Imaging lens suitable for wide spectral range

Abstract

The invention belongs to the technical field of optical imaging lenses, and particularly relates to an imaging lens applicable to a wide spectral range, which sequentially comprises a first lens with positive focal power, a second lens with positive focal power, a third lens with negative focal power, a fourth lens with positive focal power and a diaphragm from an object space to an image space, the system comprises a first lens with positive focal power, a second lens with negative focal power, a third lens with positive focal power, a fifth lens with positive focal power, a sixth lens with negative focal power, a seventh lens with positive focal power, and an eighth lens with negative focal power. Wherein the third lens and the fourth lens are glued to form a first doublet lens, and the sixth lens and the seventh lens are glued to form a second doublet lens. According to the invention, imaging at any wave band within the range of 400-2500nm can be realized, and the device can be directly matched with a multispectral camera for use so as to obtain a multichannel spectral image. The characteristic that the refractive index and the Abbe number are large in difference is utilized, chromatic aberration in wave bands and between the wave bands is eliminated through combination of the positive lens and the negative lens, and therefore high-definition imaging is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical imaging lenses, and particularly relates to an imaging lens suitable for a wide spectral range. Background Art

[0002] With the development of optical imaging technology, the importance of wide-spectrum imaging technology has become increasingly prominent in multiple fields. Currently, wide-spectrum lenses on the market can usually only provide clear imaging effects within a specific spectral range (such as 400 - 1100nm), while in a wider spectral range, such as the 400 - 2500nm range from visible to short-wave infrared, the imaging performance is often poor. This is because traditional lenses do not fully consider chromatic aberration correction and light transmittance issues within the wide spectral range. The difference in refractive indices of light with different wavelengths causes chromatic aberration, which affects imaging clarity. The light transmittance of traditional lens materials is limited within the wide spectral range, especially in the ultraviolet and infrared regions, resulting in insufficient imaging brightness and making it difficult for existing lenses to maintain high-resolution imaging across the entire wide spectral range.

[0003] Wide-spectrum imaging technology can provide rich spectral information, which is crucial for accurately identifying and classifying substances. Within the wide spectral range of 400 - 2500nm, an imaging spectrometer can capture spectral information from visible light to short-wave infrared. For example, in the field of industrial inspection, ultraviolet light can be used to detect tiny surface cracks, visible light for conventional inspection, and near-infrared light for analyzing the internal properties of materials; in remote sensing imaging, wide-spectrum imaging can improve the accuracy of ground object classification; in medical diagnosis, light of different wavelengths can provide more diagnostic information for biological tissues.

[0004] In the document with the patent publication number "116299957A", "An All-Glass Spherical Wide-Spectrum Imaging Lens" is disclosed, which includes five lenses arranged in sequence from the object side to the image side, namely a first lens with a positive optical power, a second lens with a negative optical power, a third lens with a positive optical power, a fourth lens with a positive optical power, and a fifth lens with a negative optical power. The technical deficiency of this solution is that due to the design constraints of using conventional optical glass materials and a limited dispersion compensation structure, the wide-spectrum lens can only correct aberrations within the wavelength range of 340 - 1550nm, but cannot achieve imaging in longer infrared bands. In the document with the patent publication number "118981095A", "A Large Aperture Wide-Spectrum Imaging Lens and an Electronic Device" is disclosed. The deficiency of this solution is that it can only be applicable to the wavelength range of 435 - 940nm, and cannot correct various aberrations and perform clear imaging within a wider visible and near-infrared band.

[0005] None of the above solutions can work within a relatively wide wavelength range, so the working efficiency is low. At the same time, due to the irrationality in material selection and optical power distribution design, especially the failure to achieve the collaborative optimization of high-refractive-index materials and compact optical power distribution, all of the above solutions have problems of large weight and large volume.

[0006] Providing a spectral imaging lens with a wider wavelength range to meet the requirements of different application fields is an urgent problem to be solved at present. Summary of the Invention

[0007] The present invention provides an imaging lens applicable to a wide spectral range to solve the problems of narrow wavelength range, low working efficiency, large weight and large volume existing in the prior art.

[0008] To achieve the above object, the present invention is realized through the following technical solutions:

[0009] An imaging lens applicable to a wide spectral range is composed of a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens and an eighth lens sequentially arranged along the optical axis from the object side to the image side;

[0010] The first lens is a positive meniscus lens, the second lens is a positive meniscus lens, the third lens is a negative meniscus lens, the fourth lens is an asymmetric biconvex lens with positive optical power, the fifth lens is a positive meniscus lens, the sixth lens is a concave lens with negative optical power, the seventh lens is an asymmetric biconvex lens with positive optical power, and the eighth lens is a negative meniscus lens;

[0011] The third lens and the fourth lens form a first doublet lens, and the sixth lens and the seventh lens form a second doublet lens;

[0012] An aperture stop is arranged between the fourth lens and the fifth lens;

[0013] Among the first lens to the eighth lens, the first lens, the second lens and the first doublet lens form the front lens group, and the fifth lens, the second doublet lens and the eighth lens form the rear lens group.

[0014] Furthermore, a protective lens is arranged in front of the first lens.

[0015] Furthermore, the object-side optical surfaces and image-side optical surfaces of all the lenses are spherical surfaces. The fourth lens, the fifth lens and the eighth lens use ultra-low dispersion glass, where the Abbe number of the fourth lens > 90 and the Abbe number of the eighth lens > 80.

[0016] Further, the above-mentioned second lens material is BAK4, the fourth and fifth lens materials are N-FK58, and the eighth lens material is N-FK51A.

[0017] Further, the transmittance of the material used for the above-mentioned second lens is greater than 0.5, the transmittance of the materials used for the fourth and fifth lenses is greater than 0.9, and the transmittance of the material used for the eighth lens is greater than 0.7.

[0018] Further, 220mm < f1 < 260mm, 50mm < f2 < 70mm, where f1 is the combined focal length of the first lens to the fourth lens, and f2 is the combined focal length of the fifth lens to the eighth lens.

[0019] Further, nd1 > nd2 > 1.70, nd3 > nd4 > 1.70, nd6 > nd5 > 1.70, nd7 > nd8 > 1.70, where nd1, nd2, nd3, nd4, nd5, nd6, nd7, and nd8 are the refractive indices of the first lens to the eighth lens respectively.

[0020] Further, vd1 > vd2 > 70, vd4 > vd3 > 100, vd5 > vd6 > 100, vd8 > vd7 > 90, where vd1, vd2, vd3, vd4, vd5, vd6, vd7, and vd8 are the Abbe numbers of the first lens to the eighth lens respectively.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The present invention has made a reasonable design for each lens. Both the front group and the rear group of lenses are four-piece three-group structures. The first and second lenses in the front group use low-dispersion positive lenses, which preferably bear the main optical power, suppress visible light chromatic aberration and spherical aberration. The first doublet lens is glued by a negative-positive lens combination, and the high-dispersion lens and the low-dispersion lens are combined to form an achromatic system. Chromatic aberration is cancelled by the complementary dispersion characteristics of the materials, and the low-dispersion lens suppresses the long-wave secondary spectrum. In the rear group, the positive lens of the second doublet lens has a low refractive index, and the negative lens has a high refractive index. By using the difference in refractive indices, the curvature of the glued surface is increased, and the dispersion compensation efficiency is improved. Through the cooperation of the front group and the rear group of lenses, wide-spectrum apochromatism and high-order aberration balance can be effectively achieved, providing effective technical support for the collaborative correction of axial chromatic aberration and magnification chromatic aberration of an optical system in the 400 - 2500nm ultra-wide band.

[0023] 2. The present invention uses nine lenses and designs each lens accordingly. The working band covers the range of 400 - 2500 nm, which can meet various requirements from conventional optical imaging to special band analysis. By utilizing the characteristics of large differences in refractive index and Abbe number, chromatic aberration within and between bands is eliminated through the combination of positive and negative lenses, thereby achieving high-definition imaging. The lens provided by the present invention can provide high-definition and low-chromatic aberration imaging effects within the entire 400 - 2500 nm spectral range. At the same time, it can be directly used in conjunction with a multi-spectral camera to obtain multi-channel spectral images. Therefore, it provides a hardware foundation for high-efficiency work, can meet the needs of different application fields, and has a wide range of applications.

[0024] 3. Since the lenses of the present invention adopt a combination of glasses with high refractive index and low dispersion, by selecting high-refractive-index glass, the lens curvature radius can be reduced while ensuring the optical power, making the lens thinner and significantly compressing the axial size of the optical system. By using a combination of glasses with low Abbe number and high Abbe number, dispersion compensation is achieved in the doublet structure, reducing the number of additional lenses required to correct chromatic aberration. Therefore, it provides a lens device with light weight and small size for a wide-band imaging system. It is easy to prepare and has low operation difficulty, so the production cost can be effectively reduced. Description of the Drawings

[0025] Figure 1 is a schematic structural diagram of the wide-spectrum imaging lens in the embodiment of the present invention;

[0026] Figure 2 is a schematic diagram of the light path of the wide-spectrum imaging lens in the embodiment of the present invention;

[0027] Figure 3 is the spot diagram of the wide-spectrum imaging lens in the embodiment of the present invention;

[0028] Figure 4 is the MTF diagram of the wide-spectrum imaging lens in the embodiment of the present invention;

[0029] Figure 5 is the FTan(Theta) distortion curve of the wide-spectrum imaging lens in the embodiment of the present invention.

[0030] Figure 6 is the field curvature curve of the wide-spectrum imaging lens in the embodiment of the present invention.

[0031] Figure 7 is the relative illumination diagram of the wide-spectrum imaging lens in the embodiment of the present invention;

[0032] The reference numerals are as follows: 1 - first lens, 2 - second lens, 3 - third lens, 4 - fourth lens, 5 - fifth lens, 6 - sixth lens, 7 - seventh lens, 8 - eighth lens, 9 - image plane, 10 - protective lens, 11 - diaphragm. Detailed implementation manners

[0033] To more clearly illustrate the technical solutions of the present invention, the present invention will be described in detail below through embodiments or with reference to the accompanying drawings.

[0034] As Figure 1 shown, a structure of a wide-spectrum imaging lens provided by the present invention, along an optical axis from the object side to the image side, sequentially includes a first lens 1 to an eighth lens 8. A protective lens 10 is provided in front of the first lens 1, and a diaphragm 11 is provided between the fourth lens 4 and the fifth lens 5.

[0035] The first lens 1 is a meniscus lens with a positive optical power, its object side is convex, and its image side is concave; the second lens 2 is a meniscus lens with a positive optical power, its object side is concave, and its image side is convex;

[0036] The third lens 3 is a meniscus lens with a negative optical power, its object side is convex, and its image side is concave;

[0037] The fourth lens 4 is an asymmetric biconvex lens with a positive optical power;

[0038] The fifth lens 5 is a meniscus lens with a positive optical power, its object side is convex, and its image side is concave;

[0039] The sixth lens 6 is a concave lens with a negative optical power;

[0040] The seventh lens 7 is an asymmetric biconvex lens with a positive optical power;

[0041] The eighth lens 8 is a meniscus lens with a negative optical power, its object side is concave, and its image side is convex.

[0042] Wherein: the third lens 3 and the fourth lens 4 form a first doublet lens, and the sixth lens 6 and the seventh lens 7 form a second doublet lens.

[0043] Among the first lens 1 to the eighth lens 8, the first lens 1, the second lens 2 and the first doublet lens form a front lens group, and the fifth lens 5, the second doublet lens and the eighth lens 8 form a rear lens group.

[0044] The object-side optical surfaces and the image-side optical surfaces of all the lenses are spherical surfaces.

[0045] The material of the second lens 2 is BAK4, and the transmittance is greater than 0.5;

[0046] The fourth lens 4, the fifth lens 5, and the eighth lens 8 described above use ultra-low dispersion glass. The materials of the fourth lens 4 and the fifth lens 5 are N-FK58, with a material transmittance greater than 0.9 and an Abbe number > 90. The material of the eighth lens 8 is N-FK51A, with a material transmittance greater than 0.7 and an Abbe number > 80, which is used to correct chromatic aberration in a wide-spectrum optical system.

[0047] Further, 220mm < f1 < 260mm, 50mm < f2 < 70mm, where f1 is the combined focal length of the first lens 1 to the fourth lens 4, and f2 is the combined focal length of the fifth lens to the eighth lens.

[0048] Further, nd1 > nd2 > 1.70, nd3 > nd4 > 1.70, nd6 > nd5 > 1.70, nd7 > nd8 > 1.70, where nd1, nd2, nd3, nd4, nd5, nd6, nd7, and nd8 are the refractive indices of the first lens 1 to the eighth lens 8, respectively.

[0049] Further, vd1 > vd2 > 70, vd4 > vd3 > 100, vd5 > vd6 > 100, vd8 > vd7 > 90, where vd1, vd2, vd3, vd4, vd5, vd6, vd7, and vd8 are the Abbe numbers of the first lens 1 to the eighth lens 8, respectively.

[0050] In actual assembly, the total length of the lens, that is, the distance between the center of the object-side optical surface of the first lens 1 and the image plane, can be selected as: 55mm < TTHI < 65mm; 8mm < BFL < 15mm, where BFL is the back focal length of the optical imaging lens. The F# of the lens satisfies: 2 < F# < 3, where F# = f / D, and D is the entrance pupil diameter. 40mm < f < 60mm, where f is the total focal length of the imaging lens.

[0051] The following gives specific embodiments of the present invention. The specific parameters of each lens in the embodiments are shown in Table 1:

[0052] Table 1 Specific parameters of each lens

[0053]

[0054]

[0055] The present invention takes the control of the difference between high and low dispersions and the collaborative correction of aberrations as the core, adjusts the parameters of the cemented surface, the material combination, and the power distribution according to requirements, and finally realizes high-resolution imaging in the 400 - 2500nm wide band.

[0056] The wide-spectrum imaging lens provided in this embodiment has an effective focal length f of 50 mm. The combined focal length f1 of the first lens 1 to the fourth lens 4 is 239.3 mm, and the combined focal length f2 of the fifth lens 5 to the eighth lens 8 is 60.9 mm.

[0057] In this embodiment, the F# of the wide-spectrum imaging lens is 2.5, where F# = f / D, the entrance pupil diameter D = 20 mm; the field of view angle of the wide-spectrum imaging lens is 11.4°, the back focal length BFL is 10 mm, the image plane diameter is 12.3 mm, and the total length TTL of the lens is 70 mm.

[0058] The wide-spectrum imaging lens of the embodiment is tested, and the results are as follows:

[0059] See Figure 3 , it can be seen that the spot radii at different fields of view are all small, indicating that the imaging quality of the imaging lens is close to the diffraction limit. Achromatism is corrected in the wide-spectrum range, chromatic aberration and spherical aberration are corrected well, the imaging quality is high, and the spot diagram shows regular circular and symmetric distributions, and there is no significant astigmatism or asymmetric aberration in the imaging lens.

[0060] See Figure 4 , it can be seen that it is close to the diffraction limit under the condition of 90 lp / mm, has a high resolution, can resolve image details, and the aberration is also effectively controlled.

[0061] See Figure 5 , the imaging lens requires that the F Tan(Theta) distortion within the half field of view angle is less than 2%. It can be seen from the figure that the maximum distortion of the lens is 1.4%.

[0062] See Figure 6 , it can be seen that the field curvature is controlled within ±0.1. The solid line is the meridional field curvature within the half field of view angle of each wavelength, and the dotted line in the figure is the sagittal field curvature within the half field of view angle of each wavelength.

[0063] See Figure 7 , it can be seen that the relative illumination is high and well controlled, ensuring uniform relative illumination in the field of view range and uniform image stitching and overlay. The above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An imaging lens applicable to a wide spectral range, which is composed of a first lens (1), a second lens (2), a third lens (3), a fourth lens (4), a fifth lens (5), a sixth lens (6), a seventh lens (7) and an eighth lens (8) sequentially arranged from the object side to the image side along the optical axis, and is characterized in that: The first lens (1) is a meniscus lens with positive optical power, the second lens (2) is a meniscus lens with positive optical power, the third lens (3) is a meniscus lens with negative optical power, the fourth lens (4) is an asymmetric biconvex lens with positive optical power, the fifth lens (5) is a meniscus lens with positive optical power, the sixth lens (6) is a concave lens with negative optical power, the seventh lens (7) is an asymmetric biconvex lens with positive optical power, and the eighth lens (8) is a meniscus lens with negative optical power; The third lens (3) and the fourth lens (4) form a first doublet lens, and the sixth lens (6) and the seventh lens (7) form a second doublet lens; An aperture stop (11) is arranged between the fourth lens (4) and the fifth lens (5); Among the first lens (1) to the eighth lens (8), the first lens (1), the second lens (2) and the first doublet lens form a front lens group, and the fifth lens (5), the second doublet lens and the eighth lens (8) form a rear lens group.

2. The imaging lens suitable for a wide spectral range according to claim 1, characterized in that: A protective lens (10) is arranged in front of the first lens (1).

3. The imaging lens suitable for a wide spectral range according to claim 1, characterized in that: The object-side optical surfaces and the image-side optical surfaces of all the lenses are spherical surfaces. The fourth lens (4), the fifth lens (5) and the eighth lens (8) use ultra-low dispersion glass, wherein the Abbe number of the fourth lens (4) > 90, and the Abbe number of the eighth lens (8) > 80.

4. The imaging lens suitable for a wide spectral range according to claim 1, characterized in that: The material of the second lens (2) is BAK4, the materials of the fourth lens (4) and the fifth lens (5) are N-FK58, and the material of the eighth lens (8) is N-FK51A.

5. The imaging lens suitable for a wide spectral range according to claim 1, characterized in that: The transmittance of the material used for the second lens (2) is greater than 0.5, the transmittance of the materials used for the fourth lens (4) and the fifth lens (5) is greater than 0.9, and the transmittance of the material used for the eighth lens (8) is greater than 0.

7.

6. The imaging lens applicable to a wide spectral range according to claim 1, characterized in that: 220mm < f1 < 260mm, 50mm < f2 < 70mm, where f1 is the combined focal length of the first lens (1) to the fourth lens (4), and f2 is the combined focal length of the fifth lens (5) to the eighth lens (8).

7. The imaging lens applicable to a wide spectral range according to claim 1, characterized in that: nd1 > nd2 > 1.70, nd3 > nd4 > 1.70, nd6 > nd5 > 1.70, nd7 > nd8 > 1.70, where nd1, nd2, nd3, nd4, nd5, nd6, nd7, nd8 are the refractive indices of the first lens (1) to the eighth lens (8) respectively.

8. The imaging lens applicable to a wide spectral range according to claim 1, characterized in that: vd1 > vd2 > 70, vd4 > vd3 > 100, vd5 > vd6 > 100, vd8 > vd7 > 90, where vd1, vd2, vd3, vd4, vd5, vd6, vd7, vd8 are the Abbe coefficients of the first lens (1) to the eighth lens (8) respectively.

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