A long working distance double telecentric lens and optical system thereof

Abstract

The application relates to the technical field of machine vision lenses, and discloses a long-working-distance double-telecentric lens and an optical system thereof. The optical system is sequentially provided with a front group A with positive focal power, an aperture S and a rear group B with positive focal power from an object side to an image side; the front group A and the rear group B are respectively composed of a plurality of lenses, and the optical axes of all the lenses are coincident with a predetermined optical axis; 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 satisfy the relationship formula: 0.25 < |f A / f B | < 0.7. Compared with a standard object-side telecentric lens, the long-working-distance double-telecentric lens provided by the application has a longer working distance and better imaging effect through reasonable lens combination and focal length matching, and is suitable for long-working-distance high-precision detection application scenarios.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of machine vision lens, and in particular to a long working distance double telecentric lens and an optical system thereof. BACKGROUND

[0002] In a machine vision precision optical measurement system, using a common industrial lens can cause problems such as different magnification, parallax, and large distortion due to changes in object distance, which is difficult to meet high detection requirements. A telecentric lens can reduce or even eliminate the above problems. It can keep the image magnification constant within a certain object distance range. Its principle advantage makes it very suitable for precision measurement and detection fields such as semiconductor, 3C electronics, new energy, packaging and printing, intelligent logistics, automobile manufacturing, and pharmaceutical product measurement and judgment, defect detection.

[0003] Most small-size telecentric lenses on the market have a working distance of 65mm and 110mm, which are two standard distances. However, the standard working distance cannot meet the needs of some use scenarios, and a small working distance is also prone to interference with other modules such as illumination light sources. A long working distance is beneficial for light path folding and realization of more complex multi-view detection. Therefore, there is an urgent need for telecentric lens products with longer working distances.

[0004] The above information is given as background information only to assist with an understanding of the present disclosure, and does not constitute admission or recognition that any of the above information constitutes prior art with respect to the present disclosure. SUMMARY

[0005] The present application aims to provide a long working distance double telecentric lens and an optical system thereof to solve or at least partially solve the technical problems existing in the prior art.

[0006] To achieve this purpose, the present application adopts the following technical solutions:

[0007] In a first aspect, the present application provides an optical system of a long working distance double telecentric lens, comprising a front group A with positive focal power, an aperture S, and a rear group B with positive focal power arranged in order from the object side to the image side; the front group A and the rear group B are respectively composed of a plurality of lenses, and the optical axes of all the lenses coincide with a predetermined optical axis; wherein 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 satisfy the relationship: 0.25<|f B / f A |<0.7.

[0008] 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 positive optical power, and a fourth lens G4 with negative optical power; the rear group B includes a fifth lens G5 with negative optical power, a sixth lens G6 with positive optical power, and a seventh lens G7 with positive optical power.

[0009] Optionally, the third lens G3 and the fourth lens G4 are cemented together to form a first cemented lens group U1;

[0010] The focal length of the first lens G1 is f G1 , f G1 With f A Satisfies the relationship: 1.4<|f G1 / f A |<1.9;

[0011] The focal length of the second lens G2 is f G2 , f G2 With f A Satisfies the relationship: 0.75<|f G2 / f A |<1.25;

[0012] The focal length of the first cemented lens group U1 is f U1 , f U1 With f A Satisfies the relationship: 0.2<|f U1 / f A |<0.6.

[0013] Optionally, the first lens G1 and the second lens G2 are meniscus lenses, the third lens G3 is a biconvex lens, and the fourth lens G4 is a biconcave lens;

[0014] The center distance between the first lens G1 and the second lens G2 is smaller than the center distance between the second lens G2 and the third lens G3.

[0015] Optionally, the first lens G1 is made of a high-dispersion glass material, and the Abbe number of the first lens G1 is less than or equal to 35; the second lens G2 is made of a low-dispersion glass material, and the Abbe number of the second lens G2 is greater than or equal to 60.

[0016] Optionally, the fifth lens G5 and the sixth lens G6 are cemented together to form a second cemented lens group U2;

[0017] The focal length of the second cemented lens group U2 is f U2 , f U2 With f B Satisfies the relationship: |f B / f U2 |<0.45; the focal length of the seventh lens G7 is f G7, f G7 With f B The following relationship is satisfied: 0.9<|f G7 / f B |<1.7.

[0018] Optionally, the fifth lens G5 is a biconcave lens, and the sixth lens G6 and the seventh lens G7 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, the sixth lens G6 and the seventh lens G7 form a double telecentric structure, and the working distance of the double telecentric structure is greater than 250 mm and the telecentricity is less than 0.1°.

[0020] Optionally, the aperture of the diaphragm S is a circular hole, and the center of the circular hole is on the predetermined optical axis.

[0021] In a second aspect, the present invention provides a long working distance bi-telecentric lens, including an optical system of the long working distance bi-telecentric lens as described above.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The long-working-distance bi-telecentric lens provided by the present invention has a longer working distance of up to 250mm or more compared to a standard object-space telecentric lens through reasonable lens combination and focal length matching. The bi-telecentric lens also has better imaging effects and is suitable for application scenarios of high-precision detection over longer distances.

[0024] The present invention has other features and advantages that will be apparent from or will be described in detail in the accompanying drawings and the following detailed description incorporated herein, which together serve to explain certain principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 The figure is a schematic structural diagram of an optical system of a long working distance bi-telecentric lens provided by an embodiment of the present invention.

[0027] Figure 24 is an MTF curve diagram of an optical system of a long working distance bi-telecentric lens provided by an embodiment of the present invention.

[0028] Figure 3 Schematic diagram of the structure of another optical system of a long working distance bi-telecentric lens provided by an embodiment of the present invention.

[0029] Figure 4 4 is an MTF curve diagram of an optical system of another long working distance bi-telecentric lens provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0030] In order to explain in detail the possible application scenarios, technical principles, specific solutions that can be implemented, and the purpose and effects of this application, the following is a detailed description of the specific embodiments listed in conjunction with the accompanying drawings. The embodiments described herein are only used to more clearly illustrate the technical solutions of this application and are therefore only examples and are not intended to limit the scope of protection of this application.

[0031] References to "embodiments" herein mean that the specific features, structures, or characteristics described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the word "embodiment" 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 are no technical contradictions or conflicts, the various technical features mentioned in the embodiments can be combined in any manner to form a corresponding implementable technical solution.

[0032] Unless otherwise defined, the technical terms used herein have the same meanings as those generally understood by those skilled in the art to which this application belongs; the use of relevant terms herein is only for describing specific embodiments and is not intended to limit this application.

[0033] In the description of this application, the term "and / or" is used to describe a logical relationship between objects, indicating that three relationships can exist. For example, A and / or B means: A exists, B exists, and both A and B exist. In addition, the character " / " in this document generally indicates that the objects before and after are in a logical "or" relationship.

[0034] In this application, terms such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual quantity, priority or sequence relationship between these entities or operations.

[0035] Without further limitations, in this application, the words "include", "comprise", "have" or other similar expressions used in the sentences are intended to cover non-exclusive inclusion. These expressions do not exclude the presence of additional elements in the process, method or product including the elements, so that the process, method or product including a series of elements may include not only those defined elements, but also other elements not explicitly listed, or elements inherent to such process, method or product.

[0036] Consistent with the understanding in the Examination Guidelines, in this application, expressions such as "greater than," "less than," and "exceed" are understood to exclude the number itself; expressions such as "above," "below," and "within" are understood to include the number itself. Furthermore, in the description of the embodiments of this application, "multiple" means more than two (including two), and similar expressions related to "multiple" are also understood in this manner, such as "multiple groups," "multiple times," etc., unless otherwise specifically defined.

[0037] In the description of the embodiments of the present application, the space-related expressions used, such as "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "vertical", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicate the orientation or position relationship based on the orientation or position relationship shown in the specific embodiments or drawings, and are only for the convenience of describing the specific embodiments of the present application or facilitating 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, it should not be understood as a limitation on the embodiments of the present application.

[0038] Unless otherwise expressly specified or limited, in the description of the embodiments of the present application, the terms "installed", "connected", "connected", "fixed", "set", etc. used should be understood in a broad sense. For example, the "connection" can be a fixed connection, a detachable connection, or an integrated 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 elements or the interaction relationship between two elements. For those skilled in the art of the present application, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0039] Example 1:

[0040] See also Figure 1 , Figure 1 The figure is a schematic structural diagram of an optical system of a long working distance bi-telecentric lens provided by an embodiment of the present invention.

[0041] like Figure 1 As shown, the optical system includes:

[0042] A front lens group A with positive optical power, an aperture S, and a rear lens group B with positive optical power are arranged in sequence from the object side to the image side. The front lens group A and the rear lens group B are each composed of a plurality of lenses, and the optical axes of all the lenses coincide with the predetermined optical axis.

[0043] The front lens group A includes a first lens G1 with positive refractive power, a second lens G2 with positive refractive power, a third lens G3 with positive refractive power, and a fourth lens G4 with negative refractive power; the rear lens group B includes a fifth lens G5 with negative refractive power, a sixth lens G6 with positive refractive power, and a seventh lens G7 with positive refractive power;

[0044] The aperture is arranged between the fourth lens G4 and the fifth lens G5, forming a double telecentric structure of the optical system.

[0045] Furthermore, the combined focal length of the front group A and the rear group B both have positive optical power; specifically, 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: 0.25<|f B / f A |<0.7;

[0046] The focal length of the first lens G1 is f G1 , f G1 With f A Satisfies the relationship: 1.4<|f G1 / f A |<1.9.

[0047] In this embodiment, the first lens element G1 is made of a high-refractive-index, high-dispersion glass material. For telecentric lenses, increasing the working distance causes light rays to fall at a higher altitude on the first lens element G1. Choosing a high-refractive-index lens material can reduce the incident angle of light and lower tolerance sensitivity. Specifically, in this embodiment, the Abbe number of the first lens element G1 is less than or equal to 35.

[0048] The focal length of the second lens G2 is f G2 , f G2 With f A Satisfies the relationship: 0.75<|f G2 / f A |<1.25; the second lens element G2 is made of a low-dispersion glass material. Specifically, in this embodiment, the Abbe number of the second lens element G2 is greater than or equal to 60; the center distance between the first lens element G1 and the second lens element G2 is less than the center distance between the second lens element G2 and the third lens element G3.

[0049] The third lens G3 and the fourth lens G4 are cemented together to form a first cemented lens group U1;

[0050] The focal length of the first cemented lens group U1 is f U1 , f U1 With f A Satisfies the relationship: 0.2<|f U1 / f A |<0.6.

[0051] In this embodiment, the center spacing between the first lens G1 and the second lens G2 is relatively small, and they bear a greater deflection and refraction effect, which helps reduce the overall length of the lens optical system. Since the deflection and refraction power is shared by two lenses, the degree of light deflection through the lenses can be alleviated, effectively reducing aberrations. The second lens G2 maintains a large center spacing with the cemented lens group U1, so that light of different wavelengths forms different height differences on the cemented lens group U1, which helps correct the spherical aberration of the optical system.

[0052] Furthermore, the fifth lens G5 and the sixth lens G6 are cemented together to form a second cemented lens group U2;

[0053] The focal length of the second cemented lens group U2 is f U2 , f U2 With f B Satisfies the relationship: |f B / f U2 |<0.45;

[0054] The focal length of the seventh lens G7 is f G7 , f G7 With f B The following relationship is satisfied: 0.9<|f G7 / f B |<1.7.

[0055] In this embodiment, the first cemented lens group U1 and the second cemented lens group U2 can correct chromatic aberration and field curvature, and the two cemented surfaces can correct astigmatism. Since the first cemented lens group U1 has negative optical focal length, the first lens G1 and the second lens G2 can be equivalent to positive optical focal length lenses, thereby forming a telephoto system structure, which plays an important role in achieving a long working distance.

[0056] Specifically, in this embodiment, the first lens G1 and the second lens G2 are meniscus lenses, the third lens G3 is a biconvex lens, and the fourth lens G4 is a biconcave lens; the fifth lens G5 is a biconcave lens, and the sixth lens G6 and the seventh lens G7 are both biconvex lenses;

[0057] As an optional implementation, the aperture of the diaphragm S is a circular hole, and the center of the circular hole is on the predetermined optical axis. It can be understood that the aperture value of the diaphragm S needs to be adjusted according to the specific application scenario.

[0058] In this embodiment, the first lens G1, the second lens G2, the third lens G3, the fourth lens G4, the fifth lens G5, the sixth lens G6, and the seventh lens G7 are constructed into a double-telecentric structure, and the working distance of the double-telecentric structure is greater than 250 mm, and the telecentricity is less than 0.1°.

[0059] The following is a specific embodiment according to the above settings of the present embodiment, and the related data of the optical system is specifically shown in Table 1:

[0060] Table 1

[0061] Surface Radius (mm) Thickness (mm) Refractive index Abbe number G1 front surface 187.6 8.7 2.0 20 G1 rear surface 1048.3 8.0 G2 front surface 72.8 13.5 1.60 60 G2 rear surface 441.4 33.2 G3 front surface 39.2 10.2 1.70 - G3, G4 cementing surface -96.3 13.0 1.85 - G4 rear surface 16.5 28.5 Stop S ∞ 3.1 G5 front surface -36.1 4.2 1.70 - G5, G6 cementing surface 30.6 6.5 1.60 - G6 rear surface -22.6 44.3 G7 front surface 124.0 8.6 1.85 - G7 rear surface -106.0 59.2 Image surface /

[0062] It should be noted that in Table 1, the "front surface" corresponds to the left surface of the lens or lens group in Figure 1 , and the "back surface" corresponds to the right surface of the lens or lens group in Figure 1 ; or it can be understood that: the object side is on the left side, and the image side (or image surface) is on the right side, the side surface close to the object side is the "front surface", and the side surface close to the image side is the "back surface". Figure 1 Figure 1

[0063] In this example, the focal length of the first lens G1 is f G1 = 229 mm; the focal length of the second lens G2 is f G2 = 143 mm; the focal length of the first cemented lens group U1 is f U1 = -42 mm; the focal length of the second cemented lens group U2 is f U2 = 135 mm; the focal length of the seventh lens G7 is f G7 = 68 mm; the combined focal length of the front group A is f A = 138 mm; and the combined focal length of the rear group B is f B = 52 mm.

[0064] Substituting the above values into each relationship, we get:

[0065] |f B / f A | = 0.38, |f G1 / f A | = 1.66, |f G2 / f A | = 1.04, |f U1 / f A | = 0.30, and |f B ​​ / f U2 |=0.39,|f G7 / f B |=1.31;

[0066] Therefore, the relevant relationship of this embodiment is satisfied, namely:

[0067] 0.25<|f B / f A |<0.7, 1.4<|f G1 / f A |<1.9,0.75<|f G2 / f A |<1.25, 0.2<|f U1 / f A |<0.6,|f B / f U2 |<0.45,0.9<|f G7 / f B |<1.7.

[0068] Please continue to refer to Figure 2 , Figure 2 This is an MTF (Modulation Transfer Function) curve of an optical system of a long working distance bi-telecentric lens provided by an embodiment of the present invention. The maximum resolution can reach 250lp / mm, which can match a 3.45μm pixel chip.

[0069] The above lenses form an optical system with a double telecentric structure, with a working distance of 254mm, a magnification of 0.4 times, a telecentricity of less than 0.1°, a maximum imaging surface of Φ18.4mm, and supports 1.1-inch target surface cameras.

[0070] Example 2:

[0071] See also Figure 3 , Figure 3 Schematic diagram of the structure of another optical system of a long working distance bi-telecentric lens provided by an embodiment of the present invention.

[0072] like Figure 3 As shown, the optical system includes:

[0073] A front lens group A with positive optical power, an aperture S, and a rear lens group B with positive optical power are arranged in sequence from the object side to the image side. The front lens group A and the rear lens group B are each composed of a plurality of lenses, and the optical axes of all the lenses coincide with the predetermined optical axis.

[0074] The front group A includes a first lens G1 with positive refractive power, a second lens G2 with positive refractive power, a third lens G3 with positive refractive power, and a fourth lens G4 with negative refractive power; the rear group B includes a fifth lens G5 with negative refractive power, a sixth lens G6 with positive refractive power, and a seventh lens G7 with positive refractive power.

[0075] The diaphragm is arranged between the fourth lens G4 and the fifth lens G5, forming a double-telecentric structure of the optical system.

[0076] Further, the combined focal lengths of the front group A and the rear group B both have positive refractive power; specifically, 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 B satisfy the relationship: 0.25 < |f B / f A | < 0.7.

[0077] The focal length of the first lens G1 is f G1 , f G1 and f A satisfy the relationship: 1.4 < |f G1 / f A | < 1.9.

[0078] In the embodiment, the first lens G1 adopts a glass material with high refractive index and high dispersion; for a telecentric lens, the working distance increases, causing the height at which the light falls on the first lens G1 to also increase, and selecting a high-refractive-index lens material can reduce the light incidence angle and reduce the tolerance sensitivity. Specifically, in the embodiment, the Abbe number of the first lens G1 is less than or equal to 35.

[0079] The focal length of the second lens G2 is f G2 , f G2 and f A satisfy the relationship: 0.75 < |f G2 / f A | < 1.25; the second lens G2 is made of a low-dispersion glass material, and specifically, in the embodiment, the Abbe number of the second lens G2 is greater than or equal to 60; the center-to-center spacing of the first lens G1 and the second lens G2 is less than the center-to-center spacing of the second lens G2 and the third lens G3.

[0080] The third lens G3 and the fourth lens G4 are cemented to form a first cemented lens group U1;

[0081] The focal length of the first cemented lens group U1 is f U1 , f U1 and f A satisfy the relationship: 0.2 < |f U1 / fA |<0.6.

[0082] In this embodiment, the center spacing between the first lens G1 and the second lens G2 is relatively small, and they bear a greater deflection and refraction effect, which helps reduce the overall length of the lens optical system. Since the deflection and refraction power is shared by two lenses, the degree of light deflection through the lenses can be alleviated, effectively reducing aberrations. The second lens G2 maintains a large center spacing with the cemented lens group U1, so that light of different wavelengths forms different height differences on the cemented lens group U1, which helps correct the spherical aberration of the optical system.

[0083] Furthermore, the fifth lens G5 and the sixth lens G6 are cemented together to form a second cemented lens group U2;

[0084] The focal length of the second cemented lens group U2 is f U2 , f U2 With f B Satisfies the relationship: |f B / f U2 |<0.45;

[0085] The focal length of the seventh lens G7 is f G7 , f G7 With f B The following relationship is satisfied: 0.9<|f G7 / f B |<1.7.

[0086] In this embodiment, the first cemented lens group U1 and the second cemented lens group U2 can correct chromatic aberration and field curvature, and the two cemented surfaces can correct astigmatism. Since the first cemented lens group U1 has negative optical focal length, the first lens G1 and the second lens G2 can be equivalent to positive optical focal length lenses, thereby forming a telephoto system structure, which plays an important role in achieving a long working distance.

[0087] Specifically, in this embodiment, the first lens G1 and the second lens G2 are meniscus lenses, the third lens G3 is a biconvex lens, and the fourth lens G4 is a biconcave lens; the fifth lens G5 is a biconcave lens, and the sixth lens G6 and the seventh lens G7 are both biconvex lenses;

[0088] As an optional embodiment, the aperture of the diaphragm S is set as a circular hole, and the center of the circular hole is on the predetermined optical axis. It is understandable that the aperture value of the diaphragm S needs to be adjusted accordingly according to the specific application scenario.

[0089] In this embodiment, the first lens G1, the second lens G2, the third lens G3, the fourth lens G4, the fifth lens G5, the sixth lens G6 and the seventh lens G7 form a double-telecentric structure. The working distance of the double-telecentric structure is greater than 250 mm and the telecentricity is less than 0.1°.

[0090] The following is a specific embodiment based on the above-mentioned configuration of this embodiment, and the relevant data of the optical system are shown in Table 2:

[0091] Table 2

[0092] Surface Radius (mm) Thickness (mm) Refractive index Abbe number G1 front surface 164.5 11.1 1.95 18 G1 rear surface 440.8 1.0 G2 front surface 82.4 13.5 1.50 65 G2 rear surface 7296.9 35.4 G3 front surface 43.8 10.2 1.65 55 G3, G4 cementing surface -106.9 12.9 1.80 - G4 rear surface 24.7 42.9 Stop S ∞ 2.4 G5 front surface -24.7 7.6 1.70 - G5, G6 cementing surface 36.4 6.4 1.58 - G6 rear surface -23.1 56.8 G7 front surface 115.4 5.2 2.0 25 G7 rear surface -217.4 70.6 Image surface /

[0093] It should be noted that in Table 1, the “front surface” corresponds to Figure 3 The left side surface of the lens or lens group corresponds to the "back surface" Figure 3 The right side surface of the corresponding lens or lens group; or it can be understood as: the object side is Figure 3 On the left, the image side (or image plane) is Figure 1 On the right, the surface closer to the object side is the "front surface" and the surface closer to the image side is the "back surface".

[0094] In this example, the focal length of the first lens G1 is f G1 =267mm; the focal length of the second lens G2 is f G2 =166mm; the focal length of the first cemented lens group U1 is f U1 =-77mm; the focal length of the second cemented lens group U2 is f U2 =-1643mm; the focal length of the seventh lens G7 is f G7 =75mm; the combined focal length of the front group A is f A =147mm; the combined focal length of the rear group B is f B =60mm;

[0095] Substituting the above values ​​into each relational expression, we can obtain:

[0096] |f B / f A |=0.41,|f G1 / f A |=1.82,|f G2 / f A |=1.13,|f U1 / f A |=0.52,|f B / f U2 |=0.04,|f G7 / f B |=1.25;

[0097] Therefore, the relevant relationship of this embodiment is satisfied, namely:

[0098] 0.25<|f B / f A |<0.7, 1.4<|f G1 / fA |<1.9,0.75<|f G2 / f A |<1.25, 0.1<|f U1 / f A |<0.6,|f B / f U2 |<0.45,0.9<|f G7 / f B |<1.7.

[0099] Please continue to refer to Figure 4 , Figure 4 This is an MTF curve diagram of an optical system of another long working distance bi-telecentric lens provided by an embodiment of the present invention. The maximum resolution can reach 150lp / mm, which is high enough to match a 3.45μm pixel chip.

[0100] The optical system with a double telecentric structure formed by the above-mentioned lenses has a working distance of 335 mm, which is longer than that of Example 1; the magnification is 0.41 times, and it is a double telecentric structure with a telecentricity of less than 0.1°. The maximum imaging surface is Φ16 mm, supporting a 1-inch target surface camera.

[0101] Example 3:

[0102] This embodiment provides a long working distance bi-telecentric lens, comprising an optical system of a long working distance bi-telecentric lens as described in the first or second embodiment;

[0103] Since the optical system has been described in detail in the above embodiment, it will not be described again in this embodiment.

[0104] In summary, the embodiment of the present invention has a longer working distance and better double-telecentric imaging effect through reasonable lens combination and focal length matching compared to the standard object-space telecentric lens, and can be applied to application scenarios of high-precision detection at longer distances.

[0105] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some of the technical features thereof can be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An optical system with a long working distance bi-telecentric lens, characterized in that: It consists of a front lens group A with positive focal power, an aperture S, and a rear lens group B with positive focal power, which are arranged in sequence from the object side to the image side. The front lens group A and the rear lens group B are each composed of several lenses, and the optical axes of all lenses coincide with the predetermined optical axis. The combined focal length of the front lens 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: 0.25<|f B / f A |<0.7; The front lens group A consists of a first lens G1 with positive refractive power, a second lens G2 with positive refractive power, a third lens G3 with positive refractive power, and a fourth lens G4 with negative refractive power. The rear lens group B consists of a fifth lens G5 with negative refractive power, a sixth lens G6 with positive refractive power, and a seventh lens G7 with positive refractive power. The focal length of the second lens G2 is f G2 , f G2 With f A Satisfies the relationship: 0.75<|f G2 / f A |<1.25; the third lens G3 and the fourth lens G4 are cemented to form a first cemented lens group U1; the fifth lens G5 and the sixth lens G6 are cemented to form a second cemented lens group U2, and the focal length of the second cemented lens group U2 is f U2 , f U2 With f B Satisfies the relationship: |f B / f U2 |<0.

45.

2. The optical system of a long working distance bi-telecentric lens according to claim 1, characterized in that: The focal length of the first lens G1 is f G1 , f G1 With f A Satisfies the relationship: 1.4<|f G1 / f A |<1.9; The focal length of the first cemented lens group U1 is f U1 , f U1 With f A Satisfies the relationship: 0.2<|f U1 / f A |<0.

6.

3. The optical system of a long working distance bi-telecentric lens according to claim 2, characterized in that: The first lens G1 and the second lens G2 are meniscus lenses, the third lens G3 is a biconvex lens, and the fourth lens G4 is a biconcave lens; The center distance between the first lens G1 and the second lens G2 is smaller than the center distance between the second lens G2 and the third lens G3.

4. The optical system of a long working distance bi-telecentric lens according to claim 3, characterized in that: The first lens G1 is made of a high-dispersion glass material, and the Abbe number of the first lens G1 is less than or equal to 35; the second lens G2 is made of a low-dispersion glass material, and the Abbe number of the second lens G2 is greater than or equal to 60.

5. The optical system of a long working distance bi-telecentric lens according to claim 2, characterized in that: The focal length of the seventh lens G7 is f G7 , f G7 With f B The following relationship is satisfied: 0.9<|f G7 / f B |<1.

7.

6. The optical system of a long working distance bi-telecentric lens according to claim 5, characterized in that: The fifth lens G5 is a biconcave lens, and the sixth lens G6 and the seventh lens G7 are both biconvex lenses.

7. The optical system of a long working distance bi-telecentric lens according to claim 6, characterized in that: The first lens G1, the second lens G2, the third lens G3, the fourth lens G4, the fifth lens G5, the sixth lens G6 and the seventh lens G7 form a double telecentric structure. The working distance of the double telecentric structure is greater than 250 mm and the telecentricity is less than 0.1°.

8. The optical system of a long working distance bi-telecentric lens according to claim 1, 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 bi-telecentric lens, characterized in that: An optical system comprising a long working distance bi-telecentric lens as claimed in any one of claims 1 to 8.

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