Long-working-distance fixed-magnification lens and optical system thereof
By designing an optical system for long-distance fixed-magnification lenses, using specific lens combinations and high-refractive index glass, the problem of low imaging magnification at long-distance distances of fixed-focus industrial lenses is solved, and a larger magnification and higher imaging accuracy is achieved, which is suitable for high-precision detection.
Patent Information
- Application Number
- CN202510388305.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-28
- Publication Date
- 2025-07-01
Smart Images
Figure CN120233527A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of optical devices, and particularly to a fixed-magnification lens with a long working distance and its optical system. Background Art
[0002] With the development of industrial automation, industrial lenses are widely used in the field of machine vision inspection, such as product measurement and defect detection in the fields of semiconductors, 3C electronics, new energy, packaging and printing, intelligent logistics, automotive manufacturing, and pharmaceuticals. The increasing demand for detection accuracy and the widespread application of high-resolution cameras have put forward new requirements for the imaging quality and performance of industrial lenses.
[0003] At present, most fixed-focus industrial lenses on the market have a focal length concentrated below 75 mm, and the imaging magnification is low when shooting at a long working distance, resulting in a lack of accuracy. Therefore, it is necessary to improve the existing industrial lenses to meet the special application requirements of high-precision imaging at a long working distance.
[0004] The above information is given as background information only to assist in understanding the present disclosure, and it is not determined or admitted whether any of the above content can be used as prior art relative to the present disclosure. Summary of the Invention
[0005] The purpose of the present invention is to provide a fixed-magnification lens with a long working distance and its optical system to solve or at least partially solve the technical problems existing in the prior art.
[0006] To achieve this purpose, the present invention adopts the following technical solutions:
[0007] In a first aspect, the present invention provides an optical system of a fixed-magnification lens with a long working distance, including a front group A and a rear group B arranged in sequence from the object side to the image side;
[0008] The front group A includes a first lens G1 with a positive optical power; a second lens G2 with a positive optical power; a third lens G3 with a negative optical power;
[0009] The rear group B includes a fourth lens G4 with a positive optical power; a fifth lens G5 with a negative optical power; a sixth lens G6 with a positive optical power;
[0010] An aperture stop S is provided between the third lens G3 and the fourth lens G4;
[0011] The combined focal length of the front group A is f A , and the combined focal length f B of the rear group B, f A and f B satisfy the relationship: 0.75 < |f A / f B | < 1.25.
[0012] Optionally, the focal length of the first lens G1 is f1, and the combined focal length f of the front group A A satisfies the following relationship: 0.3 < |f1 / f A | < 0.8;
[0013] The second lens G2 and the third lens G3 are cemented to form a first cemented lens U1 with a negative optical power; the focal length of the first cemented lens U1 is f U1 , f U1 and f A satisfies the relationship: 0.37 < |f U1 / f A | < 0.87;
[0014] Optionally, the fourth lens G4 and the fifth lens G5 form a second cemented lens U2 with a negative optical power; the focal length of the second cemented lens U2 is f U2 , f U2 and f B satisfies the relationship: 0.6 < |f U2 / f B | < 1.0;
[0015] The focal length of the sixth lens G6 is f6, and f6 and f B satisfy the relationship: 0.25 < |f6 / f B | < 0.75.
[0016] Optionally, the refractive index of the sixth lens G6 is n6, and the Abbe number is v6, which satisfy the relationship: 1.47 < n6 < 1.55; 70 < v6 < 85.
[0017] Optionally, in the front group A, the first lens G1 and the second lens G2 are both biconvex lenses, and the third lens G3 is a biconcave lens;
[0018] In the rear group B, the fourth lens G4 is a meniscus lens, the fifth lens G5 is a biconcave lens or a plano-concave lens, and the sixth lens G6 are both biconvex lenses.
[0019] Optionally, the first lens G1, the second lens G2, the third lens G3, the fourth lens G4, the fifth lens G5, and the sixth lens G6 are all glass spherical lenses.
[0020] Optionally, the optical axes of the first lens G1, the second lens G2, the third lens G3, the fourth lens G4, the fifth lens G5, and the sixth lens G6 are all on a predetermined optical axis;
[0021] Optionally, the aperture of the diaphragm S is a circular hole, and the center of the circular hole is on the predetermined optical axis.
[0022] In a second aspect, the present invention provides a fixed-magnification lens with a long working distance, including the optical system of a fixed-magnification lens with a long working distance as described above.
[0023] Compared with the prior art, the present invention has the following beneficial effects:
[0024] The fixed-magnification lens with a long working distance provided by the present invention has a focal length much larger than that of an ordinary fixed-focus industrial lens; when shooting at a long distance, compared with an ordinary fixed-focus industrial lens, it has a larger magnification and higher precision, and is more suitable for application scenarios of long-distance and high-precision detection.
[0025] The present invention has other characteristics and advantages, which will be obvious from the accompanying drawings incorporated herein and the subsequent specific embodiments, or will be described in detail in the accompanying drawings incorporated herein and the subsequent specific embodiments, and these accompanying drawings and specific embodiments are jointly used to explain the specific principles of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS
[0026] 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 accompanying drawings required for describing the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention, and those of ordinary skill in the art can also obtain other accompanying drawings without creative efforts based on these accompanying drawings.
[0027] Figure 1 It is a schematic structural diagram of the optical system of a fixed-magnification lens with a long working distance provided in Embodiment 1 of the present invention.
[0028] Figure 2 It is an MTF curve graph of the optical system of a fixed-magnification lens with a long working distance provided in Embodiment 1 of the present invention.
[0029] Figure 3 It is a distortion graph of the optical system of a fixed-magnification lens with a long working distance provided in Embodiment 2 of the present invention.
[0030] Figure 4 It is an MTF curve graph of the optical system of a fixed-magnification lens with a long working distance provided in Embodiment 2 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS
[0031] To describe in detail the possible application scenarios, technical principles, specific implementable solutions, achievable purposes and effects, etc. of the present application, the following will be described in detail in combination with the specific embodiments listed and the accompanying drawings. The embodiments described herein are only used to more clearly illustrate the technical solutions of the present application, so they are only examples and cannot be used to limit the protection scope of the present application.
[0032] References to "embodiments" in this document mean that the specific features, structures, or characteristics described in connection with the embodiments can be included in at least one embodiment of this application. The term "embodiment" that appears in various places in the specification does not necessarily refer to the same embodiment, nor does it particularly limit its independence or relevance to other embodiments. In principle, in this application, as long as there is no technical contradiction or conflict, the various technical features mentioned in each embodiment can be combined in any way to form corresponding implementable technical solutions.
[0033] Unless otherwise defined, the meanings of the technical terms used in this document are the same as those commonly understood by those skilled in the technical field to which this application belongs; the use of the relevant terms in this document is only for describing specific embodiments and is not intended to limit this application.
[0034] In the description of this application, the phrase "and / or" is an expression used to describe the logical relationship between objects, indicating that three relationships can exist. For example, A and / or B means: the existence of A, the existence of B, and the simultaneous existence of A and B. In addition, the character " / " in this document generally represents an "or" logical relationship between the associated objects before and after.
[0035] In this application, terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual quantitative, primary-secondary, or sequential relationships between these entities or operations.
[0036] Without further limitation, in this application, the use of "including", "comprising", "having" or other similar expressions in a statement is intended to cover non-exclusive inclusion. These expressions do not exclude the possibility that there may be additional elements in the process, method, or product that includes the said elements. Thus, a process, method, or product that includes a series of elements may include not only those defined elements, but also other elements that are not explicitly listed, or elements that are inherent to such a process, method, or product.
[0037] Similar to the understanding in the Examination Guidelines, in this application, expressions such as "greater than", "less than", "exceeding", etc. are understood not to include the number itself; expressions such as "above", "below", "within", etc. are understood to include the number itself. In addition, in the description of the embodiments of this application, the meaning of "a plurality of" is two or more (including two), and similar expressions related to "many", such as "multiple groups", "multiple times", etc., are understood in this way unless otherwise specifically defined.
[0038] In the description of the embodiments of the present application, the spatially related expressions used, such as "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "perpendicular", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., the indicated orientation or positional relationship is based on the orientation or positional relationship shown in the specific embodiments or the drawings, and is only for the convenience of describing the specific embodiments of the present application or for the reader's understanding, rather than indicating or implying that the device or component referred to must have a specific position, a specific orientation, or be constructed or operated in a specific orientation. Therefore, it should not be construed as a limitation on the embodiments of the present application.
[0039] Unless otherwise clearly specified or limited, in the description of the embodiments of the present application, the terms such as "installed", "connected", "connected", "fixed", "set", etc. should be understood in a broad sense. For example, the "connection" may be a fixed connection, a detachable connection, or an integral setting; it may be a mechanical connection, an electrical connection, or a communication connection; it may be directly connected, or indirectly connected through an intermediate medium; it may be the communication inside two elements or the interaction relationship between two elements. For those skilled in the art to which the present application pertains, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific circumstances.
[0040] Embodiment 1:
[0041] Please refer to Figure 1 , Figure 1 which is a schematic structural diagram of an optical system of a telecentric fixed-magnification lens provided in Embodiment 1 of the present invention.
[0042] As Figure 1 shown, the optical system includes:
[0043] including a front group A and a rear group B arranged in sequence from the object side to the image side;
[0044] The front group A includes a first lens G1 with positive optical power; a second lens G2 with positive optical power; a third lens G3 with negative optical power;
[0045] The rear group B includes a fourth lens G4 with positive optical power; a fifth lens G5 with negative optical power; a sixth lens G6 with positive optical power;
[0046] An aperture S is provided between the third lens G3 and the fourth lens G4;
[0047] The combined focal length of the front group A is f A , and the combined focal length of the rear group B is f B , f A and f BSatisfy the relational expression: 0.75 < |f A / f B | < 1.25.
[0048] Specifically, the focal length of the first lens G1 is f1, and the combined focal length f of the first lens G1 and the front group A A Satisfy the following relational expression: 0.3 < |f1 / f A | < 0.8;
[0049] The second lens G2 and the third lens G3 are cemented to form a first cemented lens U1 with a negative optical power; the focal length of the first cemented lens U1 is f U1 f U1 and f A Satisfy the relational expression: 0.37 < |f U1 / f A | < 0.87;
[0050] It should be noted that, in this embodiment, the first lens G1 is made of a high refractive index glass material; the first lens G1 with a high refractive index can reduce the curvature of the lens, thereby reducing the higher order aberrations and the tolerance sensitivity;
[0051] The cemented lens U1 has a relatively large central thickness, which can correct the chromatic aberration of the system and is beneficial to correcting the field curvature and astigmatism of the system.
[0052] Specifically, the fourth lens G4 and the fifth lens G5 form a second cemented lens U2 with a negative optical power; the focal length of the second cemented lens U2 is f U2 f U2 and f B Satisfy the relational expression: 0.6 < |f U2 / f B | < 1.0;
[0053] The focal length of the sixth lens G6 is f6, and f6 and f B Satisfy the relational expression: 0.25 < |f6 / f B | < 0.75.
[0054] It should be noted that, in this embodiment, the second cemented lens U2 is a new type of achromatic cemented lens. On the one hand, this kind of lens is beneficial to balancing the field curvature of the system. On the other hand, it can also balance the higher order aberrations by using the residual spherical aberration amount, so as to achieve a good imaging effect with fewer lenses.
[0055] Furthermore, the refractive index of the sixth lens G6 is n6, and the Abbe number is v6, and they satisfy the relational expression: 1.47 < n6 < 1.55; 70 < v6 < 85. By satisfying the above refractive index and dispersion, it is beneficial to balance the spherical aberration, coma and distortion.
[0056] Specifically, in this embodiment, in the front group A, the first lens G1 and the second lens G2 are both double convex lenses, and the third lens G3 is a double concave lens;
[0057] In the rear group B, the fourth lens G4 is a meniscus lens, the fifth lens G5 is a double concave lens or a plano-concave lens, and the sixth lens G6 is a double convex lens.
[0058] More specifically, the first lens G1, the second lens G2, the third lens G3, the fourth lens G4, the fifth lens G5, and the sixth lens G6 are all spherical glass lenses.
[0059] In this embodiment, the optical axes of the first lens G1, the second lens G2, the third lens G3, the fourth lens G4, the fifth lens G5, and the sixth lens G6 are all on the predetermined optical axis;
[0060] The aperture of the diaphragm S is a circular hole, and the center of the circular hole is on the predetermined optical axis.
[0061] It can be understood that the aperture value of the diaphragm S needs to be adjusted according to the specific application scenario.
[0062] To verify whether the above optical system meets the design purpose, the following is a specific test example given according to the above settings of this embodiment:
[0063] In this test example, the data of each lens of the optical system are shown in Table 1 below:
[0064] Table 1
[0065]
[0066]
[0067] It should be noted that in Table 1, "front surface" corresponds to Figure 1 the left surface of the corresponding lens or lens group, and "rear surface" corresponds to Figure 1 the right surface of the corresponding lens or lens group; or it can be understood that: the object side is on the Figure 1 left side, the image side (or image plane) is on the Figure 1 right side, the surface closer to the object side is the "front surface", and the surface closer to the image side is the "rear surface".
[0068] In this test example, the combined focal length of the front group A is f A = 304 mm; the combined focal length of the rear group B is f B = 275 mm; the focal length of the first lens G1 is f1 = 158 mm; the focal length of the first cemented lens U1 is f U1 = -172 mm; the focal length of the second cemented lens U2 is f U2= -223 mm; the focal length of the sixth lens G6 is f6 = 129 mm.
[0069] Substituting the above values into each relational expression, we respectively obtain:
[0070] |f A / f B | = 1.105, |f1 / f A | = 0.520, |f U1 / f A | = 0.566, |f U2 / f B | = 0.811, |f6 / f B | = 0.469.
[0071] Therefore, it satisfies the relevant relational expressions of this embodiment, that is:
[0072] 0.75 < |f A / f B | < 1.25, 0.3 < |f1 / f A | < 0.8, 0.37 < |f U1 / f A | < 0.87, 0.6 < |f U2 / f B | < 1.0, 0.25 < |f6 / f B | < 0.75.
[0073] Please refer to Figure 2 Figure 2 which is the MTF (Modulation Transfer Function) curve graph of an optical system of a long working distance fixed magnification lens provided in Embodiment 1 of the present invention.
[0074] The focal length f' of the lens optical system shown in this test example is 194 mm, and at a working distance of 700 mm, the magnification can reach 0.4X.
[0075] In summary, for the optical system of a long working distance fixed magnification lens provided in this embodiment, its focal length is much greater than that of an ordinary fixed focus industrial lens; when shooting at a long distance, compared with an ordinary fixed focus industrial lens, it has a larger magnification and higher precision, and is more suitable for application scenarios of long distance and high precision detection.
[0076] Embodiment 2:
[0077] Please refer to Figure 3 , Figure 3 which is a schematic structural diagram of an optical system of a long working distance fixed magnification lens provided in Embodiment 2 of the present invention.
[0078] As shown in Figure 3As shown, the optical system includes:
[0079] It includes a front group A and a rear group B arranged in sequence from the object side to the image side;
[0080] The front group A includes a first lens G1 with a positive focal power; a second lens G2 with a positive focal power; a third lens G3 with a negative focal power;
[0081] The rear group B includes a fourth lens G4 with a positive focal power; a fifth lens G5 with a negative focal power; a sixth lens G6 with a positive focal power;
[0082] An aperture stop S is provided between the third lens G3 and the fourth lens G4;
[0083] The combined focal length of the front group A is f A , and the combined focal length f of the rear group B B , f A and f B satisfy the relationship: 0.75 < |f A / f B | < 1.25.
[0084] Specifically, the focal length of the first lens G1 is f1, and it satisfies the following relationship with the combined focal length f of the front group A A : 0.3 < |f1 / f A | < 0.8;
[0085] The second lens G2 and the third lens G3 are cemented to form a first cemented lens U1 with a negative focal power; the focal length of the first cemented lens U1 is f U1 , f U1 and f A satisfy the relationship: 0.37 < |f U1 / f A | < 0.87;
[0086] It should be noted that in this embodiment, the first lens G1 is made of a high-refractive-index glass material; the first lens G1 with a high refractive index can reduce the curvature of the lens, thereby reducing higher-order aberrations and lowering the tolerance sensitivity;
[0087] The cemented lens U1 has a relatively large central thickness, which can correct the chromatic aberration of the system and is beneficial to correcting the field curvature and astigmatism of the system.
[0088] Specifically, the fourth lens G4 and the fifth lens G5 form a second cemented lens U2 with a negative focal power; the focal length of the second cemented lens U2 is f U2 , f U2 and f B satisfy the relationship: 0.6 < |f U2 / f B | < 1.0;
[0089] The focal length of the sixth lens G6 is f6, and f6 and f B satisfy the relationship: 0.25 < |f6 / f B | < 0.75.
[0090] It should be noted that in this embodiment, the second cemented lens U2 is a new type of achromatic cemented lens. On the one hand, this kind of lens is beneficial to balance the field curvature of the system. On the other hand, it can also use the residual spherical aberration to balance the higher-order aberrations, so as to achieve good imaging effects with fewer lenses.
[0091] Furthermore, the refractive index of the sixth lens G6 is n6, and the Abbe number is v6, which satisfy the relationship: 1.47 < n6 < 1.55; 70 < v6 < 85. By satisfying the above refractive index and dispersion, it is beneficial to balance spherical aberration, coma and distortion.
[0092] Specifically, in this embodiment, in the front group A, the first lens G1 and the second lens G2 are both biconvex lenses, and the third lens G3 is a biconcave lens;
[0093] In the rear group B, the fourth lens G4 is a meniscus lens, the fifth lens G5 is a biconcave lens or a plano-concave lens, and the sixth lens G6 are all biconvex lenses.
[0094] More specifically, the first lens G1, the second lens G2, the third lens G3, the fourth lens G4, the fifth lens G5 and the sixth lens G6 are all glass spherical lenses.
[0095] In this embodiment, the optical axes of the first lens G1, the second lens G2, the third lens G3, the fourth lens G4, the fifth lens G5 and the sixth lens G6 are all on the predetermined optical axis;
[0096] The aperture of the aperture stop S is a circular hole, and the center of the circular hole is on the predetermined optical axis.
[0097] It can be understood that the aperture value of the aperture stop S needs to be adjusted correspondingly according to the specific application scenario.
[0098] To verify whether the above optical system meets the design purpose, the following is a specific test example given according to the above settings of this embodiment:
[0099] In this test example, the data of each lens of the optical system are shown in Table 2 below:
[0100] Table 2
[0101] Surface Radius (mm) Thickness (mm) Refractive Index Abbe Number Front Surface of G1 418.2 8.0 1.85 - Rear Surface of G1 -212.2 16.1 Front Surface of G2 44.3 12.4 1.5 80 Bonding Surface of G2 and G3 -130.6 18.0 1.75 - Rear Surface of G3 40.0 11.8 Diaphragm S ∞ 3.5 Front Surface of G4 -118.1 10.0 1.80 - Bonding Surface of G4 and G5 -24.9 2.4 1.75 - Rear Surface of G5 ∞ 12.1 Front Surface of G6 396.5 5.0 1.5 80 Rear Surface of G6 -89.7 226 Image Plane /
[0102] It should be noted that in Table 2, "front surface" corresponds to Figure 3For the left surface of the corresponding lens or lens group, the "rear surface" corresponds to Figure 3 the right surface of the corresponding lens or lens group; or it can be understood that the object side is Figure 3 on the left, and the image side (or image plane) is Figure 3 on the right. The surface closer to the object side is the "front surface", and the surface closer to the image side is the "rear surface".
[0103] In this test example, the combined focal length of the front group A is f A = 318 mm; the combined focal length of the rear group B is f B = 338 mm; the focal length of the first lens G1 is f1 = 165 mm; the focal length of the first cemented lens U1 is f U1 = -174 mm; the focal length of the second cemented lens U2 is f U2 = -215 mm; the focal length of the sixth lens G6 is f6 = 146 mm.
[0104] Substituting the above values into each relational expression, we respectively obtain:
[0105] |f A / f B | = 0.941, |f1 / f A | = 0.519, |f U1 / f A | = 0.547, |f U2 / f B | = 0.636, |f6 / f B | = 0.432.
[0106] Therefore, the relevant relational expressions of this embodiment are satisfied, that is:
[0107] 0.75 < |f A / f B | < 1.25, 0.3 < |f1 / f A | < 0.8, 0.37 < |f U1 / f A | < 0.87, 0.6 < |f U2 / f B | < 1.0, 0.25 < |f6 / f B | < 0.75.
[0108] Please refer to Figure 4 , Figure 4 which is the MTF curve graph of the optical system of a fixed-magnification lens with a long working distance provided in the second embodiment of the present invention;
[0109] The focal length f' of the lens optical system shown in this embodiment is 232 mm, which is much larger than that of a common fixed-focus industrial lens. At a working distance of 800 mm, the magnification reaches 0.42X, making it suitable for application scenarios of long-distance high-precision detection.
[0110] Embodiment 3:
[0111] This embodiment provides a fixed-magnification lens with a long working distance, including the optical system of a fixed-magnification lens with a long working distance as described in Embodiment 1 or Embodiment 2.
[0112] Based on the relatively detailed description of the optical system in the above embodiments, it will not be elaborated in this embodiment.
[0113] In summary, the fixed-magnification lens with a long working distance provided in this embodiment has a focal length much larger than that of a common fixed-focus industrial lens; when shooting at a long distance, it has a larger magnification and higher precision compared to a common fixed-focus industrial lens, and is more suitable for application scenarios of long-distance and high-precision detection.
[0114] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims
1. An optical system of a long working distance fixed magnification lens, characterized in that: It includes sequentially setting a front group A and a rear group B from the object side to the image side; The front group A includes a first lens G1 having positive refractive power, a second lens G2 having positive refractive power, and a third lens G3 having negative refractive power. The rear group B includes a fourth lens G4 having positive refractive power, a fifth lens G5 having negative refractive power, and a sixth lens G6 having positive refractive power. A stop S is provided between the third lens G3 and the fourth lens G4; The combined focal length of the front group A is f A , the combined focal length of the rear group B is f B , f A and f B Satisfies the relationship: 0.75<|f A / f B |<1.
25.
2. The optical system of a long working distance fixed magnification lens according to claim 1, characterized in that: The focal length of the first lens G1 is f1, and the combined focal length of the lens and the front lens group A is f A Satisfies the following relationship: 0.3<|f1 / f A |<0.8; The second lens G2 and the third lens G3 are cemented together to form a first cemented lens U1 with negative optical power; the focal length of the first cemented lens U1 is f U1 , f U1 With f A Satisfies the relationship: 0.37<|f U1 / f A |<0.
87.
3. The optical system of a long working distance fixed magnification lens according to claim 2, characterized in that: The fourth lens G4 and the fifth lens G5 form a second cemented lens U2 with negative optical power; the focal length of the second cemented lens U2 is f U2 , f U2 With f B Satisfies the relationship: 0.6<|f U2 / f B |<1.0; The focal length of the sixth lens G6 is f6, and f6 is equal to f B Satisfies the relationship: 0.25<|f6 / f B |<0.
75.
4. The optical system of a long working distance fixed magnification lens according to claim 3, characterized in that: The refractive index of the sixth lens G6 is n6, and the Abbe number is v6, which satisfies the relationship: 1.47 <n6<1.55;70<v6<85。 5. The optical system of a long working distance fixed magnification lens according to claim 3, characterized in that: In the front group A, the first lens G1 and the second lens G2 are both biconvex lenses, and the third lens G3 is a biconcave lens; In the rear group B, the fourth lens G4 is a meniscus lens, the fifth lens G5 is a biconcave lens or a plano-concave lens, and the sixth lens G6 is a biconvex lens.
6. The optical system of a long working distance fixed magnification lens according to claim 5, characterized in that: The first lens G1 , the second lens G2 , the third lens G3 , the fourth lens G4 , the fifth lens G5 and the sixth lens G6 are all glass spherical lenses.
7. The optical system of a long working distance fixed magnification lens according to claim 1, characterized in that: Optical axes of the first lens G1 , the second lens G2 , the third lens G3 , the fourth lens G4 , the fifth lens G5 , and the sixth lens G6 are all on a predetermined optical axis.
8. The optical system of a long working distance fixed magnification lens according to claim 7, characterized in that: The aperture of the diaphragm S is a circular hole, and the center of the circular hole is on the predetermined optical axis.
9. A long working distance fixed magnification lens, characterized in that: An optical system comprising a long working distance fixed magnification lens as described in any one of claims 1-8.