Lens and thermal imager

Abstract

A lens and a thermal imager are provided. The lens has only two lenses, including a first lens and a second lens. The first lens is a positive meniscus lens, which includes a first surface and a second surface. The first surface is convex and faces the object side, and the second surface is concave and faces the image side. The second lens is a negative meniscus lens, which includes a third surface and a fourth surface. The third surface is concave and faces the object side, and the fourth surface is convex and faces the image side. The first lens and the second lens are arranged sequentially along the optical axis from the object side to the image side. In this way, the lens can have low cost and good portability.

Description

Technical Field

[0001] This application relates to the field of optical components, and more specifically to a lens and a thermal imager. Background Technology

[0002] Infrared lenses have a wide range of applications, especially infrared gun sights. Current technology typically improves image quality by increasing the number of lenses, but this often leads to increased weight and cost. Achieving low-cost design for infrared lenses while maintaining good image quality is a pressing issue that needs to be addressed. Summary of the Invention

[0003] This application is made in view of the state of the prior art described above. The object of this application is to provide a lens and thermal imager that can overcome at least one of the disadvantages described in the background art.

[0004] To achieve the above objectives, this application adopts the following technical solution.

[0005] This application provides a lens having only two lenses, the lens comprising: a first lens, which is a positive meniscus lens, the first lens including a first surface and a second surface, the first surface being convex and facing the object side, and the second surface being concave and facing the image side; and a second lens, which is a negative meniscus lens, the second lens including a third surface and a fourth surface, the third surface being concave and facing the object side, and the fourth surface being convex and facing the image side, wherein the first lens and the second lens are arranged sequentially along the optical axis from the object side to the image side.

[0006] In one alternative embodiment, the first surface and / or the second surface are spherical, with the radius of curvature of the first surface being 10 mm to 40 mm and the radius of curvature of the second surface being 20 mm to 50 mm.

[0007] In another alternative embodiment, the third surface and / or the fourth surface is an aspherical surface, and the aspherical surface satisfies

[0008]

[0009] Where z is the sag of a point on the aspherical surface along the optical axis, r is the shortest distance between the point and the optical axis, c is the curvature of the vertex of the aspherical surface, k is the conic coefficient of the aspherical surface, and α i Let be the aspherical coefficients of the aspherical surface, i be the index of the polynomial terms in the aspherical surface, and N be the total number of polynomial terms in the aspherical surface.

[0010] In another alternative, the third surface satisfies -0.05mm.-1 ≤c≤-0.02mm -1 , k = -21.21, α2 = -5.77e-5, α3 = 5.17e-8, α4 = 1.16e-08, α5 = -1.30e-10, α6 = 4.68e-13, the fourth surface satisfies -0.04mm. -1 ≤c≤-0.02mm -1 , k=0.48, α2=1.24e-5, α3=6.44e-7, α4=-1.07e-8, α5=1.29e-10, α6=-5.74e-13.

[0011] In another alternative embodiment, the third surface is a diffraction surface, which satisfies...

[0012]

[0013] Where Φ is the phase of the diffraction surface, M is the diffraction order of the diffraction surface, and A i ρ represents the coefficients of each term in the diffraction surface, ρ represents the normalized radial aperture coordinates of the diffraction surface, i represents the index of the polynomial term in the diffraction surface, and N represents the total number of polynomial terms in the diffraction surface.

[0014] In another alternative scheme, the third face satisfies M = 100, A1 = -1.51e+3, and A2 = 1.20e+5.

[0015] In another alternative, the first lens is made of germanium glass, and / or the second lens is made of chalcogenide glass.

[0016] In another alternative embodiment, the lens has a focal length of 35mm, an F-number of 1.0, a field of view greater than or equal to 16°, an optical length less than or equal to 43.5mm, an optical back focal length greater than or equal to 11mm, and an operating wavelength of 8μm to 12μm.

[0017] In another alternative embodiment, the first lens has a thickness of 5 mm on the optical axis, the second lens has a thickness of 9 mm on the optical axis, and the air gap between the first lens and the second lens on the optical axis is 18 mm.

[0018] This application also provides a thermal imager that includes the lens and photosensitive element described above.

[0019] By employing the above technical solution, the lens can achieve high-quality imaging with only two lenses, resulting in a simpler structure and effectively reducing costs. Furthermore, the smaller number of lenses contributes to the lens's lighter weight and improved portability. Attached Figure Description

[0020] Figure 1 A schematic diagram of a thermal imager according to one embodiment of this application is shown.

[0021] Figure 2 It shows Figure 1 The optical modulation transfer function curve of the lens of the thermal imager at 20°C.

[0022] Figure 3 It shows Figure 1 The optical modulation transfer function curve of the lens of the thermal imager at -40℃.

[0023] Figure 4 It shows Figure 1 The optical modulation transfer function curve of the lens of the thermal imager at 60°C.

[0024] Figure 5 It shows Figure 1 The field curvature diagram of the lens of the thermal imager.

[0025] Figure 6 It shows Figure 1 The distortion image of the lens of the thermal imager.

[0026] Figure 7 It shows Figure 1 The relative illumination map of the lens of the thermal imager.

[0027] Explanation of reference numerals in the attached figures

[0028] 1. Lens; 11. First lens; 12. Second lens; 13. Flat glass;

[0029] 2. Photosensitive element;

[0030] S1 First side; S2 Second side; S3 Third side; S4 Fourth side;

[0031] A-axis. Detailed Implementation

[0032] Exemplary embodiments of this application are described below with reference to the accompanying drawings. It should be understood that these specific descriptions are for teaching those skilled in the art how to implement this application only, and are not intended to exhaust all possible methods of this application, nor to limit the scope of this application.

[0033] In this application, unless otherwise specified, "e" denotes scientific notation. For example, -5.77e-5 means -5.77 × 10⁻⁵. -5 "From one number to another" includes both a number and another number.

[0034] Figure 1 A thermal imager according to an embodiment of the present application is shown, which may include a lens 1 and a photosensitive element 2.

[0035] Reference Figure 1 Lens 1 can be an infrared gun sight lens, which may include a first lens 11, a second lens 12, and a flat glass 13.

[0036] Specifically, the first lens 11 can be a positive meniscus lens, which can be made of germanium glass. The thickness of the first lens 11 along the optical axis A can be 5 mm. The first lens 11 can include a first surface S1 and a second surface S2. The first surface S1 can be a convex surface, which can face the object side. The second surface S2 can be a concave surface, which can face the image side. The first surface S1 and the second surface S2 can be spherical. The radius of curvature of the first surface S1 can be from 10 mm to 40 mm, for example, 29.46 mm. The radius of curvature of the second surface S2 can be from 20 mm to 50 mm, for example, 35.61 mm.

[0037] Furthermore, the first surface S1 can be provided with a diamond-like carbon (DLC) film. The diamond-like carbon film has high hardness, which enables the lens 1 to have better impact and scratch resistance, such as resistance to sand and gravel impacts, thereby improving the reliability of the lens 1.

[0038] The second lens 12 can be a negative meniscus lens, made of chalcogenide glass, such as IRG203 chalcogenide glass produced by Hubei Xinhua Optoelectronic Materials Co., Ltd. The thickness of the second lens 12 along the optical axis A can be 9 mm. The second lens 12 may include a third surface S3 and a fourth surface S4. The third surface S3 can be concave and face the object side. The fourth surface S4 can be convex and face the image side.

[0039] The third surface S3 and the fourth surface S4 can be aspherical surfaces, and aspherical surfaces can satisfy...

[0040]

[0041] Where z is the sag of a point on the aspherical surface along the optical axis A, r is the shortest distance between the point and the optical axis A, c is the curvature of the vertex of the aspherical surface, k is the conic coefficient of the aspherical surface, and α iLet be the aspherical coefficients of the aspherical surface, i be the index of the polynomial term in the aspherical surface, and N be the total number of polynomial terms in the aspherical surface. For example, the third surface S3 can satisfy -0.05mm. -1 ≤c≤-0.02mm -1 , k = -21.21, α2 = -5.77e-5, α3 = 5.17e-8, α4 = 1.16e-08, α5 = -1.30e-10, α6 = 4.68e-13. The fourth surface S4 can satisfy -0.04mm. -1 ≤c≤-0.02mm -1 , k=0.48, α2=1.24e-5, α3=6.44e-7, α4=-1.07e-8, α5=1.29e-10, α6=-5.74e-13.

[0042] Furthermore, the third surface S3 can be a diffraction surface, and the diffraction surface can satisfy...

[0043]

[0044] Where Φ is the phase of the diffraction plane, M is the diffraction order of the diffraction plane, and A i Let ρ be the coefficients of each term in the diffraction plane, ρ be the normalized radial aperture coordinates of the diffraction plane, i be the index of the polynomial term in the diffraction plane, and N be the total number of polynomial terms in the diffraction plane. For example, the third plane S3 can be a binary diffraction plane, which can satisfy M = 100, A1 = -1.51e+3, A2 = 1.20e+5.

[0045] The first lens 11, the second lens 12, and the plate glass 13 can be arranged sequentially along the optical axis A from the object side to the image side. The air gap between the first lens 11 and the second lens 12 on the optical axis A can be 18 mm, and the air gap between the second lens 12 and the plate glass 13 on the optical axis A can be 9.94 mm. The plate glass 13 can be disposed between the second lens 12 and the photosensitive element 2 to protect the second lens 12 and the photosensitive element 2. Of course, the plate glass 13 is not mandatory. The focal length of the lens 1 can be 35 mm. The F-number of the lens 1 can be 1.0. The field of view of the lens 1 can be greater than or equal to 16°. The total optical length of the lens 1 can be less than or equal to 43.5 mm. The optical back focal length of the lens 1 can be greater than or equal to 11 mm.

[0046] The photosensitive element 2 can be an uncooled long-wave infrared detector. For example, the resolution of the photosensitive element 2 can be 640×512, and the pixel pitch of the photosensitive element 2 can be 12μm. Correspondingly, the operating wavelength of the lens 1 can be from 8μm to 12μm.

[0047] Reference Figures 2 to 4The diagram shows the optical modulation transfer function (MTF) curve of lens 1. The horizontal axis represents spatial frequency in lp / mm, and the vertical axis represents the coefficients of the optical transfer function (OTF).

[0048] Specifically, Figure 2 The diagram shows the meridional (T) and sagittal (S) modulation transfer function curves of lens 1 at 20°C, with image plane heights of 0.0000 mm, 2.4600 mm, 3.4790 mm, 4.2608 mm, and 4.9200 mm, and operating wavelengths from 8 μm to 12 μm, for 42 line pairs. Figure 2 It can be seen that the meridional and sagittal modulation transfer functions of the central field of view (image plane height of 0.0000mm) are greater than 0.46, while the modulation transfer functions of the other fields of view are greater than 0.33. Lens 1 has higher meridional and sagittal modulation transfer function curves, indicating that lens 1 has better image quality.

[0049] Figure 3 The diagram shows the meridional and sagittal modulation transfer function curves of lens 1 at -40°C, with image plane heights of 0.0000mm, 2.4600mm, 3.4790mm, 4.2608mm, and 4.9200mm, and operating wavelengths from 8μm to 12μm, for 42 line pairs. From... Figure 3 It can be seen that the meridional and sagittal modulation transfer function curves of the central field of view are greater than 0.38, while the modulation transfer functions of the other fields of view are greater than 0.2. Lens 1 has higher meridional and sagittal modulation transfer function curves, indicating that lens 1 has better image quality.

[0050] Figure 4 The diagram shows the meridional and sagittal modulation transfer function curves of lens 1 at 60°C, with image plane heights of 0.0000mm, 2.5000mm, 3.5355mm, 4.3301mm, and 4.9200mm, and operating wavelengths from 8μm to 12μm, for 42 line pairs. From... Figure 4 It can be seen that the meridional and sagittal modulation transfer function curves of the central field of view are greater than 0.45, while the modulation transfer functions of the other fields of view are greater than 0.29. Lens 1 has higher meridional and sagittal modulation transfer function curves, indicating that lens 1 has better image quality.

[0051] Reference Figure 5 This diagram shows the field curvature of lens 1 at operating wavelengths of 8μm, 10μm, and 12μm. The horizontal axis represents the field curvature in mm, and the vertical axis represents the field of view. Curve T is the meridional field curvature curve, and curve S is the sagittal field curvature curve. Figure 5 It can be seen that the meridional curvature and sagittal curvature of lens 1 are both controlled within the range of -0.10mm to 0.10mm.

[0052] Reference Figure 6 This diagram shows the distortion of lens 1. The horizontal axis represents the percentage of distortion, and the vertical axis represents the field of view. From... Figure 6 It can be seen that the distortion of lens 1 is less than 2%, thus avoiding image distortion.

[0053] Reference Figure 7 This diagram shows the relative illumination of lens 1. The horizontal axis represents the image plane height of the optical system, in mm. The vertical axis represents the normalized illuminance. From... Figure 7 It can be seen that the center relative illumination of lens 1 is 1, with no energy loss. The edge relative illumination of lens 1 is greater than 0.88. Therefore, the relative illumination of lens 1 is greater than 0.88.

[0054] Thus, with the above configuration, lens 1 can achieve high-quality imaging with only two lenses (first lens 11 and second lens 12), allowing lens 1 to have a relatively simple structure and effectively reduce the cost of lens 1. In addition, due to the small number of lenses, lens 1 can have a small weight, making lens 1 more portable.

[0055] Furthermore, by making the first surface S1 and the second surface S2 spherical, the first lens 11 can be processed by grinding and polishing. By making the third surface S3 and the fourth surface S4 aspherical, the second lens 12 can be processed by molding. Both grinding and polishing and molding have low processing costs, which further reduces the cost of the lens 1. In addition, the overall optical length of the lens 1 is short, which allows the lens 1 to have a smaller size, thereby further improving the portability of the lens 1.

[0056] It should be understood that the above embodiments are merely exemplary and are not intended to limit this application. Those skilled in the art can make various modifications and changes to the above embodiments under the teachings of this application without departing from the scope of this application.

[0057] It should be understood that in the formulas for aspherical and diffractive surfaces, the coefficients of terms not given in the polynomial are 0.

[0058] It should be understood that the first surface S1 and the second surface S2 are not limited to being spherical surfaces. For example, one of the first surface S1 and the second surface S2 can be a sphere, while the other can be a surface other than a sphere. The third surface S3 and the fourth surface S4 are not limited to being aspherical surfaces. For example, one of the third surface S3 and the fourth surface S4 can be an aspherical surface, while the other can be a surface other than an aspherical surface.

[0059] It should be understood that the first lens 11 is not limited to being made of germanium glass; for example, it can be made of materials such as zinc selenide single crystal, silicon single crystal, or zinc sulfide single crystal. The second lens 12 is not limited to being made of chalcogenide glass; for example, it can be made of materials such as germanium single crystal, zinc selenide single crystal, or silicon single crystal.

[0060] It should be understood that the radius of curvature of the first surface S1 is not limited to 10mm, 40mm, and 29.46mm, but may also include 15mm, 20mm, 25mm, 30mm, and 35mm. The radius of curvature of the second surface S2 is not limited to 20mm, 50mm, and 35.61mm, but may also include 25mm, 30mm, 35mm, 40mm, and 45mm. The curvature of the third surface S3 is not limited to -0.05mm. -1 and -0.02mm -1 For example, it can also include -0.045mm. -1 -0.04mm -1 -0.035mm -1 -0.03mm -1 and -0.025mm -1 The radius of curvature of the fourth surface S4 is not limited to -0.04 mm. -1 and -0.02mm -1 For example, it can also include -0.035mm. -1 -0.03mm -1 and -0.025mm -1 .

Claims

1. A lens having only two lenses, characterized in that, The lens (1) has a focal length of 35mm, and the lens includes: A first lens (11), which is a positive meniscus lens, includes a first surface (S1) and a second surface (S2), the first surface (S1) being convex and facing the object side, and the second surface (S2) being concave and facing the image side; and The second lens (12) is a negative meniscus lens. The second lens (12) includes a third surface (S3) and a fourth surface (S4). The third surface (S3) is concave and faces the object side, and the fourth surface (S4) is convex and faces the image side. The first lens (11) and the second lens (12) are arranged sequentially from the object side to the image side along the optical axis (A). The thickness of the first lens (11) on the optical axis (A) is 5 mm, and the thickness of the second lens (12) on the optical axis (A) is 9 mm. The air gap between the first lens (11) and the second lens (12) on the optical axis (A) is 18 mm. The first surface (S1) and the second surface (S2) are spherical surfaces. The radius of curvature of the first surface (S1) is 10 mm to 40 mm, and the radius of curvature of the second surface (S2) is 20 mm to 50 mm. The third surface (S3) and the fourth surface (S4) are aspherical surfaces, and the aspherical surfaces satisfy the following conditions: Where z is the sag of a point on the aspherical surface along the optical axis (A), r is the shortest distance between the point and the optical axis (A), c is the curvature of the vertex of the aspherical surface, k is the conic coefficient of the aspherical surface, and α i Let be the aspherical coefficients of the aspherical surface, i be the index of the polynomial term in the aspherical surface, and N be the total number of polynomial terms in the aspherical surface. The third surface (S3) satisfies -0.05mm. -1 ≤c≤-0.02mm -1 , k=-21.21, α2=-5.77e-5, α3=5.17e-8, α4=1.16e-08, α5=-1.30e-10, α6=4.68e-13, The fourth surface (S4) satisfies -0.04mm. -1 ≤c≤-0.02mm -1 , k=0.48, α2=1.24e-5, α3=6.44e-7, α4=-1.07e-8, α5=1.29e-10, α6=-5.74e-13.

2. The lens according to claim 1, characterized in that, The third surface (S3) is a diffraction surface, and the diffraction surface satisfies... Where Φ is the phase of the diffraction surface, M is the diffraction order of the diffraction surface, and A i ρ represents the coefficients of each term in the diffraction surface, ρ represents the normalized radial aperture coordinates of the diffraction surface, i represents the index of the polynomial term in the diffraction surface, and N represents the total number of polynomial terms in the diffraction surface.

3. The lens according to claim 2, characterized in that, The third surface (S3) satisfies M = 100, A1 = -1.51e+3, and A2 = 1.20e+5.

4. The lens according to claim 1, characterized in that, The first lens (11) is made of germanium glass, and The second lens (12) is made of chalcogenide glass.

5. The lens according to claim 1, characterized in that, The lens (1) has an F-number of 1.0, a field of view of 16° or greater, an optical length of 43.5 mm or less, an optical back focal length of 11 mm or greater, and an operating wavelength of 8 μm to 12 μm.

6. A thermal imager, characterized in that, It includes a lens (1) and a photosensitive element (2) as described in any one of claims 1 to 5.

Images