A long working distance large numerical aperture object side telecentric lens

Abstract

The application discloses a long-working-distance large-numerical-aperture object-side telecentric lens, which comprises, in sequence from the object side to the image side along the optical axis of the lens, a front lens group, an aperture diaphragm and a rear lens group. The front lens group comprises a first lens, a second lens, a fourth lens, a sixth lens and an eighth lens with positive refractive powers, and a third lens, a fifth lens, a seventh lens and a ninth lens with negative refractive powers, wherein the third lens and the fourth lens form a first set of double cemented lenses, the eighth lens and the ninth lens form a second set of double cemented lenses, and the fifth lens, the sixth lens and the seventh lens form a first set of triple cemented lenses. The rear lens group comprises a tenth lens and a twelfth lens with positive refractive powers, and an eleventh lens and a thirteenth lens with negative refractive powers. The application adopts thirteen spherical glass lenses, and by reasonably distributing the refractive powers of the lenses, the lens has the advantages of long working distance, large numerical aperture, ultrahigh resolution, high relative illuminance, wide spectral range and high telecentricity, solves the problem of low resolution of a long-working-distance object-side telecentric lens, is beneficial to improving the measurement precision of a detection lens, and meets the demand of some application scenes for higher-performance lenses.

Description

Technical Field

[0001] The present invention relates to the field of optical imaging technology, and in particular to an object-space telecentric lens with a long working distance and a large numerical aperture. Background Art

[0002] With the continuous development of science and technology, machine vision technology is increasingly being applied in more and more fields. As a core component in machine vision technology, optical lenses largely determine the performance of the entire system. Object-space telecentric lenses are primarily designed to address the insufficient measurement accuracy caused by parallax in traditional industrial lenses. The aperture diaphragm of object-space telecentric lenses is located at the system's image-space focal plane, eliminating measurement errors caused by inaccurate object-space focusing. Furthermore, object-space telecentric lens systems offer unique properties such as large depth of field and low distortion, making them widely used in measurement applications.

[0003] The rapid development of the machine vision industry has led to increasingly stringent performance requirements for the optical lenses that support it. Long working distance and high numerical aperture (i.e., high resolution) have become two key design criteria for lenses, requiring larger system apertures and more complex optical structures. However, these two parameters often constrain each other, creating a design challenge. Currently, long-working-distance lenses on the market have lower resolution, while high-resolution lenses have shorter working distances. When ultra-high-resolution imaging of tiny objects at long working distances is required, existing lenses struggle to meet the demand.

[0004] Therefore, in order to address this technical challenge, it is of great significance to explore and optimize the design of optical lenses that can ensure long working distance and achieve high resolution. This not only requires designers to have a deep understanding of optical principles, but also requires the combination of advanced manufacturing processes and precise testing methods to achieve a comprehensive improvement in lens performance and meet the growing and diverse needs in the field of machine vision. Summary of the Invention

[0005] In order to overcome the deficiencies of the above-mentioned prior art, the present invention provides a long working distance and large numerical aperture object-space telecentric lens. The lens has the advantages of long working distance, large numerical aperture, ultra-high resolution, high relative illumination, wide spectral range and high telecentricity, and solves the problem of low resolution of long working distance object-space telecentric lenses.

[0006] According to one aspect of the present invention, a long working distance and large numerical aperture object-side telecentric lens is provided, the lens comprising a front lens group G1, an aperture stop STOP, and a rear lens group G2, which are arranged in sequence from the object side to the image side along the lens optical axis. The front lens group G1 comprises a first lens L1, a second lens L2, a fourth lens L4, a sixth lens L6, and an eighth lens L8, all having positive focal power, and a third lens L3, a fifth lens L5, a seventh lens L7, and a ninth lens L9, all having negative focal power, wherein the third lens L3 and the fourth lens L4 form a first group of doublets, the eighth lens L8 and the ninth lens L9 form a second group of doublets, and the fifth lens L5, the sixth lens L6, and the seventh lens L7 form a first group of triplets. The rear lens group G2 comprises a tenth lens L1, a second lens L2, a fourth lens L4, a sixth lens L6, and an eighth lens L8, all having positive focal power. 10 and the twelfth lens L 12 , and an eleventh lens L having negative refractive power 11 and the thirteenth lens L 13 .

[0007] Furthermore, the thirteen lenses are all spherical glass lenses.

[0008] Furthermore, the optical power of the front lens group G1 is The optical power of the rear lens group G2

[0009] Furthermore, the first lens L1 has a concave surface facing the object side and a convex surface facing the image side. The focal length of the first lens L1 is 192.1 mm. <f1<201.5mm;

[0010] The second lens L2 has a convex surface facing the object side and a convex surface facing the image side. The focal length of the second lens L2 is 170.5 mm. <f2<175.2mm;

[0011] The third lens L3 has a concave surface facing the object side and a concave surface facing the image side. The focal length of the third lens L3 is -110.3 mm. <f3<-105.0mm;

[0012] The fourth lens L4 has a convex surface facing the object side and a convex surface facing the image side. The focal length of the fourth lens L4 is 115.6 mm. <f4<128.5mm;

[0013] The fifth lens L5 has a convex surface facing the object side and a concave surface facing the image side. The focal length of the fifth lens L5 is -130.0 mm. <f5<-125.4mm;

[0014] The sixth lens L6 has a convex surface facing the object side and a convex surface facing the image side. The focal length of the sixth lens L6 is 91.4 mm. <f6<100.2mm;

[0015] One side of the seventh lens L7 facing the object side is concave, and one side facing the image side is convex. The focal length of the seventh lens L7 satisfies -193.2mm < f7 < -180.8mm;

[0016] One side of the eighth lens L8 facing the object side is convex, and one side facing the image side is convex. The focal length of the eighth lens L8 satisfies 100.7mm < f8 < 108.0mm;

[0017] One side of the ninth lens L9 facing the object side is concave, and one side facing the image side is convex. The focal length of the ninth lens L9 satisfies -162.4mm < f9 < -155.7mm;

[0018] One side of the tenth lens L 10 facing the object side is convex, and one side facing the image side is convex. The tenth lens L 10 has a focal length satisfying 88.7mm < f 10 < 93.5mm;

[0019] One side of the eleventh lens L 11 facing the object side is concave, and one side facing the image side is concave. The eleventh lens L 11 has a focal length satisfying -193.2mm < f 11 < -185.5mm;

[0020] One side of the twelfth lens L 12 facing the object side is convex, and one side facing the image side is concave. The twelfth lens L 12 has a focal length satisfying 71.5mm < f 12 < 76.4mm;

[0021] One side of the thirteenth lens L 13 facing the object side is concave, and one side facing the image side is concave. The thirteenth lens L 13 has a focal length satisfying -60.3mm < f 13 < -48.3mm.

[0022] Furthermore, the refractive index of the first lens L1 satisfies 1.65 < Nd1 < 1.75, and the dispersion coefficient satisfies 25 < Vd < 35;

[0023] The refractive index of the second lens L2 satisfies 1.45 < Nd2 < 1.55, and the dispersion coefficient Vd2 > 80;

[0024] The refractive index of the third lens L3 satisfies 1.55 < Nd3 < 1.65, and the dispersion coefficient satisfies 55 < Vd < 65;

[0025] The refractive index of the fourth lens L4 satisfies 1.45 < Nd4 < 1.55, and the dispersion coefficient Vd4 > 90;

[0026] The refractive index of the fifth lens L5 satisfies 1.75 < Nd5 < 1.85, and the dispersion coefficient 40 < Vd5 < 50;

[0027] The refractive index of the sixth lens L6 satisfies 1.45 < Nd6 < 1.55, and the dispersion coefficient Vd6 > 90;

[0028] The refractive index of the seventh lens L7 satisfies 1.80 < Nd7 > 1.85, and the dispersion coefficient 20 < Vd7 < 30;

[0029] The refractive index of the eighth lens L8 satisfies 1.45 < Nd8 < 1.55, and the dispersion coefficient Vd8 > 80;

[0030] The refractive index of the ninth lens L9 satisfies 1.65 < Nd9 < 1.75, and the dispersion coefficient 50 < Vd9 < 60;

[0031] The refractive index of the tenth lens L 10 satisfies 1.75 < Nd 10 < 1.85, and the dispersion coefficient 30 < Vd 10 < 40;

[0032] The refractive index of the eleventh lens L 11 satisfies 1.70 < Nd 11 < 1.80, and the dispersion coefficient 40 < Vd 11 < 50;

[0033] The refractive index of the twelfth lens L 12 satisfies 1.60 < Nd 12 < 1.70, and the dispersion coefficient 25 < Vd 12 < 35;

[0034] The refractive index of the thirteenth lens L 13 satisfies 1.45 < Nd 13 < 1.55, and the dispersion coefficient Vd 13 > 90.

[0035] Furthermore, the working distance WD of the lens satisfies WD ≥ 100 mm, the optical resolution δ on the object side satisfies δ ≤ 1 μm, the numerical aperture NA on the object side satisfies NA ≥ 0.37, the magnification β of the lens satisfies -3.4 ≤ β ≤ -3.5, the telecentricity σ on the object side satisfies σ ≤ 0.01°, the working wavelength range satisfies 486 nm ≤ λ ≤ 656 nm, and the image plane height h satisfies h ≤ 8.1 mm.

[0036] The beneficial effects of the present invention are as follows: the present invention uses thirteen spherical glass lenses, and by reasonably distributing the optical focal length of each lens, under the condition that the working distance is greater than 100 mm, it can achieve an object-side numerical aperture NA ≥ 0.37 and an object-side resolution δ ≤ 1 μm, which are much higher than the existing similar lenses on the market. At the same time, the lens has the advantages of high relative illumination, wide spectral range and high telecentricity, which solves the problem of low resolution of object-side telecentric lenses with long working distances, is beneficial to improving the measurement accuracy of detection lenses, and expands the application scenarios of lenses. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a schematic diagram of the optical structure of an object-space telecentric lens with a long working distance and a large numerical aperture according to the present invention;

[0038] Figure 2 This is a light path diagram of the optical lens in an embodiment of the present invention;

[0039] Figure 3 is a point diagram of the optical lens in an embodiment of the present invention;

[0040] Figure 4 : is an MTF curve diagram of the optical lens in an embodiment of the present invention;

[0041] Figure 5 2 is a relative illumination diagram of the optical lens in an embodiment of the present invention. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0043] The present invention provides an object-side telecentric lens with a long working distance and a large numerical aperture. The surface of the lens adjacent to the object plane is the object-side surface, and the surface of the lens adjacent to the image plane is the image-side surface. The lens includes a front lens group G1, an aperture stop STOP, and a rear lens group G2, which are arranged in sequence along the optical axis from the object side to the image side. The front lens group G1 has positive optical focal length, and the rear lens group G2 has negative optical focal length. There is a certain distance between the front lens group G1 and the rear lens group G2, and the aperture stop STOP is located between the front lens group G1 and the rear lens group G2. Light rays first converge through the positive lens group G1 and then diverge through the negative lens group G2. This lens structure configuration is conducive to shortening the total length of the lens. Since the lens group G1 bears a larger optical focal length, the front lens group G1 is more complex than the rear lens group G2. The front lens group G1 includes a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, a seventh lens L7, an eighth lens L8, and a ninth lens L9, wherein:

[0044] The first lens L1 has a concave surface facing the object side and a convex surface facing the image side. The object-side numerical aperture is larger, and the surface close to the object side is curved toward the object plane, which helps reduce the angle of incidence of light on the lens surface, thereby reducing spherical aberration of the system. The positive focal length of the first lens L1 can reduce the angle of incidence of light on the surface of the second lens L2.

[0045] The second lens L2 has a convex surface facing the object side and a convex surface facing the image side. The focal length of the second lens L2 is positive, which further converges light and helps reduce the aperture of the rear lens.

[0046] The third lens L3 has a concave surface facing the object side and a concave surface facing the image side, and has a negative focal length.

[0047] The fourth lens L4 has a convex surface facing the object side and a convex surface facing the image side, and has a positive focal length.

[0048] The third lens L3 and the fourth lens L4 form the first group of doublet lenses with a negative focal length. The doublet lens helps to reduce the sensitivity of lens tolerances, reduce the difficulty of later lens installation and adjustment, and can also correct the chromatic aberration of the system.

[0049] The fifth lens L5 has a convex surface facing the object side and a concave surface facing the image side, and has a negative focal length.

[0050] The sixth lens L6 has a convex surface facing the object side and a convex surface facing the image side, and has a positive focal length.

[0051] The seventh lens L7 has a concave surface facing the object side and a convex surface facing the image side, and has a negative focal length.

[0052] The fifth lens L5, the sixth lens L6, and the seventh lens L7 form the first triplet lens group with a negative focal length. By properly selecting the glass, the triplet lens can effectively enhance the correction of chromatic aberration, especially the correction of secondary spectrum by using special dispersion glass.

[0053] The eighth lens L8 has a convex surface facing the object side and a convex surface facing the image side, and has a positive focal length.

[0054] The ninth lens L9 has a concave surface facing the object side and a convex surface facing the image side, and has a negative focal length.

[0055] The eighth lens L8 and the ninth lens L9 form a second doublet lens group and have a positive focal length.

[0056] The focal length of the rear lens group G2 is negative, which can reduce the incident angle of the main light on the image plane, which is beneficial to improve the relative illumination and shorten the length of the lens. The rear lens group G2 includes the tenth lens L 10 , the eleventh lens L 11 , the twelfth lens L12 and the thirteenth lens L 13 ,in:

[0057] Tenth lens L 10 The side facing the object side is convex, the side facing the image side is convex, and the focal length is positive;

[0058] Eleventh lens L 11 The side facing the object side is concave, the side facing the image side is concave, and the focal length is negative;

[0059] The twelfth lens L 12 The side facing the object side is convex, the side facing the image side is concave, and the focal length is positive;

[0060] Thirteenth lens L 13 The side facing the object side is concave, the side facing the image side is concave, and the focal length is negative;

[0061] The "positive-negative-positive-negative" lens structure is beneficial to the correction of system astigmatism.

[0062] For further explanation, a preferred embodiment is given. The optical path diagram of this embodiment is as follows: Figure 2 As shown, the lens indicators are as follows:

[0063] (1) Working distance: 107nm;

[0064] (2) Target diameter: 16.2 mm;

[0065] (3) Object-space numerical aperture: 0.37;

[0066] (4) Object space resolution: 0.97 μm;

[0067] (5) Operating wavelength: 486nm~656nm;

[0068] (6) Lens magnification: -3.4×;

[0069] (7) Relative illumination: >98%;

[0070] (8) Object telecentricity: <0.01°;

[0071] (9) Modulation transfer function MTF: @150lp / mm>0.4

[0072] The specific parameters of the lens of this preferred embodiment are shown in the following table.

[0073]

[0074] Figure 3This is the spot diagram of the lens of the embodiment of the present invention. The spot diagram represents the size of the geometric spot after a point light source passes through the optical lens. It can be used to evaluate the optical lens in the spatial domain. The smaller the size of the geometric spot in the spot diagram, the better the aberration correction of the optical lens and the stronger the lens's ability to resolve objects. Figure 2 It can be seen that the radius of the Airy disk of this lens is 3.295μm, and the light spots of all fields of view in the point diagram are within the Airy disk, indicating that the aberration correction of each field of view of this lens is good, ensuring the consistency of imaging performance between the edge field of view and the center field of view.

[0075] Figure 4 This is the modulation transfer function (MTF) curve of the lens of the embodiment of the present invention. In the spatial domain, a point diagram can be used to evaluate an optical lens. The imaging of an optical system can be regarded as the result of the system's propagation of different spatial frequency components. In the frequency domain, the imaging quality of the lens can be evaluated using the modulation transfer function (MTF). The modulation transfer function is the modulus of the optical transfer function. It describes the system's ability to transmit the contrast of each frequency component. With spatial frequency as a variable, the high-frequency part corresponds to the details of the image, the mid-frequency part corresponds to the image's hierarchy, and the low-frequency part corresponds to the image's outline. The higher the MTF value, the better the performance of the lens. Figure 3 It can be seen that the MTF value of the lens at the maximum field of view of 150lp / mm is greater than 0.4, and the MTF curves of each field of view are close to the diffraction limit, indicating that the lens has excellent resolving power.

[0076] Figure 5 This is a relative illumination curve for the lens of an embodiment of the present invention. The higher the relative illumination, the more uniform the brightness of the image formed by the lens, and the smaller the difference in brightness between the center field of view and the edge field of view. The relative illumination of the entire field of view of this lens is greater than 98%, ensuring a high degree of uniformity in the brightness of the lens image.

[0077] In summary, the present invention uses thirteen spherical glass lenses and rationally distributes the optical power of each lens, resulting in a lens with advantages such as long working distance, ultra-high resolution, high relative illumination, wide spectral range, and high telecentricity. This solves the problem of low resolution of telecentric lenses with long working distances, is beneficial to improving the measurement accuracy of inspection lenses, and meets the demand for higher-performance lenses.

[0078] Parts not described in detail in the present invention belong to the well-known technology in the field.

[0079] The above description is only part of the specific implementation methods of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any person familiar with the art within the technical scope disclosed in the present invention should be covered by the protection scope of the present invention.

Claims

1. A long working distance and large numerical aperture object-space telecentric lens, characterized by: The invention comprises a front lens group G1, an aperture stop STOP and a rear lens group G2 which are arranged in sequence from the object side to the image side along the optical axis of the lens, wherein the front lens group G1 comprises a first lens L1, a second lens L2, a fourth lens L4, a sixth lens L6 and an eighth lens L8 with positive focal length, and a third lens L3, a fifth lens L5, a seventh lens L7 and a ninth lens L9 with negative focal length, wherein the third lens L3 and the fourth lens L4 form a first group of doublets, the eighth lens L8 and the ninth lens L9 form a second group of doublets, the fifth lens L5, the sixth lens L6 and the seventh lens L7 form a triplet, and the rear lens group G2 comprises a tenth lens L1 with positive focal length. 10 and the twelfth lens L 12 , and an eleventh lens L having negative refractive power 11 and the thirteenth lens L 13 .

2. The object-space telecentric lens with a long working distance and a large numerical aperture according to claim 1, characterized in that: The first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5, the sixth lens L6, the seventh lens L7, the eighth lens L8, the ninth lens L9, the tenth lens L 10 , the eleventh lens L1, the twelfth lens L 12 and the thirteenth lens L 13 All are spherical glass lenses.

3. The object-space telecentric lens with a long working distance and a large numerical aperture according to claim 1, wherein: The optical power of the front lens group G1 The optical power of the rear lens group G2 4. The object-space telecentric lens with a long working distance and a large numerical aperture according to claim 1, wherein: One side of the first lens L1 facing the object side is concave, and the side facing the image side is convex. The focal length of the first lens L1 satisfies 192.1mm < f1 < 201.5mm; One side of the second lens L2 facing the object side is convex, and the side facing the image side is convex. The focal length of the second lens L2 satisfies 170.5mm < f2 < 175.2mm; One side of the third lens L3 facing the object side is concave, and the side facing the image side is concave. The focal length of the third lens L3 satisfies -110.3mm < f3 < -105.0mm; One side of the fourth lens L4 facing the object side is convex, and the side facing the image side is convex. The focal length of the fourth lens L4 satisfies 115.6mm < f4 < 128.5mm; One side of the fifth lens L5 facing the object side is convex, and the side facing the image side is concave. The focal length of the fifth lens L5 satisfies -130.0mm < f5 < -125.4mm; One side of the sixth lens L6 facing the object side is convex, and the side facing the image side is convex. The focal length of the sixth lens L6 satisfies 91.4mm < f6 < 100.2mm; One side of the seventh lens L7 facing the object side is concave, and the side facing the image side is convex. The focal length of the seventh lens L7 satisfies -193.2mm < f7 < -180.8mm; One side of the eighth lens L8 facing the object side is convex, and the side facing the image side is convex. The focal length of the eighth lens L8 satisfies 100.7mm < f8 < 108.0mm; One side of the ninth lens L9 facing the object side is concave, and the side facing the image side is convex. The focal length of the ninth lens L9 satisfies -162.4mm < f9 < -155.7mm; The tenth lens L 10 The side facing the object side is convex, the side facing the image side is convex, the tenth lens L 10 Focal length 88.7mm <f 10 <93.5mm; The eleventh lens L 11 The side facing the object side is concave, the side facing the image side is concave, the eleventh lens L 11 Focal length - 193.2mm <f 11 <-185.5mm; The twelfth lens L 12 The side facing the object side is convex, and the side facing the image side is concave. The twelfth lens L 12 Focal length 71.5mm <f 12 <76.4mm; The thirteenth lens L 13 The side facing the object side is concave, and the side facing the image side is concave. The thirteenth lens L 13 Focal length - 60.3mm <f 13 <-48.3mm.

5. The object-space telecentric lens with a long working distance and a large numerical aperture according to any one of claims 1 to 4, characterized in that: The refractive index of the first lens L1 satisfies 1.65 < Nd1 < 1.75, and the Abbe number satisfies 25 < Vd1 < 35; The refractive index of the second lens L2 satisfies 1.45 < Nd2 < 1.55, and the Abbe number Vd2 > 80; The refractive index of the third lens L3 satisfies 1.55 < Nd3 < 1.65, and the Abbe number satisfies 55 < Vd3 < 65; The refractive index of the fourth lens L4 satisfies 1.45 < Nd4 < 1.55, and the Abbe number Vd4 > 90; The refractive index of the fifth lens L5 satisfies 1.75 < Nd5 < 1.85, and the Abbe number satisfies 40 < Vd5 < 50; The refractive index of the sixth lens L6 satisfies 1.45 < Nd6 < 1.55, and the Abbe number Vd6 > 90; The refractive index of the seventh lens L7 satisfies 1.80 < Nd7 > 1.85, and the Abbe number satisfies 20 < Vd7 < 30; The refractive index of the eighth lens L8 satisfies 1.45 < Nd8 < 1.55, and the Abbe number Vd8 > 80; The refractive index of the ninth lens L9 satisfies 1.65 < Nd9 < 1.75, and the Abbe number satisfies 50 < Vd9 < 60; The tenth lens L 10 Refractive index 1.75 <Nd 10 <1.85, dispersion coefficient 30 <Vd 10 <40; The eleventh lens L 11 Refractive index 1.70 <Nd 11 <1.80, dispersion coefficient 40 <Vd 11 <50; The twelfth lens L 12 Refractive index 1.60 <Nd 12 <1.70, dispersion coefficient 25 <Vd 12 <35; The thirteenth lens L 13 Refractive index 1.45 <Nd 13 <1.55, dispersion coefficient Vd 13 >90.

6. The object-space telecentric lens with a long working distance and a large numerical aperture according to any one of claims 1 to 4, characterized in that: The working distance WD of the lens is ≥100 mm, the optical resolution δ of the object space is ≤1 μm, the numerical aperture NA of the object space is ≥0.37, the magnification of the lens is -3.5≤β≤-3.4, the telecentricity σ of the object space is ≤0.01°, the working wavelength range is 486 nm≤λ≤656 nm, and the image plane height h is ≤8.1 mm.

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