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, the four lenses are a first lens, a second lens, a third lens and a fourth lens in sequence, the first lens is a meniscus lens with at least one aspheric surface, the second lens is a meniscus lens with at least one aspheric surface, and the third lens is a meniscus lens with at least one aspheric surface. The third lens and the fourth lens are arranged to have opposite focal power symbols; the convex surface of the first lens faces the object side, R1gt; r1 and R2 are curvature radiuses of the object side and the image side of the first lens respectively; the concave surface of the second lens faces the object side, R3lt; r3 and R4 are respectively the curvature radius of the object side and the curvature radius of the image side of the second lens; the object side surface of the third lens is a convex surface; the image side surface of the fourth lens is a convex surface; f1 / fgt; f is the equivalent focal length of the system, and f1 is the equivalent focal length of the first lens; f2 / fgt; f2 is the equivalent focal length of the first lens; f12 / flt; f12 is the equivalent focal length of the combination of the first lens and the second lens. 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, an illumination module (including light source and illumination optical components) is required to project light onto the image source DMD. This requires the projection lens to have a long back focus and sufficient space for light to irradiate the image source without obstruction. Figure 1 As shown in the figure, the architecture of a typical DLP projection system is shown. The light energy of the light source 2 (mostly a high-power light-emitting diode LED) is collimated by the illumination lens 3, and the light is regulated by the reflector 6 to the image source DMD5, and then reflected from the DMD5, and then incident coupled into the projection lens 1, and finally projected onto the receiving surface. In order to achieve a sufficiently high image quality, some projection lenses will adopt the optical lenses of traditional DLP projectors, which generally have up to 7 lenses, which makes the assembly complicated, heavy and has a large space volume. For example, China Invention Patent Application Publication No. CN115598795A, with the application publication date of January 13, 2023, discloses a vehicle-mounted projection lens that meets the requirements of athermalization and large bias, and includes, from the object side to the image side, a first lens group, a second lens group, an aperture, a third lens group, a fourth lens group, a dichroic prism and an image sensor; the first lens group includes a first lens with negative focal power and a second lens with positive focal power; the second lens group and the third lens group are both cemented lens groups, wherein the second lens group is formed by cementing a third lens with positive focal power and a fourth lens with negative focal power, and the third lens group is formed by cementing a fifth lens with positive focal power and a sixth lens with negative focal power; the fourth lens group includes a seventh lens with positive focal power and an eighth lens with positive focal power.

[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] In view of the problems existing in the above-mentioned prior art, it is necessary to provide a technology that can fully utilize the advantages of plastic lenses and glass lenses while avoiding the disadvantages of both, 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, it is necessary to provide a projection lens with the advantages of long back focus, heat elimination and low cost to address the problems of the existing technology.

[0007] In order 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, a third lens, and a fourth lens in sequence. The first lens is a meniscus lens with at least one aspherical surface, and the second lens is a meniscus lens with at least one aspherical surface. The third lens and the fourth lens are arranged to have opposite optical power signs, that is, when the third lens has positive optical power, the fourth lens has negative optical power; when the third lens has negative optical power, the fourth lens has positive optical power; and it satisfies the following conditional formula:

[0008] The convex surface of the first lens faces the object side, |R1|>|R2|, where R1 and R2 are the curvature radii of the object side and image side of the first lens respectively;

[0009] The concave surface of the second lens faces the object side, |R3|<|R4|, where R3 and R4 are the curvature radii of the object side and image side of the second lens respectively;

[0010] The object side surface of the third lens is a convex surface, and the image side surface of the fourth lens is a convex surface;

[0011] |f1| / f>3.0, where f is the equivalent focal length of the system, and f1 is the equivalent focal length of the first lens;

[0012] |f2| / f>5, where f2 is the equivalent focal length of the second lens;

[0013] f12 / f<-3.0, where f12 is the equivalent focal length of the first lens and the second lens combination lens group;

[0014] 1.9>f34 / f>1.1, wherein f34 is the equivalent focal length of the third lens and the fourth lens combination lens group;

[0015] d14 / OAL<0.65, wherein d14 is the length of the lens group from the first lens to the fourth lens group, and OAL is the total system working length of the entire optical projection lens including the lens group and the imaging surface.

[0016] Preferably, the adjacent surface between the third lens and the fourth lens is set as a convex surface, and the adjacent surface between the fourth lens and the third lens is set as a concave surface.

[0017] Preferably, the adjacent surface between the third lens and the fourth lens is set as a concave surface, and the adjacent surface between the fourth lens and the third lens is set as a convex surface.

[0018] Preferably, the first lens and the second lens are both configured as injection-molded aspheric lenses, and the third lens and the fourth lens are both configured as spherical glass lenses.

[0019] Preferably, the third lens and the fourth lens are glued into one body.

[0020] Preferably, the third lens and the fourth lens are arranged separately.

[0021] 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.

[0022] Preferably, a prism is arranged between the fourth lens and the image side surface.

[0023] Preferably, the materials of the third lens and the fourth lens are different, and the difference between the Abbe numbers of the third lens and the fourth lens is greater than 20.

[0024] The beneficial effects of the present invention are:

[0025] 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;

[0026] 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.

[0027] 3. The present invention is a glass-plastic hybrid design, which can improve performance while reducing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the architecture of a typical DLP projection system.

[0029] Figure 2 A schematic structural diagram of embodiment 1 of the present invention.

[0030] Figure 3 This is an MTF curve diagram of the first embodiment of the present invention.

[0031] Figure 4 It is a structural diagram of embodiment 2 of the present invention.

[0032] Figure 5 This is an MTF curve diagram of the second embodiment of the present invention.

[0033] Figure 6 This is a schematic diagram of the structure of the third embodiment of the present invention.

[0034] Figure 7 This is an MTF curve diagram of the fourth embodiment of the present invention.

[0035] The reference numerals are: a first lens 10 , a second lens 11 , a third lens 12 , a fourth lens 13 , and a field lens 14 . DETAILED DESCRIPTION

[0036] 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.

[0037] refer to Figures 2 to 7 .

[0038] 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 10, a second lens 11, a third lens 12, and a fourth lens 13 in sequence. The first lens 10 is a meniscus lens with at least one aspherical surface, and the second lens 11 is a meniscus lens with at least one aspherical surface. The third lens 12 and the fourth lens 13 are configured to have opposite optical power signs, that is, when the third lens 12 has a positive optical power, the fourth lens 13 has a negative optical power; when the third lens 12 has a negative optical power, the fourth lens 13 has a positive optical power.

[0039] It satisfies the following conditions:

[0040] The convex surface of the first lens 10 faces the object side, |R1|>|R2|, where R1 and R2 are the curvature radii of the object side and the image side of the first lens 10 respectively;

[0041] The concave surface of the second lens 11 faces the object side, |R3|<|R4|, where R3 and R4 are the curvature radii of the object side and the image side of the second lens 11 respectively;

[0042] The object side surface of the third lens 12 is convex, and the image side surface of the fourth lens 13 is convex;

[0043] |f1| / f>3.0, where f is the equivalent focal length of the system, and f1 is the equivalent focal length of the first lens 10;

[0044] |f2| / f>5, where f2 is the equivalent focal length of the second lens 11;

[0045] f12 / f<-3.0, where f12 is the equivalent focal length of the combined lens group of the first lens 10 and the second lens 11;

[0046] Through the above arrangement, the optical power of the first lens 10 and the second lens 11 is very small, and even if there is a temperature change, the optical performance of the system is slightly affected.

[0047] 1.9>f34 / f>1.1, wherein f34 is the equivalent focal length of the third lens 12 and the fourth lens 13 combined lens group; through such an arrangement, the third lens 12 and the fourth lens 13 made of glass material bear the main optical focal length, and because the glass performance is stable, the temperature change has little effect on the optical performance of the system.

[0048] In order to set up the system with a longer rear space to accommodate the lighting module without affecting the incident light energy, by setting

[0049] d14 / OAL<0.65, wherein d14 is the length of the lens group from the first lens 10 to the fourth lens 13, and OAL is the total system working length of the entire optical projection lens including the lens group and the imaging surface.

[0050] Preferably, the adjacent surface between the third lens 12 and the fourth lens 13 is set as a convex surface, and the adjacent surface between the fourth lens 13 and the third lens 12 is set as a concave surface.

[0051] Preferably, the adjacent surface between the third lens 12 and the fourth lens 13 is set as a concave surface, and the adjacent surface between the fourth lens 13 and the third lens 12 is set as a convex surface.

[0052] Preferably, the first lens 10 and the second lens 11 are both configured as injection-molded aspheric lenses, and the third lens 12 and the fourth lens 13 are both configured as spherical glass lenses.

[0053] Preferably, the third lens 12 and the fourth lens 13 are glued together as one body, which is beneficial to assembly and reduces energy loss.

[0054] Preferably, the third lens 12 and the fourth lens 13 are separately arranged. Because the separation increases a surface degree of freedom, it can sometimes reduce aberrations.

[0055] Preferably, a field lens 14 is disposed between the fourth lens 13 and the image side surface, and the distance between the field lens 14 and the fourth lens 13 is greater than 1.3 times the effective focal length, thereby ensuring that sufficient rear space is reserved for the lighting unit.

[0056] Preferably, a prism is provided between the fourth lens 13 and the image side surface for coupling the illumination light path.

[0057] Preferably, the materials of the third lens 12 and the fourth lens 13 are different, and the difference between the Abbe numbers of the third lens 12 and the fourth lens 13 is greater than 20, thereby achieving an achromatic effect.

[0058] Embodiment 1: In this embodiment, the third lens 12 with negative optical power and the fourth lens 13 with positive optical power are separate lenses, and the structural diagram is shown in FIG. Figure 2 , MTF curve is as follows Figure 3 .

[0059] Table 1, Parameters of each surface of Example 1

[0060] Surface serial number Surface type Curvature radius R(mm) Thickness(mm) Refractive Index Abbe number S1 Aspheric 6.147 2.240 1.537 56.1 S2 Aspheric 3.846 2.950 S3 Aspheric -3.490 5.000 1.537 56.1 S4 Aspheric -5.129 3.444 S5 Spherical 11.226 0.840 1.755 27.6 S6 Spherical 5.895 0.300 S7 Spherical 6.631 3.200 1.496 81.6 S8 Spherical -6.893 13.000 S9(Image plane) Spherical endless 0.000

[0061] Table 2, Parameters of each surface of Example 1

[0062]

[0063] The expression for aspheric surface is as follows:

[0064]

[0065] 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.

[0066] Table 3, design parameters of the optical lens of Example 1

[0067]

[0068] Table 4, constraint relationship of embodiment 1

[0069] Constraints Design Results |R1|>|R2| From the parameter table, we know that |R3|<|R4| From the parameter table, we know that |f1| / f>3.0 |f1| / f=3.61 Knowing that |f2| / f>5.0 |f2| / f=37.1Knowledge satisfaction f12 / f<-3.0 f12 / f=-6.41 is enough 1.9>f34 / f>1.1 f34 / f=1.46 is known to satisfy d14 / OAL<0.65 d14 / OAL=0.58Satisfied

[0070] Embodiment 2: In this embodiment, the third lens is a negative lens, the fourth lens is a positive lens, the two lenses are glued together, and the projection distance of the optical system is 1m. The structural diagram is as follows: Figure 4 , MTF curve is as follows Figure 5 .

[0071] Table 5, Parameters of each surface of Example 2

[0072] Surface serial number Surface type Curvature radius R(mm) Thickness(mm) Refractive Index Abbe number S1 Aspheric 6.140 2.240 1.537 56.1 S2 Aspheric 3.907 2.950 S3 Aspheric -3.440 5.500 1.537 56.1 S4 Aspheric -5.855 2.137 S5 Spherical 9.782 0.840 1.753 28.9 S6 Spherical 5.468 3.333 1.496 81.6 S7 Spherical -7.549 13.000 S8(Image plane) Spherical infinity 0.000

[0073] Table 6, parameters of each surface of Example 2

[0074]

[0075] The expression for aspheric surface is as follows:

[0076]

[0077] 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.

[0078] Table 7, design parameters of the optical lens of Example 2

[0079]

[0080] Table 8, constraint relationship of Example 2

[0081] Constraints Design Results |R1|>|R2| From the parameter table, we know that |R3|<|R4| From the parameter table, we know that |f1| / f>3.0 |f1| / f=3.84 Knowing that |f2| / f>5.0 |f2| / f=9.55 Knowing that you are satisfied f12 / f<-3.0 f12 / f=-3.6 is satisfied 1.9>f34 / f>1.1 f34 / f=1.38 is known to satisfy d14 / OAL<0.65 d14 / OAL=0.56Satisfied

[0082] Embodiment 3: This embodiment shows that in actual use, a field lens 14 is arranged between the fourth lens 13 and the image side surface to improve the control ability of the edge beam and reduce the lens aperture without affecting the optical properties of the entire projection lens group. The third lens 12 of this embodiment is a positive lens, and the fourth lens 13 is a negative lens, which are glued together. Figure 6 As described above; the MTF curve is as follows Figure 7 shown.

[0083] Table 9, parameters of each surface of Example 3

[0084] Surface serial number Surface type Curvature radius R(mm) Thickness(mm) Refractive Index Abbe number S1 Aspheric 8.020 2.240 1.537 56.1 S2 Aspheric 5.671 2.950 S3 Aspheric -2.869 5.000 1.537 56.1 S4 Aspheric -5.052 4.764 S5 Spherical 12.615 2.706 1.496 81.5 S6 Spherical -5.069 0.840 1.753 28.9 S7 Spherical -8.195 13.000 S8 Spherical 10.000 1.500 1.589 61.3 S9 Spherical endless 1.000 S10 (image plane) Spherical endless 0.000

[0085] Table 10, Parameters of each surface of Example 3

[0086]

[0087] The expression for aspheric surface is as follows:

[0088]

[0089] 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.

[0090] Table 11, design parameters of the optical lens of Example 3

[0091]

[0092] Table 12, constraint relationship of embodiment 3

[0093] Constraints Design Results |R1|>|R2| From the parameter table, we know that |R3|<|R4| From the parameter table, we know that |f1| / f>3.0 |f1| / f=6.73 Knowing that it is satisfied |f2| / f>5.0 |f2| / f=7.75 Knowing that it is satisfied f12 / f<-3.0 f12 / f=-4.55 is enough 1.9>f34 / f>1.1 f34 / f=1.6 is known to be satisfied d14 / OAL<0.65 d14 / OAL=0.54Satisfied

[0094] 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.

[0095] 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 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 present invention patent shall be subject to the attached claims.

Claims

1. A projection lens, It is characterized in that The optical system comprises four lenses from the object side to the image side along the optical axis, which are sequentially a first lens (10), a second lens (11), a third lens (12), and a fourth lens (13); the first lens (10) is a meniscus lens with at least one aspherical surface, the second lens (11) is a meniscus lens with at least one aspherical surface, and the third lens (12) and the fourth lens (13) are arranged to have opposite optical power signs; It satisfies the following conditions: The convex surface of the first lens (10) faces the object side, |R1|>|R2|, wherein R1 and R2 are the curvature radii of the object side and image side of the first lens (10), respectively; The concave surface of the second lens (11) faces the object side, and |R3|<|R4|, wherein R3 and R4 are the curvature radii of the object side and image side of the second lens (11), respectively; The object side surface of the third lens (12) is a convex surface, and the image side surface of the fourth lens (13) is a convex surface; |f1| / f>3.0, wherein f is the equivalent focal length of the system, and f1 is the equivalent focal length of the first lens (10); |f2| / f>5, wherein f2 is the equivalent focal length of the second lens (11); f12 / f<-3.0, wherein f12 is the equivalent focal length of the combined lens group of the first lens (10) and the second lens (11); 1.9>f34 / f>1.1, wherein f34 is the equivalent focal length of the lens assembly composed of the third lens (12) and the fourth lens (13); d14 / OAL<0.65, wherein d14 is the length of the lens group from the first lens (10) to the fourth lens (13), and OAL is the total system working length of the entire optical projection lens including the lens group and the imaging surface.

2. A projection lens according to claim 1, It is characterized in that The adjacent surfaces of the third lens (12) and the fourth lens (13) are arranged as convex surfaces, and the adjacent surfaces of the fourth lens (13) and the third lens (12) are arranged as concave surfaces.

3. The projection lens according to claim 1, It is characterized in that The adjacent surfaces of the third lens (12) and the fourth lens (13) are arranged as concave surfaces, and the adjacent surfaces of the fourth lens (13) and the third lens (12) are arranged as convex surfaces.

4. The projection lens according to claim 1, It is characterized in that The first lens (10) and the second lens (11) are both configured as injection-molded aspheric lenses, and the third lens (12) and the fourth lens (13) are both configured as spherical glass lenses.

5. The projection lens according to claim 1, It is characterized in that The third lens (12) and the fourth lens (13) are glued together into one body.

6. The projection lens according to claim 1, It is characterized in that The third lens (12) and the fourth lens (13) are arranged separately.

7. The projection lens according to claim 1, It is characterized in that A field lens (14) is arranged between the fourth lens (13) and the image side surface, and the distance between the field lens (14) and the fourth lens (13) is greater than 1.3 times the effective focal length.

8. The projection lens according to claim 1, It is characterized in that A prism is arranged between the fourth lens (13) and the image side surface.

9. The projection lens according to claim 1, It is characterized in that The materials of the third lens (12) and the fourth lens (13) are different, and the difference between the Abbe numbers of the third lens (12) and the fourth lens (13) is greater than 20.

Images