Microobjective with super-long working distance

Abstract

The invention relates to a microscope objective with an ultra-long working distance. The microscope objective comprises a first lens group, a second lens group, a diaphragm and a third lens group which are sequentially arranged in a light incidence direction, the first lens group has positive focal length and comprises a first lens, a second lens, a third lens, a fourth lens, a fifth lens and a sixth lens which are sequentially arranged along the incident direction of light; the second lens group has a negative focal length and comprises a seventh lens and an eighth lens which are sequentially arranged along the incident direction of the light; and 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 which are sequentially arranged along the light incident direction. The device has the advantage of ultra-long working distance, and can realize long-distance and large-multiplying-power monitoring.

Description

Technical Field

[0001] The present invention relates to the field of optical technology, and particularly to an ultra-long working distance microscopic objective lens. Background Art

[0002] In machine vision industrial inspection, there is a type of inspection where, due to the extremely harsh environment in which the object to be inspected is located, special lenses are often required. For example, in the monitoring of high-temperature boilers, heat-resistant lenses made of heat-resistant materials are generally needed; in some experiments, there are high-temperature and high-radiation environments, and the monitoring lenses need to be made heat-resistant and radiation-resistant. However, if the monitoring distance is increased and moved away from the harsh environment, the lens does not need to be specially treated and is durable, reducing the design difficulty and cost.

[0003] The working distance (WD) of a microscopic objective lens refers to the distance from the front lens surface of the objective lens to the surface of the object to be observed (or the top surface of the cover glass) when the microscope is correctly focused. This distance is an important parameter during the use of the microscope because it directly affects the flexibility and safety of operating the sample. The size of the working distance mainly depends on the numerical aperture (NA) and focal length of the objective lens. Generally speaking, for high-magnification objective lenses with a large numerical aperture, their working distance is shorter. For example, the working distance of a 10x objective lens may be 6.5 mm, while that of a 40x objective lens may be only 0.48 mm; currently, industrial lenses on the market are usually not designed with a large magnification, and microscopic objective lenses with a large magnification are not designed with a long working distance.

[0004] To solve the above situation, an ultra-long working distance microscopic objective lens (with a working distance of up to 500 mm) is proposed to achieve long-distance and large-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 microscopic objective lens.

[0006] An ultra-long working distance microscopic objective lens includes a first lens group, a second lens group, a diaphragm, and a third lens group arranged in sequence from the light incident direction; 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 in sequence along the light incident direction; the second lens group has a negative focal length and includes a seventh lens and an eighth lens arranged in sequence along the light incident direction; 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 in sequence along the light incident direction.

[0007] Compared with the prior art, the objective lens of the present invention has the advantage of an ultra-long working distance and can achieve long-distance and large-magnification monitoring.

[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 exit 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 exit 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 exit side; the seventh lens is a meniscus positive lens with its convex surface facing the light incident side and its concave surface facing the light exit 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 exit 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; the thirteenth lens is a biconcave negative lens; wherein, the second lens and the third lens form a first doublet lens, the fourth lens and the fifth lens form a second doublet lens, and the ninth lens, the tenth lens and the eleventh lens form a triplet lens.

[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 working distance WD of the objective lens is 500 mm, its effective focal length f is 40 mm, and its numerical aperture NA is 0.05.

[0011] In one embodiment, the focal lengths between each lens group satisfy the following conditions: -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.

[0012] In one embodiment, the focal length values of each lens are as follows:

[0013] The focal length f1 of the first lens takes a value of 87.28 mm;

[0014] The focal length f2 of the second lens takes a value of -79.44 mm;

[0015] The focal length f3 of the third lens takes a value of 129.49 mm;

[0016] The focal length f4 of the fourth lens takes a value of 70.78 mm;

[0017] The focal length f5 of the fifth lens takes a value of -46.12 mm;

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

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

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

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

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

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

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

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

[0026] In one embodiment, the sizes of the lenses satisfy the following conditions:

[0027] For the first lens, the radius of curvature of its front surface is -67.193 mm, the radius of curvature of its rear surface is 264.448 mm, and the distance between the centers of its front and rear surfaces is 8.47 mm.

[0028] For the second lens, the radius of curvature of its front surface is -64.786 mm, the radius of curvature of its rear surface is -30.592 mm, and the distance between the centers of its front and rear surfaces is 1.78 mm.

[0029] For the third lens, the radius of curvature of its front surface is -30.592 mm, the radius of curvature of its rear surface is -61.436 mm, and the distance between the centers of its front and rear surfaces is 7.29 mm.

[0030] For the fourth lens, the radius of curvature of its front surface is -37.345 mm, the radius of curvature of its rear surface is 170.233 mm, and the distance between the centers of its front and rear surfaces is 9.67 mm.

[0031] For the fifth lens, the radius of curvature of its front surface is 170.233 mm, the radius of curvature of its rear surface is -47.639 mm, and the distance between the centers of its front and rear surfaces is 1.88 mm.

[0032] For the sixth lens, the radius of curvature of its front surface is -28.087 mm, the radius of curvature of its rear surface is -206.876 mm, and the distance between the centers of its front and rear surfaces is 8.46 mm.

[0033] For the seventh lens, the radius of curvature of its front surface is -26.624 mm, the radius of curvature of its rear surface is -45.441 mm, and the distance between the centers of its front and rear surfaces is 5.59 mm.

[0034] For the eighth lens, the radius of curvature of its front surface is -258.827 mm, the radius of curvature of its rear surface is -21.031 mm, and the distance between the centers of its front and rear surfaces is 1.54 mm.

[0035] For the ninth lens, the radius of curvature of its front surface is 31.463 mm, the radius of curvature of its rear surface is -6.017 mm, and the distance between the centers of its front and rear surfaces is 2.22 mm.

[0036] For the tenth lens, the radius of curvature of its front surface is -6.017 mm, the radius of curvature of its rear surface is 8.341 mm, and the distance between the centers of its front and rear surfaces is 4.01 mm.

[0037] For the eleventh lens, the radius of curvature of its front surface is 8.341 mm, the radius of curvature of its rear surface is -14.917 mm, and the distance between the centers of its front and rear surfaces is 2.00 mm.

[0038] For the twelfth lens, the radius of curvature of its front surface is -10.897 mm, the radius of curvature of its rear surface is 69.949 mm, and the distance between the centers of its front and rear surfaces is 2.67 mm.

[0039] For the thirteenth lens, the radius of curvature of its front surface is 11.574 mm, the radius of curvature of its rear surface is -73.154 mm, and the distance between the centers of its front and rear surfaces is 1.50 mm;

[0040] Wherein, the two side surfaces of the lens are defined as the front and rear surfaces according to the light incident direction.

[0041] In an embodiment, the positional relationship of each component satisfies the following conditions:

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

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

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

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

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

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

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

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

[0050] The central 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 has a value range of Nd3 ∈ (1.42, 1.46), and its dispersion Vd3 has a value range of Vd3 ∈ (94, 95);

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

[0054] In one embodiment, the refractive index Nd1 of the first lens has a value of 1.62, and its dispersion Vd1 has a value of 53.9;

[0055] The refractive index Nd2 of the second lens has a value of 1.74, and its dispersion Vd2 has a value of 28.3;

[0056] The refractive index Nd3 of the third lens has a value of 1.44, and its dispersion Vd3 has a value of 94.5;

[0057] The refractive index Nd4 of the fourth lens has a value of 1.44, and its dispersion Vd4 has a value of 94.5;

[0058] The refractive index Nd5 of the fifth lens has a value of 1.80, and its dispersion Vd5 has a value of 42.3;

[0059] The refractive index Nd6 of the sixth lens has a value of 1.57, and its dispersion Vd6 has a value of 71.3;

[0060] The refractive index Nd7 of the seventh lens has a value of 1.92, and its dispersion Vd7 has a value of 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 is 1.58, and its dispersion Vd 10 is 40.9;

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

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

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

[0067] For better understanding and implementation, the present invention will be described in detail below with reference to the accompanying drawings. Brief Description of the Drawings

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

[0069] Figure 2 is the structural schematic diagram of each lens of the objective lens provided by the present invention;

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

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

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

[0073] Figure 6 is the MTF curve graph of the objective lens provided by the present invention;

[0074] Figure 7 is the optical distortion graph of the objective lens provided by the present invention. Detailed Embodiments

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

[0076] As Figures 1 to 2 shown, a super-long working distance microscopic objective lens of the present invention includes a first lens group 10, a second lens group 20, a diaphragm 40, and a third lens group 30 arranged in sequence from the light incident direction. Among them, 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 in sequence 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 in sequence 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 in sequence along the light incident direction.

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

[0078] In the present application, the focal length f 10 of the first lens group 10 and the focal length f 20 of the second lens group 20 satisfy the following condition: -0.9 < f 10 / f 20 < -0.75.

[0079] In the present application, the focal length f 20 of the second lens group 20 and the focal length f 30 of the third lens group 30 satisfy the following condition: 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 light incident side and its concave surface facing the light exit side; the third lens 13 is a meniscus positive lens with its convex surface facing the light incident side and its concave surface facing the light exit 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 light incident side and its concave surface facing the light exit side; among them, the second lens 12 and the third lens 13 form a first doublet lens, and the fourth lens 14 and the fifth lens 15 form a second doublet lens.

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

[0082] In this application, the focal length f of the second doublet lens 14+15 and the effective focal length f of the objective lens satisfy 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 has a value range of Nd3 ∈ (1.42, 1.46), and its dispersion Vd3 has a value 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 has a value range of Nd4 ∈ (1.42, 1.46), and its dispersion Vd4 has a value 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 exit 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 exit 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. Among them, the ninth lens 31, the tenth lens 32, and the eleventh lens 33 form a triplet 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 at the same time is used 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 large magnification; among them, the first doublet lens and the second doublet lens are used to correct chromatic aberration.

[0088] Specifically, the materials of the lenses satisfy the following conditions:

[0089]

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

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

[0092] Preferably, the refractive index Nd3 of the third lens 13 has a value of 1.44, and its dispersion Vd3 has a value of 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 10 is 1.58, and its dispersion Vd 10 is 40.9.

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

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

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

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

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

[0105]

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

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

[0108] Specifically, for the third lens 13, the radius of curvature of its front surface S13A is -30.592 mm, the radius of curvature of its rear surface S13B is -61.436 mm, and the distance between the centers of its front and rear surfaces is 7.29 mm.

[0109] Specifically, for the fourth lens 14, the radius of curvature of its front surface S14A is -37.345 mm, the radius of curvature of its rear surface S14B is 170.233 mm, and the distance between the centers of its front and rear surfaces is 9.67 mm.

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

[0111] Specifically, for the sixth lens 16, the radius of curvature of its front surface S16A is -28.087 mm, the radius of curvature of its rear surface S16B is -206.876 mm, and the distance between the centers of its front and rear surfaces is 8.46 mm.

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

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

[0114] Specifically, for the ninth lens 31, the radius of curvature of its front surface S31A is 31.463 mm, the radius of curvature of its rear surface S31B is -6.017 mm, and the distance between the centers of its front and rear surfaces is 2.22 mm.

[0115] Specifically, for the tenth lens 32, the radius of curvature of its front surface S32A is -6.017 mm, the radius of curvature of its rear surface S32B is 8.341 mm, and the distance between the centers of its front and rear surfaces is 4.01 mm.

[0116] Specifically, for the eleventh lens 33, the radius of curvature of its front surface S33A is 8.341 mm, the radius of curvature of its rear surface S33B is -14.917 mm, and the distance between the centers of its front and rear surfaces is 2.00 mm.

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

[0118] Specifically, for the thirteenth lens 35, the radius of curvature of its front surface S35A is 11.574 mm, the radius of curvature of its rear surface S35B is -73.154 mm, and the distance between the centers of its front and rear surfaces is 1.50 mm.

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

[0120]

[0121]

[0122] Among them, the distance between the diaphragm 40 and the center of the rear surface S22B of the eighth lens is 5.41 mm.

[0123] In this application, according to the parameter design requirements, an ultra-long working distance microscopic objective lens is designed, and the technical indicators achieved by this objective lens are as follows:

[0124]

[0125] Specifically, the focal lengths of each lens satisfy the following conditions:

[0126]

[0127]

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

[0129] Figure 6It is the MTF graph (Modulation Transfer Function curve graph) of the objective lens under visible light with a wavelength of 435 nm to 656 nm.

[0130] Figure 7 It is the optical distortion graph of the objective lens under visible light with a wavelength of 435 nm to 656 nm. It can be obtained that the F-tanθ optical distortion of this ultra-long working distance microscope objective lens is relatively small, basically maintaining at 0.3%.

[0131] Compared with the prior art, an ultra-long working distance microscope objective lens provided by the present invention has the advantage of an ultra-long working distance and can achieve long-distance and large-magnification monitoring.

[0132] The terms used in the embodiments of this application are only for the purpose of describing specific embodiments and are not intended to limit the embodiments of this application. The singular forms "a", "the" and "said" used in the embodiments of this application and the claims 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 only used for distinction and not for describing a specific order or sequence, nor can they be understood as indicating or implying relative importance. The term "and / or" used herein means and includes any or all possible combinations of one or more of the associated listed items. When the above description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. In the description of this application, 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.

[0133] The above-described embodiments only represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. An ultra-long working distance microscope objective lens, characterized in that, Comprising: A first lens group, a second lens group, a diaphragm, and a third lens group arranged in sequence from the light incident direction; 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 in sequence along the light incident direction; The second lens group has a negative focal length and includes a seventh lens and an eighth lens arranged in sequence along the light incident direction; 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 in sequence along the light incident direction.

2. The objective lens according to claim 1, characterized in that: 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 exit 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 exit 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 exit side; The seventh lens is a meniscus positive lens, with its convex surface facing the light incident side and its concave surface facing the light exit 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 exit 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; the thirteenth lens is a biconcave negative lens; Wherein, the second lens and the third lens form a first doublet lens, the fourth lens and the fifth lens form a second doublet lens, and the ninth lens, the tenth lens, and the eleventh lens form a triplet lens.

3. The objective lens according to claim 2, characterized in that: The working distance WD of the objective lens and its effective focal length f satisfy the following condition: 12 < WD / f < 13.

4. The objective lens according to claim 3, characterized in that: The working distance WD of the objective lens is 500 mm, its effective focal length f is 40 mm, and its numerical aperture NA is 0.

05.

5. The objective lens according to claim 4, characterized in that, The focal lengths between each lens group satisfy the following conditions: -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.

6. The objective lens according to claim 5, characterized in that, The focal length values of each lens are: The focal length f1 of the first lens takes a value of 87.28 mm; the focal length f2 of the second lens takes a value of -79.44 mm; the focal length f3 of the third lens takes a value of 129.49 mm; the focal length f4 of the fourth lens takes a value of 70.78 mm; the focal length f5 of the fifth lens takes a value of -46.12 mm; the focal length f6 of the sixth lens takes a value of 55.96 mm; the focal length f7 of the seventh lens takes a value of 60.25 mm; the focal length f8 of the eighth lens takes a value of -28.99 mm; the focal length f9 of the ninth lens takes a value of -7.09 mm; the focal length f10 of the tenth lens takes a value of 6.66 mm; the focal length f11 of the eleventh lens takes a value of -6.80 mm; the focal length f12 of the twelfth lens takes a value of 12.11 mm; the focal length f13 of the thirteenth lens takes a value of -13.08 mm.

7. The objective lens according to claim 6, characterized in that, The dimensions of each lens satisfy the following conditions: For the first lens, the radius of curvature of its front surface is -67.193 mm, the radius of curvature of its rear surface is 264.448 mm, and the central distance between its front and rear surfaces is 8.47 mm. For the second lens, the radius of curvature of its front surface is -64.786 mm, the radius of curvature of its rear surface is -30.592 mm, and the central distance between its front and rear surfaces is 1.78 mm. For the third lens, the radius of curvature of its front surface is -30.592 mm, the radius of curvature of its rear surface is -61.436 mm, and the central distance between its front and rear surfaces is 7.29 mm. For the fourth lens, the radius of curvature of its front surface is -37.345 mm, the radius of curvature of its rear surface is 170.233 mm, and the central distance between its front and rear surfaces is 9.67 mm. For the fifth lens, the radius of curvature of its front surface is 170.233 mm, the radius of curvature of its rear surface is -47.639 mm, and the central distance between its front and rear surfaces is 1.88 mm. For the sixth lens, the radius of curvature of its front surface is -28.087 mm, the radius of curvature of its rear surface is -206.876 mm, and the central distance between its front and rear surfaces is 8.46 mm. For the seventh lens, the radius of curvature of its front surface is -26.624 mm, the radius of curvature of its rear surface is -45.441 mm, and the central distance between its front and rear surfaces is 5.59 mm. For the eighth lens, the radius of curvature of its front surface is -258.827 mm, the radius of curvature of its rear surface is -21.031 mm, and the central distance between its front and rear surfaces is 1.54 mm. For the ninth lens, the radius of curvature of its front surface is 31.463 mm, the radius of curvature of its rear surface is -6.017 mm, and the central distance between its front and rear surfaces is 2.22 mm. For the tenth lens, the radius of curvature of its front surface is -6.017 mm, the radius of curvature of its rear surface is 8.341 mm, and the central distance between its front and rear surfaces is 4.01 mm. For the eleventh lens, the radius of curvature of its front surface is 8.341 mm, the radius of curvature of its rear surface is -14.917 mm, and the central distance between its front and rear surfaces is 2.00 mm. For the twelfth lens, the radius of curvature of its front surface is -10.897 mm, the radius of curvature of its rear surface is 69.949 mm, and the central distance between its front and rear surfaces is 2.67 mm. For the thirteenth lens, the radius of curvature of its front surface is 11.574 mm, the radius of curvature of its rear surface is -73.154 mm, and the central distance between its front and rear surfaces is 1.50 mm; Among them, the two side surfaces of the lens are defined as the front and rear surfaces according to the light incident direction.

8. The objective lens according to claim 7, characterized in that, The positional relationship of each component satisfies the following conditions: The central distance between the rear surface of the first lens and the front surface of the second lens is 0.49 mm; The central distance between the rear surface of the third lens and the front surface of the fourth lens is 0.15 mm; The central distance between the rear surface of the fifth lens and the front surface of the sixth lens is 0.15 mm; The central distance between the rear surface of the sixth lens and the front surface of the seventh lens is 1.75 mm; The central distance between the rear surface of the seventh lens and the front surface of the eighth lens is 2.04 mm; The central distance between the diaphragm and the rear surface of the eighth lens is 5.41 mm; The central distance between the rear surface of the eighth lens and the front surface of the ninth lens is 29.50 mm; The central distance between the rear surface of the eleventh lens and the front surface of the twelfth lens is 0.84 mm; The central distance between the rear surface of the twelfth lens and the front surface of the thirteenth lens is 2.59 mm.

9. The objective lens according to claim 8, characterized in that, The materials of the third lens and the fourth lens satisfy the following conditions: The refractive index Nd3 of the third lens has a value range of Nd3 ∈ (1.42, 1.46), and its dispersion Vd3 has a value range of Vd3 ∈ (94, 95); The refractive index Nd4 of the fourth lens has a value range of Nd4 ∈ (1.42, 1.46), and its dispersion Vd4 has a value range of Vd4 ∈ (94, 95).

10. The objective lens according to claim 9, wherein: The refractive index Nd1 of the first lens has a value of 1.62, and its dispersion Vd1 has a value of 53.9; The refractive index Nd2 of the second lens has a value of 1.74, and its dispersion Vd2 has a value of 28.3; The refractive index Nd3 of the third lens has a value of 1.44, and its dispersion Vd3 has a value of 94.5; The refractive index Nd4 of the fourth lens has a value of 1.44, and its dispersion Vd4 has a value of 94.5; The refractive index Nd5 of the fifth lens has a value of 1.80, and its dispersion Vd5 has a value of 42.3; The refractive index Nd6 of the sixth lens has a value of 1.57, and its dispersion Vd6 has a value of 71.3; The refractive index Nd7 of the seventh lens has a value of 1.92, and its dispersion Vd7 has a value of 20.9; The refractive index Nd8 of the eighth lens has a value of 1.79, and its dispersion Vd8 has a value of 47.5; The refractive index Nd9 of the ninth lens has a value of 1.69, and its dispersion Vd9 has a value of 54.5; The refractive index Nd of the tenth lens 10 is 1.58, and its dispersion Vd 10 is 40.9; The refractive index Nd of the eleventh lens 11 is 1.75, and its dispersion Vd 11 is 52.3; The refractive index Nd of the twelfth lens 12 is 1.79, and its dispersion Vd 12 is 44.2; The refractive index Nd of the thirteenth lens 13 is 1.75, and its dispersion Vd 13 is 52.3.

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