High-resolution double-telecentric optical system

Abstract

The utility model discloses a high resolution double telecentric optical system, which sequentially comprises a front lens group, a fixed diaphragm and a rear lens group from an object plane to an image plane along a light path direction, light emitted by an object space passes through the front lens group to form parallel light beams, the parallel light beams pass through the fixed diaphragm, and the rear lens group passes through the fixed diaphragm. Parallel light beams passing through the fixed diaphragm pass through the rear lens group to be converged and imaged on the image sensor, and the high-resolution imaging lens is characterized in that through reasonable matching of lens surface types and focal power, the light trend in the lens can be controlled, aberration can be reduced, high-resolution imaging is achieved, only six lenses are used, and the cost is low. And the production cost is greatly saved on the basis of ensuring high-resolution imaging.

Description

Technical Field

[0001] The utility model relates to a double telecentric optical system, in particular to a high-resolution double telecentric optical system. Background Art

[0002] In traditional imaging systems, the design of lens groups often causes light rays emitted from different parts of an object to enter the imaging system at different angles. This angular difference produces a perspective effect, which is particularly obvious in large field-of-view or close-range imaging. Perspective errors can lead to a decrease in accuracy, especially in precision applications where the size or position of an object needs to be evaluated. To overcome this problem, telecentric optical systems have been developed, including double telecentric optical systems. The design of a double telecentric system enables light rays emitted from each point on an object to enter the imaging system almost at a right angle (or parallel to the system's main axis), thereby eliminating perspective errors and ensuring that the image magnification does not change with the change in the distance between the object and the lens.

[0003] The principle of a double telecentric optical system is based on two key components:

[0004] ① Front telecentric design: By using a lens group with a finite focal length between the objective lens and the first lens, it is ensured that the light rays emitted from the object become parallel light rays after passing through this lens group. This requires the object to be located on or near the rear focal plane of the lens group.

[0005] ② Rear telecentric design: On the imaging side, the system focuses the parallel light rays onto the imaging sensor again through a lens group, which is usually achieved by placing the sensor at the rear focal plane position of the lens group. Since the light beam of the object remains parallel when passing through the entire optical system, the imaging magnification remains constant regardless of how slightly the distance between the object and the lens changes. This characteristic is crucial for precision measurement and detection.

[0006] Technical advantages of a double telecentric optical system:

[0007] ① No perspective error: Since the light rays remain parallel in both the object space and the image space, the size of the object in the image does not change regardless of how the object moves within a certain range.

[0008] ② High depth of field: Double telecentric lenses usually have a large depth of field, enabling relatively thick objects or scenes to remain clear as a whole.

[0009] ③ Consistent image magnification: Since perspective errors are eliminated, the image magnification remains consistent throughout the entire field of view.

[0010] ④ Edge measurement accuracy: Particularly suitable for applications that require precise measurement of the edge spacing or contour of an object

[0011] In the field of machine vision, especially in application scenarios that require high-precision imaging and measurement, to enable the lens to capture minute defects, detailed textures, or tiny features of precision parts, it is necessary to ensure that the optical system can resolve extremely small points or line pairs in object details to achieve high-definition imaging. For example, in the defect detection during the manufacturing process of liquid crystal panels, a double telecentric system can be used to detect pixel defects, cracks, foreign objects, etc. in the liquid crystal panels; another example is that in the semiconductor chip manufacturing process, especially in processes such as image measurement and detection, a double telecentric lens can provide a high-precision and highly stable imaging system to ensure the quality and reliability of the chips. In fine operations such as detecting the pin pitch of semiconductor chips, a double telecentric lens can meet the extremely high measurement accuracy requirements (such as 0.01 mm) and can detect whether there are defects or surface scratches on the chip pins.

[0012] Existing double telecentric systems applied in the field of machine vision usually increase the number of lenses to obtain high-resolution imaging. However, an increase in the number of lenses will lead to an increase in production costs and a decrease in the optical transmittance of the system. Although the number of lenses can be reduced by using cemented lenses, problems such as delamination or air bubbles may occur on the cemented surfaces of the cemented lenses, thereby affecting the optical performance and service life of the double telecentric optical system. The Chinese invention patent application with the application number 202311041696.8 provides a design method for a high-precision double telecentric lens. Within a 3.3 mm field of view, 7 single lenses are used to ensure that the full-field distortion is <0.1%, but the numerical aperture value is only 0.1. The Chinese invention patent application with the application number 202311742194.8 provides a double telecentric lens for machine vision detection. Under a 40 mm large field of view, the full-field distortion is <0.12%, but there are as many as 6 cemented lenses.

[0013] Therefore, how to rationally utilize the combination of single lenses and cemented lenses to design a double telecentric lens with high resolution, low distortion, and low cost has become a development direction of the current double telecentric optical system. Summary of the Utility Model

[0014] The technical problem to be solved by the present utility model is to provide a high-resolution double telecentric optical system that can ensure that the magnification of the image remains basically unchanged within a certain object distance range, and at the same time can achieve ultra-low distortion, enhanced depth of field, and high-resolution imaging, so as to meet the requirements of precision measurement and high-quality imaging.

[0015] The technical solution adopted by the present utility model to solve the above technical problems is as follows: A high-resolution double telecentric optical system, which sequentially includes a front lens group, a fixed aperture stop, and a rear lens group along the optical path direction from the object plane to the image plane. The light emitted from the object side becomes a parallel light beam after passing through the front lens group and passes through the fixed aperture stop. The parallel light beam passing through the fixed aperture stop passes through the rear lens group and converges to form an image on the imaging sensor. It is characterized in that the front lens group is composed of a first lens, a second lens, and a third lens, the rear lens group is composed of a fourth lens, a fifth lens, and a sixth lens, the fixed aperture stop is arranged between the third lens and the fourth lens, the first lens is a meniscus positive lens with the absolute value of the object surface curvature radius less than the absolute value of the image surface curvature radius, the second lens is a biconvex positive lens with the absolute value of the object surface curvature radius less than the absolute value of the image surface curvature radius, the third lens is a biconcave negative lens with the absolute value of the object surface curvature radius less than the absolute value of the image surface curvature radius, the fourth lens is a biconvex positive lens with the absolute value of the object surface curvature radius less than the absolute value of the image surface curvature radius, the fifth lens is a cemented doublet positive lens with the absolute value of the object surface curvature radius less than the absolute value of the image surface curvature radius, and the sixth lens is a biconvex positive lens with the absolute value of the object surface curvature radius less than the absolute value of the image surface curvature radius.

[0016] Compared with the prior art, the advantages of the present utility model are as follows:

[0017] 1) Double telecentric design: By placing the aperture stop in the middle position of the optical system, the chief rays on the object side and the imaging side entering are always parallel to the optical axis, that is, both object-side telecentricity and image-side telecentricity can be achieved simultaneously, ensuring that the magnification remains unchanged within a certain object distance range, thus solving the parallax problem and improving the accuracy and stability of imaging;

[0018] 2) High resolution: By reasonably matching the lens surface types and optical powers, the light path inside the lens can be controlled, and aberrations can be reduced, thereby achieving high-resolution imaging, and the resolution can reach above 0.3@150 lp / mm;

[0019] 3) Low distortion: Optimizing the optical path based on the double telecentric optical principle makes the distortion amount of the double telecentric optical system lower than 0.01%, which helps for more accurate imaging, especially suitable for occasions with high precision requirements;

[0020] 4) Adaptable working distance: The working distance range of this double telecentric lens is 110 - 130 mm, suitable for a variety of detection scenarios;

[0021] 5) Low cost: This double telecentric optical system only uses 6 lenses, greatly saving the production cost on the basis of ensuring high-resolution imaging.

[0022] Preferably, the radius of curvature of the object surface of the first lens is 30 mm to 55 mm, the radius of curvature of the image surface of the first lens is -600 mm to -400 mm, the thickness of the first lens is 4 mm to 6 mm, the distance between the first lens and the second lens is 4 mm to 6 mm, the radius of curvature of the object surface of the second lens is 15 mm to 45 mm, the radius of curvature of the image surface of the second lens is -45 mm to -15 mm, the thickness of the second lens is 5 mm to 8 mm, the distance between the second lens and the third lens is 9 mm to 12 mm, the radius of curvature of the object surface of the third lens is -100 mm to -70 mm, the radius of curvature of the image surface of the third lens is 70 mm to 100 mm, the thickness of the third lens is 2 mm to 6 mm, the distance between the third lens and the fixed diaphragm is 11 mm to 15 mm, the distance between the fixed diaphragm and the fourth lens is 14 mm to 17 mm, the radius of curvature of the object surface of the fourth lens is 15 mm to 45 mm, the radius of curvature of the image surface of the fourth lens is -45 mm to -15 mm, the central thickness of the fourth lens is 2 mm to 6 mm, the distance between the fourth lens and the fifth lens is 10 mm to 13 mm, the radius of curvature of the object surface of the fifth lens is -45 mm to -15 mm, the radius of curvature of the image surface of the fifth lens is -45 mm to -15 mm, the thickness of the fifth lens is 6 mm to 9 mm, the distance between the fifth lens and the sixth lens is 10 mm to 13 mm, the radius of curvature of the object surface of the sixth lens is 90 mm to 120 mm, the radius of curvature of the image surface of the sixth lens is -120 mm to -90 mm, and the thickness of the sixth lens is 3 mm to 6 mm.

[0023] Preferably, the radius of curvature of the object surface of the first lens is 50 mm, the radius of curvature of the image surface of the first lens is -550 mm, the central thickness of the first lens is 4.5 mm, the distance between the first lens and the second lens is 5.31 mm, the radius of curvature of the object surface of the second lens is 20 mm, the radius of curvature of the image surface of the second lens is -22 mm, the central thickness of the second lens is 6 mm, the distance between the second lens and the third lens is 10.38 mm; the radius of curvature of the object surface of the third lens is -90 mm, the radius of curvature of the image surface of the third lens is 95 mm, the central thickness of the third lens is 3.62 mm, the distance between the third lens and the fixed diaphragm is 13.08 mm, the distance between the fixed diaphragm and the fourth lens is 15.97 mm; the radius of curvature of the object surface of the fourth lens is 23.51 mm, the radius of curvature of the image surface of the fourth lens is -25 mm, the central thickness of the fourth lens is 2.25 mm, the distance between the fourth lens and the fifth lens is 11.54 mm; the radius of curvature of the object surface of the fifth lens is -36 mm, the radius of curvature of the cemented surface of the fifth lens is 23.51 mm, the radius of curvature of the image surface of the fifth lens is -40 mm, the central thickness of the fifth lens is 7.66 mm, the distance between the fifth lens and the sixth lens is 12.87 mm; the radius of curvature of the object surface of the sixth lens is 100 mm, the radius of curvature of the image surface of the sixth lens is -105 mm, the central thickness of the sixth lens is 4.5 mm, and the distance between the sixth lens and the image sensor is 38 mm.

[0024] Preferably, the refractive index of the first lens is 1.75 - 1.95, the Abbe number of the first lens is 15 - 25, the refractive index of the second lens is 1.6 - 1.8, the Abbe number of the second lens is 25 - 30, the refractive index of the third lens is 1.6 - 1.8, the Abbe number of the third lens is 25 - 30, the refractive index of the fourth lens is 1.5 - 1.8, the Abbe number of the fourth lens is 28 - 39, the refractive index of the first cemented lens in the fifth lens is 1.5 - 1.8, the Abbe number is 40 - 60, the refractive index of the second cemented lens in the fifth lens is 1.48 - 1.6, the Abbe number of the second cemented lens in the fifth lens is 50 - 70, the refractive index of the sixth lens is 1.8 - 1.95, and the Abbe number of the sixth lens is 15 - 20.

[0025] Preferably, the refractive index of the first lens is 1.92, and the Abbe number is 21.5; the refractive index of the second lens is 1.76, and the Abbe number is 27.5; the refractive index of the third lens is 1.72, and the Abbe number is 29.5; the refractive index of the fourth lens is 1.64, and the Abbe number is 35.4; the refractive index of the first cemented lens in the fifth lens is 1.58, and the Abbe number is 59.5; the refractive index of the second cemented lens in the fifth lens is 1.5, and the Abbe number is 64.7; the refractive index of the sixth lens is 1.92, and the Abbe number is 18.9.

[0026] Preferably, multilayer antireflection films with a reflectivity less than 0.5% are provided on the object surfaces and image surfaces of the first lens, the second lens, the third lens, the fourth lens, the fifth lens, and the sixth lens. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic optical structure diagram of a high-resolution dual-telecentric optical system according to an embodiment of the present invention;

[0028] Figure 2 is a spot diagram of a high-resolution dual-telecentric optical system according to an embodiment of the present invention;

[0029] Figure 3 is a field curvature diagram of a high-resolution dual-telecentric optical system according to an embodiment of the present invention;

[0030] Figure 4 is a distortion diagram of a high-resolution dual-telecentric optical system according to an embodiment of the present invention;

[0031] Figure 5 is an optical transfer function diagram of a high-resolution dual-telecentric optical system according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] The present invention will be further described in detail below with reference to the embodiments in the drawings.

[0033] Embodiment:

[0034] The optical structure of the high-resolution dual-telecentric optical system of the present invention is as Figure 1As shown, the double telecentric optical system includes, along the light propagation direction from the object plane to the image plane, a front lens group 1 composed of a first lens L1, a second lens L2, and a third lens L3, a fixed aperture 2, and a rear lens group 3 composed of a fourth lens L4, a fifth lens L5, and a sixth lens L6. The light emitted from the object side passes through the first lens L1, the second lens L2, and the third lens L3 to become a parallel light beam, and continues to propagate through the fixed aperture 2 to the fourth lens L4. The light propagating to the fourth lens L4 continues to propagate along the fifth lens L5 and the sixth lens L6 and converges to form an image on an image sensor (not shown in the figure). The first lens L1 is a meniscus positive lens, the curvature radius of the object surface of the first lens L1 is 50 mm, the curvature radius of the image surface of the first lens L1 is -550 mm, the second lens L2 is a biconvex positive lens, the curvature radius of the object surface of the second lens L2 is 20 mm, the curvature radius of the image surface of the second lens L2 is -22 mm, the third lens L3 is a biconcave negative lens, the curvature radius of the object surface of the third lens L3 is -90 mm, the curvature radius of the image surface of the third lens L3 is 95 mm. The fixed aperture 2 is placed between the third lens L3 and the fourth lens L4 to control the light input, reduce stray light, and improve the imaging contrast. The fourth lens L4 is a biconvex positive lens, the curvature radius of the object surface of the fourth lens L4 is 23.51 mm, the curvature radius of the image surface of the fourth lens L4 is -25 mm, the fifth lens L5 is a doublet positive lens, the curvature radius of the object surface of the fifth lens L5 is -36 mm, the curvature radius of the cemented surface of the fifth lens L5 is 23.51 mm, the curvature radius of the image surface of the fifth lens L5 is -40 mm, the sixth lens L6 is a biconvex positive lens, the curvature radius of the object surface of the sixth lens L6 is 100 mm, and the curvature radius of the image surface of the sixth lens L6 is -105 mm.

[0035] In this embodiment, the central thickness of the first lens L1 is 4.5 mm. The first lens L1 is made of optical glass with a refractive index of 1.92 and an Abbe number of 21.5. The distance between the first lens L1 and the second lens L2 is 5.31 mm. The central thickness of the second lens L2 is 6 mm. The second lens L2 is made of optical glass with a refractive index of 1.76 and an Abbe number of 27.5. The distance between the second lens L2 and the third lens L3 is 10.38 mm. The central thickness of the third lens L3 is 3.62 mm. The third lens L3 is made of optical glass with a refractive index of 1.72 and an Abbe number of 29.5. The distance between the third lens L3 and the fixed aperture 2 is 13.08 mm, and the distance between the fixed aperture 2 and the fourth lens L4 is 15.97 mm. The central thickness of the fourth lens L4 is 2.25 mm. The fourth lens L4 is made of optical glass with a refractive index of 1.64 and an Abbe number of 35.4. The distance between the fourth lens L4 and the fifth lens L5 is 11.54 mm. The central thickness of the fifth lens L5 is 7.66 mm, and the distance between the fifth lens L5 and the sixth lens L6 is 12.87 mm. The first cemented lens L5-1 of the fifth lens L5 is made of optical glass with a refractive index of 1.58 and an Abbe number of 59.5. The second cemented lens L5-2 of the fifth lens L5 is made of optical glass with a refractive index of 1.5 and an Abbe number of 64.7. The central thickness of the sixth lens L6 is 4.5 mm. The sixth lens L6 is made of optical glass with a refractive index of 1.92 and an Abbe number of 18.9. The distance between the sixth lens L6 and the image sensor is 38 mm.

[0036] All the optical glass is produced by Chengdu Guangming Company. Multilayer antireflection films are provided on the object surfaces and image surfaces of all the lenses, and the reflectivity is less than 0.5%.

[0037] The spot diagram of the double telecentric optical system of this embodiment is as Figure 2 shown. From the data in the spot diagram, it can be seen that the root mean square radius of the blur spot of the double telecentric optical system of the present invention is < 10 μm under the set field of view, indicating that the double telecentric optical system of the present invention can obtain a relatively clear image.

[0038] The field curvature / distortion diagram of the double telecentric optical system of this embodiment is as Figure 3 and Figure 4 shown. From the data in the field curvature / distortion diagram, it can be seen that when the maximum field of view of the double telecentric optical system of the present invention is 15.2 mm, the maximum distortion is 0.0039%, and the distortion value is very small, which can provide a distortion-free imaging quality.

[0039] The optical transfer function diagram MTF of the double telecentric optical system of this embodiment is as Figure 5As shown, the abscissa is the spatial resolution in lp / mm, the ordinate is the contrast, and the value range is 0 to 1. The curves in the figure represent the meridional and sagittal components of the MTF under different fields of view. The entire MTF curve in the figure is relatively compact, indicating that the double telecentric optical system of the present invention performs well in terms of contrast and resolution and has high measurement accuracy. From the data in the optical transfer function, when the contrast is 0.3, the resolution of each field of view of the double telecentric optical system of the present invention is greater than 150 lp / mm, and the MTF curves of each field of view approach the diffraction limit line, indicating that the double telecentric optical system of the present invention has good imaging quality.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not restrictive. Although this patent belongs to the technical field of optical systems, on the basis of this patent, it can also be used for industrial detection of electronic components, defect detection, etc. Although the present invention has been described in detail according to the embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A high-resolution double telecentric optical system, which sequentially includes a front lens group, a fixed aperture, and a rear lens group from the object plane to the image plane along the optical path direction. The light emitted from the object side becomes a parallel beam after passing through the front lens group, passes through the fixed aperture, and the parallel beam passing through the fixed aperture passes through the rear lens group and converges to form an image on the image sensor. It is characterized in that The front lens group is composed of a first lens, a second lens, and a third lens. The rear lens group is composed of a fourth lens, a fifth lens, and a sixth lens. The fixed aperture is disposed between the third lens and the fourth lens. The first lens is a meniscus positive lens with the absolute value of the object surface curvature radius less than the absolute value of the image surface curvature radius. The second lens is a biconvex positive lens with the absolute value of the object surface curvature radius less than the absolute value of the image surface curvature radius. The third lens is a biconcave negative lens with the absolute value of the object surface curvature radius less than the absolute value of the image surface curvature radius. The fourth lens is a biconvex positive lens with the absolute value of the object surface curvature radius less than the absolute value of the image surface curvature radius. The fifth lens is a cemented doublet positive lens with the absolute value of the object surface curvature radius less than the absolute value of the image surface curvature radius. The sixth lens is a biconvex positive lens with the absolute value of the object surface curvature radius less than the absolute value of the image surface curvature radius.

2. The high-resolution double telecentric optical system according to claim 1, characterized in that The curvature radius of the object surface of the first lens is 30 mm to 55 mm, the curvature radius of the image surface of the first lens is -600 mm to -400 mm, the thickness of the first lens is 4 mm to 6 mm, the distance between the first lens and the second lens is 4 mm to 6 mm, the curvature radius of the object surface of the second lens is 15 mm to 45 mm, the curvature radius of the image surface of the second lens is -45 mm to -15 mm, the thickness of the second lens is 5 mm to 8 mm, the distance between the second lens and the third lens is 9 mm to 12 mm, the curvature radius of the object surface of the third lens is -100 mm to -70 mm, the curvature radius of the image surface of the third lens is 70 mm to 100 mm, the thickness of the third lens is 2 mm to 6 mm, the distance between the third lens and the fixed aperture is 11 mm to 15 mm, the distance between the fixed aperture and the fourth lens is 14 mm to 17 mm, the curvature radius of the object surface of the fourth lens is 15 mm to 45 mm, the curvature radius of the image surface of the fourth lens is -45 mm to -15 mm, the central thickness of the fourth lens is 2 mm to 6 mm, the distance between the fourth lens and the fifth lens is 10 mm to 13 mm, the curvature radius of the object surface of the fifth lens is -45 mm to -15 mm, the curvature radius of the image surface of the fifth lens is -45 mm to -15 mm, the thickness of the fifth lens is 6 mm to 9 mm, the distance between the fifth lens and the sixth lens is 10 mm to 13 mm, the curvature radius of the object surface of the sixth lens is 90 mm to 120 mm, the curvature radius of the image surface of the sixth lens is -120 mm to -90 mm, and the thickness of the sixth lens is 3 mm to 6 mm.

3. A high-resolution double telecentric optical system according to claim 1, characterized in that The radius of curvature of the object surface of the first lens is 50 mm, the radius of curvature of the image surface of the first lens is -550 mm, the central thickness of the first lens is 4.5 mm, the distance between the first lens and the second lens is 5.31 mm, the radius of curvature of the object surface of the second lens is 20 mm, the radius of curvature of the image surface of the second lens is -22 mm, the central thickness of the second lens is 6 mm, the distance between the second lens and the third lens is 10.38 mm; the radius of curvature of the object surface of the third lens is -90 mm, the radius of curvature of the image surface of the third lens is 95 mm, the central thickness of the third lens is 3.62 mm, the distance between the third lens and the fixed diaphragm is 13.08 mm, the distance between the fixed diaphragm and the fourth lens is 15.97 mm; the radius of curvature of the object surface of the fourth lens is 23.51 mm, the radius of curvature of the image surface of the fourth lens is -25 mm, the central thickness of the fourth lens is 2.25 mm, the distance between the fourth lens and the fifth lens is 11.54 mm; the radius of curvature of the object surface of the fifth lens is -36 mm, the radius of curvature of the cemented surface of the fifth lens is 23.51 mm, the radius of curvature of the image surface of the fifth lens is -40 mm, the central thickness of the fifth lens is 7.66 mm, the distance between the fifth lens and the sixth lens is 12.87 mm; the radius of curvature of the object surface of the sixth lens is 100 mm, the radius of curvature of the image surface of the sixth lens is -105 mm, the central thickness of the sixth lens is 4.5 mm, and the distance between the sixth lens and the image sensor is 38 mm.

4. A high-resolution double telecentric optical system according to claim 1, characterized in that The refractive index of the first lens is 1.75 - 1.95, the Abbe number of the first lens is 15 - 25, the refractive index of the second lens is 1.6 - 1.8, the Abbe number of the second lens is 25 - 30, the refractive index of the third lens is 1.6 - 1.8, the Abbe number of the third lens is 25 - 30, the refractive index of the fourth lens is 1.5 - 1.8, the Abbe number of the fourth lens is 28 - 39, the refractive index of the first cemented lens in the fifth lens is 1.5 - 1.8, the Abbe number is 40 - 60, the refractive index of the second cemented lens in the fifth lens is 1.48 - 1.6, the Abbe number of the second cemented lens in the fifth lens is 50 - 70, the refractive index of the sixth lens is 1.8 - 1.95, and the Abbe number of the sixth lens is 15 - 20.

5. A high-resolution double telecentric optical system according to claim 1, characterized in that The refractive index of the first lens is 1.92 and the Abbe number is 21.5; the refractive index of the second lens is 1.76 and the Abbe number is 27.5; the refractive index of the third lens is 1.72 and the Abbe number is 29.5; the refractive index of the fourth lens is 1.64 and the Abbe number is 35.4; the refractive index of the first cemented lens in the fifth lens is 1.58 and the Abbe number is 59.5; the refractive index of the second cemented lens in the fifth lens is 1.5 and the Abbe number is 64.7; the refractive index of the sixth lens is 1.92 and the Abbe number is 18.

9.

6. The high-resolution double telecentric optical system according to claim 1, wherein The object surface and the image surface of the first lens, the second lens, the third lens, the fourth lens, the fifth lens and the sixth lens are all provided with a multilayer antireflection film with a reflectivity less than 0.5%.

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