Symmetrical microobjective with low magnification, ultra-large field of view and high resolution

Abstract

The invention discloses a low-magnification ultra-large-field-of-view high-resolution symmetric microscope objective. The microscope objective comprises a front lens group, a diaphragm and a rear lens group which are sequentially arranged from an object side to an image side, the front lens group comprises a first lens to a fifteenth lens which are sequentially arranged, and a second lens, a third lens, a fifth lens, a sixth lens, a seventh lens, an eighth lens, an eleventh lens, a twelfth lens, a thirteenth lens and the fifteenth lens have positive focal power; the rear lens group comprises a sixteenth lens to a thirtieth lens, and all the lenses in the front lens group and the rear lens group are symmetrical about the diaphragm. By defining low magnification and setting a reasonable numerical aperture, the optical system has the characteristics of symmetrical structure, low distortion, ultra-large field of view and high resolution, and solves the core problems of low resolution of a low-magnification objective lens, small field of view of a high-magnification microscope objective lens and high lens processing difficulty; and an image sensor with large target surface size and high resolution can be directly connected for photoelectric conversion imaging.

Description

Technical Field

[0001] The present invention relates to the technical field of microscopic objectives, and more particularly to a symmetric microscopic objective with low magnification, ultra-large field of view and high resolution. Background Art

[0002] With the continuous development of scientific research and industrial production detection technologies, the demand for high-precision optical imaging systems is increasing day by day. Such systems are commonly used in devices such as microscopes and spectrometers, enabling the observation and analysis of microscopic structures and physical phenomena. In industrial production detection, microscopic objectives are used for quality control, defect detection, and precision measurement to ensure the quality and consistency of products. In these fields, microscopic objectives not only need to have high resolution but also must be able to provide an imaging effect with low distortion to ensure the accuracy and reliability of images. In addition, the characteristic of low magnification is also crucial for achieving imaging with a large field of view, which helps to improve detection efficiency and coverage. However, existing low-magnification microscopic objectives have many deficiencies in terms of numerical aperture, distortion control, field-of-view size, and resolution, making it difficult to meet the requirements of high-precision applications.

[0003] For example, the Chinese patent document with the publication number CN116430567A discloses a microscopic objective applicable to devices such as microscopes. The microscopic objective sequentially includes, from the exit pupil to the object side: a first lens with positive refractive power, a second lens with negative refractive power, a third lens with positive refractive power, a fourth lens with negative refractive power, and a fifth lens with positive refractive power. The focal length of the microscopic objective is f, the focal length of the first lens is f1, the focal length of the second lens is f2, the focal length of the third lens is f3, the axial distance from the object plane of the microscopic objective to the object side surface of the fifth lens is WD, the numerical aperture is NA, and the total optical length is TTL, and the following are satisfied: 0.68 ≤ f3 / f ≤ 2.00; -2.20 ≤ f2 / f1 ≤ -1.40; 0.15 ≤ WD / TTL ≤ 0.35; 6.00 ≤ f*NA ≤ 9.00. This microscopic objective has the characteristics of 1.5 times magnification and long working distance.

[0004] Although this microscopic objective can achieve a certain resolution, it is often accompanied by relatively large distortion, resulting in image distortion and being unable to accurately reflect the shape and size of the actual object. According to the Rayleigh criterion, the resolution of the objective is closely related to its numerical aperture (NA). To obtain higher resolution, the objective needs to have a larger numerical aperture. However, the increase in numerical aperture will lead to an increase in optical aberrations, which will seriously affect the imaging quality. Currently, the numerical aperture of low-magnification (1X) objectives is usually only 0.03, with low resolution, and the field of view of microscopic objectives with large numerical apertures is relatively small.

[0005] For another example, a Chinese patent document with the publication number CN118377125A discloses a microscope objective lens, which is composed of a first lens with positive refractive power, a second lens with negative refractive power, a third lens with negative refractive power, a fourth lens with negative refractive power, a fifth lens with positive refractive power, a sixth lens with positive refractive power, a seventh lens with negative refractive power, an eighth lens with positive or negative refractive power, a ninth lens with positive refractive power, a tenth lens with positive refractive power, an eleventh lens with negative refractive power, a twelfth lens with positive refractive power, a thirteenth lens with negative refractive power, and a fourteenth lens with positive refractive power, which are arranged in sequence from the exit side to the object side. This microscope objective lens has a large numerical aperture and meets the design requirements of a 10-fold magnification and a long working distance.

[0006] For yet another example, a Chinese patent document with the publication number CN119355939A discloses a planachromat objective lens, which includes a first lens group, a second lens group, and a third lens group arranged in sequence from the object plane to the image plane. The first lens group and the second lens group both have positive refractive power, and the third lens group has positive refractive power or negative refractive power. The first lens group includes at least two sub-lens groups with positive refractive power, and the sub-lens group is a single lens or a cemented lens composed of at least two single lenses cemented together. The second lens group includes at least one cemented lens with positive refractive power and at least one cemented lens with positive refractive power or negative refractive power. The third lens group includes at least one cemented lens with positive refractive power and at least one cemented lens with positive refractive power or negative refractive power. This microscope objective lens has a large numerical aperture and meets the design requirements of a 20-fold magnification, a long working distance, and a large field of view.

[0007] However, although the above-mentioned high numerical magnification microscope objective lenses meet the requirements of high numerical aperture and high resolution, the field of view is still too small, and the lens processing is difficult.

[0008] The reason for the too small field of view is that when designing the objective lens, it is necessary to control the optical aberration while increasing the numerical aperture to enhance the resolution, which often results in the limitation of the field of view of the objective lens. The disadvantage of a small field of view is particularly obvious in practical applications. For example, when observing a biological tissue section or a microelectronic chip with a large size, it is necessary to frequently move the sample or perform a mosaic operation, which is not only time-consuming and laborious, but also may affect the overall observation effect due to the imaging differences between the fields of view.

[0009] The reason for the difficult lens processing is that: ① In order to achieve a high numerical aperture and high resolution, the lenses of the objective lens usually bear a large optical power, so the radius of curvature is relatively small, and the processing is complex and difficult; ② The material selection and processing of the lenses are also relatively complex, and factors such as the optical properties, mechanical properties, and processing properties of the materials need to be considered, which further increases the processing difficulty.

[0010] Therefore, there is an urgent need for a microscope objective lens that can have a large numerical aperture at a low magnification, achieve low distortion, an ultra-large field of view, high resolution, and low processing difficulty. Summary of the Invention

[0011] Aiming at the deficiencies of the existing technology, the present invention provides a low-magnification ultra-large-field-of-view high-resolution symmetric microscope objective lens, which has a large numerical aperture at a low magnification and can simultaneously achieve low distortion, an ultra-large field of view, and high resolution; it can obtain high-resolution images to a great extent while avoiding multiple splicings of images, and greatly improves the detection efficiency; furthermore, it can be directly connected to an image sensor with a large target surface size and high resolution for optoelectronic conversion imaging, saving the tube lens necessary for an infinity objective lens; and all lenses have appropriate curvature radius sizes, with low processing difficulty.

[0012] To achieve the above object, the present invention mainly provides the following technical solutions:

[0013] A low-magnification ultra-large-field-of-view high-resolution symmetric microscope objective lens, characterized in that it includes a front lens group, a diaphragm, and a rear lens group arranged in sequence from the object side to the image side; the lenses in the front lens group and the rear lens group are symmetric about the diaphragm;

[0014] The front lens group includes the first lens to the fifteenth lens arranged in sequence. Among them, the second lens, the third lens, the fifth lens, the sixth lens, the seventh lens, the eighth lens, the eleventh lens, the twelfth lens, the thirteenth lens, and the fifteenth lens have positive optical power; the first lens, the fourth lens, the ninth lens, the tenth lens, and the fourteenth lens have negative optical power;

[0015] The rear lens group includes the sixteenth lens to the thirtieth lens arranged in sequence. Among them, the sixteenth lens, the eighteenth lens, the nineteenth lens, the twentieth lens, the twenty-third lens, the twenty-fourth lens, the twenty-fifth lens, the twenty-sixth lens, the twenty-eighth lens, and the twenty-ninth lens have positive optical power; the seventeenth lens, the twenty-first lens, the twenty-second lens, the twenty-seventh lens, and the thirtieth lens have negative optical power.

[0016] In the present invention, the ultra-large field of view refers to The resolution corresponds to the numerical aperture. The larger the numerical aperture, the higher the resolution. The low magnification refers to 1×.

[0017] The present invention first realizes the combination of low magnification, large numerical aperture NA, and low distortion in a microscope objective lens, while maintaining an ultra-large field of view Far exceeding the performance of existing low-magnification objective lenses; compared with high-magnification objective lenses, the objective lens of the present invention not only has significant advantages in the field of view size, but also greatly reduces the processing difficulty, achieving multiple performance breakthroughs in the field of microscopic objective lenses, such as NA = 0.3, low distortion, and large field of view, with an optical distortion of almost 0%. Through complex symmetric optical design, the present invention has significant creativity and application potential.

[0018] Preferably, the wavelength range value of the microscopic objective lens is 435nm ≤ λ ≤ 656nm.

[0019] Preferably, the effective field of view on the object side of the microscopic objective lens is The numerical aperture on the object side is 0.3; the effective field of view on the image side of the microscopic objective lens is The numerical aperture on the image side is 0.3.

[0020] Preferably, the first lens to the thirtieth lens are all glass spherical lenses.

[0021] Preferably, in the front lens group, the third lens and the fourth lens are cemented together, the eighth lens and the ninth lens are cemented together, and the thirteenth lens, the fourteenth lens, and the fifteenth lens are cemented together;

[0022] In the rear lens group, the sixteenth lens, the seventeenth lens, and the eighteenth lens are cemented together, the twenty-second lens and the twenty-third lens are cemented together, and the twenty-seventh lens and the twenty-eighth lens are cemented together.

[0023] Preferably, in the front lens group, the object side and the image side structures of each lens are as follows:

[0024] The object side of the first lens is concave, and the image side is concave;

[0025] The object side of the second lens is concave, and the image side is convex;

[0026] The object side of the third lens is concave, and the image side is convex;

[0027] The object side of the fourth lens is concave, and the image side is convex;

[0028] The object side of the fifth lens is concave, and the image side is convex;

[0029] The object side of the sixth lens is flat, and the image side is convex;

[0030] The object side of the seventh lens is convex, and the image side is convex;

[0031] The object side of the eighth lens is convex, and the image side is convex;

[0032] The object side of the ninth lens is concave, and the image side is concave;

[0033] The object surface side of the tenth lens is concave, and the image surface side is flat;

[0034] The object surface side of the eleventh lens is concave, and the image surface side is convex;

[0035] The object surface side of the twelfth lens is convex, and the image surface side is convex;

[0036] The object surface side of the thirteenth lens is convex, and the image surface side is convex;

[0037] The object surface side of the fourteenth lens is concave, and the image surface side is concave;

[0038] The object surface side of the fifteenth lens is convex, and the image surface side is convex.

[0039] Preferably, in the rear lens group, the object surface side and the image surface side structures of each lens are as follows:

[0040] The object surface side of the sixteenth lens is convex, and the image surface side is convex;

[0041] The object surface side of the seventeenth lens is concave, and the image surface side is concave;

[0042] The object surface side of the eighteenth lens is convex, and the image surface side is convex;

[0043] The object surface side of the nineteenth lens is convex, and the image surface side is convex;

[0044] The object surface side of the twentieth lens is convex, and the image surface side is concave;

[0045] The object surface side of the twenty-first lens is flat, and the image surface side is concave;

[0046] The object surface side of the twenty-second lens is concave, and the image surface side is concave;

[0047] The object surface side of the twenty-third lens is convex, and the image surface side is convex;

[0048] The object surface side of the twenty-fourth lens is convex, and the image surface side is convex;

[0049] The object surface side of the twenty-fifth lens is convex, and the image surface side is flat;

[0050] The object surface side of the twenty-sixth lens is convex, and the image surface side is concave;

[0051] The object surface side of the twenty-seventh lens is convex, and the image surface side is concave;

[0052] The object surface side of the twenty-eighth lens is convex, and the image surface side is concave;

[0053] The object side of the twenty-ninth lens is convex, and the image side is concave;

[0054] The object side of the thirtieth lens is concave, and the image side is concave.

[0055] Preferably, in the front lens group, the parameters of each lens are required as follows:

[0056] The refractive index Nd1, dispersion coefficient Vd1 and focal length f1 of the first lens satisfy the following conditions: 1.8 < Nd1 < 1.9, 35 < Vd1 < 40, -60 mm < f1 < -45 mm;

[0057] The refractive index Nd2, dispersion coefficient Vd2 and focal length f2 of the second lens satisfy the following conditions: 1.9 < Nd2 < 2.0, 15 < Vd2 < 20, 150 mm < f2 < 170 mm;

[0058] The refractive index Nd3, dispersion coefficient Vd3 and focal length f3 of the third lens satisfy the following conditions: 1.7 < Nd3 < 1.8, 20 < Vd3 < 30, 100 mm < f3 < 130 mm;

[0059] The refractive index Nd4, dispersion coefficient Vd4 and focal length f4 of the fourth lens satisfy the following conditions: 1.8 < Nd4 < 1.9, 35 < Vd4 < 40, -85 mm < f4 < -65 mm;

[0060] The refractive index Nd5, dispersion coefficient Vd5 and focal length f5 of the fifth lens satisfy the following conditions: 1.9 < Nd5 < 2.0, 20 < Vd5 < 30, 185 mm < f5 < 200 mm;

[0061] The refractive index Nd6, dispersion coefficient Vd6 and focal length f6 of the sixth lens satisfy the following conditions: 1.4 < Nd6 < 1.5, 80 < Vd6 < 90, 95 mm < f6 < 120 mm;

[0062] The refractive index Nd7, dispersion coefficient Vd7 and focal length f7 of the seventh lens satisfy the following conditions: 1.5 < Nd7 < 1.6, 50 < Vd7 < 60, 90 mm < f7 < 110 mm;

[0063] The refractive index Nd8, dispersion coefficient Vd8 and focal length f8 of the eighth lens satisfy the following conditions: 1.5 < Nd8 < 1.6, 50 < Vd8 < 60, 60 mm < f8 < 80 mm;

[0064] The refractive index Nd9, dispersion coefficient Vd9 and focal length f9 of the ninth lens satisfy the following conditions: 1.8 < Nd9 < 1.9, 30 < Vd9 < 40, -40 mm < f9 < -20 mm;

[0065] The refractive index Nd10, dispersion coefficient Vd10, and focal length f10 of the tenth lens satisfy the following conditions: 1.8 < Nd10 < 1.9, 30 < Vd10 < 40, -50 mm < f10 < -35 mm;

[0066] The refractive index Nd11, dispersion coefficient Vd11, and focal length f11 of the eleventh lens satisfy the following conditions: 1.9 < Nd11 < 2.0, 20 < Vd11 < 25, 70 mm < f11 < 80 mm;

[0067] The refractive index Nd12, dispersion coefficient Vd12, and focal length f12 of the twelfth lens satisfy the following conditions: 1.5 < Nd12 < 1.6, 80 < Vd12 < 90, 100 mm < f12 < 120 mm;

[0068] The refractive index Nd13, dispersion coefficient Vd13, and focal length f13 of the thirteenth lens satisfy the following conditions: 1.5 < Nd13 < 1.6, 70 < Vd13 < 80, 140 mm < f13 < 160 mm;

[0069] The refractive index Nd14, dispersion coefficient Vd14, and focal length f14 of the fourteenth lens satisfy the following conditions: 1.9 < Nd14 < 2.0, 20 < Vd14 < 30, -95 mm < f14 < -80 mm;

[0070] The refractive index Nd15, dispersion coefficient Vd15, and focal length f15 of the fifteenth lens satisfy the following conditions: 1.5 < Nd15 < 1.6, 60 < Vd15 < 70, 280 mm < f15 < 305 mm.

[0071] Preferably, in the rear lens group, the parameter requirements of each lens are as follows:

[0072] The refractive index Nd16, dispersion coefficient Vd16, and focal length f16 of the sixteenth lens satisfy the following conditions: 1.5 < Nd16 < 1.6, 60 < Vd16 < 70, 280 mm < f16 < 305 mm;

[0073] The refractive index Nd17, dispersion coefficient Vd17, and focal length f17 of the seventeenth lens satisfy the following conditions: 1.9 < Nd17 < 2.0, 20 < Vd17 < 30, -95 mm < f17 < -80 mm;

[0074] The refractive index Nd18, dispersion coefficient Vd18, and focal length f18 of the eighteenth lens satisfy the following conditions: 1.5 < Nd18 < 1.6, 70 < Vd18 < 80, 140 mm < f18 < 160 mm;

[0075] The refractive index Nd19, dispersion coefficient Vd19, and focal length f19 of the nineteenth lens satisfy the following conditions: 1.5 < Nd19 < 1.6, 80 < Vd19 < 90, 100 mm < f19 < 120 mm;

[0076] The refractive index Nd20, dispersion coefficient Vd20, and focal length f20 of the twentieth lens satisfy the following conditions: 1.9 < Nd20 < 2.0, 20 < Vd20 < 25, 70 mm < f20 < 80 mm;

[0077] The refractive index Nd21, dispersion coefficient Vd21, and focal length f21 of the twenty - first lens satisfy the following conditions: 1.8 < Nd21 < 1.9, 30 < Vd21 < 40, - 50 mm < f21 < - 35 mm;

[0078] The refractive index Nd22, dispersion coefficient Vd22, and focal length f22 of the twenty - second lens satisfy the following conditions: 1.8 < Nd22 < 1.9, 30 < Vd22 < 40, - 40 mm < f22 < - 20 mm;

[0079] The refractive index Nd23, dispersion coefficient Vd23, and focal length f23 of the twenty - third lens satisfy the following conditions: 1.5 < Nd23 < 1.6, 50 < Vd23 < 60, 60 mm < f23 < 80 mm;

[0080] The refractive index Nd24, dispersion coefficient Vd24, and focal length f24 of the twenty - fourth lens satisfy the following conditions: 1.5 < Nd24 < 1.6, 50 < Vd24 < 60, 90 mm < f24 < 110 mm;

[0081] The refractive index Nd25, dispersion coefficient Vd25, and focal length f25 of the twenty - fifth lens satisfy the following conditions: 1.4 < Nd25 < 1.5, 80 < Vd25 < 90, 95 mm < f25 < 120 mm;

[0082] The refractive index Nd26, dispersion coefficient Vd26, and focal length f26 of the twenty - sixth lens satisfy the following conditions: 1.9 < Nd26 < 2.0, 20 < Vd26 < 30, 185 mm < f26 < 200 mm;

[0083] The refractive index Nd27, dispersion coefficient Vd27, and focal length f27 of the twenty - seventh lens satisfy the following conditions: 1.8 < Nd27 < 1.9, 35 < Vd27 < 40, - 85 mm < f27 < - 65 mm;

[0084] The refractive index Nd28, dispersion coefficient Vd28, and focal length f28 of the twenty-eighth lens satisfy the following conditions: 1.7 < Nd28 < 1.8, 20 < Vd28 < 30, 100 mm < f28 < 130 mm;

[0085] The refractive index Nd29, dispersion coefficient Vd29, and focal length f29 of the twenty-ninth lens satisfy the following conditions: 1.9 < Nd29 < 2.0, 15 < Vd29 < 20, 150 mm < f29 < 170 mm;

[0086] The refractive index Nd30, dispersion coefficient Vd30, and focal length f30 of the thirtieth lens satisfy the following conditions: 1.8 < Nd30 < 1.9, 30 < Vd30 < 40, -60 mm < f30 < -45 mm.

[0087] Compared with the prior art, the present invention has the following beneficial effects:

[0088] The low-magnification, ultra-large field of view, high-resolution, symmetric microscope objective lens realized by the present invention has a numerical aperture of 0.3, which is significantly higher than 0.03 of existing commercial low-power objective lenses. It can achieve higher resolution, making the details of small patterns clearer. In scientific research and industrial production inspection, it can observe and detect microstructures and defects more accurately. At the same time, low distortion can be achieved, ensuring that the imaged pattern is highly consistent with the actual object, avoiding pattern distortion, and improving the accuracy and reliability of the image. Moreover, the characteristic of low magnification realizes ultra-large field of view imaging, avoiding the time-consuming and laborious process of multiple imaging and stitching and the possible imaging differences, greatly improving the detection efficiency and coverage. Furthermore, it can be directly connected to an image sensor with a large target surface size and high resolution for photoelectric conversion imaging, eliminating the need for a tube lens required for an infinity objective lens. And all lenses have appropriate curvature radius sizes, and the lens processing difficulty is much lower than that of high-power objective lenses. Based on the above characteristics, the present invention has a very large application prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0089] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0090] Figure 1 It is a schematic optical path diagram of the microscope objective lens provided by the embodiment of the present invention.

[0091] Figure 2 It is an MTF curve diagram of the microscope objective lens provided by Embodiment 1 of the present invention.

[0092] Figure 3 It is the distortion curve graph of the microscope objective lens provided in Embodiment 1 of the present invention.

[0093] Figure 4 It is the MTF curve graph of the microscope objective lens provided in Embodiment 2 of the present invention.

[0094] Figure 5 It is the distortion curve graph of the microscope objective lens provided in Embodiment 2 of the present invention. Detailed implementation manners

[0095] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be noted that the following embodiments are intended to facilitate the understanding of the present invention and do not limit it in any way.

[0096] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0097] It should be noted that all the directional indications (such as up, down, left, right, front, back...) in the embodiments of the present invention are only used to explain the relative positional relationship and movement conditions between components in a specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indications will also change accordingly.

[0098] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, such descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one such feature.

[0099] For the convenience of understanding, the technical terms involved in the present invention will be explained and described below first.

[0100] A microscope objective lens is a key optical element in a microscope for magnifying the details of tiny objects. It images and magnifies the tiny structures of a sample so that they can be further observed and analyzed through an eyepiece or an imaging system.

[0101] Object side, image side: Taking the objective lens as the boundary, the side where the object to be photographed is located is the object side, and the surface of the objective lens close to the object side can be called the object side surface; taking the objective lens as the boundary, the side where the image of the object to be photographed is located is the image side, and the surface of the objective lens close to the image side can be called the image side surface.

[0102] Focal length: Also known as the focal distance, it is a measure of how the objective lens converges or diverges light. It refers to the distance from the optical center of the objective lens to the focal point when an infinitely distant scene forms a clear image on the focal plane through the objective lens. It can also be understood as the perpendicular distance from the optical center of the objective lens to the focal plane. From a practical perspective, it can be understood as the distance from the objective lens to the imaging plane.

[0103] Diaphragm: It refers to the edge, frame, or specially set perforated barrier of the optical element in an optical component used to limit the size of the imaging light beam or the imaging space unit.

[0104] Distortion, also known as aberration, is the degree of distortion of the image formed by the objective lens of an object relative to the object itself. Distortion is due to the influence of spherical aberration of the diaphragm. The height of the principal ray of different fields of view passing through the objective lens and intersecting with the Gaussian image plane is not equal to the ideal image height, and the difference between the two is the distortion. Therefore, distortion only changes the imaging position of off-axis object points on the ideal plane, causing the shape of the image to be distorted, but does not affect the clarity of the image.

[0105] MTF (Modulation Transfer Function), also known as the modulation transfer function, is an important tool for evaluating the imaging quality of an objective lens. It provides a scientific basis for optical design, manufacturing, and evaluation by quantifying the ability of the objective lens to transfer image details. MTF combines two indicators, resolution and contrast, and represents the ability of the imaging system to convert resolution into contrast. Specifically, MTF measures the ability of the objective lens to transfer image contrast at different spatial frequencies. Spatial frequency refers to the density of details in an image. Low spatial frequencies correspond to large-scale features in the image, while high spatial frequencies correspond to small-scale details in the image. The value of MTF ranges from 0 to 1, where 1 represents perfect transfer, that is, the contrast of the input signal is completely retained in the output; 0 represents no transfer at all, that is, the contrast of the input signal is completely lost in the output. The closer the MTF value is to 1, the higher the imaging quality of the objective lens.

[0106] As Figure 1 shown, a low magnification, ultra-large field of view, high-resolution symmetric microscope objective lens includes a front lens group, a diaphragm, and a rear lens group arranged in sequence from the object side to the image side; the lenses in the front lens group and the rear lens group are symmetric about the diaphragm.

[0107] The front lens group includes a first lens 1 with negative optical power, a second lens 2 with positive optical power, a third lens 3 with positive optical power, a fourth lens 4 with negative optical power, a fifth lens 5 with positive optical power, a sixth lens 6 with positive optical power, a seventh lens 7 with positive optical power, an eighth lens 8 with positive optical power, a ninth lens 9 with negative optical power, a tenth lens 10 with negative optical power, an eleventh lens 11 with positive optical power, a twelfth lens 12 with positive optical power, a thirteenth lens 13 with positive optical power, a fourteenth lens 14 with negative optical power, and a fifteenth lens 15 with positive optical power, which are arranged in sequence from the object side to the image side.

[0108] The rear lens group includes a sixteenth lens 16 with positive optical power, a seventeenth lens 17 with negative optical power, an eighteenth lens 18 with positive optical power, a nineteenth lens 19 with positive optical power, a twentieth lens 20 with positive optical power, a twenty - first lens 21 with negative optical power, a twenty - second lens 22 with negative optical power, a twenty - third lens 23 with positive optical power, a twenty - fourth lens 24 with positive optical power, a twenty - fifth lens 25 with positive optical power, a twenty - sixth lens 26 with positive optical power, a twenty - seventh lens 27 with negative optical power, a twenty - eighth lens 28 with positive optical power, a twenty - ninth lens 29 with positive optical power, and a thirtieth lens 30 with negative optical power, which are arranged in sequence from the object side to the image side.

[0109] In one implementation, the wavelength range value of the microscope objective is 435nm ≤ λ ≤ 656nm.

[0110] In one implementation, the effective field of view on the object side of the microscope objective is The numerical aperture on the object side is 0.3; the effective field of view on the image side of the microscope objective is The numerical aperture on the image side is 0.3.

[0111] All thirty lenses from the first lens to the thirtieth lens are glass spherical lenses.

[0112] Among them, the object - side surface of the first lens 1 is concave, and the image - side surface is concave;

[0113] The object - side surface of the second lens 2 is concave, and the image - side surface is convex;

[0114] The object - side surface of the third lens 3 is concave, and the image - side surface is convex;

[0115] The object - side surface of the fourth lens 4 is concave, and the image - side surface is convex;

[0116] The object - side surface of the fifth lens 5 is concave, and the image - side surface is convex;

[0117] The object - side surface of the sixth lens 6 is flat, and the image - side surface is convex;

[0118] The object side of the seventh lens 7 is convex, and the image side is convex;

[0119] The object side of the eighth lens 8 is convex, and the image side is convex;

[0120] The object side of the ninth lens 9 is concave, and the image side is concave;

[0121] The object side of the tenth lens 10 is concave, and the image side is flat;

[0122] The object side of the eleventh lens 11 is concave, and the image side is convex;

[0123] The object side of the twelfth lens 12 is convex, and the image side is convex;

[0124] The object side of the thirteenth lens 13 is convex, and the image side is convex;

[0125] The object side of the fourteenth lens 14 is concave, and the image side is concave;

[0126] The object side of the fifteenth lens 15 is convex, and the image side is convex;

[0127] The object side of the sixteenth lens 16 is convex, and the image side is convex;

[0128] The object side of the seventeenth lens 17 is concave, and the image side is concave;

[0129] The object side of the eighteenth lens 18 is convex, and the image side is convex;

[0130] The object side of the nineteenth lens 19 is convex, and the image side is convex;

[0131] The object side of the twentieth lens 20 is convex, and the image side is concave;

[0132] The object side of the twenty - first lens 21 is flat, and the image side is concave;

[0133] The object side of the twenty - second lens 22 is concave, and the image side is concave;

[0134] The object side of the twenty - third lens 23 is convex, and the image side is convex;

[0135] The object side of the twenty - fourth lens 24 is convex, and the image side is convex;

[0136] The object side of the twenty - fifth lens 25 is convex, and the image side is flat;

[0137] The object side of the twenty - sixth lens 26 is convex, and the image side is concave;

[0138] The object side of the twenty - seventh lens 27 is convex, and the image side is concave;

[0139] The second - eighth lens 28 has a convex surface on the object - side and a concave surface on the image - side;

[0140] The twenty - ninth lens 29 has a convex surface on the object - side and a concave surface on the image - side;

[0141] The thirtieth lens 30 has a concave surface on the object - side and a concave surface on the image - side.

[0142] In addition, the refractive index Nd1, dispersion coefficient Vd1, and focal length f1 of the first lens 1 satisfy the following conditions: 1.8 < Nd1 < 1.9, 35 < Vd1 < 40, - 60mm < f1 < - 45mm;

[0143] The refractive index Nd2, dispersion coefficient Vd2, and focal length f2 of the second lens 2 satisfy the following conditions: 1.9 < Nd2 < 2.0, 15 < Vd2 < 20, 150mm < f2 < 170mm;

[0144] The refractive index Nd3, dispersion coefficient Vd3, and focal length f3 of the third lens 3 satisfy the following conditions: 1.7 < Nd3 < 1.8, 20 < Vd3 < 30, 100mm < f3 < 130mm;

[0145] The refractive index Nd4, dispersion coefficient Vd4, and focal length f4 of the fourth lens 4 satisfy the following conditions: 1.8 < Nd4 < 1.9, 35 < Vd4 < 40, - 85mm < f4 < - 65mm;

[0146] The refractive index Nd5, dispersion coefficient Vd5, and focal length f5 of the fifth lens 5 satisfy the following conditions: 1.9 < Nd5 < 2.0, 20 < Vd5 < 30, 185mm < f5 < 200mm;

[0147] The refractive index Nd6, dispersion coefficient Vd6, and focal length f6 of the sixth lens 6 satisfy the following conditions: 1.4 < Nd6 < 1.5, 80 < Vd6 < 90, 95mm < f6 < 120mm;

[0148] The refractive index Nd7, dispersion coefficient Vd7, and focal length f7 of the seventh lens 7 satisfy the following conditions: 1.5 < Nd7 < 1.6, 50 < Vd7 < 60, 90mm < f7 < 110mm;

[0149] The refractive index Nd8, dispersion coefficient Vd8, and focal length f8 of the eighth lens 8 satisfy the following conditions: 1.5 < Nd8 < 1.6, 50 < Vd8 < 60, 60mm < f8 < 80mm;

[0150] The refractive index Nd9, dispersion coefficient Vd9, and focal length f9 of the ninth lens 9 satisfy the following conditions: 1.8 < Nd9 < 1.9, 30 < Vd9 < 40, - 40mm < f9 < - 20mm;

[0151] The refractive index Nd10, dispersion coefficient Vd10, and focal length f10 of the tenth lens 10 satisfy the following conditions: 1.8 < Nd10 < 1.9, 30 < Vd10 < 40, -50 mm < f10 < -35 mm;

[0152] The refractive index Nd11, dispersion coefficient Vd11, and focal length f11 of the eleventh lens 11 satisfy the following conditions: 1.9 < Nd11 < 2.0, 20 < Vd11 < 25, 70 mm < f11 < 80 mm;

[0153] The refractive index Nd12, dispersion coefficient Vd12, and focal length f12 of the twelfth lens 12 satisfy the following conditions: 1.5 < Nd12 < 1.6, 80 < Vd12 < 90, 100 mm < f12 < 120 mm;

[0154] The refractive index Nd13, dispersion coefficient Vd13, and focal length f13 of the thirteenth lens 13 satisfy the following conditions: 1.5 < Nd13 < 1.6, 70 < Vd13 < 80, 140 mm < f13 < 160 mm;

[0155] The refractive index Nd14, dispersion coefficient Vd14, and focal length f14 of the fourteenth lens 14 satisfy the following conditions: 1.9 < Nd14 < 2.0, 20 < Vd14 < 30, -95 mm < f14 < -80 mm;

[0156] The refractive index Nd15, dispersion coefficient Vd15, and focal length f15 of the fifteenth lens 151 satisfy the following conditions: 1.5 < Nd15 < 1.6, 60 < Vd15 < 70, 280 mm < f15 < 305 mm;

[0157] The refractive index Nd16, dispersion coefficient Vd16, and focal length f16 of the sixteenth lens 16 satisfy the following conditions: 1.5 < Nd16 < 1.6, 60 < Vd16 < 70, 280 mm < f16 < 305 mm;

[0158] The refractive index Nd17, dispersion coefficient Vd17, and focal length f17 of the seventeenth lens 17 satisfy the following conditions: 1.9 < Nd17 < 2.0, 20 < Vd17 < 30, -95 mm < f17 < -80 mm;

[0159] The refractive index Nd18, dispersion coefficient Vd18, and focal length f18 of the eighteenth lens 18 satisfy the following conditions: 1.5 < Nd18 < 1.6, 70 < Vd18 < 80, 140 mm < f18 < 160 mm;

[0160] The refractive index Nd19, dispersion coefficient Vd19, and focal length f19 of the nineteenth lens 19 satisfy the following conditions: 1.5 < Nd19 < 1.6, 80 < Vd19 < 90, 100 mm < f19 < 120 mm;

[0161] The refractive index Nd20, dispersion coefficient Vd20, and focal length f20 of the twentieth lens 20 satisfy the following conditions: 1.9 < Nd20 < 2.0, 20 < Vd20 < 25, 70 mm < f20 < 80 mm;

[0162] The refractive index Nd21, dispersion coefficient Vd21, and focal length f21 of the twenty - first lens 21 satisfy the following conditions: 1.8 < Nd21 < 1.9, 30 < Vd21 < 40, - 50 mm < f21 < - 35 mm;

[0163] The refractive index Nd22, dispersion coefficient Vd22, and focal length f22 of the twenty - second lens 22 satisfy the following conditions: 1.8 < Nd22 < 1.9, 30 < Vd22 < 40, - 40 mm < f22 < - 20 mm;

[0164] The refractive index Nd23, dispersion coefficient Vd23, and focal length f23 of the twenty - third lens 23 satisfy the following conditions: 1.5 < Nd23 < 1.6, 50 < Vd23 < 60, 60 mm < f23 < 80 mm;

[0165] The refractive index Nd24, dispersion coefficient Vd24, and focal length f24 of the twenty - fourth lens 24 satisfy the following conditions: 1.5 < Nd24 < 1.6, 50 < Vd24 < 60, 90 mm < f24 < 110 mm;

[0166] The refractive index Nd25, dispersion coefficient Vd25, and focal length f25 of the twenty - fifth lens 25 satisfy the following conditions: 1.4 < Nd25 < 1.5, 80 < Vd25 < 90, 95 mm < f25 < 120 mm;

[0167] The refractive index Nd26, dispersion coefficient Vd26, and focal length f26 of the twenty - sixth lens 26 satisfy the following conditions: 1.9 < Nd26 < 2.0, 20 < Vd26 < 30, 185 mm < f26 < 200 mm;

[0168] The refractive index Nd27, dispersion coefficient Vd27, and focal length f27 of the twenty - seventh lens 27 satisfy the following conditions: 1.8 < Nd27 < 1.9, 35 < Vd27 < 40, - 85 mm < f27 < - 65 mm;

[0169] The refractive index Nd28, dispersion coefficient Vd28, and focal length f28 of the twenty-eighth lens 28 satisfy the following conditions: 1.7 < Nd28 < 1.8, 20 < Vd28 < 30, 100 mm < f28 < 130 mm;

[0170] The refractive index Nd29, dispersion coefficient Vd29, and focal length f29 of the twenty-ninth lens 29 satisfy the following conditions: 1.9 < Nd29 < 2.0, 15 < Vd29 < 20, 150 mm < f29 < 170 mm;

[0171] The refractive index Nd30, dispersion coefficient Vd30, and focal length f30 of the thirtieth lens 30 satisfy the following conditions: 1.8 < Nd30 < 1.9, 30 < Vd30 < 40, -60 mm < f30 < -45 mm.

[0172] Example 1

[0173] In this example, the specific parameters of the low magnification, ultra-large field of view, high-resolution symmetric micro-objective lens are shown in Table 1, where the units of the radius of curvature and thickness are both millimeters (mm).

[0174] The numbers of the surfaces of each lens in the table are numbered in sequence according to Figure 1 the order of the surfaces from the object side of the first lens 1 to the image side of the thirtieth lens 30; for example, S1 is the number of the object side of the first lens 1; S2 is the number of the image side of the first lens 1; S3 is the number of the object side of the second lens 2; S4 is the number of the image side of the second lens 2. Some of the lenses are cemented and share a surface, so there will be fewer. The specific cemented lenses include: the third lens and the fourth lens are cemented, and their surfaces are S5 - S7 in sequence; the eighth lens 8 and the ninth lens 9 are cemented, and their surfaces are S14 - S16 in sequence; the thirteenth lens 13, the fourteenth lens 14, and the fifteenth lens 15 are cemented, and their surfaces are S23 - S27 in sequence; the sixteenth lens 16, the seventeenth lens 17, and the eighteenth lens 18 are cemented, and their surfaces are S29 - S33 in sequence; the twenty-second lens 22 and the twenty-third lens 23 are cemented, and their surfaces are S40 - S42 in sequence; the twenty-seventh lens 27 and the twenty-eighth lens 28 are cemented, and their surfaces are S49 - S51 in sequence.

[0175] Table 1

[0176]

[0177]

[0178] As Figure 2 shown, it is the theoretical MTF curve of the micro-objective lens provided in Example 1, which can ensure a contrast greater than 0.3 at 650 lp / mm and has a good imaging effect. As Figure 3As shown, it is the theoretical distortion curve of the microscope objective lens provided in Embodiment 1, and the distortion is 0%.

[0179] Embodiment 2

[0180] Compared with Embodiment 1, the number and type of lenses in Embodiment 2 are basically the same, except that the specific lens parameters are different.

[0181] In this embodiment, the specific parameters of the low magnification, ultra-large field of view, high-resolution symmetric microscope objective lens are shown in Table 2, where the unit of the radius of curvature and the thickness is millimeter (mm).

[0182] Table 2

[0183]

[0184]

[0185]

[0186] As Figure 4 shown, it is the theoretical MTF curve of the microscope objective lens provided in Embodiment 2, which can ensure a contrast greater than 0.3 at 650 lp / mm, and the imaging effect is good. As Figure 5 shown, it is the theoretical distortion curve of the microscope objective lens provided in Embodiment 2, and the distortion is 0%.

[0187] Based on the above Embodiment 1 and Embodiment 2, it can be seen that the low magnification, ultra-large field of view, high-resolution symmetric microscope objective lens provided by the embodiments of the present invention has a compact overall structure and stable performance. The numerical aperture reaches 0.3, which is significantly higher than 0.03 of the existing commercial low magnification objective lenses, and can achieve higher resolution, making the details of the micrographs clearer. This can more accurately observe and detect microscopic structures and defects in scientific research and industrial production inspections; at the same time, low distortion is achieved to ensure that the imaged pattern is highly consistent with the actual object, avoid pattern distortion, and improve the accuracy and reliability of the image; moreover, the characteristic of low magnification enables ultra-large field of view imaging, avoiding the time-consuming and laborious process of multiple imaging and stitching and the possible imaging differences, and greatly improving the detection efficiency and coverage; furthermore, it can be directly connected to an image sensor with a large target surface size and high resolution for photoelectric conversion imaging, eliminating the need for a tube lens required for an infinity objective lens; and the lens processing difficulty is much lower than that of high magnification objective lenses.

[0188] The above-described embodiments have detailed the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, supplements, and equivalent replacements made within the scope of the principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A low magnification, ultra-large field of view, high resolution, symmetric microscope objective lens, characterized in that, It includes a front lens group, a diaphragm, and a rear lens group that are sequentially arranged from the object side to the image side; the lenses in the front lens group and the rear lens group are symmetric about the diaphragm; The front lens group includes a first lens (1) to a fifteenth lens (15) arranged in sequence. Among them, the second lens (2), the third lens (3), the fifth lens (5), the sixth lens (6), the seventh lens (7), the eighth lens (8), the eleventh lens (11), the twelfth lens (12), the thirteenth lens (13), and the fifteenth lens (15) have positive optical powers; the first lens (1), the fourth lens (4), the ninth lens (9), the tenth lens (10), and the fourteenth lens (14) have negative optical powers; The rear lens group includes a sixteenth lens (16) to a thirtieth lens (30) arranged in sequence. Among them, the sixteenth lens (16), the eighteenth lens (18), the nineteenth lens (19), the twentieth lens (20), the twenty-third lens (23), the twenty-fourth lens (24), the twenty-fifth lens (25), the twenty-sixth lens (26), the twenty-eighth lens (28), and the twenty-ninth lens (29) have positive optical powers; the seventeenth lens (17), the twenty-first lens (21), the twenty-second lens (22), the twenty-seventh lens (27), and the thirtieth lens (30) have negative optical powers.

2. The low magnification, ultra-large field of view, high resolution, symmetric micro objective lens according to claim 1, characterized in that, The wavelength range value of the microscopic objective lens is 435nm ≤ λ ≤ 656nm.

3. The low magnification, ultra-large field of view, high resolution, symmetric microscope objective according to claim 1, characterized in that, The effective field of view on the object side of the microscope objective is The numerical aperture on the object side is 0.3; the effective field of view on the image side of the microscope objective is The numerical aperture on the image side is 0.

3.

4. The low magnification, ultra-large field of view, high resolution symmetric microscope objective according to claim 1, characterized in that, The first lens (1) to the thirtieth lens (30) are all glass spherical lenses.

5. The low magnification, ultra-large field of view, high resolution symmetric microscope objective lens according to claim 1, characterized in that, In the front lens group, the third lens (3) and the fourth lens (4) are cemented together, the eighth lens (8) and the ninth lens (9) are cemented together, and the thirteenth lens (13), the fourteenth lens (14), and the fifteenth lens (15) are cemented together; In the rear lens group, the sixteenth lens (16), the seventeenth lens (17), and the eighteenth lens (18) are cemented together, the twenty-second lens (22) and the twenty-third lens (23) are cemented together, and the twenty-seventh lens (27) and the twenty-eighth lens (28) are cemented together.

6. The low magnification, ultra-large field of view, high resolution symmetric microscope objective according to claim 1, characterized in that, In the front lens group, the object-side and image-side structures of each lens are as follows: The object side of the first lens (1) is concave, and the image side is concave; The object side of the second lens (2) is concave, and the image side is convex; The object side of the third lens (3) is concave, and the image side is convex; The object side of the fourth lens (4) is concave, and the image side is convex; The object side of the fifth lens (5) is concave, and the image side is convex; The object side of the sixth lens (6) is flat, and the image side is convex; The object side of the seventh lens (7) is convex, and the image side is convex; The object side of the eighth lens (8) is convex, and the image side is convex; The object side of the ninth lens (9) is concave, and the image side is concave; The object side of the tenth lens (10) is concave, and the image side is flat; The object side of the eleventh lens (11) is concave, and the image side is convex; The object side of the twelfth lens (12) is convex, and the image side is convex; The object side of the thirteenth lens (13) is convex, and the image side is convex; The object side of the fourteenth lens (14) is concave, and the image side is concave; The object side of the fifteenth lens (15) is convex, and the image side is convex.

7. The low magnification, ultra-large field of view, high resolution symmetric microscope objective according to claim 1, characterized in that In the rear lens group described above, the structures of the object side and the image side of each lens are as follows: The object side of the sixteenth lens (16) is convex, and the image side is convex; The object side of the seventeenth lens (17) is concave, and the image side is concave; The object side of the eighteenth lens (18) is convex, and the image side is convex; The object side of the nineteenth lens (19) is convex, and the image side is convex; The object side of the twentieth lens (20) is convex, and the image side is concave; The object side of the twenty-first lens (21) is flat, and the image side is concave; The object side of the twenty-second lens (22) is concave, and the image side is concave; The object side of the twenty-third lens (23) is convex, and the image side is convex; The object side of the twenty-fourth lens (24) is convex, and the image side is convex; The object side of the twenty-fifth lens (25) is convex, and the image side is flat; The object side of the twenty-sixth lens (26) is convex, and the image side is concave; The object side of the twenty-seventh lens (27) is convex, and the image side is concave; The object side of the twenty-eighth lens (28) is convex, and the image side is concave; The object side of the twenty-ninth lens (29) is convex, and the image side is concave; The object side of the thirtieth lens (30) is concave, and the image side is concave.

8. The low magnification, ultra-large field of view, high resolution symmetric microscope objective according to claim 1, wherein In the front lens group described above, the parameter requirements for each lens are as follows: The refractive index Nd1, the dispersion coefficient Vd1, and the focal length f1 of the first lens (1) satisfy the following conditions: 1.8 < Nd1 < 1.9, 35 < Vd1 < 40, -60 mm < f1 < -45 mm; The refractive index Nd2, the dispersion coefficient Vd2, and the focal length f2 of the second lens (2) satisfy the following conditions: 1.9 < Nd2 < 2.0, 15 < Vd2 < 20, 150 mm < f2 < 170 mm; The refractive index Nd3, the dispersion coefficient Vd3, and the focal length f3 of the third lens (3) satisfy the following conditions: 1.7 < Nd3 < 1.8, 20 < Vd3 < 30, 100 mm < f3 < 130 mm; The refractive index Nd4, the dispersion coefficient Vd4, and the focal length f4 of the fourth lens (4) satisfy the following conditions: 1.8 < Nd4 < 1.9, 35 < Vd4 < 40, -85 mm < f4 < -65 mm; The refractive index Nd5, the dispersion coefficient Vd5, and the focal length f5 of the fifth lens (5) satisfy the following conditions: 1.9 < Nd5 < 2.0, 20 < Vd5 < 30, 185 mm < f5 < 200 mm; The refractive index Nd6, the dispersion coefficient Vd6, and the focal length f6 of the sixth lens (6) satisfy the following conditions: 1.4 < Nd6 < 1.5, 80 < Vd6 < 90, 95 mm < f6 < 120 mm; The refractive index Nd7, the dispersion coefficient Vd7, and the focal length f7 of the seventh lens (7) satisfy the following conditions: 1.5 < Nd7 < 1.6, 50 < Vd7 < 60, 90 mm < f7 < 110 mm; The refractive index Nd8, dispersion coefficient Vd8, and focal length f8 of the eighth lens (8) satisfy the following conditions: 1.5 < Nd8 < 1.6, 50 < Vd8 < 60, 60 mm < f8 < 80 mm; The refractive index Nd9, dispersion coefficient Vd9, and focal length f9 of the ninth lens (9) satisfy the following conditions: 1.8 < Nd9 < 1.9, 30 < Vd9 < 40, -40 mm < f9 < -20 mm; The refractive index Nd10, dispersion coefficient Vd10, and focal length f10 of the tenth lens (10) satisfy the following conditions: 1.8 < Nd10 < 1.9, 30 < Vd10 < 40, -50 mm < f10 < -35 mm; The refractive index Nd11, dispersion coefficient Vd11, and focal length f11 of the eleventh lens (11) satisfy the following conditions: 1.9 < Nd11 < 2.0, 20 < Vd11 < 25, 70 mm < f11 < 80 mm; The refractive index Nd12, dispersion coefficient Vd12, and focal length f12 of the twelfth lens (12) satisfy the following conditions: 1.5 < Nd12 < 1.6, 80 < Vd12 < 90, 100 mm < f12 < 120 mm; The refractive index Nd13, dispersion coefficient Vd13, and focal length f13 of the thirteenth lens (13) satisfy the following conditions: 1.5 < Nd13 < 1.6, 70 < Vd13 < 80, 140 mm < f13 < 160 mm; The refractive index Nd14, dispersion coefficient Vd14, and focal length f14 of the fourteenth lens (14) satisfy the following conditions: 1.9 < Nd14 < 2.0, 20 < Vd14 < 30, -95 mm < f14 < -80 mm; The refractive index Nd15, dispersion coefficient Vd15, and focal length f15 of the fifteenth lens (15) satisfy the following conditions: 1.5 < Nd15 < 1.6, 60 < Vd15 < 70, 280 mm < f15 < 305 mm.

9. The low magnification, ultra-large field of view, high resolution symmetric microscope objective according to claim 1, characterized in that, In the rear lens group described above, the parameter requirements for each lens are as follows: The refractive index Nd16, dispersion coefficient Vd16, and focal length f16 of the sixteenth lens (16) satisfy the following conditions: 1.5 < Nd16 < 1.6, 60 < Vd16 < 70, 280 mm < f16 < 305 mm; The refractive index Nd17, dispersion coefficient Vd17, and focal length f17 of the seventeenth lens (17) satisfy the following conditions: 1.9 < Nd17 < 2.0, 20 < Vd17 < 30, -95 mm < f17 < -80 mm; The refractive index Nd18, dispersion coefficient Vd18, and focal length f18 of the eighteenth lens (18) satisfy the following conditions: 1.5 < Nd18 < 1.6, 70 < Vd18 < 80, 140 mm < f18 < 160 mm; The refractive index Nd19, dispersion coefficient Vd19, and focal length f19 of the nineteenth lens (19) satisfy the following conditions: 1.5 < Nd19 < 1.6, 80 < Vd19 < 90, 100 mm < f19 < 120 mm; The refractive index Nd20, Abbe number Vd20 and focal length f20 of the 20th lens (20) satisfy the following conditions: 1.9 < Nd20 < 2.0, 20 < Vd20 < 25, 70 mm < f20 < 80 mm; The refractive index Nd21, Abbe number Vd21 and focal length f21 of the 21st lens (21) satisfy the following conditions: 1.8 < Nd21 < 1.9, 30 < Vd21 < 40, -50 mm < f21 < -35 mm; The refractive index Nd22, Abbe number Vd22 and focal length f22 of the 22nd lens (22) satisfy the following conditions: 1.8 < Nd22 < 1.9, 30 < Vd22 < 40, -40 mm < f22 < -20 mm; The refractive index Nd23, Abbe number Vd23 and focal length f23 of the 23rd lens (23) satisfy the following conditions: 1.5 < Nd23 < 1.6, 50 < Vd23 < 60, 60 mm < f23 < 80 mm; The refractive index Nd24, Abbe number Vd24 and focal length f24 of the 24th lens (24) satisfy the following conditions: 1.5 < Nd24 < 1.6, 50 < Vd24 < 60, 90 mm < f24 < 110 mm; The refractive index Nd25, Abbe number Vd25 and focal length f25 of the 25th lens (25) satisfy the following conditions: 1.4 < Nd25 < 1.5, 80 < Vd25 < 90, 95 mm < f25 < 120 mm; The refractive index Nd26, Abbe number Vd26 and focal length f26 of the 26th lens (26) satisfy the following conditions: 1.9 < Nd26 < 2.0, 20 < Vd26 < 30, 185 mm < f26 < 200 mm; The refractive index Nd27, Abbe number Vd27 and focal length f27 of the 27th lens (27) satisfy the following conditions: 1.8 < Nd27 < 1.9, 35 < Vd27 < 40, -85 mm < f27 < -65 mm; The refractive index Nd28, Abbe number Vd28 and focal length f28 of the 28th lens (28) satisfy the following conditions: 1.7 < Nd28 < 1.8, 20 < Vd28 < 30, 100 mm < f28 < 130 mm; The refractive index Nd29, Abbe number Vd29 and focal length f29 of the 29th lens (29) satisfy the following conditions: 1.9 < Nd29 < 2.0, 15 < Vd29 < 20, 150 mm < f29 < 170 mm; The refractive index Nd30, Abbe number Vd30 and focal length f30 of the 30th lens (30) satisfy the following conditions: 1.8 < Nd30 < 1.9, 30 < Vd30 < 40, -60 mm < f30 < -45 mm.

Images