A high-resolution microscope objective with a large numerical aperture and a wide field of view

Abstract

The application discloses a high-resolution microscopic objective with a large numerical aperture and a wide field of view, comprising a front converging group with positive focal power, an aberration correction group with negative focal power and a rear imaging telecentric group with positive focal power arranged in sequence from the object side to the image side; the front converging group undertakes preliminary convergence of the object side light rays, lays a foundation for large field of view and high numerical aperture imaging; the aberration correction group is the core of system aberration correction, and can effectively correct field curvature, distortion and chromatic aberration; the rear imaging telecentric group is responsible for final high-performance imaging and guarantees the object side telecentric characteristic, simultaneously realizes flat field, low distortion and complex achromatism under a super large field of view, so as to ensure the imaging quality of the objective, and better meet the wide field of view, high resolution and precise measurement requirements in the field of semiconductor detection.

Description

Technical Field

[0001] This invention relates to the field of microscope objectives, specifically to a high-resolution microscope objective with a large numerical aperture and a wide field of view. Background Technology

[0002] Compared to high-magnification microscope objectives, low-magnification microscope objectives have a wider field of view and a longer working distance, enabling the observation of large samples in a single operation. This facilitates sample size measurement and large-size image resolution, and therefore they are widely used in fields such as industrial inspection, biological observation, and materials science.

[0003] With the increasing market demand for wide-field, high-resolution, low-magnification microscope objectives, existing products struggle to simultaneously meet the design requirements of plan and apochromatic aberration at longer working distances. This significantly increases the difficulty of lens design, while also presenting technical challenges such as difficulties in apochromatic correction and optimization of pupillary aberration. Summary of the Invention

[0004] Technical objective: To address the shortcomings of existing low-magnification microscope objectives, this invention discloses a high-resolution microscope objective with a large numerical aperture and wide field of view, which combines a wide field of view, high resolution, and plan and apochromatic properties.

[0005] Technical solution: To achieve the above technical objectives, the present invention adopts the following technical solution: A high-resolution microscope objective with a large numerical aperture and a wide field of view includes a front converging group with positive optical power, an aberration correction group with negative optical power, and a rear imaging telecentric group with positive optical power arranged sequentially from the object side to the image side. The focal lengths f1 of the front converging group, f2 of the aberration correction group, and f3 of the rear imaging telecentric group satisfy the following relationships with the focal length f of the microscope objective: 0.5≤|f1 / f|≤3; 15≤|f2 / f|≤30; 5≤|f3 / f|≤20.

[0006] Preferably, the front converging group of the present invention consists of a first lens, a second lens, and a third lens arranged sequentially along the optical path direction. The first lens and the second lens are cemented together to form a doublet lens with positive optical power; the third lens is a biconvex lens with positive optical power.

[0007] Preferably, the d-ray refractive index and Abbe number of the first lens of the present invention are n1 and v1, respectively, where 1.43≤n1≤1.52 and 80≤v1≤96; The d-ray refractive index and Abbe number of the second lens are n2 and v2, respectively, 1.54≤n2≤1.74, 45≤v2≤65; The d-ray refractive index and Abbe number of the third lens are n3 and v3, respectively, with 1.49≤n3≤1.69 and 58≤v3≤78.

[0008] Preferably, the aberration correction group of the present invention consists of a fourth lens, a fifth lens, a sixth lens, a seventh lens, and an eighth lens arranged sequentially along the optical path direction; the fifth lens and the sixth lens are cemented together to form a negative optical power cemented doublet, and the seventh lens and the eighth lens are cemented together to form a positive optical power cemented doublet; wherein, the fourth lens, the fifth lens, and the seventh lens are positive optical power lenses, and the sixth lens and the eighth lens are negative optical power lenses.

[0009] Preferably, the d-ray refractive index and Abbe number of the fourth lens of the present invention are n4 and v4, respectively, 1.43≤n4≤1.52, 80≤v4≤96; The d-ray refractive index and Abbe number of the fifth lens are n5 and v5, respectively, 1.43≤n5≤1.53, 80≤v5≤96; The d-ray refractive index and Abbe number of the sixth lens are n6 and v6, respectively, where 1.6≤n6≤1.8 and 20≤v6≤40. The d-ray refractive index and Abbe number of the seventh lens are n7 and v7, respectively, 1.71≤n7≤1.91, 17≤v7≤33; The d-ray refractive index and Abbe number of the eighth lens are n8 and v8, respectively, with 1.51≤n8≤1.71 and 34≤v8≤54.

[0010] Preferably, the rear imaging telecentric group of the present invention consists of a ninth lens and a tenth lens arranged along the optical path direction, and the ninth lens and the tenth lens are cemented together to form a doublet lens with positive optical power.

[0011] Preferably, the d-ray refractive index and Abbe number of the ninth lens of the present invention are n9 and v9, respectively, 1.52≤n9≤1.72, 27≤v9≤47; The d-ray refractive index and Abbe number of the tenth lens are n10 and v10, respectively, with 1.65≤n10≤1.85 and 42≤v10≤62.

[0012] Beneficial effects: The high-resolution microscope objective with a large numerical aperture and wide field of view disclosed in this invention has the following beneficial effects: 1. This invention optimizes the ratio of the three lens groups (front converging group, aberration correction group, and rear imaging telecentric group) to the total focal length f of the objective lens, thereby achieving a reasonable distribution of optical power in the system. While maintaining a parfocal length of 95mm, the field of view reaches 35mm, the NA reaches 0.225, the working distance reaches 30mm, and the MTF of the entire field of view is close to the diffraction limit. While effectively correcting the field curvature to ±1.3μm, it maintains the object-side telecentricity with a telecentricity of <0.22°, thus improving the imaging stability of high-precision measurements.

[0013] 2. The front converging group of this invention ensures the long working distance of the objective lens. The incident surface of the first lens is designed with a large radius and weak positive curvature, and the object side is almost flat-field incident, allowing large-aperture light to enter the microscope objective at a gentle angle, avoiding excessive optical power of the front group that would compress the working distance. At the same time, the main positive optical power is moved to the cementing surface of the first and second lenses, and the light is converged by the small radius and strong negative curvature of the cementing surface. This "front weak positive incident surface + internal strong negative cementing surface" rear-positioned optical power layout, under the large aperture condition of NA=0.225 in this embodiment of the invention, extends the object-side working distance to 30.95mm. Compared with the Mitutoyo M Plan Apo HR 5× objective, which has an NA of 0.21, a field of view of 24mm, and a working distance of 25.5mm, the microscope objective of this embodiment of the invention breaks through the conventional upper limit of the working distance of objectives of the same NA level.

[0014] 3. The cemented surfaces of the first and second lenses of this invention, in conjunction with the ultra-low dispersion positive lens of the first lens and the medium dispersion lens of the second lens, utilize the Abbe number difference to cancel the primary axial chromatic aberration, significantly suppressing the secondary spectrum under large aperture, and laying the foundation for apochromatic aberration of the entire system.

[0015] 4. The aberration correction group of this invention adopts a correction architecture of "single positive lens + negative cemented lens + positive cemented lens". The negative optical power cemented doublet composed of the fifth and sixth lenses serves as the core of field curvature correction, generating a strong divergence effect on off-axis rays, accurately canceling the positive field curvature introduced by the front and rear positive lens groups, and performing transverse chromatic aberration correction; the positive optical power cemented doublet composed of the seventh and eighth lenses corrects axial chromatic aberration, and performs directional correction for the three major problems of field curvature, transverse chromatic aberration, and distortion introduced by the large field of view. It simultaneously achieves field flatness, low distortion, and apochromatic aberration under ultra-large field of view to ensure the imaging quality of the objective lens.

[0016] 5. The post-imaging telecentric group of the present invention utilizes the negative curvature of the surface of the ninth lens to deflect the principal ray, control the telecentricity of the field of view, and achieves a compensating cemented pairing of a low Abbe number negative lens and a medium-to-high Abbe number positive lens by cementing the ninth and tenth lenses, correcting the residual axial chromatic aberration and spherical aberration of the entire system, and ensuring the final imaging quality. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0018] Figure 1 This is a structural diagram of the microscope objective of the present invention; Among them, 1-first lens, 2-second lens, 3-third lens, 4-fourth lens, 5-fifth lens, 6-sixth lens, 7-seventh lens, 8-eighth lens, 9-ninth lens, 10-tenth lens, 11-front converging group, 12-aberration correction group, 13-rear imaging telecentric group. Detailed Implementation

[0019] Reference will now be made in detail to embodiments of the present disclosure, one or more of which are set forth herein. Each embodiment and example is provided by way of explanation of the apparatus, composition, and materials of the present disclosure, and not by way of limitation. Rather, the following description provides convenient illustrations for implementing exemplary embodiments of the present disclosure. Indeed, it will be apparent to those skilled in the art that various modifications and variations can be made to the teachings of the present disclosure without departing from the scope or spirit of the present disclosure.

[0020] like Figure 1 As shown, this invention discloses a high-resolution microscope objective with a large numerical aperture and a wide field of view, comprising a front converging group 11 with positive optical power, an aberration correction group 12 with negative optical power, and a rear imaging telecentric group 13 with positive optical power arranged sequentially from the object side to the image side; the focal length f1 of the front converging group 11, the focal length f2 of the aberration correction group 12, the focal length f3 of the rear imaging telecentric group 13 and the focal length f of the microscope objective satisfy the following conditions: 0.5≤|f1 / f|≤3; 15≤|f2 / f|≤30; 5≤|f3 / f|≤20.

[0021] The front convergence group 11 is responsible for the initial convergence of object-side rays, laying the foundation for large field of view and high numerical aperture (NA) imaging; the aberration correction group 12 is the core of system aberration correction, which can effectively correct field curvature, distortion and chromatic aberration; the rear imaging telecentric group 13 is responsible for the final high-performance imaging and ensures the object-side telecentric characteristics.

[0022] Specifically, the front converging group 11 of the present invention is composed of a first lens 1, a second lens 2 and a third lens 3 arranged sequentially along the optical path direction. The first lens 1 and the second lens 2 are cemented together to form a doublet lens with positive optical power; the third lens 3 is a biconvex lens with positive optical power.

[0023] The d-ray refractive index and Abbe number of the first lens 1 are n1 and v1, respectively, 1.43≤n1≤1.52, 80≤v1≤96; The d-ray refractive index and Abbe number of the second lens 2 are n2 and v2, respectively, 1.54≤n2≤1.74, 45≤v2≤65; The d-ray refractive index and Abbe number of the third lens 3 are n3 and v3, respectively, with 1.49≤n3≤1.69 and 58≤v3≤78.

[0024] The aberration correction group 12 of the present invention consists of a fourth lens 4, a fifth lens 5, a sixth lens 6, a seventh lens 7, and an eighth lens 8 arranged sequentially along the optical path direction; the fifth lens 5 and the sixth lens 6 are cemented together to form a negative optical power cemented doublet, and the seventh lens 7 and the eighth lens 8 are cemented together to form a positive optical power cemented doublet; wherein, the fourth lens 4, the fifth lens 5, and the seventh lens 7 are positive optical power lenses, and the sixth lens 6 and the eighth lens 8 are negative optical power lenses.

[0025] The d-ray refractive index and Abbe number of the fourth lens 4 are n4 and v4, respectively, 1.43≤n4≤1.52, 80≤v4≤96; The d-ray refractive index and Abbe number of the fifth lens 5 are n5 and v5, respectively, 1.43≤n5≤1.53, 80≤v5≤96; The refractive index of the d-ray of the sixth lens 6 and the Abbe number are n6 and v6, respectively, where 1.6≤n6≤1.8 and 20≤v6≤40. The d-ray refractive index and Abbe number of the seventh lens 7 are n7 and v7, respectively, 1.71≤n7≤1.91, 17≤v7≤33; The d-ray refractive index and Abbe number of the eighth lens 8 are n8 and v8, respectively, with 1.51≤n8≤1.71 and 34≤v8≤54.

[0026] The rear imaging telecentric group 13 of the present invention consists of a ninth lens 9 and a tenth lens 10 arranged along the optical path direction. The ninth lens 9 and the tenth lens 10 are cemented together to form a doublet lens with positive optical power.

[0027] The d-ray refractive index and Abbe number of the ninth lens 9 are n9 and v9, respectively, 1.52≤n9≤1.72, 27≤v9≤47; The d-ray refractive index and Abbe number of the tenth lens 10 are n10 and v10, respectively, with 1.65≤n10≤1.85 and 42≤v10≤62.

[0028] The following is a detailed description using an example of a 40mm objective lens. Table 1 shows the specific lens parameters of the microscope objective lens in this embodiment of the invention.

[0029] Table 1: Parameters of Microscope Objective Lenses

[0030] Among them, cemented lenses are grouped together, and the surface numbering is done sequentially from the object side to the image side according to the surface of the lens. The cementing surfaces of cemented lenses use the same number. For example, when the first lens 1 and the second lens 2 are cemented together, S2 is the cementing surface of the first lens 1 and the second lens 2. The thickness represents the distance from the current surface to the next surface, and the object side thickness represents the distance from the object side to the S1 surface.

[0031] The optical properties of the microscope objectives in the embodiments of the present invention are shown in Table 2.

[0032] Table 2: Performance Parameters of Microscope Objectives

[0033] The microscope objective of this invention achieves a field of view of 35mm, NA=0.225, and working distance ≥30mm with a parfocal distance of 95mm, while also possessing both planar field and apochromatic performance; it can meet the wide field of view and high-resolution precision measurement requirements of fields such as semiconductor testing.

[0034] The present invention designs the surface S1 of the first lens 1 with a large radius and weak positive curvature, which is 180.70 mm in the embodiment. The object side is nearly flat-field incident, allowing the large aperture light to enter the system at a gentle angle, avoiding the compression of the working distance due to the excessive focal length of the front group; at the same time, the main positive focal length is moved to the surface S2, and the light is gathered by the small radius and strong negative curvature, which is -17.91 mm in the embodiment.

[0035] By effectively focusing the light rays across the entire aperture of surface S2, the beam diameter and aberration load are reduced for subsequent correction groups. In conjunction with the pairing of the ultra-low dispersion positive lens of the first lens 1 and the medium dispersion lens of the second lens 2, the difference in Abbe number is used to cancel the primary axial chromatic aberration, thereby significantly suppressing the secondary spectrum under large aperture and laying the foundation for apochromatic aberration of the entire system.

[0036] The third lens 3 adopts a symmetrical biconvex lens structure to gently converge the beam output from the front cemented lens, compressing the beam aperture to a size suitable for the subsequent correction group; the symmetrical surface shape can suppress the spherical aberration and astigmatism introduced by itself, and the high Abbe number material reduces the accumulation of aberrations in the front group.

[0037] In aberration correction group 12, a method different from conventional single-group negative lens is adopted for field curvature correction. This invention uses a cemented doublet lens with negative optical power formed by cementing the fifth lens 5 and the sixth lens 6 as the core of field curvature correction. The surface S10 has a strong positive curvature of 15.57mm, which produces a strong divergence effect on off-axis rays, accurately canceling the positive field curvature introduced by the front and rear positive lens groups. Together with the fourth lens 4, the cemented seventh lens 7 and the eighth lens 8, a "positive-negative-positive" optical power structure is formed, which ultimately controls the field curvature of the entire field of view within ±1.3μm, which is far better than the flat field design standard of ±13.5μm.

[0038] Simultaneously, the aberration correction group 12 uses two sets of cemented doublet lenses to correct axial and transverse chromatic aberrations, achieving apochromatic aberration across the entire 400~700nm wavelength range. The fifth lens uses an ultra-low dispersion material with an Abbe number of 95.2, and the sixth lens 6 uses flint glass with an Abbe number of 31.2. The difference in Abbe number between the two exceeds 60, resulting in extremely strong dispersion compensation capabilities. This cemented doublet lens is located in the middle of the optical path, with a high incident height for off-axis rays, leading to high efficiency in correcting transverse chromatic aberration and specifically addressing the chromatic aberration problem at the edges of a large field of view. The seventh lens 7 uses an extremely low Abbe number heavy flint material with an Abbe number of 22.6, forming a reverse dispersion complement with the previous set of cemented doublet lenses, further offsetting the second-order spectrum of axial chromatic aberration. Ultimately, the longitudinal aberration across the entire wavelength range is controlled within the range of -0.005mm~0.007mm, achieving apochromatic aberration levels.

[0039] In addition, the fourth lens 4 adopts a biconvex lens structure with positive optical power, and the seventh lens 7 and the eighth lens 8 are cemented together to form a meniscus shape. The two work together to progressively constrain the propagation angle of the off-axis principal rays, suppressing distortion under a large field of view, and finally achieving a full field of view distortion of <0.36%. At the same time, the symmetrical design of the surface shape also effectively corrects astigmatism and ensures the consistency of imaging in the meridional and sagittal directions.

[0040] Therefore, the aberration correction group 12 of the present invention can achieve flat field, low distortion and apochromatic aberration in a large field of view, thus solving the problem that a large field of view and high imaging quality cannot be achieved at the same time.

[0041] The aperture stop of the present invention is disposed within the aberration correction group 12, within the rear imaging telecentric group 13, or between the aberration correction group 12 and the rear imaging telecentric group 13, for constraining the main optical path. The specific placement position can be selected according to imaging requirements. In the embodiment of the present invention, it is disposed between the aberration correction group 12 and the rear imaging telecentric group 13.

[0042] The aperture stop of this invention, in conjunction with the double cemented lens of the telecentric imaging group 13, images the aperture stop to infinity on the object side, making the principal ray of the object side parallel to the optical axis, thus achieving telecentricity on the object side. The surface S14 of the ninth lens 9 has a strong negative curvature of -13.01mm, which accurately deflects the principal ray. Combined with the axial position of the aperture stop, the telecentricity of the entire field of view is controlled to <0.22°. The telecentric design ensures that the incident angle of the principal ray on the image plane is consistent throughout the entire field of view, avoiding the problem of vignetting at the edges under a large field of view. Finally, the relative illumination of the entire field of view is >99.8%, and the brightness is uniform within a large field of view, improving the reliability of high-precision measurement.

[0043] Meanwhile, the ninth lens 9 and the tenth lens 10 adopt a compensating cemented pairing of a low Abbe number negative lens and a medium-to-high Abbe number positive lens to correct the residual axial chromatic aberration and spherical aberration of the entire system, so that the MTF of the entire field of view is close to the diffraction limit and the final imaging quality is guaranteed.

[0044] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A high-resolution microscope objective with a large numerical aperture and a wide field of view, characterized in that, It consists of a front convergent group (11) with positive optical power, an aberration correction group (12) with negative optical power, and a rear telecentric group (13) with positive optical power arranged sequentially from the object side to the image side; the focal length f1 of the front convergent group (11), the focal length f2 of the aberration correction group (12), the focal length f3 of the rear telecentric group (13) and the focal length f of the microscope objective satisfy the following: 0.5≤|f1 / f|≤3; 15≤|f2 / f|≤30; 5≤|f3 / f|≤20; The front converging group (11) is composed of a first lens (1), a second lens (2) and a third lens (3) arranged sequentially along the optical path direction. The first lens (1) and the second lens (2) are cemented together to form a doublet lens with positive optical power; the third lens (3) is a biconvex lens with positive optical power. The aberration correction group (12) consists of a fourth lens (4), a fifth lens (5), a sixth lens (6), a seventh lens (7), and an eighth lens (8) arranged sequentially along the optical path; the fourth lens (4) is a biconvex lens with positive optical power; the fifth lens (5) and the sixth lens (6) are cemented together to form a cemented doublet with negative optical power, and the seventh lens (7) and the eighth lens (8) are cemented together to form a cemented doublet with positive optical power; wherein, the fifth lens (5) and the seventh lens (7) are positive optical power lenses, and the sixth lens (6) and the eighth lens (8) are negative optical power lenses; The post-image telecentric group (13) consists of a ninth lens (9) and a tenth lens (10) arranged along the optical path direction. The ninth lens (9) and the tenth lens (10) are cemented together to form a doublet lens with positive optical power.

2. The high-resolution microscope objective with a large numerical aperture and wide field of view according to claim 1, characterized in that, The d-ray refractive index and Abbe number of the first lens (1) are n1 and v1, respectively, 1.43≤n1≤1.52, 80≤v1≤96; The d-ray refractive index and Abbe number of the second lens (2) are n2 and v2, respectively, 1.54≤n2≤1.74, 45≤v2≤65; The d-ray refractive index and Abbe number of the third lens (3) are n3 and v3, respectively, 1.49≤n3≤1.69, 58≤v3≤78.

3. A high-resolution microscope objective with a large numerical aperture and a wide field of view according to claim 1, characterized in that, The d-ray refractive index and Abbe number of the fourth lens (4) are n4 and v4, respectively, 1.43≤n4≤1.52, 80≤v4≤96; The d-ray refractive index and Abbe number of the fifth lens (5) are n5 and v5, respectively, 1.43≤n5≤1.53, 80≤v5≤96; The d-ray refractive index and Abbe number of the sixth lens (6) are n6 and v6, respectively, 1.6≤n6≤1.8, 20≤v6≤40; The d-ray refractive index and Abbe number of the seventh lens (7) are n7 and v7, respectively, 1.71≤n7≤1.91, 17≤v7≤33; The d-ray refractive index and Abbe number of the eighth lens (8) are n8 and v8, respectively, 1.51≤n8≤1.71, 34≤v8≤54.

4. A high-resolution microscope objective with a large numerical aperture and a wide field of view according to claim 1, characterized in that, The d-ray refractive index and Abbe number of the ninth lens (9) are n9 and v9, respectively, 1.52≤n9≤1.72, 27≤v9≤47; The d-ray refractive index and Abbe number of the tenth lens (10) are n10 and v10, respectively, 1.65≤n10≤1.85, 42≤v10≤62.

Images