A large aperture three-piece lens

Abstract

The application discloses a large-aperture three-piece lens, which comprises three lenses from an object side to an image side along an optical axis, is provided with a first lens with positive focal length and both convex surfaces, a second lens with negative focal length and an M-shaped object side surface, and a third lens with positive focal length and both convex surfaces, and satisfies the following conditional expressions: |r3|<|r4|, wherein r3 and r4 are the radii of curvature of the object side and the image side of the second lens respectively; 1.4>f1 / f3>0.7, wherein f1 is the equivalent focal length of the first lens, and f3 is the equivalent focal length of the third lens; 2.48>=f12 / f3>=1.81, wherein f12 is the equivalent focal length of the combination of the first lens and the second lens; 1.03>=f3 / f>=0.87, wherein f is the equivalent focal length of an optical system; 1.99<=OAL / f<=2.23, wherein OAL is the total length of the optical system; and NA>0.6, wherein NA is the numerical aperture. The light energy utilization rate is improved by increasing the numerical aperture, the brightness is improved, and the thermal stability is good.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical imaging display, and specifically discloses a large-aperture three-piece lens. BACKGROUND

[0002] The optical part of the low beam of the traditional existing vehicle headlight system adopting the projection principle is composed of a combination of a light source, a light energy collecting element, a bright-dark cutoff line structure and a convex lens. The newly developed pixel headlight, also known as a matrix headlight, uses a light digital projection technology, so that the vehicle headlight not only has an illumination function, but also can project patterns on the ground, such as weather conditions, road navigation, or other symbols for pedestrians or vehicles outside to identify, as a kind of lamp language.

[0003] The implementation of the optical system of the pixel headlight requires light-emitting pixels, which can be mini LED, micro LED, LCD liquid crystal screen, LCOS or DMD digital micro mirror, and a projection optical lens. In order to make the projected pattern clear and visible, the lens needs to achieve good optical performance, and needs to eliminate chromatic aberration, field curvature, astigmatism and other optical aberrations. Generally, a good optical lens needs to be properly used in combination with multiple positive and negative lenses to eliminate aberrations. The number of optical lenses used is related to the parameters, performance indicators, and optical materials and optical processes of the optical system. A slightly complex optical system can have more than 10 lenses, and the current mobile phone lens is more than 6 lenses.

[0004] The pixel headlight has the functions of illumination and imaging, so on the one hand it needs higher energy utilization and higher brightness, and on the other hand the projected image has certain image quality requirements, especially low chromatic aberration. In addition, due to the particularity of the application of the automobile, it needs higher thermal reliability, better shock reliability, lighter quality (the need for weight reduction), and lower cost, so as to be competitive in the market.

[0005] At present, the lens design either uses more lenses, such as 4 or 5 lenses, or uses more expensive optical glass materials, or has low light energy utilization, or poor thermal stability.

[0006] A low-cost design scheme can be based on the most classic Cook three-piece lens, as shown in FIG. 1. Figure 1 It can correct various aberrations well and have good imaging quality. However, the disadvantage is that the numerical aperture of the original design is small, generally not more than 0.2, which means that the light energy utilization is very small. The lens needs to be adjusted very accurately, and the tolerance of manufacturing and processing is small, which requires high requirements.

[0007] In summary, as the application of pixel headlamp, it is necessary to have high energy utilization, i.e. large numerical aperture, and relatively stable performance at different working temperatures (-45℃ to +85℃).

[0008] In view of the above, it is urgent to provide an optical imaging display system which can improve energy utilization, has appropriate imaging quality, and has stable performance at different working temperatures. SUMMARY

[0009] Therefore, it is necessary to provide a large-aperture three-piece lens which can improve light energy utilization by increasing the numerical aperture, improve brightness, and has good thermal stability.

[0010] To solve the problems in the prior art, the present application discloses a large-aperture three-piece lens, which comprises three lenses along the optical axis from the object side to the image side, and the three lenses are sequentially a first lens with positive focal power and both sides being convex, a second lens with negative focal power and the object side being an M-shaped surface, and a third lens with positive focal power and both sides being convex.

[0011] And it satisfies the following conditional expression:

[0012] |r3|<|r4|, wherein r3 and r4 are the radii of curvature of the object side and the image side of the second lens, respectively;

[0013] 1.4>f1 / f3>0.7, wherein f1 is the equivalent focal length of the first lens, and f3 is the equivalent focal length of the third lens;

[0014] 2.48≥f12 / f3≥1.81, wherein f12 is the equivalent focal length of the combination of the first lens and the second lens;

[0015] 1.03≥f3 / f≥0.87, wherein f is the equivalent focal length of the optical system;

[0016] 1.99≤OAL / f≤2.23, wherein OAL is the total length of the optical system;

[0017] NA>0.6, wherein NA is the numerical aperture.

[0018] Preferably, the first lens and the second lens are injection molded lenses.

[0019] Preferably, the third lens is a glass cemented lens.

[0020] Preferably, the Abbe number of the optical material used by the first lens and the third lens is greater than the Abbe number of the material used by the second lens by more than 20.

[0021] Preferably, the surface shape of the first lens and the second lens is set as aspheric surface.

[0022] The present application has the advantages that compared with the traditional lens, the light energy utilization rate is improved, the system efficiency is more limited, and the system length is more compact,

[0023] 1. The object side surface of the second lens is designed as M type, which can effectively adjust the spherical aberration of large aperture and reduce the thickness difference of the second lens, and reduce the processing difficulty;

[0024] 2. 1.4>f1 / f3>0.7, by reasonably distributing f1 and f3, the optical power of the two convex lenses is kept in balance, so as to avoid that a single lens bears large optical power and large aberration;

[0025] 3. The first lens and the second lens are plastic aspheric lenses, and the third lens is a glass lens. The glass lens has more stable performance at different temperatures. The setting makes the optical power of the lens group of the first lens and the second lens relative to the glass lens small, and the main optical power is borne by the third lens, so that the whole optical system has good thermal stability;

[0026] 4. 1.99≤OAL / f≤2.23, which can make the volume of the optical system smaller, and the application space requirement is lower;

[0027] 5. NA>0.6, the numerical aperture of the optical lens is large, so the energy utilization rate is high. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 It is a schematic diagram of the optical path of the classic Cooke three-piece lens.

[0029] Figure 2 It is a structural schematic diagram of the embodiment one of the present application.

[0030] Figure 3 It is the astigmatism and field curvature curve and the distortion curve of the embodiment one of the present application.

[0031] Figure 4 It is the axial chromatic aberration curve of the embodiment one of the present application.

[0032] Figure 5 It is the magnification chromatic aberration curve of the embodiment one of the present application.

[0033] Figure 6 It is a structural schematic diagram of the embodiment two of the present application.

[0034] Figure 7 It is the astigmatism and field curvature curve and the distortion curve of the embodiment two of the present application.

[0035] Figure 8The chromatic aberration curve on the axis of the second embodiment of the present application.

[0036] Figure 9 The magnification chromatic aberration curve of the second embodiment of the present application.

[0037] The reference signs are: first lens 10, second lens 11, third lens 12. DETAILED DESCRIPTION

[0038] In order to further understand the features, technical means and specific purposes and functions achieved by the present application, the present application is described in further detail below in combination with the drawings and specific embodiments.

[0039] Reference Figures 2 to 9 .

[0040] The basic embodiment of the present application discloses a large-aperture three-piece lens, which comprises three lenses along the optical axis from the object side to the image side, which are in turn a first lens 10 with positive focal power and both sides are convex, a second lens 11 with negative focal power and the object side is M-shaped, and a third lens 12 with positive focal power and both sides are convex; the object side of the second lens is designed as M-shaped, which can effectively adjust the spherical aberration of the large aperture and reduce the thickness difference of the second lens, and reduce the processing difficulty;

[0041] And it satisfies the following conditional expression:

[0042] |r3|<|r4|, wherein r3 and r4 are the radii of curvature of the object side and the image side of the second lens 11 respectively;

[0043] 1.4>f1 / f3>0.7, wherein f1 is the equivalent focal length of the first lens 10, and f3 is the equivalent focal length of the third lens 12; by reasonably allocating f1 and f3, the focal power of the two convex lenses is kept in balance, thereby avoiding that a single lens bears a large focal power and a large aberration occurs;

[0044] 2.48≥f12 / f3≥1.81, wherein f12 is the equivalent focal length of the combined lens group of the first lens 10 and the second lens 11;

[0045] 1.03≥f3 / f≥0.87, wherein f is the equivalent focal length of the optical system;

[0046] 1.99≤OAL / f≤2.23, wherein OAL is the total length of the optical system; by such setting, the volume of the optical system can be small, and the space requirement is lower;

[0047] NA>0.6, wherein NA is the numerical aperture, and by such setting, the numerical aperture of the optical lens is large, and the energy utilization rate is high.

[0048] The first lens 10 and the second lens 11 are injection molded lenses. The third lens 12 is a glass cemented lens. The first lens and the second lens are plastic aspheric lenses, and the third lens is a glass lens, which has more stable performance at different temperatures. The arrangement makes the focal power of the lens group of the first lens and the second lens relative to the glass lens small, and the main focal power is borne by the third lens, so that the overall optical system has good thermal stability.

[0049] The Abbe number of the optical material used by the first lens 10 and the third lens 12 is greater than the Abbe number of the material used by the second lens 11 by 20 or more.

[0050] The surface shape of the first lens 10 and the second lens 11 is set to be aspheric.

[0051] Compared with the conventional lens, the present application can improve the light energy utilization rate, make the system efficiency more limited, and the system length more compact.

[0052] In embodiment one, the structure is as shown in Figure 2 The astigmatism and field curvature curve and the distortion curve are as shown in Figure 3 The on-axis chromatic aberration curve is as shown in Figure 4 The magnification chromatic aberration curve is as shown in Figure 5 The surface parameters of the present embodiment are as follows.

[0053] Table 1

[0054] Surface No. Surface Type Curvature Radius R (mm) Thickness (mm) Refractive Index Abbe Number S1 Asphere 17.15 11.25 1.492 57.98 S2 Asphere -10.46 1.23 S3 Asphere -12.40 7.33 1.584 27.86 S4 Asphere 327.80 0.50 S5 Sphere 15.32 8.68 1.788 47.50 S6 Sphere -22.68 3.91 Image Side Sphere Infinity 0.00

[0055] The expression of the aspheric surface is as follows:

[0056]

[0057] Where z is the sag of the aspheric surface at the position r; c is the paraxial curvature of the aspheric 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.

[0058] Table 2

[0059]

[0060] Table 3

[0061]

[0062] Table 4, constraint relationship of embodiment one

[0063]

[0064]

[0065] From the data, the numerical aperture reaches 0.76, which is only about 0.2 compared with the original Cook three-piece, greatly improving the energy utilization.

[0066] In Example Two, the structure is as shown in Figure 6 The astigmatism and field curvature curves and distortion curve are as shown in Figure 7 The on-axis chromatic aberration curve is as shown in Figure 8 The magnification chromatic aberration curve is as shown in Figure 9 The surface parameters of this embodiment are as follows.

[0067] Table 5

[0068] Surface No. Surface Type Curvature Radius R (mm) Thickness (mm) Refractive Index Abbe Number S1 Asphere 21.88 9.88 1.492 57.98 S2 Asphere -7.57 0.70 S3 Asphere -12.77 4.00 1.584 27.86 S4 Asphere 65.34 4.50 S5 Sphere 18.14 7.40 1.788 47.50 S6 Sphere -32.91 4.02 Image Side Sphere Infinity 0.00

[0069] The aspherical expression is as follows:

[0070]

[0071] Wherein z is the sag of the aspherical surface at the 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 radius of curvature R of the surface); k is the conic coefficient; A, B,.., J are high-order term coefficients.

[0072] Table 6

[0073]

[0074] Table 7

[0075]

[0076] Table 8, constraint relationship of Example Two

[0077] Constraints Results |r3|<|r4| From Table 5, it is known that 1.4 > f1 / f3 > 0.7 From Table 5, it is known that 2.48 ≥ f12 / f3 ≥ 1.81 From Table 5, it is known that f12 / f3 = 1.81, which satisfies 1.03 ≥ f3 / f ≥ 0.87 From Table 5, it is known that f3 / f = 1.03, which satisfies 1.99 ≤ OAL / f ≤ 2.23 From Table 5, it is known that OAL / f = 1.99, which satisfies Numerical Aperture NA > 0.6 From Table 5, it is known that NA = 0.85, which satisfies Back-Flux > 2 mm From Table 5, it is known that the back-flux is 4 mm, which satisfies

[0078] From the data, the numerical aperture reaches 0.85, which is only about 0.2 compared with the original Cook three-piece, greatly improving the energy utilization.

[0079] The above-described embodiments only express two embodiments of the present application, which are described in more detail and in more detail, but should not be understood as limiting the scope of the patent of the present application. It should be noted that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of protection of the present application. Therefore, the scope of protection of the patent of the present application should be subject to the appended claims.

Claims

1. A large-aperture three-element lens, characterized in that, Along the optical axis from the object side to the image side, there are three lenses, namely, a first lens (10) with positive optical power and both sides being convex, a second lens (11) with negative optical power and the object side being M-shaped, and a third lens (12) with positive optical power and both sides being convex. The aperture stop is set at the focal point of the object side. And it satisfies the following condition: |r3|<|r4|, where r3 and r4 are the radii of curvature on the object side and image side of the second lens (11), respectively; 1.4>f1 / f3>0.7, where f1 is the equivalent focal length of the first lens (10) and f3 is the equivalent focal length of the third lens (12); 2.48≥f12 / f3≥1.81, where f12 is the equivalent focal length of the combined lens group of the first lens (10) and the second lens (11); 1.03≥f³ / f≥0.87, where f is the equivalent focal length of the optical system; 1.99≤OAL / f≤2.23, where OAL is the total length of the optical system; NA>0.6, where NA is the numerical aperture.

2. The large-aperture three-element lens according to claim 1, characterized in that, The first lens (10) and the second lens (11) are configured as injection-molded lenses.

3. A large-aperture three-element lens according to claim 1, characterized in that, The third lens (12) is configured as a cemented glass lens.

4. A large-aperture three-element lens according to claim 1, characterized in that, The Abbe number of the optical materials used in the first lens (10) and the third lens (12) is more than 20 greater than the Abbe number of the material used in the second lens (11).

5. A large-aperture three-element lens according to claim 2, characterized in that, The surface shape of both the first lens (10) and the second lens (11) is set to aspherical.

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