A limited conjugate distance lens

Abstract

The application discloses a limited conjugate distance lens, which comprises a first lens group, an aperture diaphragm and a second lens group arranged in sequence along the optical axis direction from the object side to the image side; the first lens group has positive focal power, the second lens group has negative focal power, the end surface of the first lens group away from the aperture diaphragm is a convex surface, the end surface of the first lens group close to the aperture diaphragm is a plane, the end surface of the second lens group away from the aperture diaphragm is a concave surface, and the end surface of the second lens group close to the aperture diaphragm is a convex surface. Through the reasonable arrangement of the five lenses, the long working distance, -1X limited conjugate distance, high resolution, small distortion imaging are realized by using a small number of lenses, the imaging quality is ensured, the cost is effectively reduced, the cumulative tolerance in lens assembly is effectively reduced by the small number of lenses, and the imaging effect is ensured.

Description

Technical Field

[0001] This application belongs to the field of optical devices, and specifically relates to a finite conjugate distance lens. Background Technology

[0002] Most imaging lens designs employ an infinite conjugate distance imaging approach, where the object or image is at infinity. However, in practical scientific or engineering applications, most objectives are finite conjugate distance imaging, meaning both the object distance and image distance are finite. This leads to a decrease in image quality or even unsuitability of the designed infinite conjugate distance lens in practical use with finite conjugate distances. Existing -1X finite conjugate distance imaging lenses typically have an object distance <300mm, making it difficult to meet the requirements for equal magnification imaging at long working distances. Furthermore, existing -1X finite conjugate distance imaging lenses have large F / # values ​​and small apertures at larger object distances, making it difficult to meet the requirements for high-resolution imaging. Chinese patent CN115407494A discloses a large-aperture object-side telecentric lens comprising nine lenses. The lens structure disclosed in this patent is relatively complex, limiting its practical application. Summary of the Invention

[0003] To address some of the technical problems existing in the prior art, this technical solution provides a -1X finite conjugate distance lens for image extraction in space-constrained devices. It has a simple structure and meets the requirements of long working distance, high image resolution, and small distortion. In particular, this lens can be used for alignment imaging in lithography equipment.

[0004] To achieve the above-mentioned technical objectives, the technical solution adopted in this application is as follows:

[0005] A finite conjugate distance lens is provided, comprising a first lens group, an aperture stop, and a second lens group arranged sequentially from the object side to the image side along the optical axis.

[0006] The first lens group has positive optical power and is used to receive light emitted from the object surface and converge the light, thereby transmitting the light through the aperture stop to the second lens group;

[0007] The second lens group has negative optical power and is used to image light passing through the aperture stop onto the image plane;

[0008] The end face of the first lens group furthest from the aperture stop is convex, while the end face of the first lens group closest to the aperture stop is flat.

[0009] The end face of the second lens group away from the aperture stop is concave, and the end face of the second lens group near the aperture stop is convex.

[0010] As a preferred embodiment, the first lens group includes a first cemented group and a third lens with positive optical power arranged sequentially along the optical axis from the object side to the image side.

[0011] As a preferred embodiment, the first adhesive assembly includes a first lens and a second lens glued together, wherein the first lens has positive optical power and the second lens has negative optical power, and the adhesive surface of the first adhesive assembly is convex to the image side.

[0012] Preferably, the object side of the first lens is convex, the image side is convex, and the refractive index is 1.5 < n1 < 1.7.

[0013] Preferably, the object side of the second lens is concave, the image side is convex, and the refractive index is 1.85 < n2 < 1.95.

[0014] Preferably, the object-side surface of the third lens is convex, the image-side surface is planar, and the refractive index is 1.75 < n3 < 1.85.

[0015] As a preferred embodiment, the second lens group includes a fourth lens and a fifth lens arranged sequentially along the optical axis from the object side to the image side, wherein the fourth lens has negative optical power and the fifth lens has positive optical power.

[0016] Preferably, the object side of the fourth lens 4 is convex, the image side is concave, and the refractive index is 1.60 < n4 < 1.70.

[0017] Preferably, the object side of the fifth lens 5 is convex, the image side is concave, and the refractive index is 1.85 < n5 < 1.95.

[0018] As a preferred embodiment, the aperture stop is disposed between the third lens and the fourth lens.

[0019] Furthermore, the aperture of the aperture stop is 45 < Ds < 55.

[0020] As a preferred embodiment, the focal length F1 of the first lens group and the focal length F2 of the second lens group satisfy the following relationship: -0.15 < F1 / F2 < -0.27.

[0021] As a preferred embodiment, the total focal length F of the finite conjugate distance lens and the focal length F of the first cemented group are... 10 The following relationship must be satisfied: 3 < F 10 / F < 4.

[0022] As a preferred embodiment, the total focal length F of the finite conjugate distance lens and the focal length f3 of the third lens satisfy the following relationship: 1 < f3 / F < 1.7.

[0023] And / or,

[0024] The total focal length F of the finite conjugate distance lens and the focal length f4 of the fourth lens satisfy the following relationship: -2.3 < f4 / F < -1.3.

[0025] And / or,

[0026] The total focal length F of the finite conjugate distance lens and the focal length f5 of the fifth lens satisfy the following relationship: 2.5 < f5 / F < 3.5.

[0027] As a preferred embodiment, the parameters of the finite conjugate distance lens satisfy the following relationship:

[0028] F = (-βL) / (1-β) ^ 2

[0029] Where F is the total focal length of the finite conjugate lens, β is the magnification of the finite conjugate lens, and L is the conjugate distance of the finite conjugate lens.

[0030] Furthermore, β=-1

[0031] As a preferred embodiment, the first lens is made of crown glass.

[0032] And / or,

[0033] The second lens is made of heavy flint glass.

[0034] And / or,

[0035] The third lens is made of heavy lanthanum flint glass.

[0036] And / or,

[0037] The fourth lens is made of heavy flint glass.

[0038] And / or,

[0039] The fifth lens is made of heavy lanthanum flint glass.

[0040] As a preferred embodiment, the object-side field of view of the finite conjugate distance lens meets the size requirements of a 1-inch CMOS / CCD sensor.

[0041] As a preferred embodiment, the MTF (Modulation Transfer Function) of the finite conjugate distance lens is ≥0.2@160lp / mm.

[0042] As a preferred embodiment, the working distance L of the finite conjugate distance lens w The following conditions must be met: 500 mm ≤ Lw ≤ 600 mm.

[0043] As a preferred embodiment, the lens distortion of the finite conjugate distance lens is <0.02%.

[0044] As a preferred embodiment, the imaging wavelength of the finite conjugate distance lens is 632.8 nm, and the set band is 613 nm to 653 nm, which is suitable for He-Ne laser illumination.

[0045] Due to the adoption of the above technical solution, the technical advantages of this application are as follows: This technical solution describes a long working distance, high resolution, low distortion -1X finite conjugate distance lens, which can be used for image extraction and analysis in long working distance, space-constrained equipment. In particular, this lens can be used for alignment imaging in lithography equipment, while meeting the requirements of high resolution and low distortion. The object-side effective field of view design can be used in 1-inch CMOS / CCD cameras to achieve large target surface imaging. This technical solution achieves long working distance, -1X finite conjugate distance, high resolution, and low distortion imaging with a smaller number of lenses through the reasonable arrangement of 5 lenses. While ensuring imaging quality, it effectively reduces costs. At the same time, the smaller number of lenses effectively reduces the cumulative tolerance in lens assembly, ensuring imaging effect. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of a finite conjugate distance lens provided in one embodiment of the present invention;

[0047] Figure 2 This is a schematic diagram of the MTF of a finite conjugate distance lens provided in one embodiment of the present invention;

[0048] Figure 3 This is a schematic diagram of field curvature and distortion of a finite conjugate distance lens provided in one embodiment of the present invention;

[0049] Figure 4 This is a schematic diagram of a finite conjugate distance lens provided in one embodiment of the present invention.

[0050] In the diagram: 001 - object plane; A - first lens group; B - second lens group; S - aperture stop; 10 - first cemented carbide group; 1 - first lens; 2 - second lens; 3 - third lens; 4 - fourth lens; 5 - fifth lens; 002 - image plane. Detailed Implementation

[0051] The features and exemplary embodiments of various aspects of this application will be described in detail below. To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are intended only to explain this application and not to limit it. For those skilled in the art, this application can be implemented without some of these specific details. The following description of the embodiments is merely to provide a better understanding of this application by illustrating examples.

[0052] To facilitate understanding of the optical lenses provided in the embodiments of this application, the relevant terms used in this application are explained as follows:

[0053] Object surface: The working surface to be detected, marked with 001 in the figure;

[0054] Image plane: The plane on which the clear image of the working surface is formed by the optical lens, marked with 002 in the figure;

[0055] The optical axis is an axis that passes through the center of each optical lens.

[0056] With the lens as the boundary, the side where the object is located is called the object side, and the surface of the lens closest to the object side is called the object side surface.

[0057] With the lens as the boundary, the side on which the image of the object is located is called the image side, and the surface of the lens closest to the image side is called the image-side surface.

[0058] Positive optical power, also known as positive refractive power, indicates that a lens has a positive focal length.

[0059] Negative optical power, also known as negative refractive power, indicates that a lens has a negative focal length.

[0060] Focal length is a measure in optical systems of the convergence or divergence of light; it refers to the distance from the optical center of a lens to the focal point where parallel light converges.

[0061] In one embodiment of this application, such as Figure 1 As shown, a finite conjugate distance lens is provided, comprising an object plane 001, a first lens group A, an aperture stop S, a second lens group B, and an image plane 002 arranged sequentially from the object side to the image side along the optical axis.

[0062] The first lens group A has positive optical power and is used to receive light emitted from the object surface 001 and converge the light, thereby transmitting the light through the aperture stop S to the second lens group B;

[0063] The second lens group B has negative optical power and is used to image the light rays passing through the aperture stop S onto the image plane 002;

[0064] The end face of the first lens group A furthest from the aperture stop is convex, while the end face of the first lens group A closest to the aperture stop is flat.

[0065] The end face of the second lens group B away from the aperture stop is concave, and the end face of the second lens group B near the aperture stop is convex.

[0066] In this application, the chromatic aberration problem of the system is effectively solved by setting a first cemented lens. The first cemented group 10, the third lens 3, the fourth lens 4, and the fifth lens 5 adopt an optical power setting of "+, +, -, +". This design is beneficial for aberration correction in large focal length and large aperture optical systems, while achieving a smaller incident angle of light on each lens surface, effectively reducing the tolerance sensitivity of the optical system and improving the assembly yield of the optical system. Using this design scheme, fewer lenses can be used while ensuring the performance parameters of the optical system, effectively reducing costs.

[0067] In some embodiments, the first lens group A includes a first cemented group 10 and a third lens 3 having positive optical power, arranged sequentially from the object side to the image side along the optical axis.

[0068] In this application, the first cemented group is set up, which can effectively solve the system chromatic aberration problem; the first cemented group 10 and the third lens 3 are both positive optical power. The total optical power of the first lens group A is reasonably distributed through these two positive lenses, which effectively reduces the aberration borne by a single lens group, which is beneficial for aberration correction and reducing tolerance sensitivity.

[0069] In some embodiments, the first adhesive assembly 10 includes a first lens 1 and a second lens 2 glued together, wherein the first lens 1 has a positive optical power and the second lens 2 has a negative optical power, and the adhesive surface of the first adhesive assembly 10 is convex to the image side.

[0070] In some embodiments, the object side of the first lens 1 is convex, the image side is convex, and the refractive index is 1.5 < n1 < 1.7.

[0071] In some embodiments, the object side of the second lens 2 is concave and the image side is convex, with a refractive index of 1.85 < n2 < 1.95. The first lens 1 and the second lens 2 are respectively made of two materials with low and high refractive indices to form a cemented lens, which can achieve the effect of achromatic aberration.

[0072] In some embodiments, the object-side surface of the third lens 3 is convex, the image-side surface is planar, and the refractive index is 1.75 < n3 < 1.85.

[0073] In some embodiments, the second lens group B includes a fourth lens 4 and a fifth lens 5 arranged sequentially along the optical axis from the object side to the image side, wherein the fourth lens 4 has negative optical power and the fifth lens 5 has positive optical power.

[0074] In some embodiments, the object-side surface of the fourth lens 4 is convex, the image-side surface is concave, and the refractive index is 1.60 < n4 < 1.70.

[0075] In some embodiments, the object-side surface of the fifth lens 5 is convex, the image-side surface is concave, and the refractive index is 1.85 < n5 < 1.95. The five lenses are set with different refractive indices to effectively reduce system aberrations and chromatic aberrations and improve system imaging resolution.

[0076] In some embodiments, the aperture stop S is disposed between the third lens 3 and the fourth lens 4.

[0077] In some embodiments, the aperture of the aperture stop S is 45 < Ds < 55. This setting is beneficial for achieving a larger aperture value, ensuring that off-axis aberrations are well corrected, and obtaining higher resolution.

[0078] In some embodiments, the focal length F1 of the first lens group A and the focal length F2 of the second lens group B satisfy the following relationship: -0.15 < F1 / F2 < -0.27. This relationship defines the focal length ratio of the first lens group A and the second lens group B. This optical power distribution allows the optical system to effectively achieve finite conjugate distance imaging with a long working distance. The focal length of the first lens group A is smaller than that of the second lens group B, meaning the optical power of the first lens group A is greater. This setting is mainly used to increase the focal length of the optical system, achieving imaging at a larger conjugate distance.

[0079] In some embodiments, the total focal length F of the finite conjugate distance lens and the focal length F of the first cemented assembly 10 10 The following relationship must be satisfied: 3 < F 10 / F < 4.

[0080] In some embodiments, the total focal length F of the finite conjugate distance lens and the focal length f3 of the third lens 3 satisfy the following relationship: 1 < f3 / F < 1.7.

[0081] And / or,

[0082] The total focal length F of the finite conjugate distance lens and the focal length f4 of the fourth lens 4 satisfy the following relationship: -2.3 < f4 / F < -1.3.

[0083] And / or,

[0084] The total focal length F of the finite conjugate distance lens and the focal length f5 of the fifth lens 5 satisfy the following relationship: 2.5 < f5 / F < 3.5.

[0085] In some embodiments, the parameters of the finite conjugate distance lens satisfy the following relationship:

[0086] F = (-βL) / (1-β) ^2

[0087] Where F is the total focal length of the finite conjugate lens, β is the magnification of the finite conjugate lens, and L is the conjugate distance of the finite conjugate lens. Using this relationship to set the parameters of the optical system ensures a large working distance while achieving -1X imaging.

[0088] Furthermore, β=-1

[0089] In some embodiments, the first lens 1 is made of crown glass.

[0090] And / or,

[0091] The second lens 2 is made of heavy flint glass.

[0092] And / or,

[0093] The third lens 3 is made of heavy lanthanum flint glass.

[0094] And / or,

[0095] The fourth lens 4 is made of heavy flint glass.

[0096] And / or,

[0097] The fifth lens 5 is made of heavy lanthanum flint glass.

[0098] The lens materials mentioned above have different refractive indices and Abbe numbers. By combining them appropriately, optical system aberrations and chromatic aberrations can be effectively reduced, system resolution can be improved, system tolerance sensitivity can be reduced, and assembly yield can be increased.

[0099] In some embodiments, the object-side field of view of the finite conjugate distance lens meets the size requirements of a 1-inch CMOS / CCD sensor.

[0100] In some embodiments, the MTF (Modulation Transfer Function) of the finite conjugate distance lens is ≥0.2@160lp / mm.

[0101] In some embodiments, the lens working distance L of the finite conjugate distance lens wThe following conditions must be met: 500 mm ≤ Lw ≤ 600 mm.

[0102] In some embodiments, the lens distortion of the finite conjugate distance lens is <0.02%.

[0103] In some embodiments, the imaging wavelength of the finite conjugate distance lens is 632.8 nm, and the set band is 613 nm to 653 nm, which is suitable for He-Ne laser illumination.

[0104] In one specific embodiment of this application, a finite conjugate distance lens as shown in Table 1 is provided.

[0105] Table 1 Parameters of finite conjugate distance lenses

[0106]

[0107] In one specific embodiment of this application, a lens as shown in Table 1 is provided, wherein the first lens 1 and the second lens 2 constitute the first cemented assembly 10, and the focal length F of the first cemented assembly 10 is... 10 =945.566; the focal length of the third lens 3 is f3=366.163; the focal length of the fourth lens 4 is f4=-509.239; the focal length of the fifth lens 5 is f5=818.139; all units are mm.

[0108] In this embodiment, the magnification of the finite conjugate distance lens is β=-1X, the effective field of view on the object side of the lens is φ17mm, which can be used in a 1-inch CMOS / CCD camera, and the paraxial F / # of the lens is 5.1. Due to the above parameter design, the object distance of the finite conjugate distance lens provided in this application is 550mm, which can realize large object distance operation.

[0109] Figure 2 The modulation function (MTF) diagram of the finite conjugate distance lens provided in this embodiment shows that the MTF of each field of view is >0.2@160lp / mm, which can achieve high-resolution imaging.

[0110] Figure 3 The field curvature and distortion diagram of the finite conjugate distance lens provided in this embodiment are shown in the figure. The lens distortion is <0.02%, which is extremely small and effectively suppresses distortion during the imaging process.

[0111] Figure 4 The optical blur pattern of the finite conjugate distance lens provided in this embodiment is shown in the figure. The blur patterns in the central field of view and the edge field of view are mostly within the radius of the Airy disk. The energy concentration and aberration correction at the on-axis and off-axis points are good, achieving ideal resolution.

[0112] In this embodiment, the lens uses an imaging wavelength of 632.8nm and a band of 613nm~653nm, which is suitable for He-Ne laser illumination. In particular, the lens of this scheme can be used for alignment imaging in lithography equipment.

Claims

1. A finite conjugate distance lens characterized by: The first lens group, the aperture stop and the second lens group are arranged in sequence along the optical axis direction from the object side to the image side; The first lens group has positive focal power, is used for receiving light emitted from an object plane and converging the light, and then transmitting the light to the second lens group through the aperture stop; The second lens group has negative focal power, is used for imaging the light passing through the aperture stop on an image plane; An end surface of the first lens group away from the aperture stop is a convex surface, and an end surface of the first lens group close to the aperture stop is a plane, An end surface of the second lens group away from the aperture stop is a concave surface, and an end surface of the second lens group close to the aperture stop is a convex surface; The first lens group comprises a first cemented group and a third lens with positive focal power arranged in sequence along the optical axis from the object side to the image side; The first cemented group comprises a first lens and a second lens cemented with each other, The object side surface of the first lens is a convex surface, the image side surface is a convex surface, and the refractive index is 1.5 < n1 < 1.7, And / or, The object side surface of the second lens is a concave surface, the image side surface is a convex surface, and the refractive index is 1.85 < n2 < 1.95, And / or, The object side surface of the third lens is a convex surface, the image side surface is a plane, and the refractive index is 1.75 < n3 < 1.85; The first lens has positive focal power, the second lens has negative focal power, and the cemented surface of the first cemented group is convex to the image side; The second lens group comprises a fourth lens and a fifth lens arranged in sequence along the optical axis from the object side to the image side, the fourth lens has negative focal power, and the fifth lens has positive focal power; The object side surface of the fourth lens 4 is a convex surface, the image side surface is a concave surface, and the refractive index is 1.60 < n4 < 1.70, And / or, The object side surface of the fifth lens 5 is a convex surface, the image side surface is a concave surface, and the refractive index is 1.85 < n5 < 1.95; The aperture stop is arranged between the third lens and the fourth lens, and the aperture of the aperture stop is 45 < Ds < 55; The parameters of the finite conjugate distance lens satisfy the following relationships: F = (-βL) / (1 - β) ^2 Wherein, F is the total focal length of the finite conjugate distance lens, β is the magnification of the finite conjugate distance lens, and L is the conjugate distance of the finite conjugate distance lens.

2. The finite conjugate lens of claim 1, wherein: The focal length F1 of the first lens group and the focal length F2 of the second lens group satisfy the following relationship: -0.15 < F1 / F2 < -0.

27.

3. The finite conjugate distance lens of claim 1, wherein: total focal length F of the finite conjugate length lens and focal length F of the first cemented group 10 satisfies the following relationship: 3 < F 10 / F < 4.

4. The finite conjugate distance lens of claim 1, wherein: The total focal length F of the finite conjugate distance lens and the focal length f3 of the third lens satisfy the following relationship: 1 < f3 / F < 1.

7.

5. The limited conjugate distance lens of claim 1, wherein: The total focal length F of the finite conjugate distance lens and the focal length f4 of the fourth lens satisfy the following relationship: -2.3 < f4 / F < -1.3, And / or, The total focal length F of the finite conjugate distance lens and the focal length f5 of the fifth lens satisfy the following relationship: 2.5 < f5 / F < 3.

5.

6. The finite conjugate distance lens of claim 1, wherein: β=-1。 7. The finite conjugate distance lens according to claim 6, wherein: The material of the first lens comprises heavy crown glass material, And / or, the material of the second lens comprises heavy flint glass material, And / or, the material of the third lens comprises heavy lanthanum flint glass material.

8. The finite conjugate distance lens according to claim 1, wherein: The fourth lens is made of heavy flint glass material, and / or, The fifth lens is made of heavy lanthanum flint glass material.

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