A low-distortion projection lens

Abstract

This invention discloses a low-distortion projection lens, which consists of a first lens group with negative optical power, a second lens group with positive optical power, and a third lens group with positive optical power from the object side to the image side. The projection ratio TR of the low-distortion projection lens satisfies: 0.6≤TR≤0.8, and the focal length f and total optical length TTL satisfy: 10≤TTL / f≤15. The focal lengths f1 of the first lens group, f2 of the second lens group, and f3 of the third lens group satisfy: -0.4≤f1 / f2≤-0.2, -2.0≤f1 / f≤-1.0, 3.8≤f2 / f≤6.8, and 2.0≤f3 / f≤3.0, respectively. The advantage is that, while ensuring that the distortion across the entire field of view is less than 0.12%, the lens group structure is optimized and the optical power of each lens group is reasonably allocated to control the divergence and convergence of the beam, thereby achieving high-resolution imaging. It is suitable for various scenarios such as industrial inspection, positioning guidance, and 3D measurement.

Description

Technical Field

[0001] This invention relates to a projection lens, and more particularly to a low-distortion projection lens. Background Technology

[0002] Ultraviolet light projection technology based on digital micromirror arrays projects coded patterns onto the surface of objects through a projection lens and supports rapid modification of the patterns via programming. It is widely used in industrial inspection, positioning guidance, and 3D measurement. These applications place stringent demands on the performance of the projection lens, and the accuracy of the projected pattern directly affects the accuracy of subsequent measurements, positioning, or reconstruction.

[0003] In industrial inspection and 3D measurement, especially in scenarios involving the inspection of large objects, projection lenses typically require high magnification to achieve wide field-of-view coverage. However, even minor distortions present in the lens under a wide field of view can directly cause geometric distortion of the projected pattern, significantly impacting measurement accuracy. Furthermore, since the projected image originates from digital micromirror devices with extremely small pixel sizes, the root-mean-square (RMS) spot size of the projection lens reflects its ability to reproduce fine structures and is a key indicator of image quality. To improve image quality, aspherical lenses are commonly used in existing technologies to reduce distortion and improve illumination uniformity. However, in large-aperture projection lenses required for inspection applications, aspherical lenses have large apertures, significantly increasing their processing and manufacturing costs, making it difficult to balance high performance with low cost.

[0004] In positioning guidance and industrial inspection, it is often necessary to handle objects that are difficult to measure with traditional visible light, such as transparent glass panels, polished metal highly reflective surfaces, and dark light-absorbing materials. Short-wavelength light like violet light has low reflection interference on these material surfaces, effectively improving measurement reliability. However, the adhesives used in ordinary optical glass and cemented lenses exhibit significant absorption of violet light, resulting in generally low transmittance of conventional projection lenses, limiting measurement distance and signal-to-noise ratio. Furthermore, to avoid absorption issues, cemented lenses are typically not used, sacrificing aberration correction capabilities to some extent. In scenarios such as robot guidance and online inspection, systems need high-speed projection capabilities to capture dynamic processes. While projection systems based on digital micromirror arrays support kilohertz refresh rates, limitations in optical system transmittance and contrast often lead to insufficient projection brightness and reduced image clarity in high-speed modes, making it difficult to meet the needs of real-time inspection and guidance.

[0005] The projection lens must also be precisely matched with the digital micromirror array (DMI) chip to avoid energy loss, increased stray light, reduced transmittance, and decreased contrast. Specifically, the projection lens should maintain a telecentric design on the DMI chip side to ensure that the magnification of the projected image remains unchanged when the DMI chip defocuses slightly, thereby improving imaging accuracy.

[0006] Chinese utility model patent CN219957964U discloses a projection lens for semiconductor 3D inspection and imaging, featuring low distortion, high resolution, and good telecentricity. However, the use of a cemented lens affects light transmittance. Chinese invention patent application CN120949425A discloses a projection lens, projection system, and electronic device. This projection lens offers high resolution and high relative illumination, but suffers from slightly higher distortion. Chinese invention patent application CN114660775A discloses a low-distortion, large-aperture, full HD micro-projection lens that does not use a cemented lens, offering good transmittance, high resolution, and good telecentricity. While this structure is relatively low-cost, its small lens diameter and narrow field of view limit its application to industrial measurement fields with limited field of view. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a low-distortion projection lens with good transmittance, high resolution and good telecentricity, which can balance high performance and low cost and can be widely used in various scenarios such as industrial inspection, positioning guidance and three-dimensional measurement.

[0008] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: a low-distortion projection lens, comprising, from the object side to the image side, a first lens group with negative optical power, a second lens group with positive optical power, and a third lens group with positive optical power. The projection ratio TR of the low-distortion projection lens satisfies: 0.6 ≤ TR ≤ 0.8. The focal length f and total optical length TTL of the low-distortion projection lens satisfy: 10 ≤ TTL / f ≤ 15. The focal length f of the low-distortion projection lens, the focal length f1 of the first lens group, the focal length f2 of the second lens group, and the third lens group... The focal lengths f3 of the three lens groups satisfy the following conditions: -0.4 ≤ f1 / f2 ≤ -0.2, -2.0 ≤ f1 / f ≤ -1.0, 3.8 ≤ f2 / f ≤ 6.8, and 2.0 ≤ f3 / f ≤ 3.0. The low-distortion projection lens has a telecentric structure with an image-side telecentricity of less than 0.16°. The first lens group consists of a front lens with positive optical power, a rear lens with negative optical power, and a middle lens. Both surfaces of the front lens are spherical, and the object-side surface of the front lens is convex. The image-side surface of the rear lens is concave. The focal length f1 of the front lens is... 前 With the focal length f1 of the rear lens 后 They respectively satisfy: -15≤f1 前 / f1≤-5,1.2≤f1 后 / f1≤3.4,-7≤f1 前 / f1 后 ≤-4.

[0009] Compared with existing technologies, the advantages of this invention are that, while ensuring that the distortion across the entire field of view is less than 0.12%, it controls the divergence and convergence of the beam by optimizing the lens group structure and rationally allocating the optical power of each lens group, adjusting the focal length of the low-distortion projection lens, obtaining a telecentric image-side structure, and forming a projection field of view suitable for industrial inspection to meet projection requirements. At the same time, it achieves high-resolution imaging by optimizing aberrations. While achieving high-precision imaging and telecentric image-side structure, it also has good edge illumination consistency, and balances high performance with low cost, making it suitable for various scenarios such as industrial inspection, positioning guidance, and 3D measurement.

[0010] In one feasible implementation, the intermediate lens includes a first intermediate lens with negative optical power, which is a meniscus lens with its convex surface facing the object side and a focal length of f11. 中 The condition 1.8 ≤ f11 is satisfied. 中 / f1≤2.8.

[0011] In one feasible implementation, the intermediate lens comprises a first intermediate lens with negative optical power, a second intermediate lens with negative optical power, and a third intermediate lens with positive optical power. The image-side surface of the second intermediate lens is concave, the third intermediate lens is a biconvex lens, and the focal length of the second intermediate lens is f12. 中 With the focal length f13 of the third lens 中 They respectively satisfy: 1.2≤f12 中 / f1≤3.4,-2.8≤f13 中 / f1≤-1.8.

[0012] In some feasible implementations, the rear lens can be a meniscus lens with a concave image side or a biconcave lens.

[0013] In a feasible implementation, the object-side and image-side surfaces of the first lens are aspherical.

[0014] In one feasible implementation, the second lens group includes a biconvex first positive lens.

[0015] In some feasible implementations, the second lens group consists of a first positive lens and a first negative lens from the object side to the image side, wherein the first negative lens is a meniscus lens with its convex surface facing the object side.

[0016] In one feasible implementation, the second lens group consists of a second positive lens, a first positive lens, and a first negative lens from the object side to the image side. The second positive lens is a meniscus lens with its convex surface facing the image side, and the first negative lens is a meniscus lens with its convex surface facing the object side.

[0017] In a feasible implementation, the third lens group consists of a third positive lens, a second negative lens, a fourth positive lens, and a fifth positive lens sequentially from the object side to the image side. The image-side surface of the third positive lens is convex, the image-side surface of the second negative lens is concave, the fourth positive lens is a biconvex lens, the fifth positive lens is a biconvex lens, and the focal length f of the third positive lens is... 3正 The focal length f of the second negative lens 2负 The focal length f of the fourth positive lens 4正 The focal length f of the fifth positive lens 5正 They respectively satisfy: 1.4≤f 3正 / f3≤1.7,-1.6≤f 2负 / f3≤-1.1,1.8≤f 4正 / f3≤2.5,1.3≤f 5正 / f3≤1.6.

[0018] In one feasible implementation, the Abbe number Vd of the third positive lens 3正 The Abbe number Vd of the second negative lens 2负 The Abbe number Vd of the fourth positive lens 4正 They respectively satisfy: 30≤|Vd 3正 -Vd 2负 |≤46,30≤|Vd 2负 -Vd 4正 |≤46. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the optical system in Example 1 of the present invention;

[0020] Figure 2 This is a graph of the optical modulation transfer function of Example 1 of the present invention;

[0021] Figure 3 This is a distortion curve diagram of Example 1 of the present invention;

[0022] Figure 4 This is a schematic diagram of the optical system in Example 2 of the present invention;

[0023] Figure 5 This is a graph of the optical modulation transfer function of Example 2 of the present invention;

[0024] Figure 6 This is a distortion curve diagram of Example 2 of Embodiment 2 of the present invention;

[0025] Figure 7 This is a schematic diagram of the optical system in Example 3 of Embodiment 3 of the present invention;

[0026] Figure 8This is a graph of the optical modulation transfer function of Example 3 of the present invention;

[0027] Figure 9 This is a distortion curve diagram of Example 3 of Embodiment 3 of the present invention;

[0028] Figure 10 This is a schematic diagram of the optical system in Example 4 of the present invention;

[0029] Figure 11 This is a graph of the optical modulation transfer function of Example 4 of the present invention;

[0030] Figure 12 This is a distortion curve diagram of Example 4 of Embodiment 4 of the present invention;

[0031] Figure 13 This is a schematic diagram of the optical system in Example 5 of the present invention;

[0032] Figure 14 This is a graph of the optical modulation transfer function of Example 5 of the present invention;

[0033] Figure 15 This is a distortion curve diagram of Example 5 of Embodiment 5 of the present invention;

[0034] Figure 16 This is a schematic diagram of the optical system in Example Six of Embodiment 6 of the present invention;

[0035] Figure 17 This is a graph of the optical modulation transfer function of Example Six of Embodiment 6 of the present invention;

[0036] Figure 18 This is a distortion curve diagram of Example Six of Embodiment 6 of the present invention.

[0037] Explanation of reference numerals in the attached figures:

[0038] 1. First lens group; G 前 Front lens; G 后 Rear lens; G1 中 First intermediate lens; G2 中 Second lens; G3 中 1. Third lens; 2. Second lens group; G1 正 First positive lens; G1 负 First negative lens; G2 正 1. Second positive lens; 2. Third lens group; G3 正 Third positive lens; G2 负 Second negative lens; G4 正 Fourth positive lens; G5 正 Fifth positive lens; DMD, digital micromirror array chip; STO, aperture stop. Detailed Implementation

[0039] The following description, in conjunction with the accompanying drawings, illustrates specific examples of the present invention. The drawings are for reference and illustration only and do not constitute a limitation on the scope of patent protection of the present invention.

[0040] In the accompanying drawings, the thickness, size, and shape of the lenses have been slightly exaggerated for ease of illustration. The drawings are for illustrative purposes only and are not drawn to scale.

[0041] Figure 1 , Figure 4 , Figure 7 , Figure 10 , Figure 13 and Figure 16 The following are examples of low-distortion projection lenses according to embodiments of the present invention, which are composed of a first lens group 1 with negative optical power, a second lens group 2 with positive optical power, and a third lens group 3 with positive optical power from the object side to the image side.

[0042] The throw ratio TR of a low-distortion projection lens satisfies the condition: 0.6 ≤ TR ≤ 0.8. The throw ratio is a crucial indicator for users, defined as the ratio of projection distance to the size of the projected image. In practical applications, the image source of the low-distortion projection lens is a digital micromirror array (DMD) chip, which is magnified and projected onto the object. For design convenience, the optical system is reversed to optimize parameters. The object side of the low-distortion projection lens is the larger projected object, while the image side is the smaller DMD chip. Therefore, the throw ratio TR of the low-distortion projection lens in this application is the ratio of the object-side working distance D to the object surface size W. The object-side working distance D is the distance from the object surface to the first optical surface on the object side of the projection lens, satisfying: 0.6 ≤ TR ≤ 0.8. Controlling this value to not exceed the lower limit controls the object surface size W, improving sharpness and brightness uniformity; controlling it to not exceed the upper limit reduces the object-side working distance D, allowing the low-distortion projection lens to operate in small spaces.

[0043] The focal length f and total optical length TTL of the low-distortion projection lens satisfy: 10≤TTL / f≤15. The focal length f of the low-distortion projection lens, the focal length f1 of the first lens group 1, the focal length f2 of the second lens group 2, and the focal length f3 of the third lens group 3 satisfy: -0.4≤f1 / f2≤-0.2, -2.0≤f1 / f≤-1.0, 3.8≤f2 / f≤6.8, and 2.0≤f3 / f≤3.0, respectively. By rationally allocating the optical power of each lens group, the divergence and convergence of the beam are controlled. By adjusting the lens focal length, a telecentric structure is obtained, with a telecentricity of less than 0.16°, forming a projection field of view suitable for industrial inspection, meeting projection requirements, optimizing aberrations, and achieving high-resolution imaging. The first lens group 1 has a larger optical power and is used to collect and diverge the beam, expand the field of view, reduce field curvature, and extend the working distance range. The second lens group 2 has a smaller optical power and is used to converge the light beam, compensate for the divergence of the first lens group 1, smooth the light path, reduce lens sensitivity, and optimize aberrations. The third lens group 3 has a larger optical power and is used to collect the light beam to form an image.

[0044] The first lens group 1 consists of the front lens G 前 Rear lens G 后 It consists of a central lens and a front lens G. 前 On the object side, the optical power is positive and the focal length is f1. 前 Rear lens G 后 On the image side, the optical power is negative, and the focal length is f1. 后 The front lens G on the object side 前 The object-side surface is convex, responsible for collecting the light beam and controlling the beam angle; the image-side rear lens G... 后 The image side is concave, responsible for diverging the beam. Together, these two elements reduce field curvature and distortion, ensuring clear imaging of both the central and peripheral fields of view. Furthermore, the front lens G... 前 focal length f1 前 With rear lens G 后 focal length f1 后 They respectively satisfy: -15≤f1 前 / f1≤-5,1.2≤f1 后 / f1≤3.4,-7≤f1 前 / f1 后 ≤-4.

[0045] The front lens G in the first lens group 1 前 Both surfaces are spherical, which avoids the high manufacturing cost caused by an excessively large aperture of the first lens.

[0046] Figure 13 In Example 5 shown, the intermediate lens can consist of three lenses, with the first intermediate lens G1 having negative optical power, arranged sequentially from the object side to the image side. 中 The second intermediate lens G2 with negative optical power中 The third intermediate lens G3 with positive optical power 中 The first intermediate lens G1 中 It is a meniscus lens with its convex side facing the object side and a focal length of f / 11. 中 Second lens G2 中 The image side is concave, and the focal length is f12. 中 Third lens G3 中 It is a biconvex lens with a focal length of f / 13. 中 First intermediate lens G1 中 focal length f11 中 Second lens G2 中 focal length f12 中 Third intermediate lens G3 中 focal length f13 中 They respectively satisfy: 1.8 ≤ f11 中 / f1≤2.8,1.2≤f12 中 / f1≤3.4,-2.8≤f13 中 / f1≤-1.8.

[0047] and Figure 1 , Figure 4 , Figure 7 , Figure 10 and Figure 16 In other examples shown, the intermediate lens can be simply a single lens, namely a first intermediate lens G1 with negative optical power. 中 The first intermediate lens G1 中 Also a meniscus lens with its convex surface facing the object side, with a focal length of f / 11. 中 It still satisfies: 1.8 ≤ f11 中 / f1≤2.8.

[0048] exist Figure 13 and 16 In the example shown, the rear lens G 后 It could be a meniscus lens, while in other examples, the rear lens G 后 It can be a biconcave lens.

[0049] First intermediate lens G1 中 It can be an aspherical surface. The aspherical surface is positioned at the front lens G. 前 The first intermediate lens G1 at the second position behind 中 This avoids the front lens G being affected by the position of the first element. 前 The high manufacturing cost resulting from the large aperture can avoid insufficient aberration correction capability due to the position being too far back, thus achieving a reasonable balance between cost and performance.

[0050] In this embodiment, the aspherical lens used has a surface shape that satisfies the following equation:

[0051] .

[0052] in, y The radial coordinate value representing the lens perpendicular to the optical axis. The aspherical lens is at a height of [missing information] along the optical axis. y When the position is such that the distance from the vertex of the non-spherical surface is the sag; c =1 / R, where R represents the radius of curvature at the center of the corresponding aspherical lens surface. k The conic coefficients are represented by parameters B, C, D, and E, which are the coefficients of the 4th, 6th, 8th, and 10th order terms of the higher-order aspherical polynomials, respectively.

[0053] exist Figure 16 In Example 6 shown, the second lens group 2 is a biconvex first positive lens G1. 正 .

[0054] and Figure 13 In Example 5 shown, the second lens group 2 consists of a second positive lens G2 sequentially from the object side to the image side. 正 First positive lens G1 正 and the first negative lens G1 负 Composition, second positive lens G2 正 A meniscus lens with its convex surface facing the image side, the first negative lens G1 负 It is a meniscus lens with its convex side facing the object.

[0055] And in Figure 1 , Figure 4 , Figure 7 and Figure 10 In other examples shown, the second lens group 2 consists of two lenses from the object side to the image side, namely the first positive lens G1 on the object side. 正 and the first negative lens G1 on the image side 负 .

[0056] In all the examples shown, the third lens group 3 consists of a third positive lens G3 from the object side to the image side. 正 Second negative lens G2 负 Fourth positive lens G4 正 and the fifth positive lens G5 正 Composition, third positive lens G3 正 The image side is convex, and the second negative lens G2 负 The image side is concave, and the fourth positive lens is G4. 正 and the fifth positive lens G5 正 All are biconvex lenses, with a third positive lens G3. 正 focal length f 3正 Second negative lens G2 负 focal length f 2负 Fourth positive lens G4正 focal length f 4正 Fifth positive lens G5 正 focal length f 5正 They respectively satisfy: 1.4≤f 3正 / f3≤1.7,-1.6≤f 2负 / f3≤-1.1,1.8≤f 4正 / f3≤2.5,1.3≤f 5正 / f3≤1.6. The third positive lens G3 in the third lens group 3. 正 To the fifth positive lens G5 正 The focal lengths are relatively close, which allows the light beam to pass through smoothly, reduces lens sensitivity, minimizes aberrations, and optimizes the telecentricity of the projection lens.

[0057] Fifth positive lens G5 正 Optical components without optical power, such as protective glass and prisms, can also be placed between the lens and the image plane. The protective glass can be made of fused silica to reduce the absorption of ultraviolet light and improve the lens transmittance.

[0058] Third positive lens G3 正 Abbe number Vd 3正 Second negative lens G2 负 Abbe number Vd 2负 Fourth positive lens G4 正 Abbe number Vd 4正 They respectively satisfy: 30≤|Vd 3正 -Vd 2负 |≤46,30≤|Vd 2负 -Vd 4正 |≤46. The difference in Abbe number can create an achromatic structure, effectively suppressing chromatic aberration, while avoiding the reduction in lens transmittance caused by using cemented lenses.

[0059] In this embodiment, all lenses are single lenses, which avoids the absorption of violet light by the adhesive layer in cemented lenses and improves the transmittance of the lens.

[0060] The following are specific examples provided in this embodiment.

[0061] Example 1: such as Figure 1 As shown, from the object side to the image side, it includes the front lens G in sequence. 前 First intermediate lens G1 中 Rear lens G 后 First positive lens G1 正 First negative lens G1 负 Third positive lens G3 正 Second negative lens G2 负 Fourth positive lens G4 正 and the fifth positive lens G5正 .

[0062] Front lens G 前 When the optical power is positive, the object side is convex and the image side is concave.

[0063] First intermediate lens G1 中 The optical power is negative, the object side is convex, and the image side is concave.

[0064] Rear lens G 后 When the optical power is negative, the object side is concave, and the image side is concave.

[0065] First positive lens G1 正 When the optical power is positive, the object side is convex, and the image side is convex.

[0066] First negative lens G1 负 The optical power is negative, the object side is convex, and the image side is concave.

[0067] Third positive lens G3 正 When the optical power is positive, the object side is convex, and the image side is convex.

[0068] Second negative lens G2 负 The optical power is negative, the object side is convex, and the image side is concave.

[0069] Fourth positive lens G4 正 When the optical power is positive, the object side is convex, and the image side is convex.

[0070] Fifth positive lens G5 正 The optical power is positive, the object side is convex, and the image side is convex.

[0071] The main optical structural parameters of Example 1 are shown in Table 1.

[0072] Table 1

[0073]

[0074] The aspherical parameters of Example 1 are shown in Table 2.

[0075] Table 2

[0076]

[0077] Figure 2 The imaging performance of this example is as follows: at 100 lp / mm, the MTF of the center field of view at 0 mm image height is >0.8, and the MTF of the edge field of view at 12.5 mm is >0.3, indicating good imaging sharpness.

[0078] Figure 3The three curves in the middle correspond to the distortion curves of Example 1 at wavelengths of 0.39μm, 0.405μm, and 0.42μm, respectively. Among them, the distortion curve at the center wavelength of 0.405μm has a peak-valley distortion of 0.0897% in the Zemax optical design simulation software, which is relatively small.

[0079] Example 2: such as Figure 4 As shown, from the object side to the image side, it includes the front lens G in sequence. 前 First intermediate lens G1 中 Rear lens G 后 First positive lens G1 正 First negative lens G1 负 Third positive lens G3 正 Second negative lens G2 负 Fourth positive lens G4 正 and the fifth positive lens G5 正 .

[0080] Compared to Example 1, Example 2 adjusted the surface curvature radius, thickness, refractive index, and Abbe number of each lens. The focal length of most lenses increased, and the light deflection was reduced. Therefore, the MTF of the central field of view decreased slightly, but the MTF of the peripheral field of view increased significantly.

[0081] The main optical structural parameters of Example 2 are shown in Table 3.

[0082] Table 3

[0083]

[0084] The aspherical parameters of Example 2 are shown in Table 4.

[0085] Table 4

[0086]

[0087] Figure 5 The imaging performance of Example 2 is as follows: at 100 lp / mm, the MTF of the center field of view at 0 mm image height is >0.75, and the MTF of the edge field of view at 12.5 mm is >0.55, indicating good imaging sharpness.

[0088] Figure 6 The three curves in the middle correspond to the distortion curves of Example 2 at wavelengths of 0.39μm, 0.405μm, and 0.42μm, respectively. Among them, the distortion curve at the center wavelength of 0.405μm has a peak-valley distortion of 0.1100% in the Zemax optical design simulation software, which is relatively small.

[0089] Example 3: such as Figure 7 As shown, from the object side to the image side, it includes the front lens G in sequence. 前 First intermediate lens G1中 Rear lens G 后 First positive lens G1 正 First negative lens G1 负 Third positive lens G3 正 Second negative lens G2 负 Fourth positive lens G4 正 and the fifth positive lens G5 正 .

[0090] Compared to Example 2, in Example 3, the front lens G 前 The increased focal length affects beam collection, resulting in a slight decrease in relative illumination and a reduction in distortion.

[0091] The main optical structural parameters of Example 3 are shown in Table 5.

[0092] Table 5

[0093]

[0094] The aspherical parameters of Example 3 are shown in Table 6.

[0095] Table 6

[0096]

[0097] Figure 8 The imaging performance of Example 3 is as follows: at 100 lp / mm, the MTF of the center field of view at 0 mm image height is >0.75, and the MTF of the edge field of view at 12.5 mm is >0.5, indicating good imaging sharpness.

[0098] Figure 9 The three curves in the middle correspond to the distortion curves of Example 3 at wavelengths of 0.39μm, 0.405μm, and 0.42μm, respectively. Among them, the distortion curve at the center wavelength of 0.405μm has a peak-valley distortion of 0.0662% in the Zemax optical design simulation software, which is relatively small.

[0099] Example 4: (e.g.) Figure 10 As shown, from the object side to the image side, it includes the front lens G in sequence. 前 First intermediate lens G1 中 Rear lens G 后 First positive lens G1 正 First negative lens G1 负 Third positive lens G3 正 Second negative lens G2 负 Fourth positive lens G4 正 and the fifth positive lens G5 正 .

[0100] Compared to Example 3, in Example 4, the front lens G 前It becomes a biconvex lens, the second negative lens G2 负 It becomes a biconcave lens, the first intermediate lens G1 中 Both surfaces are made aspherical, which improves relative illumination, but also slightly increases distortion.

[0101] The main optical structural parameters of Example 4 are shown in Table 7.

[0102] Table 7

[0103]

[0104] The aspherical parameters for Example 4 are shown in Table 8.

[0105] Table 8

[0106]

[0107] Figure 11 The imaging performance of Example 4 is as follows: at 100 lp / mm, the MTF of the center field of view at 0 mm image height is >0.7, and the MTF of the edge field of view at 12.5 mm is >0.4, indicating good imaging sharpness.

[0108] Figure 12 The three curves in the middle correspond to the distortion curves of Example 4 at wavelengths of 0.39μm, 0.405μm, and 0.42μm, respectively. Among them, the distortion curve at the center wavelength of 0.405μm has a peak-valley distortion of 0.0954% in the Zemax optical design simulation software, which is relatively small.

[0109] Example 5: such as Figure 13 As shown, from the object side to the image side, it includes the front lens G in sequence. 前 First intermediate lens G1 中 Second lens G2 中 Third intermediate lens G3 中 Rear lens G 后 Second positive lens G2 正 First positive lens G1 正 First negative lens G1 负 Third positive lens G3 正 Second negative lens G2 负 Fourth positive lens G4 正 and the fifth positive lens G5 正 .

[0110] Compared to Example 4, in Example 5, the first lens G1 中 A second lens, G2, was later added. 中 and the third lens G3 中 In the first positive lens G1 正 A second positive lens G2 was added to the front. 正The first lens G1 中 The two surfaces were changed to spheres, the optical path was readjusted, the distortion and RMS spot radius were reduced, but the MTF of the edge field of view decreased significantly.

[0111] The main optical structural parameters of Example 5 are shown in Table 9.

[0112] Table 9

[0113]

[0114] Figure 14 The imaging performance of Example 5 is as follows: at 100 lp / mm, the MTF of the center field of view at 0 mm image height is >0.7, and the MTF of the edge field of view at 12.5 mm is >0.25, which shows good imaging sharpness.

[0115] Figure 15 The three curves in the middle correspond to the distortion curves of Example 5 at wavelengths of 0.39μm, 0.405μm, and 0.42μm, respectively. Among them, the distortion curve at the center wavelength of 0.405μm has a peak-valley distortion of 0.0653% in the Zemax optical design simulation software, which is relatively small.

[0116] Example 6: (e.g.) Figure 16 As shown, from the object side to the image side, it includes the front lens G in sequence. 前 First intermediate lens G1 中 Rear lens G 后 First positive lens G1 正 Third positive lens G3 正 Second negative lens G2 负 Fourth positive lens G4 正 and the fifth positive lens G5 正 .

[0117] Compared to Examples 1 through 4, Example 6 subtracts the first negative lens G1. 负 The reduced number of lenses resulted in a slight decrease in the MTF of the peripheral field of view.

[0118] The main optical structural parameters of Example 6 are shown in Table 10.

[0119] Table 10

[0120]

[0121] The aspherical parameters of Example 6 are shown in Table 11.

[0122] Table 11

[0123]

[0124] Figure 17The imaging performance of Example 6 is as follows: at 100 lp / mm, the MTF of the center field of view at 0 mm image height is >0.75, and the MTF of the edge field of view at 12.5 mm is >0.2, indicating good imaging sharpness.

[0125] Figure 18 The three curves in the middle correspond to the distortion curves of Example 6 at wavelengths of 0.39μm, 0.405μm, and 0.42μm, respectively. Among them, the distortion curve at the center wavelength of 0.405μm has a peak-valley distortion of 0.0659% in the Zemax optical design simulation software, which is relatively small.

[0126] The performance parameters for the six examples above are shown in Table 12.

[0127] Table 12

[0128]

[0129] The above examples are merely individual examples of the present invention and do not limit the scope of protection of the present invention. Therefore, equivalent changes made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A low-distortion projection lens, characterized in that, The low-distortion projection lens consists of a first lens group with negative optical power, a second lens group with positive optical power, and a third lens group with positive optical power, arranged from object side to image side. The projection ratio TR of the low-distortion projection lens satisfies: 0.6 ≤ TR ≤ 0.

8. The focal length f and total optical length TTL of the low-distortion projection lens satisfy: 10 ≤ TTL / f ≤ 15. The focal length f of the low-distortion projection lens, the focal length f1 of the first lens group, the focal length f2 of the second lens group, and the focal length f3 of the third lens group respectively satisfy: -0 0.4≤f1 / f2≤-0.2, -2.0≤f1 / f≤-1.0, 3.8≤f2 / f≤6.8, 2.0≤f3 / f≤3.0; the low-distortion projection lens has an image-side telecentric structure with a telecentricity of less than 0.16°; the first lens group consists of a front lens with positive optical power, a rear lens with negative optical power, and a middle lens. Both surfaces of the front lens are spherical, the object-side surface of the front lens is convex, the image-side surface of the rear lens is concave, and the focal length of the front lens is f1. 前 With the focal length f1 of the rear lens 后 They respectively satisfy: -15≤f1 前 / f1≤-5,1.2≤f1 后 / f1≤3.4,-7≤f1 前 / f1 后 ≤-4.

2. The low-distortion projection lens as described in claim 1, characterized in that, The intermediate lens includes a first intermediate lens with negative optical power, which is a meniscus lens with its convex surface facing the object side and a focal length of f11. 中 The condition 1.8 ≤ f11 is satisfied. 中 / f1≤2.

8.

3. A low-distortion projection lens as described in claim 2, characterized in that, The intermediate lens consists of a first intermediate lens with negative optical power, a second intermediate lens with negative optical power, and a third intermediate lens with positive optical power. The image-side surface of the second intermediate lens is concave, and the third intermediate lens is a biconvex lens. The focal length of the second intermediate lens is f12. 中 The focal length f13 of the third lens mentioned above 中 They respectively satisfy: 1.2≤f12 中 / f1≤3.4,-2.8≤f13 中 / f1≤-1.

8.

4. A low-distortion projection lens as described in claim 2 or 3, characterized in that, The rear lens is a meniscus lens with a concave image side.

5. A low-distortion projection lens as described in claim 2 or 3, characterized in that, The object-side and image-side surfaces of the first lens are aspherical.

6. A low-distortion projection lens as described in claim 1, characterized in that, The second lens group includes a biconvex first positive lens.

7. A low-distortion projection lens as described in claim 6, characterized in that, The second lens group consists of a first positive lens and a first negative lens from the object side to the image side. The first negative lens is a meniscus lens with its convex surface facing the object side.

8. A low-distortion projection lens as described in claim 6, characterized in that, The second lens group consists of a second positive lens, a first positive lens, and a first negative lens from the object side to the image side. The second positive lens is a meniscus lens with its convex surface facing the image side, and the first negative lens is a meniscus lens with its convex surface facing the object side.

9. A low-distortion projection lens as described in claim 6, 7, or 8, characterized in that, The third lens group, from the object side to the image side, consists of a third positive lens, a second negative lens, a fourth positive lens, and a fifth positive lens. The image-side surface of the third positive lens is convex, the image-side surface of the second negative lens is concave, the fourth positive lens is a biconvex lens, the fifth positive lens is a biconvex lens, and the focal length f of the third positive lens is... 3正 The focal length f of the second negative lens 2负 The focal length f of the fourth positive lens 4正 The focal length f of the fifth positive lens 5正 They respectively satisfy: 1.4≤f 3正 / f3≤1.7,-1.6≤f 2负 / f3≤-1.1,1.8≤f 4正 / f3≤2.5,1.3≤f 5正 / f3≤1.

6.

10. A low-distortion projection lens as described in claim 9, characterized in that, The Abbe number Vd of the third positive lens 3正 The Abbe number Vd of the second negative lens 2负 The Abbe number Vd of the fourth positive lens 4正 They respectively satisfy: 30≤|Vd 3正 -Vd 2负 |≤46,30≤|Vd 2负 -Vd 4正 |≤46.

Images