Long working distance plan apochromatic microscope objectives capable of generating phase contrast

Abstract

The present invention belongs to the technical field of microscope objective optical design. It provides a long working distance plan-field apochromatic microscope objective capable of forming a phase difference, so as to solve the technical problem that existing microscope objective lenses have poor imaging effects on transparent samples. A switchable coated phase ring is provided at the rear focal plane to delay the phase of the sample light wave and interfere with the background light to form a phase difference. The optical system also includes a first cemented lens, a third lens, a second cemented lens, a seventh lens, and an eighth lens coaxially arranged in sequence along the optical axis from the image side to the object side. The focal lengths of the lenses meet the following requirements: f G1 / f <0;0< f G2 / f <6;0< f 3 / f <10;0< f 7 / f <3;0< f 8 / f <10. While ensuring a 3.0mm long working distance and system resolution, it can correct secondary spectral chromatic aberration to achieve apochromatism, while solving the field curvature defects of the optical system and improving the imaging quality at the edge of the field of view. It can be applied in the fields of bioengineering and medical technology.

Description

Technical Field

[0001] The invention belongs to the technical field of microscope objective optical design. Background Art

[0002] With the continuous development of the biology and medical industries in recent years, the requirements for microscope objectives have also been continuously increasing. Microscope objectives used in precision biomedical research are basically required to be flat and apochromatic. For example, a Chinese patent (A wide-spectrum flat-field apochromatic microscope objective, application number 201710387651.4) provides a microscope objective that meets the design requirements of flat-field apochromatism, but its working distance is short, the RMS radius is not within the radius of the Airy disk, and the MTF is not close to the diffraction limit, resulting in poor imaging effects and mediocre acquisition effect for brightfield transparent samples. Summary of the Invention

[0003] The object of the present invention is to provide a plan apochromatic microscope objective lens with a long working distance, a large numerical aperture and improved imaging quality for transparent samples.

[0004] A long-working-distance plan-field apochromatic microscope objective capable of forming a phase difference is provided with a switchable coated phase ring at the rear focal plane for delaying the phase of the sample light wave and interfering with the background light to form a phase difference; the objective also includes an optical system, which is coaxially provided with a first cemented lens, a third lens, a second cemented lens, a seventh lens, and an eighth lens along the optical axis from the image side to the object side, wherein the first cemented lens is used to reduce chromatic aberration and dispersion compensation, the third lens is used to reduce the focus deviation between the marginal light and the central light, the second cemented lens is used to correct the secondary spectrum to achieve apochromatism, the seventh lens is used to increase the overall optical power of the optical system, and the eighth lens is used to correct the overall field curvature of the optical system;

[0005] The focal lengths of the lenses satisfy:

[0006] -6<f G1 / f<0,

[0007] 0<f G2 / f<6,

[0008] 0<f3 / f<10,

[0009] 0<f7 / f<3,

[0010] 0<f8 / f<10,

[0011] Where f is the total focal length of the long working distance plan apochromatic microscope objective, f G1 represents the focal length of the first doublet lens, f G2 f7 represents the focal length of the seventh lens, and f8 represents the focal length of the eighth lens.

[0012] The first cemented lens with negative optical power is formed by cementing a first lens and a second lens, wherein the first lens is a positive meniscus lens and the second lens is a negative meniscus lens; the second cemented lens with positive optical power is formed by cementing a fourth lens, a fifth lens and a sixth lens, wherein the fourth lens is a biconvex positive lens, the fifth lens is a biconcave negative lens and the sixth lens is a biconvex positive lens; the third lens is a convex meniscus positive lens, the seventh lens (7) is a biconvex positive lens and the eighth lens (8) is a convex meniscus positive lens.

[0013] Technical effects:

[0014] The present invention adopts multiple pieces of H-PK and H-FK series low-dispersion glass with low refractive index and high Abbe number. Its unique dispersion properties can effectively solve the dispersion problem of the optical system. The use of a doublet lens group (G1) and a triplet lens group (G2) not only reduces the number of lens groups and simplifies the overall structure of the microscope objective optical system, but also corrects secondary spectral chromatic aberration and high-order aberrations while ensuring a long working distance of 3.0 mm and system resolution. The chromatic aberration range is further compressed by using three materials with significantly different Abbe numbers to achieve apochromatism, while reducing the influence of assembly errors on imaging, solving the field curvature defects of the optical system, and improving the imaging quality at the edge of the field of view.

[0015] By setting up a coated phase ring, the phase shift of light passing through this ring is +1 / 4λ, and the phase of light scattered by the sample that does not pass through this ring is usually shifted by -1 / 4λ. Interference occurs between the background light and the scattered light to form a 180° phase difference, such as Figure 2 and Figure 3 As shown, colorless and transparent samples produce light and dark differences due to different refractive indices, which is particularly suitable for observing transparent biological samples (such as living cells), unstained specimens or other low-contrast samples. It can be applied in the fields of bioengineering technology, medicine and microscope imaging technology.

[0016] Figure 4 is the full-field axial chromatic aberration curve of the embodiment, the ordinate is the normalized radius of the entrance pupil, Figure 4 It can be seen that the axial chromatic aberration is well corrected. At full aperture, the chromatic aberration at the three bands of the 0.707 annular zone is much smaller than the focal depth of the optical system of 2.57μm, meeting the requirements of apochromatism.

[0017] Figure 5 The field curvature diagram of the embodiment, the ordinate is the field of view of the optical system, the abscissa is the field curvature defocus amount, Figure 5 It can be seen that the edge field curvature value is less than 2μm and the astigmatism is less than 1%, which meets the flat field requirement of the microscope objective.

[0018] Figure 6The distortion diagram of the embodiment, the ordinate is the field of view of the optical system, the abscissa is the distortion percentage, Figure 6 It can be seen that the maximum distortion of the optical system is less than 0.3%.

[0019] Figure 7 The MTF curve of the embodiment shows that the transfer function approaches the diffraction limit. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the structure of a long working distance plan-field apochromatic microscope objective.

[0021] Figure 2 Schematic diagram of the effect of bright field observation of transparent samples.

[0022] Figure 3 Schematic diagram of the dark field observation effect of transparent samples.

[0023] Figure 4 This is a graph showing the full-field axial chromatic aberration curve for a long working distance plan-apochromatic microscope objective.

[0024] Figure 5 A plot of the field curvature for a long working distance plan-apochromat microscope objective.

[0025] Figure 6 Distortion diagram of a long working distance plan-apochromatic microscope objective.

[0026] Figure 7 This is the MTF curve of a long working distance plan apochromatic microscope objective. DETAILED DESCRIPTION

[0027] like Figure 1 As shown, the embodiment of the present invention is provided with a switchable coated phase ring 9 at the rear focal plane for delaying the phase of the sample light wave and interfering with the background light to form a brightness difference. The phase absorption film of the phase ring is coated on the glass substrate with annular thin films of different materials, such as a single-layer MgF2 film and a light-absorbing Cr film. Furthermore, a semicircular ring buckle is provided between the first cemented lens G1 and the screw thread of the microscope objective housing to achieve targeted switching between bright and dark fields, thereby producing images with higher contrast. A compensation ring can also be added to the screw thread of the microscope objective housing at the same time, the purpose of which is to solve the influence of different refractive indices of different thicknesses and media of various loads or samples on the imaging effect; the distance between the microscope objective and the sample can be changed by rotating the compensation ring. When changing the sample or load, it is only necessary to rotate the compensation ring to keep the optical path length unchanged, thereby obtaining better imaging quality, greatly improving the efficiency of the observation experiment, and improving work efficiency.

[0028] The optical system further comprises a first cemented lens G1, a third lens 3, a second cemented lens G2, a seventh lens 7, and an eighth lens 8, which are coaxially arranged along the optical axis from the image side to the object side. The first cemented lens G1 is used to reduce chromatic aberration and compensate for dispersion. The third lens 3 is used to reduce the focus deviation between the peripheral and central rays. The second cemented lens G2 is used to correct the secondary spectrum to achieve apochromatism. The seventh lens 7 is used to increase the overall optical power of the optical system. The eighth lens 8 is used to correct the overall field curvature of the optical system. The first cemented lens G1, which has negative focal power, is cemented together with the first lens 1 and the second lens 2. The first lens 1 is a positive meniscus lens, and the second lens 2 is a negative meniscus lens. The second cemented lens G2, which has positive focal power, is cemented together with the fourth lens 4, the fifth lens 5, and the sixth lens 6. The fourth lens 4 is a biconvex positive lens, the fifth lens 5 is a biconcave negative lens, and the sixth lens 6 is a biconvex positive lens. The third lens 3 is a convex meniscus positive lens, the seventh lens 7 is a biconvex positive lens, and the eighth lens 8 is a convex meniscus positive lens.

[0029] In the first cemented lens G1 or the second cemented lens G2, the Abbe number difference Δν between adjacent positive lenses and negative lenses satisfies the inequality 0<Δν<60.

[0030] The image-side surface S1 of the first cemented lens G1 is convex, and the object-side surface S3 is convex;

[0031] The image-side surface S4 of the third lens 3 is convex, and the object-side surface S5 is convex;

[0032] The image-side surface S6 of the second cemented lens G2 is convex, and the object-side surface S9 is concave;

[0033] The image-side surface S10 of the seventh lens element 7 is convex, and the object-side surface S11 is concave;

[0034] The image-side surface S12 of the eighth lens 8 is a convex surface, and the object-side surface S13 is a convex surface.

[0035] The focal lengths of the lenses satisfy:

[0036] -6<f G1 / f<0,

[0037] 0<f G2 / f<6,

[0038] 0<f3 / f<10,

[0039] 0<f7 / f<3,

[0040] 0<f8 / f<10,

[0041] Where f is the total focal length of the long working distance plan apochromatic microscope objective, f G1 represents the focal length of the first cemented lens G1, f G2f represents the focal length of the second cemented lens G2 , f3 represents the focal length of the third lens 3 , f7 represents the focal length of the seventh lens 7 , and f8 represents the focal length of the eighth lens 8 .

[0042] Furthermore, the curvature radius r1 of the image side surface S1 of the first cemented lens G1 satisfies: 5<r1<15; the curvature radius r2 of the cemented surface S2 of the first lens 1 and the second lens 2 satisfies: 0<r2<10; the curvature radius r3 of the object side surface S3 of the first cemented lens G1 satisfies: 0<r3<10; the curvature radius r4 of the image side surface S4 of the third lens 3 satisfies: 5<r4<15; the curvature radius r5 of the object side surface S5 of the third lens 3 satisfies: 0<r 5<10; the curvature radius r6 of the image-side surface S6 of the second cemented lens G2 satisfies: 10<r6<20; the curvature radius r7 of the cemented surface S7 of the fourth lens 4 and the fifth lens 5 satisfies: -10<r7<0; the curvature radius r8 of the cemented surface S8 of the fifth lens and the sixth lens satisfies: 5<r8<15; the curvature radius r9 of the object-side surface S9 of the second cemented lens G2 satisfies: -15<r9<-5; the curvature radius r10 of the image-side surface S10 of the seventh lens 7 satisfies: 10 Satisfaction: 5<r 10 <15; the curvature radius r of the object-side surface S11 of the seventh lens 7 11 Satisfy: -55<r 11 <-25; the curvature radius r of the image side surface S12 of the eighth lens 8 12 Satisfy: 0<r 12 <15; the curvature radius r of the object-side surface S13 of the eighth lens 8 13 Satisfy: 0<r 13 <10.

[0043] A set of parameter value examples are given below, as shown in the table below, where the units of the mirror curvature radius, lens thickness, and air gap are all in mm.

[0044]

[0045] Each lens in the optical system is a spherical lens, but optical lenses with aspherical surfaces, free-form surfaces, etc. can also be used.

[0046] The embodiment of the present invention provides a plan-apochromatic microscope objective lens with a focal length of 10 mm, a full object field of view of 4.4 mm, a numerical aperture greater than 0.4, a back working distance greater than 3 mm, and a visible light band. The objective lens can switch between bright and dark fields when observing culture dishes, cell factories, and other instruments, effectively improving observation efficiency. While ensuring a long working distance and system resolution, the field curvature distortion and secondary spectral chromatic aberration of the optical system are also well corrected.

Claims

1. A long working distance plan-apochromatic microscope objective capable of forming a phase difference, characterized in that: A switchable coated phase ring (9) is provided at the rear focal plane for delaying the phase of the sample light wave and interfering with the background light to form a phase difference; the optical system also includes an optical system, which is coaxially provided with a first cemented lens (G1), a third lens (3), a second cemented lens (G2), a seventh lens (7), and an eighth lens (8) along the optical axis from the image side to the object side, wherein the first cemented lens (G1) is used to reduce chromatic aberration and dispersion compensation, the third lens (3) is used to reduce the focus deviation between the edge light and the central light, the second cemented lens (G2) is used to correct the secondary spectrum to achieve apochromatism, the seventh lens (7) is used to increase the overall optical power of the optical system, and the eighth lens (8) is used to correct the overall field curvature of the optical system; The focal lengths of the lenses satisfy: -6<f G1 / f<0, 0<f G2 / f<6, 0<f3 / f<10, 0<f7 / f<3, 0<f8 / f<10, Where f is the total focal length of the long working distance plan apochromatic microscope objective, f G1 represents the focal length of the first cemented lens (G1), f G2 represents the focal length of the second cemented lens (G2), f3 represents the focal length of the third lens (3), f7 represents the focal length of the seventh lens (7), and f8 represents the focal length of the eighth lens (8); A first cemented lens (G1) with negative optical power is formed by cementing a first lens (1) and a second lens (2), wherein the first lens (1) is a positive meniscus lens and the second lens (2) is a negative meniscus lens; a second cemented lens (G2) with positive optical power is formed by cementing a fourth lens (4), a fifth lens (5) and a sixth lens (6), wherein the fourth lens (4) is a biconvex positive lens, the fifth lens (5) is a biconcave negative lens and the sixth lens (6) is a biconvex positive lens; The third lens (3) is a convex meniscus positive lens, the seventh lens (7) is a double convex positive lens, and the eighth lens (8) is a convex meniscus positive lens.

2. The long working distance plan-apochromatic microscope objective capable of forming a phase difference according to claim 1, characterized in that: In the first cemented lens (G1) or the second cemented lens (G2), the Abbe number difference Δν between adjacent positive lenses and negative lenses satisfies the inequality 0<Δν<60.

3. The long working distance plan-apochromatic microscope objective capable of forming a phase difference according to claim 1, characterized in that: The image-side surface S1 of the first cemented lens (G1) is a convex surface, and the object-side surface S3 is a convex surface; the curvature radius r1 of the image-side surface S1 of the first cemented lens (G1) satisfies: 5<r1<15; the curvature radius r2 of the cemented surface S2 of the first lens 1 and the second lens 2 satisfies: 0<r2<10; The curvature radius r3 of the object-side surface S3 of the first cemented lens G1 satisfies: 0<r3<10; The image side surface S6 of the second cemented lens (G2) is a convex surface, and the object side surface S9 is a concave surface; the curvature radius r6 of the image side surface S6 of the second cemented lens (G2) satisfies: 10<r6<20; the curvature radius r7 of the cemented surface S7 of the fourth lens (4) and the fifth lens (5) satisfies: -10<r7<0; the curvature radius r8 of the cemented surface S8 of the fifth lens (5) and the sixth lens (6) satisfies: 5<r8<15; the curvature radius r9 of the object side surface S9 of the second cemented lens (G2) satisfies: -15<r9<-5.

4. The long working distance plan apochromatic microscope objective capable of forming a phase difference according to claim 1, characterized in that: The image side surface S4 of the third lens (3) is a convex surface, and the object side surface S5 is a convex surface; the curvature radius r4 of the image side surface S4 of the third lens 3 satisfies: 5<r4<15; the curvature radius r5 of the object side surface S5 of the third lens 3 satisfies: 0<r5<10; The image side surface S10 of the seventh lens (7) is convex, and the object side surface S11 is concave; the curvature radius r of the image side surface S10 of the seventh lens 7 is 10 Satisfaction: 5<r 10 <15; the curvature radius r of the object-side surface S11 of the seventh lens 7 11 Satisfy: -55<r 11 <-25; The image side surface S12 of the eighth lens (8) is convex, and the object side surface S13 is convex; the curvature radius r of the image side surface S12 of the eighth lens 8 is 12 Satisfy: 0<r 12 <15; the curvature radius r of the object-side surface S13 of the eighth lens 8 13 Satisfy: 0<r 13 <10.

5. The long working distance plan apochromatic microscope objective capable of forming a phase difference according to claim 1, characterized in that: Its focal length is 10mm, the object space full field of view is 4.4mm, the numerical aperture is greater than 0.4, the back working distance is greater than 3mm, and the wavelength band is visible light.

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