Limited distance correction microscope objective for scanning applications

Abstract

A finite distance correction microscope objective (2) for scanning applications is designed such that it has a numerical aperture (NA) of at least 0.9, has an object field diameter (dobj = 2 hobj) of at least 1 mm, is apochromatic corrected over a spectral bandwidth of at least 200 nanometers, and the distance (dOI) between the object plane (O) and an intermediate image plane (I) conjugated thereto is not greater than 250 mm.

Description

[0001] This application claims the priority of German patent application DE 10 2023 206 339.5, the content of which is incorporated herein by reference. Technical Field

[0002] The invention relates to a finite distance corrected microscope objective for scanning applications. The invention also relates to an optical assembly and a microscope having such an objective. Finally, the invention relates to the use of a corresponding objective and to a method for automatically scanning a sample. Background Art

[0003] Depending on the area of ​​application, microscope objectives have to meet various requirements.

[0004] Microscope objectives with high resolution are known from the prior art. Such objectives are usually very large and their use requires expert knowledge.

[0005] US 2019 / 0324246, US 9746658 and US 8350904 relate to dry objectives with high etendue. US 8988780, JP 2011075982 and DE 102011109783 relate to immersion objectives with high etendue. These objectives are infinitely corrected. Finitely corrected objectives are known from US 9939622 and US 8350904. These are large and / or have a large number of lenses and / or their image quality drops sharply towards the periphery. Summary of the invention

[0006] It is an object of the present invention to improve microscope objectives. A particular object is to provide a finite distance corrected microscope objective having a simplified arrangement, a compact design and improved optical properties.

[0007] This object is achieved by the microscope objective according to the invention.

[0008] The objective is corrected for finite distance. This means that it is designed for use in a finite distance optical unit, i.e. for a defined tube length. In particular, the objective produces a real intermediate image at a defined finite distance.

[0009] According to a first aspect, the objective lens can be designed such that the distance (d OI ) is not greater than 250 mm. In particular, the distance (d OI ) may not be greater than 205mm.

[0010] According to the invention it has been recognized that in particular for scanning applications in which large, in particular large-area samples are examined it is advantageous if the microscope objective used for this purpose has a large field of view and at the same time provides a high resolution over the entire field of view.

[0011] The field of view is also called the object field.

[0012] The Strehl ratio can be used to characterize the resolution. Despite their reduced complexity, the objectives according to the invention can have a Strehl ratio of at least 0.8, in particular at least 0.85, in particular at least 0.89.

[0013] In particular, the objective can have such a high Strehl ratio over at least 50%, in particular at least 70%, in particular at least 90%, in particular at least 95%, in particular over the entire field of view.

[0014] In particular, the objective can have such a high Strehl ratio over a partial field of view region having an area of ​​at least 1 square millimeter.

[0015] This ensures high resolution over a large field of view area, in particular over the entire field of view. This makes it easier to assemble multiple partially overlapping images into a mosaic image.

[0016] The reduced complexity leads in particular to cost savings and an increase in system robustness.

[0017] In particular, the objective can have a vignetting of less than 5%, in particular less than 3%, in particular less than 1%.

[0018] In particular, the objective can be apochromatically corrected over a spectral bandwidth of at least 200 nm, in particular in the range of 400 nm to 800 nm. In particular, the objective can be apochromatically corrected over a spectral bandwidth of at least 200 nm, in particular in the range of 400 nm to 700 nm. In particular, the objective can be apochromatically corrected over a spectral bandwidth of at least 200 nm, in particular in the range of 400 nm to 660 nm.

[0019] Apochromatic correction means that the maximum deviation of the focus position within the spectrum relative to the reference wavelength is within the depth of field.

[0020] The objective can preferably have a numerical aperture of at least 0.9, in particular at least 0.95.

[0021] The objectives according to the invention can be produced particularly cost-effectively. However, they result in a high robustness of the optical system.

[0022] Particularly for scanning applications, it may be necessary to take a large number of images and then assemble them into a mosaic image. Preferably, this is done automatically.

[0023] The objective lens may in particular have an object field diameter (d obj =2h obj ). The object field diameter is also called the field of view size.

[0024] For high throughput, the time required to record each image is a key factor. It is always desirable to reduce the time required to record each image. This leads to faster results and increased throughput. Typically, this leads to lower costs.

[0025] An important factor affecting the time required to record individual images is the field of view size of the optical system. A larger field of view size enables a larger area to be recorded in each image. Therefore, fewer frames are required to image a large number of samples. This results in reduced scanning time and a reduction in the effort required to assemble the images into a mosaic.

[0026] However, when the field size is enlarged, it is crucial that the objective has high resolution for all relevant wavelength ranges throughout the field of view. This requirement for high resolution with a large field of view corresponds to an increase in etendue, in particular, a maximization of etendue. Etendue is proportional to the square of the linear size (in particular the diameter) of the field of view. It is also proportional to the square of the numerical aperture (NA).

[0027] At the same time, in particular for conventional applications, it may be desirable to reduce the complexity of the microscope objective. In particular, this can lead to cost savings. Reduced complexity is particularly understood to mean a reduction in the number of required optical elements (in particular lenses). In particular, the number of aspherical lenses is preferably reduced. It has been shown that this leads to significant cost savings.

[0028] According to one aspect, the objective has a maximum of 18 optical elements, in particular a maximum of 17 optical elements, in particular a maximum of 16 optical elements. In particular, lenses can be used as optical elements.

[0029] The reduced number of optical elements, in particular lenses, results in considerable cost savings.

[0030] The optical elements may in particular be arranged in groups, in particular in groups of nine. In particular, glued elements are referred to as groups.

[0031] The objectives according to the invention have a significantly reduced complexity, in particular a lower number of lenses for a given etendue. Due to their high Strehl ratio, they still ensure high resolution over the entire field of view.

[0032] According to one aspect, the objective lens can be designed as a dry objective lens. This is advantageous for simplifying the scanning method.

[0033] The objective lens can have a numerical aperture (NA) in the range of 0.9 to 1.0. This results in a particularly high resolution.

[0034] The objective lens may have a chief ray angle on the image side (CRAI, image side chief ray angle) of not more than 5°. This ensures that the objective lens can be used with standardized digital image sensors. A small chief ray angle is advantageous in particular for the relative illumination and efficiency of the image sensor.

[0035] According to another aspect, the distance (BFL, back focal length) between the rearmost optical surface and the intermediate image plane (I) may be at least 50 mm, in particular at least 58 mm. A large distance may simplify the assembly of the optical system.

[0036] According to another aspect, the objective can be designed without aspherical lenses at all. This further reduces the complexity of the objective. This leads in particular to a reduction in costs.

[0037] The lenses of the objective can be made from at least 8, in particular at least 10, in particular at least 12 different types of glass.

[0038] It has been shown that particularly good optical properties of the objective can be achieved by suitable selection of different types of glass.

[0039] The optical elements of the objective, in particular the lenses, can be arranged in three groups G1, G2, G3. Each of these groups can have subgroups.

[0040] The first group G1 may have positive refractive power.

[0041] The second group G2 may have positive refractive power.

[0042] The third group G3 may have negative refractive power.

[0043] According to another aspect, the third lens group G3 may have three sub-groups (G31, G32, and G33). The first sub-group (G31) may have positive refractive power. The second sub-group (G32) may have negative refractive power. The third sub-group (G33) may have negative refractive power.

[0044] Here and below, the order of the optical elements of the objective is indicated in the direction from the object field to the image field.With respect to the objective, "front" refers to the side facing the object field and "rear" refers to the side facing away from the object field.

[0045] According to another aspect, the first lens group G1 of the objective can have cemented elements, in particular a cemented triplet.

[0046] According to another aspect, the second lens group G2 of the objective can have three cemented elements, in particular three cemented doublets.

[0047] According to another aspect, the third lens group G3 of the objective may have two cemented elements, in particular two cemented doublets G31 , G33 .

[0048] Further possible details of the objective lens are described below.

[0049] The objective lens may have a relatively short working distance. In particular, the following may apply:

[0050] d: L<4.9×10 -3 ,

[0051] where d indicates the distance from the cover glass to the periphery of the foremost lens surface of the objective, and L indicates the total distance between the object field and the vertex of the rearmost lens surface of the objective (in the direction of the light beam).

[0052] The working distance of the objective lens can also meet the following conditions:

[0053] d0: L<9×10 -3 ,

[0054] where d0 represents the distance from the object field to the vertex of the frontmost lens surface.

[0055] If the maximum distance of a light ray emitted from an object on the optical axis to the optical axis is defined as h1, h2, and h3 in the three sub-groups G31, G32, and G33 of the third lens group G3, these parameters may specifically satisfy the following inequality:

[0056] 1.1

[0057] 1.2 <h2:h3<1.6。

[0058] Another object of the invention is to improve microscopes, in particular for scanning applications, in particular for optical mapping.

[0059] This object is achieved by a microscope having an objective according to the preceding description.The advantages are apparent from the preceding description.

[0060] The microscope may include an automatic scanning device. The scanning device may enable a one-dimensional (linear) displacement of the sample, a two-dimensional displacement of the sample or a three-dimensional displacement of the sample. In addition to the linear displacement, the scanning device may also have one, two or three rotational degrees of freedom. This allows for a very flexible arrangement of the samples, in particular for their displacement.

[0061] The scanning device may comprise an image acquisition device, in particular a digital image acquisition device, in particular a digital camera.

[0062] The scanning device may include image processing means. In particular, the latter may enable automated processing. In particular, this simplifies the splicing of frames into a mosaic image.

[0063] ​The microscope objective described above is particularly advantageous for use in scanning applications, in particular for optical mapping. In particular, the microscope objective simplifies the automated scanning of large (in particular large area) samples.

[0064] Another object of the present invention is to improve a method for automatically scanning a sample. This object is achieved by a method comprising the following steps:

[0065] - providing a microscope according to the preceding description,

[0066] - provide samples to be inspected,

[0067] - acquiring at least two images of different parts of the sample, wherein the parts have overlapping areas, and

[0068] - Assembling said images into a mosaic image.

[0069] In particular, the method may be an optical mapping method.

[0070] Before assembling the images, they may be analyzed and / or processed using image processing algorithms. This may simplify and / or improve the assembly of the images.

[0071] The assembled mosaic image may also be analyzed and / or processed after the images have been assembled using an image processing algorithm. This may further improve the quality.

[0072] In order to record images of different parts of the sample, the sample can be displaced linearly, two-dimensionally or three-dimensionally. The sample can in particular be displaced stepwise.

[0073] In particular, the displacement of the sample and the recording of successive images of different parts of the sample can be automated. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Further details of the present invention will become apparent from the description of the embodiments with reference to the accompanying drawings. The accompanying drawings show:

[0075] Figure 1 Schematic showing the microscope setup,

[0076] Figure 2 shows a schematic longitudinal section through the optical components of a microscope objective according to a first variant (E4),

[0077] Figure 3 Schematic diagram showing the Figure 2 The distribution of the Strehl ratio of the objective lens over the field of view, and

[0078] Figure 4 The distribution of the intensity of the incident light illumination on the field of view of the objective lens E4 is schematically shown. DETAILED DESCRIPTION

[0079] Figure 1 By way of example, a basic setup of a microscope 1 is schematically shown. This description is to be understood as an example and not as a limitation.

[0080] The microscope 1 comprises a finite distance optical unit. This means that the beam path 3 downstream of the objective 2 passes through a real intermediate image plane 7 at a defined distance. The intermediate image can be observed using an eyepiece 8. It can also be guided to an image acquisition device, in particular in the form of a camera 9. The camera 9 can in particular be a digital camera.

[0081] Figure 1 Also shown is an illumination device 10 as an example. The illumination device 10 has a radiation source unit 11. In particular, a laser can be used as the radiation source unit 11.

[0082] The illumination device 10 may also have a beam splitter 12. By means of the beam splitter 12, the illumination radiation 3 may be guided through the objective 2 to the sample 13 to be observed. The beam splitter 12 may be arranged in the convergence region between the objective 2 and the intermediate image plane 7.

[0083] Figure 1 The beam path schematically shown in FIG. 1 is particularly suitable for incident light (epi-fluorescence) systems. The illumination can be in the form of Köhler illumination. Critical illumination is also possible.

[0084] Instead of the beam splitter 12, a prism, in particular a cubic prism, may also be provided.Alternative variants for coupling in the illumination radiation are known from the prior art.

[0085] Figure 1 Schematically shown is also a scanning device 14. The scanning device 14 comprises one or more displacement devices 15. By means of the displacement device 15, the sample 13 can be displaced in the microscope 1 relative to the beam path 3, in particular relative to the objective 2.

[0086] To illustrate the working distance of the objective lens 2, as an example, Figure 1 The distance d from the cover glass 16 to the periphery of the frontmost lens surface 17 of the objective lens 2 is shown in FIG.

[0087] The distance from the object plane 18 to the vertex 19 of the frontmost lens surface 17 is shown as d0.

[0088] L represents the total distance between the object plane 18 and the vertex 19 of the rearmost lens surface of the objective 2 (in the direction of the beam). Figure 1 Clearly shown in.

[0089] The microscope 1 can have a footprint with a width b of not more than 250 mm, in particular not more than 205 mm.

[0090] Figure 2 A longitudinal section through the arrangement of optical components of objective 2 is shown.

[0091] The illustrated variant E4 of the objective is suitable for use with a cover glass 16 having a thickness of 0.188 mm, a refractive index nd=1.523 and an Abbe number vd=54.52 (based on the d-line of 587.562 nm).

[0092] Figure 2 By way of example, the contours of a central principal ray HS and two marginal rays RS1 , RS2 are shown.

[0093] For the sake of clarity, the mechanical components of objective 2 are not shown. Figure 2 Shown in.

[0094] The objective 2 is in particular an apochromatic objective 2 .

[0095] Figure 2 The variant shown in (E4) is in particular a dry objective.

[0096] according to Figure 2 The objective lens 2 has 16 lenses L1 to L16. The lenses L1 to L16 are arranged in 3 groups, 9 subgroups in total. Each subgroup is formed by a single lens or a cemented element.

[0097] according to Figure 2 The optical design data of the objective lens 2 is shown in Table 1.

[0098] Table 1: According to Figure 2 The optical design data of objective lens 2 in the opposite direction (i.e. from the image side to the object side) are:

[0099]

[0100] The refractive index (nd) and the Abbe number (vd) refer to the d-line (587.562 nm). The data refer to the use of a cover glass 16 with a thickness of 0.188 mm.

[0101] Additional data for objective 2:

[0102] Magnification: 10 times

[0103] NA: 0.95

[0104] L: 140.39mm

[0105] Distance between object field and intermediate image (dOI): 200 mm

[0106] d: 0.661mm

[0107] d0: 1.096mm

[0108] d: L=4.7×10 -3

[0109] d0: L=7.8×10 -3

[0110] h obj : 0.8mm

[0111] Back focal length: 59.61mm

[0112] Image side chief ray angle (CRAI): 4.65°

[0113] The objective lens 2 has three lens groups G1, G2 and G3. The first lens group G1 has positive refractive power and includes lenses L1 to L5.

[0114] Lenses L3 to L5 form a cemented triplet.

[0115] The second lens group G2 has positive refractive power. The second lens group G2 includes lenses L6 to L11.

[0116] Lenses L6 and L7 form a cemented doublet.

[0117] Lenses L8 and L9 form a cemented doublet.

[0118] Lenses L10 and L11 form a cemented doublet.

[0119] The third lens group G3 has negative refractive power.

[0120] The third lens group G3 includes lenses L12 to L16.

[0121] Lenses L12 and L13 form a cemented doublet lens. They form subgroup G31. Subgroup G31 has positive refractive power.

[0122] The lens L14 forms a subgroup G32. The subgroup G32 has negative refractive power.

[0123] Lenses L15 and L16 form a cemented doublet lens. They form subgroup G33. Subgroup G33 has negative refractive power.

[0124] If the maximum distance of a light ray emitted from an object on the optical axis to the optical axis is defined as h1, h2, and h3 in the three sub-groups G31, G32, and G33 of the third lens group G3, then:

[0125] h1=16.28mm,

[0126] h2=9.78mm,

[0127] h3=6.84mm

[0128] And therefore

[0129] h1:h2=1.665, and

[0130] h2:h3=1.430.

[0131] Figure 3 Shown according to Figure 2 Strehl ratios of objective lens 2 for light with wavelengths of λ1=460nm, λ2=546nm and λ3=660nm respectively.

[0132] from Figure 3 As can be seen in FIG, the Strehl ratio over the entire field of view is greater than 0.8. For a single wavelength or a limited wavelength range, the Strehl ratio over the entire field of view is even greater, particularly greater than 0.83, and particularly greater than 0.89.

[0133] exist Figure 4 , the relative illumination intensity over the field of view at a wavelength of 546.074 nm is shown in order to illustrate the peripheral light drop.

[0134] from Figure 4 As can be seen in FIG. 2 , objective 2 under incident light illumination results in a homogeneous illumination of the field of view with slight vignetting.

Claims

1. A finite distance corrected microscope objective (2) for scanning applications, comprising: 1.

1. A first lens group (G1) having positive refractive power, 1.

2. A second lens group (G2) having positive refractive power, and 1.

3. A third lens group (G3) having negative refractive power, 1.

4. Wherein, the microscope objective lens (2) has 1.4.

1. A numerical aperture (NA) of at least 0.9, 1.4.

2. Object field diameter of at least 1 mm (dobj = 2hobj), 1.4.

3. Less than 5% vignetting, and 1.4.

4. Apochromatically corrected over a spectral bandwidth of at least 200 nm, 1.4.

5. Wherein, the microscope objective (2) is designed so that the distance (dOI) between the object plane (O) and the intermediate image plane (I) conjugated thereto is not greater than 250 mm.

2. The microscope objective (2) according to claim 1, characterized in that The object field diameter (d obj ) is at least 1.5 mm.

3. Microscope objective (2) according to any one of the preceding claims, characterized in that The microscope objective (2) has a Strehl ratio of at least 0.8 over at least 70% of the field of view.

4. Microscope objective (2) according to any one of the preceding claims, characterized in that The microscope objective (2) comprises a maximum of 18 optical elements (L1; 1≤i≤18).

5. Microscope objective (2) according to any one of the preceding claims, characterized in that The microscope objective (2) is designed as a dry objective.

6. Microscope objective (2) according to any one of the preceding claims, characterized in that The chief ray angle on the image side (CRAI) is not greater than 5°.

7. Microscope objective (2) according to any one of the preceding claims, characterized in that The distance (BFL) between the rearmost optical surface and said intermediate image plane (I) is at least 50 mm.

8. Microscope objective (2) according to any one of the preceding claims, characterized in that The microscope objective (2) is apochromatically corrected over a bandwidth of at least 200 nm in the wavelength range between 400 nm and 800 nm.

9. Microscope objective (2) according to any one of the preceding claims, wherein: The third lens group (G3) has three sub-groups (G31, G32 and G33), wherein the first sub-group (G31) has positive refractive power, the second sub-group (G32) has negative refractive power, and the third sub-group (G33) has negative refractive power.

10. Microscope objective (2) according to any one of the preceding claims, characterized in that The microscope objective has no aspherical lenses.

11. Microscope objective (2) according to any one of the preceding claims, characterized in that Optical design data below (in reverse order):

12. A microscope (1) comprising a microscope objective (2) according to any one of claims 1 to 11.

13. The microscope (1) according to claim 12, characterized in that The microscope (1) has a footprint no larger than 250 mm x 200 mm.

14. The microscope (1) according to any one of claims 12 to 13, characterized in that Automatic scanning device (14).

15. A method for automatically scanning a sample, comprising the steps of: 15.

1. Provide a microscope according to any one of claims 12 to 14, 15.

2. Provide samples for inspection, 15.

3. Acquire at least two images of different parts of the sample, wherein the parts have overlapping areas, 15.

4. Assemble the images into a mosaic image.

Images