Long-working-distance flat-field apochromatic microscope objective capable of forming phase difference

Abstract

The invention belongs to the technical field of microobjective optical design, and provides a long-working-distance flat-field apochromatic microobjective capable of forming phase difference, so as to solve the technical problem that an existing microobjective is poor in imaging effect on a transparent sample, a switchable phase ring with a coating film is arranged at a rear focal plane and used for delaying the light wave phase of the sample, and the imaging effect of the sample is improved. Phase difference is formed by interference with background light; the optical system is sequentially and coaxially provided with a first balsaming lens, a third lens, a second balsaming lens, a seventh lens and an eighth lens from the image space to the object space along the optical axis, and the focal lengths of the lenses meet the condition that fG1 / f is larger than-6 and smaller than 0; 0 < fG2 / f < 6; 0 < f3 / f < 10; 0 < f7 / f < 3; and f8 / f is greater than 0 and less than 10, so that a working distance of 3.0 mm and system resolution are ensured, secondary spectral aberration can be corrected to realize apochromatic, the field curvature defect of an optical system is overcome, the imaging quality of the field edge is improved, and the optical system can be applied to the technical fields of bioengineering and medicine.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical design of microscopic objectives. Background Art

[0002] With the continuous development of the biological and medical industries in recent years, the requirements for microscopic objectives are also constantly increasing. Microscopic objectives used in precision biomedical research basically require a flat field and apochromatism. For example, the Chinese patent (a wide-spectrum flat-field apochromatic microscopic objective, application number 201710387651.4) provides a microscopic objective. Although it meets the design requirements of flat-field apochromatism, its working distance is short, the RMS radius is not within the Airy disk radius, and the MTF does not approach the diffraction limit, resulting in poor imaging effects and general acquisition effects for bright-field transparent samples. Summary of the Invention

[0003] The purpose of the present invention is to provide a flat-field apochromatic microscopic objective with a long working distance, a large numerical aperture, and improved imaging quality for transparent samples.

[0004] A long-working-distance flat-field apochromatic microscopic 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. It 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 in sequence from the image side to the object side along the optical axis. The first cemented lens is used to reduce chromatic aberration and compensate for dispersion, the third lens is used to reduce the focal deviation between the marginal rays and the central rays, 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 each lens satisfy:

[0006] -6 < / < 0,

[0007] 0 < / < 6,

[0008] 0 < / < 10,

[0009] 0 < / < 3,

[0010] 0 < / < 10,

[0011] Wherein, represents the total focal length of the long working distance apochromatic microscopic objective lens, represents the focal length of the first cemented lens, represents the focal length of the second cemented lens, represents the focal length of the third lens, represents the focal length of the seventh lens, represents the focal length of the eighth lens.

[0012] Technical effects:

[0013] The present invention adopts multiple pieces of low-dispersion glass of the H-PK and H-FK series, which have low refractive index and high Abbe number. Their unique dispersion properties can effectively solve the dispersion problem of the optical system; the adoption of the doublet lens group (G1) and the triplet lens group (G2) not only reduces the number of lens groups and simplifies the overall structure of the microscopic objective lens optical system, but also while ensuring a long working distance of 3.0 mm and the system resolution, it can not only correct the secondary spectrum chromatic aberration and higher-order aberrations, further compress the chromatic aberration range through three materials with significantly different Abbe numbers to achieve apochromatism, and at the same time reduce the influence of assembly errors on imaging, solve the field curvature defect of the optical system, and improve the imaging quality at the edge of the field of view.

[0014] By setting a coated phase ring, the phase shift here is +¼λ. For the light scattered due to the sample properties that does not pass through here, its phase usually shifts -¼λ. Interference occurs between the background light and the scattered light to form a 180° phase difference, as Figure 2 and Figure 3 shown. Colorless and transparent samples have light and dark differences due to different refractive indices, and are especially suitable for observing transparent biological samples (such as living cells), unstained specimens or other low-contrast samples, and can be applied in the fields of bioengineering technology, medicine, and microscopic objective lens imaging technology.

[0015] Figure 4 is the axial chromatic aberration curve graph of the embodiment. The ordinate is the normalized radius of the entrance pupil. As can be seen from Figure 4 , the axial chromatic aberration is well corrected. At the full aperture, the chromatic aberration at the three wavelength bands in the 0.707 annulus is much smaller than the focal depth of the optical system of 2.57 μm, meeting the requirements of apochromatism.

[0016] Figure 5 is the field curvature graph of the embodiment. The ordinate is the field of view of the optical system, and the abscissa is the field curvature defocus amount. As can be seen from Figure 5 , the field curvature value at the edge of the field of view is less than 2 μm, and the astigmatism is less than 1%, meeting the flat field requirements of the microscopic objective lens.

[0017] Figure 6 is the distortion graph of the embodiment. The ordinate is the field of view of the optical system, and the abscissa is the distortion percentage. As can be seen from Figure 6 , the maximum distortion of the optical system is less than 0.3%.

[0018] Figure 7 For the MTF curve graph of the embodiment, the transfer function approximates the diffraction limit. Brief Description of the Drawings

[0019] Figure 1 It is a schematic structural diagram of a long working distance planachromatic apochromatic microscope objective.

[0020] Figure 2 It is a schematic diagram of the effect of observing a transparent sample in bright field.

[0021] Figure 3 It is a schematic diagram of the effect of observing a transparent sample in dark field.

[0022] Figure 4 It is the axial chromatic aberration curve graph of the full field of view of a long working distance planachromatic apochromatic microscope objective.

[0023] Figure 5 It is the field curvature graph of a long working distance planachromatic apochromatic microscope objective.

[0024] Figure 6 It is the distortion graph of a long working distance planachromatic apochromatic microscope objective.

[0025] Figure 7 It is the MTF curve graph of a long working distance planachromatic apochromatic microscope objective. Detailed Embodiment

[0026] As Figure 1 shown, in the embodiment of the present invention, a switchable coated phase ring 9 is provided at the rear focal plane, which is used to delay the phase of the sample light wave and interfere with the background light to form a brightness difference. The phase absorption thin film of the phase ring is a ring-shaped thin film of different materials plated on a glass substrate, such as a single-layer MgF2 thin film and an absorbent Cr thin film. Further, between the first cemented lens G1 and the thread of the microscope objective housing, a semi-circular buckle is provided to achieve targeted bright and dark field switching, so that an image with higher contrast can be generated. A compensation ring can also be added to the thread of the microscope objective housing at the same time. The purpose is to solve the influence of different refractive indexes of each stage or sample thickness and medium on the imaging effect; by rotating the compensation ring, the distance between the microscope objective and the sample can be changed. When replacing the sample or stage, only need to rotate the compensation ring to keep the optical path length unchanged, so as to obtain better imaging quality and greatly improve the observation experiment efficiency and work efficiency.

[0027] It further includes an optical system, which successively and coaxially arranges 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. The first cemented lens G1 is used to reduce chromatic aberration and compensate for dispersion. The third lens 3 is used to reduce the focal deviation between marginal rays 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 with positive optical power is composed of a first lens 1 and a second lens 2 cemented together. The first lens 1 is a meniscus positive lens, and the second lens 2 is a meniscus negative lens. The second cemented lens G2 with positive optical power is composed of a fourth lens 4, a fifth lens 5, and a sixth lens 6 cemented together. 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 negative lens, the seventh lens 7 is a biconvex positive lens, and the eighth lens 8 is a convex meniscus positive lens.

[0028] In the first cemented lens G1 or the second cemented lens G2, the difference in Abbe numbers between adjacent positive and negative lenses satisfies the inequality 0 < < 60.

[0029] The image side S1 of the first cemented lens G1 is convex, and the object side S3 is convex;

[0030] The image side S4 of the third lens 3 is convex, and the object side S5 is convex;

[0031] The image side S6 of the second cemented lens G2 is convex, and the object side S9 is concave;

[0032] The image side S10 of the seventh lens 7 is convex, and the object side S11 is concave;

[0033] The image side S12 of the eighth lens 8 is convex, and the object side S13 is convex.

[0034] The following relationships are satisfied among the focal lengths of the respective lenses:

[0035] -6 < / < 0,

[0036] 0 < / < 6,

[0037] 0 < / < 10,

[0038] 0 < / < 3,

[0039] 0 < / <10,

[0040] wherein, represents the total focal length of the long working distance apochromatic microscopic objective lens, represents the focal length of the first cemented lens G1, represents the focal length of the second cemented lens G2, represents the focal length of the third lens 3, represents the focal length of the seventh lens 7, represents the focal length of the eighth lens 8.

[0041] Furthermore, the radius of curvature r1 of the image side S1 of the first cemented lens G1 satisfies: 5 < r1 < 15; the radius of curvature r2 of the cemented surface S2 of the first lens 1 and the second lens 2 satisfies: 0 < r2 < 10; the radius of curvature r3 of the object side S3 of the first cemented lens G1 satisfies: 0 < r3 < 10; the radius of curvature r4 of the image side S4 of the third lens 3 satisfies: 5 < r4 < 15; the radius of curvature r5 of the object side S5 of the third lens 3 satisfies: 0 < r5 < 10; the radius of curvature r6 of the image side S6 of the second cemented lens G2 satisfies: 10 < r6 < 20; the radius of curvature r7 of the cemented surface S7 of the fourth lens 4 and the fifth lens 5 satisfies: -10 < r7 < 0; the radius of curvature r8 of the cemented surface S8 of the fifth lens and the sixth lens satisfies: 5 < r8 < 15; the radius of curvature r9 of the object side S9 of the second cemented lens G2 satisfies: -15 < r9 < -5; the radius of curvature r 10 satisfies: 5 < r 10 <15; the radius of curvature r 11 of the object side S11 of the seventh lens 7 satisfies: -55 < r 11 < -25; the radius of curvature r 12 of the image side S12 of the eighth lens 8 satisfies: 0 < r 12 <15; the radius of curvature r 13 of the object side S13 of the eighth lens 8 satisfies: 0 < r 13 <10.

[0042] Now, a set of parameter value examples is given as shown in the following table, where the units of the mirror surface radius of curvature, lens thickness, and air gap are all mm.

[0043]

[0044] All the lenses in the optical system are spherical lenses, and aspherical, free-form surface, etc. optical lenses can also be used.

[0045] An embodiment of the present invention provides a planapochromatic microscope objective with a focal length of 10 mm, a full field of view in the object space of 4.4 mm, a numerical aperture greater than 0.4, a back working distance greater than 3 mm, and a visible light band, which can realize bright and dark field switching when observing instruments such as culture dishes and cell factories, effectively improving the observation work efficiency. While ensuring a long working distance and system resolution, the field curvature distortion and secondary spectrum chromatic aberration of the optical system are also well corrected.

Claims

1. A long working distance apochromatic microscope objective lens 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. It 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) in sequence from the image side to the object side along the optical axis. The first cemented lens (G1) is used to reduce chromatic aberration and perform dispersion compensation. The third lens (3) is used to reduce the focal deviation between the marginal rays and the 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 focal lengths of each lens satisfy: -6＜ / ＜0， 0＜ / ＜6， 0＜ / ＜10， 0＜ / ＜3， 0＜ / ＜10， Among them, represents the total focal length of the long working distance apochromatic microscopic objective lens, represents the focal length of the first cemented lens (G1), represents the focal length of the second cemented lens (G2), represents the focal length of the third lens (3), represents the focal length of the seventh lens (7), represents the focal length of the eighth lens (8).

2. The long working distance flat field apochromatic microscope objective lens capable of forming a phase difference according to claim 1, characterized in that, The first cemented lens (G1) with positive optical power is composed of a first lens (1) and a second lens (2) cemented together. The first lens (1) is a meniscus positive lens, and the second lens (2) is a meniscus negative lens. The second cemented lens (G2) with positive optical power is composed of a fourth lens (4), a fifth lens (5), and a sixth lens (6) cemented together. 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.

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

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

5. The long working distance flat field apochromatic microscope objective lens capable of forming a phase difference according to claim 1, wherein The third lens (3) is a convex meniscus negative lens, the seventh lens (7) is a biconvex positive lens, and the eighth lens (8) is a convex meniscus positive lens.

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

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

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