High numerical aperture water immersion microscope objective
Patent Information
- Application Number
- CN202522201577.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-17
- Publication Date
- 2026-09-08
- Estimated Expiration
- 2035-10-17
AI Technical Summary
[0003]然而，现有水浸物镜设计存在诸多技术痛点：一方面，水的折射率低于油浸物镜所用浸液，导致水浸物镜的数值孔径通常较低，难以满足高分辨率成像需求；另一方面，为实现高数值孔径与像差校正的平衡，现有设计常采用复杂的透镜组结构，不仅增加了加工难度和生产成本，还可能引入冗余像差；此外，部分设计在材料选择上未充分考虑与浸液的兼容性及长期使用的稳定性，且机械结构对浸液密封性、工作距离控制的精度要求严苛，进一步限制了其商业化应用
1、本实用新型一种高数值孔径水浸显微物镜，采用“双高斯、复消色差和齐明透镜”混合结构，通过8片球面透镜实现光焦度合理分配，数值孔径达0.9，785nm～850nm近红外波段内成像质量接近衍射极限，分辨率与像差校正能力优异，满足高精密显微成像需求，光学性能好。
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Figure CN224732239U_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of imaging technology of optical lenses, and specifically relates to a high numerical aperture water immersion microscope objective. Background Technology
[0002] A water immersion objective is a core component of a microscope that uses a liquid medium (such as water) as the imaging medium between the objective and the sample. Its design aims to overcome the limitations of air as the medium in optical imaging. Because the refractive index of a liquid medium is higher than that of air, a water immersion objective can significantly increase the numerical aperture (NA) of the optical system, thereby enhancing imaging resolution and sharpness. Compared to dry objectives, water immersion objectives effectively reduce light refraction and scattering at the sample-objective interface, reducing the impact of aberrations such as spherical and chromatic aberration on imaging. This advantage is particularly pronounced when observing small or low-contrast samples at high magnification. It also reduces optical damage to some extent, making it suitable for long-term observation of living samples.
[0003] However, existing water immersion microscope objectives suffer from several technical challenges: firstly, water's refractive index is lower than that of the immersion liquid used in oil immersion objectives, resulting in typically lower numerical apertures that fail to meet high-resolution imaging requirements; secondly, to achieve a balance between high numerical aperture and aberration correction, existing designs often employ complex lens group structures, which not only increase processing difficulty and production costs but may also introduce redundant aberrations; furthermore, some designs do not adequately consider material compatibility with the immersion liquid and long-term stability in material selection, and the mechanical structure has stringent requirements for immersion liquid sealing and working distance control precision, further limiting their commercial application. Therefore, developing a water immersion microscope objective that combines high numerical aperture, excellent imaging quality, and ease of fabrication has become an urgent need in the industry. Utility Model Content
[0004] To address the aforementioned problems, this invention proposes a high numerical aperture water immersion microscope objective.
[0005] To achieve the above objectives, the present invention adopts the following technical solution: A high numerical aperture water immersion microscope objective comprises, along the optical axis from image side to object side, a first lens, a second lens, a third lens, a fourth lens, an aperture, a fifth lens, a sixth lens, a seventh lens, and an eighth lens, with a liquid layer and a coverslip disposed between the eighth lens and the sample; each lens has a standard spherical or planar surface; the first lens is a positive power plano-convex lens with its planar surface facing the object side and its convex surface facing the image side; the second lens is a negative power plano-concave lens with its planar surface facing the image side and its concave surface facing the object side; the first and second lenses are cemented together to form a first cemented doublet lens group; the third lens is a negative power plano-concave lens. The first lens has a flat surface facing the object side and a concave surface facing the image side; the fourth lens is a positive power plano-convex lens with a convex surface facing the object side and a flat surface facing the image side; the third lens and the fourth lens are cemented together to form a second cemented doublet lens group; the fifth lens is a positive power biconvex lens; the sixth lens is a negative power plano-concave lens with a concave surface facing the object side and a flat surface facing the image side; the fifth lens and the sixth lens are cemented together to form a third cemented doublet lens group; the seventh lens is a positive power meniscus lens with a concave surface facing the object side and a convex surface facing the image side; the eighth lens is a positive power meniscus lens with a concave surface facing the object side and a convex surface facing the image side.
[0006] Furthermore, the optical power of the first cemented doublet lens group is negative; the optical power of the second cemented doublet lens group is negative; and the optical power of the third cemented doublet lens group is positive.
[0007] Furthermore, the radii of curvature of each lens satisfy the following: the radius of curvature of the first lens facing the image side is 7.5–8.5 mm, and the radius of curvature of the lens near the second lens is infinite; the radius of curvature of the second lens near the third lens is 3.5–4.5 mm, and the radius of curvature of the lens near the first lens is infinite; the radius of curvature of the third lens near the second lens is -4.5 to -3.5 mm, and the radius of curvature of the lens near the fourth lens is infinite; the radius of curvature of the fourth lens near the aperture stop is -7.5–8.5 mm, and the radius of curvature of the lens near the third lens is infinite; the radius of curvature of the fifth lens near the aperture stop is -7.5–8.5 mm, and the radius of curvature of the lens near the aperture stop ... The radius of curvature on the near stop side is 10.5–11.5 mm, and the radius of curvature on the side near the sixth lens is -11.5–-10.5 mm; the radius of curvature of the sixth lens on the side near the seventh lens is infinite, and the radius of curvature on the side near the fifth lens is -11.5–-10.5 mm; the radius of curvature of the seventh lens on the side near the sixth lens is 6.5–7.5 mm, and the radius of curvature on the side near the eighth lens is 23.7–24.7 mm; the radius of curvature of the eighth lens on the side near the seventh lens is 3.2–4.2 mm, and the radius of curvature on the side near the liquid layer is 1.2–2.2 mm.
[0008] Furthermore, the refractive index and Abbe number of each lens satisfy the following conditions: the first lens has a refractive index of 1.79–1.81 and an Abbe number of 25–26; the second lens has a refractive index of 1.45–1.55 and an Abbe number of 64–65; the third lens has a refractive index of 1.85–1.95 and an Abbe number of 17–20; the fourth lens has a refractive index of 1.80–1.90 and an Abbe number of 37–42; the fifth lens has a refractive index of 1.70–1.80 and an Abbe number of 52–56; the sixth lens has a refractive index of 1.85–1.95 and an Abbe number of 17–20; the seventh lens has a refractive index of 1.72–1.82 and an Abbe number of 45–48; and the eighth lens has a refractive index of 1.85–1.95 and an Abbe number of 33–36.
[0009] Furthermore, the center thickness of each lens and the air gap between adjacent elements satisfy the following conditions: the center thickness of the first lens is 2.6–3.6 mm, the center thickness of the second lens is 0.8–1.6 mm, the center thickness of the third lens is 2.6–3.6 mm, the center thickness of the fourth lens is 2.6–3.6 mm, the center thickness of the fifth lens is 2.8–3.6 mm, the center thickness of the sixth lens is 1.0–2.0 mm, the center thickness of the seventh lens is 2.6–3.6 mm, and the center thickness of the eighth lens is 3 mm. The aperture is 2–4.2 mm; the aperture stop is located between the fourth lens and the fifth lens, the air gap between the aperture stop and the fourth lens is 0.1–0.3 mm, the air gap between the aperture stop and the fifth lens is 0.1–0.2 mm; the air gap between the second lens and the third lens is 3.0–4.0 mm; the air gap between the fourth lens and the fifth lens is 0.1–0.3 mm; the air gap between the sixth lens and the seventh lens is 3.5–4.5 mm; the air gap between the seventh lens and the eighth lens is 0.1–0.15 mm.
[0010] Furthermore, the cover glass has a thickness of 0.17 mm, a refractive index of 1.51, and an Abbe number of 63.4; the liquid layer has a thickness of 0.6 mm, a refractive index of 1.33, and an Abbe number of 54.
[0011] After adopting the above technical solution, the present invention has the following beneficial effects: 1. This utility model discloses a high numerical aperture water immersion microscope objective, which adopts a hybrid structure of "double Gaussian, apochromatic and uniform lens", and achieves reasonable distribution of optical power through 8 spherical lenses. The numerical aperture reaches 0.9, and the imaging quality in the 785nm-850nm near-infrared band is close to the diffraction limit. It has excellent resolution and aberration correction capabilities, meets the requirements of high-precision microscopic imaging, and has good optical performance.
[0012] 2. This utility model provides a high numerical aperture water immersion microscope objective. All lenses adopt a standard spherical or planar design, avoiding the high difficulty and cost of aspherical processing. The centering coefficient of each lens is greater than 0.15, and the assembly accuracy is easy to control. At the same time, environmentally friendly glass material with a melting frequency of 1 is selected to reduce the difficulty and cost of mass production.
[0013] 3. This utility model discloses a high numerical aperture water immersion microscope objective with good matching between the material's refractive index and Abbe number, exhibiting no optical performance degradation even after long-term contact with water. The image plane is reinforced with H-K5 glass to prevent total internal reflection, further enhancing system stability and making it suitable for long-term use. The system has a compact structure (total length 31.29 mm) and ample performance margin, making it widely applicable in fields such as biomedicine and precision testing, with broad commercial prospects. Attached Figure Description
[0014] Figure 1 This is a schematic diagram of the structure and optical path of the high numerical aperture water immersion microscope objective of this utility model; Figure 2 This is a schematic diagram of the light aberration curve of an embodiment of the present invention; Figure 3 This is a schematic diagram of the wavefront aberration curve of this utility model embodiment at a wavelength of 785nm; Figure 4 This is a schematic diagram of the wavefront aberration curve of this utility model embodiment at a wavelength of 810nm; Figure 5 This is a schematic diagram of the wavefront aberration curve of an embodiment of the present invention at a wavelength of 850nm; Figure 6 This is a schematic diagram of the MTF curve of polychromatic light diffraction according to an embodiment of the present invention; Figure 7 This is a schematic diagram of the axial aberration curve of an embodiment of the present invention; Figure 8 This is a schematic diagram of the field curvature curve of an embodiment of the present invention; Figure 9 This is a schematic diagram of the distortion curve of an embodiment of the present invention.
[0015] The reference numerals in the figure are as follows: L1, First lens; L2, Second lens; L3, Third lens; L4, Fourth lens; L5, Fifth lens; L6, Sixth lens; L7, Seventh lens; L8, Eighth lens; L9, Ninth lens; 1, Light shield. Detailed Implementation
[0016] To make the objectives, technical solutions, and advantages of this utility model clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this utility model.
[0017] like Figures 1 to 9 As shown, a high numerical aperture water immersion microscope objective comprises, along the optical axis from image side to object side, a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, an aperture, a fifth lens L5, a sixth lens L6, a seventh lens L7, and an eighth lens L8. A liquid layer and a coverslip are disposed between the eighth lens L8 and the sample. The surfaces of each lens are standard spherical or planar surfaces. The first lens L1 is a positive optical power plano-convex lens, with its planar surface facing the object side and its convex surface facing the image side. The second lens L2 is a negative optical power plano-concave lens, with its planar surface facing the image side and its concave surface facing the object side. The first lens L1 and the second lens L2 are cemented together to form a first cemented doublet lens group. The third lens L3 is a negative optical power plano-concave lens. The first lens is a plano-concave lens with a positive optical power, its flat surface facing the object side and its concave surface facing the image side; the second lens is a plano-convex lens with a positive optical power, its convex surface facing the object side and its flat surface facing the image side; the third lens is cemented with the fourth lens to form a second cemented doublet lens group; the third lens is a biconvex lens with a positive optical power; the fourth lens is a plano-concave lens with a negative optical power, its concave surface facing the object side and its flat surface facing the image side; the fifth lens is cemented with the sixth lens to form a third cemented doublet lens group; the fifth lens is a meniscus lens with a positive optical power, its concave surface facing the object side and its convex surface facing the image side; the fifth lens is a meniscus lens with a positive optical power, its concave surface facing the object side and its convex surface facing the image side.
[0018] The optical power of the first cemented doublet lens group is negative; the optical power of the second cemented doublet lens group is negative; and the optical power of the third cemented doublet lens group is positive.
[0019] The radii of curvature of each lens satisfy the following conditions: the radius of curvature of the first lens L1 facing the image side is 7.5–8.5 mm, and the radius of curvature near the second lens L2 is infinite; the radius of curvature of the second lens L2 near the third lens L3 is 3.5–4.5 mm, and the radius of curvature near the first lens L1 is infinite; the radius of curvature of the third lens L3 near the second lens L2 is -4.5 to -3.5 mm, and the radius of curvature near the fourth lens L4 is infinite; the radius of curvature of the fourth lens L4 near the aperture stop is -7.5–8.5 mm, and the radius of curvature near the third lens L3 is infinite; the radius of curvature of the fifth lens L5 near the aperture stop is -7.5–8.5 mm. The radius of curvature on one side of the aperture stop is 10.5–11.5 mm, and the radius of curvature on the side near the sixth lens L6 is -11.5–-10.5 mm; the radius of curvature of the sixth lens L6 near the seventh lens L7 is infinite, and the radius of curvature on the side near the fifth lens L5 is -11.5–-10.5 mm; the radius of curvature of the seventh lens L7 near the sixth lens L6 is 6.5–7.5 mm, and the radius of curvature on the side near the eighth lens L8 is 23.7–24.7 mm; the radius of curvature of the eighth lens L8 near the seventh lens L7 is 3.2–4.2 mm, and the radius of curvature on the side near the liquid layer is 1.2–2.2 mm.
[0020] The refractive indices and Abbe numbers of each lens satisfy the following conditions: the first lens L1 has a refractive index of 1.79–1.81 and an Abbe number of 25–26; the second lens L2 has a refractive index of 1.45–1.55 and an Abbe number of 64–65; the third lens L3 has a refractive index of 1.85–1.95 and an Abbe number of 17–20; the fourth lens L4 has a refractive index of 1.80–1.90 and an Abbe number of 37–42; the fifth lens L5 has a refractive index of 1.70–1.80 and an Abbe number of 52–56; the sixth lens L6 has a refractive index of 1.85–1.95 and an Abbe number of 17–20; the seventh lens L7 has a refractive index of 1.72–1.82 and an Abbe number of 45–48; and the eighth lens L8 has a refractive index of 1.85–1.95 and an Abbe number of 33–36.
[0021] The center thickness of each lens and the air gap between adjacent elements satisfy the following conditions: the center thickness of the first lens L1 is 2.6–3.6 mm, the center thickness of the second lens L2 is 0.8–1.6 mm, the center thickness of the third lens L3 is 2.6–3.6 mm, the center thickness of the fourth lens L4 is 2.6–3.6 mm, the center thickness of the fifth lens L5 is 2.8–3.6 mm, the center thickness of the sixth lens L6 is 1.0–2.0 mm, the center thickness of the seventh lens L7 is 2.6–3.6 mm, and the center thickness of the eighth lens L8 is 3.2–4.2 mm. The aperture stop is located between the fourth lens L4 and the fifth lens L5. The air gap between the aperture stop and the fourth lens L4 is 0.1–0.3 mm, and the air gap between the aperture stop and the fifth lens L5 is 0.1–0.2 mm. The air gap between the second lens L2 and the third lens L3 is 3.0–4.0 mm. The air gap between the fourth lens L4 and the fifth lens L5 is 0.1–0.3 mm. The air gap between the sixth lens L6 and the seventh lens L7 is 3.5–4.5 mm. The air gap between the seventh lens L7 and the eighth lens L8 is 0.1–0.15 mm.
[0022] The cover glass has a thickness of 0.17 mm, a refractive index of 1.51, and an Abbe number of 63.4; the liquid layer has a thickness of 0.6 mm, a refractive index of 1.33, and an Abbe number of 54.
[0023] The high numerical aperture water immersion microscope objective of this invention will be further described in detail below with reference to specific parameters and accompanying drawings: I. Parameter Settings for Implementation Examples In this embodiment, the specific optical parameters of the high numerical aperture water immersion microscope objective are as follows: Radius of curvature (unit: mm): First lens L1: convex surface (facing the image side) 7.811, flat surface (near L2) infinity; Second lens L2: concave surface (near L3) 4.148, flat surface (near L1) infinite; Third lens L3: concave (near L2) -4.628, flat (near L4) infinity; Fourth lens L4: Convex surface (near L3) -8.542, flat surface (near the aperture stop) infinity; Fifth lens L5: 10.730 near the aperture stop, -10.867 near L6; Sixth lens L6: concave (near L5) -10.867, flat (near L7) infinity; Seventh lens L7: concave surface (near L6) 6.956, convex surface (near L8) 24.111; Eighth lens L8: concave surface (close to L7) 3.838, convex surface (close to the liquid layer) 1.763.
[0024] The refractive index and Abbe number are respectively: First lens L1: 1.79, 25.5; Second lens L2: 1.50, 64.0; Third lens L3: 1.92, 18.0; Fourth lens L4: 1.86, 40.0; Fifth lens L5: 1.70, 55.0; Sixth lens L6: 1.92, 18.0; Seventh lens L7: 1.78, 46.5; Eighth lens L8: 1.91, 35.0.
[0025] Center thickness and spacing (unit: mm): Lens center thickness: L1=3.300, L2=1.300, L3=3.300, L4=3.300, L5=3.400, L6=1.450, L7=3.000, L8=3.500; Air gaps: L2 and L3 = 4.000, L4 and aperture = 0.170, aperture and L5 = 0.100, L4 and L5 = 0.270, L6 and L7 = 4.000, L7 and L8 = 0.100; Auxiliary components: Cover glass thickness 0.17mm, liquid layer thickness 0.6mm, image plane H-K5 glass.
[0026] II. System Performance Indicators and Verification The high numerical aperture water immersion microscope objective of this embodiment is applicable to the wavelength range of 785nm to 850nm, with a focal length of 4.75mm, a numerical aperture of 0.9, a full-field image height of 0.707mm, and a total system length of 31.29mm. Optical performance simulation was performed using Zemax OpticStudio software, and the results are as follows: Aberration correction: such as Figure 2 (Light aberration curve) Figure 3-5 As shown in the wavefront aberration curve, within the 785nm~850nm band, the wavefront aberration peak value (PV) ≤ 0.25 wavefront and the root mean square value (RMS) ≤ 0.05 wavefront, indicating excellent aberration correction effect and effectively ensuring image clarity. Resolution: such as Figure 6 As shown in the MTF curve, the MTF value is close to the diffraction limit across the entire field of view, and the MTF is ≥0.3 at 2400 periods / mm, which meets the requirements for high-resolution imaging. Distortion control: such as Figure 9As shown in the distortion curve, the system distortion rate is ≤1%, which meets the stringent distortion requirements of precision microscopic imaging. Stability: such as Figure 7 (Axial aberration curve) Figure 8 As shown in the field curvature curve, the axial aberration is ≤2μm, the field curvature is ≤0.1mm, the imaging plane has good stability, and it is suitable for long-term observation scenarios.
[0027] The above description is merely a preferred embodiment of this utility model, but the protection scope of this utility model is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this utility model should be included within the protection scope of this utility model. Therefore, the protection scope of this utility model should be determined by the scope of the claims.
Claims
1. A high numerical aperture water immersion microscope objective, characterized in that: Along the optical axis from image side to object side, the lens comprises, in sequence, a first lens (L1), a second lens (L2), a third lens (L3), a fourth lens (L4), an aperture stop, a fifth lens (L5), a sixth lens (L6), a seventh lens (L7), and an eighth lens (L8), with a liquid layer and a coverslip placed between the eighth lens (L8) and the sample; each lens has a standard spherical or planar surface; the first lens (L1) is a plano-convex lens with positive optical power, its planar surface facing the object side and its convex surface facing the image side; the second lens (L2) is a plano-concave lens with negative optical power, its planar surface facing the image side and its concave surface facing the object side; the first lens (L1) and the second lens (L2) are cemented together to form a first cemented doublet lens group; the third lens (L3) is a negative optical power... The first lens is a plano-concave lens with its flat surface facing the object side and its concave surface facing the image side; the second lens (L4) is a plano-convex lens with positive optical power, with its convex surface facing the object side and its flat surface facing the image side; the third lens (L3) and the fourth lens (L4) are cemented together to form a second cemented doublet lens group; the third lens (L5) is a biconvex lens with positive optical power; the fourth lens (L6) is a plano-concave lens with negative optical power, with its concave surface facing the object side and its flat surface facing the image side; the fifth lens (L5) and the sixth lens (L6) are cemented together to form a third cemented doublet lens group; the fifth lens (L7) is a meniscus lens with positive optical power, with its concave surface facing the object side and its convex surface facing the image side; the fifth lens (L8) is a meniscus lens with positive optical power, with its concave surface facing the object side and its convex surface facing the image side.
2. The high numerical aperture water immersion microscope objective as described in claim 1, characterized in that: The optical power of the first cemented doublet lens group is negative; the optical power of the second cemented doublet lens group is negative; and the optical power of the third cemented doublet lens group is positive.
3. The high numerical aperture water immersion microscope objective as described in claim 1, characterized in that, The radii of curvature of each lens satisfy the following conditions: the radius of curvature of the first lens (L1) facing the image side is 7.5–8.5 mm, and the radius of curvature near the second lens (L2) is infinite; the radius of curvature of the second lens (L2) near the third lens (L3) is 3.5–4.5 mm, and the radius of curvature near the first lens (L1) is infinite; the radius of curvature of the third lens (L3) near the second lens (L2) is -4.5 to -3.5 mm, and the radius of curvature near the fourth lens (L4) is infinite; the radius of curvature of the fourth lens (L4) near the aperture stop is -7.5–8.5 mm, and the radius of curvature near the third lens (L3) is infinite; the fifth lens (L5)... The radius of curvature on the side near the aperture stop is 10.5–11.5 mm, and the radius of curvature on the side near the sixth lens (L6) is -11.5–-10.5 mm; the radius of curvature of the sixth lens (L6) near the seventh lens (L7) is infinite, and the radius of curvature on the side near the fifth lens (L5) is -11.5–-10.5 mm; the radius of curvature of the seventh lens (L7) near the sixth lens (L6) is 6.5–7.5 mm, and the radius of curvature on the side near the eighth lens (L8) is 23.7–24.7 mm; the radius of curvature of the eighth lens (L8) near the seventh lens (L7) is 3.2–4.2 mm, and the radius of curvature on the side near the liquid layer is 1.2–2.2 mm.
4. A high numerical aperture water immersion microscope objective as described in claim 1, characterized in that, The refractive indices and Abbe numbers of each lens satisfy the following conditions: the first lens (L1) has a refractive index of 1.79–1.81 and an Abbe number of 25–26; the second lens (L2) has a refractive index of 1.45–1.55 and an Abbe number of 64–65; the third lens (L3) has a refractive index of 1.85–1.95 and an Abbe number of 17–20; and the fourth lens (L4) has a refractive index of 1.80–1.90 and an Abbe number of… The refractive index of the fifth lens (L5) is 1.70–1.80, and the Abbe number is 52–56; the refractive index of the sixth lens (L6) is 1.85–1.95, and the Abbe number is 17–20; the refractive index of the seventh lens (L7) is 1.72–1.82, and the Abbe number is 45–48; the refractive index of the eighth lens (L8) is 1.85–1.95, and the Abbe number is 33–36.
5. A high numerical aperture water immersion microscope objective as described in claim 1, characterized in that, The center thickness of each lens and the air gap between adjacent elements satisfy the following conditions: the center thickness of the first lens (L1) is 2.6–3.6 mm, the center thickness of the second lens (L2) is 0.8–1.6 mm, the center thickness of the third lens (L3) is 2.6–3.6 mm, the center thickness of the fourth lens (L4) is 2.6–3.6 mm, the center thickness of the fifth lens (L5) is 2.8–3.6 mm, the center thickness of the sixth lens (L6) is 1.0–2.0 mm, the center thickness of the seventh lens (L7) is 2.6–3.6 mm, and the center thickness of the eighth lens (L8) is 3.2–4.2 mm; the light... The aperture stop is located between the fourth lens (L4) and the fifth lens (L5). The air gap between the aperture stop and the fourth lens (L4) is 0.1-0.3 mm, and the air gap between the aperture stop and the fifth lens (L5) is 0.1-0.2 mm. The air gap between the second lens (L2) and the third lens (L3) is 3.0-4.0 mm. The air gap between the fourth lens (L4) and the fifth lens (L5) is 0.1-0.3 mm. The air gap between the sixth lens (L6) and the seventh lens (L7) is 3.5-4.5 mm. The air gap between the seventh lens (L7) and the eighth lens (L8) is 0.1-0.15 mm.
6. A high numerical aperture water immersion microscope objective as described in claim 1, characterized in that: The cover glass has a thickness of 0.17 mm, a refractive index of 1.51, and an Abbe number of 63.4; the liquid layer has a thickness of 0.6 mm, a refractive index of 1.33, and an Abbe number of 54.