25-fold liquid immersion objective lens for microscopic imaging

Abstract

The invention discloses a 25-time liquid immersion objective lens for microscopic imaging, which is characterized in that silicone oil is used as a liquid immersion medium, and the focal length of each lens group and the structures of a middle lens group and a rear lens group are selected; the refractive indexes of the first lens and the last lens in the front lens group and the air interval change range of the third balsaming lens in the middle lens group and the last lens in the front lens group are selected; the third balsaming lens moves back and forth relative to the last lens in the lens group to adjust the system aberration caused by the thickness change of the cover glass, and meanwhile, the refractive index, the focal length and the ratio of the focal length to the outer diameter of the last lens in the front lens group are selected to control the spherical aberration of the marginal light; the fifth balsaming lens is selected as negative focal power to correct the field curvature of the system, and the sixteenth lens is matched with the fifth balsaming lens to reduce astigmatism of the system, so that the problem in living cell imaging is solved.

Description

Technical Field

[0001] The invention relates to a microscopic imaging objective lens, in particular to a 25-fold liquid immersion objective lens for microscopic imaging. Background Art

[0002] Live cell imaging is an optical technique for studying real-time dynamic physiological processes in living cells. It can provide spatial and temporal information of dynamic molecular events occurring in single cells, intracellular networks, and even whole organisms. These characteristics make it an essential technique for studying dynamic physiological processes in cell biology, cancer, developmental biology, and neuroscience.

[0003] With the rapid development of electronics, optics and biochemistry in recent years, researchers can more easily realize live cell imaging, but at the same time, higher requirements are also placed on the image quality of the microscopic imaging objective lens used in the imaging system. In live cell microscopic imaging, liquid immersion objectives are generally used to observe cells. Liquid immersion objectives refer to objectives immersed in liquid or other media between the objective lens and the specimen. This design is mainly to increase the numerical aperture and thus improve the imaging quality and resolution of the objective lens. The most commonly used liquid immersion objectives are oil immersion objectives and water immersion objectives. These objective lenses are mature in technology and are relatively easy to obtain on the market, but they have some disadvantages in the application of live cell microscopic imaging. Due to the difference between the refractive index of oil (ne≈1.52) and the refractive index of living tissue cells (ne≈1.38), this refractive index mismatch will cause spherical aberration and lead to a decrease in image quality. Researchers cannot obtain deeper and brighter cell images when using oil immersion objectives. The numerical aperture of the water immersion objective is smaller than that of the oil immersion objective, which makes its imaging resolution lower. In addition, some live cell microscopy imaging needs to be monitored for a long time at a stable environment of 37°C. The water immersion objective needs to be replenished regularly due to the evaporation of water, and it is impossible to achieve long-term stable real-time observation. In addition, the existing medium-magnification objective of about 25× in China does not have an adjustment ring for spherical aberration compensation, and cannot compensate for the spherical aberration caused by the change in cover glass thickness, thus affecting the observation effect of cells; the objective mirror image field of view is only 22mm in diameter, and it is impossible to observe a larger cell field of view in real time. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a 25x silicone oil immersion objective lens suitable for microscopic imaging of living cells, which can better adapt to the variation of cover glass thickness from 0.11mm to 0.23mm, match the refractive index of living tissue, and simultaneously have a larger image field of view and wide spectrum chromatic aberration correction.

[0005] The technical solution adopted by the present invention to solve the above technical problems is: a 25x liquid immersion objective lens for microscopic imaging, the liquid immersion in the liquid immersion objective lens is silicone oil immersion, and from the object side to the image side, it is composed of a front lens group with positive focal power, a middle lens group with negative focal power, and a rear lens group with positive focal power arranged in sequence on the same optical axis, the focal length fobj of the entire 25x liquid immersion objective lens is 7.6mm~8.4mm, the focal length fm1 of the front lens group satisfies: 7mm≤fm1≤9mm, the focal length fm2 of the middle lens group satisfies: -200mm≤fm2≤-60mm, and the focal length fm3 of the rear lens group satisfies: 80mm≤fm3≤120mm; the refractive index of the first lens in the front lens group nd1 satisfies: 1.4<nd1<1.5, the middle lens group consists of a third cemented lens with a focal length of 40mm~70mm which can be moved along the optical axis and a fourth cemented lens with a focal length of -20mm~-10mm which is fixed in position; the air gap between the third cemented lens and the last lens in the front lens group varies in the range of 0.7mm~0.9mm, the last lens in the front lens group is a positive lens with a refractive index greater than 1.9, a focal length of 45mm~60mm, and a focal length to outer diameter ratio greater than 2, the rear lens group consists of a fifth cemented lens with negative focal power, a sixteenth lens with positive focal power and a seventeenth lens with positive focal power, and the refractive index of the sixteenth lens is greater than 1.75.

[0006] Compared with the prior art, the advantages of the present invention are that silicone oil is used as an immersion medium (the refractive index of silicone oil is ne≈1.4), the focal length of each lens group and the structure of the middle lens group and the rear lens group are selected, and the refractive index of the first lens and the last lens in the front lens group and the air interval variation range between the third cemented lens in the middle lens group and the last lens in the front lens group are selected, the third cemented lens is moved forward and backward relative to the last lens in the lens group to adjust the system aberration caused by the change of the cover glass thickness, and the spherical aberration of the edge light is controlled by selecting the refractive index, focal length and focal length to outer diameter ratio of the last lens in the front lens group, and the fifth cemented lens is selected as a negative The optical power is used to correct the field curvature of the system, and the astigmatism of the system is reduced by cooperating the sixteenth lens with the fifth cemented lens, so as to solve the problems of mismatch of the refractive index of the immersion medium of the conventional oil immersion and water immersion objective lenses in the prior art in the imaging of living cells, insufficient numerical aperture, insufficiently large field of view clarity range, insufficient stability of the immersion medium, and inability to correct the aberration for the change of the cover glass thickness, etc. The numerical aperture of the liquid immersion objective lens of the present invention reaches 1.05, which can be adapted to the change of the cover glass thickness of 0.11mm~0.23mm, the refractive index of the immersion medium can be effectively matched with the refractive index of the living tissue (ne≈1.38), and at the same time, it has a large field of view of 25mm on the image side and wide spectrum chromatic aberration correction.

[0007] Preferably, the front lens group consists of a first cemented lens with a focal length of 20 mm to 40 mm, a third lens with a focal length of 15 mm to 30 mm, a second cemented lens and a seventh lens with a focal length of 45 mm to 60 mm, the first cemented lens consists of a first lens and a second lens, the refractive index of the first lens satisfies: 1.4<nd1<1.5, the refractive index nd1 of the first lens and the refractive index nd2 of the second lens satisfy: nd2-nd1>0.35, the Abbe number vd1 of the first lens and the Abbe number vd2 of the second lens satisfy: | vd1-vd2|≥25, the second cemented lens is composed of a fourth lens, a fifth lens and a sixth lens, the fourth lens L4 is a positive lens, the fifth lens L5 is a negative lens, the sixth lens L6 is a positive lens, and satisfies: |vd4-vd5|≥40 and |vd5-vd6|≥40, wherein vd4 is the Abbe number of the fourth lens, vd5 is the Abbe number of the fifth lens, and vd6 is the Abbe number of the sixth lens, and the air gap between the seventh lens and the second cemented lens varies in the range of 0.7mm~0.9mm. The combination of the first lens and the second lens can effectively collect object light and reduce the angle of light after incidence. The second cemented lens uses a positive-negative-positive lens structure and realizes chromatic aberration correction by increasing the difference in dispersion coefficients of adjacent lenses.

[0008] Preferably, the third cemented lens is composed of an eighth lens with positive focal power, a ninth lens with negative focal power, and a tenth lens with positive focal power, and the fourth cemented lens is composed of an eleventh lens with negative focal power, a twelfth lens with positive focal power, and a thirteenth lens with negative focal power. The third cemented lens is a triplet of a positive-negative-positive structure, and the fourth cemented lens is a triplet of a negative-positive-negative structure. The two can cooperate with each other to correct the secondary spectrum and achieve wide-spectrum apochromatism.

[0009] Preferably, the first lens is a hemispherical lens with a plane on the object side, the second lens is a meniscus lens with a concave object side, the third lens is a meniscus lens with a concave object side, the eleventh lens has a convex object side and a concave image side, the twelfth lens has a convex object side and a convex image side, the sixteenth lens is a meniscus lens with a concave object side and a convex image side, and the seventeenth lens has a convex object side and a convex image side.

[0010] Preferably, the fifth cemented lens is composed of a fourteenth lens with negative optical power and a fifteenth lens with positive optical power, the fourteenth lens has a concave surface on the object side and a concave surface on the image side, and the fifteenth lens has a convex surface on the object side and a convex surface on the image side.

[0011] Preferably, the Abbe number vd8 of the eighth lens, the Abbe number vd9 of the ninth lens and the Abbe number vd10 of the tenth lens satisfy: |vd8-vd9|≥40 and |vd9-vd10|≥40, and the Abbe number vd11 of the eleventh lens, the Abbe number vd12 of the twelfth lens and the Abbe number vd13 of the thirteenth lens satisfy: |vd11-vd12|≥40 and |vd12-vd13|≥40.

[0012] Preferably, the air gap between the first cemented lens and the third lens is 0.1mm~0.2mm, the air gap between the third lens and the second cemented lens is 0.1mm~0.2mm, the air gap between the second cemented lens and the seventh lens is 0.1mm~0.2mm, the air gap between the fifth cemented lens and the sixteenth lens is 1mm~2mm, and the air gap between the sixteenth lens and the seventeenth lens is 0.1mm~0.2mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a schematic structural diagram of a 25x liquid immersion objective lens according to Example 1 of the embodiment of the present invention; Figure 2 This is a field curvature curve diagram of Example 1 of the embodiment of the present invention when the cover glass thickness is 0.17 mm; the ordinate in the figure is the angle of the incident light, which corresponds to the field number of the objective lens, and the abscissa is the magnitude of the field curvature, and different curves correspond to different wavelengths; Figure 3 This is a field curvature curve diagram of Example 1 of the embodiment of the present invention when the cover glass thickness is 0.11 mm; Figure 4 This is a field curvature curve diagram of Example 1 of the embodiment of the present invention when the cover glass thickness is 0.23 mm; Figure 5 This is a distortion curve diagram of Example 1 of the embodiment of the present invention when the cover glass thickness is 0.17 mm. The ordinate in the diagram is the angle of the incident light, which corresponds to the field of view number of the objective lens, and the abscissa is the magnitude of the distortion. Different curves correspond to different wavelengths. Figure 6 This is a distortion curve diagram of Example 1 of the embodiment of the present invention when the cover glass thickness is 0.11 mm; Figure 7 This is a distortion curve diagram of Example 1 of the embodiment of the present invention when the cover glass thickness is 0.23 mm; Figure 8 This is an optical transfer function MTF curve of Example 1 of the embodiment of the present invention with a cover glass thickness of 0.17 mm, where the ordinate represents the magnitude of the MTF value and the abscissa represents the spatial frequency; Fig. 9This is an optical transfer function MTF curve of Example 1 of the embodiment of the present invention with a cover glass thickness of 0.11 mm; Fig.10 This is an optical transfer function MTF curve of Example 1 of the embodiment of the present invention with a cover glass thickness of 0.23 mm; Fig.11 This is an axial aberration curve diagram of Example 1 of the embodiment of the present invention when the cover glass thickness is 0.17 mm, the ordinate represents the normalized pupil, and the abscissa represents the spherical aberration value of different color lights in the on-axis field of view; Fig.12 This is an axial aberration curve diagram of Example 1 of the embodiment of the present invention when the cover glass thickness is 0.11 mm; Fig.13 This is an axial aberration curve diagram of Example 1 of the embodiment of the present invention when the cover glass thickness is 0.23 mm; Fig.14 This is a schematic structural diagram of a 25x liquid immersion objective lens according to Example 2 of the embodiment of the present invention; Fig.15 This is a field curvature curve diagram of Example 2 of the embodiment of the present invention with a cover glass thickness of 0.17 mm; the ordinate in the figure is the angle of the incident light, which corresponds to the field number of the objective lens, and the abscissa is the magnitude of the field curvature, and different curves correspond to different wavelengths; Fig.16 This is a field curvature curve diagram of Example 2 of the embodiment of the present invention when the cover glass thickness is 0.11 mm; Fig.17 This is a field curvature curve diagram of Example 2 of the embodiment of the present invention when the cover glass thickness is 0.23 mm; Fig.18 This is a distortion curve diagram of Example 2 of the embodiment of the present invention when the cover glass thickness is 0.17 mm. The ordinate in the diagram is the angle of the incident light, which corresponds to the field of view number of the objective lens, and the abscissa is the magnitude of the distortion. Different curves correspond to different wavelengths. Fig.19 This is a distortion curve diagram of Example 2 of the embodiment of the present invention when the cover glass thickness is 0.11 mm; Fig. 20 This is a distortion curve diagram of Example 2 of the embodiment of the present invention when the cover glass thickness is 0.23 mm; Fig.21 This is an optical transfer function MTF curve of Example 2 of the embodiment of the present invention with a cover glass thickness of 0.17 mm, where the ordinate represents the magnitude of the MTF value and the abscissa represents the spatial frequency; Fig. 22 This is an optical transfer function MTF curve of Example 2 of the embodiment of the present invention when the cover glass thickness is 0.11 mm; Fig.23 This is an optical transfer function MTF curve of Example 2 of the embodiment of the present invention with a cover glass thickness of 0.23 mm; Fig.24 This is an axial aberration curve diagram of Example 2 of the embodiment of the present invention when the cover glass thickness is 0.17 mm, the ordinate represents the normalized pupil, and the abscissa represents the spherical aberration value of different color lights in the on-axis field of view; Fig.25 This is an axial aberration curve diagram of Example 2 of the embodiment of the present invention when the cover glass thickness is 0.11 mm; Fig.26 This is an axial aberration curve diagram of Example 2 of the embodiment of the present invention when the cover glass thickness is 0.23 mm; Fig. 27 This is a schematic structural diagram of a 25x liquid immersion objective lens according to Example 3 of the embodiment of the present invention; Fig.28 This is a field curvature curve diagram of Example 3 of the embodiment of the present invention with a cover glass thickness of 0.17 mm; the ordinate in the figure is the angle of the incident light, which corresponds to the field number of the objective lens, and the abscissa is the magnitude of the field curvature, and different curves correspond to different wavelengths; Fig.29 This is a field curvature curve diagram of Example 3 of the embodiment of the present invention when the cover glass thickness is 0.11 mm; Fig.30 This is a field curvature curve diagram of Example 3 of the embodiment of the present invention when the cover glass thickness is 0.23 mm; Fig.31 This is a distortion curve diagram of Example 3 of the embodiment of the present invention when the cover glass thickness is 0.17 mm. The ordinate in the diagram is the angle of the incident light, which corresponds to the field of view number of the objective lens, and the abscissa is the magnitude of the distortion. Different curves correspond to different wavelengths. Fig.32 This is a distortion curve diagram of Example 3 of the embodiment of the present invention when the cover glass thickness is 0.11 mm; Fig.33 This is a distortion curve diagram of Example 3 of the embodiment of the present invention when the cover glass thickness is 0.23 mm; Fig.34 This is an optical transfer function MTF curve of Example 3 of the embodiment of the present invention with a cover glass thickness of 0.17 mm, where the ordinate represents the magnitude of the MTF value and the abscissa represents the spatial frequency; Fig.35 This is an optical transfer function MTF curve of Example 3 of the embodiment of the present invention when the cover glass thickness is 0.11 mm; Fig.36 This is an optical transfer function MTF curve of Example 3 of the embodiment of the present invention when the cover glass thickness is 0.23 mm; Fig.37 This is an axial aberration curve diagram of Example 3 of the embodiment of the present invention when the cover glass thickness is 0.17 mm, the ordinate represents the normalized pupil, and the abscissa represents the spherical aberration value of different color lights in the on-axis field of view; Fig.38This is an axial aberration curve diagram of Example 3 of the embodiment of the present invention when the cover glass thickness is 0.11 mm; Fig.39 This is an axial aberration curve diagram of Example 3 of the embodiment of the present invention when the cover glass thickness is 0.23 mm. DETAILED DESCRIPTION

[0014] The present invention is further described in detail below with reference to the accompanying drawings.

[0015] like Figure 1 , 14 As shown in Figure 27, a 25x liquid immersion objective lens for microscopic imaging, the liquid immersion in the liquid immersion objective lens is silicone oil immersion, and from the object side to the image side, it is composed of a front lens group M1 with positive optical focal length, a middle lens group M2 with negative optical focal length, and a rear lens group M3 with positive optical focal length, which are arranged in sequence on the same optical axis. The focal length fobj of the entire 25x liquid immersion objective lens is 7.6mm~8.4mm, the focal length fm1 of the front lens group M1 satisfies: 7mm≤fm1≤9mm, the focal length fm2 of the middle lens group M2 satisfies: -200mm≤fm2≤-60mm, and the focal length fm3 of the rear lens group M3 satisfies: 80mm≤fm3≤120mm.

[0016] The front lens group M1 is composed of a first cemented lens GL1 with a focal length of 20mm~40mm, a third lens L3 with a focal length of 15mm~30mm, a second cemented lens GL2 and a seventh lens L7 with a focal length of 45mm~60mm. The first cemented lens GL1 is composed of a first lens L1 and a second lens L2. The first lens L1 is a hemispherical lens with a flat surface facing the object, and the second lens L2 is a meniscus lens with a concave surface facing the object. The refractive index nd1 of the first lens L1 and the refractive index nd2 of the second lens L2 satisfy: 1.4<nd1<1.5, nd2-nd1>0.35, the Abbe number vd1 of the first lens L1 and the Abbe number vd2 of the second lens L2 satisfy: |vd1-vd2|≥25, the second cemented lens GL2 is composed of the fourth lens L4, the fifth lens L5 and the sixth lens L6, the fourth lens L4 is a positive lens, the fifth lens L5 is a negative lens, and the sixth lens L6 is a positive lens, satisfying: |vd4-vd5|≥40 and |vd5-vd6|≥40, wherein vd4 is the value of the fourth lens L 4, vd5 is the Abbe number of the fifth lens L5, vd6 is the Abbe number of the sixth lens L6, the refractive index nd7 of the seventh lens L7 satisfies: nd7>1.9, the focal length fl7 of the seventh lens L7 is 45 mm~60 mm, the outer diameter d of the seventh lens L7 satisfies: fl7 / d>2, the air gap between the first cemented lens GL1 and the third lens L3 is 0.1 mm~0.2 mm, the air gap between the third lens L3 and the second cemented lens GL2 is 0.1 mm~0.2 mm, and the air gap between the second cemented lens GL2 and the seventh lens L7 is 0.1 mm~0.2 mm.

[0017] The middle lens group M2 is composed of a third cemented lens GL3 with a focal length of 40mm~70mm which can be moved along the optical axis, and a fourth cemented lens GL4 with a focal length of -20mm~-10mm which is fixed in position. The third cemented lens GL3 adjusts the system aberration caused by the change of cover glass thickness by moving forward and backward relative to the seventh lens L7. The air gap between the seventh lens L7 and the second cemented lens GL2 varies in the range of 0.7mm~0.9mm. The third cemented lens GL3 is composed of an eighth lens L8, a ninth lens L9 and a tenth lens L10, the eighth lens L8 is a positive lens, the ninth lens L9 is a negative lens, the tenth lens L10 is a positive lens, the Abbe number vd8 of the eighth lens L8, the Abbe number vd9 of the ninth lens L9 and the Abbe number vd10 of the tenth lens L10 satisfy: |vd8-vd9|≥40 and |vd9-vd10|≥40, the eighth lens L8 has a convex surface facing the object side and a concave surface facing the image side, the ninth lens L9 has a convex surface facing the object side and a concave surface facing the image side; the fourth cemented lens GL4 is composed of the eleventh lens L8 and the ninth lens L9. The lens L11, the twelfth lens L12 and the thirteenth lens L13 are composed, the eleventh lens L11 is a negative lens, the twelfth lens L12 is a positive lens, the thirteenth lens L13 is a negative lens, the Abbe number vd11 of the eleventh lens L11, the Abbe number vd12 of the twelfth lens L12 and the Abbe number vd13 of the thirteenth lens L13 satisfy: |vd11-vd12|≥40 and |vd12-vd13|≥40, the eleventh lens L11 has a convex surface facing the object side and a concave surface facing the image side, the twelfth lens L12 has a convex surface facing the object side and a convex surface facing the image side.

[0018] The rear lens group M3 is composed of a fifth cemented lens GL5 with negative power, a sixteenth lens L16 with positive power, and a seventeenth lens L17 with positive power. The fifth cemented lens GL5 is composed of a fourteenth lens L14 and a fifteenth lens L15. The fourteenth lens L14 is a negative lens, and the fifteenth lens L15 is a positive lens. The fourteenth lens L14 has a concave surface facing the object side and a concave surface facing the image side, and the fifteenth lens L15 has a convex surface facing the object side and a convex surface facing the image side. The sixteenth lens L16 is a meniscus lens with positive focal power, and has a concave surface facing the object side and a convex surface facing the image side. The refractive index nd16 of the sixteenth lens L16 satisfies: nd16>1.75; the seventeenth lens L17 is a positive lens, and has a convex surface facing the object side and a convex surface facing the image side; the air gap between the fifth cemented lens GL5 and the sixteenth lens L16 is 1 mm~2 mm, and the air gap between the sixteenth lens L16 and the seventeenth lens L17 is 0.1 mm~0.2 mm.

[0019] The present embodiment is described in detail below through three examples.

[0020] Example 1: Structural description of the 25x liquid immersion objective in this example and the embodiment Figure 1 The same, composed of front lens group M1, middle lens group M2 and rear lens group M3, the focal length of the 25x liquid immersion objective lens is fobj=7.99mm, the numerical aperture NA=1.05, the magnification β=-25×, the immersion layer thickness is 0.55mm, the cover glass thickness is 0.17mm, the spectral range is 410nm~656nm, the field of view range is 25mm, and the immersion medium is silicone oil 100. The 25x liquid immersion objective lens has the following characteristics: The focal length of the front lens group M1 is fm1=8.61mm, the focal length of the middle lens group M2 is fm2=-197.86mm, the focal length of the rear lens group M3 is fm3=114.55mm, the refractive index of the first lens L1 is nd1=1.45, the refractive index of the second lens L2 is nd2=1.88, and nd2-nd1=0.43. The Abbe number of the first lens L1 is vd1=67.8, the Abbe number of the second lens L2 is vd2=40.8, and |vd1-vd2|=27. The focal length of the first cemented lens GL1 is 36.46mm. The focal length fl3 of the third lens L3 is 24.47mm. The Abbe number vd4 of the fourth lens L4 = 95, the Abbe number vd5 of the fifth lens L5 = 44.3, the Abbe number vd6 of the sixth lens L6 = 95, |vd4-vd5| = 50.7 and |vd5-vd6| = 50.7.

[0021] The refractive index nd7 of the seventh lens L7 is 1.92, the focal length fl7 is 53.71 mm, the outer diameter d is 20.4 mm, and fl7 / d is 2.6. The air gap between the first cemented lens GL1 and the third lens L3 is 0.15 mm, the air gap between the third lens L3 and the second cemented lens GL2 is 0.11 mm, and the air gap between the second cemented lens GL2 and the seventh lens L7 is 0.12 mm. The Abbe number vd8 of the eighth lens L8 is 95, the Abbe number vd9 of the ninth lens L9 is 44.3, the Abbe number vd10 of the tenth lens L10 is 95, |vd8-vd9|=50.7 and |vd9-vd10|=50.7. The focal length fgl3 of the third cemented lens GL3 is 43.2 mm, and the air gap between the seventh lens L7 and the third cemented lens GL3 is 0.71 mm.

[0022] The Abbe number vd11 of the eleventh lens L11 is 44.3, the Abbe number vd12 of the twelfth lens L12 is 95, the Abbe number vd13 of the thirteenth lens L13 is 26.6, |vd11-vd12|=50.7, |vd12-vd13|=68.4. The focal length fgl4 of the fourth cemented lens GL4 is -15.4 mm.

[0023] The refractive index nd16 of the sixteenth lens L16 is 1.8, the focal length fl17 of the seventeenth lens L17 is 42.66 mm, the air interval between the fifth cemented lens GL5 and the sixteenth lens L16 is 1.1 mm, and the air interval between the sixteenth lens L16 and the seventeenth lens L17 is 0.13 mm.

[0024] The lens parameters of the 25x liquid immersion objective lens of Example 1 are shown in Table 1.

[0025] Table 1 Among them, the radius refers to the radius of curvature of the surface, and the thickness refers to the on-axis distance from the current surface to the next surface. For example, the thickness of the object plane of surface L1 is the distance from the object plane L1 to the object plane L2, which may be the on-axis thickness of the medium or lens, or the on-axis air gap between them.

[0026] In this example, when the cover glass thickness becomes 0.11 mm, the interval d1 between the seventh lens L7 and the third cemented lens GL3 is 0.75 mm, and the interval d2 between the third cemented lens GL3 and the fourth cemented lens GL4 is 0.9 mm.

[0027] When the thickness of the cover glass becomes 0.23 mm, the interval d1 between the seventh lens L7 and the third cemented lens GL3 is 0.67 mm, and the interval d2 between the third cemented lens GL3 and the fourth cemented lens GL4 is 0.98 mm.

[0028] from Figure 2~Figure 4 Field curvature plots and Figure 5~Figure 7 From the distortion curve, we can see that the maximum value of field curvature at the edge of the field of view within the full aperture range under different cover glass thicknesses is no more than 1um, and the maximum distortion is within 0.1%. Both field curvature and distortion are well corrected.

[0029] from Figure 8~Figure 10 It can be seen from the optical transfer function MTF curve that the cutoff frequency of the optical system is 4000lp / mm, and the MTF curves of each field of view under different cover glass thicknesses are close to the diffraction limit, and the system can obtain good imaging quality.

[0030] from Figure 11~Figure 13 From the axial aberration curve, it can be seen that spherical aberration has been strictly corrected within the full aperture range, and the spectrum covers 410nm~656nm, meeting the requirements of apochromatism.

[0031] Example 2: Fig.14As shown, the 25x liquid immersion objective lens consists of a front lens group M1, a middle lens group M2 and a rear lens group M3. The focal length of the 25x liquid immersion objective lens is fobj=8mm, NA=1.05, magnification β=-25×, immersion layer thickness is 0.55mm, cover glass thickness is 0.17mm, spectral range is 410nm~656nm, field of view range is 25mm, and immersion medium is silicone oil 100. The 25x liquid immersion objective lens has the following characteristics: The focal length of the front lens group M1 is fm1=8.46mm, the focal length of the middle lens group M2 is fm2=-164.24mm, the focal length of the rear lens group M3 is fm3=109.14mm, the refractive index of the first lens L1 is nd1=1.45, the refractive index of the second lens L2 is nd2=1.88, and nd2-nd1=0.43. The Abbe number of the first lens L1 is vd1=67.8, the Abbe number of the second lens L2 is vd2=40.8, and |vd1-vd2|=27. The focal length of the first cemented lens GL1 is 23.28mm, and the focal length of the third lens L3 is fl3 25.23mm. The Abbe number vd4 of the fourth lens L4 = 95, the Abbe number vd5 of the fifth lens L5 = 44.1, the Abbe number vd6 of the sixth lens L6 = 90.9, |vd4-vd5| = 50.9 and |vd5-vd6| = 46.8.

[0032] The refractive index nd7 of the seventh lens L7 is 1.92, the focal length fl7 is 49.48 mm, the outer diameter d is 20.5 mm, and fl7 / d is 2.4. The air gap between the first cemented lens GL1 and the third lens L3 is 0.2 mm, the air gap between the third lens L3 and the second cemented lens GL2 is 0.15 mm, and the air gap between the second cemented lens GL2 and the seventh lens L7 is 0.17 mm.

[0033] The Abbe number vd8 of the eighth lens L8 is 95, the Abbe number vd9 of the ninth lens L9 is 39.1, and the Abbe number vd10 of the tenth lens L10 is 95, |vd8-vd9|=55.9 and |vd9-vd10|=55.9. The focal length fgl3 of the third cemented lens GL3 is 42.74 mm, and the air gap between the seventh lens L7 and the third cemented lens GL3 is 0.74 mm.

[0034] The Abbe number vd11 of the eleventh lens L11 is 46.6, the Abbe number vd12 of the twelfth lens L12 is 94.8, the Abbe number vd13 of the thirteenth lens L13 is 27.5, |vd11-vd12| is 48.2, |vd12-vd13| is 67.3. The focal length fgl4 of the fourth cemented lens GL4 is -14.24 mm.

[0035] The refractive index nd16 of the sixteenth lens L16 is 1.8, the focal length fl17 of the seventeenth lens L17 is 54.15 mm, the air interval between the fifth cemented lens GL5 and the sixteenth lens L16 is 1.5 mm, and the air interval between the sixteenth lens L16 and the seventeenth lens L17 is 0.15 mm.

[0036] The lens parameters of the 25x liquid immersion objective of Example 2 are shown in Table 2.

[0037] Table 2 In this example, when the cover glass thickness becomes 0.11 mm, the interval d1 between the seventh lens L7 and the third cemented lens GL3 is 0.78 mm, and the interval d2 between the third cemented lens GL3 and the fourth cemented lens GL4 is 0.9 mm.

[0038] When the thickness of the cover glass becomes 0.23 mm, the interval d1 between the seventh lens L7 and the third cemented lens GL3 is 0.7 mm, and the interval d2 between the third cemented lens GL3 and the fourth cemented lens GL4 is 0.98 mm.

[0039] from Figure 15~Figure 17 Field curvature plots and Figure 18~Figure 20 From the distortion curve, we can see that the maximum value of field curvature at the edge of the field of view within the full aperture range under different cover glass thicknesses is no more than 2um, and the maximum distortion is within 0.3%. Both field curvature and distortion are well corrected.

[0040] from Figure 21~Figure 23 It can be seen from the optical transfer function MTF curve that the cutoff frequency of the optical system is 4000lp / mm, and the MTF curves of each field of view under different cover glass thicknesses are close to the diffraction limit, and the system can obtain good imaging quality.

[0041] from Figure 24~Figure 26 From the axial aberration curve, it can be seen that spherical aberration has been strictly corrected within the full aperture range, and the spectrum covers 410nm~656nm, meeting the requirements of apochromatism.

[0042] Example 3: Fig. 27 As shown, the 25x liquid immersion objective lens consists of a front lens group M1, a middle lens group M2 and a rear lens group M3. The focal length of the 25x liquid immersion objective lens is fobj=7.99mm, NA=1.05, magnification β=-25×, immersion layer thickness is 0.55mm, cover glass thickness is 0.17mm, spectral range is 410nm~656nm, field of view range is 25mm, and immersion medium is silicone oil. The 25x liquid immersion objective lens has the following features: The focal length of the front lens group M1 is fm1=7.62mm, the focal length of the middle lens group M2 is fm2=-73.82mm, the focal length of the rear lens group M3 is fm3=80.97mm, the refractive index of the first lens L1 is nd1=1.5, the refractive index of the second lens L2 is nd2=1.88, and nd2-nd1=0.38. The Abbe number of the first lens L1 is vd1=69.5, the Abbe number of the second lens L2 is vd2=40.8, and |vd1-vd2|=28.7; the focal length of the first cemented lens GL1 is 24.88 mm, the focal length fl3 of the third lens L3 is 17.68 mm, the Abbe number of the fourth lens L4 is vd4=95, the Abbe number of the fifth lens L5 is vd5=44.1, and the Abbe number of the sixth lens L6 is vd6=90.9, |vd4-vd5|=50.9 and |vd5-vd6|=46.8.

[0043] The refractive index nd7 of the seventh lens L7 is 1.95, the focal length fl7 is 55.68 mm, the outer diameter d is 20 mm, and fl7 / d is 2.78. The air gap between the first cemented lens GL1 and the third lens L3 is 0.1 mm, the air gap between the third lens L3 and the second cemented lens GL2 is 0.13 mm, and the air gap between the second cemented lens GL2 and the seventh lens L7 is 0.2 mm.

[0044] The Abbe number vd8 of the eighth lens L8 is 90.2, the Abbe number vd9 of the ninth lens L9 is 36.4, and the Abbe number vd10 of the tenth lens L10 is 94.9, |vd8-vd9|=53.8 and |vd9-vd10|=58.5. The focal length fgl3 of the third cemented lens GL3 is 68.07 mm, and the air gap between the seventh lens L7 and the third cemented lens GL3 is 0.8 mm.

[0045] The Abbe number vd11 of the eleventh lens L11 is 46.6, the Abbe number vd12 of the twelfth lens L12 is 94.8, the Abbe number vd13 of the thirteenth lens L13 is 27.5, |vd11-vd12| is 48.2, |vd12-vd13| is 67.3. The focal length fgl4 of the fourth cemented lens GL4 is -18.68 mm.

[0046] The refractive index nd16 of the sixteenth lens L16 is 1.78, and the focal length fl17 of the seventeenth lens L17 is 52.48 mm. The air interval between the fifth cemented lens GL5 and the sixteenth lens L16 is 2 mm, and the air interval between the sixteenth lens L16 and the seventeenth lens L17 is 0.1 mm.

[0047] The lens parameters of the 25x liquid immersion objective lens of Example 3 are shown in Table 3.

[0048] Table 3 In this example, when the cover glass thickness becomes 0.11 mm, the interval d1 between the seventh lens L7 and the third cemented lens GL3 is 0.9 mm, and the interval d2 between the third cemented lens GL3 and the fourth cemented lens GL4 is 0.9 mm.

[0049] When the thickness of the cover glass becomes 0.23 mm, the interval d1 between the seventh lens L7 and the third cemented lens GL3 is 0.7 mm, and the interval d2 between the third cemented lens GL3 and the fourth cemented lens GL4 is 1.1 mm.

[0050] from Figure 28~Figure 30 Field curvature plots and Figure 31~Figure 33 From the distortion curve, we can see that the maximum value of field curvature at the edge of the field of view within the full aperture range under different cover glass thicknesses is no more than 4um, and the maximum distortion is within 0.2%. Both field curvature and distortion are well corrected.

[0051] from Figure 34~Figure 36 It can be seen from the optical transfer function MTF curve that the cutoff frequency of the optical system is 4000lp / mm, and the MTF curves of each field of view under different cover glass thicknesses are close to the diffraction limit, and the system can obtain good imaging quality.

[0052] from Figure 37~Figure 39 From the axial aberration curve, it can be seen that spherical aberration has been strictly corrected within the full aperture range, and the spectrum covers 410nm~656nm, meeting the requirements of apochromatism.

Claims

1. A 25x liquid immersion objective lens for microscopic imaging, wherein the liquid immersion in the liquid immersion objective lens is silicone oil immersion, characterized in that From the object side to the image side, it includes a front lens group with positive focal power, an intermediate lens group with negative focal power, and a rear lens group with positive focal power, which are arranged in sequence on the same optical axis. The focal length fobj of the entire 25x liquid immersion objective lens is 7.6mm~8.4mm. The focal length fm1 of the front lens group satisfies: 7mm≤fm1≤9mm, the focal length fm2 of the intermediate lens group satisfies: -200mm≤fm2≤-60mm, and the focal length fm3 of the rear lens group satisfies: 80mm≤fm3≤120mm; the refractive index nd1 of the first lens in the front lens group satisfies: 1.4<nd1<1.5, the refractive index nd1 of the first lens in the intermediate lens group satisfies: 1.4<nd1<1.5, the focal length fobj of the entire 25x liquid immersion objective lens is 7.6mm~8.4mm, the focal length fm1 of the front lens group satisfies: 7mm≤fm1≤9mm, the focal length fm2 of the intermediate lens group satisfies: -200mm≤fm2≤-60mm, and the focal length fm3 of the rear lens group satisfies: 80mm≤fm3≤120mm. The invention is composed of a third cemented lens with a focal length of 40mm to 70mm which can be moved along the optical axis and a fourth cemented lens with a focal length of -20mm to -10mm which is fixed in position; the air gap between the third cemented lens and the last lens in the front lens group varies in the range of 0.7mm to 0.9mm; the last lens in the front lens group is a positive lens with a refractive index greater than 1.9, a focal length of 45mm to 60mm, and a focal length to outer diameter ratio greater than 2; the rear lens group is composed of a fifth cemented lens with negative focal power, a sixteenth lens with positive focal power and a seventeenth lens with positive focal power, and the refractive index of the sixteenth lens is greater than 1.

75.

2. A 25x liquid immersion objective lens for microscopic imaging as claimed in claim 1, characterized in that The front lens group consists of a first cemented lens with a focal length of 20mm~40mm, a third lens with a focal length of 15mm~30mm, a second cemented lens and a seventh lens with a focal length of 45mm~60mm. The first cemented lens consists of a first lens and a second lens. The refractive index of the first lens satisfies: 1.4<nd1<1.5, the refractive index nd1 of the first lens and the refractive index nd2 of the second lens satisfy: nd2-nd1>0.35, and the Abbe number vd1 of the first lens and the Abbe number vd2 of the second lens satisfy: | vd1-vd2|≥25, the second cemented lens is composed of a fourth lens, a fifth lens and a sixth lens, the fourth lens is a positive lens, the fifth lens is a negative lens, and the sixth lens is a positive lens, satisfying: |vd4-vd5|≥40 and |vd5-vd6|≥40, wherein vd4 is the Abbe number of the fourth lens, vd5 is the Abbe number of the fifth lens, vd6 is the Abbe number of the sixth lens, and the air gap between the seventh lens and the second cemented lens varies in the range of 0.7mm~0.9mm.

3. A 25x liquid immersion objective lens for microscopic imaging as claimed in claim 2, characterized in that The third cemented lens is composed of an eighth lens with positive focal power, a ninth lens with negative focal power and a tenth lens with positive focal power, and the fourth cemented lens is composed of an eleventh lens with negative focal power, a twelfth lens with positive focal power and a thirteenth lens with negative focal power.

4. A 25x liquid immersion objective lens for microscopic imaging as claimed in claim 3, characterized in that The first lens is a hemispherical lens with a plane on the object side, the second lens is a meniscus lens with a concave object side, the third lens is a meniscus lens with a concave object side, the eleventh lens has a convex object side and a concave image side, the twelfth lens has a convex object side and a convex image side, the sixteenth lens is a meniscus lens with a concave object side and a convex image side, and the seventeenth lens has a convex object side and a convex image side.

5. A 25x liquid immersion objective lens for microscopic imaging as claimed in claim 2, characterized in that The fifth cemented lens is composed of a fourteenth lens with negative optical power and a fifteenth lens with positive optical power. The fourteenth lens has a concave surface on the object side and a concave surface on the image side, and the fifteenth lens has a convex surface on the object side and a convex surface on the image side.

6. A 25x liquid immersion objective lens for microscopic imaging as claimed in claim 3, characterized in that The Abbe number vd8 of the eighth lens, the Abbe number vd9 of the ninth lens and the Abbe number vd10 of the tenth lens satisfy: |vd8-vd9|≥40 and |vd9-vd10|≥40, the Abbe number vd11 of the eleventh lens, the Abbe number vd12 of the twelfth lens and the Abbe number vd13 of the thirteenth lens satisfy: |vd11-vd12|≥40 and |vd12-vd13|≥40.

7. A 25x liquid immersion objective lens for microscopic imaging as claimed in claim 2, characterized in that The air gap between the first cemented lens and the third lens is 0.1mm~0.2mm, the air gap between the third lens and the second cemented lens is 0.1mm~0.2mm, the air gap between the second cemented lens and the seventh lens is 0.1mm~0.2mm, the air gap between the fifth cemented lens and the sixteenth lens is 1mm~2mm, and the air gap between the sixteenth lens and the seventeenth lens is 0.1mm~0.2mm.

Images