A long-wave dual-view infrared lens and imaging device

Abstract

The application belongs to the field of infrared optical technology and discloses a long-wave double-view-field infrared lens and an imaging device. The lens comprises a front fixed group, a view-field switching mirror and a rear fixed group which are coaxially arranged in sequence along the transmission direction of the optical axis. The front fixed group is a first lens. The view-field switching mirror is a second lens. The second lens is moved along the optical axis to realize the switching of a short-focus 55mm view field and a long-focus 220mm view field. The rear fixed group is composed of a third lens, a fourth lens, a fifth lens, a sixth lens and a seventh lens which are arranged in sequence. The lens realizes the switching of two grades of short-focus 55mm and long-focus 220mm only by the movement of the view-field switching mirror, and the switching of the view field is convenient. The lens does not need to additionally set an adjusting lens and a diffraction surface for temperature and distance compensation, and the imaging quality is good. The lens can match a detector with 640*512 image elements and 15um image element size. The working waveband is 7.7um-9.3um, and the lens is especially suitable for target detection in a harsh environment with smoke, clouds and the like.

Description

Technical Field

[0001] This technology belongs to the field of infrared optics technology, and specifically relates to a long-wavelength dual-field infrared lens and imaging device. Background Technology

[0002] Infrared lenses are widely used in military and security fields because they can penetrate smoke, fog, haze, snow and other smudges and can be identified by camouflage. They are not blinded by strong light or flashes and can be used for long-distance, all-weather observation. They are especially suitable for target detection at night and under adverse weather conditions.

[0003] Dual-field-of-view optical systems can rapidly change the field of view, combining the wide coverage of a short focal length field of view with the high resolution of a long focal length field of view. Working together, they can achieve both wide-field-of-view target search and narrow-field-of-view tracking and measurement. With the development of infrared detectors, higher demands are being placed on their compatible optical systems. To achieve longer detection distances, lenses with large target surfaces and long focal lengths are required.

[0004] However, in the design of dual-field-of-view optical systems, especially lenses with large target surfaces and long focal lengths, in order to further compensate for the effects of temperature and distance, in addition to the adjustment lenses for field-of-view switching, additional adjustment lenses for temperature and distance compensation are required, which further complicates the structure of the dual-field-of-view optical system. Alternatively, diffraction technology may be used, reducing the system's transmittance.

[0005] Compared to mid-wave cooled detectors, long-wave infrared detectors are less prone to image trailing when capturing high-speed moving targets, and their penetration distance is longer under dusty conditions. With the development of long-wave infrared detectors, existing long-wave dual-field-of-view infrared lenses can no longer meet their requirements. Summary of the Invention

[0006] To address the above problems, this invention provides a long-wave dual-field-of-view infrared lens. It proposes a long-wave dual-field-of-view infrared lens that uses a field-of-view switching lens to achieve two-stage switching between a short focal length of 55mm and a long focal length of 220mm, resulting in good image quality.

[0007] A long-wavelength dual-field-of-view infrared lens, comprising a front fixed group, a field-of-view switching mirror, and a rear fixed group arranged coaxially along the optical axis transmission direction; the front fixed group is a first lens; the field-of-view switching mirror is a second lens; the second lens moves along the optical axis to switch between a short focal length 55mm field of view and a long focal length 220mm field of view; the rear fixed group consists of a third lens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens arranged in sequence.

[0008] Furthermore, the first, third, and seventh lenses are made of germanium; the second, fourth, and fifth lenses are made of chalcogenide glass; and the sixth lens is made of zinc selenide.

[0009] Furthermore, the operating wavelength of the lens is 7.7μm-9.3μm.

[0010] Furthermore, the image-side surface of the first lens, the object-side surface of the second lens, the object-side surface of the fourth lens, the object-side surface of the fifth lens, the object-side surface of the sixth lens, and the image-side surface of the seventh lens are all aspherical surfaces, and satisfy the aspherical surface formula:

[0011]

[0012] 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.

[0013] Further, the first lens has a center thickness of 9 mm, an object-side radius of curvature of 105.45 mm, and an image-side radius of curvature of 130.64 mm; the second lens has a center thickness of 3 mm, an object-side radius of curvature of -67.83 mm, and an image-side radius of curvature of 75.83 mm; the third lens has a center thickness of 6 mm, an object-side radius of curvature of 66.36 mm, and an infinite image-side radius of curvature; the fourth lens has a center thickness of 5 mm, an object-side radius of curvature of -19.1 mm, and an image-side radius of curvature of -24 mm; the fifth lens has a center thickness of 10 mm, an object-side radius of curvature of -29.1 mm, and an image-side radius of curvature of -29.86 mm; the sixth lens has a center thickness of 6 mm, an object-side radius of curvature of 31.96 mm, and an image-side radius of curvature of 26.51 mm; and the seventh lens has a center thickness of 5 mm, an object-side radius of curvature of 36.33 mm, and an image-side radius of curvature of 451.24 mm.

[0014] Furthermore, the air gap between the first lens and the second lens is adjustable in the range of 74.38-104.08 mm; the air gap between the second lens and the third lens is adjustable in the range of 39.70-10 mm; the air gap between the third lens and the fourth lens is 12.56 mm; the air gap between the fourth lens and the fifth lens is 1.57 mm; the air gap between the fifth lens and the sixth lens is 47.80 mm; and the air gap between the sixth lens and the seventh lens is 1.82 mm.

[0015] Furthermore, the lens also includes a protective window, a chopper window, and a cold screen arranged sequentially after the rear fixing group.

[0016] Another object of the present invention is to provide an imaging device, including the above-described long-wave dual-field infrared lens and a detector for receiving the image formed by the long-wave dual-field infrared lens.

[0017] Furthermore, the detector is a cooled detector with 640×512 pixels and a pixel size of 15μm.

[0018] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects:

[0019] The lens of this invention achieves two-stage switching between a short focal length of 55mm and a long focal length of 220mm simply by moving the field-of-view switching mirror, making field-of-view switching convenient; it eliminates the need for additional adjustment lenses and diffraction surfaces for temperature and distance compensation, resulting in good image quality; it can be matched with detectors with a pixel count of 640×512 and a pixel size of 15μm; and it operates in the 7.7μm-9.3μm band, making it particularly suitable for target detection in harsh environments such as smoke and clouds. Attached Figure Description

[0020] 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.

[0021] Figure 1 This is a diagram showing the lens composition of the long-wave dual-field infrared lens in Example 1;

[0022] Figure 2 This is the optical path diagram of the long-wave dual-field infrared lens in Example 1;

[0023] Figure 3 This is a dot plot of the 220mm focal length of the long-wave dual-field infrared lens in Example 1;

[0024] Figure 4 MTF diagram of the long-wave dual-field infrared lens with a focal length of 220mm in Example 1;

[0025] Figure 5 This is a dot plot of the 55mm focal length of the long-wave dual-field infrared lens in Example 1;

[0026] Figure 6 The image shows the MTF diagram of the long-wave dual-field infrared lens with a focal length of 55mm in Example 1.

[0027] Reference numerals: 1. First lens; 2. Second lens; 3. Third lens; 4. Fourth lens; 5. Fifth lens; 6. Sixth lens; 7. Seventh lens; 8. Protective window; 9. Chopper window; 10. Cold screen; 11. Focal plane array of the detector. Detailed Implementation

[0028] 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.

[0029] Example 1

[0030] This embodiment provides a long-wavelength dual-field-of-view infrared lens. The following example uses a long-wavelength dual-field-of-view infrared lens applied to a 640×512, 15μm cooled detector, with a working wavelength of 7.7μm-9.3μm.

[0031] like Figure 1 As shown, the lens includes a front fixed group, a field-of-view switching mirror, and a rear fixed group arranged coaxially along the optical axis transmission direction; the front fixed group is a first lens 1; the field-of-view switching mirror is a second lens 2; the rear fixed group consists of a third lens 3, a fourth lens 4, a fifth lens 5, a sixth lens 6, and a seventh lens 7 arranged in sequence.

[0032] like Figure 2 As shown, the light beam passes sequentially from left to right through the first lens 1, the second lens 2, the third lens 3, the fourth lens 4, the fifth lens 5, the sixth lens 6, and the seventh lens 7. After passing through the protective window 8, the chopper window 9, and the cold screen 10 located after the rear fixed group, it images onto the detector's focal plane array 11. During focus adjustment, the second lens 2 moves along the optical axis between the first lens 1 and the third lens 3 to switch between a short focal length of 55mm and a long focal length of 220mm.

[0033] As shown in Table 1, in one specific embodiment, the first lens 1 has a center thickness of 9mm, an object-side radius of curvature of 105.45mm, and an image-side radius of curvature of 130.64mm; the second lens 2 has a center thickness of 3mm, an object-side radius of curvature of -67.83mm, and an image-side radius of curvature of 75.83mm; the third lens 3 has a center thickness of 6mm, an object-side radius of curvature of 66.36mm, and an infinite image-side radius of curvature; the fourth lens 4 has a center thickness of 5mm, an object-side radius of curvature of -67.83mm, and an image-side radius of curvature of 130.64mm; The fifth lens 5 has a center thickness of 10mm, an object-side radius of curvature of -29.1mm, and an image-side radius of curvature of -29.86mm; the sixth lens 6 has a center thickness of 6mm, an object-side radius of curvature of 31.96mm, and an image-side radius of curvature of 26.51mm; the seventh lens 7 has a center thickness of 5mm, an object-side radius of curvature of 36.33mm, and an image-side radius of curvature of 451.24mm. It can be understood that along the optical axis from left to right, the left side is the object side and the right side is the image side, such as the S1 surface of the first lens 1 being the object side and the S2 surface being the image side. Other lenses will not be described further here.

[0034] The air gap between the third lens 3 and the fourth lens 4 is 12.56 mm; the air gap between the fourth lens 4 and the fifth lens 5 is 1.57 mm; the air gap between the fifth lens 5 and the sixth lens 6 is 47.80 mm; and the air gap between the sixth lens 6 and the seventh lens 7 is 1.82 mm. The air gaps between the second lens 2 and both the first lens 1 and the second lens 2 are adjustable. The air gap between the first lens 1 and the second lens 2 can be adjusted within a range of 74.38 / 104.08 mm; the air gap between the second lens 2 and the third lens 3 can be adjusted within a range of 39.70 / 10 mm.

[0035] Adjusting the second lens 2 to switch between large and small fields of view: When changing to a short focal length of 55mm, the second lens 2 moves towards the object side until the air gap between the first lens 1 and the second lens 2 is 74.38mm and the air gap between the second lens 2 and the third lens 3 is 39.70mm; when changing to a long focal length of 220mm, the second lens 2 moves towards the image side until the air gap between the first lens 1 and the second lens 2 is 104.08mm and the air gap between the second lens 2 and the third lens 3 is 10mm.

[0036] The first lens 1, the third lens 3, and the seventh lens 7 are made of germanium; the second lens 2, the fourth lens 4, and the fifth lens 5 are made of chalcogenide glass; and the sixth lens 6 is made of zinc selenide.

[0037] Table 1 Parameters of each lens

[0038]

[0039] As shown in Table 2, the image-side surface S2 of the first lens 1, the object-side surface S3 of the second lens 2, the object-side surface S7 of the fourth lens 4, the object-side surface S9 of the fifth lens, the object-side surface S11 of the sixth lens, and the image-side surface S14 of the seventh lens are all aspherical surfaces and satisfy the aspherical surface formula:

[0040]

[0041] 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.

[0042] Table 2 Aspheric coefficient data

[0043]

[0044] Figure 4 , Figure 6 The figures show the MTF (Mean Transmission Factor) curves for long-wave dual-field infrared lenses at both long and short focal lengths. The horizontal axis represents different spatial frequencies, and the vertical axis represents modulation degree. The MTF curves for all fields of view representing the meridional plane are shown as the curve labeled T in the figure, while the MTF curve representing the sagittal plane is shown as the curve labeled S in the figure. The symbol DIFF.LIMIT represents the diffraction limit. Figure 3 , Figure 5 The images show dot plots for long-wave dual-field infrared lenses at both long and short focal lengths. 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 Airy disk diameter, and the image quality is good.

[0045] The long-wave dual-field infrared lens provided in this embodiment has a focal length of f′=55 / 220mm, a resolution of 640×512, 15μm, an F number of 2, and operates in the long-wave band of 7.7μm-9.3μm. It has strong penetration and good imaging quality, and is especially suitable for target detection in harsh environments such as smoke and clouds.

[0046] 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 long-wavelength dual-field-of-view infrared lens, characterized in that, The lens includes a front fixed group, a field-of-view switching lens, and a rear fixed group arranged coaxially along the optical axis transmission direction; the front fixed group is a first lens; the field-of-view switching lens is a second lens, and the second lens moves along the optical axis to achieve field-of-view switching between a short focal length of 55mm and a long focal length of 220mm; the rear fixed group consists of a third lens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens arranged in sequence. The lens contains 7 lenses with optical power. The first, third, and seventh lenses are made of germanium; the second lens is made of IRG206, the fourth lens is made of IRG201, the fifth lens is made of IRG203; and the sixth lens is made of zinc selenide. The first lens has a center thickness of 9 mm, an object-side radius of curvature of 105.45 mm, and an image-side radius of curvature of 130.64 mm; the second lens has a center thickness of 3 mm, an object-side radius of curvature of -67.83 mm, and an image-side radius of curvature of 75.83 mm; the third lens has a center thickness of 6 mm, an object-side radius of curvature of 66.36 mm, and an infinity image-side radius of curvature; the fourth lens has a center thickness of 5 mm, an object-side radius of curvature of -19.1 mm, and an image-side radius of curvature of -24 mm; the fifth lens has a center thickness of 10 mm, an object-side radius of curvature of -29.1 mm, and an image-side radius of curvature of -29.86 mm; the sixth lens has a center thickness of 6 mm, an object-side radius of curvature of 31.96 mm, and an image-side radius of curvature of 26.51 mm; and the seventh lens has a center thickness of 5 mm, an object-side radius of curvature of 36.33 mm, and an image-side radius of curvature of 451.24 mm.

2. The long-wavelength dual-field infrared lens according to claim 1, characterized in that, The lens operates in the wavelength range of 7.7μm-9.3μm.

3. The long-wave dual-field 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 fourth lens, the object-side surface of the fifth lens, the object-side surface of the sixth lens, and the image-side surface of the seventh lens are all 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.

4. The long-wavelength dual-field infrared lens according to claim 1, characterized in that, The air gap between the first lens and the second lens is adjustable from 74.38 mm to 104.08 mm; the air gap between the second lens and the third lens is adjustable from 39.70 mm to 10 mm; the air gap between the third lens and the fourth lens is 12.56 mm; the air gap between the fourth lens and the fifth lens is 1.57 mm; the air gap between the fifth lens and the sixth lens is 47.80 mm; and the air gap between the sixth lens and the seventh lens is 1.82 mm.

5. The long-wavelength dual-field infrared lens according to claim 1, characterized in that, The lens also includes a protective window, a chopper window, and a cold screen, which are arranged sequentially after the rear fixing group.

6. An imaging device, characterized in that, It includes the long-wave dual-field infrared lens as described in any one of claims 1 to 5 and a detector for receiving the image formed by the long-wave dual-field infrared lens.

7. The imaging apparatus according to claim 6, characterized in that, The detector is a cooled detector with 640×512 pixels and a pixel size of 15μm.

Images