Projection lens

Abstract

The invention discloses a projection lens which comprises four lenses from an object side surface to an image side surface along an optical axis, and the four lenses are a first lens, a second lens, a diaphragm, a third lens and a fourth lens in sequence. The first lens has negative focal power, the object side surface of the first lens is a convex surface, and the image side surface of the first lens is a concave surface; the second lens has positive focal power, the object side surface of the second lens is a convex surface, and the image side surface of the second lens is a concave surface; the third lens has negative focal power, the object side surface of the third lens is a convex surface, and the image side surface of the third lens is a concave surface; the fourth lens has positive focal power, the object side face of the fourth lens is a convex face, and the image side face of the fourth lens is a convex face. The following conditional expression is satisfied: f12 / flt; -5.0, 2.0 gt,-5.0, 2.0 gt; f34 / fgt; 1.3, d < 14 > / OALlt; and 0.65. The catalyst has the advantages of long back focus, athermalization and low cost.

Description

Technical Field

[0001] The invention relates to the technical field of optical imaging display, and in particular discloses a projection lens. Background Art

[0002] With the development of new energy vehicles, the market has many demands for on-board projection imaging optoelectronic technology, such as high-pixel headlights with millions of pixels, on-board micro dynamic welcome light carpets, and in-car projection entertainment systems. Most of these applications require the use of digital micromirror technology (DMD or DLP). Since DMD itself does not emit light, a lighting module, including a light source and lighting optical components, is required to project light onto the image source DMD. This requires the projection lens to have a long back focus and enough space for light to irradiate the image source without obstruction. Figure 1 As shown, Figure 1 The architecture of a typical DLP projection system is shown. The light energy of the light source 2 is collimated by the illumination lens 3, and the reflector 6 controls the light to the image source DMD 5, and then reflects from the DMD, and then couples into the projection lens 1, and finally projects onto the receiving surface. The light source 2 here is mostly a high-power light-emitting diode LED. In order to achieve sufficiently high image quality, some projection lenses will adopt the optical lens of a traditional DLP projector. Generally, there are a large number of lenses, and some are equipped with up to 7 pieces, which makes the assembly complicated, the weight heavy, and the space volume large. For example, China application publication number CN117369085A, the application publication date is January 9, 2024, which discloses an athermal ultra-short back-focus projection lens, which relates to the field of lens design technology. The athermal ultra-short back-focus projection lens includes: a lens system; a lens system, which includes, in sequence, from the object side to the image side along the optical axis: a first lens, a second lens, a third lens, a fourth lens, an aperture stop and a fifth lens; the third lens and the fourth lens are cemented together; the first lens is an aspheric lens with negative optical power, the object side surface is convex, and the image side surface is concave; the second lens is an aspheric lens with positive optical power, and the image side surface is convex; the third lens is a spherical lens with negative optical power, and the image side surface is concave; the fourth lens is a spherical lens with positive optical power, the object side surface is convex, and the image side surface is convex; the fifth lens is a spherical lens with positive optical power, the object side surface is convex, and the image side surface is flat.

[0003] In addition, due to the complex driving environment of the car, the application environment of the headlights may also be relatively harsh. It is necessary to meet the ambient temperature of -45℃ to 85℃ for normal operation without major changes in performance. Therefore, the projection lens of the high-pixel headlights is required to have stable back focus within a large temperature range of -45℃ to 85℃.

[0004] Cost is also a very important consideration for automotive projection lenses. A basic fact is that spherical glass lenses are cheaper than aspherical glass lenses, while injection molded plastic lenses are cheaper than spherical lenses of the same caliber, and can use free-form surfaces or aspherical surfaces, which gives them greater design freedom. In addition, plastic lenses are lightweight and shock-resistant. However, injection molded plastic lenses have an obvious disadvantage, which is poor thermal stability, which is mainly reflected in the large changes in refractive index and thermal expansion coefficient with temperature. If the design is not appropriate, the optical performance of the lens will deteriorate dramatically in high and low temperature environments. But the advantage of plastic lenses is that the surface shape can have more design freedom, and they are lightweight and less expensive.

[0005] Therefore, it is necessary to provide a method that can fully utilize the advantages of plastic lenses and glass lenses while avoiding their disadvantages, targeting the long back focus characteristics of DLP and the requirement of a wide application temperature range. Summary of the invention

[0006] Based on this, the present invention provides a projection lens having the advantages of long back focus, heat elimination and low cost.

[0007] To solve the problems of the prior art, the present invention discloses a projection lens, which includes four lenses from the object side to the image side along the optical axis, which are a first lens, a second lens, an aperture, a third lens, and a fourth lens in sequence; the first lens has a negative optical power, the object side of the first lens is a convex surface, and the image side of the first lens is a concave surface; the second lens has a positive optical power, the object side of the second lens is a convex surface, and the image side of the second lens is a concave surface; the third lens has a negative optical power, the object side of the third lens is a convex surface, and the image side of the third lens is a concave surface; the fourth lens has a positive optical power, the object side of the fourth lens is a convex surface, and the image side of the fourth lens is a convex surface; the concavity and convexity of the surface of the first lens, the second lens, the third lens, and the fourth lens are defined by comparing the edge of the surface with the center of the surface. If the center of the surface is more concave than the edge of the surface, the surface is defined as concave, otherwise, it is convex;

[0008] It satisfies the following conditions:

[0009] f12 / f<-5.0, where f12 is the equivalent focal length of the combination of the first lens and the second lens, and f is the equivalent focal length of the system;

[0010] 2.0>f34 / f>1.3, wherein f34 is the equivalent focal length of the third lens and the fourth lens combination lens group;

[0011] d14 / OAL<0.65, wherein d14 is the length of the lens group from the first lens to the fourth lens, and OAL is the total length of the entire optical projection lens system including the lens group and the imaging surface.

[0012] Preferably, the first lens and the second lens are made of injection-molded aspherical surfaces, and the third lens and the fourth lens are made of spherical glass.

[0013] Preferably, the third lens and the fourth lens are configured as a glued-in-one structure.

[0014] Preferably, the third lens and the fourth lens are arranged as discrete structures.

[0015] Preferably, the third lens and the fourth lens are made of different materials, and the difference between the Abbe numbers of the third lens and the fourth lens is greater than 20.

[0016] Preferably, a field lens is provided between the fourth lens and the image side surface, and the distance between the field lens and the fourth lens is greater than 1.3 times the effective focal length.

[0017] Preferably, a prism is provided in the middle of the air gap between the imaging plane and the fourth lens.

[0018] The beneficial effects of the present invention are:

[0019] 1. The lens of the present invention has the characteristic of long back focus, which can provide sufficient rear mechanical space for the DLP illumination optical module;

[0020] 2. The present invention has excellent thermal stability. The first lens and the second lens are mainly used to correct the high-order aberrations of the system, and the optical power is small, which can make the influence of temperature extremely small. The other lenses use glass lenses, and the optical performance of glass lenses changes little with temperature. Therefore, the combined application can make the lens adapt to the field with a wide range of temperature applications.

[0021] 3. The present invention is a glass-plastic hybrid design, which can improve performance while reducing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the architecture of a typical DLP projection system.

[0023] Figure 2 A schematic structural diagram of embodiment 1 of the present invention.

[0024] Figure 3 This is an MTF curve diagram of the first embodiment of the present invention.

[0025] Figure 4 It is a structural diagram of embodiment 2 of the present invention.

[0026] Figure 5 This is an MTF curve diagram of the second embodiment of the present invention.

[0027] Figure 6 This is a schematic diagram of the structure of the third embodiment of the present invention.

[0028] Figure 7 This is an MTF curve diagram of the fourth embodiment of the present invention.

[0029] The reference numerals are: a first lens 11 , a second lens 12 , an aperture 10 , a third lens 13 , a fourth lens 14 , and a field lens 15 . DETAILED DESCRIPTION

[0030] In order to further understand the features, technical means, specific objectives and functions of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0031] refer to Figures 2 to 7 .

[0032] The basic embodiment of the present invention discloses a projection lens, which includes four lenses from the object side to the image side along the optical axis, which are a first lens 11, a second lens 12, an aperture 10, a third lens 13, and a fourth lens 14 in sequence;

[0033] The first lens 11 has negative optical power, the object side surface of the first lens 11 is convex, and the image side surface of the first lens 11 is concave;

[0034] The second lens 12 has positive refractive power, the object side surface of the second lens 12 is convex, and the image side surface of the second lens 12 is concave;

[0035] The third lens 13 has negative optical power, the object side surface of the third lens 13 is convex, and the image side surface of the third lens 13 is concave;

[0036] The fourth lens 14 has positive refractive power, the object side surface of the fourth lens 14 is convex, and the image side surface of the fourth lens 14 is convex;

[0037] The concavity and convexity of the surface of the first lens 11, the second lens 12, the third lens 13, and the fourth lens 14 are defined by comparing the edge of the surface with the center of the surface. If the center of the surface is more concave than the edge of the surface, the surface is defined as concave, otherwise, it is convex;

[0038] It satisfies the following conditions:

[0039] f12 / f<-5.0, where f12 is the equivalent focal length of the combination of the first lens 11 and the second lens 12, and f is the equivalent focal length of the system; if this condition is met, the focal powers of the first lens 11 and the second lens 12 are very small, so even if there is a temperature change, the optical performance of the system is less affected;

[0040] 2.0>f34 / f>1.3, where f34 is the equivalent focal length of the third lens 13 and the fourth lens 14 combined lens group; if this condition is met, the third lens 13 and the fourth lens 14 made of glass material bear the main focal length, and because the glass has stable performance, the temperature change has little effect on the optical performance of the system;

[0041] In order to provide the system with a longer rear space to accommodate the lighting module without affecting the incident light energy, d14 / OAL<0.65 is set, wherein d14 is the length of the lens group from the first lens 11 to the fourth lens 14, and OAL is the total length of the entire optical projection lens system including the lens group and the imaging surface.

[0042] Preferably, the first lens 11 and the second lens 12 are made of injection-molded aspherical surfaces, and the third lens 13 and the fourth lens 14 are made of spherical glass.

[0043] Preferably, the third lens 13 and the fourth lens are configured as a glued structure. The third lens 13 and the fourth lens are configured as separate structures. Gluing is beneficial to assembly and reducing energy loss, while separation can sometimes reduce aberrations because it increases a surface degree of freedom.

[0044] Preferably, the third lens 13 and the fourth lens 14 are made of different materials, and the difference in Abbe numbers between the third lens 13 and the fourth lens is greater than 20. For achromatization, the third lens 13 and the fourth lens 14 are made of different materials.

[0045] Preferably, a field lens 15 is arranged between the fourth lens 14 and the image side, and the distance between the field lens 15 and the fourth lens 14 is greater than 1.3 times the effective focal length. With such an arrangement, sufficient rear space is still guaranteed to be reserved for the lighting unit.

[0046] Preferably, a prism is provided in the middle of the air gap between the imaging plane and the fourth lens 14 for coupling the illumination light path.

[0047] The lens of the present invention has the characteristic of long back focus, and can provide sufficient rear mechanical space for the DLP lighting optical module; the present invention has excellent thermal stability, the first lens and the second lens are mainly used to correct the high-order aberrations of the system, and the optical focal length is small, which can make the influence of temperature extremely small, and other lenses use glass lenses, and the optical performance of glass lenses changes little with respect to temperature, so the combined application can make the lens adapt to the field with a wide range of temperature applications; the present invention is a glass-plastic hybrid design, which can improve performance while reducing costs.

[0048] Embodiment 1, the structural diagram is as follows Figure 2 , MTF curve is as follows Figure 3 .

[0049] Table 1, Parameters of each surface of Example 1

[0050] Surface serial number Surface type Curvature radius R(mm) Thickness(mm) Refractive Index Abbe number Lens diameter S1 Aspheric 4.932 1.500 1.537 56.1 8.796 S2 Aspheric 2.506 9.479 7.446 S3 Aspheric 13.465 4.369 1.587 29.9 8.227 S4 Aspheric 284.923 4.852 6.923 S5(Aperture) Spherical infinity 0.000 5.906 S6 Spherical 25.159 1.000 1.496 81.5 6.258 S7 Spherical 8.056 2.800 1.753 28.9 6.419 S8 Spherical -8.431 13.944 6.786 S9(Image plane) Spherical infinity 0.000

[0051] Table 2, Parameters of each surface of Example 1

[0052]

[0053]

[0054] The expression for aspheric surface is as follows:

[0055]

[0056] Where z is the vector height of the aspheric surface at position r; c is the paraxial curvature of the aspheric surface, c = 1 / R (i.e., the paraxial curvature c is the inverse of the surface curvature radius R); k is the cone coefficient; A~J are high-order coefficients.

[0057] Table 3, design parameters of the optical lens of Example 1

[0058]

[0059] Table 4, constraint relationship of embodiment 1

[0060] Constraints Design Results f12 / f<-5.0 f12 / f=-9.96 is enough 2.0>f34 / f>1.3 f34 / f=1.62 is known to be satisfied d14 / OAL<0.65 d14 / OAL=0.55Satisfied

[0061] Embodiment 2, the structural diagram is as follows Figure 4 , MTF curve is as follows Figure 5 .

[0062] Table 5, Parameters of each surface of Example 2

[0063] Surface serial number Surface type Curvature radius R(mm) Thickness(mm) Refractive Index Abbe number Lens diameter S1 Aspheric 5.007 1.500 1.537 56.1 8.349 S2 Aspheric 2.452 9.190 7.109 S3 Aspheric 17.979 2.481 1.587 29.9 7.939 S4 Aspheric -35.000 5.230 7.221 S5(Aperture) Spherical infinity 0.000 5.958 S6 Spherical 25.668 1.000 1.496 81.5 6.022 S7 Spherical 7.603 2.800 1.753 28.9 6.133 S8 Spherical -8.824 13.937 6.496 S9(Image plane) Spherical infinity 0.000

[0064] Table 6, Parameters of each surface of Example 2

[0065]

[0066] The expression for aspheric surface is as follows:

[0067]

[0068] Where z is the vector height of the aspheric surface at position r; c is the paraxial curvature of the aspheric surface, c = 1 / R (i.e., the paraxial curvature c is the inverse of the surface curvature radius R); k is the cone coefficient; A~J are high-order coefficients.

[0069] Table 7, design parameters of the optical lens of Example 2

[0070]

[0071] Table 8, constraint relationship of Example 2

[0072] Constraints Design Results f12 / f<-5.0 f12 / f=-44.88 is enough 2.0>f34 / f>1.3 f34 / f=1.74 is known to satisfy d14 / OAL<0.65 d14 / OAL=0.61Satisfied

[0073] Embodiment three, as Figure 6 As described above; the MTF curve is as follows Figure 7 shown.

[0074] Table 9, parameters of each surface of Example 3

[0075] Surface serial number Surface type Curvature radius R(mm) Thickness(mm) Refractive Index Abbe number Lens diameter S1 Aspheric 4.544 1.600 1.537 56.1 8.144 S2 Aspheric 2.141 7.726 6.910 S3 Aspheric 15.051 2.539 1.587 29.9 8.043 S4 Aspheric -39.292 5.919 7.292 S5(Aperture) Spherical infinity 0.000 5.947 S6 Spherical 24.266 1.000 1.846 23.7 5.960 S7 Spherical 7.494 2.800 1.617 63.4 6.078 S8 Spherical -9.491 12.416 6.460 S9 Spherical 15.000 3.000 1.589 61.3 5.735 S10 Spherical infinity 0.934 5.276 S11(Image plane) Spherical 0.000 0.000

[0076] Table 10, Parameters of each surface of Example 3

[0077]

[0078]

[0079] The expression for aspheric surface is as follows:

[0080]

[0081] Where z is the vector height of the aspheric surface at position r; c is the paraxial curvature of the aspheric surface, c = 1 / R (i.e., the paraxial curvature c is the inverse of the surface curvature radius R); k is the cone coefficient; A~J are high-order coefficients.

[0082] Table 11, design parameters of the optical lens of Example 3

[0083]

[0084] Table 12, constraint relationship of embodiment 3

[0085] Constraints Design Results f12 / f<-5.0 f12 / f=-11.86 is enough 2.0>f34 / f>1.3 f34 / f=1.83 is known to satisfy d14 / OAL<0.65 d14 / OAL=0.56Satisfied

[0086] The above-mentioned embodiments only express three implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A projection lens, characterized in that: The optical axis includes four lenses from the object side to the image side, which are a first lens (11), a second lens (12), an aperture (10), a third lens (13), and a fourth lens (14) in sequence; The first lens (11) has negative optical power, the object side surface of the first lens (11) is a convex surface, and the image side surface of the first lens (11) is a concave surface; The second lens (12) has positive optical power, the object side surface of the second lens (12) is a convex surface, and the image side surface of the second lens (12) is a concave surface; The third lens (13) has negative optical power, the object side surface of the third lens (13) is a convex surface, and the image side surface of the third lens (13) is a concave surface; The fourth lens (14) has positive refractive power, the object side surface of the fourth lens (14) is a convex surface, and the image side surface of the fourth lens (14) is a convex surface; The concavity and convexity of the surface of the first lens (11), the second lens (12), the third lens (13), and the fourth lens (14) are defined by comparing the edge of the surface with the center of the surface. If the center of the surface is more concave than the edge of the surface, the surface is defined as concave, otherwise, it is a convex surface; It satisfies the following conditions: f12 / f<-5.0, wherein f12 is the equivalent focal length of the combination of the first lens (11) and the second lens (12), and f is the equivalent focal length of the system; 2.0>f34 / f>1.3, wherein f34 is the equivalent focal length of the lens assembly composed of the third lens (13) and the fourth lens (14); d14 / OAL<0.65, wherein d14 is the length of the lens group from the first lens (11) to the fourth lens (14), and OAL is the total length of the entire optical projection lens system including the lens group and the imaging surface.

2. The projection lens according to claim 1, characterized in that: The first lens (11) and the second lens (12) are made of injection-molded aspheric surfaces, and the third lens (13) and the fourth lens (14) are made of spherical glass.

3. The projection lens according to claim 1, characterized in that: The third lens (13) and the fourth lens are arranged to be glued together into one structure.

4. The projection lens according to claim 1, characterized in that: The third lens (13) and the fourth lens are arranged as separate structures.

5. The projection lens according to claim 1, characterized in that: The third lens (13) and the fourth lens are made of different materials, and the difference between the Abbe numbers of the third lens (13) and the fourth lens is greater than 20.

6. A projection lens according to any one of claims 1 to 5, characterized in that: A field lens (15) is arranged between the fourth lens (14) and the image side surface, and the distance between the field lens (15) and the fourth lens (14) is greater than 1.3 times the effective focal length.

7. The projection lens according to claim 6, characterized in that: A prism is arranged in the middle of the air gap between the imaging surface and the fourth lens (14).

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