A compact long working distance constant-magnification lens and an optical system thereof

Abstract

This invention relates to the field of optical imaging technology, and discloses a compact long working distance fixed-magnification lens and its optical system. The optical system includes a front group with positive optical power, a middle group with negative optical power, an aperture stop, and a rear group with positive optical power; the focal length of the optical system is f, the optical rear focal length is BFL, and the focal length of the front group is f0. S1 The focal length of the middle group is f S2 The focal length of the rear element is f. S3 They respectively satisfy the relation: 0.4 < |f S1 / f|<0.75, 1.1<|f S2 / f|<1.7, 1.50<|f S3 / f|<8.00, 0.05<|BFL / f|<0.35. This invention realizes a long working distance fixed-magnification lens with high resolution, a lens magnification of 0.94X, a maximum resolution of 100 lp / mm, can be matched with 5-micron pixel chips, has a maximum target surface size of 1.2″, and also has low distortion performance.

Description

Technical Field

[0001] This invention relates to the field of optical imaging technology, and in particular to a compact long working distance fixed magnification lens and its optical system. Background Technology

[0002] With the rapid development of industrial inspection, machine vision, and precision instruments, long working distance lenses are widely used in high-precision imaging optical systems because they can achieve high-precision imaging over long distances without interfering with the object being measured or avoiding environmental interference. Fixed-magnification lenses, due to their simple structure and stable imaging, have significant advantages in standardized inspection scenarios. However, the insufficient compatibility between long working distances and compact designs in existing technologies has become a key bottleneck restricting the widespread application of these lenses. Especially at high magnification (≥0.9X), long working distances often limit the numerical aperture and resolution of the lens, making it difficult to meet the needs of micron-level inspection.

[0003] Existing industrial fixed-magnification lenses on the market suffer from three major contradictions: the spatial conflict between long working distance and compact structure, the challenge of aberration correction under fixed magnification constraints, and the dilemma of balancing high resolution and low distortion. These problems severely restrict the improvement of equipment integration and inspection accuracy. Therefore, the research and development of fixed-magnification optical lenses with high resolution, low distortion, and long working distance is even more urgent.

[0004] The above information is provided as background information only to aid in understanding this disclosure and does not constitute an assertion or admission that any of the above content can be used as prior art relative to this disclosure. Summary of the Invention

[0005] The purpose of this invention is to provide a compact long working distance fixed magnification lens and its optical system to solve or at least partially solve the technical problems existing in the prior art.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides an optical system for a compact long working distance fixed magnification lens, comprising a front group having positive optical power, a middle group having negative optical power, an aperture stop, and a rear group having positive optical power arranged sequentially from the object side to the image side.

[0008] The optical system has a focal length f, a back focal length BFL, and a front focal length f. S1 The focal length of the middle group is f S2 The focal length of the rear element is f. S3 They respectively satisfy the following relation:

[0009] 0.4<|f S1 / f|<0.75, 1.1<|f S2 / f|<1.7, 1.50<|f S3 / f|<8.00,0.05<| BFL / f|<0.35.

[0010] Optionally, the front group includes a first lens with positive optical power, wherein the first lens is a biconvex lens;

[0011] The distance from the vertex of the front surface of the first lens to the vertex of the rear surface of the rear group is L, and L and f satisfy the relationship: 0.7 < |L / f| < 1.50.

[0012] Optionally, the middle group includes a second lens with negative optical power, a third lens with positive optical power, a fourth lens with negative optical power, a fifth lens with positive optical power, and a sixth lens with negative optical power; the second lens, the third lens, and the fourth lens are cemented together to form a first cemented lens group with negative optical power, and the fifth lens and the sixth lens are cemented together to form a second cemented lens group with positive optical power.

[0013] The focal length of the first cemented lens group is f. U1 f U1 The relationship between f and is: 0.65 < |f U1 / f|<1.15;

[0014] The focal length of the second cemented lens group is f. U2 f U2 The relationship between f and 1 is: 1.8 < |f U2 / f|<3.80.

[0015] Optionally, the second lens is a meniscus lens, the third and fifth lenses are both biconvex lenses, the fourth lens is a meniscus lens or a biconcave lens, and the sixth lens is a biconcave lens.

[0016] Optionally, the rear group includes a seventh lens with negative optical power, an eighth lens with positive optical power, a ninth lens with negative optical power, and a tenth lens with positive optical power; the seventh lens and the eighth lens are cemented together to form a third cemented lens group with positive optical power.

[0017] The focal length of the third cemented lens group is f. U3 f U3 The relationship between f and 1 is: 1.00 < |f U3 / f|<2.50;

[0018] The focal length of the ninth lens is f G9 f G9 The relationship between f and f is: 0.18 < |f G9 / f|<0.40;

[0019] The focal length of the tenth lens is f G10 fG10 The relationship between f and f is: 0.25 < |f G10 / f|<0.60.

[0020] Optionally, the seventh and ninth lenses are both biconcave lenses, the eighth lens is a biconvex lens, and the tenth lens is a meniscus lens or a plano-convex lens.

[0021] Optionally, the first lens, second lens, third lens, fourth lens, fifth lens, sixth lens, seventh lens, eighth lens, ninth lens and tenth lens are all spherical mirrors, and the optical axes of all spherical mirrors coincide with the predetermined optical axis.

[0022] Optionally, the half-image height of the optical system is y';

[0023] The relationship between y' and f is: |y' / f| < 0.12.

[0024] Optionally, the aperture of the stop is a circular aperture, and the center of the circular aperture is on the predetermined optical axis; the aperture value of the stop can be adjusted from F2.8 to F16.

[0025] Secondly, the present invention provides a compact long working distance fixed magnification lens, including the optical system of a compact long working distance fixed magnification lens as described above;

[0026] The compact long working distance fixed magnification lens has a magnification of 0.94X.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The optical system of the long working distance fixed magnification lens provided by the present invention has a lens magnification of 0.94X, a maximum imaging surface of φ19.2mm, a maximum resolution of 100lp / mm, can be matched with a 5-micron pixel chip, and at the corresponding maximum chip size, its pixel count can reach seven million pixels. The maximum optical distortion across the entire field of view can be less than 0.10%, and the working distance can reach 264mm.

[0029] The present invention has other features and advantages, which will be apparent from or will be set forth in detail in the accompanying drawings and the following detailed description, which together serve to explain the particular principles of the invention. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of the optical system of a compact long working distance fixed magnification lens provided in an embodiment of the present invention.

[0032] Figure 2 This is the optical distortion curve of an optical system for a compact long working distance fixed magnification lens provided in an embodiment of the present invention.

[0033] Figure 3 This is a schematic diagram of the optical system of another compact long working distance fixed magnification lens provided in an embodiment of the present invention.

[0034] Figure 4 This is the optical distortion curve of another compact long working distance fixed magnification lens optical system provided in the embodiment of the present invention. Detailed Implementation

[0035] To illustrate the possible application scenarios, technical principles, implementable specific solutions, and achievable objectives and effects of this application in detail, the following description, in conjunction with the listed specific embodiments and accompanying drawings, provides a detailed explanation. The embodiments described herein are merely illustrative of the technical solutions of this application and are therefore intended to limit the scope of protection of this application.

[0036] In this document, the term "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The term "embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment, nor does it specifically limit its independence or connection with other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the technical features mentioned in each embodiment can be combined in any way to form corresponding implementable technical solutions.

[0037] Unless otherwise defined, the technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the use of related terms herein is merely for the purpose of describing particular embodiments and is not intended to limit this application.

[0038] In the description of this application, the term "and / or" is used to describe the logical relationship between objects, indicating that three relationships can exist. For example, A and / or B means: A exists, B exists, and A and B exist simultaneously. Additionally, the character " / " in this document generally indicates that the preceding and following objects have an "or" logical relationship.

[0039] In this application, terms such as “first” and “second” are used only to distinguish one entity or operation from another, and do not necessarily require or imply any actual quantity, hierarchy or order relationship between these entities or operations.

[0040] Unless otherwise specified, the use of terms such as “comprising,” “including,” “having,” or other similar expressions in this application is intended to cover non-exclusive inclusion, which does not exclude the presence of additional elements in a process, method, or product that includes the stated elements, such that a process, method, or product that includes a list of elements may include not only those defined elements but also other elements not expressly listed, or elements inherent to such a process, method, or product.

[0041] As understood in the Examination Guidelines, in this application, expressions such as "greater than," "less than," and "exceeding" are understood to exclude the stated number; expressions such as "above," "below," and "within" are understood to include the stated number. Furthermore, in the description of the embodiments in this application, "multiple" means two or more (including two), and similar expressions related to "multiple" are also understood in this way, such as "multiple groups" and "multiple times," unless otherwise explicitly specified.

[0042] In the description of the embodiments of this application, the space-related expressions used, such as "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "vertical," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential," indicate the orientation or positional relationship based on the orientation or positional relationship shown in the specific embodiments or drawings. They are only for the purpose of describing the specific embodiments of this application or for the reader's understanding, and do not indicate or imply 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, they should not be construed as limitations on the embodiments of this application.

[0043] Unless otherwise expressly specified or limited, the terms "installation," "connection," "linking," "fixing," and "setting," as used in the description of the embodiments of this application, should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral setting; it can be a mechanical connection, an electrical connection, or a communication connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal connection of two components or the interaction between two components. For those skilled in the art to which this application pertains, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances. Example 1

[0044] Please see Figure 1 , Figure 1 This is a schematic diagram of the optical system of a compact long working distance fixed magnification lens provided in an embodiment of the present invention;

[0045] like Figure 1 As shown, the optical system includes a front group S1 with positive optical power, a middle group S2 with negative optical power, an aperture A0, and a rear group S3 with positive optical power arranged sequentially from the object side to the image side.

[0046] The focal length of the optical system is f, the optical back focal length of the optical system is BFL, and the focal length of the front group S1 is f. S1 The focal length of the middle group S2 is f S2 The focal length of the rear group S3 is f. S3 They respectively satisfy the following relation:

[0047] 0.4<|f S1 / f|<0.75, 1.1<|f S2 / f|<1.7, 1.50<|f S3 / f|<8.00,0.05<| BFL / f|<0.35.

[0048] Furthermore, the half-image height of the optical system is y';

[0049] The relationship between y' and f is: |y' / f| < 0.12.

[0050] Specifically, the front group S1 includes a first lens G1 with positive optical power, and the first lens G1 is a biconvex lens;

[0051] For ease of explanation, in this embodiment, the front surface of the lens or lens group refers to the surface of the lens or lens group closest to the object, i.e. Figure 1 The left surface of the lens or lens group; correspondingly, the rear surface of the lens or lens group refers to the surface of the lens or lens group closest to the image side, i.e. Figure 1 The right side surface of the middle lens or lens group.

[0052] In this embodiment, the front surface of the first lens G1 ( Figure 1 The vertex of the left surface of the first lens G1 to the rear surface of the rear group S3 ( Figure 1 The distance between the vertex of the right surface of the ninth lens G9 and the vertex of the lens is L. L and f satisfy the relationship: 0.7 < |L / f| < 1.50.

[0053] Specifically, the middle group S2 includes a second lens G2 with negative optical power, a third lens G3 with positive optical power, a fourth lens G4 with negative optical power, a fifth lens G5 with positive optical power, and a sixth lens G6 with negative optical power; the second lens G2, the third lens G3, and the fourth lens G4 are cemented together to form a first cemented lens group U1 with negative optical power, and the fifth lens G5 and the sixth lens G6 are cemented together to form a second cemented lens group U2 with positive optical power;

[0054] The focal length of the first cemented lens group U1 is f U1 f U1 The relationship between f and is: 0.65 < |f U1 / f|<1.15;

[0055] The focal length of the second cemented lens group U2 is f U2 f U2 The relationship between f and 1 is: 1.8 < |f U2 / f|<3.80.

[0056] Specifically, the second lens G2 is a meniscus lens, the third lens G3 and the fifth lens G5 are both biconvex lenses, the fourth lens G4 is a meniscus lens or a biconcave lens, and the sixth lens G6 is a biconcave lens.

[0057] Specifically, the rear group S3 includes a seventh lens G7 with negative optical power, an eighth lens G8 with positive optical power, a ninth lens G9 with negative optical power, and a tenth lens G10 with positive optical power; the seventh lens G7 and the eighth lens G8 are cemented together to form a third cemented lens group U3 with positive optical power.

[0058] The focal length of the third cemented lens group U3 is f U3 f U3 The relationship between f and 1 is: 1.00 < |f U3 / f|<2.50;

[0059] The focal length of the ninth lens G9 is f G9 f G9 The relationship between f and f is: 0.18 < |f G9 / f|<0.40;

[0060] The focal length of the tenth lens G10 is f G10f G10 The relationship between f and f is: 0.25 < |f G10 / f|<0.60.

[0061] Specifically, the seventh lens G7 and the ninth lens G9 are both biconcave lenses, the eighth lens G8 is a biconvex lens, and the tenth lens G10 is a meniscus lens or a plano-convex lens.

[0062] Specifically, the first lens G1, the second lens G2, the third lens G3, the fourth lens G4, the fifth lens G5, the sixth lens G6, the seventh lens G7, the eighth lens G8, the ninth lens G9, and the tenth lens G10 are all spherical mirrors, and the optical axes of all the spherical mirrors coincide with the predetermined optical axis.

[0063] Specifically, the aperture of stop A0 is a circular aperture, and the center of the circular aperture is on the predetermined optical axis; the aperture value of stop A0 can be adjusted from F2.8 to F16.

[0064] More specifically, the aperture of the stop A0 is set as a circular hole, and the center of the circular hole is on the predetermined optical axis;

[0065] In this embodiment, the aperture value of the aperture stop A0 can be adjusted, and the adjustment range of the aperture value is F2.8 to F16.

[0066] The following are specific application examples of optical systems employing the above structure:

[0067] Example 1:

[0068] In this example, the relevant data for the optical system are shown in Table 1;

[0069] Table 1

[0070] surface Radius (mm) Thickness (mm) Refractive index G1 front surface 79.72 4.14 1.81 G1 rear surface -342.19 24.66 　 U1 front surface 165.84 1.50 1.85 U1 Adhesive Surface 1 27.05 6.57 1.60 U1 Adhesive Surface Two -36.51 1.50 1.81 U1 rear surface -239.6 0.20 　 U2 front surface 32.1 5.64 1.65 U2 adhesive surface -35.05 1.50 1.65 U2 rear surface 32.83 2.84 　 aperture flat 31.11 　 U3 front surface -53.41 1.50 1.71 U3 adhesive surface 24.74 4.61 1.69 U3 rear surface -40.11 36.97 　 G9 front surface -78.91 1.50 1.50 G9 rear surface 26.96 31.09 　 G10 front surface 28.63 3.01 1.53 G10 rear surface 98.4 23.12 　 Image flat

[0071] It should be noted that in Table 1, "front surface" corresponds to... Figure 1 The left surface of the lens or lens group corresponds to the middle surface, while the rear surface corresponds to the left surface. Figure 1 The middle corresponds to the right surface of the lens or lens group; that is, the "front" corresponds to... Figure 1 On the left, "after" corresponds Figure 1 On the right side.

[0072] In this example, the focal length f of the optical system is 152.27 mm, the object-side numerical aperture NA = 0.06, and the focal length f of the front group S1 is... S1 =80.18mm, the focal length f of the middle group S2 S2 =-209.60mm, the focal length f of the rear group S3 S3=1010.07mm, the distance L from the vertex of the front surface of the first lens G1 to the imaging plane is 171.84mm, the optical back focal length BFL is 23.12mm, the half-image height y' is 9.66mm, and the focal length f of the first cemented lens group is... U1 =-155.00mm, focal length f of the second cemented lens group U2 =457.64mm, focal length f of the third cemented lens group U3 =252.89mm, the focal length f of the ninth lens G9 G9 =-40.00mm, the focal length f of the tenth lens G10 G10 =75.06mm.

[0073] Substituting the above values ​​into the corresponding relations, we obtain:

[0074] |f S1 / f|=0.53;|f S2 / f|=1.38;|f S3 / f|=6.63; |L / f|=1.13; |BFL / f|=0.15; |y' / f|=0.06; |f U1 / f|=1.02;|f U2 / f|=3.01;|f U3 / f|=1.66;|f G9 / f|=0.26;|f G10 / f|=0.49.

[0075] The obtained values ​​satisfy the respective relations, as shown below:

[0076] 0.4<|f S1 / f|<0.75; 1.1<|f S2 / f|<1.7; 1.50<|f S3 / f|<8.00; 0.7<|L / f |<1.50; 0.05<|BFL / f|<0.60; |y' / f|<0.12; 0.65<|f U1 / f|<1.15;1.8<|f U2 / f|<3.80;

[0077] 1.00 < |f U3 / f| < 2.50; 0.18 < |f G9 / f| < 0.40; 0.25 < |f G10 / f|<0.60.

[0078] Please continue to refer to this. Figure 2 , Figure 2This is the optical distortion curve of an optical system for a compact, long-working-distance fixed-magnification lens provided in an embodiment of the present invention, such as... Figure 2 As shown, the maximum optical distortion across the entire field of view is less than 0.10%.

[0079] Example 2:

[0080] Please refer to Figure 3 , Figure 3 This is a schematic diagram of the optical system of another compact long working distance fixed magnification lens provided in an embodiment of the present invention.

[0081] In this example, the relevant data for the optical system are shown in Table 2;

[0082] Table 2

[0083] surface Radius (mm) Thickness (mm) Refractive index G1 front surface 80.68 3.88 1.81 G1 rear surface -738.6 27.80 　 U1 front surface 45.9 1.50 1.90 U1 Adhesive Surface 1 24.22 6.51 1.55 U1 Adhesive Surface Two -43.57 1.52 1.67 U1 rear surface 70.02 1.15 　 U2 front surface 31.65 5.09 1.68 U2 adhesive surface -40.06 1.50 1.69 U2 rear surface 33.69 1.62 　 aperture flat 30.89 　 U3 front surface -52.14 1.50 1.71 U3 adhesive surface 31.77 4.24 1.72 U3 rear surface -41.81 49.50 　 G9 front surface -20.2 1.50 1.50 G9 rear surface 2070 19.61 　 G10 front surface -291.4 9.99 1.58 G10 rear surface -35.14 13.60 　 Image flat

[0084] It should be noted that in Table 2, "front surface" corresponds to... Figure 3 The left surface of the lens or lens group corresponds to the middle surface, while the rear surface corresponds to the left surface. Figure 3 The middle corresponds to the right surface of the lens or lens group; that is, the "front" corresponds to... Figure 3 On the left, "after" corresponds Figure 3 On the right side.

[0085] In this example, the focal length f of the optical system is 168.09 mm, the object-side numerical aperture NA = 0.06, and the focal length f of the front group S1 is... S1 =89.99mm, the focal length f of the middle group S2 S2 =-219.11mm, the focal length f of the rear group S3 S3 =369.06mm, the distance L from the vertex of the front surface of the first lens G1 to the imaging plane is 181.30mm, the optical back focal length BFL is 13.060mm, the half-image height y' is 9.66mm, and the focal length f of the first cemented lens group is... U1 =-155.06mm, focal length f of the second cemented lens group U2 =401.56mm, focal length f of the third cemented lens group U3 =213.11mm, the focal length f of the ninth lens G9 G9 =-40.00mm, the focal length f of the tenth lens G10 G10 =67.92mm.

[0086] Substituting the above values ​​into the corresponding relations, we obtain:

[0087] |f S1 / f|=0.54;|f S2 / f|=1.30;|f S3 / f|=2.20; |L / f|=1.08; |BFL / f|=0.08; |y' / f|=0.06; |f U1 / f|=0.92;|f U2 / f|=2.39;|f U3 / f|=1.27;|f G9 / f|=0.24;|f G10 / f|=0.40.

[0088] The obtained values ​​satisfy the respective relations, as shown below:

[0089] 0.4<|f S1 / f|<0.75; 1.1<|f S2 / f|<1.7; 1.50<|f S3 / f|<8.00; 0.7<|L / f |<1.50; 0.05<|BFL / f|<0.60; |y' / f|<0.12; 0.65<|f U1 / f|<1.15;1.8<|f U2 / f|<3.80;

[0090] 1.00 < |f U3 / f| < 2.50; 0.18 < |f G9 / f| < 0.40; 0.25 < |f G10 / f|<0.60.

[0091] Please continue to refer to this. Figure 4 , Figure 4 This is the optical distortion curve of another compact long working distance fixed magnification lens optical system provided in the embodiments of the present invention, such as... Figure 4 As shown, the maximum optical distortion across the entire field of view is less than 0.12%.

[0092] This embodiment achieves an optical system for a low-distortion, high-resolution fixed-magnification lens through the above structure. The object-side NA number is 0.06, the lens magnification is 0.94X, the maximum imaging surface is φ19.2mm, the maximum resolution can reach 100lp / mm, it can be matched with a 5-micron pixel chip, and at the corresponding maximum chip size, its pixel count can reach seven million pixels. The maximum optical distortion across the entire field of view can be as low as less than 0.10%. The working distance can reach 264mm, and its aperture can also be flexibly adjusted. Example 2

[0093] This embodiment provides a compact long working distance fixed magnification lens, including a focusing structure and an optical system as described in Embodiment 1;

[0094] The focusing structure is used to drive the first lens group S1, the aperture A0, and the second lens group S2 together along a predetermined optical axis to move closer to or further away from the third lens group S3 in order to achieve focusing.

[0095] Since the optical system has been described in detail in Embodiment 1, it will not be repeated in this embodiment.

[0096] In summary, this embodiment achieves a long working distance fixed-magnification lens with high resolution, a lens magnification of 0.94X, a maximum resolution of 100 lp / mm, compatibility with 5-micron pixel chips, a maximum target surface size of 1.2″, and low distortion performance.

[0097] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An optical system for a compact, long-working-distance fixed-magnification lens, characterized in that, It consists of a front group with positive optical power, a middle group with negative optical power, an aperture stop, and a rear group with positive optical power, arranged sequentially from the object side to the image side. The front group consists of a first lens with positive optical power; the middle group consists of a second lens with negative optical power, a third lens with positive optical power, a fourth lens with negative optical power, a fifth lens with positive optical power, and a sixth lens with negative optical power; the rear group consists of a seventh lens with negative optical power, an eighth lens with positive optical power, a ninth lens with negative optical power, and a tenth lens with positive optical power; the second, third, and fourth lenses are cemented together to form a first cemented lens group with negative optical power; the fifth and sixth lenses are cemented together to form a second cemented lens group with positive optical power; and the seventh and eighth lenses are cemented together to form a third cemented lens group with positive optical power. The optical system has a focal length f, a back focal length BFL, and a front focal length f. S1 The focal length of the middle group is f S2 The focal length of the rear element is f. S3 They respectively satisfy the following relation: 0.4<|f S1 / f|<0.75,1.1<|f S2 / f|<1.7,1.50<|f S3 / f|<8.00,0.05<| BFL / f |<0.35。 2. The optical system of a compact long working distance fixed-magnification lens according to claim 1, characterized in that, The first lens is a biconvex lens; The distance from the vertex of the front surface of the first lens to the vertex of the rear surface of the rear group is L, and L and f satisfy the relationship: 0.7 < |L / f| < 1.

50.

3. The optical system of a compact long working distance fixed-magnification lens according to claim 2, characterized in that, The focal length of the first cemented lens group is f. U1 f U1 The relationship between f and is: 0.65 < |f U1 / f|<1.15; The focal length of the second cemented lens group is f. U2 f U2 The relationship between f and 1 is: 1.8 < |f U2 / f|<3.

80.

4. The optical system of a compact long working distance fixed-magnification lens according to claim 3, characterized in that, The second lens is a meniscus lens, the third and fifth lenses are both biconvex lenses, the fourth lens is either a meniscus lens or a biconcave lens, and the sixth lens is a biconcave lens.

5. The optical system of a compact long working distance fixed-magnification lens according to claim 3, characterized in that, The focal length of the third cemented lens group is f. U3 f U3 The relationship between f and 1 is: 1.00 < |f U3 / f|<2.50; The focal length of the ninth lens is f G9 f G9 The relationship between f and f is: 0.18 < |f G9 / f|<0.40; The focal length of the tenth lens is f G10 f G10 The relationship between f and f is: 0.25 < |f G10 / f|<0.

60.

6. The optical system of a compact long working distance fixed-magnification lens according to claim 5, characterized in that, The seventh and ninth lenses are both biconcave lenses, the eighth lens is a biconvex lens, and the tenth lens is a meniscus lens or a plano-convex lens.

7. The optical system of a compact long working distance fixed-magnification lens according to claim 5, characterized in that, The first lens, second lens, third lens, fourth lens, fifth lens, sixth lens, seventh lens, eighth lens, ninth lens and tenth lens are all spherical mirrors, and the optical axes of all spherical mirrors coincide with the predetermined optical axis.

8. The optical system of a compact long working distance fixed-magnification lens according to claim 1, characterized in that, The half-image height of the optical system is y'; The relationship between y' and f is: |y' / f| < 0.

12.

9. The optical system of a compact long working distance fixed-magnification lens according to claim 7, characterized in that, The aperture of the stop is a circular hole, and the center of the circular hole is on the predetermined optical axis; the aperture value of the stop can be adjusted from F2.8 to F16.

10. A compact, long-working-distance fixed-magnification lens, characterized in that, Including the optical system of a compact long working distance fixed magnification lens as described in any one of claims 1-9; The compact long working distance fixed magnification lens has a magnification of 0.94X.

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