Medium wave refrigeration infrared lens and imaging device

Abstract

The invention discloses a medium-wave refrigeration infrared lens, the focal length of which is 300mm, and the infrared lens comprises a first lens, a second lens, a third lens, a fourth lens and a fifth lens which are sequentially arranged along the transmission direction of an optical axis, the first lens, the third lens and the fifth lens are all meniscus positive lenses with convex surfaces facing the object side, the second lens is a meniscus negative lens with a convex surface facing the object side, and the fourth lens is a meniscus positive lens with a convex surface facing the image side; wherein the first lens and the fifth lens are made of silica glass, the second lens and the third lens are made of germanium glass, and the fourth lens is made of chalcogenide glass. By reasonably distributing the focal power, adjusting the combination and arrangement mode of the lenses and utilizing the difference of thermal characteristics between different materials, the positive focal power and the negative focal power are matched with each other, the influence caused by temperature change is compensated, and therefore athermalization is achieved under the condition that it is ensured that the size is small. The invention further discloses an imaging device.

Description

Technical Field

[0001] The present application belongs to the field of infrared lens technology, and specifically relates to a medium-wave cooled infrared lens and an imaging device. Background Art

[0002] The operating temperature requirement of general infrared lenses can reach -40℃-60℃, but due to the large thermal expansion coefficient and temperature variation coefficient of refractive index of infrared lens materials, when the ambient temperature changes, the refractive index, surface curvature, thickness of each lens and the interval between adjacent lenses will change significantly, which will cause serious defocusing of the infrared lens. The use of active athermalization will increase the size of the infrared lens. Therefore, there is an urgent need for an infrared lens that uses passive athermalization to achieve athermalization and is smaller in size. Summary of the invention

[0003] Based on this, the present application provides a medium-wave cooled infrared lens and imaging device which use a passive heat elimination method to achieve athermalization and have a relatively small size.

[0004] The technical solution proposed in this application is: A medium-wave cooling infrared lens with a focal length of 300 mm, comprising a first lens, a second lens, a third lens, a fourth lens and a fifth lens arranged in sequence along the transmission direction of the optical axis; the first lens, the third lens and the fifth lens are all positive meniscus lenses with a convex surface facing the object side, the second lens is a negative meniscus lens with a convex surface facing the object side, and the fourth lens is a positive meniscus lens with a convex surface facing the image side; The first lens and the fifth lens are made of silicon glass, the second lens and the third lens are made of germanium glass, and the fourth lens is made of chalcogenide glass.

[0005] In this way, by reasonably distributing the optical power, adjusting the combination and arrangement of the lenses, and utilizing the differences in thermal properties between different materials, the positive and negative optical powers cooperate with each other and compensate for the effects of temperature changes, thereby achieving athermalization while ensuring a small volume.

[0006] Furthermore, the air gap between the first lens and the second lens is 9.8 mm, the air gap between the second lens and the third lens is 235.61 mm, the air gap between the third lens and the fourth lens is 28.06 mm, and the air gap between the fourth lens and the fifth lens is 41.15 mm.

[0007] Further, the center thickness of the first lens is 16.02 mm, the radius of curvature of the object side is 136.74 mm, and the radius of curvature of the image side is 252.05 mm; the center thickness of the second lens is 5.58 mm, the radius of curvature of the object side is 190.87 mm, and the radius of curvature of the image side is 126.45 mm; the center thickness of the third lens is 5.55 mm, the radius of curvature of the object side is 25.88 mm, and the radius of curvature of the image side is 22.92 mm; the center thickness of the fourth lens is 5.5 mm, the radius of curvature of the object side is -13.83 mm, and the radius of curvature of the image side is -15.44 mm; the center thickness of the fifth lens is 6.23 mm, the radius of curvature of the object side is 58.476 mm, and the radius of curvature of the image side is 740.11 mm.

[0008] Furthermore, the infrared lens has an F number of 2.0, a field of view of 4°×3.2°, and an operating band of 3.7-4.8 μm.

[0009] Furthermore, the image-side surfaces of the second lens and the third lens, and the object-side surfaces of the fourth lens and the fifth lens are all 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 surface; k is the cone coefficient; A, B, C, and D are high-order aspherical coefficients.

[0010] An imaging device comprises the above-mentioned medium-wave cooled infrared lens and a detector for receiving images formed by the infrared lens, wherein the detector is a medium-wave cooled detector.

[0011] Furthermore, the detector includes a protective window, an aperture and an image plane which are arranged in sequence, and the air gap between the fifth lens and the protective window is 15 mm.

[0012] Furthermore, the distance between the object side surface of the first lens and the image plane on the optical axis is 400 mm, and the distance between the image side surface of the fifth lens and the image plane on the optical axis is 46.5 mm.

[0013] Furthermore, the number of pixels of the detector is 640×512, and the pixel size is 25 μm. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The accompanying drawings are used to provide further understanding of the present application and constitute a part of the specification. They are used to explain the present application together with the embodiments of the present application and do not constitute a limitation of the present application.

[0015] Figure 1A schematic diagram of the optical path structure of an imaging device provided in one embodiment of the present application; Figure 2 MTF diagram of the medium-wave cooled infrared lens provided for this application at 25°C; Figure 3 Spot diagram of the medium wave cooled infrared lens provided for this application at 25°C; Figure 4 MTF diagram of the medium-wave cooled infrared lens at 60°C provided for this application; Figure 5 The spot diagram of the medium-wave cooled infrared lens provided for this application at 60°C; Figure 6 MTF diagram of the medium-wave cooled infrared lens provided for this application at -40°C; Figure 7 This is the spot diagram of the medium-wave cooled infrared lens provided in this application at -40°C.

[0016] Description of labels: 11. First lens; 12. Second lens; 13. Third lens; 14. Fourth lens; 15. Fifth lens; 21. Protective window; 22. Aperture; 23. Image plane. DETAILED DESCRIPTION

[0017] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0018] The present application discloses an imaging device, including a medium-wave cooled infrared lens and a detector for receiving the image formed by the infrared lens, wherein the detector corresponds to a medium-wave cooled detector. The infrared lens has a focal length of 300 mm, an F number of 2.0, a field of view of 4°×3.2°, and a working band of 3.7-4.8 μm; the number of pixels of the detector is 640×512, and the pixel size is 25 μm.

[0019] like Figure 1As shown, in one embodiment, the infrared lens includes a first lens 11, a second lens 12, a third lens 13, a fourth lens 14 and a fifth lens 15 arranged in sequence along the transmission direction of the optical axis. The first lens 11, the third lens 13 and the fifth lens 15 are all positive meniscus lenses with convex surfaces facing the object side, the second lens 12 is a negative meniscus lens with convex surfaces facing the object side, and the fourth lens 14 is a positive meniscus lens with convex surfaces facing the image side. Among them, the materials of the first lens 11 and the fifth lens 15 are both silicon glass, the materials of the second lens 12 and the third lens 13 are both germanium glass, and the material of the fourth lens 14 is chalcogenide glass. In this way, by reasonably allocating the optical focal length, adjusting the combination and arrangement of the lenses, and utilizing the differences in thermal properties between different materials, the positive and negative optical focal lengths are coordinated with each other to compensate for the effects of temperature changes, thereby achieving athermalization while ensuring a small volume.

[0020] It should be noted that in Figure 1 In the figure, the blue light beam is the light beam of the central field of view, and the green light beam is the light beam of the maximum field of view.

[0021] In one embodiment, the detector includes a protective window 21, an aperture 22 and an image plane 23 arranged in sequence. As shown in Table 1, further, the air interval between the first lens 11 and the second lens 12 is 9.8 mm, the air interval between the second lens 12 and the third lens 13 is 235.61 mm, the air interval between the third lens 13 and the fourth lens 14 is 28.06 mm, the air interval between the fourth lens 14 and the fifth lens 15 is 41.15 mm, and the air interval between the fifth lens 15 and the protective window 21 is 15 mm.

[0022] Furthermore, the center thickness of the first lens 11 is 16.02 mm, the radius of curvature of the object side surface is 136.74 mm, and the radius of curvature of the image side surface is 252.05 mm; the center thickness of the second lens 12 is 5.58 mm, the radius of curvature of the object side surface is 190.87 mm, and the radius of curvature of the image side surface is 126.45 mm; the center thickness of the third lens 13 is 5.55 mm, the radius of curvature of the object side surface is 25.88 mm, and the radius of curvature of the image side surface is 22.92 mm; the center thickness of the fourth lens 14 is 5.5 mm, the radius of curvature of the object side surface is -13.83 mm, and the radius of curvature of the image side surface is -15.44 mm; the center thickness of the fifth lens 15 is 6.23 mm, the radius of curvature of the object side surface is 58.476 mm, and the radius of curvature of the image side surface is 740.11 mm.

[0023] It is understandable that if Figure 1As shown, the optical axis transmission direction is from left to right, and the left and right sides of the lens are the object side and the image side, respectively. Taking the first lens 11 as an example, the S1 surface on the left side of the first lens 11 is the object side, and the S2 surface on the right side is the image side. Other lenses are not described here.

[0024] Table 1 Lens parameters In one embodiment, the distance between the object side surface of the first lens 11 and the image plane 23 on the optical axis is 400 mm, that is, the total length of the optical system of the imaging device is 400 mm, and the distance between the image side surface of the fifth lens 15 and the image plane 23 on the optical axis is 46.5 mm, that is, the back focus of the optical system is 46.5 mm. In this way, a long focal length of 300 mm is achieved through a shorter back focus, which effectively shortens the total length and reduces the volume while ensuring the imaging quality.

[0025] In one embodiment, the image-side surfaces of the second lens 12 and the third lens 13 and the object-side surfaces of the fourth lens 14 and the fifth lens 15 are all aspherical surfaces, and satisfy the aspherical surface formula: Among them, Z is the distance vector height from the vertex of the aspheric surface when the aspheric surface is at a height r along the optical axis; c=1 / R; R is the paraxial curvature fitting radius of the mirror surface; k is the cone coefficient; A, B, C, D are high-order aspheric coefficients. The above-mentioned aspheric surface data are shown in Table 2.

[0026] Table 2 Aspheric surface data See also Figures 2 to 7 , Figure 2 is the MTF diagram of the infrared lens in the above embodiment at a temperature of 25°C (with a cut-off resolution of 20lp / mm), Figure 3 is a point diagram of the infrared lens in the above embodiment when the temperature is 25°C; Figure 4 is the MTF diagram of the infrared lens in the above embodiment at a temperature of 60°C (with a cut-off resolution of 20lp / mm), Figure 5 is a point diagram of the infrared lens in the above embodiment when the temperature is 60°C; Figure 6 is the MTF diagram of the infrared lens in the above embodiment at a temperature of -40°C (with a cut-off resolution of 20lp / mm), Figure 7 This is a point diagram of the infrared lens in the above embodiment when the temperature is -40°C. It can be concluded from the figure that the image quality of the infrared lens is good and the operating temperature range is wide.

[0027] In summary, the focal length of the medium-wave cooled infrared lens provided by the present application is 300mm, the F number is 2.0, the field of view is 4°×3.2°, the working band is 3.7-4.8μm, and it can match the cooled detector with a pixel number of 640×512 and a pixel size of 25μm. The structure of the infrared lens is relatively simple, and the imaging is clear. At the same time, the passive heat elimination is adopted to achieve the effect of athermalization, and the volume is small.

[0028] Although the embodiments of the present application have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present application, and that the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A medium wave cooling infrared lens, characterized in that: The focal length is 300mm, and the infrared lens comprises a first lens, a second lens, a third lens, a fourth lens and a fifth lens which are sequentially arranged along the transmission direction of the optical axis; the first lens, the third lens and the fifth lens are all positive meniscus lenses with the convex surface facing the object side, the second lens is a negative meniscus lens with the convex surface facing the object side, and the fourth lens is a positive meniscus lens with the convex surface facing the image side; The first lens and the fifth lens are made of silicon glass, the second lens and the third lens are made of germanium glass, and the fourth lens is made of chalcogenide glass.

2. The medium wave cooling infrared lens according to claim 1, characterized in that: The air space between the first lens and the second lens is 9.8 mm, the air space between the second lens and the third lens is 235.61 mm, the air space between the third lens and the fourth lens is 28.06 mm, and the air space between the fourth lens and the fifth lens is 41.15 mm.

3. The medium wave cooling infrared lens according to claim 1, characterized in that: The center thickness of the first lens is 16.02mm, the radius of curvature of the object side is 136.74mm, and the radius of curvature of the image side is 252.05mm; the center thickness of the second lens is 5.58mm, the radius of curvature of the object side is 190.87mm, and the radius of curvature of the image side is 126.45mm; the center thickness of the third lens is 5.55mm, the radius of curvature of the object side is 25.88mm, and the radius of curvature of the image side is 22.92mm; the center thickness of the fourth lens is 5.5mm, the radius of curvature of the object side is -13.83mm, and the radius of curvature of the image side is -15.44mm; the center thickness of the fifth lens is The radius of curvature of the object side is 6.23mm, the radius of curvature of the image side is 58.476mm, and the radius of curvature of the image side is 740.11mm.

4. The medium wave cooling infrared lens according to claim 1, characterized in that: The infrared lens has an F number of 2.0, a field of view of 4°×3.2°, and a working band of 3.7-4.8 μm.

5. The medium wave cooling infrared lens according to claim 1, characterized in that: The image-side surfaces of the second lens and the third lens, and the object-side surfaces of the fourth lens and the fifth lens are all 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 surface; k is the cone coefficient; A, B, C, and D are high-order aspherical coefficients.

6. An imaging device, characterized in that: It comprises the medium wave cooled infrared lens as described in any one of claims 1 to 5 and a detector for receiving images formed by the infrared lens, wherein the detector is a medium wave cooled detector.

7. The imaging device according to claim 6, characterized in that The detector comprises a protective window, an aperture and an image plane which are arranged in sequence, and the air gap between the fifth lens and the protective window is 15 mm.

8. The imaging device according to claim 7, characterized in that: The distance between the object side surface of the first lens and the image plane on the optical axis is 400 mm, and the distance between the image side surface of the fifth lens and the image plane on the optical axis is 46.5 mm.

9. The imaging device according to claim 6, characterized in that: The number of pixels of the detector is 640×512, and the pixel size is 25 μm.

Images