A projection lens

Abstract

The application discloses a projection lens, which comprises four lenses along an optical axis from an object side to an image side, and the four lenses are sequentially a first lens, a second lens, a third lens and a fourth lens. The first lens is a meniscus lens with at least one aspherical surface, and the second lens is also a meniscus lens with at least one aspherical surface. The third lens and the fourth lens are arranged to have opposite optical power signs. The convex surface of the first lens faces the object side, and |R1|>|R2|, wherein R1 and R2 are the radii of curvature of the object side and the image side of the first lens respectively. The concave surface of the second lens faces the object side, and |R3|<|R4|, wherein R3 and R4 are the radii of curvature of the object side and the image side of the second lens respectively. 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. |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. |f2| / f>5, wherein f2 is the equivalent focal length of the first lens. f12 / f<‑3.0, wherein f12 is the equivalent focal length of the combination of the first lens and the second lens. The projection lens has the advantages of long back focus, athermalization and low cost.

Description

Technical Field

[0001] This invention relates to the field of optical imaging and display technology, and specifically discloses a projection lens. Background Technology

[0002] With the development of new energy vehicles, the market has seen a surge in demand for automotive projection imaging optoelectronic technologies, such as high-pixel headlights with millions of pixels, in-vehicle miniature dynamic welcome light carpets, and in-vehicle projection entertainment systems. These applications often require the use of digital micromirror display (DMD) or digital light transmission (DLP) technology. Since DMDs themselves do not emit light, an illumination module (including a light source and illumination optics) is needed to project light onto the image source DMD. This necessitates a projection lens with a long back focal length and sufficient space to allow unobstructed light to reach the image source. For example... Figure 1 As shown in the figure, the architecture of a typical DLP projection system is illustrated. The light energy of the light source 2 (mostly high-power light-emitting diodes LED) is collimated by the illumination lens 3, and then controlled by the reflector 6 to be directed onto the image source DMD5. The light is then reflected from the DMD5, incidentally coupled into the projection lens 1, and finally projected onto the receiving surface. To achieve sufficiently high image quality, some projection lenses use traditional DLP projector lenses, typically with up to seven lenses, resulting in complex assembly, heavy weight, and large volume. For example, Chinese invention patent application publication number CN115598795A, published on January 13, 2023, discloses a vehicle-mounted projection lens that meets the requirements of heatless operation and large offset. From object to image, it sequentially includes a first lens group, a second lens group, an aperture stop, a third lens group, a fourth lens group, a beam splitter, and an image sensor. The first lens group includes a first lens with negative optical power and a second lens with positive optical power. The second and third lens groups are both cemented lens groups. The second lens group is cemented together with a third lens with positive optical power and a fourth lens with negative optical power, and the third lens group is cemented together with a fifth lens with positive optical power and a sixth lens with negative optical power. The fourth lens group includes a seventh lens with positive optical power and an eighth lens with positive optical power.

[0003] In addition, due to the complex driving environment of automobiles, the application environment of car lights may also be relatively harsh, requiring them to operate normally in ambient temperatures ranging from -45℃ to 85℃ without significant performance changes. This necessitates that the projection lens of high-pixel car headlights maintain stable focus over a wide temperature range of -45℃ to 85℃.

[0004] Cost is also a crucial factor to consider for automotive projection lenses. A basic fact is that spherical glass lenses are cheaper than aspherical glass lenses, and injection-molded plastic lenses are even cheaper than spherical lenses of the same diameter, while also allowing for freeform or aspherical surfaces, offering greater design freedom. In addition, plastic lenses are lightweight and shock-resistant. However, injection-molded plastic lenses have a significant drawback: poor thermal stability, primarily manifested in the large changes in refractive index and coefficient of thermal expansion with temperature. Improper design can lead to a drastic deterioration of the lens's optical performance under high and low temperature environments. On the other hand, plastic lenses offer greater design freedom in terms of surface shape, and are lightweight and lower in cost.

[0005] In view of the problems existing in the prior art, it is necessary to provide a technology that, in response to the long back focal length of DLP and the requirement of a wide application temperature range, can fully utilize the advantages of plastic lenses and glass lenses while avoiding their disadvantages. Summary of the Invention

[0006] Therefore, it is necessary to provide a projection lens that has the advantages of long back focal length, good heat dissipation, and low cost to address the existing technical problems.

[0007] To address the problems of existing technologies, this invention discloses a projection lens comprising four lenses along the optical axis from the object side to the image side, namely, a first lens, a second lens, a third lens, and a fourth lens. 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 and fourth lenses are configured to have opposite optical power signs; that is, when the third lens has positive optical power, the fourth lens has negative optical power, and when the third lens has negative optical power, the fourth lens has positive optical power. This satisfies the following condition:

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

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

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

[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 combination of the first lens and the second lens;

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

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

[0016] Preferably, the adjacent surfaces of the third lens and the fourth lens are configured as convex surfaces, and the adjacent surfaces of the fourth lens and the third lens are configured as concave surfaces.

[0017] Preferably, the adjacent surfaces of the third lens and the fourth lens are configured as concave surfaces, and the adjacent surfaces of the fourth lens and the third lens are configured as convex surfaces.

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

[0019] Preferably, the third lens and the fourth lens are cemented together as one unit.

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

[0021] Preferably, a field lens is disposed between the fourth lens and the image side, 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 disposed between the fourth lens and the image side.

[0023] Preferably, the third lens and the fourth lens are made of different materials, and the Abbe number of the third lens and the fourth lens differs by more than 20.

[0024] The beneficial effects of this invention are as follows:

[0025] 1. The lens of this invention has the feature of a long back focal length, which can provide sufficient rear mechanical space for the illumination optical module of DLP;

[0026] 2. The present invention has excellent thermal stability. The first and second lenses are mainly used to correct advanced aberrations of the system, and the optical power is small, which makes it less affected by temperature. Other lenses are made of glass, and the optical performance of glass lenses changes little with temperature. Thus, the combined application can make the lens adaptable to fields with a wide range of temperature applications.

[0027] 3. This invention features a glass-plastic hybrid design, which can improve performance while reducing costs. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of a typical DLP projection system architecture.

[0029] Figure 2 A schematic diagram of the structure of Embodiment 1 of the present invention.

[0030] Figure 3 This is an MTF curve diagram of Embodiment 1 of the present invention.

[0031] Figure 4 This is a schematic diagram of the structure of Embodiment 2 of the present invention.

[0032] Figure 5 This is an MTF curve diagram of Embodiment 2 of the present invention.

[0033] Figure 6 This is a schematic diagram of the structure of Embodiment 3 of the present invention.

[0034] Figure 7 This is the MTF curve of Embodiment 4 of the present invention.

[0035] The attached figures are labeled as follows: first lens 10, second lens 11, third lens 12, fourth lens 13, and field lens 14. Detailed Implementation

[0036] To further understand the features, technical means, and specific objectives and functions achieved by the present invention, the present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments.

[0037] refer to Figures 2 to 7 .

[0038] This invention discloses a projection lens comprising four lenses along the optical axis from the object side to the image side, namely 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, and the second lens 11 is also 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 positive optical power, the fourth lens 13 has negative optical power, and when the third lens 12 has negative optical power, the fourth lens 13 has positive optical power.

[0039] It satisfies the following condition:

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

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

[0042] The object side of the third lens 12 is convex, and the image side 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] With the above settings, the optical power of the first lens 10 and the second lens 11 is very small, so even if there are temperature changes, the impact on the optical performance of the system is small.

[0047] 1.9>f34 / f>1.1, where f34 is the equivalent focal length of the combined lens group of the third lens 12 and the fourth lens 13; with this setting, the third lens 12 and the fourth lens 13 made of glass material bear the main optical power, because the glass performance is stable, so the temperature change has little impact on the optical performance of the system.

[0048] To ensure the system has ample rear space to accommodate the lighting modules without compromising incident light energy, the following design is employed.

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

[0050] Preferably, the adjacent surfaces of the third lens 12 and the fourth lens 13 are configured as convex surfaces, and the adjacent surfaces of the fourth lens 13 and the third lens 12 are configured as concave surfaces.

[0051] Preferably, the adjacent surfaces of the third lens 12 and the fourth lens 13 are set as concave surfaces, and the adjacent surfaces of the fourth lens 13 and the third lens 12 are set as convex surfaces.

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

[0053] Preferably, the third lens 12 and the fourth lens 13 are glued together as a single unit, which facilitates assembly and reduces energy loss.

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

[0055] Preferably, a field lens 14 is provided between the fourth lens 13 and the image side, and the distance between the field lens 14 and the fourth lens 13 is greater than 1.3 times the effective focal length, so as to still ensure sufficient rear space for the illumination unit.

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

[0057] Preferably, the third lens 12 and the fourth lens 13 are made of different materials, and the Abbe number of the third lens 12 and the fourth lens 13 differs by more than 20, thereby achieving the effect of eliminating chromatic aberration.

[0058] In this embodiment, the third lens 12 with negative optical power and the fourth lens 13 with positive optical power are discrete lenses, as shown in the schematic diagram below. Figure 2 MTF curve as shown Figure 3 .

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

[0060] Surface No. Surface Type Curvature Radius R (mm) Thickness (mm) Refractive Index Abbe Number S1 Asphere 6.147 2.240 1.537 56.1 S2 Asphere 3.846 2.950 S3 Asphere -3.490 5.000 1.537 56.1 S4 Asphere -5.129 3.444 S5 Sphere 11.226 0.840 1.755 27.6 S6 Sphere 5.895 0.300 S7 Sphere 6.631 3.200 1.496 81.6 S8 Sphere -6.893 13.000 S9 (Image) Sphere Infinity 0.000

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

[0062]

[0063] The expression for an aspherical surface is as follows:

[0064]

[0065] Where z is the sag of the aspherical surface at position r; 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 to J are coefficients of higher-order terms.

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

[0067]

[0068] Table 4, Constraints in Example 1

[0069] Constraint Design Result | R1 | > | R2 | From the parameter table, it is known that |R3| < |R4| From the parameter table, it is known that | f1 / f > 3.0 | f1 / f = 3.61 it is known that | f2 / f > 5.0 | f2 / f = 37.1 it is known that f12 / f <- 3.0 f12 / f = -6.41 it is known that 1.9 > f34 / f > 1.1 f34 / f = 1.46 it is known that d14 / OAL < 0.65 d14 / OAL = 0.58 it is known that

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

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

[0072] Surface No. Surface Type Curvature Radius R (mm) Thickness (mm) Refractive Index Abbe Number S1 Asphere 6.140 2.240 1.537 56.1 S2 Asphere 3.907 2.950 S3 Asphere -3.440 5.500 1.537 56.1 S4 Asphere -5.855 2.137 S5 Sphere 9.782 0.840 1.753 28.9 S6 Sphere 5.468 3.333 1.496 81.6 S7 Sphere -7.549 13.000 S8 (Image) Sphere Infinity 0.000

[0073] Table 6, Parameters of each surface in Example 2

[0074]

[0075] The expression for an aspherical surface is as follows:

[0076]

[0077] Where z is the sag of the aspherical surface at position r; 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 to J are coefficients of higher-order terms.

[0078] Table 7. Design parameters of the optical lens in Example 2

[0079]

[0080] Table 8, Constraints in Example 2

[0081] Constraint Design Result | R1 | > | R2 | From the parameter table, it is known that |R3| < |R4| From the parameter table, it is known that | f1 / f > 3.0 | f1 / f = 3.84 it is known that | f2 / f > 5.0 | f2 / f = 9.55 it is known that f12 / f <- 3.0 f12 / f = -3.6 it is known that 1.9 > f34 / f > 1.1 f34 / f = 1.38 it is known that d14 / OAL < 0.65 d14 / OAL = 0.56 it is known that

[0082] Example 3: In practical use, a field lens 14 is provided between the fourth lens 13 and the image-side surface to improve the control of the edge beam while reducing the lens aperture, without affecting the overall optical characteristics of the projection lens assembly. In this example, the third lens 12 is a positive lens, and the fourth lens 13 is a negative lens, cemented together as shown. Figure 6 The MTF curve is as follows; Figure 7 As shown.

[0083] Table 9. Parameters of each surface in Example 3

[0084] Surface No. Surface Type Curvature Radius R (mm) Thickness (mm) Refractive Index Abbe Number S1 Asphere 8.020 2.240 1.537 56.1 S2 Asphere 5.671 2.950 S3 Asphere -2.869 5.000 1.537 56.1 S4 Asphere -5.052 4.764 S5 Sphere 12.615 2.706 1.496 81.5 S6 Sphere -5.069 0.840 1.753 28.9 S7 Sphere -8.195 13.000 S8 Sphere 10.000 1.500 1.589 61.3 S9 Sphere Infinity 1.000 S10 (Image) Sphere Infinity 0.000

[0085] Table 10, Parameters of Each Surface in Example 3

[0086]

[0087] The expression for an aspherical surface is as follows:

[0088]

[0089] Where z is the sag of the aspherical surface at position r; 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 to J are coefficients of higher-order terms.

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

[0091]

[0092] Table 12, Constraints in Example 3

[0093] Constraint Design Result | R1 | > | R2 | From the parameter table, it is known that |R3| < |R4| From the parameter table, it is known that | f1 / f > 3.0 | f1 / f = 6.73 it is known that | f2 / f > 5.0 | f2 / f = 7.75 it is known that f12 / f <- 3.0 f12 / f = -4.55 it is known that 1.9 > f34 / f > 1.1 f34 / f = 1.6 it is known that d14 / OAL < 0.65 d14 / OAL = 0.54 it is known that

[0094] The lens of this invention features a long back focal length, providing sufficient rear mechanical space for the illumination optical module of the DLP. This invention also exhibits excellent thermal stability. The first and second lenses are primarily used to correct advanced aberrations in the system, while their low optical power minimizes temperature-related effects. Other lenses utilize glass, which exhibits relatively low temperature-dependent optical performance changes. This combination allows the lens to be adapted to a wide range of temperature-sensitive applications. Furthermore, this invention employs a glass-plastic hybrid design, which improves performance while reducing costs.

[0095] The above-described embodiments are merely three examples of implementation methods of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A projection lens, characterized in that, The optical axis consists of four lenses from the object side to the image side, namely, the first lens (10), the second lens (11), the third lens (12), and the fourth lens (13). 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 optical powers of the first lens (10), the second lens (11), the third lens (12), and the fourth lens (13) are negative, positive, negative, positive or negative, negative, negative, positive or negative, negative, positive, negative, respectively. It satisfies the following condition: The convex surface of the first lens (10) faces the object side, |R1|>|R2|, where R1 and R2 are the radii of curvature of the object side and the image side of the first lens (10), respectively; The concave surface of the second lens (11) faces the object side, |R3|<|R4|, where R3 and R4 are the radii of curvature of the object side and the image side of the second lens (11), respectively; The object side of the third lens (12) is convex, and the image side of the fourth lens (13) is convex. 6.73≥|f1| / f≥3.61, where f is the equivalent focal length of the system and f1 is the equivalent focal length of the first lens (10); 37.1≥|f2| / f≥7.75, where f2 is the equivalent focal length of the second lens (11); -6.41≤f12 / f≤-3.6, where 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≥1.38, where f34 is the equivalent focal length of the combined lens group of the third lens (12) and the fourth lens (13); d14 / OAL≤0.58, where d14 is the length of the lens group from the first lens (10) to the fourth lens (13), and OAL is the total working length of the entire optical projection lens system, including the lens group and the imaging surface.

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

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

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

5. A projection lens according to claim 1, characterized in that, The third lens (12) and the fourth lens (13) are glued together as one unit.

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

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

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

9. A projection lens according to claim 1, characterized in that, The third lens (12) and the fourth lens (13) are made of different materials, and the Abbe number of the third lens (12) and the fourth lens (13) differs by more than 20.

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