A medium wave continuous zoom infrared lens and a lens module

Abstract

The application belongs to the field of infrared optical technology and discloses a middle-wave continuous zooming infrared lens and a lens module. The lens comprises a front fixed group, a zooming group, a rear fixed group and a temperature compensation group which are arranged in sequence along an optical axis from an object side to an image side. The front fixed group is a first lens. The zooming group comprises a second lens and a third lens which are arranged in sequence. The second lens and the third lens are movable along the optical axis to realize continuous zooming. The rear fixed group comprises a fourth lens and a fifth lens. The temperature compensation group is a sixth lens. The lens is provided in the form of a six-piece lens structure which is relatively simple. The continuous zooming function is realized by moving the second lens and the third lens for zooming and the sixth lens for temperature compensation, and good imaging effect is ensured. The continuous zooming with a large zoom ratio can be realized.

Description

Technical Field

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

[0002] In recent years, infrared detection technologies such as infrared thermal imaging have been widely used in military, industrial, and civilian fields. For detectors, mid-wave cooled detectors offer a significant price advantage over similar long-wave detectors due to their high sensitivity. For lenses, compared to fixed-focus or segmented lenses, continuous zoom lenses can capture targets in a wide field of view and then adjust to a smaller field of view for aiming and tracking after target detection. Furthermore, they maintain continuity of the image of the observed target on the detector surface during focal length and field of view transitions, which is beneficial for searching and tracking high-speed moving targets and overcomes the drawback of segmented zoom lenses, which are prone to losing high-speed targets during field of view switching. Therefore, mid-wave continuous zoom infrared lenses have promising application prospects.

[0003] The existing medium-wave continuous zoom infrared lenses have the following disadvantages: (1) They generally use a large number of lenses, usually more than seven, which makes the processing difficult and increases the cost and weight of the infrared lens; (2) They have many moving elements, such as using three-element moving zoom, which makes the structure complex and the focusing inconvenient. Summary of the Invention

[0004] To address the above problems, one objective of this application is to provide a mid-wave continuous zoom infrared lens. The specific technical solution is as follows:

[0005] A mid-wave continuous zoom infrared lens includes a front fixed group, a zoom group, a rear fixed group, and a temperature compensation group arranged coaxially from the object side to the image side.

[0006] The front fixing group is the first lens, which is a meniscus lens with its convex surface facing the object and has positive optical power;

[0007] The zoom group includes a second lens and a third lens arranged in sequence; the second lens is a biconcave lens and the third lens is a biconvex lens; the second lens and the third lens can move along the optical axis to achieve continuous zoom.

[0008] The rear fixing group includes a fourth lens and a fifth lens; the fourth lens is a meniscus lens with its convex surface facing the image side and has negative optical power; the fifth lens is a meniscus lens with its convex surface facing the object side and has positive optical power.

[0009] The temperature compensation group is the sixth lens, and the sixth lens is a biconvex lens.

[0010] Furthermore, during the zoom process, the second lens and the third lens move towards each other or away from each other along the optical axis.

[0011] Furthermore, the first, third, fifth, and sixth lenses are made of silicon, while the second and fourth lenses are made of germanium.

[0012] Furthermore, the image-side surface of the first lens, the object-side surface of the second lens, the object-side surface of the third lens, the image-side surface of the third lens, the object-side surface of the fourth lens, the image-side surface of the fifth lens, the object-side surface of the sixth lens, and the image-side surface of the sixth lens are aspherical surfaces, and satisfy the aspherical surface formula:

[0013]

[0014] 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.

[0015] Furthermore, the object-side surfaces of the fourth lens and the sixth lens are binary surfaces, satisfying the aspherical formula and the equation for binary surfaces in Zemax: M(B1ρ) 2 +B2ρ 4 ); where M is the diffraction order, B1 and B2 are the phase coefficients of the binary surface, and ρ is the normalized radius.

[0016] Furthermore, the infrared lens operates in the wavelength range of 3.7μm to 4.8μm and has a focal length of 20 to 200mm.

[0017] Furthermore, the air gap between the first lens and the second lens is 12.4~24.271mm; the air gap between the second lens and the third lens is 22.788~2.7mm; the air gap between the third lens and the fourth lens is 2.6~10.817mm; the air gap between the fourth lens and the fifth lens is 0.2mm; and the air gap between the fifth lens and the sixth lens is 13.812mm.

[0018] Further, the first lens has a center thickness of 5.8 mm, an object-side radius of curvature of 49.55 mm, and an image-side radius of curvature of 96.105 mm; the second lens has a center thickness of 1.6 mm, an object-side radius of curvature of -43.573 mm, and an image-side radius of curvature of 34.713 mm; the third lens has a center thickness of 4 mm, an object-side radius of curvature of 56.762 mm, and an image-side radius of curvature of -41.466 mm; the fourth lens has a center thickness of 1.5 mm, an object-side radius of curvature of -59.488 mm, and an image-side radius of curvature of -220 mm; the fifth lens has a center thickness of 3.8 mm, an object-side radius of curvature of 7.457 mm, and an image-side radius of curvature of 5.079 mm; and the sixth lens has a center thickness of 2.8 mm, an object-side radius of curvature of 29.883 mm, and an image-side radius of curvature of -29.125 mm.

[0019] Another objective of this application is to provide a lens module, including the aforementioned continuous zoom infrared lens and a detector, wherein the detector has 640×512 pixels and a pixel size of 15μm.

[0020] Furthermore, the detector is a mid-wave cooled infrared detector, which includes a protective window, a chopper window, and a cold screen arranged sequentially between the sixth lens and the detector image plane; the chopper window has an aperture on the side near the cold screen.

[0021] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects:

[0022] (1) During the zoom process, the second lens and the third lens are adjusted to move coaxially. There are only six lenses with optical power in the overall structure, and the structure is relatively simple.

[0023] (2) It can achieve continuous zoom with a large zoom ratio, such as 10x zoom ratio and focal length of 20~200mm;

[0024] (3) Good image quality, such as a resolution of 640×512, 15μm. Attached Figure Description

[0025] 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.

[0026] Figure 1 This is the optical path diagram of the medium-wave continuous zoom infrared lens in Example 1.

[0027] Figure 2 This is a diagram showing the lens composition of the medium-wave continuous zoom infrared lens in Example 1.

[0028] Figure 3 This is a dot plot of the medium-wave continuous zoom infrared lens with a focal length of 200mm in Example 1.

[0029] Figure 4 The MTF diagram for the medium-wave continuous zoom infrared lens with a focal length of 200mm in Example 1 is shown.

[0030] Figure 5 This is a dot plot of the medium-wave continuous zoom infrared lens with a focal length of 20mm in Example 1.

[0031] Figure 6 The MTF diagram for the medium-wave continuous zoom infrared lens with a focal length of 20mm in Example 1 is shown.

[0032] Reference numerals in the attached figures: 1. First lens; 2. Second lens; 3. Third lens; 4. Fourth lens; 5. Fifth lens; 6. Sixth lens; 7. Protective window; 8. Chopper window; 9. Cold screen; 10. Detector image plane. Detailed Implementation

[0033] 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.

[0034] To facilitate understanding, the relevant terms are explained below.

[0035] The object side, along the direction of light propagation, is the side of the lens where light rays enter, i.e., the surface of the lens closest to the object; the image side, along the direction of light propagation, is the side of the lens where light rays exit, i.e., the surface of the lens closest to the image; a meniscus lens, also known as a crescent-shaped lens, has one concave surface and the other convex surface on one side near the optical axis.

[0036] like Figure 1 , Figure 2As shown, the mid-wave continuous zoom infrared lens of this application includes a front fixed group, a zoom group, a rear fixed group, and a temperature compensation group arranged sequentially along the optical axis from the object side to the image side. The front fixed group consists of a first lens 1, which is a meniscus lens with its convex surface facing the object side and has positive optical power. The zoom group includes a second lens 2 and a third lens 3 arranged sequentially; the second lens 2 is a biconcave lens, and the third lens 3 is a biconvex lens. The rear fixed group includes a fourth lens 4 and a fifth lens 5; the fourth lens 4 is a meniscus lens with its convex surface facing the image side and has negative optical power; the fifth lens 5 is a meniscus lens with its convex surface facing the object side and has positive optical power. The temperature compensation group consists of a sixth lens 6, which is a biconvex lens. The second lens 2 and the third lens 3 can move along the optical axis to achieve continuous zoom.

[0037] In this invention, the lenses in the front fixed group and the rear fixed group are in fixed relative positions. The temperature compensation group is used to compensate for the shift in image plane position at different temperatures, while the zoom group is used to achieve continuous change in focal length. Specifically, during the zoom process, the second lens 2 and the third lens 3 move towards each other or away from each other along the optical axis to achieve switching between telephoto, medium telephoto, and short telephoto.

[0038] For example, during the transition from telephoto to focal length, the second lens 2 moves towards the object side, and the third lens 3 moves towards the image side to reduce the focal length of the optical system and compensate for the image plane shift caused by the lens movement. Conversely, during the transition from focal length to telephoto, the second lens 2 moves towards the image side, and the third lens 3 moves towards the object side. When the lens is at its longest focal length, the air gap between the first lens 1 and the second lens 2 is at its maximum, the air gap between the second lens 2 and the third lens 3 is at its minimum, and the air gap between the third lens 3 and the fourth lens 4 is at its maximum. When the lens is at its shortest focal length, the air gap between the first lens 1 and the second lens 2 is at its minimum, the air gap between the second lens 2 and the third lens 3 is at its maximum, and the air gap between the third lens 3 and the fourth lens 4 is at its minimum.

[0039] In a specific implementation, the first lens 1, the third lens 3, the fifth lens 5, and the sixth lens 6 are made of silicon, while the second lens 2 and the fourth lens 4 are made of germanium.

[0040] In one specific implementation, the image-side surface S2 of the first lens, the object-side surface S3 of the second lens, the object-side surface S5 and the image-side surface S6 of the third lens, the object-side surface S7 of the fourth lens, the image-side surface S10 of the fifth lens, and the object-side surface S11 and the image-side surface S12 of the sixth lens are aspherical surfaces and satisfy the aspherical surface formula:

[0041]

[0042] 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.

[0043] The object-side surface S7 of the fourth lens and the object-side surface S11 of the sixth lens are binary surfaces, satisfying the above aspherical surface formula and the expression equation for binary surfaces in Zemax: M(B1ρ 2 +B2ρ 4 ); where M is the diffraction order, B1 and B2 are the phase coefficients of the binary surface, and ρ is the normalized radius.

[0044] Example 1

[0045] The following explanation uses a specific continuous zoom lens as an example. Specific parameters of the continuous zoom lens in this embodiment are shown in Tables 1, 2, and 3.

[0046] Table 1 Parameters of each component

[0047]

[0048] Table 2 Aspherical data of lenses

[0049]

[0050] Table 3. Two-dimensional surface data of the lens

[0051]

[0052] During focusing, the positions of the front and rear fixed lenses are relatively fixed, while the two lenses of the zoom group move along the optical axis between the front and rear fixed groups. The air gaps D2 between the first lens 1 and the second lens 2, D4 between the second lens 2 and the third lens 3, and D6 between the third lens 3 and the fourth lens 4 are all variable. For example, when the air gap D2 between the first lens 1 and the second lens 2 is 12.4 mm, the air gap D4 between the second lens 2 and the third lens 3 is 22.788 mm, and the air gap D6 between the third lens 3 and the fourth lens 4 is 2.6 mm, the system focal length is at its shortest. In this embodiment, the shortest focal length is 20 mm. When the air gap D2 between the first lens 1 and the second lens 2 is 24.271 mm, the air gap D4 between the second lens 2 and the third lens 3 is 2.7 mm, and the air gap D6 between the third lens 3 and the fourth lens 4 is 10.817 mm, the system focal length is at its longest. In this embodiment, the longest focal length is 200 mm.

[0053] Figure 3 , Figure 4The images show the dot plot and MTF chart for the lens at a telephoto focal length of 200mm. Figure 5 , Figure 6 The images show the dot plot and MTF (Mean Transformer Frequency) plot for the lens at a short focal length of 20mm. 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.

[0054] In this embodiment, the wave-continuous zoom infrared lens achieves the following optical specifications: operating wavelength is 3.7μm-4.8μm; focal length f′ is 20~200mm; resolution is 640×512, 15μm; and F number is 4.0.

[0055] Based on the same inventive concept, this embodiment provides a lens module. The lens module includes the aforementioned mid-wave continuous zoom infrared lens and a detector. The detector has 640×512 pixels and a pixel size of 15μm. The detector includes a protective window 7, a chopper window 8, and a cold screen 9, which are sequentially disposed between the sixth lens 6 and the detector image plane 10. The chopper window 8 has an aperture stop on the side closest to the cold screen 9. Specific parameters can be found in Table 1.

[0056] The lens of this application is set in a six-element lens structure, which is relatively simple; by using the second and third lenses to move and zoom, and the sixth lens to compensate for temperature, continuous zoom function is achieved while ensuring good imaging effect; continuous zoom with a large zoom ratio can be achieved.

[0057] 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 mid-wave continuous zoom infrared lens, characterized in that, It includes a front fixed group, a zoom group, a rear fixed group, and a temperature compensation group arranged coaxially from the object side to the image side; the total number of lenses with optical power in the lens is six. The front fixing group is the first lens, which is a meniscus lens with its convex surface facing the object and has positive optical power; The zoom group includes a second lens and a third lens arranged in sequence; the second lens is a biconcave lens and the third lens is a biconvex lens; the second lens and the third lens can move along the optical axis to achieve continuous zoom. The rear fixing group includes a fourth lens and a fifth lens; the fourth lens is a meniscus lens with its convex surface facing the image side and has negative optical power; the fifth lens is a meniscus lens with its convex surface facing the object side and has positive optical power. The temperature compensation group is the sixth lens, and the sixth lens is a biconvex lens.

2. The mid-wave continuous zoom infrared lens according to claim 1, characterized in that, During zooming, the second and third lenses move towards each other or away from each other along the optical axis.

3. The mid-wave continuous zoom infrared lens according to claim 1, characterized in that, The first, third, fifth, and sixth lenses are made of silicon, while the second and fourth lenses are made of germanium.

4. The mid-wave continuous zoom infrared lens according to claim 1, characterized in that, The image-side surface of the first lens, the object-side surface of the second lens, the object-side surface of the third lens, the image-side surface of the third lens, the object-side surface of the fourth lens, the image-side surface of the fifth lens, the object-side surface of the sixth lens, and the image-side surface of the sixth lens are aspherical surfaces and satisfy the aspherical surface 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.

5. The mid-wave continuous zoom infrared lens according to claim 4, characterized in that, The object-side surfaces of the fourth and sixth lenses are binary surfaces, satisfying the aspherical formula and the equation for binary surfaces in Zemax: M(B1ρ) 2 +B2ρ 4 ); where M is the diffraction order, B1 and B2 are the phase coefficients of the binary surface, and ρ is the normalized radius.

6. The mid-wave continuous zoom infrared lens according to any one of claims 1 to 5, characterized in that, The infrared lens operates in the wavelength range of 3.7μm to 4.8μm and has a focal length of 20 to 200mm.

7. The mid-wave continuous zoom infrared lens according to claim 6, characterized in that, The air gap between the first lens and the second lens is 12.4~24.271mm; the air gap between the second lens and the third lens is 22.788~2.7mm; the air gap between the third lens and the fourth lens is 2.6~10.817mm; the air gap between the fourth lens and the fifth lens is 0.2mm; and the air gap between the fifth lens and the sixth lens is 13.812mm.

8. The mid-wave continuous zoom infrared lens according to claim 6, characterized in that, The first lens has a center thickness of 5.8 mm, an object-side radius of curvature of 49.55 mm, and an image-side radius of curvature of 96.105 mm; the second lens has a center thickness of 1.6 mm, an object-side radius of curvature of -43.573 mm, and an image-side radius of curvature of 34.713 mm; the third lens has a center thickness of 4 mm, an object-side radius of curvature of 56.762 mm, and an image-side radius of curvature of -41.466 mm; the fourth lens has a center thickness of 1.5 mm, an object-side radius of curvature of -59.488 mm, and an image-side radius of curvature of -220 mm; the fifth lens has a center thickness of 3.8 mm, an object-side radius of curvature of 7.457 mm, and an image-side radius of curvature of 5.079 mm; and the sixth lens has a center thickness of 2.8 mm, an object-side radius of curvature of 29.883 mm, and an image-side radius of curvature of -29.125 mm.

9. A lens module, characterized in that, It includes a mid-wave continuous zoom infrared lens and a detector as described in any one of claims 1 to 8, wherein the detector has 640×512 pixels and a pixel size of 15μm.

10. The lens module according to claim 9, characterized in that, The detector is a mid-wave cooled infrared detector, which includes a protective window, a chopper window, and a cold screen arranged sequentially between the sixth lens and the detector image plane; the chopper window has an aperture on the side near the cold screen.

Images