Barrel lens and microscopic optical system

Abstract

The utility model provides a barrel lens and a microscopic optical system. The barrel lens comprises a first lens group, a second lens group and a third lens group which are coaxially arranged in sequence along a direction from an object space to an image space, the first lens group and the third lens group have positive focal power; the second lens group at least comprises a combined lens with negative focal power, the combined lens comprises a first lens, a second lens and a third lens which are sequentially fixed in the direction from the first lens group to the third lens group, the first lens and the third lens have negative focal power, and the second lens has positive focal power; the first lens, the second lens and the third lens meet the condition that phi 1 / v1 + phi 2 / v2 + phi 3 / v3 = 0. According to the invention, the requirements of large visual field and high resolution of the microscopic optical system can be met at the same time.

Description

Technical Field

[0001] The present application relates to the technical field of optical equipment, and in particular to a tube lens and a microscopic optical system. Background Art

[0002] Microscopic optical systems usually consist of an objective lens and a tube lens. The sample information obtained through the microscopic optical system can show the progress of microscopic imaging technology. Microscopic optical systems allow people to see clearer images and more cells and other observation objects. Therefore, high resolution and large field of view have become important indicators pursued by microscopic optical systems. However, due to the limitation of space-bandwidth product, existing microscopic optical systems cannot meet the requirements of large field of view and high resolution at the same time. Utility Model Content

[0003] One object of the present application is to provide a tube lens, by arranging a first lens group, a second lens group and a third lens group in the tube lens to obtain a larger field of view of the microscopic optical system, and arranging a combined lens in the second lens group to improve the imaging quality of the microscopic optical system, while meeting the requirements of a large field of view and high resolution of the microscopic optical system. Another object of the present application is to provide a microscopic optical system.

[0004] In order to achieve the above objectives, the present application discloses, on one hand, a tube lens, comprising a first lens group, a second lens group and a third lens group coaxially arranged in sequence from the object side to the image side;

[0005] The first lens group and the third lens group have positive optical power;

[0006] The second lens group at least includes a combined lens with negative optical power, the combined lens includes a first lens, a second lens and a third lens fixed in sequence along the direction from the first lens group to the third lens group, the first lens and the third lens have negative optical power, and the second lens has positive optical power;

[0007] The first lens, the second lens and the third lens satisfy:

[0008] Φ1 / ν1+Φ2 / ν2+Φ3 / ν3=0;

[0009] Among them, Φ1, Φ2 and Φ3 are the optical powers of the first lens, the second lens and the third lens respectively, and ν1, ν2 and ν3 are the Abbe numbers of the first lens, the second lens and the third lens respectively.

[0010] Optionally, the first lens and the third lens are biconcave lenses, and the second lens is a biconvex lens.

[0011] Optionally, the first lens, the second lens and the third lens are glued and fixed.

[0012] Optionally, the first lens group includes at least one fourth lens having positive optical power.

[0013] Optionally, the fourth lens is a plano-convex lens.

[0014] Optionally, the third lens group includes a fifth lens and a sixth lens, and the fifth lens is arranged between the second lens group and the sixth lens.

[0015] Optionally, the fifth lens is a biconvex lens, and the sixth lens is a biconcave lens.

[0016] Optionally, the first lens group, the second lens group and the third lens group satisfy:

[0017] 0<ft / fA<4, -4<ft / fB<0, 0<ft / fC<4;

[0018] Wherein, fA, fB and fC are the focal lengths of the first lens group, the second lens group and the third lens group respectively, and ft is the total focal length of the tube lens.

[0019] Optionally, the first lens, the second lens, the third lens, the fourth lens, the fifth lens and the sixth lens satisfy:

[0020] -8<ft / f1<0, 3<ft / f2<9, 0<ft / f3<4, 0<ft / f4<4, 0<ft / f5<6, -6<ft / f6<0;

[0021] Among them, f1, f2, f3, f4, f5 and f6 are the focal lengths of the first lens, the second lens, the third lens, the fourth lens, the fifth lens and the sixth lens respectively, and ft is the total focal length of the tube lens.

[0022] The present application also discloses a microscope optical system, comprising the tube lens as described above.

[0023] The barrel lens of the present application includes a first lens group, a second lens group and a third lens group coaxially arranged in sequence along the direction from the object side to the image side. Among them, the first lens group and the third lens group have positive optical power; the second lens group at least includes a combined lens with negative optical power to obtain a larger field of view of the microscopic optical system under the condition of short focal length. The combined lens includes a first lens, a second lens and a third lens fixed in sequence along the direction from the first lens group to the third lens group, the first lens and the third lens have negative optical power, the second lens has positive optical power, and the first lens, the second lens and the third lens meet: Φ1 / ν1+Φ2 / ν2+Φ3 / ν3=0. Therefore, the present application optimizes the imaging aberration of the barrel lens by arranging a combined lens in the second lens group, improves the imaging quality of the microscopic optical system and enhances the resolution requirement of the microscopic optical system. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 A schematic diagram showing the relationship between the field of view FOV of the microscope optical system and the focal length ft of the tube lens and the focal length fo of the objective lens;

[0026] Figure 2 A schematic diagram showing a specific embodiment of the tube mirror of the present application;

[0027] Figure 3 and Figure 4 Schematic diagrams of the field of view of a microscope optical system using the prior art and the tube lens of the present application are respectively shown;

[0028] Figures 5 to 8 Aberration diagrams in a specific example of the tube lens of the present application are shown. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0030] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present application described here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0031] In the present application, the terms "upper", "lower", "left", "right", "front", "back", "top", "bottom", "inner", "outer", "middle", "vertical", "horizontal", "lateral", "longitudinal" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings. These terms are mainly used to better describe the present application and its embodiments, and are not used to limit the indicated devices, elements or components to have a specific orientation, or to be constructed and operated in a specific orientation.

[0032] Positional relationships such as “parallel” or “perpendicular” include not only completely “parallel” or “perpendicular” positional relationships, but also positional relationships whose angle deviations relative to completely “parallel” or “perpendicular” are within a preset deviation range.

[0033] In addition, some of the above terms may be used to express other meanings in addition to indicating orientation or positional relationship. For example, the term "on" may also be used to express a certain dependency or connection relationship in some cases. For those of ordinary skill in the art, the specific meanings of these terms in this application can be understood according to specific circumstances.

[0034] In addition, the terms "installed", "set", "provided with", "connected", "connected", and "socketed" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection, or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be an internal connection between two devices, elements, or components. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0035] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0036] In the prior art, the space-bandwidth product is a dimensionless physical quantity used to describe the information flux of a microscopic optical system, which represents the number of optically resolvable effective pixels of a microscopic optical system within its imaging field of view. The space-bandwidth product is defined by the formula N=DΔv, where D represents the imaging field of view, and Δv is the bandwidth of the image signal that satisfies the Nyquist sampling theorem. Therefore, the higher the bandwidth Δv, the higher the resolution of the image. For a fixed optical system, the imaging field of view D is inversely proportional to the bandwidth Δv.

[0037] For a microscope optical system, when the microscope optical system is an infinite microscope, the light coming out of the infinite microscope objective lens is parallel light and cannot form an image. It needs to be converged by a tube lens to form an image. The field of view FOV of a conventional microscope is related to the focal length ft of the tube lens and the focal length fo of the objective lens, such as Figure 1 As shown, the specific relationship is shown in formula (1):

[0038]

[0039] It can be seen from formula (1) that when the focal length fo of the objective lens and the size Ig of the photosensitive chip are constant, the field of view FOV is inversely proportional to the focal length ft of the tube lens. Currently, the ft of the tube lens is mostly between 120 and 220 mm, so the field of view is relatively small.

[0040] Therefore, for a traditional microscope optical system, high resolution and large field of view are often a pair of irreconcilable contradictions, and it is difficult to improve them simply by improving optical design parameters.

[0041] In order to increase the spatial bandwidth product to obtain images with high resolution and large field of view at the same time, the conventional method is to use the spatial bandwidth product expansion technology based on field of view expansion, such as scanning and stitching a single imaging system to obtain images with high resolution and large field of view. As shown in Table 1, at time t(1,1), the optical system obtains an image FOV(1,1) with high resolution but small field of view; at time t(1,2), through the scanning of the optical system (generally using a scanning galvanometer), an image FOV(1,2) with high resolution but small field of view is obtained; and so on, until the image FOV(m,n) is obtained; then, through the algorithm, the image FOV(1,1) to the image FOV(m,n) are merged to obtain a composite image FOV with a large field of view, so that images with high resolution and large field of view can be obtained at the same time.

[0042] Table 1

[0043] FOV(1,1) FOV(1,2) …… FOV(1,n) FOV(2,1) FOV(2,2) …… FOV(2,n) …… …… …… …… FOV(m,1) …… …… FOV(m,n)

[0044] However, this method also has disadvantages. The scanning system will increase the complexity and manufacturing and maintenance costs of the entire system, and it is difficult to miniaturize it. At the same time, the processing of the entire image will take more time, which will greatly reduce the detection efficiency.

[0045] Based on the problems existing in the prior art, the present application designs the structure of the microscope tube lens, designs its focal length to be less than 95mm, and increases the field of view of the tube lens. This short-focus structure makes it more difficult to design the aberration in the tube lens. In order to improve the resolution of the tube lens, the tube lens adopts the design of an achromatic tube lens, which is used in conjunction with the objective lens. It can have excellent flatness in all the wavelength bandwidths used, and can have a sharp picture image from the center to the edge. As a result, while obtaining high resolution, the field of view size of the present application is increased by about 30% compared to conventional microscope systems.

[0046] According to one aspect of the present application, this embodiment discloses a tube mirror. Figure 2 As shown, in this embodiment, the tube lens includes a first lens group G1, a second lens group G2 and a third lens group G3 which are coaxially arranged in sequence from the object side to the image side.

[0047] The first lens group G1 and the third lens group G3 have positive refractive power; the second lens group G2 at least includes a combined lens with negative refractive power.

[0048] The combined lens includes a first lens L1, a second lens L2, and a third lens L3 fixed in sequence along a direction from the first lens group G1 to the third lens group G3, the first lens L1 and the third lens L3 have negative refractive power, and the second lens L2 has positive refractive power.

[0049] Wherein, the first lens L1, the second lens L2 and the third lens L3 satisfy:

[0050] Φ1 / ν1+Φ2 / ν2+Φ3 / ν3=0 (21

[0051] Among them, Φ1, Φ2 and Φ3 are the optical powers of the first lens L1, the second lens L2 and the third lens L3 respectively, and ν1, ν2 and ν3 are the Abbe numbers of the first lens L1, the second lens L2 and the third lens L3 respectively.

[0052] The present invention comprises a first lens group G1, a second lens group G2 and a third lens group G3 which are coaxially arranged in sequence from the object side to the image side. The first lens group G1 and the third lens group G3 have positive optical power; the second lens group G2 at least comprises a combined lens with negative optical power, so as to obtain a larger field of view of the microscopic optical system under the condition of short focal length. The combined lens comprises a first lens L1, a second lens L2 and a third lens L3 which are fixed in sequence from the first lens group G1 to the third lens group G3, the first lens L1 and the third lens L3 have negative optical power, the second lens L2 has positive optical power, and the first lens L1, the second lens L2 and the third lens L3 satisfy: Φ1 / ν1+Φ2 / ν2+Φ3 / ν3=0. Therefore, the present invention optimizes the imaging aberration of the tube lens by arranging a combined lens in the second lens group G2, thereby improving the imaging quality of the microscopic optical system and enhancing the resolution requirement of the microscopic optical system.

[0053] In an optional embodiment, the first lens L1 and the third lens L3 are biconcave lenses, and the second lens L2 is a biconvex lens.

[0054] Specifically, the combined lens includes a central biconvex lens and biconcave lenses disposed on both sides of the biconvex lens. The first lens L1, the second lens L2 and the third lens L3 are closely attached to form a combined lens, and the sum of the ratios of the optical power of the first lens L1, the second lens L2 and the third lens L3 to the Abbe number is zero. Compared with a single lens, the use of such a combined lens can well correct chromatic aberration. The reasons are as follows:

[0055] The focal length of the lens is

[0056] Φ=(n-1)(C1-C2) (3)

[0057] Where C1 and C2 are the front and back curvatures of the lens; n is the refractive index of the lens material.

[0058] Differentiating the above formula, we get:

[0059] dΦ=(C1-C2)dn (4)

[0060] For the visible light band, F, d, and C light are generally selected as the correction wavelengths. F and C light are at the two ends of the band, so dn = nF-nC, nF and nC are the refractive indices of F light and C light respectively. Substituting into (3) (4) we get:

[0061] dΦ=(C1-C2)(nF-nC)=(C1-C2)(nd-1)(nF-nC) / (nd-1)=Φd / νd (5)

[0062] For the combined lens, the focal power formula can be obtained:

[0063] Φ1+Φ2+Φ3=Φ (6)

[0064] Where Φ is the total optical power of the combined lens.

[0065] Differentiate (6) and substitute it into (5) to obtain:

[0066] dΦ=Φ1 / ν1+Φ2 / ν2+Φ3 / ν3 (7)

[0067] The total change in focal length is set to 0, that is, dΦ=0, to achieve the purpose of achromatism, and obtain formula (2). It can be seen that the present application makes the first lens L1, the second lens L2 and the third lens L3 satisfy the formula (2) Φ1 / ν1+Φ2 / ν2+Φ3 / ν3=0, which can have excellent flatness in the entire wavelength bandwidth used, so that the middle part and the peripheral part of the picture have the same clear image, optimize the imaging aberration of the tube lens, and improve the imaging quality of the microscope optical system.

[0068] In an optional embodiment, the first lens L1, the second lens L2 and the third lens L3 are glued and fixed to ensure that the first lens L1, the second lens L2 and the third lens L3 are stably fixed. Of course, in other embodiments, the first lens L1, the second lens L2 and the third lens L3 can also be fixed in other ways, which is not limited in this application.

[0069] In an optional embodiment, the first lens group G1 includes at least one fourth lens L4 with positive refractive power, and the parallel light emitted from the objective lens is initially converged to the second lens group G2 through the fourth lens L4.

[0070] Preferably, the fourth lens L4 is a plano-convex lens, and the convex side of the fourth lens L4 faces the objective lens.

[0071] The convex side surface of the fourth lens L4 is directed toward the objective lens to converge the light emitted by the objective lens.

[0072] In an optional embodiment, the third lens group G3 includes a fifth lens L5 and a sixth lens L6, and the fifth lens L5 is disposed between the second lens group G2 and the sixth lens L6.

[0073] Preferably, the fifth lens L5 is a biconvex lens, and the sixth lens L6 is a biconcave lens, which further converges the light output by the second lens group G2 and reduces the overall focal length of the tube lens.

[0074] In an optional embodiment, the first lens group G1, the second lens group G2 and the third lens group G3 satisfy:

[0075] 0<ft / fA<4, -4<ft / fB<0, 0<ft / fC<4

[0076] Among them, fA, fB and fC are the focal lengths of the first lens group G1, the second lens group G2 and the third lens group G3 respectively, and ft is the total focal length of the tube lens to achieve a short focal length design of the tube lens.

[0077] In an optional embodiment, the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5 and the sixth lens L6 satisfy:

[0078] -8<ft / f1<0, 3<ft / f2<9, 0<ft / f3<4, 0<ft / f4<4, 0<ft / f5<6, -6<ft / f6<0;

[0079] Wherein, f1, f2, f3, f4, f5 and f6 are respectively the focal lengths of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5 and the sixth lens L6, and ft is the total focal length of the tube lens. In this optional implementation, the selection method of each lens is limited by limiting the ratio range of each lens to the total focal length of the tube lens, thereby meeting the short focal length requirement of the tube lens.

[0080] Of course, it should be noted that those skilled in the art may also set parameters such as the focal length of the first lens group G1 to the third lens group G3 and the first lens L1 to the sixth lens L6 according to actual needs, and the present application does not limit this.

[0081] The present application is further described below through a specific example. In this specific example, the tube lens includes a first lens group G1, a second lens group G2, and a third lens group G3 which are coaxially arranged in sequence from the object side to the image side, that is, the tube lens includes a fourth lens L4 which is a plano-convex lens, a first lens L1 which is a biconcave lens, a second lens L2 which is a biconvex lens, a third lens L3 which is a biconcave lens, a fifth lens L5 which is a biconvex lens, and a sixth lens L6 which is a biconcave lens, as shown in FIG. Figure 2 As shown. The tube lens of the microscope optical system in this embodiment only has six lenses to converge the parallel light emitted by the objective lens, so that the total focal length ft of the tube lens reaches 95mm, which is better than the existing tube lenses whose ft is mostly 120-220mm. In addition, the field of view of the conventional microscope optical system is 32×25 small grids, such as Figure 3 At the same magnification, using the same scale, the field of view of the microscope optical system of the present application is 41×31 grids, as shown in FIG. Figure 4 As shown. Figure 3 and Figure 4It can be seen that the field of view of the microscopic optical system of this embodiment is improved by about 30% compared with the existing microscopic optical system.

[0082] In this specific example, the parameters of the first lens L1 to the sixth lens L6 are shown in Table 2. The table shows, from the left, the surface number, the radius of curvature (r), the surface spacing (d), the refractive index at a wavelength of 588nm (nd), and the Abbe number (Vd). The unit of the radius of curvature r, the surface spacing d, and other lengths is generally "mm". In addition, the distance Lp from the lens surface closest to the objective lens to the pupil surface is -823mm, the pupil diameter is 14mm, and the image height is 4.45mm.

[0083] Table 2

[0084] Face number r d Nd Vd s1 57.123 4 1.85 23.8 L1 s2 INF 25.219 s3 -161.680 1.500 1.81 25.5 L2 s4 18.388 7 1.76 52.3 L3 s5 -24.780 1.5 1.85 23.8 L4 s6 130.353 48.120 s7 38.840 3.7 1.85 23.8 L5 s8 -95.019 10.614 s9 -29.965 1.5 1.59 61.3 L6 s10 91.278 1.1846

[0085] Thus, in this specific example, the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5 and the sixth lens L6 satisfy: -8<ft / f1<0, 3<ft / f2<9, 0<ft / f3<4, 0<ft / f4<4, 0<ft / f5<6, -6<ft / f6<0, and the first lens group G1, the second lens group G2 and the third lens group G3 satisfy: 0<ft / fA<4, -4<ft / fB<0, 0<ft / fC<4.

[0086] Figures 5 to 8 Various aberration diagrams of the tube lens in this specific example are shown. Figure 5 It is a vertical axis chromatic aberration diagram. The horizontal axis is the vertical axis chromatic aberration, and the vertical axis is the image height. The vertical axis chromatic aberration is the horizontal coordinate of the point with the highest image height, which is 0.536um. Figure 6 It is a distortion aberration diagram. Different colors represent different wavelengths (F, D, and C light respectively). The vertical axis is the incident angle, and the horizontal axis is the distortion aberration expressed as a percentage. The maximum distortion is the horizontal coordinate value at the maximum incident angle, which is 0.23%. Figure 7 It is a field curvature diagram. The horizontal axis is the field curvature in mm, and the vertical axis is the incident angle. The central wavelength is 0.5876um. The solid yellow line represents the field curvature curve in the meridian direction, and the dotted line represents the field curvature curve in the sagittal direction. It can be obtained that the maximum sagittal field curvature is 13.1um, and the maximum meridian field curvature is 23.9um. Figure 8 is a point diagram, Figure 8 The spot size in each field of view is smaller than the Airy disk (the Airy disk is the circle in the figure); at the same time, the RMS radius of the spot is between 1.652 and 2.166 um; smaller than the sensor pixel size of 3.45 um. Both points indicate that its resolution is high enough to meet the needs of the microscope system.

[0087] from Figure 5 to Figure 7It can be seen that the chromatic aberration of the tube lens of this embodiment is well corrected, and the image plane has good flatness, which can meet the imaging quality requirements of the microscope. Figure 8 The spot diagram can also intuitively reflect the high resolution of the tube mirror.

[0088] The present application also discloses a microscopic optical system, which includes the tube lens as described in this embodiment. Optionally, the microscopic optical system may also include structures such as an objective lens.

[0089] Optionally, in a specific example, the microscope optical system may be an infinity microscope.

[0090] Since the tube lens included in the microscopic optical system provided in the embodiment of the present application corresponds to the tube lens provided above, the previous implementation is also applicable to the microscopic optical system provided in this embodiment and will not be described in detail here.

[0091] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0092] The above is only an embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.

Claims

1. A tube lens, characterized in that: It comprises a first lens group, a second lens group and a third lens group which are coaxially arranged in sequence from the object side to the image side; The first lens group and the third lens group have positive optical power; The second lens group at least includes a combined lens with negative optical power, the combined lens includes a first lens, a second lens and a third lens fixed in sequence along the direction from the first lens group to the third lens group, the first lens and the third lens have negative optical power, and the second lens has positive optical power; The first lens, the second lens and the third lens satisfy: Φ1 / ν1+Φ2 / ν2+Φ3 / ν3=0; Among them, Φ1, Φ2 and Φ3 are the optical powers of the first lens, the second lens and the third lens respectively, and ν1, ν2 and ν3 are the Abbe numbers of the first lens, the second lens and the third lens respectively.

2. The tube lens according to claim 1, characterized in that: The first lens and the third lens are biconcave lenses, and the second lens is a biconvex lens.

3. The tube lens according to claim 1 or 2, characterized in that: The first lens, the second lens and the third lens are glued and fixed.

4. The tube lens according to claim 1, characterized in that: The first lens group includes at least one fourth lens having positive optical power.

5. The tube lens according to claim 4, characterized in that: The fourth lens is a plano-convex lens.

6. The tube lens according to claim 4, characterized in that: The third lens group includes a fifth lens and a sixth lens, and the fifth lens is disposed between the second lens group and the sixth lens.

7. The tube lens according to claim 6, characterized in that: The fifth lens is a biconvex lens, and the sixth lens is a biconcave lens.

8. The tube lens according to claim 1, characterized in that: The first lens group, the second lens group and the third lens group satisfy: 0<ft / fA<4, -4<ft / fB<0, 0<ft / fC<4; Wherein, fA, fB and fC are the focal lengths of the first lens group, the second lens group and the third lens group respectively, and ft is the total focal length of the tube lens.

9. The tube lens according to claim 6, characterized in that: The first lens, the second lens, the third lens, the fourth lens, the fifth lens and the sixth lens satisfy: -8<ft / f1<0, 3<ft / f2<9, 0<ft / f3<4, 0<ft / f4<4, 0<ft / f5<6, -6<ft / f6<0; Among them, f1, f2, f3, f4, f5 and f6 are the focal lengths of the first lens, the second lens, the third lens, the fourth lens, the fifth lens and the sixth lens respectively, and ft is the total focal length of the tube lens.

10. A microscope optical system, characterized in that: It comprises the tube mirror as described in any one of claims 1-9.

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