A small F-number athermal long-wave infrared collimating lens

Abstract

The present invention relates to the field of optical lens technology, and in particular to 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; the first lens is a positive meniscus even-order aspheric lens with a positive focal length and a concave surface curved toward the image side; the second lens is a negative meniscus even-order aspheric lens with a negative focal length and a concave surface curved toward the object side; the third lens is a positive meniscus even-order aspheric lens with a negative focal length and a concave surface curved toward the image side; and the fourth lens is a negative meniscus even-order aspheric lens with a positive focal length and a concave surface curved toward the object side. The long-wave infrared collimating lens provided by the present invention has a stable image plane and clear imaging when the temperature changes over a wide temperature range.

Description

Technical Field

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

[0002] The increasing application of infrared imaging systems in aerospace, civil inspection, security, search and rescue, and other fields is placing increasingly stringent demands on imaging quality and environmental adaptability. Long-wave infrared optical materials have a large refractive index temperature coefficient (dn / dT). Temperature fluctuations can cause severe defocusing of the infrared collimating lens, significantly degrading system imaging quality.

[0003] Therefore, there is an urgent need to provide a long-wave infrared collimating lens with athermalization 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. The long-wave infrared collimating lens has a stable image plane and clear imaging when the temperature changes over a wide temperature range. This solves the problem that due to the large refractive index temperature coefficient of long-wave infrared optical materials, changes in ambient temperature will cause severe defocusing of the infrared collimating lens, resulting in a significant reduction in system imaging quality.

[0005] In order to achieve the above 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, which are 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 one 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 one possible design, the curvature radius of the first lens surface close to the object side is 71 mm, and the curvature radius of the first lens surface close to the image side is 234 mm.

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

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

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

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

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

[0024] In one possible design, the radius of curvature of a surface of the third lens close to the object side is 39 mm, and the radius of curvature 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 one possible design, the radius of curvature of a surface of the fourth lens element close to the object side is 57 mm, and the radius of curvature of a surface of the fourth lens element 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 filter is 8 to 12 μm.

[0032] In one possible design, the first lens and the fourth lens are made of chalcogenide glass;

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

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

[0035] The filter is made of 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, realizing an optical passive athermalization method, eliminating the influence of temperature, and obtaining an athermal effect. This ensures that the image plane of the long-wave infrared collimating lens is stable and the image is clear when the temperature changes within a wide temperature range. This solves the problem that due to the large refractive index temperature coefficient of the long-wave infrared optical material, changes in ambient temperature will cause severe defocusing of the infrared collimating lens, resulting in a significant reduction in the system imaging quality.

[0038] The long-wave infrared collimating lens provided by the present invention achieves athermalization through optical passivity, and the image plane is stable and the image is clear when the temperature changes within a wide temperature range. At the same time, it takes into account high sensitivity and low distortion, which can greatly improve the stability and accuracy of the optical system. There is no need to adopt mechanical active athermalization, which can effectively reduce production costs. 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 following briefly introduces the drawings required for use in the embodiments or the description of the prior art. 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 any 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 This is a diagram of field curvature and distortion 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, not all the embodiments. Based on the embodiments of 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, which are 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, realizing an optical passive athermalization method, eliminating the influence of temperature, and obtaining an athermal effect. This ensures that the image plane of the long-wave infrared collimating lens is stable and the image is clear when the temperature changes within a wide temperature range. This solves the problem that due to the large refractive index temperature coefficient of the long-wave infrared optical material, changes in ambient temperature will cause severe defocusing of the infrared collimating lens, resulting in a significant reduction in the system imaging quality.

[0054] The long-wave infrared collimating lens provided by the present invention achieves athermalization through optical passivity, and the image plane is stable and the image is clear when the temperature changes within a wide temperature range. At the same time, it takes into account high sensitivity and low distortion, which can greatly improve the stability and accuracy of the optical system. There is no need to adopt mechanical active athermalization, which can effectively reduce production costs.

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

[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 angle 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 distance between the aperture stop 1 and the center of 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, the surface of the first lens 2 close to the image side, the surface of the second lens 3 close to the image side, the surface of the third lens 4 close to the object side, and the surface of the fourth lens 5 close to the object side are all even-order aspheric 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 surface of the second lens 3 close to the object side is -44 mm, and the curvature radius of the surface close to the image side is -63 mm.

[0067] In some preferred embodiments, the center 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 bandpass wavelength 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 made of chalcogenide glass;

[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 made of germanium optical glass;

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

[0081] In a specific embodiment of the present invention, a small F-number athermal long-wave infrared collimating lens includes: 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, which are 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; and 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 element 3 is a negative meniscus even-order aspheric lens (ZnS optical glass) with a center thickness of 5 mm and a negative focal length (-141.92 mm) with a concave surface curved toward the object. The object-side surface has a radius of curvature of -44 mm, and the image-side surface is an even-order aspheric surface with a radius of curvature of -63 mm. The refractive index of the second lens element 3 is greater than 2.1, and the dispersion constant is less than 22.7.

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

[0085] The fourth lens element 5 is a negative meniscus even-order aspheric lens (chalcogenide glass) with a center thickness of 8mm and a positive focal length (36.63mm) and a concave surface curved toward the object. The object-side surface of the fourth lens element 5 is an even-order aspheric surface with a radius of curvature of 57mm, while the image-side surface has a radius of curvature of 467mm. The first and fourth lens elements 2 and 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 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 this 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 document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical factors in the process, method, article, or device comprising the element.

[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 various embodiments of the present invention.

Claims

1. A small F-number athermal long-wave infrared collimating lens, characterized in that: It consists of an aperture stop, a first lens, a second lens, a third lens, a fourth lens, a filter, and an image plane, which are arranged in sequence along the optical axis from the object side to the image side. 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; 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 chalcogenide glass with a refractive index greater than 2.77 and a dispersion constant less than 158; the second lens is made of ZnS optical glass with a refractive index greater than 2.1 and a dispersion constant less than 22.7; the third lens is made of germanium optical glass with a refractive index greater than 4 and a dispersion constant 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 greater 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: 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.

4. 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 center thickness of the first lens is 11 mm; and / or The focal length of the first lens is 55 mm.

5. 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 center thickness of the second lens is 5 mm; and / or The focal length of the second lens is -141.92 mm.

6. The long-wave infrared collimating lens according to claim 1, characterized in that: The curvature radius of the third lens close to the object side is 39 mm, and the curvature radius of the third lens 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.

7. The long-wave infrared collimating lens according to claim 1, characterized in that: The curvature radius of the fourth lens element close to the object side is 57 mm, and the curvature radius of the fourth lens element 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.

8. 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 filter has a bandpass wavelength of 8 to 12 μm.

9. The long-wave infrared collimating lens according to claim 1, characterized in that: The filter is made of germanium optical glass.

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