A large-aperture four-piece lens structure

Abstract

The present invention discloses a large-aperture four-piece lens structure, which sequentially includes, from the object side to the imaging surface, an aspherical first meniscus lens, a second meniscus lens with positive optical power, a third meniscus lens with negative optical power, and a double-convex fourth lens with positive optical power; the first meniscus lens, the second meniscus lens, and the third meniscus lens are all bent towards the imaging surface; it satisfies the conditional expressions: R1>0, R2>0, R3>0, R4>0, R5>0, R6>0, R7>0, R8<0, R3<R4, R5>R6; |f1| / EFL>5, where f1 is the focal length of the first meniscus lens and EFL is the effective focal length of the lens system; BFL / OAL>0.4, where BFL is the back focal length and OAL is the overall length of the lens system; OAL / EFL<1.8; BFL*0.9<f4<BFL*1.2, f4 is the focal length of the fourth lens; NA>0.35, NA is the numerical aperture of the lens system; the first meniscus lens is set as an injection-molded aspherical lens; the second meniscus lens, the third meniscus lens, and the fourth lens are all spherical glass lenses. It can reduce spherical aberration, increase the light energy utilization rate, and enable the lens to be adapted to fields with a wide temperature application range.

Description

Technical Field

[0001] The present invention relates to a projection system for intelligent pixel headlights such as automotive and motorcycle front headlights, and specifically discloses a large-aperture four-piece lens structure. Background Art

[0002] The optical part of the low beam of a traditional existing vehicle headlight system using the projection principle is composed of a light source + a light energy collection element + a cut-off line structure + a convex lens. The newly developed pixel headlights, also known as matrix headlights, use light digital projection technology, enabling vehicle headlights to not only have a lighting function but also project patterns on the ground, such as weather conditions, road navigation, or other symbols for pedestrians or vehicles outside the vehicle to identify, used as a kind of light language. In pixel headlights with a resolution of tens of thousands, micro LEDs are used as the light source. However, in high-resolution vehicle headlights with a resolution of millions, digital micromirror technology (DMD or DLP) is required. Since the DMD itself does not emit light, a projection lens needs a longer back focal length, so that the illumination optical module can have space to irradiate light energy onto the DMD, and then reflect from the DMD and be incident and coupled onto the projection lens. Some projection lenses use the optical lenses of traditional DLP projectors, usually with as many as 10 lenses. In addition, due to the complex driving environment of vehicles, the application environment of vehicle headlights may also be relatively harsh, requiring normal operation at an ambient temperature ranging from -45°C to 85°C with no significant change in performance. Therefore, it is required that the projection lens of high-resolution vehicle headlights can have a stable back focal length in a large temperature range from -45°C to 85°C. Moreover, cost is also an important factor for projection lenses. Spherical glass lenses are cheaper than aspherical glass lenses, and injection-molded plastic lenses are cheaper than spherical lenses of the same aperture and can adopt free-form surfaces or aspherical surfaces. However, injection-molded plastic lenses have an obvious disadvantage of poor thermal stability, mainly manifested in large variations in refractive index and thermal expansion coefficient with temperature. If the design is inappropriate, it will lead to a drastic deterioration of the optical performance of the lens in high and low temperature environments. However, the advantage of plastic lenses is that they have more design freedom in surface shape, are light in weight, and have lower costs. Therefore, it is necessary to provide a method that, in view of the long back focal length characteristics of DLP and the requirement of a wide range of high and low temperature applications for vehicle headlights, can make full use of the advantages of plastic lenses and glass lenses while avoiding their disadvantages. Summary of the Invention

[0003] Based on this, in view of the problems in the prior art, it is necessary to provide a large-aperture four-piece lens structure that can reduce spherical aberration, increase light energy utilization rate, and enable the lens to adapt to fields with a wide temperature application range.

[0004] To solve the problems of the prior art, the present invention discloses a large-aperture four-lens structure, which sequentially includes an aspherical first meniscus lens, a second meniscus lens with positive optical power, a third meniscus lens with negative optical power, and a double-convex fourth lens from the object side to the imaging surface; the first meniscus lens, the second meniscus lens, and the third meniscus lens are all bent towards the imaging surface;

[0005] It satisfies the conditional formula:

[0006] R1>0, R2>0, R3>0, R4>0, R5>0, R6>0, R7>0, R8<0, R3<R4, R5>R6;

[0007] |f1| / EFL>5, where f1 is the focal length of the first meniscus lens and EFL is the effective focal length of the lens system; R1 is the curvature radius of the object side surface of the first meniscus lens, R2 is the curvature radius of the image side surface of the first meniscus lens, R3 is the curvature radius of the object side surface of the second meniscus lens, R4 is the curvature radius of the image side surface of the second meniscus lens, R5 is the curvature radius of the object side surface of the third meniscus lens, R6 is the curvature radius of the image side surface of the third meniscus lens, R7 is the curvature radius of the object side surface of the fourth lens, and R8 is the curvature radius of the image side surface of the fourth lens;

[0008] BFL / OAL>0.4, where BFL is the back focal length and OAL is the total length of the lens system;

[0009] OAL / EFL<1.8;

[0010] BFL*0.9<f4<BFL*1.2, where f4 is the focal length of the fourth lens;

[0011] NA>0.35, where NA is the numerical aperture of the lens system;

[0012] The first meniscus lens is set as an injection-molded aspherical lens; the second meniscus lens, the third meniscus lens, and the fourth lens are all spherical glass lenses.

[0013] Preferably, the Abbe number of the optical materials used for the second meniscus lens and the fourth lens is more than 25 greater than the Abbe number of the material used for the third meniscus lens.

[0014] The beneficial effects of the present invention are as follows: The first three lenses all use meniscus lenses, which can reduce spherical aberration and increase the utilization rate of light energy; the first meniscus lens is mainly used to correct the high-order aberrations of the system, and with a small optical power, it can make the influence of temperature extremely small. The second meniscus lens, the third meniscus lens, and the fourth lens use glass lenses, and the relative change of the optical properties of glass lenses with temperature is small. Therefore, through combined application, the lens can be adapted to fields with a wide temperature application range. Description of the Drawings

[0015] Figure 1 It is a schematic structural diagram of the first embodiment of the present invention.

[0016] Figure 2 It is the MTF curve graph of the first embodiment of the present invention.

[0017] Figure 3 It is the astigmatism, field curvature curve and distortion curve graph of the first embodiment of the present invention.

[0018] Figure 4 It is a schematic structural diagram of the second embodiment of the present invention.

[0019] Figure 5 It is the MTF curve graph of the second embodiment of the present invention.

[0020] Figure 6 It is the astigmatism, field curvature curve and distortion curve graph of the second embodiment of the present invention.

[0021] Figure 7 It is a schematic structural diagram of the third embodiment of the present invention.

[0022] Figure 8 It is the MTF curve graph of the third embodiment of the present invention.

[0023] Figure 9 It is the astigmatism, field curvature curve and distortion curve graph of the third embodiment of the present invention.

[0024] The reference numerals are: the first meniscus lens 11, the second meniscus lens 12, the third meniscus lens 13, and the fourth lens 14. Detailed implementation manners

[0025] To further understand the features, technical means, specific purposes and functions achieved by the present invention, the present invention will be further described in detail below in conjunction with the drawings and specific implementation manners.

[0026] Refer to Figures 1 to 3 , the optical path diagram is as shown in Figure 1 , the MTF curve graph is as shown in Figure 2 , and its relative astigmatism curve and distortion curve are as shown in Figure 3 .

[0027] The basic embodiment of the present invention discloses a large-aperture four-lens lens structure, which sequentially includes an aspherical first meniscus lens 11, a second meniscus lens 12 with positive optical power, a third meniscus lens 13 with negative optical power, and a double-convex fourth lens 14 with positive optical power from the object side to the imaging surface; the first meniscus lens 11, the second meniscus lens 12, and the third meniscus lens 13 are all bent towards the imaging surface;

[0028] It satisfies the conditional formula:

[0029] R1 > 0, R2 > 0, R3 > 0, R4 > 0, R5 > 0, R6 > 0; These constraints can limit the first meniscus lens 11 to the third meniscus lens 13 to be uniform meniscus lenses; R3 < R4, R5 > R6, and these two constraints limit the second meniscus lens 12 to be a positive lens and the third meniscus lens 13 to be a negative lens; R7 > 0, R8 < 0, and this constraint limits the fourth lens 14 to be a biconvex lens. R1 is the radius of curvature of the object side of the first meniscus lens, R2 is the radius of curvature of the image side of the first meniscus lens, R3 is the radius of curvature of the object side of the second meniscus lens, R4 is the radius of curvature of the image side of the second meniscus lens, R5 is the radius of curvature of the object side of the third meniscus lens, R6 is the radius of curvature of the image side of the third meniscus lens, R7 is the radius of curvature of the object side of the fourth lens, and R8 is the radius of curvature of the image side of the fourth lens.

[0030] |f1| / EFL > 5, where f1 is the focal length of the first meniscus lens 11 and EFL is the effective focal length of the lens system; in this embodiment, |f1| / EFL = 1378. This defines the contribution of the optical power of the first lens to the optical power of the system. Since the first lens is realized by injection molding and the optical properties of plastic lenses change greatly in high and low temperature environments, by reducing its contribution of optical power in the system, the influence of it on the optical performance of the system in high and low temperature environments can be limited.

[0031] BFL / OAL > 0.4, where BFL is the back focal length and OAL is the total length of the lens system; in this embodiment, BFL / OAL = 0.44. This index defines the proportion of the back focal length in the total length of the system, making the back focal length long enough. Because it is used in conjunction with an imaging surface for DMD applications, a long back focal length is required to provide enough space for the illumination light path to couple light energy.

[0032] OAL / EFL < 1.8; in this embodiment, OAL / EFL = 1.46. This index defines the ratio of the total length of the system to the effective focal length of the lens system, making the design of the lens compact enough to reduce the space occupied by the lens.

[0033] BFL * 0.9 < f4 < BFL * 1.2, where f4 is the focal length of the fourth lens 14; this index defines that the optical power of the fourth lens 14 is in a relatively reasonable range, so as to provide better imaging quality and reduce aberration.

[0034] NA > 0.35, where NA is the numerical aperture of the lens system; this index defines that the system can have a high light energy utilization rate, and the larger the value, the higher the light energy utilization rate.

[0035] The first meniscus lens 11 is set as an injection-molded aspherical lens, which is realized by injection molding, so as to reduce costs, and is designed as an aspherical surface, thereby increasing the degree of freedom of design.

[0036] The second meniscus lens 12, the third meniscus lens 13, and the fourth lens 14 are all spherical glass lenses.

[0037] The Abbe number of the optical material used for the second meniscus lens 12 and the fourth lens 14 is more than 25 greater than the Abbe number of the material used for the third meniscus lens 13.

[0038] Table 1, Design parameters of each surface in the first embodiment

[0039] Surface serial number Surface type Radius of curvature R (mm) Thickness (mm) Refractive index Abbe number L1a Aspherical surface 118.291 2.000 1.585 29.5 L1b Aspherical surface 117.844 1.921 L2a Spherical surface 36.024 9.625 1.677 55.6 L2b Spherical surface 122.036 10.118 L3a Spherical surface 70.586 2.200 1.846 23.8 L3b Spherical surface 26.683 9.853 L4a Spherical surface 43.984 11.283 1.666 52.7 L4b Spherical surface -67.454 36.390 L5 Spherical surface Infinity 1.100 1.516 64.2 L6 Spherical surface Infinity 0.510 L7 Spherical surface Infinity 0.000

[0040] Table 2, Aspherical high-order parameters in the first embodiment

[0041]

[0042] The expression of the aspherical surface is as follows:

[0043]

[0044] Where z is the sag height at the position of the aspherical surface with r position; c is the paraxial curvature of the aspherical surface, c = 1 / R, (i.e., the paraxial curvature c is the reciprocal of the surface curvature radius R); k is the conic coefficient; A, B,.., J are the high-order term coefficients.

[0045] Table 3, Other system parameters in the first embodiment are

[0046] Parameter Equivalent focal length f (mm) f1 (mm) f2 (mm) f3 (mm) f4 (mm) NA FOV (deg) OAL BFL BFL / OAL Value 58.00 79964 10.75 58.90 9.20 0.39 14 85.00 38.00 0.447058824

[0047] Table 4, Constraint relationships in the first embodiment

[0048] Constraint condition Design result |f1| / EFL > 5 |f1| / EFL = 1378, known to be satisfied BFL / OAL > 0.4 BFL / OAL = 0.44, known to be satisfied R1>0 Known to be satisfied from design parameters R2>0 Known to be satisfied from design parameters R3>0 Known to be satisfied from design parameters R4>0 Known to be satisfied from design parameters R5>0 Known to be satisfied from design parameters R6>0 Known to be satisfied from design parameters R7>0 Known to be satisfied from design parameters R8<0 Known to be satisfied from design parameters OAL / EFL < 1.8 OAL / EFL = 1.46, known to be satisfied BFL * 0.9 < f4 < BFL * 1.2 Known to be satisfied from design parameters NA > 0.35 Known to be satisfied from design parameters

[0049] Embodiment 2, reference Figures 4 to 6 , the optical path diagram is as Figure 4 , the MTF curve diagram is as Figure 5 , its relative astigmatism curve and distortion curve are as Figure 6 .

[0050] The basic embodiment of the present invention discloses a large-aperture four-piece lens structure, which sequentially includes an aspherical first meniscus lens 11, a second meniscus lens 12 with positive optical power, a third meniscus lens 13 with negative optical power, and a double-convex fourth lens 14 with positive optical power from the object side to the imaging surface; the first meniscus lens 11, the second meniscus lens 12, and the third meniscus lens 13 are all bent towards the imaging surface;

[0051] It satisfies the conditional formula:

[0052] R1 > 0, R2 > 0, R3 > 0, R4 > 0, R5 > 0, R6 > 0; These constraints can limit the first meniscus lens 11 to the third meniscus lens 13 to be uniform meniscus lenses; R3 < R4, R5 > R6, and these two constraints limit the second meniscus lens 12 to be a positive lens and the third meniscus lens 13 to be a negative lens; R7 > 0, R8 < 0, and this constraint limits the fourth lens 14 to be a biconvex lens. R1 is the radius of curvature of the object side of the first meniscus lens, R2 is the radius of curvature of the image side of the first meniscus lens, R3 is the radius of curvature of the object side of the second meniscus lens, R4 is the radius of curvature of the image side of the second meniscus lens, R5 is the radius of curvature of the object side of the third meniscus lens, R6 is the radius of curvature of the image side of the third meniscus lens, R7 is the radius of curvature of the object side of the fourth lens, and R8 is the radius of curvature of the image side of the fourth lens.

[0053] |f1| / EFL > 5, where f1 is the focal length of the first meniscus lens 11 and EFL is the effective focal length of the lens system; in this embodiment, |f1| / EFL = 7.58. This defines the contribution of the optical power of the first lens to the optical power of the system. Since the first lens is realized by injection molding and the optical properties of plastic lenses change greatly in high and low temperature environments, by reducing its contribution of optical power in the system, the influence of its optical properties on the system in high and low temperature environments can be limited.

[0054] BFL / OAL > 0.4, where BFL is the back focal length and OAL is the total length of the lens system; in this embodiment, BFL / OAL = 0.43. This index defines the proportion of the back focal length in the total length of the system, making the back focal length long enough. Since it is used in conjunction with an imaging surface for DMD applications, a long back focal length is required to provide enough space for the illumination optical path to couple light energy.

[0055] OAL / EFL < 1.8; in this embodiment, OAL / EFL = 1.45. This index defines the ratio of the total length of the system to the effective focal length of the lens system, making the design of the lens compact enough to reduce the space occupied by the lens.

[0056] BFL * 0.9 < f4 < BFL * 1.2, where f4 is the focal length of the fourth lens 14; this index defines that the optical power of the fourth lens 14 is in a relatively reasonable range, so as to provide better imaging quality and reduce aberration.

[0057] NA > 0.35, where NA is the numerical aperture of the lens system; this index defines that the system can have a high light energy utilization rate, and the larger the value, the higher the light energy utilization rate.

[0058] The first meniscus lens 11 is set as an injection-molded aspherical lens, which is realized by injection molding, so as to reduce costs, and is designed as an aspherical surface, thereby increasing the degree of freedom of design.

[0059] The second meniscus lens 12, the third meniscus lens 13, and the fourth lens 14 are all spherical glass lenses.

[0060] The Abbe number of the optical material used for the second meniscus lens 12 and the fourth lens 14 is more than 25 greater than the Abbe number of the material used for the third meniscus lens 13.

[0061] Table 5, Design parameters of each surface in the second embodiment

[0062]

[0063]

[0064] Table 6, Aspherical high-order parameters in the second embodiment

[0065]

[0066] The expression of the aspherical surface is as follows:

[0067]

[0068] Where z is the sag height at the aspherical surface position of r position; c is the paraxial curvature of the aspherical surface, c = 1 / R, (i.e., the paraxial curvature c is the reciprocal of the surface curvature radius R); k is the conic coefficient; A, B,.., J are high-order term coefficients.

[0069] Table 7, Design parameters of the optical lens in the second embodiment

[0070] Parameter Equivalent focal length EFL (mm) f1 (mm) f2 (mm) f3 (mm) f4 (mm) NA FOV (deg) OAL BFL BFL / OAL Value 41.68 -315.9 51.60 -40.43 28.38 0.42 16 60.45 26.45 0.43754

[0071] Table 8, Constraint relationships in the second embodiment

[0072] Constraint condition Design result |f1| / EFL > 5 |f1| / EFL = 7.58, known to be satisfied BFL / OAL > 0.4 BFL / OAL = 0.43, known to be satisfied |R2| / |R1|*FOV < 21 |R2| / |R1|*FOV = 3.96, known to be satisfied R1>0 Known to be satisfied from design parameters R2>0 Known to be satisfied from design parameters R3>0 Known to be satisfied from design parameters R4>0 Known to be satisfied from design parameters R5>0 Known to be satisfied from design parameters R6>0 Known to be satisfied from design parameters R7>0 Known to be satisfied from design parameters R8<0 Known to be satisfied from design parameters OAL / EFL < 1.8 OAL / EFL = 1.45, known to be satisfied BFL * 0.9 < f4 < BFL * 1.2 Known to be satisfied from design parameters NA > 0.35 Known to be satisfied from design parameters

[0073] Embodiment 3, reference Figures 7 to 9 , the optical path diagram is as Figure 7 , the MTF curve diagram is as Figure 8 , its relative astigmatism curve and distortion curve are as Figure 9 .

[0074] The basic embodiment of the present invention discloses a large-aperture four-piece lens structure, which sequentially includes an aspherical first meniscus lens 11, a second meniscus lens 12 with positive optical power, a third meniscus lens 13 with negative optical power, and a double-convex fourth lens 14 with positive optical power from the object side to the imaging surface; the first meniscus lens 11, the second meniscus lens 12, and the third meniscus lens 13 are all bent towards the imaging surface;

[0075] It satisfies the conditional formula:

[0076] R1 > 0, R2 > 0, R3 > 0, R4 > 0, R5 > 0, R6 > 0; These constraints can limit the first meniscus lens 11 to the third meniscus lens 13 to be uniform meniscus lenses; R3 < R4, R5 > R6, and these two constraints limit the second meniscus lens 12 to be a positive lens and the third meniscus lens 13 to be a negative lens; R7 > 0, R8 < 0, and this constraint limits the fourth lens 14 to be a biconvex lens. R1 is the radius of curvature of the object side of the first meniscus lens, R2 is the radius of curvature of the image side of the first meniscus lens, R3 is the radius of curvature of the object side of the second meniscus lens, R4 is the radius of curvature of the image side of the second meniscus lens, R5 is the radius of curvature of the object side of the third meniscus lens, R6 is the radius of curvature of the image side of the third meniscus lens, R7 is the radius of curvature of the object side of the fourth lens, and R8 is the radius of curvature of the image side of the fourth lens.

[0077] |f1| / EFL > 5, where f1 is the focal length of the first meniscus lens 11 and EFL is the effective focal length of the lens system; in this embodiment, |f1| / EFL = 7.58. This defines the contribution of the optical power of the first lens to the optical power of the system. Since the first lens is realized by injection molding and the optical properties of plastic lenses change greatly in high and low temperature environments, by reducing its contribution of optical power in the system, the influence of its optical performance on the system in high and low temperature environments can be limited.

[0078] BFL / OAL > 0.4, where BFL is the back focal length and OAL is the overall length of the lens system; in this embodiment, BFL / OAL = 0.43. This index defines the proportion of the back focal length in the overall length of the system, making the back focal length long enough. Since it is used in conjunction with an imaging surface for DMD applications, a long back focal length is required to provide enough space for the illumination optical path to couple light energy.

[0079] OAL / EFL < 1.8; in this embodiment, OAL / EFL = 1.45. This index defines the ratio of the overall length of the system to the effective focal length of the lens system, making the design of the lens compact enough to reduce the space occupied by the lens.

[0080] BFL * 0.9 < f4 < BFL * 1.2, where f4 is the focal length of the fourth lens 14; this index defines that the optical power of the fourth lens 14 is within a reasonable range, so as to provide better imaging quality and reduce aberration.

[0081] NA > 0.35, where NA is the numerical aperture of the lens system; this index defines that the system can have a high light energy utilization rate, and the larger the value, the higher the light energy utilization rate.

[0082] The first meniscus lens 11 is set as an injection-molded aspherical lens, which is realized by injection molding, thereby reducing costs, and is designed as an aspherical surface, thereby increasing the degree of freedom of design.

[0083] The second meniscus lens 12, the third meniscus lens 13, and the fourth lens 14 are all spherical glass lenses.

[0084] The Abbe number of the optical materials used for the second meniscus lens 12 and the fourth lens 14 is more than 25 greater than the Abbe number of the material used for the third meniscus lens 13.

[0085] Table 9, Design parameters of each surface in the third embodiment

[0086] Surface serial number Surface type Radius of curvature R (mm) Thickness (mm) Refractive index Abbe number L1a Aspherical surface 126.794 2.200 1.585 29.5 L1b Aspherical surface 127.831 1.344 L2a Spherical surface 28.835 10.735 1.631 58.2 L2b Spherical surface 91.279 7.729 L3a Spherical surface 70.985 2.200 1.855 26.6 L3b Spherical surface 21.668 2.971 L4a Spherical surface 28.453 10.641 1.673 51.8 L4b Spherical surface -60.075 28.294 L5 Spherical surface Infinity 1.188 1.755 27.6 L6 Spherical surface Infinity 0.551 L7 Spherical surface Infinity -0.032

[0087] Table 10, Aspherical high-order parameters in the third embodiment

[0088]

[0089] The expression of the aspherical surface is as follows:

[0090]

[0091] Where z is the sag height at the position of the aspherical surface with r position; c is the paraxial curvature of the aspherical surface, c = 1 / R, (that is, the paraxial curvature c is the reciprocal of the surface curvature radius R); k is the conic coefficient; A, B,.., J are the high-order term coefficients.

[0092] Table 11, Design parameters of the optical lens in the third embodiment

[0093] Parameter Equivalent focal length EFL (mm) f1 (mm) f2 (mm) f3 (mm) f4 (mm) NA FOV (deg) OAL BFL BFL / OAL Value 41.68 -315.9 51.60 -40.43 28.38 0.42 16 60.45 26.45 0.44

[0094] Table 12, Constraint relationships in the third embodiment

[0095]

[0096]

[0097] The first three lenses of the present invention all adopt meniscus lenses, which can reduce spherical aberration and increase the light energy utilization rate; the first meniscus lens is mainly used to correct the high-order aberration of the system, and the optical power is small, which can make the influence of temperature extremely small. The second meniscus lens, the third meniscus lens, and the fourth lens use glass lenses, and the relative temperature optical performance of the glass lenses changes little. Therefore, through combined application, the lens can be adapted to fields with a wide temperature application range.

[0098] The above-described embodiments only represent three implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation to the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention should be subject to the appended claims.

Claims

1. A large-aperture four-piece lens structure, characterized in that, From the object side to the imaging surface, it sequentially includes an aspherical first meniscus lens (11), a second meniscus lens (12) with positive optical power, a third meniscus lens (13) with negative optical power, and a double-convex fourth lens (14) with positive optical power; the first meniscus lens (11), the second meniscus lens (12), and the third meniscus lens (13) are all bent towards the imaging surface; It satisfies the conditional formula: R1>0, R2>0, R3>0, R4>0, R5>0, R6>0, R7>0, R8<0, R3<R4, R5>R6; |f1| / EFL>5, where f1 is the focal length of the first meniscus lens (11), and EFL is the effective focal length of the lens system; R1 is the curvature radius of the object side surface of the first meniscus lens, R2 is the curvature radius of the image side surface of the first meniscus lens, R3 is the curvature radius of the object side surface of the second meniscus lens, R4 is the curvature radius of the image side surface of the second meniscus lens, R5 is the curvature radius of the object side surface of the third meniscus lens, R6 is the curvature radius of the image side surface of the third meniscus lens, R7 is the curvature radius of the object side surface of the fourth lens, and R8 is the curvature radius of the image side surface of the fourth lens; BFL / OAL>0.4, where BFL is the back focal length and OAL is the total length of the lens system; OAL / EFL<1.8; BFL*0.9<f4<BFL*1.2, where f4 is the focal length of the fourth lens (14); NA>0.35, where NA is the numerical aperture of the lens system; The first meniscus lens (11) is set as an injection-molded aspherical lens; the second meniscus lens (12), the third meniscus lens (13), and the fourth lens (14) are all spherical glass lenses.

2. The large-aperture four-piece lens structure according to claim 1, wherein, The Abbe number of the optical materials used for the second meniscus lens (12) and the fourth lens (14) is more than 25 greater than the Abbe number of the material used for the third meniscus lens (13).

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