Image space telecentric lens for imaging spectrometer and imaging spectrometer

Abstract

The invention belongs to the technical field of optical imaging, and relates to an image space telecentric lens for an imaging spectrometer and the imaging spectrometer. The lens comprises a first negative lens, a second negative lens, a first positive lens, a diaphragm, a second positive lens, a third negative lens, a third positive lens and a fourth positive lens which are sequentially and coaxially arranged in the light path propagation direction. Wherein the first negative lens is meniscus-shaped, and one side, close to the second negative lens, of the first negative lens is a concave surface; the second negative lens and the third negative lens are biconcave lenses; one side, close to the second negative lens, of the first positive lens is a concave surface; the second positive lens, the third positive lens and the fourth positive lens are all biconvex lenses. The multi-layer positive lens and the multi-layer negative lens are combined and alternated, the shape of each lens is limited, the negative lens is used for expanding light rays, and the positive lens is used for focusing and adjusting the light rays, so that the lens can still keep high imaging quality in a large view field range, aberration and distortion are reduced, and chromatic aberration of light rays with different wavelengths is effectively compensated.

Description

Technical Field

[0001] The present invention relates to the technical field of optical imaging, and in particular to an image-side telecentric lens for an imaging spectrometer and an imaging spectrometer. Background Art

[0002] The objective lens of a hyperspectral imager is a key component in the spectral imaging system. It is responsible for focusing light onto the target object and collecting the light reflected or emitted by the target object. These lights are split by the spectrometer and imaged by the detector to finally obtain a spectral image of the target object. Since the performance of the objective lens directly affects the imaging quality and spectral resolution of the hyperspectral imager, it is necessary to design an objective lens with a large detection field of view and achromatic performance at a long working distance to improve the imaging quality of the spectral imager.

[0003] The patent with publication number CN113741015A discloses a miniaturized visible near-infrared image-side telecentric lens, including a positive lens, a negative lens, a positive lens, a negative lens and a positive lens arranged in sequence along the incident direction of light. Each lens adopts aspherical technology to correct and balance the aberration. The lens can be used as a telescope system of a visible infrared imaging spectrometer, and can also be used directly as a visible near-infrared imaging lens. However, due to the use of multiple high-order aspherical surfaces, it not only increases the difficulty and cost of production, but also makes the field of view of the lens smaller, only 24°, thereby limiting the light flux passing through the lens, affecting the overall light collection capability of the imaging spectrometer, and resulting in a decrease in imaging quality. The patent with publication number CN106680977A discloses a large field of view, long working distance, distortion-free apochromatic lens for machine vision inspection, which is composed of a positive lens, a negative lens and an aperture surface. Each lens and the aperture surface are coaxial with the center of the object plane. The order of arrangement from the incident direction of light is the aperture surface, the first positive lens, the second positive lens, the first negative lens, the third positive lens, the second negative lens, the fourth positive lens, the fifth positive lens, the third negative lens, the sixth positive lens and the seventh positive lens. The lens reduces chromatic aberration by alternating multiple positive and negative lenses and utilizing the dispersion characteristics of different optical glasses. However, it can only achieve apochromatism within the wavelength range of 400 to 700 nm and cannot effectively correct light with a wider wavelength. In addition, the field of view of the lens is small, only 35 mm*35 mm, and the imaging spectrometer needs to capture and analyze a larger range of spectral data. Therefore, the lens cannot be used for imaging spectrometers.

[0004] In summary, the existing image-space telecentric lenses have a small field of view and cannot achieve apochromatism in the long-wave band, which results in the inability to be better applied to imaging spectrometers to improve imaging quality. Summary of the invention

[0005] To this end, the technical problem to be solved by the present invention is to overcome the problem that the image-space telecentric lens in the prior art has a small field of view and cannot achieve apochromatism in the long-wave band, thereby resulting in the inability to be better applied to imaging spectrometers to improve imaging quality.

[0006] In order to solve the above technical problems, the present invention provides an image-side telecentric lens for an imaging spectrometer, comprising a first negative lens, a second negative lens, a first positive lens, an aperture, a second positive lens, a third negative lens, a third positive lens and a fourth positive lens which are coaxially arranged in sequence along the propagation direction of the light path;

[0007] Among them, the first negative lens is meniscus-shaped, and its side close to the second negative lens is concave; the second negative lens and the third negative lens are both double concave lenses; the first positive lens is meniscus-shaped, and its side close to the second negative lens is concave; the second positive lens, the third positive lens and the fourth positive lens are all double convex lenses.

[0008] Preferably, the first negative lens and the first positive lens are both made of H-ZLAF3; the second negative lens is made of H-LAF2; the second positive lens is made of H-FK61; the third negative lens is made of H-TF5; the third positive lens and the fourth positive lens are both made of H-ZPK7.

[0009] Preferably, the thickness of the first negative lens, the first positive lens and the third negative lens is 3.5 mm ± 0.2 mm; the thickness of the second negative lens is 1.5 mm ± 0.2 mm; the thickness of the second positive lens is 2.62 mm ± 0.2 mm; the thickness of the third positive lens is 2.48 mm ± 0.2 mm; and the thickness of the fourth positive lens is 3.05 ± 0.2 mm.

[0010] Preferably, the aperture of the aperture is 4.5 mm.

[0011] Preferably, the optical distance between the first negative lens and the second negative lens is 5.27mm±0.2mm; the optical distance between the second negative lens and the first positive lens is 3.86mm±0.2mm; the optical distance between the first positive lens and the aperture is 17.36nn±0.2mm; the optical distance between the aperture and the second positive lens is 0.8mm±0.2mm; the optical distance between the second positive lens and the third negative lens is 1.22mm±0.2mm; the optical distance between the third negative lens and the third positive lens is 1.54mm±0.2mm; the optical distance between the third positive lens and the fourth positive lens is 0.8mm±0.2mm.

[0012] Preferably, the optical distance between the fourth positive lens and the image plane is 8.0 mm±0.2 mm.

[0013] Preferably, the object-side field of view of the image-side telecentric lens for the imaging spectrometer is 42°, and the image-side field of view diameter is 6.0 mm.

[0014] Preferably, the image-space telecentric lens for the imaging spectrometer has a focal length of 8.0 mm, a relative aperture of F / 3.0, and a distortion value of less than ±0.5%.

[0015] Preferably, the incident angle of the chief ray of the image plane in the entire field of view is less than 0.3°.

[0016] The present invention also provides an imaging spectrometer, which comprises the above-mentioned image-side telecentric lens for an imaging spectrometer.

[0017] The image-side telecentric lens for an imaging spectrometer provided by the present application comprises a first negative lens, a second negative lens, a first positive lens, an aperture, a second positive lens, a third negative lens, a third positive lens and a fourth positive lens which are coaxially arranged in sequence along the propagation direction of the optical path; wherein the first negative lens is meniscus-shaped, and can expand the light beam and control the divergence of the light, while reducing the front focal length of the lens and increasing the imaging width; the second negative lens is a biconcave lens, and when the light enters the second negative lens, the biconcave lens can further expand the light beam, adjust the propagation direction of the light and reduce the aberration, so that the imaging is more uniform; and then the meniscus-shaped first positive lens is used to focus the light, The shape of the crescent can reduce the distortion of light, making the light more concentrated, thereby guiding the light to the aperture; the aperture controls the amount of incident light and the size of the light beam, thereby reducing glare; the second positive lens after the aperture is a biconvex lens, which can re-converge the light emitted by the aperture to reduce aberrations; the third negative lens is a biconcave lens, which can additionally expand the light to further reduce the distortion of the imaging; the third positive lens is a biconvex lens, which further corrects the aberrations and improves the imaging quality by increasing the angle of the light path; the fourth positive lens at the end is a biconvex lens, which ensures the clarity and accuracy of the final image by correcting the distribution of light. The present application uses a combination of multiple layers of positive and negative lenses alternately, uses negative lenses to expand light and reduce excessive convergence of light, uses positive lenses to focus and adjust light, and corrects and calibrates the propagation path of light, so that the lens can still maintain high imaging quality within a larger field of view and reduce aberrations and distortions; at the same time, by limiting the shape of each lens, the chromatic aberration of light of different wavelengths is effectively compensated, and apochromatism can be achieved within the 400-1000nm band. It has large field of view, low distortion and apochromatism characteristics, and can be better applied to imaging spectrometers, thereby improving the accuracy of spectral imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0019] Figure 1 A schematic diagram of the structure of an image-side telecentric lens for an imaging spectrometer provided in this application;

[0020] Figure 2 A schematic diagram of the modulation transfer function of the image-side telecentric lens for the imaging spectrometer provided in the first embodiment;

[0021] Figure 3 A schematic diagram of the modulation transfer function of the image-side telecentric lens for the imaging spectrometer provided in the second embodiment;

[0022] Figure 4 A schematic diagram of the modulation transfer function of the image-side telecentric lens for an imaging spectrometer provided in Example 3;

[0023] Figure 5 A point diagram of the image-side telecentric lens for the imaging spectrometer provided in the first embodiment;

[0024] Figure 6 A point diagram of an image-side telecentric lens for an imaging spectrometer provided in Example 2;

[0025] Figure 7 The spot diagram of the image-side telecentric lens for the imaging spectrometer provided in the third embodiment;

[0026] Figure 8 A schematic diagram of field curvature and distortion of an image-side telecentric lens for an imaging spectrometer provided in Example 1;

[0027] Fig. 9 A schematic diagram of field curvature and distortion of an image-side telecentric lens for an imaging spectrometer provided in Example 2;

[0028] Fig.10 A schematic diagram of field curvature and distortion of an image-side telecentric lens for an imaging spectrometer provided in Example 3;

[0029] Fig.11 A schematic diagram of longitudinal aberration of an image-side telecentric lens for an imaging spectrometer provided in Example 1;

[0030] Fig.12 A schematic diagram of longitudinal aberration of an image-side telecentric lens for an imaging spectrometer provided in Example 2;

[0031] Fig.13 A schematic diagram of longitudinal aberration of an image-side telecentric lens for an imaging spectrometer provided in Example 3;

[0032] Fig.14A diffraction surround energy distribution diagram of the image-side telecentric lens for the imaging spectrometer provided in Example 1;

[0033] Fig.15 A diffraction surround energy distribution diagram of the image-side telecentric lens for an imaging spectrometer provided in Example 2;

[0034] Fig.16 The diffraction surround energy distribution diagram of the image-side telecentric lens for the imaging spectrometer provided in the third embodiment;

[0035] Explanation of the accompanying drawings in the specification: 1. first negative lens; 2. second negative lens; 3. first positive lens; 4. aperture; 5. second positive lens; 6. third negative lens; 7. third positive lens; 8. fourth positive lens; 9. image plane. DETAILED DESCRIPTION

[0036] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0037] See also Figure 1 , Figure 1 The figure shows a schematic diagram of the structure of an image-side telecentric lens for an imaging spectrometer provided in the present application, wherein the lens comprises a first negative lens 1, a second negative lens 2, a first positive lens 3, an aperture 4, a second positive lens 5, a third negative lens 6, a third positive lens 7, a fourth positive lens 8 and an image plane 9 which are coaxially arranged in sequence along the propagation direction of the light path.

[0038] The first negative lens 1 is meniscus-shaped, and its side close to the second negative lens 2 is concave. Light is incident from the convex surface of the first negative lens 1. Since its incident surface is convex, the light is slightly converged on the incident surface. Then the light is refracted inside the first negative lens 1 to be dispersed or expanded, and then emitted from the concave surface of the first negative lens 1. Since the light is refracted again at the concave surface, the light is further dispersed, resulting in a wider light beam emitted from the first negative lens 1.

[0039] The second negative lens 2 is a double concave negative lens. Since both the incident surface and the exit surface of the second negative lens 2 are concave surfaces, when the light emitted from the first negative lens 1 enters the incident surface of the second negative lens 2, it will be refracted, causing the light to diverge. When the light is emitted from the exit surface of the second negative lens 2, it will be refracted again and further diffused, thereby further diffusing the light and further increasing the beam diameter; at the same time, the second negative lens 2 can correct aberrations to a certain extent and improve imaging quality by expanding the beam and adjusting the propagation path of the light.

[0040] The first positive lens 3 is meniscus-shaped, and the side thereof close to the second negative lens 2 is concave. When the light enters the incident surface of the first positive lens 3, it is refracted, and the transmission path of the light is changed. Since the exit surface is convex, the light is converged to a focus or near the focus when it exits the exit surface of the first positive lens 3, so that the light is concentrated and thus converges toward the aperture 4.

[0041] The aperture 4 controls the light beam emitted by the first positive lens 3, reduces the brightness by blocking part of the light, and reduces the aberration and improves the image quality by limiting the incident angle of the light.

[0042] The second positive lens 5 is a double convex lens. Since both the incident surface and the exit surface of the second positive lens 5 are convex, light rays from different directions are uniformly converged when incident and exit, reducing aberrations caused by focusing differences of different light rays and optimizing imaging quality.

[0043] The third negative lens 6 is a biconcave lens. The light focused by the second positive projection lens 5 is diverged again by the third negative lens 6 to adjust the propagation direction of the light, so that the light can converge in a more uniform manner when passing through the subsequent biconvex positive projection lens, making the image clearer and less distorted; at the same time, the third negative lens 6 can also adjust the focal length and change the final imaging position.

[0044] The third positive lens 7 and the fourth positive lens 8 are both biconvex lenses. The third positive lens 7 is used to preliminarily focus the light emitted by the third negative lens 6, and the fourth positive lens 8 is used to further adjust the propagation and focusing of the light, correct the aberration of the previous lens, and thus optimize the imaging quality.

[0045] The present application uses a combination of multiple layers of positive and negative lenses alternately, uses negative lenses to expand light and reduce excessive convergence of light, uses positive lenses to focus and adjust light, and corrects and calibrates the propagation path of light, so that the lens can still maintain high imaging quality within a larger field of view and reduce aberrations and distortions; at the same time, by limiting the shape of each lens, the chromatic aberration of light of different wavelengths is effectively compensated, and apochromatism can be achieved within the 400-1000nm band. It has large field of view, low distortion and apochromatism characteristics, and can be better applied to imaging spectrometers, thereby improving the accuracy of spectral imaging.

[0046] Lenses made of different materials will change the refractive index of the lens, thereby changing the degree of bending of light in the lens, affecting the focal length and imaging quality of the lens. Different materials refract light of different wavelengths to different degrees, which will cause chromatic aberration and affect imaging quality.

[0047] Therefore, preferably, in some embodiments of the present application, the materials of the first negative lens 1 and the first positive lens 3 are both H-ZLAF3; since the first negative lens 1 made of H-ZLAF3 material is a high-dispersion negative lens, it can reduce chromatic aberration and improve the color of the image. At the same time, the first positive lens 3 uses the same material as the first negative lens 1, and can perform preliminary focusing adjustments on the light.

[0048] The material of the second negative lens 2 is H-LAF2; this is because H-LAF2 has a lower refractive index and high dispersion, so the second negative lens 2 made of H-ZLAF2 material can help reduce the curvature of light and improve dispersion.

[0049] The material of the second positive lens 5 is H-FK61; this is because H-FK61 has a higher refractive index, which can reduce the dispersion of light and enhance the clarity of the image.

[0050] The material of the third negative lens 6 is H-TF5; H-TF5 is a negative lens with specific dispersion characteristics, which can help further correct the chromatic aberration generated during the light transmission process.

[0051] The materials of the third positive lens 7 and the fourth positive lens 8 are both H-ZPK7; H-ZPK7 is a high-quality positive lens with good optical properties and can improve image clarity. The fourth positive lens 8 and the third positive lens 7 are made of the same material to ensure consistent optical properties.

[0052] Therefore, the embodiments of the present application limit the material of each lens, thereby effectively correcting various aberrations and providing high-quality images.

[0053] In some embodiments of the present application, the thickness of the first negative lens 1, the first positive lens 3 and the third negative lens 6 is 3.5 mm ± 0.2 mm; the thickness of the second negative lens 2 is 1.5 mm ± 0.2 mm; the thickness of the second positive lens 5 is 2.62 mm ± 0.2 mm; the thickness of the third positive lens 7 is 2.48 mm ± 0.2 mm; the thickness of the fourth positive lens 8 is 3.05 ± 0.2 mm. The aperture of the aperture 4 is 4.5 mm.

[0054] By changing the thickness of each lens, the propagation direction and focal position of the light can be adjusted, while the uniformity and transmittance of the light can be changed, and image distortion can be controlled, thereby achieving more precise optical design, optimizing the brightness and contrast of the final image, and ensuring that the geometric image of the image is as close to the real shape as possible.

[0055] In some embodiments, the aperture of the aperture 4 is 4.5 mm. By controlling the aperture size, aberrations can be reduced, the sharpness and clarity of the image can be improved, scattered light from the light source can be reduced, glare and halo phenomena can be reduced, light distortion at the edge of the aperture can be avoided, and the uniformity and quality of the entire image can be improved.

[0056] In some embodiments of the present application, the optical spacing between the first negative lens 1 and the second negative lens 2 is 5.27mm±0.2mm; the optical spacing between the second negative lens 2 and the first positive lens 3 is 3.86mm±0.2mm; the optical spacing between the first positive lens 3 and the aperture 4 is 17.36nn±0.2mm; the optical spacing between the aperture 4 and the second positive lens 5 is 0.8mm±0.2mm; the optical spacing between the second positive lens 5 and the third negative lens 6 is 1.22mm±0.2mm; the optical spacing between the third negative lens 6 and the third positive lens 7 is 1.54mm±0.2mm; the optical spacing between the third positive lens 7 and the fourth positive lens 8 is 0.8mm±0.2mm.

[0057] The optical distance between the fourth positive lens 8 and the image plane 9 is 8.0 mm±0.2 mm.

[0058] By changing the distance between each lens, not only can the focal length of the lens be adjusted to achieve different magnifications or viewing angles, but it can also help correct aberrations, optimize the optical path, and reduce light scattering and reflection. At the same time, reasonable optical spacing can also ensure accurate lens alignment and reduce image distortion and errors; and, by limiting the distance between the fourth positive lens 8 and the image plane 9, aberrations and distortions can be further reduced, and the geometric distortion and optical errors of the image can be reduced; therefore, the present application further improves the imaging quality of the lens by limiting the distance between each lens and the image plane.

[0059] Specifically, the image-space telecentric lens for an imaging spectrometer provided based on the above-mentioned embodiment can achieve achromatic aberration in the wavelength range of 400 to 1000 nm, an object-space field of view of 42°, and an image-space field of view diameter of 6.0 mm; the focal length is 8.0 mm, the relative aperture is F / 3.0, and the distortion value is less than ±0.5%; the incident angle of the main ray of the image plane in the full field of view is less than 0.3°.

[0060] Based on the image-space telecentric lens for an imaging spectrometer provided in the above embodiment, the present application also provides an imaging spectrometer, which includes the above image-space telecentric lens for an imaging spectrometer. Since the image-space telecentric lens provided in the above embodiment has the characteristics of a large field of view, low distortion, and apochromatism, the imaging spectrometer provided in the embodiment of the present application including the image-space telecentric lens has high imaging quality and imaging accuracy.

[0061] The technical solution of the present application is described in more detail below in combination with embodiments and comparative examples, but it should be understood that the following embodiments and comparative examples are only for explaining and illustrating the technical solution and do not limit the scope of the present application.

[0062] Example 1

[0063] This embodiment provides an image-side telecentric lens for an imaging spectrometer, which includes a first negative lens, a second negative lens, a first positive lens, an aperture, a second positive lens, a third negative lens, a third positive lens, and a fourth positive lens, which are coaxially arranged in sequence along the propagation direction of the light path.

[0064] The first negative lens is meniscus-shaped, and its side close to the second negative lens is concave; the material of the first negative lens is H-ZLAF3; both surfaces of the first negative lens are standard spherical surfaces, and the radius of the side away from the second negative lens is 10.43mm, and the radius of the side close to the second negative lens is 8.17mm; the thickness of the first negative lens is 3.50mm;

[0065] The second negative lens is a double concave lens; the material of the second negative lens is H-LAF2; both surfaces of the second negative lens are standard spherical surfaces, the radius of the side away from the first positive lens is -49.04mm, and the radius of the side close to the first positive lens is 14.45mm; the thickness of the second negative lens is 1.50mm;

[0066] The first positive lens is meniscus-shaped, and its side close to the second negative lens is concave; the material of the first positive lens is H-ZLAF3; the two surfaces of the first positive lens are standard spherical surfaces, the radius of the side away from the aperture is -23.27mm, and the radius of the side close to the aperture is -13.29mm; the thickness of the first positive lens is 3.50mm;

[0067] The second positive lens is a double convex lens; the material of the second positive lens is H-FK61; both surfaces of the second positive lens are standard spherical surfaces, the radius of the side away from the third negative lens is 5.74mm, and the radius of the side close to the third negative lens is -12.38mm; the thickness of the second positive lens is 2.62mm;

[0068] The third negative lens is a double concave lens; the material of the third negative lens is H-TF5; both surfaces of the third negative lens are standard spherical surfaces, the radius of the side away from the third positive lens is -6.60mm, and the radius of the side close to the third positive lens is 6.60mm; the thickness of the third negative lens is 3.50mm;

[0069] The third positive lens is a double convex lens; the material of the third positive lens is H-ZPK7; both surfaces of the third positive lens are standard spherical surfaces, the radius of the side away from the fourth positive lens is 45.27mm, and the radius of the side close to the fourth positive lens is -10.12mm; the thickness of the third positive lens is 2.48mm;

[0070] The fourth positive lens is a double convex lens; the material of the fourth positive lens is H-ZPK7; both surfaces of the fourth positive lens are standard spherical surfaces, the radius of the side close to the third positive lens is 10.15 mm, and the radius of the side away from the third positive lens is -28.23 mm; the thickness of the fourth positive lens is 3.05 mm;

[0071] The optical distance between the first negative lens and the second negative lens is 5.27mm; the optical distance between the second negative lens and the first positive lens is 3.86mm; the optical distance between the first positive lens and the aperture is 17.36mm; the optical distance between the aperture and the second positive lens is 0.80mm; the optical distance between the second positive lens and the third negative lens is 1.22mm; the optical distance between the third negative lens and the third positive lens is 1.54mm; the optical distance between the third positive lens and the fourth positive lens is 0.80mm; the optical distance between the fourth positive lens and the image plane is 8.00mm.

[0072] Example 2

[0073] This embodiment provides an image-side telecentric lens for an imaging spectrometer, which includes a first negative lens, a second negative lens, a first positive lens, an aperture, a second positive lens, a third negative lens, a third positive lens, and a fourth positive lens, which are coaxially arranged in sequence along the propagation direction of the light path.

[0074] The first negative lens is meniscus-shaped, and its side close to the second negative lens is concave; the material of the first negative lens is H-ZLAF3; both surfaces of the first negative lens are standard spherical surfaces, and the radius of the side away from the second negative lens is 10.33mm, and the radius of the side close to the second negative lens is 8.22mm; the thickness of the first negative lens is 3.30mm;

[0075] The second negative lens is a double concave lens; the material of the second negative lens is H-LAF2; both surfaces of the second negative lens are standard spherical surfaces, the radius of the side away from the first positive lens is -45.36mm, and the radius of the side close to the first positive lens is 14.59mm; the thickness of the second negative lens is 1.30mm;

[0076] The first positive lens is meniscus-shaped, and its side close to the second negative lens is concave; the material of the first positive lens is H-ZLAF3; the two surfaces of the first positive lens are standard spherical surfaces, the radius of the side away from the aperture is -23.53mm, and the radius of the side close to the aperture is -13.22mm; the thickness of the first positive lens is 3.30mm;

[0077] The second positive lens is a double convex lens; the material of the second positive lens is H-FK61; both surfaces of the second positive lens are standard spherical surfaces, the radius of the side away from the third negative lens is 5.71mm, and the radius of the side close to the third negative lens is -12.55mm; the thickness of the second positive lens is 2.66mm;

[0078] The third negative lens is a double concave lens; the material of the third negative lens is H-TF5; both surfaces of the third negative lens are standard spherical surfaces, the radius of the side away from the third positive lens is -6.58mm, and the radius of the side close to the third positive lens is 6.58mm; the thickness of the third negative lens is 3.30mm;

[0079] The third positive lens is a double convex lens; the material of the third positive lens is H-ZPK7; both surfaces of the third positive lens are standard spherical surfaces, the radius of the side away from the fourth positive lens is 48.63mm, and the radius of the side close to the fourth positive lens is -9.94mm; the thickness of the third positive lens is 2.47mm;

[0080] The fourth positive lens is a double convex lens; the material of the fourth positive lens is H-ZPK7; both surfaces of the fourth positive lens are standard spherical surfaces, the radius of the side close to the third positive lens is 10.32 mm, and the radius of the side away from the third positive lens is -27.45 mm; the thickness of the fourth positive lens is 3.04 mm;

[0081] The optical distance between the first negative lens and the second negative lens is 5.33mm; the optical distance between the second negative lens and the first positive lens is 4.06mm; the optical distance between the first positive lens and the aperture is 17.52mm; the optical distance between the aperture and the second positive lens is 0.80mm; the optical distance between the second positive lens and the third negative lens is 1.23mm; the optical distance between the third negative lens and the third positive lens is 1.55mm; the optical distance between the third positive lens and the fourth positive lens is 0.95mm; the optical distance between the fourth positive lens and the image plane is 8.00mm.

[0082] Example 3

[0083] This embodiment provides an image-side telecentric lens for an imaging spectrometer, which includes a first negative lens, a second negative lens, a first positive lens, an aperture, a second positive lens, a third negative lens, a third positive lens, and a fourth positive lens, which are coaxially arranged in sequence along the propagation direction of the light path.

[0084] The first negative lens is meniscus-shaped, and its side close to the second negative lens is concave; the material of the first negative lens is H-ZLAF3; both surfaces of the first negative lens are standard spherical surfaces, and the radius of the side away from the second negative lens is 10.48mm, and the radius of the side close to the second negative lens is 8.17mm; the thickness of the first negative lens is 3.70mm;

[0085] The second negative lens is a double concave lens; the material of the second negative lens is H-LAF2; both surfaces of the second negative lens are standard spherical surfaces, the radius of the side away from the first positive lens is -46.18mm, and the radius of the side close to the first positive lens is 14.21mm; the thickness of the second negative lens is 1.50mm;

[0086] The first positive lens is meniscus-shaped, and its side close to the second negative lens is concave; the material of the first positive lens is H-ZLAF3; the two surfaces of the first positive lens are standard spherical surfaces, the radius of the side away from the aperture is -23.06mm, and the radius of the side close to the aperture is -13.24mm; the thickness of the first positive lens is 3.70mm;

[0087] The second positive lens is a double convex lens; the material of the second positive lens is H-FK61; both surfaces of the second positive lens are standard spherical surfaces, the radius of the side away from the third negative lens is 5.75mm, and the radius of the side close to the third negative lens is -12.36mm; the thickness of the second positive lens is 2.46mm;

[0088] The third negative lens is a double concave lens; the material of the third negative lens is H-TF5; both surfaces of the third negative lens are standard spherical surfaces, the radius of the side away from the third positive lens is -6.62mm, and the radius of the side close to the third positive lens is 6.62mm; the thickness of the third negative lens is 3.70mm;

[0089] The third positive lens is a double convex lens; the material of the third positive lens is H-ZPK7; both surfaces of the third positive lens are standard spherical surfaces, the radius of the side away from the fourth positive lens is 47.38mm, and the radius of the side close to the fourth positive lens is -9.99mm; the thickness of the third positive lens is 2.50mm;

[0090] The fourth positive lens is a double convex lens; the material of the fourth positive lens is H-ZPK7; both surfaces of the fourth positive lens are standard spherical surfaces, the radius of the side close to the third positive lens is 10.23mm, and the radius of the side away from the third positive lens is -27.05mm; the thickness of the fourth positive lens is 3.10mm;

[0091] The optical distance between the first negative lens and the second negative lens is 5.23mm; the optical distance between the second negative lens and the first positive lens is 3.56mm; the optical distance between the first positive lens and the aperture is 17.06mm; the optical distance between the aperture and the second positive lens is 0.80mm; the optical distance between the second positive lens and the third negative lens is 1.23mm; the optical distance between the third negative lens and the third positive lens is 1.55mm; the optical distance between the third positive lens and the fourth positive lens is 0.80mm; the optical distance between the fourth positive lens and the image plane is 8.00mm.

[0092] Comparative Example

[0093] The present comparative example provides a large field of view, long working distance, distortion-free apochromatic lens, which is composed of a positive lens, a negative lens and an aperture surface. Each lens, the aperture surface and the center of the object plane are coaxial, and the order of arrangement from the incident light ray is: the aperture surface, the first positive lens, the second positive lens, the first negative lens, the third positive lens, the second negative lens, the fourth positive lens, the fifth positive lens, the third negative lens, the sixth positive lens and the seventh positive lens. The distance from the vertex of the first positive lens to the object plane is the working distance of the lens.

[0094] The thickness of the first positive lens is 3.97mm; the thickness of the second positive lens is 7.43mm; the thickness of the first negative lens is 4.51mm; the thickness of the third positive lens is 6.81mm; the thickness of the second negative lens is 8.2mm; the thickness of the fourth positive lens is 3.71mm; the thickness of the fifth positive lens is 3.5mm; the thickness of the third negative lens is 9.3mm; the thickness of the sixth positive lens is 3.17mm; the thickness of the seventh positive lens is 8.58mm;

[0095] The distance between the first positive lens and the second positive lens is 6.45mm; the second positive lens and the first negative lens form a first doublet lens; the distance between the first negative lens and the third positive lens is 0.39mm; the distance between the third positive lens and the second negative lens is 1.62mm; the second negative lens and the fourth positive lens form a second doublet lens; the distance between the fourth positive lens and the fifth positive lens is 32.23mm; the fifth positive lens and the third negative lens form a third doublet lens; the distance between the third negative lens and the sixth positive lens is 19.85mm; the sixth positive lens and the seventh positive lens form a fourth doublet lens; the distance between the seventh positive lens and the image plane is 27.5mm.

[0096] like Figure 2 FIG. 1 is a schematic diagram of a modulation transfer function of an image-side telecentric lens for an imaging spectrometer provided in Example 1; Figure 3 FIG. 1 is a schematic diagram of a modulation transfer function of an image-side telecentric lens for an imaging spectrometer provided in Embodiment 2; Figure 4The figure shows a schematic diagram of the modulation transfer function of the image-side telecentric lens for an imaging spectrometer provided in Example 3; the modulation transfer function is used to characterize the resolution capability of the lens at different spatial frequencies. It can be seen from the figure that the lenses provided in Examples 1 to 3 are all able to remain stable in the medium and low spatial frequency ranges, and have less attenuation at high spatial frequencies, indicating that the lens provided in the present application has good high-frequency response and can effectively transmit contrast in the medium and low spatial frequency ranges.

[0097] like Figure 5 Shown is a point diagram of an image-side telecentric lens for an imaging spectrometer provided in the first embodiment; Figure 6 Shown is a point diagram of an image-side telecentric lens for an imaging spectrometer provided in Embodiment 2;

[0098] Figure 7 The figure shows the spot diagram of the image-side telecentric lens for the imaging spectrometer provided in Example 3; the spot diagram can characterize the imaging capability of the lens for a single light point. It can be seen from the figure that the root mean square radius of the spot diagram at the maximum visible field of view of the lenses provided in Examples 1 to 3 is less than 3.6 μm, indicating that the imaging quality of the lens provided in the present application is better, and its resolution and detail retention capabilities are stronger.

[0099] like Figure 8 FIG. 1 is a schematic diagram of field curvature and distortion of an image-side telecentric lens for an imaging spectrometer provided in Example 1; Fig. 9 FIG. 1 is a schematic diagram of field curvature and distortion of an image-side telecentric lens for an imaging spectrometer provided in Example 2; Fig.10 The figure shows the field curvature and distortion diagram of the image-side telecentric lens for an imaging spectrometer provided in Example 3; wherein, the field curvature means that the imaging surface is not an ideal plane but is curved, and the field curvature diagram can indicate whether the imaging surface is flat; the distortion is divided into barrel distortion and pincushion distortion, the barrel distortion indicates that the center of the image is convex and the edges are concave, and the pincushion distortion indicates that the center of the image is concave and the edges are convex, and the distortion diagram can indicate the degree to which the straight lines in the image are bent; it can be seen from the figure that the distortion of the lenses provided in Examples 1 to 3 is less than ±0.5%.

[0100] like Fig.11 FIG. 1 is a schematic diagram of longitudinal aberration of an image-side telecentric lens for an imaging spectrometer provided in Example 1; Fig.12 FIG. 1 is a schematic diagram of longitudinal aberration of an image-side telecentric lens for an imaging spectrometer provided in Example 2; Fig.13The figure shows a schematic diagram of the longitudinal aberration of the image-side telecentric lens for an imaging spectrometer provided in Example 3; the ordinate in the schematic diagram of the longitudinal aberration is a normalized wide-pupil coordinate, which refers to the coordinate value after standardized processing of different positions of the imaging plane, and these coordinates represent the longitudinal chromatic aberration at different spot positions. Ideally, the longitudinal aberration curve should be as smooth as possible, indicating that the chromatic aberration change at different field of view positions is small, and the spacing between different curves should be as small as possible, indicating that the chromatic aberration is not obvious; it can be seen from the figure that by changing the thickness and optical spacing of each lens, the longitudinal aberration curve of the lens obtained is not large in aberration, and its chromatic aberration change is small.

[0101] like Fig.14 The figure shows the diffraction surround energy distribution diagram of the image-side telecentric lens for the imaging spectrometer provided in the first embodiment; Fig.15 The figure shows the diffraction surround energy distribution diagram of the image-side telecentric lens for the imaging spectrometer provided in the second embodiment; Fig.16 The figure shows the diffraction ambient energy distribution diagram of the image-side telecentric lens for the imaging spectrometer provided in Example 3; the diffraction ambient energy distribution diagram of the lens can represent the energy distribution of light spots or targets within different radius ranges. It can be seen from the figure that the diffraction ambient energy distribution curves of the lenses provided in Examples 1 to 3 are relatively smooth, indicating that the light spots are more concentrated and the image clarity is higher when the lens provided in the present application is imaged.

[0102] In addition, the object side field of view of the lenses provided in Examples 1 to 3 fluctuates around 42°, while the object side field of view of the lens provided in the comparative example is 35mm*35mm, which indicates that the lens provided in the present application has a larger field of view and can cover a larger field of view; the image side field of view diameter of the lenses provided in Examples 1 to 3 fluctuates around 6mm, while the image side field of view of the lens provided in the comparative example is 11.3mm*11.3mm, indicating that although the lens provided in the present application can cover a wide range of scenes, the actual area displayed by the formed image on the imaging plane is smaller, and it is more suitable for scenes that require wide-angle shooting but require high resolution on the imaging plane; in addition, the lenses provided in Examples 1 to 3 can all achieve apochromatism in the 400-1000nm band, while the lens provided in the comparative example can only achieve apochromatism in the 400-700nm band, indicating that the lens provided in the present application can effectively correct a wider range of wavelengths of light and has better apochromatism characteristics.

[0103] Obviously, the above embodiments are merely examples for the purpose of clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. An image-side telecentric lens for an imaging spectrometer, characterized in that: It includes a first negative lens, a second negative lens, a first positive lens, an aperture, a second positive lens, a third negative lens, a third positive lens and a fourth positive lens which are coaxially arranged in sequence along the propagation direction of the light path; Among them, the first negative lens is meniscus-shaped, and its side close to the second negative lens is concave; the second negative lens and the third negative lens are both double concave lenses; the first positive lens is meniscus-shaped, and its side close to the second negative lens is concave; the second positive lens, the third positive lens and the fourth positive lens are all double convex lenses.

2. The image-space telecentric lens for an imaging spectrometer according to claim 1, characterized in that: The materials of the first negative lens and the first positive lens are both H-ZLAF3; the material of the second negative lens is H-LAF2; The material of the second positive lens is H-FK61; the material of the third negative lens is H-TF5; the materials of the third positive lens and the fourth positive lens are both H-ZPK7.

3. The image-space telecentric lens for an imaging spectrometer according to claim 1, characterized in that: The thickness of the first negative lens, the first positive lens and the third negative lens is 3.5 mm ± 0.2 mm; the thickness of the second negative lens is 1.5 mm ± 0.2 mm; the thickness of the second positive lens is 2.62 mm ± 0.2 mm; the thickness of the third positive lens is 2.48 mm ± 0.2 mm; and the thickness of the fourth positive lens is 3.05 ± 0.2 mm.

4. The image-space telecentric lens for an imaging spectrometer according to claim 1, characterized in that: The aperture of the diaphragm is 4.5 mm.

5. The image-space telecentric lens for an imaging spectrometer according to claim 1, characterized in that: The optical distance between the first negative lens and the second negative lens is 5.27mm±0.2mm; the optical distance between the second negative lens and the first positive lens is 3.86mm±0.2mm; the optical distance between the first positive lens and the aperture is 17.36nn±0.2mm; the optical distance between the aperture and the second positive lens is 0.8mm±0.2mm; the optical distance between the second positive lens and the third negative lens is 1.22mm±0.2mm; the optical distance between the third negative lens and the third positive lens is 1.54mm±0.2mm; the optical distance between the third positive lens and the fourth positive lens is 0.8mm±0.2mm.

6. The image-space telecentric lens for an imaging spectrometer according to claim 1, characterized in that: The optical distance between the fourth positive lens and the image plane is 8.0 mm±0.2 mm.

7. The image-space telecentric lens for an imaging spectrometer according to claim 1, characterized in that: The object-side field of view of the image-side telecentric lens for the imaging spectrometer is 42°, and the image-side field of view diameter is 6.0 mm.

8. The image-space telecentric lens for an imaging spectrometer according to claim 1, characterized in that: The image-space telecentric lens for the imaging spectrometer has a focal length of 8.0 mm, a relative aperture of F / 3.0, and a distortion value of less than ±0.5%.

9. The image-space telecentric lens for an imaging spectrometer according to claim 1, characterized in that: The incident angle of the chief ray of the image plane in the entire field of view is less than 0.3°.

10. An imaging spectrometer, characterized in that: The imaging spectrometer comprises the image-space telecentric lens for an imaging spectrometer according to any one of claims 1 to 9.

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