An imaging lens suitable for a wide spectral range

Abstract

The application belongs to the technical field of optical imaging lenses, and particularly relates to an imaging lens suitable for a wide spectral range, wherein the lens sequentially comprises, from an object side to an image side, a first lens with positive refractive power, a second lens also with positive refractive power, a third lens with negative refractive power, a fourth lens with positive refractive power, a diaphragm, a fifth lens with positive refractive power, a sixth lens with negative refractive power, a seventh lens with positive refractive power, and an eighth lens with negative refractive power. The third lens and the fourth lens are glued to form a first double-glued lens, and the sixth lens and the seventh lens are glued to form a second double-glued lens. The application can realize imaging at any waveband in the range of 400-2500 nm, and can be directly used with a multispectral camera to obtain a multi-channel spectral image. By virtue of the characteristics of a large difference in refractive index and Abbe number, the combination of positive and negative lenses can eliminate intra-waveband and inter-waveband chromatic aberration, so that high-definition imaging is realized.

Description

TECHNICAL FIELD

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

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

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

[0004] In the file with patent publication number "116299957A", an "all-glass spherical wide-spectrum imaging lens" is disclosed, which includes five lenses arranged in order from the object side to the image side, respectively a first lens with positive optical power, a second lens with negative optical power, a third lens with positive optical power, a fourth lens with positive optical power, and a fifth lens with negative optical power. The technical deficiencies of this scheme are that due to the design constraints of using conventional optical glass materials and limited chromatic dispersion compensation structure, the wide-spectrum lens can only correct aberrations in the 340-1550nm wavelength range, but cannot achieve imaging in longer infrared wavelengths. In the file with patent publication number "118981095A", a "large-aperture wide-spectrum imaging lens and electronic equipment" is disclosed. The deficiencies of this scheme are that it can only be applied to the wavelength range of 435-940nm, and cannot correct various aberrations and perform clear imaging in a wider visible and near-infrared wavelength range.

[0005] The above schemes cannot work in a wide wavelength range, thus low working efficiency, and due to unreasonable material selection and power distribution design, especially the failure to realize the synergistic optimization of high refractive index material and compact power distribution, the above schemes have problems of large weight and large volume.

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

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

[0008] To achieve the above purpose, the present application realizes the following technical scheme:

[0009] An imaging lens suitable for 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 arranged in order along the optical axis from the object side to the image side.

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

[0011] The third lens and the fourth lens form a first double cemented lens, and the sixth lens and the seventh lens form a second double cemented lens.

[0012] An aperture 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 double cemented lens form a front lens group, and the fifth lens, the second double cemented lens and the eighth lens form a rear lens group.

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

[0015] Further, the object end optical surface and the image end optical surface of all the lenses are spherical surfaces, the fourth lens, the fifth lens and the eighth lens use ultra-low dispersion glass, and the Abbe number of the fourth lens is greater than 90 and the Abbe number of the eighth lens is greater than 80.

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

[0017] Further, the transmittance of the material used by the second lens is greater than 0.5, the transmittance of the material used by the fourth lens and the fifth lens is greater than 0.9, and the transmittance of the material used by the eighth lens is greater than 0.7.

[0018] Further, 220mm<f1<260mm, 50mm<f2<70mm, wherein 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, wherein nd1, nd2, nd3, nd4, nd5, nd6, nd7, nd8 are the refractive indexes of the first lens to the eighth lens, respectively.

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

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

[0022] 1、 the present application reasonably designs each lens, the front group and the rear group of lenses are both four-piece three-group structure, the first lens and the second lens of the front group use low-dispersion positive lenses, preferentially bear the main optical power, suppress the chromatic aberration and the spherical aberration of visible light, the first double cemented lens is cemented by a negative-positive lens, the high-dispersion lens and the low-dispersion lens are combined to form an achromatic system, the chromatic aberration is offset by the complementary dispersion characteristics of the materials, and the low-dispersion lens suppresses the long-wave secondary spectrum.

[0023] 2、The lens adopts nine lenses and through corresponding design of each lens, the working wave band covers 400-2500nm wave band, can meet various needs from normal optical imaging to special wave band analysis, utilizes the characteristics of large difference of refractive index and Abbe coefficient, eliminates wave band and inter-wave band chromatic aberration through combination of positive and negative lenses, so that high definition imaging is realized. The lens provided by the application can provide high definition, low chromatic aberration imaging effect in the whole 400-2500nm spectral range, and can be directly used with a multi-spectral camera to obtain multi-channel spectral images, so that a hardware foundation for high efficiency work is provided, can meet the needs of different application fields, and has wide application range.

[0024] 3、The lens adopts high refractive index, low dispersion glass combination, through selection of high refractive index glass, the curvature radius of the lens can be reduced while the refractive power is ensured, the lens is thinner, the optical system axial size is significantly compressed, the low Abbe number and high Abbe number glass combination is adopted, the dispersion is complementary in the double cemented structure, the number of additional lenses required for correcting chromatic aberration is reduced, so that a light weight, small size lens device is provided for a wide wave band imaging system. Preparation is easy, and the operation difficulty is low, so that the production cost can be effectively reduced. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a structure schematic diagram of a wide spectrum imaging lens in the application example;

[0026] Figure 2 is a light path schematic diagram of a wide spectrum imaging lens in the application example;

[0027] Figure 3 is a point array diagram of a wide spectrum imaging lens in the application example;

[0028] Figure 4 is an MTF diagram of a wide spectrum imaging lens in the application example;

[0029] Figure 5 is an FTan(Theta) distortion curve of a wide spectrum imaging lens in the application example.

[0030] Figure 6 is a field curvature curve of a wide spectrum imaging lens in the application example.

[0031] Figure 7 is a relative luminance diagram of a wide spectrum imaging lens in the application example;

[0032] The reference signs 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

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

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

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

[0036] The third lens 3 is a meniscus lens with 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 positive optical power;

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

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

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

[0041] The eighth lens 8 is a meniscus lens with 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 constitute the first cemented doublet lens, and the sixth lens 6 and the seventh lens 7 constitute the second cemented doublet lens.

[0043] In the first lens 1 to the eighth lens 8, the first lens 1, the second lens 2 and the first cemented doublet lens constitute the front lens group, and the fifth lens 5, the second cemented doublet lens and the eighth lens 8 constitute the rear lens group.

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

[0045] The second lens 2 is made of BAK4 material and has a transmittance greater than 0.5.

[0046] The fourth lens 4, the fifth lens 5 and the eighth lens 8 use ultra-low dispersion glass, wherein the material of the fourth lens 4 and the fifth lens 5 is N-FK58, the material transmittance is greater than 0.9, and the Abbe number is greater than 90; the material of the eighth lens 8 is N-FK51A, the material transmittance is greater than 0.7, and the Abbe number is greater than 80, which is used for correcting chromatic aberration in a wide-spectrum optical system.

[0047] Further, 220mm < f1 < 260mm, 50mm < f2 < 70mm, wherein 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, and nd1, nd2, nd3, nd4, nd5, nd6, nd7 and nd8 are the refractive indexes of the first lens 1 to the eighth lens 8, respectively.

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

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

[0051] The following gives specific embodiments of the present application, and 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 application takes the difference between high and low dispersion as the core of control and aberration correction, adjusts the cemented surface parameters, material combination and power distribution according to the requirements, and finally realizes the high-resolution imaging of a wide waveband of 400-2500nm.

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

[0057] In the embodiment, the F# of the wide spectrum imaging lens is 2.5, which is defined as F# = f / D, the entrance pupil diameter D is 20mm; the field of view angle of the wide spectrum imaging lens is 11.4°, the back working distance BFL is 10mm, the image surface diameter is 12.3mm, and the total length TTL of the lens is 70mm.

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

[0059] Referring to Figure 3 It can be seen that the spot radii of different fields of view are small, which indicates that the imaging quality of the imaging lens is close to the diffraction limit, the chromatic aberration and the aberration are corrected well in the wide spectrum range, the imaging quality is high, and the spot diagram presents a regular circle and a symmetrical distribution, and the imaging lens has no significant astigmatism or asymmetrical aberration.

[0060] Referring to Figure 4 It can be seen that the resolution is close to the diffraction limit under the condition of 90lp / mm, the image details can be distinguished, and the aberration is also effectively controlled.

[0061] Referring to Figure 5 The FTan(Theta) distortion of the imaging lens in the half field of view is required to be less than 2%. It can be seen from the figure that the maximum distortion of the lens is 1.4%.

[0062] Referring to Figure 6 It can be seen that the field curvature is controlled between ±0.1, the solid line is the meridional field curvature in the half field of view of each wavelength, and the dashed line in the figure is the sagittal field curvature in the half field of view of each wavelength.

[0063] Referring to Figure 7 It can be seen that the relative luminance is high and well controlled, the relative luminance in the field of view range is uniform, and the image splicing and superposition are uniform. The above only describes the preferred embodiments of the present application and is not used to limit the present application, although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments or make equivalent replacement for some technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An imaging lens suitable for a wide spectral range, comprising 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) arranged sequentially along the optical axis from the object side to the image side, characterized in that: The spectral range of the lens is 400 - 2500 nm; The first lens (1) is a positive meniscus lens, the second lens (2) is a positive meniscus lens, the third lens (3) is a negative meniscus lens, the fourth lens (4) is an asymmetric biconvex lens with positive optical power, the fifth lens (5) is a positive meniscus lens, the sixth lens (6) is a negative concave lens, the seventh lens (7) is an asymmetric biconvex lens with positive optical power, and the eighth lens (8) is a negative meniscus lens; 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 provided 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 the front lens group, and the fifth lens (5), the second doublet lens and the eighth lens (8) form the rear lens group; 220 mm < f1 < 260 mm, 50 mm < f2 < 70 mm, 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).

2. An imaging lens suitable for a wide spectral range according to claim 1, characterized in that: A protective lens (10) is provided before the first lens (1).

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

4. An 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. An 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. An imaging lens suitable for 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.

7. An imaging lens suitable for 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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