Object space telecentric lens with long working distance and large numerical aperture

Abstract

The invention discloses an object space telecentric lens with a long working distance and a large numerical aperture. The object space telecentric lens comprises a front lens group, an aperture diaphragm and a rear lens group which are sequentially arranged from an object space to an image space along an optical axis of the lens. The front lens group comprises a first lens with positive focal power, a second lens with positive focal power, a fourth lens with positive focal power, a sixth lens with positive focal power, an eighth lens with negative focal power, a third lens with negative focal power, a fifth lens with negative focal power, a seventh lens with negative focal power and a ninth lens with negative focal power, the eighth lens and the ninth lens form a second group of doublet lenses, and the fifth lens, the sixth lens and the seventh lens form a first group of triplet lenses. The rear lens group includes a tenth lens and a twelfth lens having positive refractive power, and an eleventh lens and a thirteenth lens having negative refractive power. According to the invention, the thirteen spherical glass lenses are adopted, and the focal power of each lens is reasonably distributed, so that the lens has the advantages of long working distance, large numerical aperture, ultrahigh resolution, high relative illumination, wide spectral range, high telecentricity and the like, and the problem of low resolution of a long-working-distance object space telecentric lens is solved. The measurement precision of the detection lens is improved, and the requirements of some application scenes for higher-performance lenses are met.

Description

Technical Field

[0001] The invention relates to the technical field of optical imaging, 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 to more fields. As the core component of machine vision technology, optical lenses largely determine the performance of the entire system. The object-side telecentric lens is mainly used to solve the problem of insufficient measurement accuracy caused by parallax of traditional industrial lenses. The aperture diaphragm of the object-side telecentric lens is located at the focal plane of the image side of the system, which can eliminate the measurement error caused by inaccurate object-side focusing. At the same time, the object-side telecentric lens system has unique properties such as large depth of field and low distortion, which makes this type of lens widely used in the field of measurement.

[0003] With the rapid development of the machine vision industry, higher and higher requirements have been placed on the performance of the optical lenses that go with it. Long working distance and large numerical aperture (i.e., high resolution) have become two key indicators for lens design, which require larger system apertures and more complex optical structure designs. However, these two parameters often restrict each other, forming a design challenge. In the current market, long working distance lenses have lower resolutions, while high-resolution lenses have shorter working distances. In situations where ultra-high-resolution imaging of tiny objects is required at long working distances, existing lenses are difficult to meet the demand.

[0004] Therefore, in response to 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-side telecentric lens, which 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-side telecentric lenses.

[0006] According to one aspect of the present invention, there is provided a long working distance and large numerical aperture object-side telecentric lens, the lens comprising a front lens group G1, an aperture stop STOP and a rear lens group G2 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 having positive focal power, and a third lens L3, a fifth lens L5, a seventh lens L7 and a ninth lens L9 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 having positive focal power, a second lens L2, a fourth lens L4, a sixth lens L6 and an eighth lens L8 having positive focal power, and a third lens L3, a fifth lens L5, a seventh lens L7 and a ninth lens L9 having negative 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 focal length 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 < Vd1 < 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 < Vd3 < 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 of the object side satisfies δ ≤ 1 μm, the numerical aperture NA of the object side satisfies NA ≥ 0.37, the magnification β of the lens satisfies -3.4 ≤ β ≤ -3.5, the telecentricity σ of 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 allocating the optical focal length of each lens, under the condition that the working distance is greater than 100 mm, the object-side numerical aperture NA≥0.37 and the object-side resolution δ≤1μm can be achieved, which are much higher than the existing lenses of the same type on the market. At the same time, the lens has the advantages of high relative illumination, wide spectral range and high telecentricity, etc., 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 expanding 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 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 4 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 solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with 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 a long working distance and large numerical aperture object-side telecentric lens. 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 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. 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 interval 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 comprises 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 numerical aperture angle on the object side is larger, and the surface close to the object side is bent toward the object plane, which is beneficial to reducing the angle of light incident on the lens surface, thereby reducing the spherical aberration of the system. The focal length of the first lens L1 is positive, which can reduce the incident angle of light incident 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 the light and is beneficial to reducing 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 a first group of double cemented lenses with a negative focal length. The cemented lenses help reduce the sensitivity of lens tolerances, reduce the difficulty of later lens installation and adjustment, and can 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, a convex surface facing the image side, and a negative focal length;

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

[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, a convex surface facing the image side, and a negative focal length;

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

[0056] The focal length of the rear lens group G2 is negative, which can reduce the incident angle of the principal ray 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 11th 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 numerical aperture: 0.37;

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

[0067] (5) Working 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 3The spot diagram of the lens of the embodiment of the present invention indicates the size of the geometric spot after the point light source passes through the optical lens, and 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 is, and the stronger the lens's ability to resolve objects is. Figure 2 It can be seen that the radius of the Airy disk of the 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 the 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 MTF curve of the lens of the embodiment of the present invention. In the spatial domain, the optical lens can be evaluated by using the point diagram. The imaging of the 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 by using the MTF. The MTF is the modulus of the optical transfer function. It describes the system's ability to transmit the contrast of each frequency component. With the 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 diagram of 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 brightness difference between the center field of view and the edge field of view. The relative illumination of the full field of view of the lens is greater than 98%, ensuring the high uniformity of the lens imaging brightness.

[0077] In summary, the present invention adopts thirteen spherical glass lenses and reasonably distributes the optical focal length of each lens, so that the lens has the advantages of long working distance, ultra-high resolution, high relative illumination, wide spectral range and high telecentricity, etc., which solves the problem of low resolution of telecentric lenses with long working distances, is beneficial to improving the measurement accuracy of the detection lens, and meets the demand for higher performance lenses.

[0078] The parts not described in detail in the present invention belong to the well-known technology in the art.

[0079] The above descriptions are only some 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 within the protection scope of the present invention.

Claims

1. A long working distance and large numerical aperture object-space telecentric lens, characterized in that: 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 power, and a third lens L3, a fifth lens L5, a seventh lens L7 and a ninth lens L9 with 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, 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 power. 10 and the twelfth lens L 12 , and an eleventh lens L having negative 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, characterized in that: The focal length of the front lens group G1 is The focal length 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, characterized in that: 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, and 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, and 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-side 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-side 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 ≥100mm, the optical resolution δ of the object side is ≤1μm, the numerical aperture NA of the object side is ≥0.37, the magnification of the lens is -3.4≤β≤-3.5, the telecentricity σ of the object side is ≤0.01°, the working wavelength range is 486nm≤λ≤656nm, and the image plane height h≤8.1mm.

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