lens, the third lens is a biconvex lens, the fourth lens is a meniscus negative lens with its convex surface facing the image side, and the fifth lens is a biconvex lens. Continuous zoom of the infrared lens is achieved by driving the second and third lenses to move along the same optical axis. The first lens has a center thickness of 16.093 mm, an object-side radius of curvature of 323.577 mm, and an image-side radius of curvature of 525.066 mm; the second lens has a center thickness of 4.5 mm, an object-side radius of curvature of -421.303 mm, and an image-side radius of curvature of 300.398 mm; the third lens has a center thickness of 9.75 mm, an object-side radius of curvature of 560.838 mm, and an image-side radius of curvature of -421.137 mm; the fourth lens has a center thickness of 3.75 mm, an object-side radius of curvature of -127.290 mm, and an image-side radius of curvature of 525.066 mm. The diameter is -176.103mm; the center thickness of the fifth lens is 4.5mm, the object-side radius of curvature is 557.872mm, and the image-side radius of curvature is -385.298mm; the air gap between the first and second lenses is 151.178mm~40.185mm; the air gap between the second and third lenses is 10.539mm~186.646mm; the air gap between the third and fourth lenses is 76.189mm~11.075mm; and the air gap between the fourth and fifth lenses is 66.464mm. The lens has a focal length of 30mm to 300mm; the detector has 1280×1024 pixels and a pixel size of 12μm.

2. The continuous zoom infrared lens according to claim 1, characterized in that, The first lens, the second lens, the third lens, the fourth lens, and the fifth lens are all made of germanium single crystal.

3. The continuous zoom infrared lens according to claim 1, characterized in that, The object-side surfaces of the fourth lens and the fifth lens are aspherical and satisfy the aspherical formula: Where Z is the distance vector from the vertex of the aspherical surface at a height r along the optical axis; c = 1 / R; R is the paraxial curvature fitting radius of the mirror; k is the conic coefficient; A, B, C, D, and E are higher-order aspherical coefficients.

4. The continuous zoom infrared lens according to claim 3, characterized in that, The object-side surface of the second lens and the image-side surface of the third lens are binary surfaces, satisfying the aspherical formula and the equation for the binary surface in Zemax: M(B1ρ) 2 +B2ρ 4 +B3ρ 6 ); where M is the diffraction order, B1, B2, and B3 are the binary surface phase coefficients, and ρ is the normalized radius.

5. The continuous zoom infrared lens according to claim 1, characterized in that, The fourth lens has an aperture stop on its object side.

6. The continuous zoom infrared lens according to any one of claims 1 to 5, characterized in that, The infrared lens operates in the 8μm~12μm wavelength range.

7. A lens module, characterized in that, Includes the continuous zoom infrared lens and detector as described in any one of claims 1 to 6.

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