Small-F-number athermalization long-wave infrared collimating lens

Abstract

The invention relates to the technical field of optical lenses, in particular to a small-F-number athermalization long-wave infrared collimating lens, which comprises an aperture diaphragm, a first lens, a second lens, a third lens, a fourth lens, an optical filter and an image surface which are sequentially arranged along an optical axis from an object space to an image space, the first lens is a positive meniscus even-order aspheric lens which has a concave surface bent towards the image side and has a positive focal length. The second lens is a negative meniscus even-order aspheric lens with a concave surface bent towards the object side and a negative focal length; the third lens is a positive meniscus even-order aspheric lens which has a concave surface bent towards the image side and has a negative focal length; and the fourth lens is a negative meniscus even-order aspheric lens with a concave surface bent towards the object side and a positive focal length. The long-wave infrared collimating lens provided by the invention is stable in image surface and clear in imaging when the temperature changes in a wide temperature range.

Description

Technical Field

[0001] The invention relates to the technical field of optical lenses, and in particular to a small F-number athermal long-wave infrared collimating lens. Background Art

[0002] As the application of infrared imaging systems in aerospace, civil detection, security and search and rescue continues to deepen, higher and higher requirements are placed on the imaging quality and environmental adaptability of infrared imaging systems. The refractive index temperature coefficient dn / dT of long-wave infrared optical materials is relatively large, and changes in ambient temperature will cause severe defocusing of the infrared collimating lens, resulting in a significant reduction in the imaging quality of the system.

[0003] Therefore, there is an urgent need to provide a long-wave infrared collimating lens with athermal difference to meet the demand for high-quality imaging in a wide temperature range. Summary of the invention

[0004] In order to solve one or more technical problems in the prior art, the present invention provides a small F-number athermal long-wave infrared collimating lens, which has a stable image plane and clear imaging when the temperature changes within a wide temperature range, and solves the problem that due to the large refractive index temperature coefficient of long-wave infrared optical materials, changes in ambient temperature will cause serious defocusing of the infrared collimating lens, resulting in a significant reduction in the imaging quality of the system.

[0005] In order to achieve the above-mentioned object, the present invention provides a small F-number athermal long-wave infrared collimating lens, comprising: an aperture stop, a first lens, a second lens, a third lens, a fourth lens, a filter and an image plane arranged in sequence along the optical axis from the object side to the image side;

[0006] The first lens is a positive meniscus even-order aspheric lens with a concave surface curved toward the image side and a positive focal length;

[0007] The second lens is a negative meniscus even-order aspheric lens with a concave surface curved toward the object and a negative focal length;

[0008] The third lens is a positive meniscus even-order aspheric lens with a concave surface curved toward the image side and a negative focal length;

[0009] The fourth lens is a negative meniscus even-order aspheric lens with a concave surface curved toward the object and a positive focal length;

[0010] The first lens and the fourth lens are made of the same optical glass, with a refractive index greater than 2.77 and a dispersion constant less than 158; the refractive index of the second lens is greater than 2.1, and the dispersion constant is less than 22.7; the refractive index of the third lens is greater than 4, and the dispersion constant is less than 34.8.

[0011] In one possible design, the long-wave infrared collimating lens has an operating band of 8 μm to 12 μm, a field of view of 12°, a focal length of 50 mm, an F number of 1, a distortion of less than 0.2%, an exit pupil distance greater than 250 mm, and an athermal temperature range of -40°C to 60°C.

[0012] In a possible design, the distance between the aperture stop and the center of the first lens is 10 mm;

[0013] The center distance between the first lens and the second lens is 18 mm;

[0014] The center distance between the second lens and the third lens is 2 mm;

[0015] The center distance between the third lens and the fourth lens is 10 mm; and / or

[0016] The center distance between the fourth lens and the filter is 5 mm.

[0017] In a possible design, a surface of the first lens close to the image side, a surface of the second lens close to the image side, a surface of the third lens close to the object side, and a surface of the fourth lens close to the object side are all even-order aspherical surfaces.

[0018] In a possible design, the curvature radius of a surface of the first lens close to the object side is 71 mm, and the curvature radius of a surface close to the image side is 234 mm;

[0019] The central thickness of the first lens is 11 mm; and / or

[0020] The focal length of the first lens is 55 mm.

[0021] In a possible design, the curvature radius of a surface of the second lens close to the object side is -44 mm, and the curvature radius of a surface close to the image side is -63 mm;

[0022] The central thickness of the second lens is 5 mm; and / or

[0023] The focal length of the second lens is -141.92 mm.

[0024] In a possible design, the curvature radius of a surface of the third lens close to the object side is 39 mm, and the curvature radius of a surface close to the image side is 32 mm;

[0025] The central thickness of the third lens is 5 mm; and / or

[0026] The focal length of the third lens is -104.88 mm.

[0027] In a possible design, the curvature radius of a surface of the fourth lens close to the object side is 57 mm, and the curvature radius of a surface close to the image side is 467 mm;

[0028] The center thickness of the fourth lens is 8 mm;

[0029] The focal length of the fourth lens is 36.63 mm.

[0030] In one possible design, the center thickness of the filter is 2 mm; and / or

[0031] The bandpass wavelength of the optical filter is 8 to 12 μm.

[0032] In a possible design, the first lens and the fourth lens are chalcogenide glasses;

[0033] The second lens is made of ZnS optical glass;

[0034] The third lens is made of germanium optical glass;

[0035] The filter is germanium optical glass.

[0036] Compared with the prior art, the present invention has at least the following beneficial effects:

[0037] The present invention matches the thermal properties (refractive index, dispersion constant, etc.) of the optical materials of each lens so that the temperature focal shifts of the optical system within the working environment temperature range compensate or offset each other, realizes an optical passive athermalization method, eliminates the influence of temperature, and obtains an athermal effect, so that the image plane of the long-wave infrared collimating lens is stable and the imaging is clear when the temperature changes within a wide temperature range, and solves the problem that the environmental temperature change will cause the infrared collimating lens to be seriously defocused due to the large refractive index temperature coefficient of the long-wave infrared optical material, resulting in a significant reduction in the imaging quality of the system.

[0038] The long-wave infrared collimating lens provided by the present invention realizes athermalization by optical passivity, and the image plane is stable and the imaging is clear when the temperature changes within a wide temperature range; at the same time, high sensitivity and low distortion are taken into account, which can greatly improve the stability and accuracy of the optical system, and there is no need to adopt mechanical active athermalization, which can effectively reduce the production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0040] Figure 1This is the optical path diagram of the long-wave infrared collimating lens provided by the present invention;

[0041] Figure 2 It is a field curvature and distortion diagram of the long-wave infrared collimating lens provided by the present invention;

[0042] Figure 3 This is the MTF curve of the long-wave infrared collimating lens provided by the present invention at room temperature;

[0043] Figure 4 This is the MTF curve of the long-wave infrared collimating lens provided by the present invention at -40°C;

[0044] Figure 5 This is the MTF curve of the long-wave infrared collimating lens provided by the present invention at 60°C;

[0045] Among them, 1-aperture stop, 2-first lens, 3-second lens, 4-third lens, 5-fourth lens, 6-filter, 7-image plane. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0047] like Figure 1 As shown, the present invention provides a small F-number athermal long-wave infrared collimating lens, comprising: an aperture stop 1, a first lens 2, a second lens 3, a third lens 4, a fourth lens 5, a filter 6 and an image plane 7 arranged in sequence along the optical axis from the object side to the image side;

[0048] The first lens 2 is a positive meniscus even-order aspheric lens with a concave surface curved toward the image side and a positive focal length;

[0049] The second lens 3 is a negative meniscus even-order aspheric lens with a concave surface curved toward the object and a negative focal length;

[0050] The third lens 4 is a positive meniscus even-order aspheric lens with a concave surface curved toward the image side and a negative focal length;

[0051] The fourth lens 5 is a negative meniscus even-order aspheric lens with a concave surface curved toward the object and a positive focal length;

[0052] The first lens 2 and the fourth lens 5 are made of the same optical glass, with a refractive index greater than 2.77 and a dispersion constant less than 158; the refractive index of the second lens 3 is greater than 2.1, and the dispersion constant is less than 22.7; the refractive index of the third lens 4 is greater than 4, and the dispersion constant is less than 34.8.

[0053] The present invention matches the thermal properties (refractive index, dispersion constant, etc.) of the optical materials of each lens so that the temperature focal shifts of the optical system within the working environment temperature range compensate or offset each other, realizes an optical passive athermalization method, eliminates the influence of temperature, and obtains an athermal effect, so that the image plane of the long-wave infrared collimating lens is stable and the imaging is clear when the temperature changes within a wide temperature range, and solves the problem that the environmental temperature change will cause the infrared collimating lens to be seriously defocused due to the large refractive index temperature coefficient of the long-wave infrared optical material, resulting in a significant reduction in the imaging quality of the system.

[0054] The long-wave infrared collimating lens provided by the present invention realizes athermalization by optical passivity, and the image plane is stable and the imaging is clear when the temperature changes within a wide temperature range; at the same time, high sensitivity and low distortion are taken into account, which can greatly improve the stability and accuracy of the optical system, and there is no need to adopt mechanical active athermalization, which can effectively reduce the production cost.

[0055] The long-wave infrared collimating lens provided by the present invention has a longer exit pupil distance and a larger relative aperture, and can be used in target detection, infrared surveying and mapping optical systems, and the like.

[0056] In some preferred embodiments, the long-wave infrared collimating lens has an operating band of 8 μm to 12 μm, a field of view of 12°, a focal length of 50 mm, an F number of 1, a distortion of less than 0.2%, an exit pupil distance greater than 250 mm, and an athermal temperature range of -40°C to 60°C.

[0057] In some preferred embodiments, the center distance between the aperture stop 1 and the first lens 2 is 10 mm;

[0058] In some preferred embodiments, the center distance between the first lens 2 and the second lens 3 is 18 mm.

[0059] In some preferred embodiments, the center distance between the second lens 3 and the third lens 4 is 2 mm.

[0060] In some preferred embodiments, the center distance between the third lens 4 and the fourth lens 5 is 10 mm.

[0061] In some preferred embodiments, the center distance between the fourth lens 5 and the filter 6 is 5 mm.

[0062] In some preferred embodiments, a surface of the first lens 2 close to the image side, a surface of the second lens 3 close to the image side, a surface of the third lens 4 close to the object side, and a surface of the fourth lens 5 close to the object side are all even-order aspherical surfaces.

[0063] In some preferred embodiments, the curvature radius of the surface of the first lens 2 close to the object side is 71 mm, and the curvature radius of the surface close to the image side is 234 mm.

[0064] In some preferred embodiments, the center thickness of the first lens 2 is 11 mm.

[0065] In some preferred embodiments, the focal length of the first lens 2 is 55 mm.

[0066] In some preferred embodiments, the curvature radius of the side of the second lens 3 close to the object side is -44 mm, and the curvature radius of the side close to the image side is -63 mm.

[0067] In some preferred embodiments, the central thickness of the second lens 3 is 5 mm.

[0068] In some preferred embodiments, the focal length of the second lens 3 is -141.92 mm.

[0069] In some preferred embodiments, the curvature radius of the surface of the third lens 4 close to the object side is 39 mm, and the curvature radius of the surface close to the image side is 32 mm.

[0070] In some preferred embodiments, the central thickness of the third lens 4 is 5 mm.

[0071] In some preferred embodiments, the focal length of the third lens 4 is -104.88 mm.

[0072] In some preferred embodiments, the curvature radius of the surface of the fourth lens 5 close to the object side is 57 mm, and the curvature radius of the surface close to the image side is 467 mm;

[0073] In some preferred embodiments, the center thickness of the fourth lens 5 is 8 mm;

[0074] In some preferred embodiments, the focal length of the fourth lens 5 is 36.63 mm.

[0075] In some preferred embodiments, the center thickness of the filter 6 is 2 mm; and / or

[0076] In some preferred embodiments, the passband of the optical filter 6 is 8 to 12 μm.

[0077] In some preferred embodiments, the first lens 2 and the fourth lens 5 are chalcogenide glasses;

[0078] In some preferred embodiments, the second lens 3 is made of ZnS optical glass;

[0079] In some preferred embodiments, the third lens 4 is germanium optical glass;

[0080] In some preferred embodiments, the filter 6 is germanium optical glass.

[0081] In a specific embodiment of the present invention, a small F-number athermal long-wave infrared collimating lens comprises: an aperture stop 1, a first lens 2, a second lens 3, a third lens 4, a fourth lens 5, a filter 6 and an image plane 7 arranged in sequence along the optical axis from the object side to the image side; the center distance between the aperture stop 1 and the first lens 2 is 10 mm; the center distance between the first lens 2 and the second lens 3 is 18 mm; the center distance between the second lens 3 and the third lens 4 is 2 mm; the center distance between the third lens 4 and the fourth lens 5 is 10 mm; the center distance between the fourth lens 5 and the filter 6 is 5 mm.

[0082] The first lens 2 is a positive meniscus even-order aspheric lens (chalcogenide glass) with a center thickness of 11 mm and a concave surface curved toward the image side and a positive focal length (55 mm). The radius of curvature of the side close to the object side is 71 mm, and the side close to the image side is an even-order aspheric surface with a radius of curvature of 234 mm.

[0083] The second lens 3 is a negative meniscus even-order aspheric lens (ZnS optical glass) with a center thickness of 5 mm and a concave surface curved toward the object and a negative focal length (-141.92 mm). The radius of curvature of the side close to the object is -44 mm, and the side close to the image is an even-order aspheric surface with a radius of curvature of -63 mm. The refractive index of the second lens 3 is greater than 2.1, and the dispersion constant is less than 22.7.

[0084] The third lens 4 is a positive meniscus even-order aspheric lens (germanium optical glass) with a center thickness of 5 mm and a concave surface curved toward the image side and a negative focal length (-104.88 mm); the surface of the third lens 4 close to the object side is an even-order aspheric surface with a curvature radius of 39 mm, and the surface close to the image side has a curvature radius of 32 mm; the refractive index of the third lens 4 is greater than 4, and the dispersion constant is less than 34.8.

[0085] The fourth lens 5 is a negative meniscus even-order aspheric lens (chalcogenide glass) with a center thickness of 8 mm and a concave surface curved toward the object and a positive focal length (36.63 mm); the surface of the fourth lens 5 close to the object is an even-order aspheric surface with a curvature radius of 57 mm, and the surface close to the image has a curvature radius of 467 mm. The first lens 2 and the fourth lens 5 are made of the same optical glass, with a refractive index greater than 2.77 and a dispersion constant less than 158.

[0086] The filter 6 is made of germanium optical glass, with a center thickness of 2 mm and a passband of 8 to 12 μm.

[0087] Depend on Figure 2 It can be seen that the wide-band athermal long-wave infrared characteristic measurement lens provided by the embodiment of the present invention has a small distortion (less than 0.2%). Figure 3-5 It can be seen that under the conditions of -40℃, room temperature and 60℃, the MTF curves of the lens are close to the diffraction limit curve, indicating that the lens can be athermalized under the conditions of -40 ~ 60℃ and can meet the high-quality imaging conditions under the conditions of -40 ~ 60℃.

[0088] It should be noted that, in this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the statement "comprise a ..." do not exclude the existence of other identical factors in the process, method, article or device including the elements.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A small F-number athermal long-wave infrared collimating lens, characterized in that: include: An aperture stop, a first lens, a second lens, a third lens, a fourth lens, a filter and an image plane are arranged in sequence along the optical axis from the object side to the image side; The first lens is a positive meniscus even-order aspheric lens with a concave surface curved toward the image side and a positive focal length; The second lens is a negative meniscus even-order aspheric lens with a concave surface curved toward the object and a negative focal length; The third lens is a positive meniscus even-order aspheric lens with a concave surface curved toward the image side and a negative focal length; The fourth lens is a negative meniscus even-order aspheric lens with a concave surface curved toward the object and a positive focal length; The first lens and the fourth lens are made of the same optical glass, with a refractive index greater than 2.77 and a dispersion constant less than 158; the refractive index of the second lens is greater than 2.1, and the dispersion constant is less than 22.7; the refractive index of the third lens is greater than 4, and the dispersion constant is less than 34.

8.

2. The long-wave infrared collimating lens according to claim 1, characterized in that: The long-wave infrared collimating lens has an operating band of 8 μm to 12 μm, a field of view of 12°, a focal length of 50 mm, an F number of 1, a distortion of less than 0.2%, an exit pupil distance of more than 250 mm, and an athermal temperature range of -40°C to 60°C.

3. The long-wave infrared collimating lens according to claim 1, characterized in that: The distance between the aperture stop and the center of the first lens is 10 mm; The center distance between the first lens and the second lens is 18 mm; The center distance between the second lens and the third lens is 2 mm; The center distance between the third lens and the fourth lens is 10 mm; and / or The center distance between the fourth lens and the filter is 5 mm.

4. The long-wave infrared collimating lens according to claim 1, characterized in that: A surface of the first lens close to the image side, a surface of the second lens close to the image side, a surface of the third lens close to the object side, and a surface of the fourth lens close to the object side are all even-order aspherical surfaces.

5. The long-wave infrared collimating lens according to claim 1, characterized in that: The curvature radius of the first lens close to the object side is 71 mm, and the curvature radius of the first lens close to the image side is 234 mm. The central thickness of the first lens is 11 mm; and / or The focal length of the first lens is 55 mm.

6. The long-wave infrared collimating lens according to claim 1, characterized in that: The curvature radius of the second lens close to the object side is -44 mm, and the curvature radius of the second lens close to the image side is -63 mm; The central thickness of the second lens is 5 mm; and / or The focal length of the second lens is -141.92 mm.

7. The long-wave infrared collimating lens according to claim 1, characterized in that: The curvature radius of the side of the third lens close to the object side is 39 mm, and the curvature radius of the side close to the image side is 32 mm; The central thickness of the third lens is 5 mm; and / or The focal length of the third lens is -104.88 mm.

8. The long-wave infrared collimating lens according to claim 1, characterized in that: The curvature radius of the fourth lens close to the object side is 57 mm, and the curvature radius of the fourth lens close to the image side is 467 mm. The center thickness of the fourth lens is 8 mm; The focal length of the fourth lens is 36.63 mm.

9. The long-wave infrared collimating lens according to claim 1, characterized in that: The center thickness of the filter is 2 mm; and / or The bandpass wavelength of the optical filter is 8 to 12 μm.

10. The long-wave infrared collimating lens according to claim 1, characterized in that: The first lens and the fourth lens are chalcogenide glass; The second lens is made of ZnS optical glass; The third lens is made of germanium optical glass; The filter is germanium optical glass.

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