Continuous zooming infrared lens and lens module

Abstract

The invention belongs to the technical field of infrared optics, 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 sequentially arranged on the same optical axis from an object side to an image side. The first lens is a meniscus positive lens of which the convex surface faces 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 of which the convex surface faces the image side, and the fifth lens is a biconvex lens; continuous zooming of the infrared lens is realized by driving the second lens and the third lens to move along the same optical axis. According to the invention, continuous and adjustable conversion can be carried out between a wide field of view and a narrow field of view, and the focal length can be continuously changed; continuous zooming with a large zoom ratio can be realized; only five lenses with focal power are arranged in the whole structure, so that the structure is relatively simple; the image quality is excellent and the target surface is large.

Description

Technical Field

[0001] The present technology belongs to the field of infrared optical technology, and in particular relates to a continuous zoom infrared lens and a lens module. Background Art

[0002] Infrared lenses are widely used in military, security and other fields because of their advantages such as clear imaging in bad weather and all-day operation. Compared with fixed-focus lenses and step-by-step lenses, continuous zoom infrared lenses can not only capture targets in a large field of view, but also adjust to a small field of view to aim and track targets after discovering the target; and in the process of focal length and field of view conversion, the continuity of the image of the observed target on the detector target surface can be maintained, which is conducive to the search and tracking of high-speed moving targets, and solves the defect of step-by-step zoom lenses that high-speed targets are easily lost when the field of view is switched.

[0003] However, changes in ambient temperature will cause changes in the refractive index and surface curvature of the infrared lens, resulting in blurred imaging, which can lead to target loss in the fields of infrared guidance and tracking. In order to eliminate the degradation of imaging quality caused by temperature changes, it is usually necessary to adopt certain compensation technologies so that the optical system can maintain good imaging quality within a larger temperature range. This technology is called athermal technology. At present, athermal technology is mainly divided into optical athermalization, mechanical active athermalization, and mechanical passive athermalization technology. Optical athermalization and mechanical passive athermalization technology generally require more lenses, more complex systems, and larger volumes.

[0004] In order to improve the ability of infrared equipment to detect and identify targets, it is often hoped that the infrared lens can have a longer focal length. However, when using long-focus imaging, it is difficult to simultaneously meet the requirements of athermalization and imaging quality, making it difficult to obtain high-quality optical imaging. In addition, the existing common long-wave infrared zoom systems generally have a relatively small magnification (such as less than 5 times), and most of them use small target surface movements with low resolution (such as 640×480, 25μm). Summary of the invention

[0005] In order to solve the above problems, one object of the present invention is to provide a continuous zoom infrared lens, and the specific technical solution is as follows: A continuous zoom infrared lens comprises a first lens, a second lens, a third lens, a fourth lens and a fifth lens which are arranged in sequence on the same optical axis from the object side to the image side; the first lens is a positive meniscus lens with a convex surface facing the object side, the second lens is a double concave lens, the third lens is a double convex lens, the fourth lens is a negative meniscus lens with a convex surface facing the image side, and the fifth lens is a double convex lens; the continuous zoom of the infrared lens is achieved by driving the second lens and the third lens to move along the same optical axis.

[0006] Furthermore, the first lens, the second lens, the third lens, the fourth lens and the fifth lens are all made of germanium single crystal.

[0007] Furthermore, the object side surface of the fourth lens and the object side surface of the fifth lens are aspherical surfaces and satisfy the aspherical surface formula: Among them, Z is the distance vector height from the vertex of the aspherical surface when the aspherical surface is at a height r along the optical axis; c=1 / R; R is the paraxial curvature fitting radius of the mirror; k is the cone coefficient; A, B, C, D, and E are high-order aspherical coefficients.

[0008] Furthermore, the object side surface of the second lens and the image side surface of the third lens are binary surfaces, satisfying the aspheric surface formula and the expression equation of the binary surface in Zemax: M(B1ρ 2 +B2ρ 4 +B3ρ 6 ), where M is the diffraction order, B1, B2, B3 are the binary surface phase coefficients, and ρ is the normalized radius.

[0009] Furthermore, a stop is provided on the object side of the fourth lens.

[0010] Furthermore, the infrared lens has an operating band of 8 μm to 12 μm and a focal length of 30 to 300 mm.

[0011] Further, the center thickness of the first lens is 16.093mm, the radius of curvature of the object side is 323.577mm, and the radius of curvature of the image side is 525.066mm; the center thickness of the second lens is 4.5mm, the radius of curvature of the object side is -421.303mm, and the radius of curvature of the image side is 300.398mm; the center thickness of the third lens is 9.75mm, the radius of curvature of the object side is 560.838mm, and the radius of curvature of the image side is -421.137mm; the center thickness of the fourth lens is 3.75mm, the radius of curvature of the object side is -127.290mm, and the radius of curvature of the image side is -176.103mm; the center thickness of the fifth lens is 4.5mm, the radius of curvature of the object side is 557.872mm, and the radius of curvature of the image side is -385.298mm.

[0012] 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.

[0013] Another object of the present invention is to provide a lens module, comprising the above-mentioned continuous zoom infrared lens and a detector, wherein the number of pixels of the detector is 1280×1024 and the pixel size is 12 μm.

[0014] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects: (1) It can continuously and adjustablely switch between wide and narrow fields of view, and the focal length can be changed continuously without any mutation points, which can effectively avoid the system from getting stuck during the zoom process; (2) During the zooming process, the second lens and the third lens are adjusted to move coaxially; there are only five lenses with optical power in the overall structure, and the structure is relatively simple; (3) Ability to achieve continuous zoom with large zoom ratio, such as 10x zoom ratio (30 to 300 mm); (4) Excellent image quality and large target surface, such as a resolution of 1280×1024, 12μm, horizontal field of view of 2.93°~28.7°; vertical field of view of 2.35°~23.15°. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0016] Figure 1 This is a diagram showing the lens composition of the continuous zoom infrared lens of Example 1.

[0017] Figure 2 This is a light path diagram of the continuous zoom infrared lens of Example 1.

[0018] Figure 3 This is a point diagram of the continuous zoom infrared lens of Example 1 at a focal length of 30 mm.

[0019] Figure 4 This is the MTF diagram of the continuous zoom infrared lens of Example 1 at a focal length of 30 mm.

[0020] Figure 5 This is a point diagram of the continuous zoom infrared lens of Example 1 at a focal length of 300 mm.

[0021] Figure 6 This is the MTF diagram of the continuous zoom infrared lens of Example 1 at a focal length of 300 mm.

[0022] 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 DESCRIPTION

[0023] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. It should be noted that the terms "first" and "second" are only used for the purpose of convenience of description and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features.

[0024] like Figure 1 As shown, a continuous zoom infrared lens comprises a first lens 1, a second lens 2, a third lens 3, a fourth lens 4, and a fifth lens 5 which are arranged in sequence on the same optical axis from the object side to the image side.

[0025] The first lens 1 is a positive meniscus lens with its convex surface facing the object side, the second lens 2 is a double concave lens, the third lens 3 is a double convex lens, the fourth lens 4 is a negative meniscus lens with its convex surface facing the image side, and the fifth lens 5 is a double convex lens.

[0026] In this solution, continuous zooming of the infrared lens is achieved by driving the second lens 2 and the third lens 3 to move along the same optical axis. For example, when the focal length of the lens needs to be adjusted from the telephoto end to the short focal end, the second lens 2 should be moved away from the image plane, while the third lens 3 should be moved close to the image plane.

[0027] 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 reaches the second lens 2, diverged by the second lens 2 and reaches the third lens 3, converged by the third lens 3 and reaches the fourth lens 4, diverged by the fourth lens 4 and reaches the fifth lens 5, and after being converged by the fifth lens 5, it passes through the protective window 6 and is imaged on the detector image plane 7. As a specific implementation, the materials of the first lens 1 , the second lens 2 , the third lens 3 , the fourth lens 4 , and the fifth lens 5 are all germanium single crystals.

[0028] As a 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: Among them, Z is the distance vector height from the vertex of the aspherical surface when the aspherical surface is at a height r along the optical axis; c=1 / R; R is the paraxial curvature fitting radius of the mirror; k is the cone coefficient; A, B, C, D, and E are high-order aspherical coefficients.

[0029] The object side S3 of the second lens 2 and the image side S6 of the third lens 3 are two-dimensional surfaces, which satisfy the above aspheric surface formula and the expression equation of the two-dimensional surface in Zemax: M(B1ρ 2 +B2ρ 4 +B3ρ 6 ), where M is the diffraction order, B1, B2, B3 are the binary surface phase coefficients, and ρ is the normalized radius.

[0030] Example 1 The following is an explanation using a specific infrared lens as an example. The center thickness of the first lens 1 is 16.093mm, the radius of curvature of the object side is 323.577mm, and the radius of curvature of the image side is 525.066mm; the center thickness of the second lens 2 is 4.5mm, the radius of curvature of the object side is -421.303mm, and the radius of curvature of the image side is 300.398mm; the center thickness of the third lens 3 is 9.75mm, the radius of curvature of the object side is 560.838mm, and the radius of curvature of the image side is -421.137mm; the center thickness of the fourth lens 4 is 3.75mm, the radius of curvature of the object side is -127.290mm, and the radius of curvature of the image side is -176.103mm; the center thickness of the fifth lens 5 is 4.5mm, the radius of curvature of the object side is 557.872mm, and the radius of curvature of the image side is -385.298mm.

[0031] The air interval between the first lens 1 and the second lens 2 is adjustable, the air interval between the second lens 2 and the third lens 3 is adjustable, and the air interval between the third lens 3 and the fourth lens 4 is adjustable. When 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 focal length of the system is 300 mm, the air gap between the first lens 1 and the second lens 2 is 151.178 mm, the air gap between the second lens 2 and the third lens 3 is 10.539 mm, and the air gap between the third lens 3 and the fourth lens 4 is 76.189 mm; when the focal length is 165 mm, the air gap between the first lens 1 and the second lens 2 is 133.193 mm, the air gap between the second lens 2 and the third lens 3 is 51.463 mm, and the air gap between the third lens 3 and the fourth lens 4 is 53.249 mm; when the focal length is 30 mm, the air gap between the first lens 1 and the second lens 2 is 40.18 mm, the air gap between the second lens 2 and the third lens 3 is 186.646 mm, and the air gap between the third lens 3 and the fourth lens 4 is 11.075 mm.

[0032] It is understood that the side of the lens where light is incident is the object side, and the side where light is emitted is the image side. For example, for the first lens 1, S1 is the object side, and S2 is the image side. Other lenses are not described here. The parameters of each component are shown in Table 1.

[0033] Table 1 Parameters of each component Aspheric surface data of the object-side surface S7 of the fourth lens 4 and the object-side surface S9 of the fifth lens 5 are shown in Table 2 (the table adopts scientific notation).

[0034] Table 2 Aspheric surface data of lens 1 As shown in Table 3 and Table 4, the object side surface S3 of the second lens 2 and the image side surface S6 of the third lens 3 are two-dimensional surfaces, which satisfy the above aspheric surface formula and the expression equation of the two-dimensional surface 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.

[0035] Table 3 Aspheric surface data of lens 2 Table 4 Binary surface data of lens The infrared lens of this embodiment achieves the following indicators: Working band: 8μm~12μm; Focal length: f′=30~300mm; Resolution: 1280×1024, 12μm; F number: 1.4; Horizontal field of view: 2.93°~28.7°; Vertical field of view: 2.35°~23.15°.

[0036] The lens of this embodiment can be applied to a lens module. The lens module includes the above-mentioned continuous zoom infrared lens and a detector. The number of pixels of the detector is 1280×1024, and the pixel size is 12 μm.

[0037] Figure 3 , Figure 4 They are the point diagram and MTF diagram of the lens at a focal length of 30mm. Figure 5 , Figure 6 The following are the spot diagram and MTF diagram of the lens at a focal length of 300mm. In the MTF diagram, the horizontal axis represents different spatial frequencies and the vertical axis represents the modulation degree. All fields of view represent the MTF curve of the meridian plane. It can be seen that the MTF is close to the diffraction limit, the root mean square diameter of the diffuse spot is smaller than the diameter of the Airy disk, and the image quality is good.

[0038] Obviously, the above embodiments are merely examples for clearly explaining the technical solutions of the present invention, and are not intended to limit the implementation methods of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the protection of the claims of the present invention.

Claims

1. A continuous zoom infrared lens, characterized in that: The invention comprises a first lens, a second lens, a third lens, a fourth lens and a fifth lens which are arranged in sequence on the same optical axis from the object side to the image side; the first lens is a positive meniscus lens with the convex surface facing the object side, the second lens is a double concave lens, the third lens is a double convex lens, the fourth lens is a negative meniscus lens with the convex surface facing the image side, and the fifth lens is a double convex lens; continuous zooming of the infrared lens is achieved by driving the second lens and the third lens to move along the same optical axis.

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 surface of the fourth lens and the object side surface of the fifth lens are aspherical surfaces and satisfy the aspherical surface formula: Among them, Z is the distance vector height from the vertex of the aspherical surface when the aspherical surface is at a height r along the optical axis; c=1 / R; R is the paraxial curvature fitting radius of the mirror; k is the cone coefficient; A, B, C, D, and E are high-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 two-dimensional surfaces, satisfying the aspheric surface formula and the expression equation of the two-dimensional surface in Zemax: M(B1ρ 2 +B2ρ 4 +B3ρ 6 ), where M is the diffraction order, B1, B2, 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: An aperture stop is provided on the object side of the fourth lens.

6. The continuous zoom infrared lens according to any one of claims 1 to 5, characterized in that: The infrared lens has an operating band of 8 μm to 12 μm and a focal length of 30 to 300 mm.

7. The continuous zoom infrared lens according to claim 6, characterized in that: The center thickness of the first lens is 16.093mm, the radius of curvature of the object side is 323.577mm, and the radius of curvature of the image side is 525.066mm; the center thickness of the second lens is 4.5mm, the radius of curvature of the object side is -421.303mm, and the radius of curvature of the image side is 300.398mm; the center thickness of the third lens is 9.75mm, the radius of curvature of the object side is 560.838mm, and the radius of curvature of the image side is -421.137mm; the center thickness of the fourth lens is 3.75mm, the radius of curvature of the object side is -127.290mm, and the radius of curvature of the image side is -176.103mm; the center thickness of the fifth lens is 4.5mm, the radius of curvature of the object side is 557.872mm, and the radius of curvature of the image side is -385.298mm.

8. The continuous zoom infrared lens according to claim 7, characterized in that: The air gap between the first lens and the second lens is 151.178mm~40.185mm; the air gap between the second lens and the third lens is 10.539mm~186.646mm; the air gap between the third lens and the fourth lens is 76.189mm~11.075mm; the air gap between the fourth lens and the fifth lens is 66.464mm.

9. A lens module, characterized in that: It comprises the continuous zoom infrared lens and the detector as claimed in any one of claims 1 to 8, wherein the number of pixels of the detector is 1280×1024 and the pixel size is 12 μm.

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