A 2x microscope objective with large numerical aperture and wide field

Abstract

The application discloses a 2-fold microscopic objective with a large numerical aperture and a wide field of view, which is applied to a 430-720nm visible light band and comprises a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power and a third lens group G3 with positive refractive power which are sequentially arranged from an object side to an image side; wherein a diaphragm of the microscopic objective is arranged on the right side of the third lens group G3 and close to the image side. The microscopic objective disclosed by the application has a field of view number of ≤35mm and a maximum numerical aperture of ≤0.11, and simultaneously has flat field and complex achromatism performance, thereby solving the problem that existing low-power microscopic objectives are difficult to have optical performances such as wide field of view, high resolution, flat field and complex achromatism in design.

Description

Technical Field

[0001] This invention relates to the field of low-magnification microscope objective imaging technology, and in particular to a 2x microscope objective with a large numerical aperture and a wide field of view. Background Technology

[0002] Compared to high-magnification objectives, low-magnification microscope objectives offer a wider field of view and a longer working distance, allowing for the observation of large image samples in a single magnification, thus facilitating sample size measurement and large-scale image resolution. Therefore, low-magnification microscope objectives are widely used in industry, biology, and materials science. However, the increasing demand for wide-field-of-view, high-resolution low-magnification microscope objectives not only increases the complexity of lens design but also introduces challenges in correcting apochromatic and pupillary aberrations. Therefore, a low-magnification microscope objective that combines a wide field of view, high resolution, and field-planar apochromatic correction is needed. Summary of the Invention

[0003] Purpose of the invention: The purpose of this invention is to provide a 2x microscope objective that combines a wide field of view, high resolution, and field-flat apochromatic aberration.

[0004] Technical Solution: To achieve the above objectives, the present invention provides a 2x microscope objective with a large numerical aperture and wide field of view, applicable in the 430-720nm visible light band. It comprises a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power, and a third lens group G3 with positive refractive power, arranged sequentially from the object side to the image side. The aperture of the microscope objective is located to the right of the third lens group G3, close to the image side. The microscope objective has a field of view ≤35mm, a maximum numerical aperture ≤0.11, and simultaneously possesses field-planar and apochromatic properties.

[0005] The working distance of the microscope objective (the distance from the object side of the objective to the center of the R1 surface of the L1 lens) is 35-37mm, and the focal length is 100mm.

[0006] The focal lengths f1 of the first lens group G1, f2 of the second lens group G2, and f3 of the third lens group G3 satisfy the following relationship with the focal length f of the 2x microscope objective:

[0007] 0.3≤|f1 / f|≤0.85;

[0008] 0.1 ≤ |f² / f| ≤ 0.5;

[0009] 0.05≤|f3 / f|≤0.6.

[0010] The first lens group G1 includes a first lens L1, which is a biconvex lens with positive optical power.

[0011] The d-ray refractive index n1 and Abbe number v1 of the first lens L1 satisfy the following relationships: 1.8≤n1≤2, 20≤v1≤30.

[0012] The second lens group G2 includes a second lens L2, which is a biconcave lens with negative optical power.

[0013] The d-ray refractive index n2 and Abbe number v2 of the second lens L2 satisfy the following relationships: 1.6≤n2≤1.8, 25≤v2≤35.

[0014] The third lens group G3 includes a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, a seventh lens L7, and an eighth lens L8. The third lens L3, the fourth lens L4, and the eighth lens L8 are all biconvex lenses, the seventh lens L7 is a biconcave lens, and the fifth lens L5 and the sixth lens L6 form a cemented doublet negative lens. The third lens L3, the fourth lens L4, the fifth lens L5, and the eighth lens L8 are positive focal length lenses, and the sixth lens L6 and the seventh lens L7 are negative focal length lenses.

[0015] Wherein, the refractive index and Abbe number of the third lens L3 are n3 and v3, respectively; the refractive index and Abbe number of the fourth lens L4 are n4 and v4, respectively; the refractive index and Abbe number of the fifth lens L5 are n5 and v5, respectively; the refractive index and Abbe number of the sixth lens L6 are n6 and v6, respectively; the refractive index and Abbe number of the seventh lens L7 are n7 and v7, respectively; and the refractive index and Abbe number of the eighth lens L8 are n8 and v8, respectively, and they respectively satisfy the following relationships:

[0016] 1.8≤n1≤2, 20≤v1≤30;

[0017] 1.6≤n²≤1.8, 25≤v²≤35;

[0018] 1.4≤n3≤1.6, 77≤v3≤87;

[0019] 1.6≤n4≤1.8, 40≤v4≤50;

[0020] 1.4≤n5≤1.6, 77≤v5≤87;

[0021] 1.6≤n6≤1.8, 28≤v6≤38;

[0022] 1.6≤n7≤1.8, 28≤v7≤38;

[0023] 1.8≤n8≤2, 20≤v8≤30.

[0024] Beneficial effects: The present invention has the following advantages: 1. By optimizing the relationship between each lens group and the focal length f of the 2x microscope objective, the present invention ensures that the microscope objective has a moderate refractive power for visible light, so that when imaging under the conditions of NA≤0.11 and field number≤35, it can correct field curvature and image plane curvature, and maintain the uniformity of field illumination and telecentric characteristics.

[0025] 2. The 2x microscope objective described in this invention has both a large numerical aperture and a wide field of view, allowing for the observation of a larger sample area, while also having high resolution, thus meeting various microscopic observation needs.

[0026] 3. This invention achieves apochromatic function of the microscope objective by matching the refractive index and Abbe number of each lens material, thereby improving imaging quality. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of a 2x microscope objective.

[0028] Figure 2 Field curvature and distortion diagrams for a 2x microscope objective lens;

[0029] Figure 3 The transfer function curve for a 2x microscope objective;

[0030] Figure 4 This is a dot plot of a 2x microscope objective.

[0031] Figure 5 This is a longitudinal chromatic aberration diagram for a 2x microscope objective. Detailed Implementation

[0032] The technical solution of the present invention will be described in detail below with reference to the embodiments and accompanying drawings.

[0033] The numerical aperture (NA) of an objective lens measures its light-gathering ability; a larger NAV means the lens collects more light and achieves higher resolution. For the same image size, a lower magnification objective lens corresponds to a larger object-side field of view, while a higher magnification objective lens corresponds to a smaller object-side field of view. Field number = Objective lens field of view * Magnification.

[0034] like Figure 1 As shown, the 2x microscope objective with a large numerical aperture and wide field of view of the present invention includes a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power, and a third lens group G3 with positive refractive power, arranged sequentially from the object side to the image side. The aperture stop of the microscope objective is located to the right of the third lens group G3, closer to the image side.

[0035] The focal lengths f1 of the first lens group G1, f2 of the second lens group G2, and f3 of the third lens group G3 satisfy the following relationship with the focal length f of the microscope objective:

[0036] 0.3≤|f1 / f|≤0.85;

[0037] 0.1 ≤ |f² / f| ≤ 0.5;

[0038] 0.05≤|f3 / f|≤0.6.

[0039] Specifically, the first lens group G1 includes a first lens L1. The first lens L1 is a biconvex lens, and its d-ray refractive index n1 and Abbe number v1 satisfy the following relationships: 1.8≤n1≤2, 20≤v1≤30.

[0040] The second lens group G2 includes the second lens L2. The second lens L2 is a biconcave lens, and its d-ray (587nm) refractive index n2 and Abbe number v2 satisfy the following relationships: 1.6≤n2≤1.8, 25≤v2≤35.

[0041] The third lens group G3 includes lens L3, lens L4, lens L5, lens L6, lens L7, and lens L8. Lens L3, L4, and L8 are all biconvex lenses, lens L7 is a biconcave lens, and lens L5 and L6 form a cemented doublet negative lens. Specifically, lens L3, L4, L5, and L8 are positive focal length lenses, while lens L6 and L7 are negative focal length lenses.

[0042] The refractive index and Abbe number of the third lens L3 are n3 and v3, respectively; the refractive index and Abbe number of the fourth lens L4 are n4 and v4, respectively; the refractive index and Abbe number of the fifth lens L5 are n5 and v5, respectively; the refractive index and Abbe number of the sixth lens L6 are n6 and v6, respectively; the refractive index and Abbe number of the seventh lens L7 are n7 and v7, respectively; and the refractive index and Abbe number of the eighth lens L8 are n8 and v8, respectively, and they respectively satisfy the following relationships:

[0043] 1.8≤n1≤2, 20≤v1≤30;

[0044] 1.6≤n²≤1.8, 25≤v²≤35;

[0045] 1.4≤n3≤1.6, 77≤v3≤87;

[0046] 1.6≤n4≤1.8, 40≤v4≤50;

[0047] 1.4≤n5≤1.6, 77≤v5≤87;

[0048] 1.6≤n6≤1.8, 28≤v6≤38;

[0049] 1.6≤n7≤1.8, 28≤v7≤38;

[0050] 1.8≤n8≤2, 20≤v8≤30.

[0051] In optical systems like microscope objectives that require high-precision imaging, the focal length configuration of each lens group has a crucial impact on the overall imaging quality. Specifically, in the relationship between the focal lengths of the three lens groups and the focal length f of the microscope objective, if |f1 / f| < 0.3, |f2 / f| < 0.1, and |f3 / f| < 0.05, meaning the focal lengths of each lens group are set too short, the refractive power of the first lens group G1, the second lens group G2, or the third lens group G3 becomes too strong. The light beam will be excessively converged when passing through these lens groups, leading to increased field curvature and image plane bending during imaging. This affects the accuracy of imaging, especially during high-precision measurements, where field curvature and image plane bending introduce errors. If |f1 / f|>0.85, |f2 / f|>0.5, and |f3 / f|>0.6, meaning the focal length of each lens group is set too long, the refractive power of the first lens group G1, the second lens group G2, or the third lens group G3 becomes too weak. The telecentricity of the object side (i.e., the convergence and divergence of the beam when it reaches the image plane throughout the entire field of view) is difficult to maintain, resulting in a reduction in the uniformity of illumination within the field of view. If applied to high-precision measurement techniques such as interferometry, the non-uniformity of illumination will affect the uniformity of the interference fringes, thereby seriously affecting the accuracy of the measurement.

[0052] To ensure that the 2x microscope objective described in this invention can achieve high-precision imaging and measurement with NA≤0.11 (high resolution) and a field of view number of 35 (wide field of view), it is necessary to optimize the relationship between each lens group and the focal length f of the microscope objective. This ensures that the refractive power of the microscope objective is moderate, avoiding field curvature and image plane bending while maintaining uniform illumination and telecentric characteristics. At the same time, the refractive index and Abbe number of the lenses must be distributed within the above-defined range. By matching the refractive index and Abbe number, the apochromatic function of the microscope objective can be achieved.

[0053] This embodiment lists the optimal design schemes for parameters such as curvature, thickness, spacing, and material of each lens of the 2x microscope objective, as shown in Table 1:

[0054] Table 1: Parameters of each lens element in a 2x microscope objective

[0055]

[0056]

[0057] In this embodiment, the optical performance of the 2x microscope objective designed based on the above lens parameters is shown in Table 2:

[0058] Table 2: Parameters of 2x Microscope Objectives

[0059] 2x microscope objective parameters index Focal length f [mm] 100 Maximum numerical aperture 0.11 Maximum field of view 35 Working distance [mm] ＞36 distortion[%] ＜0.2 Telecentricity [°] <0.3

[0060] like Figure 2-5 The figure shows the optical performance test curve of the 2x microscope objective designed in this embodiment.

[0061] Depend on Figure 2 It can be seen that the field curvature range of this microscope objective is ±13.8μm, which is smaller than the flat field design standard of ±60μm, thus achieving the flat field function. At the same time, the distortion is <0.2%, which is also well corrected.

[0062] Depend on Figure 3 , Figure 4 It can be seen that the diameter of the diffusion spot of this microscope objective is within the Airy spot, reaching the diffraction limit. Furthermore, compared with the existing Mitutoyo 2X standard objective, the numerical aperture (NA) of this invention reaches 0.11, while that of the other is 0.055. The fact that this invention's 2x microscope objective reaches the diffraction limit with NA ≤ 0.11 indicates that this microscope objective has high resolution.

[0063] Depend on Figure 5 It can be seen that the longitudinal aberration of this microscope objective is -0.012mm to 0.016mm, which is less than ±0.024mm. This indicates that the pupil aberration and chromatic aberration of the objective are well corrected. By selecting and optimizing the refractive index and Abbe number of the lens, the apochromatic function is achieved.

Claims

1. A 2x microscope objective with a large numerical aperture and a wide field of view, applicable in the 430-720nm visible light band, characterized in that, The microscope objective consists of a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power, and a third lens group G3 with positive refractive power, arranged sequentially from the object side to the image side. The aperture of the microscope objective is located to the right of the third lens group G3, close to the image side. The microscope objective has a field number of ≤35mm, a maximum numerical aperture of ≤0.11, and also has field plan and apochromatic properties. The first lens group G1 includes only the first lens L1, which is a biconvex lens with positive optical power; the second lens group G2 includes only the second lens L2, which is a biconcave lens with negative optical power; the third lens group G3 consists of a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, a seventh lens L7, and an eighth lens L8, with the fifth lens L5 and the sixth lens L6 forming a cemented doublet negative lens; wherein, the third lens L3, the fourth lens L4, the fifth lens L5, and the eighth lens L8 are biconvex lenses with positive optical power, and the sixth lens L6 and the seventh lens L7 are biconcave lenses with negative optical power; The focal lengths f1 of the first lens group G1, f2 of the second lens group G2, and f3 of the third lens group G3 satisfy the following relationship with the focal length f of the 2x microscope objective: 0.85； 0.5； 0.6。 2. The 2x microscope objective with a large numerical aperture and wide field of view as described in claim 1, characterized in that, The working distance of the microscope objective is 35-37mm, and the focal length is 100mm.

3. The 2x microscope objective with a large numerical aperture and wide field of view as described in claim 1, characterized in that, The d-ray refractive index n1 and Abbe number v1 of the first lens L1 satisfy the following relationships: 2, 30.

4. The 2x microscope objective with a large numerical aperture and wide field of view as described in claim 1, characterized in that, The d-ray refractive index n2 and Abbe number v2 of the second lens L2 satisfy the following relationships: 1.8, 35.

5. The 2x microscope objective with a large numerical aperture and wide field of view as described in claim 1, characterized in that, The refractive index and Abbe number of the third lens L3 are n3 and v3, respectively; the refractive index and Abbe number of the fourth lens L4 are n4 and v4, respectively; the refractive index and Abbe number of the fifth lens L5 are n5 and v5, respectively; the refractive index and Abbe number of the sixth lens L6 are n6 and v6, respectively; the refractive index and Abbe number of the seventh lens L7 are n7 and v7, respectively; and the refractive index and Abbe number of the eighth lens L8 are n8 and v8, respectively, and they respectively satisfy the following relationships: 2, 30； 1.8, 35； 1.6, 87； 1.8, 50； 1.6, 87； 1.8, 38； 1.8, 38； 2, 30。

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