A microscope objective

Abstract

The present application relates to the technical field of optical instruments, and discloses a microscope objective, which is suitable for at least a temperature environment of 50K to 150K and comprises: a front group unit, which comprises at least a first lens and a second lens arranged in sequence along an optical path, and is suitable for converging light rays and correcting spherical aberration; a middle group unit, which is arranged on the rear side of the optical path of the front group unit, comprises at least a first middle group and a second middle group, and is arranged in sequence along the optical path, each middle group is provided with at least two lenses arranged at intervals, and is suitable for correcting chromatic aberration; and a rear group unit, which is arranged on the rear side of the optical path of the middle group unit and comprises at least two lenses arranged at intervals; each lens contained in the front group unit, the middle group unit and the rear group unit is a single lens. By arranging each lens as a single lens, the combination connection of each unit and the whole microscope objective is avoided, the problems of damage, falling or air leakage in an extreme environment such as low temperature are avoided, and the application in a low-temperature environment is met.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical instruments, in particular to a microscope objective. BACKGROUND

[0002] Visual imaging is an important research method in low-temperature imaging research in many fields, such as epoxy resin electric tree growth, liquid nitrogen two-phase fluid dynamics, etc.

[0003] However, conventional microscope objectives usually adopt double cemented lens or triple cemented lens group to correct lens chromatic aberration, so as to achieve excellent imaging effect. However, the cemented lens may be separated and outgassed in a low-temperature environment, which affects the imaging effect and structural life of the objective. SUMMARY

[0004] Therefore, the present application provides a microscope objective to solve the problem that the existing microscope objective cannot effectively detect in a low-temperature environment.

[0005] In a first aspect, the present application provides a microscope objective, which is suitable for at least a temperature environment of 50K to 150K, and comprises: a front group unit, which comprises at least a first lens and a second lens arranged in sequence along an optical path, and is adapted to converge light and correct spherical aberration; a middle group unit, which is arranged on the rear side of the optical path of the front group unit, comprises at least a first middle group and a second middle group, and is arranged in sequence along the optical path, each middle group is provided with at least two lenses arranged at intervals, and is adapted to correct chromatic aberration; and a rear group unit, which is arranged on the rear side of the optical path of the middle group unit, and comprises at least two lenses arranged at intervals; each lens contained in the front group unit, the middle group unit and the rear group unit is a single lens.

[0006] Beneficial effects

[0007] By setting each lens contained in the front group unit, the middle group unit and the rear group unit as a single lens, the combination connection of the cemented lens is avoided in each unit and the whole microscope objective, so as to avoid the problems of damage, separation or outgassing in an extreme environment such as low temperature, and meet the application in a low-temperature environment. At the same time, the front group unit, the middle group unit and the rear group unit are respectively set to correct the spherical aberration, chromatic aberration and off-axis aberration, and the aplanatization is realized by the separate lenses, so as to ensure that the microscope objective has sufficient observation accuracy.

[0008] In an optional embodiment, the first lens and the second lens are arranged as positive lenses, and are arranged in the same direction with a curved arc, are adapted to be concave to the object to be observed, and jointly provide positive focal power.

[0009] In an optional embodiment, the refractive index of the first lens is higher than that of the second lens; the first lens is composed of a low Abbe number material, and the second lens is composed of a high Abbe number material.

[0010] In an alternative embodiment, the middle group unit further comprises a third middle group, which is disposed on the rear side of the second middle group along the optical path.

[0011] In an alternative embodiment, the first middle group comprises a third lens, a fourth lens and a fifth lens, which are disposed in sequence along the optical path, the fourth lens is disposed as a negative lens, adapted to provide negative focal power, the third lens and the fifth lens are disposed as positive lenses, adapted to provide positive focal power respectively; the refractive index of the fourth lens is higher than that of the third lens and the fifth lens respectively, adapted to adjust coma, the fourth lens is composed of a material with low Abbe number, and the third lens and the fifth lens are composed of a material with high Abbe number.

[0012] In an alternative embodiment, the second middle group comprises a sixth lens and a seventh lens respectively, and the third middle group comprises an eighth lens and a ninth lens respectively, the sixth lens, the seventh lens, the eighth lens and the ninth lens are disposed in sequence along the optical path, the sixth lens and the eighth lens are disposed as negative lenses, adapted to provide negative focal power, the seventh lens and the ninth lens are disposed as positive lenses, adapted to provide positive focal power; the refractive index of the sixth lens is greater than that of the seventh lens, the refractive index of the eighth lens is greater than that of the ninth lens, the sixth lens and the eighth lens are composed of a material with low Abbe number respectively, and the seventh lens and the ninth lens are composed of a material with high Abbe number.

[0013] In an alternative embodiment, the rear group unit is disposed in a symmetric double-Gaussian structure, comprising a tenth lens, an eleventh lens, a twelfth lens and a thirteenth lens distributed in sequence along the optical path, the eleventh lens and the twelfth lens are disposed as negative lenses, adapted to provide negative focal power, and the tenth lens and the thirteenth lens are disposed as positive lenses, adapted to provide positive focal power.

[0014] In an alternative embodiment, the refractive index of the thirteenth lens is greater than that of the tenth lens, the eleventh lens and the twelfth lens; the thirteenth lens and the eleventh lens are composed of a material with low Abbe number respectively, and the tenth lens and the twelfth lens are composed of a material with high Abbe number.

[0015] In an alternative embodiment, the focal length of the microscope objective is fx, the focal length of the first lens is f1, and 4.1≤f1 / fx≤4.5; the focal length of the second lens is f2, and 6.7≤f2 / fx≤7.1.

[0016] In an alternative embodiment, the focal length of the front group is fa, 2.3≤fa / fx≤2.7, the focal length of the first middle group is fb, 6.5≤fb / fx≤6.9, the focal length of the second middle group is fc, 12.8≤fc / fx≤14.2, the focal length of the third middle group is fd, 50≤fd / fx≤54, and the focal length of the rear group is fe, -7.9≤fe / fx≤-7.5.

[0017] In an alternative embodiment, 3.9mm≤fx≤4.1mm.

[0018] In an alternative embodiment, the aperture of the microscope objective is NA, 0.8≤NA≤0.9.

[0019] In an alternative embodiment, the object-side field of view of the microscope objective is B, 0≤B≤0.4mm; and / or, the distance between the first lens and the object to be observed is C, C≥1.6mm.

[0020] In an alternative embodiment, the thirteenth lens is an aspherical lens, the ninth lens is an aspherical lens, and the fifth lens is an aspherical lens. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings needed in the description of the embodiments or the prior art. Obviously, the drawings described below are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0022] Figure 1 The structure and optical path of a microscope objective according to an embodiment of the present application are shown in the following figure:

[0023] Figure 2 The structure and optical path of a microscope objective according to an embodiment of the present application are shown in the following figure: Figure 1 The ray aberration curve of the microscope objective shown in the following figure:

[0024] Figure 3 The ray aberration curve of the microscope objective shown in the following figure: Figure 1 The wavefront aberration curve of the microscope objective shown in the following figure:

[0025] Figure 4 The wavefront aberration curve of the microscope objective shown in the following figure: Figure 1 The MTF curve of the microscope objective shown in the following figure:

[0026] Figure 5 The MTF curve of the microscope objective shown in the following figure: Figure 1 The axial aberration curve of the microscope objective shown in the following figure:

[0027] Figure 6 The axial aberration curve of the microscope objective shown in the following figure:Figure 1 Field curvature and distortion curve diagram of the micro objective shown in the figure;

[0028] Explanation of reference signs:

[0029] 1, front group unit; 11, first lens; 12, second lens; 2, first middle group; 21, third lens; 22, fourth lens; 23, fifth lens; 3, second middle group; 31, sixth lens; 32, seventh lens; 4, third middle group; 41, eighth lens; 42, ninth lens; 5, rear group unit; 51, tenth lens; 52, eleventh lens; 53, twelfth lens; 54, thirteenth lens. DETAILED DESCRIPTION

[0030] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0031] As Figures 1-6 , in a first aspect, the present application provides a micro objective, in the present embodiment, the micro objective is suitable for a temperature environment of 50K to 150K, preferably, the temperature environment can be provided by immersing in liquid nitrogen or the like, it can be understood that the use environment temperature of the micro objective can also be higher than 150K or lower than 50K.

[0032] The micro objective comprises a front group unit 1, a middle group unit and a rear group unit 5, and is defined as follows: along the observation direction, the light path front side is relatively close to the target to be observed, and the light path rear side is relatively far away from the target to be observed.

[0033] The front group unit 1 comprises at least a first lens 11 and a second lens 12 arranged in sequence along the light path front and rear, and is suitable for converging light rays and correcting spherical aberration. The middle group unit is arranged on the light path rear side of the front group unit 1, comprises at least a first middle group 2 and a second middle group 3, and is arranged in sequence along the light path front and rear, each middle group is provided with at least two lenses arranged at intervals, and is suitable for correcting chromatic aberration; the rear group unit 5 is arranged on the light path rear side of the middle group unit, comprises at least two lenses arranged at intervals, and is suitable for correcting off-axis aberration.

[0034] Preferably, each lens contained in the front group unit 1, the middle group unit and the rear group unit 5 is a single lens. In the present embodiment, the single lens can be connected with the external structure such as a lens barrel through connection modes such as clamping, sealing abutment, interference fit, magnetic attraction, threaded connection, etc., to avoid being connected with the adjacent lens or external structure through adhesive connection.

[0035] By setting each lens contained in the front group unit 1, the middle group unit and the rear group unit 5 as a single lens, each unit and the whole microscopic objective lens avoids setting a cemented lens to realize the combined connection, avoids the problems of damage, falling or air leakage in the low temperature and other extreme environments, meets the application in the low temperature environment, and at the same time, by respectively setting the front group unit 1, the middle group unit and the rear group unit 5 to realize the correction of spherical aberration, chromatic aberration and axial aberration, the separated lens realizes aplanatism, and the microscopic objective lens has sufficient observation accuracy.

[0036] Preferably, the front group unit 1 only includes the first lens 11 and the second lens 12 arranged in sequence along the optical path. As a transformable embodiment, the front group unit 1 can also include three lenses.

[0037] In the embodiment, the first lens 11 and the second lens 12 are arranged as positive lenses, and are arranged in the same direction, suitable for concave to the object to be observed, and together provide positive focal power.

[0038] The first lens 11 and the second lens 12 in the front group unit 1 are both positive lenses providing focal power for the whole objective lens, can converge the light rays on the object side, reduce the light divergence angle, realize the correction of spherical aberration, and at the same time prepare for the correction of chromatic aberration by the middle group.

[0039] The refractive index of the first lens 11 is higher than that of the second lens 12, in addition, the first lens 11 is composed of a low Abbe number material, and the second lens 12 is composed of a high Abbe number material, in this embodiment, the low Abbe number material refers to the Abbe number of the material being equal to or lower than 50; the high Abbe number material refers to the Abbe number of the material being higher than 50.

[0040] By setting the front group unit 1 to include only two lenses, not only the material can be reduced, the cost can be saved, at the same time, combined with the size setting of the refractive index and the Abbe number of the two, the axial volume can be shorter under the premise of ensuring the imaging effect of the front group unit 1, the processing cost is lower, and the assembly difficulty is further reduced.

[0041] Preferably, the middle group unit also includes a third middle group 4, and the third middle group 4 is arranged at the rear side of the second middle group 3 along the optical path. As a transformable embodiment, the third middle group 4 can also not be arranged.

[0042] The arrangement of the third middle group 4 not only can realize the effect of correcting the chromatic aberration of the whole system in cooperation with the first middle group 2 and the second middle group 3, but also can assist the rear group unit 5 to improve the axial aberration correction ability of the rear group unit 5 by adjusting the distance between the two.

[0043] In the embodiment, the first middle group 2 comprises the third lens 21, the fourth lens 22 and the fifth lens 23, and is arranged in sequence along the optical path; the fourth lens 22 is arranged as a negative lens and is adapted to provide a negative focal power; and the third lens 21 and the fifth lens 23 are arranged as positive lenses and are adapted to provide positive focal powers respectively.

[0044] When the focal power structure of "negative-positive-negative" is adopted in the case of the same overall focal length, the positive lens in the middle part needs to bear a large focal power, the surface shape is relatively steep, the light incidence angle is large, the processing difficulty is high, and the subsequent antireflection film coating is difficult to improve. The first middle group 2 adopts the focal power structure of "positive-negative-positive", and the focal power is borne by two positive lenses, which can make the light transmission smooth, and at the same time, the processing difficulty of the lens is reduced.

[0045] In the embodiment, the refractive index of the fourth lens 22 is higher than that of the third lens 21 and the fifth lens 23 respectively, and is adapted to adjust coma; the fourth lens 22 is composed of a low Abbe number material, and the third lens 21 and the fifth lens 23 are composed of a high Abbe number material.

[0046] The second middle group 3 comprises the sixth lens 31 and the seventh lens 32 respectively, and the third middle group 4 comprises the eighth lens 41 and the ninth lens 42 respectively; the sixth lens 31, the seventh lens 32, the eighth lens 41 and the ninth lens 42 are arranged in sequence along the optical path; the sixth lens 31 and the eighth lens 41 are arranged as negative lenses and are adapted to provide negative focal powers; and the seventh lens 32 and the ninth lens 42 are arranged as positive lenses and are adapted to provide positive focal powers.

[0047] The second middle group 3 and the third middle group 4 are located at a relatively flat position of the optical path compared with the first middle group 2, and do not need to provide a large focal power. In order to ensure the best aberration correction effect, the principle of alternating positive and negative lenses should be followed, and at the same time, the seventh lens 32 and the eighth lens 41 adjacent to each other are also arranged as alternating positive and negative lenses to achieve the effect of chromatic aberration correction. Further, since the ninth lens 42 of the third middle group 4 is close to the tenth lens 51 of the rear group unit 5, in order to improve the off-axis aberration correction ability of the rear group unit 5, there is a lens in the rear group unit 5 that cooperates with the tenth lens 51 to form a symmetrical structure. In order to meet the needs of the rear group unit 5 for correcting off-axis chromatic aberration, the refractive index of the tenth lens 51 is relatively low compared to its symmetrical lens, so the focal power of the tenth lens 51 is relatively low. In order to make up for the focal power, the ninth lens 42 needs to be arranged as a positive lens to further make up for it, and then the positive and negative forms of other lenses in the second middle group 3 and the third middle group 4 can be determined respectively.

[0048] In the embodiment, the refractive index of the sixth lens 31 is greater than that of the seventh lens 32, and the refractive index of the eighth lens 41 is greater than that of the ninth lens 42; the sixth lens 31 and the eighth lens 41 are composed of a low Abbe number material respectively, and the seventh lens 32 and the ninth lens 42 are composed of a high Abbe number material.

[0049] Preferably, the rear group unit 5 is arranged in a symmetric double Gauss structure, comprising a tenth lens 51, an eleventh lens 52, a twelfth lens 53 and a thirteenth lens 54 arranged in sequence along the optical path. The eleventh lens 52 and the twelfth lens 53 are arranged as negative lenses, suitable for providing negative focal power, and the tenth lens 51 and the thirteenth lens 54 are arranged as positive lenses, suitable for providing positive focal power.

[0050] When the numerical aperture is large, the asymmetric structure will affect the correction effect of coma. By arranging the rear group unit 5 in a symmetric double Gauss structure, the effect of correcting axial and off-axis aberrations such as coma is further provided.

[0051] The refractive index of the thirteenth lens 54 is greater than that of the tenth lens 51, the eleventh lens 52 and the twelfth lens 53; the thirteenth lens 54 and the eleventh lens 52 are respectively composed of low Abbe number materials, and the tenth lens 51 and the twelfth lens 53 are composed of high Abbe number materials, preferably, the eleventh lens 52 is a special flint material.

[0052] Preferably, the focal length of the microscope objective is fx, the focal length of the first lens 11 is f1, and 4.1≤f1 / fx≤4.5; the focal length of the second lens 12 is f2, and 6.7≤f2 / fx≤7.1. Specifically, f1 / fx can be 4.1, 4.2, 4.3, 4.4 or 4.5, and f2 / fx can be 6.7, 6.8, 6.9, 7.0 or 7.1.

[0053] It can be understood that f1 / fx can be less than 4.1 or greater than 4.5, and f1 / fx can be less than 6.7 or greater than 7.1.

[0054] Preferably, the focal length of the front group unit 1 is fa, 2.3≤fa / fx≤2.7, the focal length of the first middle group 2 is fb, 6.5≤fb / fx≤6.9, the focal length of the second middle group 3 is fc, 12.8≤fc / fx≤14.2, the focal length of the third middle group 4 is fd, 50≤fd / fx≤54, and the focal length of the rear group unit 5 is fe, -7.9≤fe / fx≤-7.5. Specifically, fa / fx can be 2.3, 2.4, 2.5, 2.6 or 2.7, fb / fx can be 6.5, 6.6, 6.7, 6.8 or 6.9, fc / fx can be 12.8, 13.0, 13.2, 13.4, 13.6, 13.8, 14.0 or 14.2, fd / fx can be 50, 51, 52, 53 or 54, and fe / fx can be -7.9, -7.8, -7.7, -7.6 or -7.5.

[0055] Understandably, fa / fx can be less than 2.3 or greater than 2.7, fb / fx can be less than 6.5 or greater than 6.9, fc / fx can be less than 12.8 or greater than 14.2, fd / fx can be less than 50 or greater than 54, and fe / fx can be less than -7.9 or greater than -7.5.

[0056] Preferably, 3.9mm ≤ fx ≤ 4.1mm. Specifically, fx can be 3.9mm, 3.95mm, 4.00mm, 4.05mm, or 4.1mm, etc.

[0057] Understandably, fx can be less than 3.9mm or greater than 4.1mm.

[0058] Preferably, the aperture of the microscope objective is NA, 0.8≤NA≤0.9. Specifically, NA can be 0.8, 0.82, 0.84, 0.86, 0.88 or 0.9, etc.

[0059] Understandably, fx can be less than 0.8 or greater than 0.9.

[0060] Furthermore, preferably, the object-side field of view of the microscope objective is B, where 0 ≤ B ≤ 0.4 mm; specifically, B can be 0, 0.1 mm, 0.2 mm, 0.3 mm, or 0.4 mm, etc. The distance between the first lens 11 and the object to be observed is C, where C ≥ 1.6 mm, and C can be 1.6 mm, 2.0 mm, 2.4 mm, 2.8 mm, 3.2 mm, or greater. Understandably, 0 ≤ B ≤ 0.4 mm and C ≥ 1.6 mm can be set to only one of them.

[0061] Understandably, B can be greater than 0.4 mm, and C can be less than 1.6 mm.

[0062] like Figure 1 As shown in Table 1, preferably, the thirteenth lens 54, the ninth lens 42, and the fifth lens 23 are aspherical lenses. This arrangement is used to compensate for aberrations caused by changes in surface shape due to large temperature differences. In addition, other lenses in the microscope objective are preferably spherical structures.

[0063] In this embodiment, the preferred microscope objective parameters are shown in the table below:

[0064] Table 1. Microscope Objective Parameters

[0065]

[0066]

[0067] Preferably, the first lens 11 and the second lens 12 are arranged as meniscus positive lenses, together providing positive focal power, and concave towards the object side; the third lens 21 is arranged as a biconvex positive lens, providing positive focal power; the fourth lens 22 is arranged as a meniscus negative lens, providing negative focal power, and concave towards the object side; the fifth lens 23 is a biconvex positive lens, providing positive focal power; the sixth lens 31 is arranged as a meniscus negative lens, providing negative focal power, and convex towards the object side; the seventh lens 32 is arranged as a biconvex positive lens, providing positive focal power; the eighth lens 41 is arranged as a meniscus negative lens, providing negative focal power, and convex towards the object side; the ninth lens 42 is arranged as a biconvex positive lens, providing positive focal power; the tenth lens 51 is arranged as a meniscus positive lens, providing positive focal power, and convex towards the object side; the eleventh lens 52 is arranged as a meniscus negative lens, providing negative focal power, and convex towards the object side; the twelfth lens 53 is arranged as a biconcave negative lens, providing negative focal power; the thirteenth lens 54 is a meniscus positive lens, providing positive focal power, and concave towards the object side.

[0068] Furthermore, the first lens 11 mainly provides positive spherical aberration, negative coma, negative astigmatism, negative field curvature, negative axial chromatic aberration; the second lens 12 mainly provides positive spherical aberration, positive coma, positive astigmatism, positive field curvature, negative axial chromatic aberration; the third lens 21 mainly provides positive spherical aberration, positive coma, positive astigmatism, positive field curvature, negative axial chromatic aberration; the fourth lens 22 mainly provides negative spherical aberration, negative coma, negative astigmatism, negative field curvature, positive axial chromatic aberration; the fifth lens 23 mainly provides positive spherical aberration, positive coma, positive astigmatism, positive field curvature, negative axial chromatic aberration; the sixth lens 31 mainly provides negative spherical aberration, positive coma, positive astigmatism, negative field curvature, positive axial chromatic aberration; the seventh lens 32 mainly provides positive spherical aberration, positive coma, positive astigmatism, positive field curvature, negative axial chromatic aberration; the eighth lens 41 mainly provides negative spherical aberration, positive coma, negative astigmatism, negative field curvature, positive axial chromatic aberration; the ninth lens 42 mainly provides positive spherical aberration, negative coma, positive astigmatism, positive field curvature, negative axial chromatic aberration; the tenth lens 51 mainly provides positive spherical aberration, negative coma, positive astigmatism, positive field curvature, negative axial chromatic aberration; the eleventh lens 52 mainly provides negative spherical aberration, negative coma, negative astigmatism, negative field curvature, positive axial chromatic aberration; the twelfth lens 53 mainly provides negative spherical aberration, positive coma, negative astigmatism, negative field curvature, positive axial chromatic aberration; the thirteenth lens 54 mainly provides positive spherical aberration, negative coma, positive astigmatism, positive field curvature, negative axial chromatic aberration.

[0069] When the microscope objective is in the above-mentioned preferred range and preferred structure, the following applies:

[0070] The ray aberration curves of the microscope objective 0° field of view are shown in Figure 2 Figure 2 ​The horizontal coordinate Py, Px represents the normalized pupil position, and the vertical coordinate ey, ex represents the sagittal aberration. The maximum value of the vertical coordinate is 2.5um, and the minimum value is -2.5um. The left curve corresponds to the meridional direction aberration curve of the light beam, and the right curve corresponds to the sagittal direction aberration curve of the light beam. Figure 2 The aberration curves of different colors correspond to 450nm, 486nm, 545nm, 587nm and 640nm wavelengths respectively. Figure 2 In the range of 0 to 0.8 pupil, the light aberration value is between 0 and ±0.25um, in the range of 0.8 to 0.9 pupil, the light aberration value is between ±0.25um and ±0.5um, and in the range of 0.9 to 1.0 pupil, the light aberration value is between ±0.5um and ±2um. The overall aberration value is small, and the imaging quality is excellent.

[0071] The 0° field of view wavefront aberration curve of the microscope objective is shown in Figure 3 Figure 3 The horizontal coordinate Py, Px represents the normalized pupil position, and the vertical coordinate w represents the wavefront aberration. The maximum value of the vertical coordinate is 0.3 times the wavelength, and the minimum value is -0.3 times the wavelength. The left curve corresponds to the meridional direction wavefront aberration curve of the light beam, and the right curve corresponds to the sagittal direction wavefront aberration curve of the light beam. Figure 3 The wavefront aberration curves of different colors correspond to 450nm, 486nm, 545nm, 587nm and 640nm wavelengths respectively. In the range of 0 to 0.5 pupil, the optical path difference value is between 0 and ±0.12 times the wavelength, and in the range of 0.5 to 1.0 pupil, the light aberration value is between ±0.12 and ±0.18 times the wavelength. The overall optical path difference value is small.

[0072] The MTF curve of the microscope objective is shown in Figure 4 Figure 4 The horizontal axis is the spatial frequency, with units of line pairs per millimeter, and the vertical axis is the OTF modulus, which is the modulation transfer function MTF. The MTF curve is greater than 0.6 at 600lp / mm, greater than 0.4 at 1000lp / mm, and greater than 0.2 at 1600lp / mm. The overall value is close to the diffraction limit, indicating good imaging quality.

[0073] The axial aberration curve of the microscope objective is shown in Figure 5 Figure 5 The horizontal axis is the system axial aberration, with units of mm, and the vertical axis is the normalized pupil coordinate. Figure 5 The wavefront aberration curves of different colors correspond to 450nm, 486nm, 545nm, 587nm and 640nm wavelengths respectively. The axial chromatic aberration value at the principal ray position is 0.63um, which is less than λ / NA 2 , satisfying the condition of complex achromatism.

[0074] ​​​The low-temperature microscopic objective field curvature and distortion curves are shown in Figure 6 Figure 6 The left graph is a field curvature graph, the horizontal axis is the field curvature value, in units of um, and the vertical axis is the field of view, in units of °. The field curvature curve of the 545 nm wavelength light ray meets the condition of , and the flat field requirement is met. The right graph has the horizontal coordinate as the percentage of distortion, and the vertical axis is the field of view, in units of °. The maximum distortion value of the 545 nm wavelength light ray at the edge of the field of view is <0.36%.

[0075] Although the embodiments of the present application are described in conjunction with the accompanying drawings, various modifications and changes can be made by those skilled in the art without departing from the spirit and scope of the present application, and such modifications and changes fall within the scope defined by the appended claims.​

Claims

1. A microscope objective, at least for use in a temperature environment of 50 K to 150 K, characterized in that The microscope objective comprises: a front group unit (1) comprising at least a first lens (11) and a second lens (12) arranged in sequence along an optical path, and adapted to converge light rays and correct spherical aberration; a middle group unit arranged at the rear side of the optical path of the front group unit (1), comprising at least a first middle group (2) and a second middle group (3) arranged in sequence along the optical path, each middle group comprising at least two lenses arranged at intervals, and adapted to correct chromatic aberration; wherein the first middle group (2) comprises a third lens (21), a fourth lens (22) and a fifth lens (23) arranged at intervals along the optical path, the fourth lens (22) is arranged as a negative lens, adapted to provide negative focal power, the third lens (21) and the fifth lens (23) are arranged as positive lenses, adapted to provide positive focal power respectively; the refractive index of the fourth lens (22) is higher than that of the third lens (21) and the fifth lens (23), adapted to adjust coma, the fourth lens (22) is composed of a low Abbe number material, and the third lens (21) and the fifth lens (23) are composed of a high Abbe number material; the second middle group (3) comprises a sixth lens (31) and a seventh lens (32) respectively, the sixth lens (31) and the seventh lens (32) are arranged at intervals along the optical path, the sixth lens (31) is arranged as a negative lens, adapted to provide negative focal power, the seventh lens (32) is arranged as a positive lens, adapted to provide positive focal power, and the refractive index of the sixth lens (31) is greater than that of the seventh lens (32), the sixth lens (31) is composed of a low Abbe number material, and the seventh lens (32) is composed of a high Abbe number material; a rear group unit (5) arranged at the rear side of the optical path of the middle group unit, comprising at least two lenses arranged at intervals, and adapted to correct off-axis chromatic aberration; the rear group unit (5) is arranged in a symmetric double Gauss structure, comprising a tenth lens (51), an eleventh lens (52), a twelfth lens (53) and a thirteenth lens (54) arranged in sequence along the optical path, the eleventh lens (52) and the twelfth lens (53) are arranged as negative lenses, adapted to provide negative focal power, the tenth lens (51) and the thirteenth lens (54) are arranged as positive lenses, adapted to provide positive focal power; each lens comprised in the front group unit (1), the middle group unit and the rear group unit (5) is a single lens.

2. The microscope objective according to claim 1, wherein: the first lens (11) and the second lens (12) are arranged as positive lenses, and are arranged in the same direction with curved arcs, adapted to concave to the object to be observed, and to provide positive focal power together.

3. The microscope objective according to claim 2, wherein: the refractive index of the first lens (11) is higher than that of the second lens (12); the first lens (11) is composed of a low Abbe number material, and the second lens (12) is composed of a high Abbe number material.

4. The microscope objective according to any one of claims 1 to 3, characterized in that the middle group unit further comprises a third middle group (4) arranged at the rear side of the second middle group (3) at intervals along the optical path.

5. The microscope objective according to claim 4, characterized in that The third middle group (4) respectively comprises an eighth lens (41) and a ninth lens (42), the eighth lens (41) and the ninth lens (42) are sequentially and spacedly arranged along the light path, the eighth lens (41) is arranged as a negative lens and is adapted to provide a negative focal power, the ninth lens (42) is arranged as a positive lens and is adapted to provide a positive focal power; the refractive index of the eighth lens (41) is greater than that of the ninth lens (42), the eighth lens (41) is composed of a low Abbe number material, and the ninth lens (42) is composed of a high Abbe number material.

6. The microscope objective according to claim 5, characterized in that The refractive index of the thirteenth lens (54) is greater than that of the tenth lens (51), the eleventh lens (52) and the twelfth lens (53); The thirteenth lens (54) and the eleventh lens (52) are respectively composed of a low Abbe number material, and the tenth lens (51) and the twelfth lens (53) are composed of a high Abbe number material.

7. The microscope objective according to claim 5 or 6, characterized in that The focal length of the microscope objective is fx, the focal length of the first lens (11) is f1, and 4.1≤f1 / fx≤4.5; The focal length of the second lens (12) is f2, and 6.7≤f2 / fx≤7.

1.

8. The microscope objective according to claim 7, characterized in that The focal length of the front group unit (1) is fa, and 2.3≤fa / fx≤2.7, the focal length of the first middle group (2) is fb, and 6.5≤fb / fx≤6.9, the focal length of the second middle group (3) is fc, and 12.8≤fc / fx≤14.2, the focal length of the third middle group (4) is fd, and 50≤fd / fx≤54, and the focal length of the rear group unit (5) is fe, and -7.9≤fe / fx≤-7.

5.

9. The microscope objective according to claim 7, characterized in that 3.9mm≤fx≤4.1mm.

10. The microscope objective according to claim 9, characterized in that The aperture of the microscope objective is NA, and 0.8≤NA≤0.

9.

11. The microscope objective according to claim 10, characterized in that The object-side field of view of the microscope objective is B, and 0≤B≤0.4mm; and / or, the distance between the first lens (11) and the object to be observed is C, and C≥1.6mm.

12. The microscope objective according to claim 5 or 6, characterized in that The thirteenth lens (54) is an aspheric lens, the ninth lens (42) is an aspheric lens, and the fifth lens (23) is an aspheric lens.

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