Apochromatic lens

Abstract

An apochromatic microscope objective (2) with a large field of view, high resolution and particularly good chromatic correction.

Description

[0001] The invention relates to an apochromatic microscope objective. The invention also relates to an optical system for a microscope. Finally, the invention relates to a microscope.

[0002] A wide variety of microscope objectives are known from the prior art. For certain requirements and / or applications, it may be desirable to have an objective with a large field of view, high resolution, and good chromatic correction. Such objectives are known, for example, from WO 2023 / 120 104 A1, WO 2023 / 095 723 A1, and US 2023 / 0185055 A1.

[0003] There is a need to further improve corresponding lenses, especially with regard to chromatic correction.

[0004] This problem is solved by a microscope objective according to the present invention. The microscope objective will also be referred to simply as the objective in the following.

[0005] The lens according to the invention features in particular high resolution over a large field of view and excellent chromatic correction.

[0006] The visual field is also referred to as the object field.

[0007] According to one aspect of the invention, the lens comprises a diverging lens made of a material with an Abbe number (vd) of at least 75, in particular at least 80, at least 85, in particular at least 90, and in particular at least 95. The diverging lens thus exhibits very low dispersion. It is also referred to as quasi-dispersion-free.

[0008] The diverging lens can be made of a material with a low refractive index. The material of the diverging lens can, in particular, have a refractive index nd of at most 1.5, and especially at most 1.45.

[0009] It has been shown that using such a lens makes it possible to create a lens design that results in a lens with particularly good chromatic correction.

[0010] The lens can be used particularly for multi-photon microscopy and / or fluorescence microscopy. Its advantages are especially evident in these applications.

[0011] The lens can be designed as a dry lens or as an immersion lens.

[0012] It could be, in particular, an infinitely corrected lens.

[0013] In general, the lens has a first lens group with positive refractive power, a second lens group with negative refractive power, and a third lens group with positive refractive power.

[0014] Here, the lens groups are counted in the direction from the object field to the image field. The lens groups are, in particular, consecutive, especially directly consecutive. The lens can, in particular, consist of three lens groups. In this case, it has no further lenses.

[0015] A lens group is understood to be an arrangement of one or more lenses.

[0016] According to one aspect, the lens is apochromatically corrected over a classic apochromatic spectral range.

[0017] The classical apochromatic spectral range is understood here to be the range from 435 nm to 656 nm.

[0018] Apochromatically corrected means that the chromatic aberration is at most as large as the depth of focus, in particular at most 0.8 times the depth of focus, and in particular at most 0.6 times the depth of focus. The e-line (546.07 nm) serves as the reference wavelength in this context.

[0019] The depth of focus corresponds to exactly half a Rayleigh length (0.5 RE).

[0020] The chromatic aberration in this case refers in particular to axial chromatic aberration.

[0021] The lens may in particular have a flat field of view with a diameter of at least 8 mm, in particular at least 10 mm.

[0022] A flattened field of view (fFOV) is understood here to be the largest field size within which a focus deviation from the axial focus is at most as large as the focus depth, i.e., at most half a Rayleigh length.

[0023] A diverging lens is a lens with negative refractive power. It is therefore also called a negative lens.

[0024] The diverging lens made of the material with the high Abbe number (vd) can in particular form the second lens in the optical path of the objective.

[0025] The lens has a high resolution. In particular, it can have a numerical aperture (NA) of at least 0.09, in particular at least 0.1, in particular at least 0.11.

[0026] According to another aspect, the product of the numerical aperture (NA) of the objective and the diameter (Obj) of the flattened field of view can be at least 1 mm, in particular at least 1.1 mm.

[0027] The lens exhibits particularly low field curvature.

[0028] According to another aspect, the first lens group (G1) can be formed as a single lens.

[0029] The lens has a particularly simple design.

[0030] According to another aspect, the second lens group (G2) can be formed as a single lens.

[0031] The lens has a particularly simple design.

[0032] The single lens of the second lens group (G2) may in particular be the diverging lens with low dispersion.

[0033] According to another aspect, the third lens group (G3) can have four lenses. In particular, it can have two cemented elements, especially two double cemented elements. The third lens group can, in particular, consist of two double cemented elements.

[0034] The lens can consist of, in particular, at most 10, in particular at most 8, in particular at most 7, in particular at most 6, lenses.

[0035] The lens has a particularly simple design. It is especially inexpensive to manufacture.

[0036] According to another aspect, the lens has a magnification of at most 5x, in particular at most 4x, in particular at most 2.5x.

[0037] This can refer to the nominal magnification indicated on the lens. The magnification is achieved particularly in combination with the specified tube system.

[0038] According to another aspect, the diverging lens is bi-concave.

[0039] According to another aspect, the lens can be apochromatically corrected over an extended apochromatic spectral range.

[0040] An extended apochromatic spectral range is understood here to be the range from 400 nm to 750 nm.

[0041] According to another aspect, the lens can be even better chromatically corrected in a smaller spectral range, particularly in the range of 530 nm to 660 nm. The axial chromatic aberration can be, in particular, at most 0.5 Rayleigh lengths over the spectral range of 530 nm to 660 nm, at most 0.3 Rayleigh lengths, and in particular at most 0.2 Rayleigh lengths.

[0042] According to another aspect, the following can apply to a ratio of a distance (t12) between the first lens group and the second lens group and a total length of the lens: t12: ta < 0.2, in particular t12 : ta < 0.18, in particular t12 : ta < 0.16, in particular t12 : ta < 0.15.

[0043] The total length ta is measured from the object-side vertex of the first, foremost lens surface to the image-side vertex of the rearmost lens surface of the objective.

[0044] The total length ta of the lens can be, in particular, at most 80 mm, in particular at most 60 mm, in particular at most 55 mm.

[0045] The lens can therefore have a compact design.

[0046] According to another aspect, the lens can have a lens arrangement according to the following design data: Oberfläche Nr. r (mm) d (mm) nd vd 1 -1825.754 3.80 1.883 40.76 2 -18.625 7.57 3 -19.781 3.19 1.434 95.22 4 18.516 22.33 5 -11.210 2.51 1.804 46.50 6 26.919 3.49 1.487 84.47 7 -12.340 0.24 8 56.402 3.67 1.434 95.22 9 -13.970 5.51 1.847 23.78 10 -16.785

[0047] Another object of the invention is to improve an optical system consisting of a microscope objective and a tube lens unit.

[0048] This task is solved by an optical system with a lens according to the previous description and a tube lens unit.

[0049] The advantages stem from those of the lens.

[0050] Another objective of the invention is to improve a microscope.

[0051] This task is solved by a microscope with an objective lens as described above.

[0052] The advantages stem from those of the lens.

[0053] The lens enables, in particular, the imaging of a large object field with high resolution and excellent axial chromatic correction. This is especially advantageous for multi-photon microscopy and fluorescence microscopy.

[0054] The microscope in question could be, in particular, a multi-photon microscope or a fluorescence microscope.

[0055] Further advantages, details, and specifics of the invention will become apparent from the description of an exemplary embodiment with reference to the figures. These show: Fig. 1. Schematic diagram of the structure of a microscope, Fig. 2 a schematic longitudinal section through the lens arrangement of the microscope objective according to one variant, Fig. 3 schematically the axial focus position in Rayleigh units as a function of wavelength and Fig. Figure 4 schematically shows a longitudinal section through the lens arrangement of a tube lens.

[0056] In the Fig. Figure 1 shows an exemplary and schematic representation of the basic structure of a microscope. This representation is intended to be exemplary and not exhaustive.

[0057] The microscope 1 has an infinity optic. This means that the beam path 3 behind the objective 2 is parallel. The area between the objective 2 and a tube lens 5 of a tube lens unit 6 is also referred to as the infinity space 4. An intermediate image is generated in an intermediate image plane 7 by means of the tube lens unit 6. The intermediate image can be viewed using an eyepiece 8. It can also be directed to an image acquisition device, in particular in the form of a camera 9. The camera 9 can, in particular, be a digital camera.

[0058] This is exemplified in the Fig. 1. In addition, a lighting device 10. The lighting device 10 has a radiation source unit 11. In particular, a laser can serve as the radiation source unit 11.

[0059] The illumination device 10 can also include a beam splitter 12. Using the beam splitter 12, the illumination radiation 3 can be directed through the objective lens 2 to a sample 13 to be examined. The beam splitter 12 is used to direct the illumination radiation 3 through the objective lens 2 to a sample 13 to be viewed. Fig. The schematically represented beam path is particularly suitable for epifluorescence systems. The illumination can be designed as Köhler illumination. Critical illumination is also possible. Instead of the beam splitter 12, a prism, in particular a cubic prism, can also be used. Alternative variants for coupling the illumination radiation are known from the prior art.

[0060] Also shown schematically is in the Fig. 1. A scanning device 14. The scanning device 14 has one or more displacement devices 15. Using the displacement devices 15, the sample 13 can be displaced relative to the beam path 3 in the microscope 1, in particular relative to the objective 2.

[0061] To illustrate the working distance of lens 2, the following is shown in the Fig. 1 The distance d from the cover glass 16 to the vertex 19 of the foremost lens surface 17 of the objective 2 is shown as an example.

[0062] The distance d0 is drawn from an object plane 18 to the vertex 19 of the foremost lens surface 17.

[0063] Fig. Figure 2 shows a longitudinal section through the arrangement of lenses L1 to L6 of the objective 2.

[0064] In the Fig. Figure 2 shows an example of the path of a central main ray HS, a marginal ray RS and another ray (without designation).

[0065] For the sake of clarity, the mechanical components of lens 2 are not shown in the figure.

[0066] The lens 2 is, in particular, an apochromatic lens 2. The lens 2 is, in particular, chromatically corrected, especially over a wide wavelength range. It is, in particular, corrected over a classic apochromatic range, preferably over an extended apochromatic range.

[0067] The lens 2 according to Fig. 2 has six lenses L1 to L6.

[0068] The lenses L1 to L6 of the objective 2 are arranged in three groups, G1, G2 and G3.

[0069] The first lens group G1 has a positive refractive power.

[0070] The second lens group, G2, has a negative refractive power.

[0071] The third lens group, G3, has a positive refractive power.

[0072] The first lens group G1 includes the first lens L1. It can, in particular, consist of the first lens L1.

[0073] The second lens group G2 includes the second lens L2. It can, in particular, consist of the second lens L2.

[0074] The second lens L2 is in particular a diverging lens, that is, a lens with negative refractive power.

[0075] The L2 lens is bi-concave.

[0076] Lens L2 is made of a material with very low dispersivity. In particular, it is made of a material with an Abbe number vd of 95.22.

[0077] Lens L2 is made of a material with a low refractive index. In particular, it is made of a material with a refractive index nd = 1.434.

[0078] The third lens group G3 has four lenses: L3, L4, L5 and L6.

[0079] The third lens group G3 has in particular one cemented element, especially a double cemented element. It can in particular have two cemented elements, especially two double cemented elements.

[0080] The distance t 12 The distance between the first lens group G1 and the second lens group G2, in particular the distance between the first lens L1 and the second lens L2, is 7.57 mm.

[0081] The distance t a The distance between the vertex 19 of the foremost lens surface 17 and a vertex 20 of a rearmost lens surface 21 in the beam path 3 of the objective 2 is 52.31 mm.

[0082] Therefore, the following applies: t 12 : t a = 0.145.

[0083] The optical design data of lens 2 according to Fig. 2 are summarized in Table 1. Table 1: Optical design data of lens 2 according to Figure 2: Surface No. r (mm) d (mm) nd vd 1 -1825.754 3.80 1.883 40.76 2 -18.625 7.57 3 -19.781 3.19 1.434 95.22 4 18.516 22.33 5 -11.210 2.51 1.804 46.50 6 26.919 3.49 1.487 84.47 7 -12.340 0.24 8 56.402 3.67 1.434 95.22 9 -13.970 5.51 1.847 23.78 10 -16.785

[0084] The values ​​for refractive index (nd) and Abbe number (vd) refer to the d-line (587.562 nm).

[0085] Lens 2 has a numerical apparatus (NA) of 0.11. It has a flattened field of view diameter (Obj) of 10 mm. The product of the numerical apparatus (NA) and the flattened field of view diameter (Obj) is 1.1, NA x Obj = 1.1.

[0086] The objective lens 2 has a magnification of 2.5. This specification refers specifically to the use of the objective lens with the tube lens 5 described below. The optical design data of the tube lens 5 according to Fig. 4 are listed in Table 2. Table 2: Optical design data of the tube lens 5 according to Figure 4: Surface No. r (mm) d (mm) nd vd 1 121.921 15.067 1.654 39.70 2 63.494 4.663 3 63.861 4.416 1.488 70.41 4 -202.192 0.154

[0087] The tube lens 5 is a 195 mm tube lens.

[0088] The lens 2 is designed for use with a cover glass 16 of a thickness of 0.17 mm, a refractive index nd = 1.523 and an Abbe number vd = 54.52.

[0089] How Fig.As can be seen from Figure 3, the lens 2 has excellent apochromatic correction in the classic apochromatic range 22 from 435 nm to 656 nm.

[0090] The lens 2 exhibits good apochromatic correction in the extended apochromatic range 23 from 400 nm to 750 nm.

[0091] The lens 2 exhibits an almost perfect apochromatic correction 24 in a narrower apochromatic range from 530 nm to 656 nm. The maximum axial deviation of the focus position from the focus position of the line (546.07 nm) is, in particular, at most 0.2 Rayleigh units (RE), and especially at most 0.1 Rayleigh units.

[0092] The lens 2 can, in particular, exhibit such good apochromatic correction over a wavelength range of at least 100 nm from the range of 300 nm to 1200 nm, in particular from the range of 400 nm to 750 nm, in particular from the range up to 700 nm, that the maximum axial variation of the focus position in this range is in particular at most 0.2 Rayleigh units (RE), in particular at most 0.1 Rayleigh units. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] WO 2023 / 120 104 A1

[0002] WO 2023 / 095 723 A1

[0002] US 2023 / 0185055 A1

[0002]

Claims

[1] Having an apochromatic microscope objective (2) 1.

1. a first lens group (G1) with positive refractive power, 1.

2. a second lens group (G2) with negative refractive power and 1.

3. a third lens group (G3) with positive refractive power, 1.

4. wherein the microscope objective (2) is apochromatically corrected over a classical apochromatic spectral range, wherein the chromatic aberration is at most as large as the focal depth of the microscope objective (2), 1.

5. wherein the microscope objective (2) has a flattened field of view (fFOV) with a diameter (Obj), and a numerical aperture (NA) such that: NA * Obj > 1 mm. [2] Apochromatic microscope objective (2) according to claim 1, wherein the second lens group (G2) comprises a diverging lens (L2) which is made of a material having an Abbe number (vd) of at least 75. [3] Apochromatic microscope objective (2) according to claim 1 or 2, characterized by that the numerical aperture (NA) is at least 0.

09. [4] Apochromatic microscope objective (2) according to any one of claims 1 to 3, wherein the microscope objective (2) has a flattened field of view (fFOV) with a diameter (Obj) of at least 8 mm. [5] Apochromatic microscope objective (2) according to any one of the preceding claims, characterized by that the first lens group (G1) is formed as a single lens (L1). [6] Apochromatic microscope objective (2) according to any one of the preceding claims, characterized by that the second lens group (G2) is formed as a single lens (L2). [7] Apochromatic microscope objective (2) according to any one of the preceding claims, characterized by that the third lens group (G3) has two cemented members. [8] Apochromatic microscope objective (2) according to any one of the preceding claims, characterized by a magnification of no more than 5x. [9] Apochromatic microscope objective (2) according to any one of the preceding claims, characterized by that the diverging lens (L2) is bi-concave. [10] Apochromatic microscope objective (2) according to any one of the preceding claims, characterized by that it is apochromatically corrected over an extended apochromatic spectral range. [11] Apochromatic microscope objective (2) according to any one of the preceding claims, characterized by , that for a ratio of a distance (t12) between the first lens group (G1) and the second lens group (G2) and a total length (ta) of the microscope objective (2) the following holds: t 12 : t a < 0.

2. [12] Apochromatic microscope objective (2) according to any one of the preceding claims, characterized byThe following optical design data: Surface No. r (mm) d (mm) and vd 1 -1825.754 3.80 1.883 40.76 2 -18.625 7.57 3 -19.781 3.19 1.434 95.22 4 18.516 22.33 5 -11.210 2.51 1.804 46.50 6 26.919 3.49 1.487 84.47 7 -12.340 0.24 8 56.402 3.67 1.434 95.22 9 -13.970 5.51 1.847 23.78 10 -16.785 [13] comprising an optical system 13.

1. a microscope objective (2) according to one of the preceding claims and 13.

2. a tube lens unit (6). [14] Microscope (1) with a microscope objective (2) according to any one of claims 1 to 12.

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