An ultralong working distance microscope objective

Abstract

The present application relates to a kind of super-long working distance microscope objective, including first lens group, second lens group, diaphragm and third lens group arranged in order from light incident direction;The first lens group has positive focal length, including first lens, second lens, third lens, fourth lens, fifth lens and sixth lens arranged in order from light incident direction;The second lens group has negative focal length, including seventh lens and eighth lens arranged in order from light incident direction;The third lens group has negative focal length, including ninth lens, tenth lens, eleventh lens, twelfth lens and thirteenth lens arranged in order from light incident direction.The present application has the advantage of super-long working distance, can realize long-distance and larger magnification monitoring.

Description

Technical Field

[0001] This invention relates to the field of optical technology, and in particular to an ultra-long working distance microscope objective. Background Technology

[0002] In machine vision industrial inspection, there is a type of inspection where the environment in which the object being inspected is extremely harsh, often requiring specially treated lenses. For example, monitoring inside a high-temperature boiler typically requires high-temperature resistant lenses made of high-temperature resistant materials; similarly, some experiments involve high-temperature and high-radiation environments, necessitating high-temperature and radiation resistant treatments for the monitoring lenses. However, if the monitoring distance is increased and the harsh environment is removed, the lens no longer requires special treatment and remains durable, reducing design complexity and cost.

[0003] The working distance (WD) of a microscope objective refers to the distance from the front lens surface of the objective to the surface of the object being observed (or the top surface of the coverslip) when the microscope is correctly focused. This distance is an important parameter in the use of a microscope because it directly affects the flexibility and safety of sample handling. The working distance mainly depends on the numerical aperture (NA) and focal length of the objective. Generally speaking, high-magnification objectives with larger numerical apertures have shorter working distances. For example, the working distance of a 10x objective might be 6.5mm, while that of a 40x objective might be only 0.48mm. Currently, industrial lenses on the market are usually not designed for high magnification, and high-magnification microscope objectives are not designed for long working distances.

[0004] To address the above issues, an ultra-long working distance microscope objective (working distance up to 500mm) is proposed to enable long-distance, high-magnification monitoring. Summary of the Invention

[0005] Based on this, the purpose of the present invention is to overcome the defects or deficiencies of the prior art and provide an ultra-long working distance microscope objective.

[0006] An ultra-long working distance microscope objective includes a first lens group, a second lens group, an aperture, and a third lens group arranged sequentially from the direction of light incidence. The first lens group has a positive focal length and includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens, and a sixth lens arranged sequentially along the direction of light incidence. The second lens group has a negative focal length and includes a seventh lens and an eighth lens arranged sequentially along the direction of light incidence. The third lens group has a negative focal length and includes a ninth lens, a tenth lens, an eleventh lens, a twelfth lens, and a thirteenth lens arranged sequentially along the direction of light incidence.

[0007] Compared to existing technologies, the objective lens of this invention has the advantage of an ultra-long working distance, enabling monitoring at long distances and high magnification.

[0008] In one embodiment, the first lens is a biconvex positive lens; the second lens is a meniscus negative lens, with its convex surface facing the light incident side and its concave surface facing the light emitting side; the third lens is a meniscus positive lens, with its convex surface facing the light incident side and its concave surface facing the light emitting side; the fourth lens is a biconvex positive lens; the fifth lens is a biconcave negative lens; the sixth lens is a meniscus positive lens, with its convex surface facing the light incident side and its concave surface facing the light emitting side; and the seventh lens is a meniscus positive lens, with its convex surface facing the light incident side and its concave surface facing the light emitting side. The eighth lens is a meniscus negative lens, with its convex surface facing the light incident side and its concave surface facing the light emitting side; the ninth lens is a biconcave negative lens; the tenth lens is a biconvex positive lens; the eleventh lens is a biconcave negative lens; the twelfth lens is a biconvex positive lens; and the thirteenth lens is a biconcave negative lens; wherein, the second and third lenses constitute a first cemented doublet, the fourth and fifth lenses constitute a second cemented doublet, and the ninth, tenth, and eleventh lenses constitute a cemented triplet.

[0009] In one embodiment, the working distance WD of the objective lens and its effective focal length f satisfy the following condition: 12 < WD / f < 13.

[0010] In one embodiment, the objective lens has a working distance WD of 500 mm, an effective focal length f of 40 mm, and a numerical aperture NA of 0.05.

[0011] In one embodiment, the focal lengths between the lens groups satisfy the following condition: -0.9 < f 10 / f 20 <-0.75, and 9 < f 20 / f 30 <10; where f 10 f is the focal length of the first lens group. 20 f is the focal length of the second lens group; 30 This is the focal length of the third lens group.

[0012] In one embodiment, the focal length of each lens is:

[0013] The focal length f1 of the first lens is 87.28 mm;

[0014] The focal length f2 of the second lens is -79.44mm;

[0015] The focal length f3 of the third lens is 129.49 mm;

[0016] The focal length f4 of the fourth lens is 70.78mm;

[0017] The focal length f5 of the fifth lens is -46.12mm;

[0018] The focal length f6 of the sixth lens is 55.96mm;

[0019] The focal length f7 of the seventh lens is 60.25mm;

[0020] The focal length f8 of the eighth lens is -28.99mm;

[0021] The focal length f9 of the ninth lens is -7.09mm;

[0022] The focal length f10 of the tenth lens is 6.66mm;

[0023] The focal length f11 of the eleventh lens is -6.80mm;

[0024] The focal length f12 of the twelfth lens is 12.11 mm;

[0025] The focal length f13 of the thirteenth lens is -13.08mm.

[0026] In one embodiment, the dimensions of each lens satisfy the following condition:

[0027] The first lens has a front surface radius of curvature of -67.193 mm, a rear surface radius of curvature of 264.448 mm, and a center distance of 8.47 mm between its front and rear surfaces.

[0028] The second lens has a front surface radius of curvature of -64.786 mm, a rear surface radius of curvature of -30.592 mm, and a center distance of 1.78 mm between its front and rear surfaces.

[0029] The third lens has a front surface radius of curvature of -30.592 mm, a rear surface radius of curvature of -61.436 mm, and a center distance of 7.29 mm between its front and rear surfaces.

[0030] The fourth lens has a front surface radius of curvature of -37.345 mm, a rear surface radius of curvature of 170.233 mm, and a center distance of 9.67 mm between its front and rear surfaces.

[0031] The fifth lens has a front surface radius of curvature of 170.233 mm, a rear surface radius of curvature of -47.639 mm, and a center distance of 1.88 mm between its front and rear surfaces.

[0032] The sixth lens has a front surface radius of curvature of -28.087 mm, a rear surface radius of curvature of -206.876 mm, and a center distance of 8.46 mm between its front and rear surfaces.

[0033] The seventh lens has a front surface radius of curvature of -26.624 mm, a rear surface radius of curvature of -45.441 mm, and a center distance of 5.59 mm between its front and rear surfaces.

[0034] The eighth lens has a front surface radius of curvature of -258.827 mm, a rear surface radius of curvature of -21.031 mm, and a center distance of 1.54 mm between its front and rear surfaces.

[0035] The ninth lens has a front surface radius of curvature of 31.463 mm, a rear surface radius of curvature of -6.017 mm, and a center distance of 2.22 mm between its front and rear surfaces.

[0036] The tenth lens has a front surface radius of curvature of -6.017 mm, a rear surface radius of curvature of 8.341 mm, and a center distance of 4.01 mm between its front and rear surfaces.

[0037] The eleventh lens has a front surface radius of curvature of 8.341 mm, a rear surface radius of curvature of -14.917 mm, and a center distance of 2.00 mm between its front and rear surfaces.

[0038] The twelfth lens has a front surface radius of curvature of -10.897 mm, a rear surface radius of curvature of 69.949 mm, and a center distance of 2.67 mm between its front and rear surfaces.

[0039] The thirteenth lens has a front surface radius of curvature of 11.574 mm, a rear surface radius of curvature of -73.154 mm, and a center distance of 1.50 mm between its front and rear surfaces.

[0040] The two surfaces of the lens are defined as the front and rear surfaces according to the direction of light incidence.

[0041] In one embodiment, the positional relationship of the components satisfies the following condition:

[0042] The center distance between the rear surface of the first lens and the front surface of the second lens is 0.49 mm;

[0043] The center distance between the rear surface of the third lens and the front surface of the fourth lens is 0.15 mm;

[0044] The center distance between the rear surface of the fifth lens and the front surface of the sixth lens is 0.15 mm;

[0045] The center distance between the rear surface of the sixth lens and the front surface of the seventh lens is 1.75 mm;

[0046] The center distance between the rear surface of the seventh lens and the front surface of the eighth lens is 2.04 mm;

[0047] The center distance between the aperture and the rear surface of the eighth lens is 5.41 mm;

[0048] The center distance between the rear surface of the eighth lens and the front surface of the ninth lens is 29.50 mm;

[0049] The center distance between the rear surface of the eleventh lens and the front surface of the twelfth lens is 0.84 mm;

[0050] The center distance between the rear surface of the twelfth lens and the front surface of the thirteenth lens is 2.59 mm.

[0051] In one embodiment, the materials of the third lens and the fourth lens satisfy the following conditions:

[0052] The refractive index Nd3 of the third lens ranges from Nd3∈(1.42,1.46), and its dispersion Vd3 ranges from Vd3∈(94,95).

[0053] The refractive index Nd4 of the fourth lens ranges from Nd4∈(1.42,1.46), and its dispersion Vd4 ranges from Vd4∈(94,95).

[0054] In one embodiment, the refractive index Nd1 of the first lens is 1.62, and its dispersion Vd1 is 53.9.

[0055] The refractive index Nd2 of the second lens is 1.74, and its dispersion Vd2 is 28.3.

[0056] The refractive index Nd3 of the third lens is 1.44, and its dispersion Vd3 is 94.5.

[0057] The fourth lens has a refractive index Nd4 of 1.44 and a dispersion Vd4 of 94.5.

[0058] The refractive index Nd5 of the fifth lens is 1.80, and its dispersion Vd5 is 42.3.

[0059] The refractive index Nd6 of the sixth lens is 1.57, and its dispersion Vd6 is 71.3.

[0060] The refractive index Nd7 of the seventh lens is 1.92, and its dispersion Vd7 is 20.9.

[0061] The refractive index Nd8 of the eighth lens is 1.79, and its dispersion Vd8 is 47.5.

[0062] The refractive index Nd9 of the ninth lens is 1.69, and its dispersion Vd9 is 54.5.

[0063] The refractive index Nd of the tenth lens 10 The value is 1.58, and its dispersion Vd 10 The value is 40.9;

[0064] The refractive index Nd of the eleventh lens 11 The value is 1.75, and its dispersion Vd 11 The value is 52.3;

[0065] The refractive index Nd of the twelfth lens 12 The value is 1.79, and its dispersion Vd 12 The value is 44.2;

[0066] The refractive index Nd of the thirteenth lens 13 The value is 1.75, and its dispersion Vd 13 The value is 52.3.

[0067] To better understand and implement this invention, the following detailed description is provided in conjunction with the accompanying drawings. Attached Figure Description

[0068] Figure 1 This is a schematic diagram of the overall structure of the objective lens provided by the present invention;

[0069] Figure 2 A schematic diagram of the lens structure of the objective lens provided by the present invention;

[0070] Figure 3 A schematic diagram of the front and rear surface structures of each lens in the first lens group of the objective lens provided by the present invention;

[0071] Figure 4 A schematic diagram of the front and rear surface structures of each lens in the second lens group of the objective lens provided by the present invention;

[0072] Figure 5 A schematic diagram of the front and rear surface structures of each lens in the third lens group of the objective lens provided by the present invention;

[0073] Figure 6 MTF curve of the objective lens provided for this invention;

[0074] Figure 7 Optical distortion diagram of the objective lens provided by this invention. Detailed Implementation

[0075] The present invention will now be described in detail with reference to the accompanying drawings.

[0076] like Figures 1 to 2 As shown, an ultra-long working distance microscope objective of the present invention includes a first lens group 10, a second lens group 20, an aperture 40, and a third lens group 30 arranged sequentially from the light incident direction. The first lens group 10 has a positive focal length and includes a first lens 11, a second lens 12, a third lens 13, a fourth lens 14, a fifth lens 15, and a sixth lens 16 arranged sequentially along the light incident direction. The second lens group 20 has a negative focal length and includes a seventh lens 21 and an eighth lens 22 arranged sequentially along the light incident direction. The third lens group 30 has a negative focal length and includes a ninth lens 31, a tenth lens 32, an eleventh lens 33, a twelfth lens 34, and a thirteenth lens 35 arranged sequentially along the light incident direction.

[0077] In this application, the working distance WD and the effective focal length f of the objective lens satisfy the following condition: 12 < WD / f < 13.

[0078] In this application, the focal length f of the first lens group 10 10 The focal length f of the second lens group 20 20 The following condition must be met: -0.9 < f 10 / f 20 <-0.75.

[0079] In this application, the focal length f of the second lens group 20 20 and the focal length f of the third lens group 30 30 The following condition must be met: 9 < f 20 / f 30 <10.

[0080] The first lens 11 is a biconvex positive lens; the second lens 12 is a meniscus negative lens, with its convex surface facing the incident light side and its concave surface facing the emitting light side; the third lens 13 is a meniscus positive lens, with its convex surface facing the incident light side and its concave surface facing the emitting light side; the fourth lens 14 is a biconvex positive lens; the fifth lens 15 is a biconcave negative lens; the sixth lens 16 is a meniscus positive lens, with its convex surface facing the incident light side and its concave surface facing the emitting light side; wherein, the second lens 12 and the third lens 13 constitute a first cemented doublet lens, and the fourth lens 14 and the fifth lens 15 constitute a second cemented doublet lens.

[0081] In this application, the focal length f of the first cemented doublet lens 12+13 The effective focal length f of the objective lens satisfies the following condition: -4.8 < f 12+13 / f<-4.5.

[0082] In this application, the focal length f of the second cemented doublet lens 14+15 The effective focal length f of the objective lens satisfies the following condition: -4.7 < f 14+15 / f<-4.3.

[0083] In this application, the material of the third lens 13 satisfies the following conditions: the refractive index Nd3 of the third lens 13 is in the range of Nd3∈(1.42,1.46), and its dispersion Vd3 is in the range of Vd3∈(94,95).

[0084] In this application, the material of the fourth lens 14 satisfies the following conditions: the refractive index Nd4 of the fourth lens 14 is in the range of Nd4∈(1.42,1.46), and its dispersion Vd4 is in the range of Vd4∈(94,95).

[0085] The seventh lens 21 is a meniscus positive lens, with its convex surface facing the light incident side and its concave surface facing the light emitting side; the eighth lens 22 is a meniscus negative lens, with its convex surface facing the light incident side and its concave surface facing the light emitting side.

[0086] The ninth lens 31 is a biconcave negative lens, the tenth lens 32 is a biconvex positive lens, the eleventh lens 33 is a biconcave negative lens, the twelfth lens 34 is a biconvex positive lens, and the thirteenth lens 35 is a biconcave negative lens. The ninth lens 31, the tenth lens 32, and the eleventh lens 33 constitute a cemented three-layer lens.

[0087] In this embodiment, the first lens group 10 with a positive focal length is used to achieve an ultra-long working distance; the second lens group 20 with a negative focal length is used to correct spherical aberration and to connect the light passing through the first lens group 10 to the third lens group 30; the third lens group 30 with a negative focal length is used to achieve a larger magnification; wherein the first cemented doublet and the second cemented doublet are used to correct chromatic aberration.

[0088] Specifically, the material of each lens must meet the following conditions:

[0089]

[0090] Preferably, the refractive index Nd1 of the first lens 11 is 1.62, and its dispersion Vd1 is 53.9.

[0091] Preferably, the refractive index Nd2 of the second lens 12 is 1.74, and its dispersion Vd2 is 28.3.

[0092] Preferably, the refractive index Nd3 of the third lens 13 is 1.44, and its dispersion Vd3 is 94.5.

[0093] Preferably, the refractive index Nd4 of the fourth lens 14 is 1.44, and its dispersion Vd4 is 94.5.

[0094] Preferably, the refractive index Nd5 of the fifth lens 15 is 1.80, and its dispersion Vd5 is 42.3.

[0095] Preferably, the refractive index Nd6 of the sixth lens 16 is 1.57, and its dispersion Vd6 is 71.3.

[0096] Preferably, the refractive index Nd7 of the seventh lens 21 is 1.92, and its dispersion Vd7 is 20.9.

[0097] Preferably, the refractive index Nd8 of the eighth lens 22 is 1.79, and its dispersion Vd8 is 47.5.

[0098] Preferably, the refractive index Nd9 of the ninth lens 31 is 1.69, and its dispersion Vd9 is 54.5.

[0099] Preferably, the refractive index Nd of the tenth lens 32 is... 10 The value is 1.58, and its dispersion Vd 10 The value is 40.9.

[0100] Preferably, the refractive index Nd of the eleventh lens 33 is... 11 The value is 1.75, and its dispersion Vd 11 The value is 52.3.

[0101] Preferably, the refractive index Nd of the twelfth lens 34 is... 12 The value is 1.79, and its dispersion Vd 12 The value is 44.2.

[0102] Preferably, the refractive index Nd of the thirteenth lens 35 is... 13 The value is 1.75, and its dispersion Vd 13 The value is 52.3.

[0103] In this application, all lenses are spherical lenses made of glass.

[0104] In this application, as Figures 3 to 5 As shown, the two side surfaces of the lens are defined as the front and rear surfaces according to the direction of light incidence; specifically, the dimensions of each lens satisfy the following conditions:

[0105]

[0106] Specifically, the first lens 11 has a front surface S11A with a radius of curvature of -67.193 mm, a rear surface S11B with a radius of curvature of 264.448 mm, and a center distance of 8.47 mm between its front and rear surfaces.

[0107] Specifically, the second lens 12 has a front surface S12A with a radius of curvature of -64.786 mm, a rear surface S12B with a radius of curvature of -30.592 mm, and a center distance of 1.78 mm between its front and rear surfaces.

[0108] Specifically, the third lens 13 has a front surface S13A with a radius of curvature of -30.592 mm, a rear surface S13B with a radius of curvature of -61.436 mm, and a center distance between the front and rear surfaces of 7.29 mm.

[0109] Specifically, the fourth lens 14 has a front surface S14A with a radius of curvature of -37.345 mm, a rear surface S14B with a radius of curvature of 170.233 mm, and a center distance between the front and rear surfaces of 9.67 mm.

[0110] Specifically, the fifth lens 15 has a front surface S15A with a radius of curvature of 170.233 mm, a rear surface S15B with a radius of curvature of -47.639 mm, and a center distance of 1.88 mm between its front and rear surfaces.

[0111] Specifically, the sixth lens 16 has a front surface S16A with a radius of curvature of -28.087 mm, a rear surface S16B with a radius of curvature of -206.876 mm, and a center distance between the front and rear surfaces of 8.46 mm.

[0112] Specifically, the seventh lens 21 has a front surface S21A radius of curvature of -26.624 mm, a rear surface S21B radius of curvature of -45.441 mm, and a center distance of 5.59 mm between its front and rear surfaces.

[0113] Specifically, the eighth lens 22 has a front surface S22A radius of curvature of -258.827 mm, a rear surface S22B radius of curvature of -21.031 mm, and a center distance of 1.54 mm between its front and rear surfaces.

[0114] Specifically, the ninth lens 31 has a front surface S31A with a radius of curvature of 31.463 mm, a rear surface S31B with a radius of curvature of -6.017 mm, and a center distance between the front and rear surfaces of 2.22 mm.

[0115] Specifically, the tenth lens 32 has a front surface S32A with a radius of curvature of -6.017 mm, a rear surface S32B with a radius of curvature of 8.341 mm, and a center distance between the front and rear surfaces of 4.01 mm.

[0116] Specifically, the eleventh lens 33 has a front surface S33A radius of curvature of 8.341 mm, a rear surface S33B radius of curvature of -14.917 mm, and a center distance between the front and rear surfaces of 2.00 mm.

[0117] Specifically, the twelfth lens 34 has a front surface S34A radius of curvature of -10.897mm, a rear surface S34B radius of curvature of 69.949mm, and a center distance of 2.67mm between its front and rear surfaces.

[0118] Specifically, the thirteenth lens 35 has a front surface S35A radius of curvature of 11.574 mm, a rear surface S35B radius of curvature of -73.154 mm, and a center distance between the front and rear surfaces of 1.50 mm.

[0119] In this application, the positional relationship between each lens is represented by the center distance between the front and rear surfaces of each lens and the front and rear surfaces of other lenses. Specifically, the following conditions must be met:

[0120]

[0121]

[0122] The distance between the aperture 40 and the center of the rear surface S22B of the eighth lens is 5.41 mm.

[0123] In this application, an ultra-long working distance microscope objective is designed according to parameter design requirements. The technical specifications achieved by this objective are as follows:

[0124]

[0125] Specifically, the focal length of each lens satisfies the following condition:

[0126]

[0127]

[0128] Based on the above embodiments, the actual test results of this objective lens are as follows:

[0129] Figure 6The MTF (Modulation Transfer Function) plot of the objective lens under visible light with wavelengths of 435 nm to 656 nm is shown.

[0130] Figure 7 The optical distortion diagram of the objective lens under visible light with wavelengths of 435nm to 656nm shows that the F-tanθ optical distortion of this ultra-long working distance microscope objective lens is small, basically maintained at 0.3%.

[0131] Compared with existing technologies, the present invention provides an ultra-long working distance microscope objective, which has the advantage of an ultra-long working distance and can realize long-distance and high magnification monitoring.

[0132] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of this application. The singular forms “a,” “the,” and “the” used in the embodiments and claims of this application are also intended to include the plural forms, unless the context clearly indicates otherwise. It should also be understood that, unless otherwise stated, “a plurality” means two or more; the terms “first,” “second,” “third,” etc., are used only to distinguish and not to describe a particular order or sequence, nor should they be construed as indicating or implying relative importance. The term “and / or” as used herein refers to and includes any or all possible combinations of one or more associated listed items. When the above description relates to drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. In the description of this application, those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0133] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. An ultralong working distance microscope objective, characterized in that The objective lens comprises: a first lens group, a second lens group, a diaphragm and a third lens group arranged in sequence from the direction of light incidence; the first lens group has a positive focal length and comprises a first lens, a second lens, a third lens, a fourth lens, a fifth lens and a sixth lens arranged in sequence from the direction of light incidence; the first lens is a biconvex positive lens; the second lens is a meniscus negative lens, the convex surface of which faces the light incidence side and the concave surface of which faces the light emission side; the third lens is a meniscus positive lens, the convex surface of which faces the light incidence side and the concave surface of which faces the light emission side; the fourth lens is a biconvex positive lens; the fifth lens is a biconcave negative lens; the sixth lens is a meniscus positive lens, the convex surface of which faces the light incidence side and the concave surface of which faces the light emission side; the second lens group has a negative focal length and comprises a seventh lens and an eighth lens arranged in sequence from the direction of light incidence; the seventh lens is a meniscus positive lens, the convex surface of which faces the light incidence side and the concave surface of which faces the light emission side; the eighth lens is a meniscus negative lens, the convex surface of which faces the light incidence side and the concave surface of which faces the light emission side; the third lens group has a negative focal length and comprises a ninth lens, a tenth lens, an eleventh lens, a twelfth lens and a thirteenth lens arranged in sequence from the direction of light incidence; the ninth lens is a biconcave negative lens; the tenth lens is a biconvex positive lens; the eleventh lens is a biconcave negative lens; the twelfth lens is a biconvex positive lens; the thirteenth lens is a biconcave negative lens; wherein the second lens and the third lens constitute a first double cemented lens, the fourth lens and the fifth lens constitute a second double cemented lens, and the ninth lens, the tenth lens and the eleventh lens constitute a triple cemented lens; the working distance WD of the objective lens and the effective focal length f thereof satisfy the following condition: 12 < WD / f < 13; the focal lengths between the lens groups satisfy the following condition: -0.9 < f 10 / f 20 < -0.75, and 9 < f 20 / f 30 < 10; where f 10 is the focal length of the first lens group, f 20 is the focal length of the second lens group; f 30 is the focal length of the third lens group.

2. The objective according to claim 1, characterized in that: the working distance WD of the objective lens is 500 mm, the effective focal length f thereof is 40 mm, and the numerical aperture NA thereof is 0.

05.

3. The objective according to claim 2, characterized in that the focal lengths of the lenses are as follows: the focal length f1 of the first lens is 87.28 mm; the focal length f2 of the second lens is -79.44 mm; the focal length f3 of the third lens is 129.49 mm; the focal length f4 of the fourth lens is 70.78 mm; the focal length f5 of the fifth lens is -46.12 mm; the focal length f6 of the sixth lens is 55.96 mm; the focal length f7 of the seventh lens is 60.25 mm; the focal length f8 of the eighth lens is -28.99 mm; the focal length f9 of the ninth lens is -7.09 mm; the focal length f10 of the tenth lens is 6.66 mm; the focal length f11 of the eleventh lens is -6.80 mm; the focal length f12 of the twelfth lens is 12.11 mm; and the focal length f13 of the thirteenth lens is -13.08 mm.

4. The objective according to claim 3, characterized in that the dimensions of the lenses satisfy the following conditions: the first lens has a front surface with a curvature radius of -67.193 mm, a back surface with a curvature radius of 264.448 mm, and a front-back surface center distance of 8.47 mm; The second lens has a front surface radius of curvature of -64.786 mm, a rear surface radius of curvature of -30.592 mm, and a center distance of 1.78 mm between its front and rear surfaces. The third lens has a front surface radius of curvature of -30.592 mm, a rear surface radius of curvature of -61.436 mm, and a center distance of 7.29 mm between its front and rear surfaces. The fourth lens has a front surface radius of curvature of -37.345 mm, a rear surface radius of curvature of 170.233 mm, and a center distance between its front and rear surfaces of 9.67 mm. The fifth lens has a front surface radius of curvature of 170.233 mm, a rear surface radius of curvature of -47.639 mm, and a center distance of 1.88 mm between its front and rear surfaces. The sixth lens has a front surface radius of curvature of -28.087 mm, a rear surface radius of curvature of -206.876 mm, and a center distance of 8.46 mm between its front and rear surfaces. The seventh lens has a front surface radius of curvature of -26.624 mm, a rear surface radius of curvature of -45.441 mm, and a center distance of 5.59 mm between its front and rear surfaces. The eighth lens has a front surface radius of curvature of -258.827 mm, a rear surface radius of curvature of -21.031 mm, and a center distance of 1.54 mm between its front and rear surfaces. The ninth lens has a front surface radius of curvature of 31.463 mm, a rear surface radius of curvature of -6.017 mm, and a center distance of 2.22 mm between its front and rear surfaces. The tenth lens has a front surface radius of curvature of -6.017 mm, a rear surface radius of curvature of 8.341 mm, and a center distance of 4.01 mm between its front and rear surfaces. The eleventh lens has a front surface radius of curvature of 8.341 mm, a rear surface radius of curvature of -14.917 mm, and a center distance of 2.00 mm between its front and rear surfaces. The twelfth lens has a front surface radius of curvature of -10.897 mm, a rear surface radius of curvature of 69.949 mm, and a center distance of 2.67 mm between its front and rear surfaces. The thirteenth lens has a front surface radius of curvature of 11.574 mm, a rear surface radius of curvature of -73.154 mm, and a center distance of 1.50 mm between its front and rear surfaces. The two surfaces of the lens are defined as the front and rear surfaces according to the direction of light incidence.

5. The objective according to claim 4, characterized in that The positional relationships of the components satisfy the following conditions: The center distance between the rear surface of the first lens and the front surface of the second lens is 0.49 mm; The center distance between the rear surface of the third lens and the front surface of the fourth lens is 0.15 mm; The center distance between the rear surface of the fifth lens and the front surface of the sixth lens is 0.15 mm; The center distance between the rear surface of the sixth lens and the front surface of the seventh lens is 1.75 mm; The center distance between the rear surface of the seventh lens and the front surface of the eighth lens is 2.04 mm; The center distance between the aperture and the rear surface of the eighth lens is 5.41 mm; The center distance between the rear surface of the eighth lens and the front surface of the ninth lens is 29.50 mm; The center distance between the rear surface of the eleventh lens and the front surface of the twelfth lens is 0.84 mm; The center distance between the rear surface of the twelfth lens and the front surface of the thirteenth lens is 2.59 mm.

6. The objective according to claim 5, characterized in that The materials of the third and fourth lenses meet the following conditions: The refractive index Nd3 of the third lens ranges from Nd3∈(1.42,1.46), and its dispersion Vd3 ranges from Vd3∈(94,95). The refractive index Nd4 of the fourth lens ranges from Nd4∈(1.42,1.46), and its dispersion Vd4 ranges from Vd4∈(94,95).

7. The objective lens according to claim 6, characterized in that: The first lens has a refractive index Nd1 of 1.62 and a dispersion Vd1 of 53.

9. The refractive index Nd2 of the second lens is 1.74, and its dispersion Vd2 is 28.

3. The refractive index Nd3 of the third lens is 1.44, and its dispersion Vd3 is 94.

5. The fourth lens has a refractive index Nd4 of 1.44 and a dispersion Vd4 of 94.

5. The refractive index Nd5 of the fifth lens is 1.80, and its dispersion Vd5 is 42.

3. The refractive index Nd6 of the sixth lens is 1.57, and its dispersion Vd6 is 71.

3. The refractive index Nd7 of the seventh lens is 1.92, and its dispersion Vd7 is 20.

9. The refractive index Nd8 of the eighth lens is 1.79, and its dispersion Vd8 is 47.

5. The refractive index Nd9 of the ninth lens is 1.69, and its dispersion Vd9 is 54.

5. a refractive index Nd of the tenth lens 10 a value of 1.58, a dispersion Vd 10 a value of 40.9; a refractive index Nd of the eleventh lens 11 a value of 1.75, a dispersion Vd 11 a value of 52.3; a refractive index Nd of the twelfth lens 12 a value of 1.79, a dispersion Vd 12 a value of 44.2; a refractive index Nd of the thirteenth lens 13 a value of 1.75, and a dispersion Vd 13 a value of 52.3.

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