Large field long working distance low aberration flat field apochromatic microscope objective

Abstract

The application relates to the technical field of optical lenses, and discloses a large-view-field long-working-distance low-aberration flat-field compound-apochromatic microscopic objective lens, which comprises, in sequence from left to right along an optical axis, a first lens group, a second lens group, a diaphragm, a third lens group and a fourth lens group. The first lens group is composed of a first lens to a fifth lens; the second lens group is composed of a sixth lens to an eighth lens and contains a three-glued lens; the third lens group is composed of a ninth lens to a fourteenth lens and contains two two-glued lenses; and the fourth lens group is composed of a thirteenth lens to a fourteenth lens. In the beneficial effects of the microscopic objective lens, the field of view of the objective lens reaches 2.3 mm, the working distance reaches 8.5 mm, and the transverse aberration is not more than 2.5 um. Meanwhile, the imaging quality of each field of view is excellent, and the chromatic aberration is well corrected in a 400-700 nm waveband. In addition, the lens edge thickness, center thickness, blockage rate and air gap are considered in the design, so that the machining and assembling difficulties are reduced.

Description

Technical Field

[0001] This invention relates to a microscope objective, and more particularly to a large field-of-view, long working distance, low-aberration plan apochromatic microscope objective. Background Technology

[0002] The microscope objective is the most important component of a microscope, and its imaging quality directly affects the overall performance of the microscope. With the development of microscopic imaging technology, research-grade microscopes have placed demands on larger fields of view and higher imaging quality. A large field of view means that the microscope can provide images covering a wider area, while high imaging quality means higher fidelity to the original image. To achieve this, the aberrations of the microscope objectives need to be optimized more effectively, and aberration correction for large fields of view at the edges must also be considered during the design process. At the same time, microscope objectives with long working distances offer greater compatibility in optical path setup, and can be widely used in scenarios such as wafer inspection, probe stations, and sample observation in vacuum environments.

[0003] With the diversification of scientific research applications, the demand for microscope objectives with large fields of view, long working distances, and low aberrations is increasing. Traditional designs, due to immature technology, cannot balance all aspects and can only selectively retain certain parameters. For example, CN114326071A states that traditional objective design technology must strike a balance between numerical aperture, planarity, and chromatic aberration correction.

[0004] Therefore, how to ensure that the multi-dimensional performance parameters of microscope objectives meet the requirements of application scenarios and design more comprehensive and optimized modern lenses is an urgent problem to be solved. Summary of the Invention

[0005] The purpose of this invention is to provide a research-grade plan-field apochromatic microscope objective with a large field of view, an ultra-long working distance, and high-quality imaging capabilities.

[0006] The technical solution adopted in this invention is as follows:

[0007] A large field-of-view, long working distance, low aberration plan apochromatic microscope objective consists of a first lens group (G1), a second lens group (G2), a third lens group (G3), and a fourth lens group (G4) arranged sequentially along the optical axis from the object side to the image side.

[0008] An aperture stop (STO) is provided between the second lens group (G2) and the third lens group (G3);

[0009] The power distribution of the first lens group (G1), the second lens group (G2), the third lens group (G3), and the fourth lens group (G4) conforms to the odd symmetry of "negative-negative-positive-positive".

[0010] Its further features are:

[0011] The ratios of the focal lengths fg3 of the third lens group (G3) and fg4 of the fourth lens group (G4) to the total focal length f of the microscope objective satisfy the following stable characteristic relationship:

[0012] Relationship 1: 1.78 ≤ fg³ / f ≤ 3.23;

[0013] Relationship 2: 0.74≤fg4 / f≤0.97.

[0014] The first lens group (G1) has negative optical power and is composed of a first lens (L1), a second lens (L2), a third lens (L3), a fourth lens (L4), and a fifth lens (L5).

[0015] The second lens group (G2) has negative optical power and consists of a sixth lens (L6), a seventh lens (L7), and an eighth lens (L8);

[0016] The third lens group (G3) has positive optical power and is composed of the ninth lens (L9), the tenth lens (L10), the eleventh lens (L11), and the twelfth lens (L12).

[0017] The fourth lens group (G4) has positive optical power and is composed of the thirteenth lens (L13) and the fourteenth lens (L14).

[0018] The sixth lens (L6), the seventh lens (L7), and the eighth lens (L8) are cemented triplet lenses; the ninth lens (L9) and the tenth lens (L10) are cemented doublet lenses; and the eleventh lens (L11) and the twelfth lens (L12) are cemented doublet lenses.

[0019] The focal lengths (f7) of the seventh lens (L7), (f10) of the tenth lens (L10), and (f11) of the eleventh lens (L11) are made of ultra-low dispersion glass material HFK95N to achieve achromatic aberration. Furthermore, the focal length ratios within each lens group (f7, f10, f11, and fg2 of the second lens group (G2) and fg3 of the third lens group (G3) satisfy the following stable characteristic relationship:

[0020] Relationship 3: -0.40≤f7 / fg2≤-0.06;

[0021] Relationship 4: 0.45 ≤ f10 / fg3 ≤ 0.91;

[0022] Relationship 5: 0.42≤f11 / fg3≤0.81.

[0023] The fourteenth lens (L14) has positive refractive power, converting light rays from the object into converging rays and guiding them to the thirteenth lens (L13). The radius of curvature r24 of the concave surface of the fourteenth lens (L14) near the object satisfies the following stable characteristic relationship with the total focal length f:

[0024] Relation 6: 0.585≤r24 / f≤0.734.

[0025] The focal length f4 of the fourth lens (L4) and the focal length fg1 of the first lens group (G1) satisfy the following stable characteristic relationship:

[0026] Relationship 7: 0.019≤|f4 / fg1|≤0.129.

[0027] The total focal length f of the microscope objective is 19–21 mm, and the parfocal distance of the optical system is 94–96 mm.

[0028] The first lens (L1), second lens (L2), third lens (L3), fourth lens (L4), and fifth lens (L5) in the first lens group (G1) are all made of glass. The refractive index and Abbe number of the first lens (L1) are n1 and v1, respectively; the refractive index and Abbe number of the second lens (L2) are n2 and v2, respectively; 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; and the refractive index and Abbe number of the fifth lens (L5) are n5 and v5, respectively. The refractive index and Abbe number of the first lens (L1) to the fifth lens (L5) satisfy the following range of values:

[0029] 1.8≤n1≤2.0,23≤v1≤25;1.9≤n2≤2.1,17≤v2≤19;1.5≤n3≤1.7,40≤v3≤42;1.9≤n4≤2.1,17≤v4≤19;1.7≤n5≤1.9,44≤v5≤46。

[0030] The sixth lens (L6), the seventh lens (L7), and the eighth lens (L8) in the second lens group (G2) are all made of glass. 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.

[0031] The refractive index and Abbe number of the eighth lens (L8) are n8 and v8, respectively, and the refractive index and Abbe number of the sixth lens (L6) to the eighth lens (L8) satisfy the following range of values:

[0032] 1.6≤n6≤1.8,40≤v6≤42;1.4≤n7≤1.6,94≤v7≤96;1.9≤n8≤2.1,17≤v8≤19。

[0033] The ninth lens (L9), tenth lens (L10), eleventh lens (L11), and twelfth lens (L12) in the third lens group (G3) are all made of glass. The refractive index and Abbe number of the ninth lens (L9) are n9 and v9, respectively; the refractive index and Abbe number of the tenth lens (L10) are n10 and v10, respectively; the refractive index and Abbe number of the eleventh lens (L11) are n11 and v11, respectively; and the refractive index and Abbe number of the twelfth lens (L12) are n12 and v12, respectively.

[0034] The refractive index and Abbe number of the ninth lens (L9) to the twelfth lens (L12) satisfy the following range:

[0035] 1.9≤n9≤2.1,17≤v9≤19;1.4≤n10≤1.6,94≤v10≤96;1.4≤n11≤1.6,94≤v11≤96;1.4≤n12≤1.6,66≤v12≤68。

[0036] The thirteenth lens (L13) and the fourteenth lens (L14) in the fourth lens group (G4) are both made of glass. The refractive index and Abbe number of the thirteenth lens (L13) are n13 and v13, respectively. The refractive index and Abbe number of the fourteenth lens (L14) are n14 and v14, respectively.

[0037] The refractive index and Abbe number of the thirteenth lens (L13) and the fourteenth lens (L14) satisfy the following range: 1.7≤n13≤1.9, 27≤v13≤29; 1.9≤n14≤2.1, 17≤v14≤19.

[0038] The beneficial effects of this invention are:

[0039] (1) Based on the principle that the material refractive index difference corresponding to adjacent wavelength intervals is the same, a total of 7 wavelengths (400-700nm) are set in the microscope objective spectrum, which is more comprehensive for the correction of aberrations of different colors of light, especially chromatic aberration.

[0040] (2) In the image quality evaluation of the microscope objectives, the Strell ratio of each field of view (except for the off-axis 3.3° field of view) in the working wavelength range of 400-700nm is almost greater than 0.95, which is approximately aberration-free; while the Strell ratio of the outermost field of view (off-axis 3.3° field of view) is also greater than 0.8 in the range of 406-700nm, reaching the diffraction limit.

[0041] (3) The field of view of the microscope objective reaches Ø2.3mm and the working distance reaches 8.5mm.

[0042] (4) The incident angle and exit angle of each lens of the microscope objective are <35°, resulting in small higher-order aberrations.

[0043] (5) The edge thickness, center thickness, blockage rate and air gap of each lens of the microscope objective are moderate, which is conducive to processing and assembly. Attached Figure Description

[0044] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments are briefly described below. It should be understood that the following drawings only show some embodiments of this application and therefore do not represent a limitation on the scope. For those skilled in the art, other drawings can be obtained from the following drawings without creative effort, and these drawings all fall within the protection scope of the present invention.

[0045] Figure 1 This is a schematic diagram of the structure of the microscope objective of Embodiment 1 of the present invention.

[0046] Figure 2 This is a graph showing the Strell ratio of the microscope objective in different fields of view as a function of wavelength in Embodiment 1 of the present invention.

[0047] Figure 3 This is the MTF plot of the microscopic object quality evaluation of Example 1 of the present invention.

[0048] Figure 4 This is a longitudinal spherical aberration diagram of the microscope objective of Embodiment 1 of the present invention.

[0049] Figure 5 This is a color focus shift diagram of the microscope objective of Embodiment 1 of the present invention.

[0050] Figure 6 This is a schematic diagram of the structure of the microscope objective of Embodiment 2 of the present invention.

[0051] Figure 7 This is a graph showing the Strell ratio of the microscope objective in different fields of view as a function of wavelength in Embodiment 2 of the present invention.

[0052] Figure 8 This is an MTF chart for evaluating the image quality of the microscope objective in Embodiment 2 of the present invention.

[0053] Figure 9 This is a longitudinal spherical aberration diagram of the microscope objective of Embodiment 2 of the present invention.

[0054] Figure 10 This is a color focus shift diagram of the microscope objective of Embodiment 2 of the present invention. Detailed Implementation

[0055] To more clearly illustrate the technical solution of this invention, a detailed and complete description will be provided below with reference to the accompanying drawings. It should be noted that the following embodiments are only some embodiments of this invention and do not represent a limitation on the scope of protection. Those skilled in the art can make similar extensions without departing from the spirit of this invention, and these extended embodiments are still within the scope of protection of this invention without involving inventive effort.

[0056] Example 1

[0057] This invention discloses a large field of view, long working distance, low aberration plan apochromatic microscope objective, consisting of a first lens group G1, a second lens group G2, a third lens group G3, and a fourth lens group G4 arranged sequentially along the optical axis from the object side to the image side.

[0058] An aperture stop STO is provided between the second lens group G2 and the third lens group G3.

[0059] The function of the first lens group G1 is to balance aberrations and control the optical path to match the entrance pupil diameter.

[0060] The function of the second lens group G2 and the third lens group G3 is to achromatic; the function of the fourth lens group G4 is to collect light into the microscope objective.

[0061] Among these four lens groups, the focal lengths fg3 of the third lens group G3 and fg4 of the fourth lens group G4 have distinct characteristics and exhibit stable refractive power during the design process. The ratios of their focal lengths fg3 and fg4 to the total focal length f of the microscope objectives satisfy the following characteristic relationship:

[0062] The range of values ​​for the relational expressions mentioned in this invention is derived from specific data in the lens document examples included in the design process. Example 1 is a preferred embodiment. The relational expressions can take multiple values ​​within the range. This description applies to relations 1 through 7.

[0063] Relation 1: 1.78 ≤ fg3 / f ≤ 3.23.

[0064] The possible values ​​for fg3 / f are 1.78, 1.98, 2.44, 2.94, 3.23, etc.

[0065] In this embodiment, the value is fg3 / f = 1.98.

[0066] Relationship 2: 0.74≤fg4 / f≤0.97.

[0067] The values ​​of fg4 / f can be 0.74, 0.77, 0.80, 0.87, 0.97, etc.

[0068] In this embodiment, the value is fg4 / f = 0.76.

[0069] The following describes the lens information that makes up this microscope objective, grouped by component:

[0070] The first lens group G1 has negative optical power and a focal length fg1 of -108.612mm. It consists of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, and the fifth lens L5.

[0071] The first lens L1 has a convex surface facing the object side and a concave surface facing the image side, and its focal length is 45.518mm;

[0072] The second lens L2 has a convex surface facing the object side and a concave surface facing the image side, and its focal length is 205.283 mm;

[0073] The third lens L3 has a convex surface facing the object side and a concave surface facing the image side, and its focal length is -65.305mm;

[0074] The fourth lens L4 has a concave surface facing both the object side and the image side, and its focal length is -12.608mm.

[0075] The fifth lens L5 has a concave surface facing the object side and a convex surface facing the image side, and its focal length is 399.464 mm.

[0076] The second lens group G2 has negative optical power and a focal length of -111.590mm. It consists of the sixth lens L6, the seventh lens L7, and the eighth lens L8.

[0077] The sixth lens L6 has a convex surface facing the object side and a concave surface facing the image side, and its focal length is 297.846 mm.

[0078] The seventh lens L7 has a convex surface facing both the object side and the image side, and its focal length is -34.648mm.

[0079] The eighth lens L8 has a concave surface facing the object side and a convex surface facing the image side, and its focal length is -69.221mm.

[0080] The third lens group G3 has positive optical power and a focal length of 39.508mm. It consists of the ninth lens L9, the tenth lens L10, the eleventh lens L11, and the twelfth lens L12.

[0081] The ninth lens L9 has a convex surface facing the object side and a concave surface facing the image side, and its focal length is 312.628 mm.

[0082] The tenth lens L10 has a convex surface facing both the object side and the image side, and its focal length is -211.426mm.

[0083] The eleventh lens L11 has a convex surface facing both the object side and the image side, and its focal length is 66.221 mm.

[0084] The twelfth lens L12 has a concave surface facing both the object side and the image side, and its focal length is -37.727mm.

[0085] The fourth lens group G4 has positive optical power and a focal length of 15.155mm, and consists of the thirteenth lens L13 and the fourteenth lens L14.

[0086] The thirteenth lens L13 has a convex surface facing both the object side and the image side, and its focal length is 35.269 mm.

[0087] The fourteenth lens L14 has a convex surface facing the object side and a concave surface facing the image side, and its focal length is 29.235mm.

[0088] As mentioned above, this microscope objective exhibits an odd symmetry in its optical power distribution, following a "negative-negative-positive-positive" pattern. This odd symmetry can be analyzed by examining the sequence of light rays passing through the lens. When light rays emitted from the observed object pass through the fourth lens group G4, the optical power of G4 should be positive to reduce the objective aperture. When the light rays pass through the third lens group G3, the optical power of G3 is positive, and the light continues to converge, which helps reduce the aperture and introduce higher-order aberrations. When the light rays pass through the second lens group G2 and the first lens group G1, due to the system's 20mm limitation on the entrance pupil size, a certain aperture size is required; therefore, the optical powers of the second lens group G2 and the first lens group G1 should ideally be negative. In summary, the odd symmetry of the "negative-negative-positive-positive" optical power distribution contributes to a more uniform optical power distribution and a smoother optical path.

[0089] Next, the significant aberrations produced by the lens are analyzed:

[0090] (1) In the early design process of this embodiment, spherical aberration is the most significant aberration, with a maximum value of up to 1 mm. Therefore, in the later design, the sum of the squares of the spherical aberrations generated by each sphere was written into the constraint function. However, spherical aberration is still the second most significant aberration in this embodiment.

[0091] In this embodiment, the spherical surfaces of the seventh lens L7 and the tenth lens L10 near the image side produce significant positive spherical aberration; the spherical surfaces of the tenth lens L10 and the thirteenth lens L13 near the image side produce significant negative spherical aberration. The values ​​of the positive and negative spherical aberrations are roughly equivalent and cancel each other out.

[0092] (2) Axial chromatic aberration is the most significant aberration produced by the lens in this embodiment. To optimize chromatic aberration, this embodiment uses three ultra-low dispersion glass HFK95N pieces placed near the aperture stop STO to achieve achromatic aberration. The upper and lower rays of the on-axis field of view and the off-axis field of view, along with the principal ray, converge after passing through the aperture stop STO and are incident on almost the same area of ​​the aperture of the seventh lens L7 and the tenth lens L10, which can simultaneously correct the chromatic aberration of the on-axis field of view and the off-axis field of view.

[0093] As mentioned above, the sixth lens L6, the seventh lens L7, and the eighth lens L8 are cemented triplet lenses; the ninth lens L9 and the tenth lens L10 are cemented doublet lenses; and the eleventh lens L11 and the twelfth lens L12 are cemented doublet lenses.

[0094] In the cemented lens, the focal lengths f7 of the seventh lens L7, f10 of the tenth lens L10, and f11 of the eleventh lens L11 are made of CDGM (Chengdu Guangming) ultra-low dispersion glass material HFK95N to achieve achromaticity. The focal length ratios of each lens (f7, f10, f11) and the focal lengths of the second lens group G2 and the third lens group G3 satisfy the following stable characteristic relationship:

[0095] Relationship 3: -0.40≤f7 / fg2≤-0.06.

[0096] The values ​​for f7 / fg2 can be -0.40, -0.34, -0.17, -0.11, -0.06, etc.

[0097] In this embodiment, the value is f7 / fg2 = -0.15.

[0098] Relationship 4: 0.45≤f10 / fg3≤0.91.

[0099] The values ​​for f10 / fg3 can be 0.45, 0.60, 0.72, 0.80, 0.91, etc.

[0100] In this embodiment, the value is f10 / fg3 = 0.72.

[0101] Relationship 5: 0.42≤f11 / fg3≤0.81.

[0102] The values ​​of f11 / fg3 can be 0.42, 0.54, 0.60, 0.75, 0.81, etc.

[0103] In this embodiment, the value is f11 / fg3 = 0.75.

[0104] In this embodiment, the fourteenth lens L14 has positive refractive power, converting light rays from the object into converging light rays and guiding them to the thirteenth lens L13. The radius of curvature r24 of the concave surface of the fourteenth lens L14 near the object satisfies the following stable characteristic relationship with the total focal length f:

[0105] Relation 6: 0.585≤r24 / f≤0.734.

[0106] The possible values ​​for r24 / f are 0.585, 0.630, 0.680, 0.700, 0.734, etc.

[0107] In this embodiment, the value is: r24 / f = 0.60.

[0108] In the microscope objective of this embodiment, the fourth lens L4 has the largest negative optical power among all lenses, and plays a role in influencing the optical path trend in the first lens group G1. The overall optical path trend of the second, third, and fourth lens groups G2, G3, and G4 is relatively smooth, and is influenced by the first lens group G1.

[0109] In this embodiment, the focal length f4 of the fourth lens L4 and the focal length fg1 of the first lens group G1 satisfy the following stable characteristic relationship:

[0110] Relationship 7: 0.019≤|f4 / fg1|≤0.129.

[0111] The values ​​of |f4 / fg1| can be 0.019, 0.037, 0.098, 0.115, 0.129, etc.

[0112] In this embodiment, the value is: |f4 / fg1|=0.12.

[0113] The total focal length of the microscope objective is 19.9997 mm, and the parfocal distance of the optical system is 95 mm.

[0114] The optical performance parameters of this embodiment 1 are shown in Table 1:

[0115]

[0116] Table 1

[0117] The specific values ​​of the characteristic relation in Example 1 are shown in Table 2:

[0118]

[0119] Table 2

[0120] In this embodiment, the specific parameters of each lens of the microscope objective are shown in Table 3. The "Surface Number" column indicates the number of each surface from the object plane to the image plane; the "Radius of Curvature (mm)" column gives the radius of curvature of each surface; the "Thickness / Spacing (mm)" column gives the axial distance between two adjacent surfaces. If the two surfaces belong to the same lens, the value of "Thickness / Spacing (mm)" represents the center thickness of the lens; otherwise, it represents the distance from the object plane or image plane to the lens or the air gap between adjacent lenses; "N" d "One column indicates the refractive index of each lens between the object plane and the image plane; "V d The "Abbe number" column indicates the Abbe number of each lens between the object plane and the image plane; the "aperture (mm)" column indicates the aperture value of the surface of each lens between the object plane and the image plane.

[0121]

[0122] Table 3

[0123] In this embodiment, regarding supplementary explanations for image quality evaluation, when observing a point light source, for an aberration-free optical system, the light beam converges to a single point at the imaging position; however, in an aberration-prone optical system, the light beam does not converge and will diffuse to some extent. When the light-gathering ratio of the imaging plane in an aberration-free optical system is taken as 100%, the light-gathering ratio in an aberration-prone optical system is called the Strehl ratio. Generally, 80% of the Strehl ratio is called the diffraction limit; in general observation, if the Strehl ratio exceeds 95%, its performance can be considered comparable to that of an aberration-free lens.

[0124] Figure 2 This graph shows the Strell ratio versus wavelength for different fields of view. From left to right, the labels are: "Approximately no aberration," "Diffraction limit," "3.3° off-axis," "2.81° off-axis," "2.31° off-axis," "1.65° off-axis," and "On-axis." The graph shows that, except for the maximum "3.3° off-axis" field of view, the Strell ratios for other fields of view are almost all above 95% in the 400–700 nm spectrum, indicating very excellent imaging quality. Furthermore, the Strell ratio for the "3.3° off-axis" field of view also reaches above the diffraction limit in the 406–700 nm spectrum.

[0125] In image quality evaluation, a crucial reference factor is the MTF (Modulation Transfer Function) curve. MTF represents the degree of contrast (i.e., amplitude) attenuation after a sinusoidal intensity distribution function at various frequencies is imaged by an optical system. When the contrast at a certain frequency drops to zero, it indicates that the light intensity distribution at that frequency has no brightness change, meaning that frequency has been cut off. The Strell ratio mentioned above can be considered as the integral value under the MTF curve, i.e., the area.

[0126] Figure 3 The MTF curves for the microscope objectives of Example 1 are presented, showing that the MTF for each field of view is close to the diffraction limit. Since the MTF is related to both the aberrations and diffraction effects of the optical system, it is an objective and reliable method for evaluating the imaging quality of the optical system. It should also be noted that the design logic prioritizes optimizing optical performance before considering practical factors such as lens manufacturability. If only optical performance is considered, the MTF curve would have a higher degree of overlap with the diffraction limit.

[0127] Figure 4 This is a longitudinal spherical aberration diagram of the microscope objective in Example 1. Figure 4 The longitudinal spherical aberration in the 0.707 band is less than 1 μm, and it can be seen that the longitudinal spherical aberration is well corrected across the entire aperture range. The longitudinal spherical aberration on the axis at the maximum wavelength of 700 nm does not exceed 2.5 μm.

[0128] For objectives with NA 0.5, to achieve apochromatic design, the relationship between maximum focus shift and depth of focus should also be considered; the maximum focus shift should not exceed half the depth of focus. The depth of focus δ is calculated using the Berek formula:

[0129]

[0130] In the formula, ω is the resolution of the naked eye, taken as 0.0014 rad; M is the total magnification, taken as 100 (objective magnification x eyepiece magnification); λ is the center wavelength, taken as 0.486 μm. Therefore, the depth of focus δ can be calculated to be 8.0 μm.

[0131] Figure 5 The figure shows the chromatic focus shift curve for Example 1. As can be seen from the figure, within the 400–700 nm wavelength range, the maximum focus shift of the microscope objective does not exceed 2.5 μm, which is less than 1 / 2 of the depth of focus, thus achieving the apochromatic design.

[0132] Example 2

[0133] In addition to Example 1, this application provides another Example 2. The only difference between Example 2 and Example 1 is the spectrum used in the system data. The spectrum used in Example 1 is 400-700 nm, and seven wavelengths are set according to the principle that the material refractive index difference corresponding to adjacent wavelengths is the same; the spectrum used in Example 2 is the three wavelength bands (d, F, C) of the conventional visual optical system.

[0134] Since the spectrum of Example 1 covers the spectrum of Example 2 well, Example 2 can be obtained by transplanting Example 1 (the glass material of the thirteenth lens L13 was changed in order to perform optimization).

[0135] The following explains the characteristic relationships and optical parameters that differ from those in Example 1:

[0136] Due to the similarity to Embodiment 1, the lens grouping remains the same: first lens group G1, second lens group G2, third lens group G3, and fourth lens group G4 arranged sequentially along the optical axis from the object side to the image side.

[0137] An aperture stop STO is provided between the second lens group G2 and the third lens group G3.

[0138] Among these four lens groups, the focal lengths fg3 of the third lens group G3 and fg4 of the fourth lens group G4 have distinct characteristics. The ratios of the focal lengths fg3 and fg4 to the total focal length f of the microscope objectives satisfy the following characteristic relationship:

[0139] The range of values ​​for the relational expressions mentioned in this invention is derived from specific data in the lens document examples included in the design process. Example 2 is a preferred embodiment. The relational expressions can take multiple values ​​within the range. This description applies to relations 1 through 7.

[0140] Relation 1: 1.78 ≤ fg3 / f ≤ 3.23.

[0141] The possible values ​​for fg3 / f are 1.78, 1.98, 2.44, 2.94, 3.23, etc.

[0142] In this embodiment, the value is fg3 / f = 1.96.

[0143] Relationship 2: 0.74≤fg4 / f≤0.97.

[0144] The values ​​of fg4 / f can be 0.74, 0.77, 0.80, 0.87, 0.97, etc.

[0145] In this embodiment, the value is fg4 / f = 0.76.

[0146] The following describes the lens information that makes up this microscope objective, grouped by component:

[0147] The first lens group G1 has negative optical power and a focal length fg1 of -108.381mm. It consists of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, and the fifth lens L5.

[0148] The first lens L1 has a convex surface facing the object side and a concave surface facing the image side, and its focal length is 44.184 mm.

[0149] The second lens L2 has a convex surface facing the object side and a concave surface facing the image side, and its focal length is 144.847 mm.

[0150] The third lens L3 has a convex surface facing the object side and a concave surface facing the image side, and its focal length is -74.797mm.

[0151] The fourth lens L4 has a concave surface facing both the object side and the image side, and its focal length is -11.945mm.

[0152] The fifth lens L5 has a concave surface facing the object side and a convex surface facing the image side, and its focal length is 354.957mm.

[0153] The second lens group G2 has negative optical power and a focal length of -153.527mm. It consists of the sixth lens L6, the seventh lens L7, and the eighth lens L8.

[0154] The sixth lens L6 has a convex surface facing the object side and a concave surface facing the image side, and its focal length is -41.274mm.

[0155] The seventh lens L7 has a convex surface facing both the object side and the image side, and its focal length is 17.687 mm.

[0156] The eighth lens L8 has a concave surface facing the object side and a convex surface facing the image side, and its focal length is -23.605mm.

[0157] The third lens group G3 has positive optical power and a focal length of 39.228mm. It consists of the ninth lens L9, the tenth lens L10, the eleventh lens L11, and the twelfth lens L12.

[0158] The ninth lens L9 has a convex surface facing the object side and a concave surface facing the image side, and its focal length is -98.442mm.

[0159] The tenth lens L10 has a convex surface facing both the object side and the image side, and its focal length is 31.319 mm.

[0160] The eleventh lens L11 has a convex surface facing both the object side and the image side, and its focal length is 27.068 mm.

[0161] The twelfth lens L12 has a concave surface facing both the object side and the image side, and its focal length is -21.500mm.

[0162] The fourth lens group G4 has positive optical power and a focal length of 15.115mm, and consists of the thirteenth lens L13 and the fourteenth lens L14.

[0163] The thirteenth lens L13 has a concave surface facing the object side and a convex surface facing the image side, and its focal length is 41.781 mm.

[0164] The fourteenth lens L14 has a convex surface facing the object side and a concave surface facing the image side, and its focal length is 25.245mm.

[0165] As mentioned above, the sixth lens L6, the seventh lens L7, and the eighth lens L8 are cemented triplet lenses; the ninth lens L9 and the tenth lens L10 are cemented doublet lenses; and the eleventh lens L11 and the twelfth lens L12 are cemented doublet lenses.

[0166] In the cemented lens, the focal length of the seventh lens L7 is f7, the focal length of the tenth lens L10 is f10, and the focal length of the eleventh lens L11 is f11. The focal length ratios within the second lens group G2 (fg2) and the third lens group G3 (fg3) satisfy the following stable characteristic relationship:

[0167] Relationship 3: -0.40≤f7 / fg2≤-0.06.

[0168] The values ​​for f7 / fg2 can be -0.40, -0.34, -0.17, -0.11, -0.06, etc.

[0169] In this embodiment, the value is f7 / fg2 = -0.12.

[0170] Relationship 4: 0.45≤f10 / fg3≤0.91.

[0171] The values ​​for f10 / fg3 can be 0.45, 0.60, 0.72, 0.80, 0.91, etc.

[0172] In this embodiment, the value is f10 / fg3 = 0.80.

[0173] Relationship 5: 0.42≤f11 / fg3≤0.81.

[0174] The values ​​of f11 / fg3 can be 0.42, 0.54, 0.60, 0.75, 0.81, etc.

[0175] In this embodiment, the value is f11 / fg3 = 0.69.

[0176] In this embodiment, the radius of curvature r24 of the concave surface of the fourteenth lens L14 near the object being observed and the total focal length f satisfy the following stable characteristic relationship:

[0177] Relation 6: 0.585≤r24 / f≤0.734.

[0178] The possible values ​​for r24 / f are 0.585, 0.630, 0.680, 0.700, 0.734, etc.

[0179] In this embodiment, the value is r24 / f = 0.59.

[0180] In this embodiment, the focal length f4 of the fourth lens L4 and the focal length fg1 of the first lens group G1 satisfy the following stable characteristic relationship:

[0181] Relationship 7: 0.019≤|f4 / fg1|≤0.129.

[0182] The values ​​of |f4 / fg1| can be 0.019, 0.037, 0.098, 0.115, 0.129, etc.

[0183] In this embodiment, the value is: |f4 / fg1|=0.11.

[0184] The total focal length of the microscope objective is 19.9999 mm, and the parfocal distance of the optical system is 95 mm.

[0185] The optical performance parameters of this embodiment 2 are shown in Table 4:

[0186]

[0187] Table 4

[0188] The specific values ​​of the characteristic relation in Example 2 are shown in Table 5:

[0189]

[0190] Table 5

[0191] The specific parameters of each lens element in the microscope objective lens of this embodiment 2 are shown in Table 6. The "Surface Number" column indicates the number of each surface from the object plane to the image plane; the "Radius of Curvature (mm)" column gives the radius of curvature of each surface; the "Thickness / Spacing (mm)" column gives the axial distance between two adjacent surfaces. If the two surfaces belong to the same lens, the value of "Thickness / Spacing (mm)" represents the center thickness of the lens; otherwise, it represents the distance from the object plane or image plane to the lens or the air gap between adjacent lenses; "N" represents the distance from the object plane or image plane to the lens. d "One column indicates the refractive index of each lens between the object plane and the image plane; "V d The "Abbe number" column indicates the Abbe number of each lens between the object plane and the image plane; the "aperture (mm)" column indicates the aperture value of the surface of each lens between the object plane and the image plane.

[0192]

[0193] Table 6

[0194] Figure 6 This is the optical path structure diagram of Example 2. It is similar to the optical path structure diagram of Example 1, except that some optical parameters are different, resulting in slight changes in the lens shape.

[0195] Figure 7 The Strell ratio is for Example 2. The wavelength range is 486–657 nm. As can be seen from the figure, the Strell ratio of the lens in Example 2 is greater than 0.95 in each field of view, indicating that there is approximately no aberration.

[0196] Figure 8 The MTF chart is shown for the microscope objective in Example 2. The MTF chart includes both geometric optics evaluation and is related to diffraction effects, making it a key parameter for evaluating a lens. Therefore, the MTF charts of the two examples are provided for comparison. Figure 8 As can be seen, the MTF curve almost coincides with the diffraction limit, which is better than Example 1 in this respect. This is attributed to the fact that Example 2 has a smaller range of considerations for wavelength selection.

[0197] Figure 9 This is a longitudinal spherical aberration diagram of the microscope objective in Example 2. It can be seen that the longitudinal spherical aberration in the 0.707 band is less than 0.2 μm, and it can be seen that the longitudinal spherical aberration is well corrected across the entire aperture range. The longitudinal spherical aberration at the maximum wavelength of 656.3 nm does not exceed 0.6 μm.

[0198] Figure 10 The figure shows the chromatic focus shift curve of the microscope objective in Example 2. The maximum focus shift in the figure does not exceed 0.6 μm, which also satisfies the condition of being less than 1 / 2 of the depth of focus.

[0199] The foregoing provides a detailed description of a large field-of-view, long working distance, low-aberration plan apochromatic microscope objective provided in this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of these embodiments are merely for the purpose of helping to understand the core ideas of the method provided in this application and are not intended to limit the scope. It should be noted that those skilled in the art can make improvements and modifications to this application based on its principles without any inventive effort, and these improvements and modifications also fall within the protection scope of the claims of this application.

Claims

1. A large field-of-view, long working distance, low-aberration plan apochromatic microscope objective, characterized in that: It consists of a first lens group (G1), a second lens group (G2), a third lens group (G3), and a fourth lens group (G4) arranged sequentially along the optical axis from the object side to the image side; An aperture stop (STO) is provided between the second lens group (G2) and the third lens group (G3); The power distribution of the first lens group (G1), the second lens group (G2), the third lens group (G3), and the fourth lens group (G4) conforms to the odd symmetry of "negative-negative-positive-positive"; The first lens group (G1) has negative optical power and is composed of a first lens (L1), a second lens (L2), a third lens (L3), a fourth lens (L4), and a fifth lens (L5). The second lens group (G2) has negative optical power and consists of a sixth lens (L6), a seventh lens (L7), and an eighth lens (L8); The third lens group (G3) has positive optical power and is composed of the ninth lens (L9), the tenth lens (L10), the eleventh lens (L11), and the twelfth lens (L12). The fourth lens group (G4) has positive optical power and is composed of the thirteenth lens (L13) and the fourteenth lens (L14).

2. The large field-of-view, long working distance, low aberration plan apochromatic microscope objective as described in claim 1, characterized in that: The ratios of the focal lengths fg3 of the third lens group (G3) and fg4 of the fourth lens group (G4) to the total focal length f of the microscope objective satisfy the following stable characteristic relationship: Relationship 1: 1.78 ≤ fg³ / f ≤ 3.23; Relationship 2: 0.74≤fg4 / f≤0.

97.

3. The large field-of-view, long working distance, low-aberration plan apochromatic microscope objective as described in claim 1, characterized in that: The sixth lens (L6), the seventh lens (L7), and the eighth lens (L8) are cemented triplet lenses; the ninth lens (L9) and the tenth lens (L10) are cemented doublet lenses; and the eleventh lens (L11) and the twelfth lens (L12) are cemented doublet lenses.

4. The large field-of-view, long working distance, low-aberration plan apochromatic microscope objective as described in claim 3, characterized in that: The focal lengths (f7) of the seventh lens (L7), (f10) of the tenth lens (L10), and (f11) of the eleventh lens (L11) are made of ultra-low dispersion glass material HFK95N to achieve achromatic aberration. Furthermore, the focal length ratios within each lens group (f7, f10, f11, and fg2 of the second lens group (G2) and fg3 of the third lens group (G3) satisfy the following stable characteristic relationship: Relationship 3: -0.40≤f7 / fg2≤-0.06; Relationship 4: 0.45 ≤ f10 / fg3 ≤ 0.91; Relationship 5: 0.42≤f11 / fg3≤0.

81.

5. The large field-of-view, long working distance, low-aberration plan apochromatic microscope objective as described in claim 1, characterized in that: The fourteenth lens (L14) has positive refractive power, converting light rays from the object into converging rays and guiding them to the thirteenth lens (L13). The radius of curvature r24 of the concave surface of the fourteenth lens (L14) near the object satisfies the following stable characteristic relationship with the total focal length f: Relation 6: 0.585≤r24 / f≤0.

734.

6. The large field-of-view, long working distance, low-aberration plan apochromatic microscope objective as described in claim 1, characterized in that: The focal length f4 of the fourth lens (L4) and the focal length fg1 of the first lens group (G1) satisfy the following stable characteristic relationship: Relationship 7: 0.019≤|f4 / fg1|≤0.

129.

7. The large field-of-view, long working distance, low aberration plan apochromatic microscope objective as described in claim 1, characterized in that: The total focal length f of the microscope objective is 19–21 mm, and the parfocal distance of the optical system is 94–96 mm.

8. The large field-of-view, long working distance, low aberration plan apochromatic microscope objective as described in claim 1, characterized in that: The first lens (L1), second lens (L2), third lens (L3), fourth lens (L4), and fifth lens (L5) in the first lens group (G1) are all made of glass. The refractive index and Abbe number of the first lens (L1) are n1 and v1, respectively; the refractive index and Abbe number of the second lens (L2) are n2 and v2, respectively; 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; and the refractive index and Abbe number of the fifth lens (L5) are n5 and v5, respectively. The refractive index and Abbe number of the first lens (L1) to the fifth lens (L5) satisfy the following range of values: 1.8≤n1≤2.0,23≤v1≤25;1.9≤n2≤2.1,17≤v2≤19;1.5≤n3≤1.7,40≤v3≤42;1.9≤n4≤2.1,17≤v4≤19;1.7≤n5≤1.9,44≤v5≤46。 9. A large field-of-view, long working distance, low-aberration plan apochromatic microscope objective as described in claim 1, characterized in that: The sixth lens (L6), the seventh lens (L7), and the eighth lens (L8) in the second lens group (G2) are all made of glass. 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. The refractive index and Abbe number of the eighth lens (L8) are n8 and v8, respectively, and the refractive index and Abbe number of the sixth lens (L6) to the eighth lens (L8) satisfy the following range of values: 1.6≤n6≤1.8,40≤v6≤42;1.4≤n7≤1.6,94≤v7≤96;1.9≤n8≤2.1,17≤v8≤19。 10. A large field-of-view, long working distance, low-aberration plan apochromatic microscope objective as described in claim 1, characterized in that: The ninth lens (L9), tenth lens (L10), eleventh lens (L11), and twelfth lens (L12) in the third lens group (G3) are all made of glass. The refractive index and Abbe number of the ninth lens (L9) are n9 and v9, respectively; the refractive index and Abbe number of the tenth lens (L10) are n10 and v10, respectively; the refractive index and Abbe number of the eleventh lens (L11) are n11 and v11, respectively; and the refractive index and Abbe number of the twelfth lens (L12) are n12 and v12, respectively. The refractive index and Abbe number of the ninth lens (L9) to the twelfth lens (L12) satisfy the following range: 1.9≤n9≤2.1,17≤v9≤19;1.4≤n10≤1.6,94≤v10≤96;1.4≤n11≤1.6,94≤v11≤96;1.4≤n12≤1.6,66≤v12≤68。 11. A large field-of-view, long working distance, low-aberration plan apochromatic microscope objective as described in claim 1, characterized in that: The thirteenth lens (L13) and the fourteenth lens (L14) in the fourth lens group (G4) are both made of glass. The refractive index and Abbe number of the thirteenth lens (L13) are n13 and v13, respectively. The refractive index and Abbe number of the fourteenth lens (L14) are n14 and v14, respectively. The refractive index and Abbe number of the thirteenth lens (L13) and the fourteenth lens (L14) satisfy the following range: 1.7≤n13≤1.9, 27≤v13≤29; 1.9≤n14≤2.1, 17≤v14≤19.

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