An apochromatic telephoto lens

Abstract

The application relates to an image-side telecentric lens which is composed of a front lens group A and a rear lens group B arranged along an optical axis from an object side to an image side in sequence, the front lens group A is sequentially arranged, along the optical axis from the object side to the image side, a positive focal length meniscus lens A1, a negative focal length meniscus lens A2, a positive focal length meniscus lens A3, a negative focal length meniscus lens A4, a negative focal length meniscus lens A5 and a double convex lens A6; the rear lens group B is sequentially arranged, along the optical axis from the object side to the image side, a double concave lens B1, a double convex lens B2 and a double convex lens B3. The application has a wide working wave band range, can be applied to a front-mounted telescope system of an imaging spectrometer, can simultaneously image and spectrally analyze a visible light spectral region and a near-infrared spectral region of a target, adopts a transmission type image-side telecentric light path design, has a compound achromatic function, effectively connects the front-mounted telescope system and a slit, makes up for the low energy utilization rate of a reflection type structure, and can guarantee image surface stability under different working distances.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of imaging lens design, and particularly relates to an image-side telecentric lens. BACKGROUND

[0002] In recent years, the spectral imaging technology at home and abroad is increasingly mature. The imaging spectrometer makes the imaging technology and the spectral technology integrate with each other, can image a target and measure the spectral characteristics of the target, and solves the technical problem that the traditional optical instrument cannot simultaneously perform image analysis and spectral analysis on the target. The imaging spectrometer has more and more wide application prospects in the aspects of mineral resources, forest resources and water resources survey, crop disease and pest monitoring, environmental pollution monitoring, space remote sensing, biomedicine and the like.

[0003] The imaging spectrometer mainly comprises a front telescopic system and a rear light splitting system. The front telescopic system is used for imaging an observation target on an entrance slit of the imaging spectrometer so as to be followed by light splitting. In order to make the image plane of the front telescopic system coincide with the slit, meet the requirements of the connection of the entrance pupil and the exit pupil, and overcome spectral overlap, the front telescopic system needs to be designed as an image-side telecentric lens. The front telescopic system is mostly of a reflective structure. Although the reflective structure has certain advantages in correcting chromatic aberration, the system has central obstruction, which leads to a reduction in energy utilization.

[0004] The China Patent Bulletin discloses a visible light near-infrared wide spectral complex achromatic image-side telecentric lens and application thereof (application number: 202010358387.3). The lens is a transmission type optical system with a coaxial structure, comprising first to eighth lenses arranged in sequence along the light incident direction, and an aperture stop arranged between the third lens and the fourth lens. The first lens and the second lens are positive lenses, the third lens is a negative lens, the fourth lens is a positive lens, the fifth lens is a negative meniscus lens, the sixth lens and the seventh lens are positive lenses, and the eighth lens is a negative meniscus lens. The negative lenses are all curved towards the aperture stop, the image-side chief ray is parallel to the optical axis or forms an angle of less than 1° with the optical axis and is perpendicular to the image plane, and the lens works in the 400nm-1000nm waveband. The lens has the following problems: (1) the working distance is infinite and cannot be adjusted, and only an infinite distance object can be imaged, and the image quality cannot be guaranteed when a close-range object is imaged; (2) the focal length is short, the imaging range is small, and the half image height is only 7.3mm; (3) the first lens and the seventh lens are very thin at the edges, the lenses are difficult to process, the light passes through the edges of the lenses, which brings difficulty to mechanical design, the fifth lens is a large convex meniscus lens, which is close to a hemisphere, and the edge is difficult to be cast, and the sixth lens is very thin, and the diameter and thickness are not uniform, and the same processing is difficult. SUMMARY

[0005] The technical problem solved by the present application is to provide a transmission type structure of an image-side telecentric lens which can be applied to the spectral imaging analysis of a close-range target.

[0006] To solve the above technical problem, the image-side telecentric lens of the present application is composed of a front lens group A and a rear lens group B arranged in sequence along the optical axis from the object side to the image side, the front lens group A is composed of a positive focal power meniscus lens A1, a negative focal power meniscus lens A2, a positive focal power meniscus lens A3, a negative focal power meniscus lens A4, a negative focal power meniscus lens A5 and a double convex lens A6 arranged in sequence along the optical axis from the object side to the image side, the rear lens group B is composed of a double concave lens B1, a double convex lens B2 and a double convex lens B3 arranged in sequence along the optical axis from the object side to the image side, the positive focal power meniscus lens A1 and the negative focal power meniscus lens A2 form a first cemented lens, the positive focal power meniscus lens A3 and the negative focal power meniscus lens A4 form a second cemented lens, the convex surfaces of the positive focal power meniscus lens A1, the negative focal power meniscus lens A2 and the negative focal power meniscus lens A5 face the object side, and the convex surfaces of the positive focal power meniscus lens A3 and the negative focal power meniscus lens A4 face the image side, and all the lens surfaces are spherical.

[0007] Further, the front and rear surface curvature radii of the positive focal power meniscus lens A1 are 22.45-24.60 mm and 53.29-80.86 mm respectively, the front and rear surface curvature radii of the negative focal power meniscus lens A2 are 53.29-80.86 mm and 9.78-9.96 mm respectively, the front and rear surface curvature radii of the positive focal power meniscus lens A3 are -25.42--23.99 mm and -10.31--10.14 mm respectively, the front and rear surface curvature radii of the negative focal power meniscus lens A4 are -10.31--10.14 mm and -28.56--26.24 mm respectively, the front and rear surface curvature radii of the negative focal power meniscus lens A5 are 29.82-36.64 mm and 15.50-16.76 mm respectively, the front and rear surface curvature radii of the double convex lens A6 are 17.65-22.50 mm and -20.04--19.57 mm respectively, the front and rear surface curvature radii of the double concave lens B1 are -17.38--13.18 mm and 74.22-211.98 mm respectively, the front and rear surface curvature radii of the double convex lens B2 are 147.48-158.31 mm and -26.94--22.46 mm respectively, and the front and rear surface curvature radii of the double convex lens B3 are 49.68-60.75 mm and -107.24--100.43 mm respectively.

[0008] Further, the central thickness of the positive meniscus lens A1 is 8.02-8.32 mm; the central thickness of the negative meniscus lens A2 is 5.16-5.32 mm; the central thickness of the positive meniscus lens A3 is 6.78-6.82 mm; the central thickness of the negative meniscus lens A4 is 2.61-2.74 mm; the central thickness of the negative meniscus lens A5 is 4.28-4.36 mm; the central thickness of the double convex lens A6 is 6.18-6.34 mm; the central thickness of the double concave lens B1 is 4.16-4.30 mm; the central thickness of the double convex lens B2 is 6.56-6.62 mm; and the central thickness of the double convex lens B3 is 7.18-7.22 mm.

[0009] The central air gap between the negative meniscus lens A2 of the first cemented lens and the positive meniscus lens A3 of the second cemented lens is 8.50-9.22 mm; the central air gap between the negative meniscus lens A4 and the negative meniscus lens A5 is 3.59-3.72 mm; the central air gap between the negative meniscus lens A5 and the double convex lens A6 is 0.96-1.04 mm; the central air gap between the double concave lens B1 and the double convex lens B2 is 1.26-1.88 mm; the central air gap between the double convex lens B2 and the double convex lens B3 is 6.06-6.50 mm; and the central air gap between the double convex lens B3 and the image plane is 12.48-12.54 mm.

[0010] Further, the center distance of the front lens group A and the rear lens group B can be adjusted according to different working distances.

[0011] The central air gap between the front lens group A and the rear lens group B is 16.10-16.88 mm.

[0012] Further, all the lenses in the application are glass materials, the refractive index Nd1 and the dispersion coefficient Vd1 of the positive focal power meniscus lens A1 satisfy the conditions: 1.9 < Nd1 < 2.0, 20 < Vd1 < 35; the refractive index Nd2 and the dispersion coefficient Vd2 of the negative focal power meniscus lens A2 satisfy the conditions: 1.5 < Nd2 < 1.6, 58 < Vd2 < 68; the refractive index Nd3 and the dispersion coefficient Vd3 of the positive focal power meniscus lens A3 satisfy the conditions: 1.6 < Nd3 < 1.7, 60 < Vd3 < 65; the refractive index Nd4 and the dispersion coefficient Vd4 of the negative focal power meniscus lens A4 satisfy the conditions: 1.7 < Nd4 < 1.8, 29 < Vd4 < 35; the refractive index Nd5 and the dispersion coefficient Vd5 of the positive focal power meniscus lens A5 satisfy the conditions: 1.6 < Nd5 < 1.8, 25 < Vd5 < 40; the refractive index Nd6 and the dispersion coefficient Vd6 of the double convex lens A6 satisfy the conditions: 1.5 < Nd6 < 1.6, 70 < Vd6 < 75; the refractive index Nd7 and the dispersion coefficient Vd7 of the double concave lens B1 satisfy the conditions: 1.9 < Nd7 < 2.0, 18 < Vd7 < 22; the refractive index Nd8 and the dispersion coefficient Vd8 of the double convex lens B2 satisfy the conditions: 1.9 < Nd8 < 2.0, 20 < Vd8 < 22; the refractive index Nd9 and the dispersion coefficient Vd9 of the double convex lens B3 satisfy the conditions: 1.8 < Nd9 < 1.9, 20 < Vd9 < 45;

[0013] The application has the advantages that the working wave band range of the lens is wide, the lens can be applied to a front-mounted telescopic system of a spectral imager, can simultaneously image and spectrally analyze the visible light spectral region and the near-infrared spectral region of a target, improves the observation and analysis capability of the lens for the target and expands the application field of the lens, the transmissive image-side telecentric optical path design is adopted, the lens has the function of compound achromatism, the front-mounted telescopic system is effectively connected with a slit, the problem of central obstruction existing in the reflective structure is avoided, the low energy utilization rate of the reflective structure is compensated, and the image surface is stable under different working distances. All the lenses are glass spherical structures, are easy to process, assemble and adjust, and reduce the cost. The lens can image under different working distances, the image quality is stable, and the distortion is low. Compared with the prior art, the working distance range of the lens is wide and the lens can image a near-distance object, the observation distance can be adjusted in the range of 1-2 m, under the condition that the detector target surface and the rear lens group B are fixed, when observing objects at different distances, only the front lens group A needs to be moved to realize image surface compensation under different working distances to ensure the image quality, the influence of adjusting the target surface is avoided, the lens can be used not only for the front-end telescopic system of a spectral imager but also for a common industrial telecentric lens, the observation distance of most industrial telecentric lenses is 150 mm-800 mm, so the lens can compensate for the lenses on the market for imaging beyond 1 m. The focal length of the lens is long, and the half image height can reach 11.64 mm, so the lens can image on a large target detector, and the detection range is wide. All the lenses in the rear lens group B are made of high-transparency glass materials, and the lens has better fogging resistance. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the image-side telecentric lens of the present invention;

[0015] Figure 2 This is a modulation transfer function curve of the image-side telecentric lens embodiment 1 of the present invention when the working distance is 1m;

[0016] Figure 3 This is a modulation transfer function curve of the image-side telecentric lens embodiment 1 of the present invention when the working distance is 1.5m;

[0017] Figure 4 This is a modulation transfer function curve of the image-side telecentric lens embodiment 1 of the present invention when the working distance is 2m;

[0018] Figure 5 This is a distortion curve diagram of the image-side telecentric lens embodiment 1 of the present invention when the working distance is 1m;

[0019] Figure 6 This is a distortion curve diagram of the image-side telecentric lens embodiment 1 of the present invention when the working distance is 1.5m;

[0020] Figure 7 This is a distortion curve diagram of the image-side telecentric lens embodiment 1 of the present invention when the working distance is 2m;

[0021] Figure 1 In the image plane, 1 represents the image plane. Detailed Implementation

[0022] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0023] like Figure 1As shown, the image-side telecentric lens of the present application is composed of a front lens group A and a rear lens group B arranged in sequence along the optical axis from the object side to the image side, the front lens group A is composed of a positive focal power meniscus lens A1, a negative focal power meniscus lens A2, a positive focal power meniscus lens A3, a negative focal power meniscus lens A4, a negative focal power meniscus lens A5 and a double convex lens A6 arranged in sequence along the optical axis from the object side to the image side, the rear lens group B is composed of a double concave lens B1, a double convex lens B2 and a double convex lens B3 arranged in sequence along the optical axis from the object side to the image side, the positive focal power meniscus lens A1 and the negative focal power meniscus lens A2 form a first cemented lens, the positive focal power meniscus lens A3 and the negative focal power meniscus lens A4 form a second cemented lens, the convex surfaces of the positive focal power meniscus lens A1, the negative focal power meniscus lens A2 and the negative focal power meniscus lens A5 face the object side, and the convex surfaces of the positive focal power meniscus lens A3 and the negative focal power meniscus lens A4 face the image side, all the lens surfaces are spherical surfaces. The known double concave lens is a negative focal power lens, and the double convex lens is a positive focal power lens.

[0024] Embodiment 1

[0025] The specific parameters of the lenses in this embodiment are shown in Table 1, wherein the surface serial numbers S1-S18 are the arrangement serial numbers of the optical surfaces from the object side to the image side.

[0026] Table 1

[0027]

[0028] In this embodiment, the working waveband of the image-side telecentric lens is 400-1000 nm, the effective focal length is 43 mm, the F number is 2.7, the maximum half field angle of the diagonal line is 15°, the back working distance is 12.5 mm, and the total optical length (the distance from the center vertex of the front surface of the first lens A1 to the image surface) is less than 101.5 mm.

[0029] Figures 2-4 The modulation transfer function curves of the image-side telecentric lens of this embodiment at working distances of 1 m, 1.5 m and 2 m show that the modulation transfer function values at a frequency of 28 lp / mm in the central field of view are all better than 0.63, the modulation transfer function values at a frequency of 28 lp / mm in the maximum field of view are all better than 0.5, and the modulation transfer function values at a frequency of 28 lp / mm in all fields of view after tolerance analysis are all better than 0.41, which meets the design requirements and the image quality is stable.

[0030] Figures 5-7 The distortion curves of the image-side telecentric lens of this embodiment at working distances of 1 m, 1.5 m and 2 m show that the maximum optical distortion in the full field of view is better than 1%, and the fidelity is good.

[0031] Embodiment 2

[0032] The specific parameters of the lenses in this embodiment are shown in Table 2.

[0033] Table 2

[0034]

[0035] In this embodiment, the working wavelength range of the image-side telecentric lens is 400-1000 nm, the effective focal length is 43 mm, the F number is 2.7, the maximum half field angle of the diagonal line is 15°, the back working distance is 12.5 mm, and the total optical length (the distance from the center vertex of the front surface of the first lens A1 to the image plane) is less than 101.5 mm.

[0036] When the working distance of the image-side telecentric lens of this embodiment is 1 m, 1.5 m, or 2 m, the modulation transfer function value at a frequency of 28 lp / mm in the central field of view is better than 0.61, the modulation transfer function value at a frequency of 28 lp / mm in the maximum field of view is better than 0.45, and the modulation transfer function value at a frequency of 28 lp / mm in all fields of view after tolerance analysis is better than 0.38, meeting the design requirements and being stable in image quality.

[0037] When the working distance of the image-side telecentric lens of this embodiment is 1 m, 1.5 m, or 2 m, the maximum optical distortion in the full field of view is better than 1.1%, and the fidelity is good.

[0038] Embodiment 3

[0039] The specific parameters of the lenses in this embodiment are shown in Table 3.

[0040] Table 3

[0041]

[0042] In this embodiment, the working wavelength range of the image-side telecentric lens is 400-1000 nm, the effective focal length is 43 mm, the F number is 2.7, the maximum half field angle of the diagonal line is 15°, the back working distance is 12.48 mm, and the total optical length (the distance from the center vertex of the front surface of the first lens A1 to the image plane) is less than 100.48 mm.

[0043] When the working distance of the image-side telecentric lens of this embodiment is 1 m, 1.5 m, or 2 m, the modulation transfer function value at a frequency of 28 lp / mm in the central field of view is better than 0.59, the modulation transfer function value at a frequency of 28 lp / mm in the maximum field of view is better than 0.46, and the modulation transfer function value at a frequency of 28 lp / mm in all fields of view after tolerance analysis is better than 0.35, meeting the design requirements and being stable in image quality.

[0044] When the working distance of the image-side telecentric lens of this embodiment is 1 m, 1.5 m, or 2 m, the maximum optical distortion in the full field of view is better than 1.13%, and the fidelity is good.

Claims

1. An image-side telecentric lens characterized by The lens comprises a front lens group A and a rear lens group B arranged in sequence from the object side to the image side along the optical axis, the front lens group A comprises a positive meniscus lens A1, a negative meniscus lens A2, a positive meniscus lens A3, a negative meniscus lens A4, a negative meniscus lens A5 and a double convex lens A6 arranged in sequence from the object side to the image side along the optical axis, and the rear lens group B comprises a double concave lens B1, a double convex lens B2 and a double convex lens B3 arranged in sequence from the object side to the image side along the optical axis; the positive meniscus lens A1 and the negative meniscus lens A2 form a first cemented lens, and the positive meniscus lens A3 and the negative meniscus lens A4 form a second cemented lens; the convex surfaces of the positive meniscus lens A1, the negative meniscus lens A2 and the negative meniscus lens A5 face the object side, and the convex surfaces of the positive meniscus lens A3 and the negative meniscus lens A4 face the image side; all the lens surfaces are spherical.

2. The image-side telecentric lens of claim 1, wherein The front and rear surface curvature radii of the positive meniscus lens A1 are 22.45-24.60 mm and 53.29-80.86 mm respectively; the front and rear surface curvature radii of the negative meniscus lens A2 are 53.29-80.86 mm and 9.78-9.96 mm respectively; the front and rear surface curvature radii of the positive meniscus lens A3 are -25.42--23.99 mm and -10.31--10.14 mm respectively; the front and rear surface curvature radii of the negative meniscus lens A4 are -10.31--10.14 mm and -28.56--26.24 mm respectively; the front and rear surface curvature radii of the negative meniscus lens A5 are 29.82-36.64 mm and 15.50-16.76 mm respectively; the front and rear surface curvature radii of the double convex lens A6 are 17.65-22.50 mm and -20.04--19.57 mm respectively; the front and rear surface curvature radii of the double concave lens B1 are -17.38--13.18 mm and 74.22-211.98 mm respectively; the front and rear surface curvature radii of the double convex lens B2 are 147.48-158.31 mm and -26.94--22.46 mm respectively; and the front and rear surface curvature radii of the double convex lens B3 are 49.68-60.75 mm and -107.24--100.43 mm respectively.

3. The image-side telecentric lens of claim 2, wherein The center thickness of the positive meniscus lens A1 is 8.02-8.32 mm; the center thickness of the negative meniscus lens A2 is 5.16-5.32 mm; the center thickness of the positive meniscus lens A3 is 6.78-6.82 mm; the center thickness of the negative meniscus lens A4 is 2.61-2.74 mm; the center thickness of the negative meniscus lens A5 is 4.28-4.36 mm; the center thickness of the double convex lens A6 is 6.18-6.34 mm; the center thickness of the double concave lens B1 is 4.16-4.30 mm; the center thickness of the double convex lens B2 is 6.56-6.62 mm; and the center thickness of the double convex lens B3 is 7.18-7.22 mm.

4. The image-side telecentric lens of claim 1, wherein The center distance of the front lens group A and the rear lens group B can be adjusted according to different working distances, the center air gap of A and B is 16.10-16.88 mm; the center air gap of the negative meniscus lens A2 of the first cemented lens and the positive meniscus lens A3 of the second cemented lens is 8.50-9.22 mm; the center air gap of the negative meniscus lens A4 and the negative meniscus lens A5 is 3.59-3.72 mm; the center air gap of the negative meniscus lens A5 and the double convex lens A6 is 0.96-1.04 mm; the center air gap of the double concave lens B1 and the double convex lens B2 is 1.26-1.88 mm; the center air gap of the double convex lens B2 and the double convex lens B3 is 6.06-6.50 mm, and the center air gap of the double convex lens B3 to the image surface is 12.48-12.54 mm.

5. The image-side telecentric lens of claim 1, wherein The center distance of the front lens group A and the rear lens group B can be adjusted according to different working distances.

6. The image-side telecentric lens of claim 5, wherein The center air gap of the front lens group A and the rear lens group B is 16.10-16.88 mm.

7. The image-side telecentric lens of claim 1, wherein All lenses are made of glass, the refractive index Nd1 and the dispersion coefficient Vd1 of the positive focal power meniscus lens A1 satisfy the conditions: 1.9Nd1<2.0, 20Vd1<35; the refractive index Nd2 and the dispersion coefficient Vd2 of the negative focal power meniscus lens A2 satisfy the conditions: 1.5Nd2<1.6, 58Vd2<68; the refractive index Nd3 and the dispersion coefficient Vd3 of the positive focal power meniscus lens A3 satisfy the conditions: 1.6Nd3<1.7, 60Vd3<65; the refractive index Nd4 and the dispersion coefficient Vd4 of the negative focal power meniscus lens A4 satisfy the conditions: 1.7Nd4<1.8, 29Vd4<35; the refractive index Nd5 and the dispersion coefficient Vd5 of the negative focal power meniscus lens A5 satisfy the conditions: 1.6Nd5<1.8, 25Vd5<40; the refractive index Nd6 and the dispersion coefficient Vd6 of the double convex lens A6 satisfy the conditions: 1.5Nd6<1.6, 70Vd6<75; the refractive index Nd7 and the dispersion coefficient Vd7 of the double concave lens B1 satisfy the conditions: 1.9Nd7<2.0, 18Vd7<22; the refractive index Nd8 and the dispersion coefficient Vd8 of the double convex lens B2 satisfy the conditions: 1.9Nd8<2.0, 20Vd8<22; the refractive index Nd9 and the dispersion coefficient Vd9 of the double convex lens B3 satisfy the conditions: 1.8Nd9<1.9, 20Vd9<45.

8. The image-side telecentric lens of claim 1, wherein The working waveband of the lens covers 400-1000nm.

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