Ultra-short-focus projection system

Abstract

The invention relates to the technical field of projection display in an optical imaging system, and discloses an ultra-short-focus projection system, which is sequentially provided with a display chip, a lens group and a reflection bowl along a light path, the lens group comprises a plurality of lenses which are arranged on the same optical axis, and the lenses from the first lens to the twelfth lens are sequentially arranged from the reflection bowl side to the display chip side. The first lens is a first aspheric lens, the second lens is a second aspheric lens, the third lens is a first spherical convex lens, the fourth lens is a spherical concave lens, the fifth lens is a second spherical convex lens, the sixth lens, the seventh lens and the eighth lens are combined into a triple cemented lens, and the ninth lens and the tenth lens are combined into a doublet lens. The eleventh lens is an aspheric lens, and the twelfth lens is a meniscus lens. A diaphragm is arranged between the fourth lens and the fifth lens, and a TIR prism is arranged between the display chip and the twelfth lens. The invention has the advantages that: short-focus projection is realized, and the imaging definition is ensured.

Description

Technical Field

[0001] The present invention relates to the field of projection display technology in an optical imaging system, and in particular to an ultra-short-throw projection system. Background Art

[0002] With the development of optical technology, projectors are being used more and more widely, and their application potential in the automotive field is becoming more and more significant. However, the current automotive projectors on the market generally face challenges such as large size, limited installation location in the car, easy interference with the driver's vision, limited passenger seating, and insufficient clarity. These problems seriously restrict the popularization of automotive projectors and the improvement of user experience. Therefore, it is urgent to develop a projection system to solve the above problems. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides an ultra-short-focus projection system, which realizes short-focus projection and ensures imaging clarity.

[0004] The present invention provides an ultra-short-throw projection system, wherein the system is provided with a display chip, a lens group and a reflection bowl in sequence along an optical path; The lens group includes a plurality of lenses arranged on the same optical axis, which are the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens, the seventh lens, the eighth lens, the ninth lens, the tenth lens, the eleventh lens and the twelfth lens from the reflection bowl side to the display chip side; the first lens is a first aspheric lens, the second lens is a second aspheric lens, the third lens is a first spherical convex lens, the fourth lens is a spherical concave lens, the fifth lens is a second spherical convex lens, the sixth lens, the seventh lens and the eighth lens are combined into a triplet lens, the ninth lens and the tenth lens are combined into a doublet lens, the eleventh lens is a third aspheric lens, and the twelfth lens is a meniscus lens; an aperture is provided between the fourth lens and the fifth lens, and a TIR prism is provided between the display chip and the twelfth lens.

[0005] Furthermore, a protective glass is provided between the TIR prism and the twelfth lens.

[0006] Further, the focal length of the first lens is f1, the focal length of the second lens is f2, the focal length of the third lens is f3, the focal length of the fourth lens is f4, and the focal length of the fifth lens is f5; the focal length of the triplet lens is f6, the focal length of the doublet lens is f7, the focal length of the eleventh lens is f8, and the focal length of the twelfth lens is f9; Among them: -53mm≤f1≤-63mm, -20mm≤f2≤-30mm, 53mm≤f3≤63mm, -69mm≤f4≤-79mm, 31mm≤f5≤41mm, 61mm≤f6≤71mm, -15mm≤f7≤-25mm, 17mm≤f8≤27mm, 51mm≤f9≤61mm; The focal length f of the reflector bowl 10 The value range is: 10mm≤f 10 ≤20mm.

[0007] Furthermore, the refractive index of the first lens is n1, the refractive index of the second lens is n2, the refractive index of the third lens is n3, the refractive index of the fourth lens is n4, the refractive index of the fifth lens is n5, and the refractive index of the sixth lens is n 61 , the refractive index of the seventh lens is n 62 , the refractive index of the eighth lens is n 63 , the refractive index of the ninth lens is n 71 , the refractive index of the tenth lens is n 72 , the refractive index of the eleventh lens is n8, and the refractive index of the twelfth lens is n9; wherein: 1.50≤n1≤1.60, 1.50≤n2≤1.60, 1.85≤n3≤1.95, 1.65≤n4≤1.75, 1.80≤n5≤1.90,1.45≤n 61 ≤1.55,2.00≤n 62 ≤2.10,1.40≤n 63 ≤1.50, 1.85≤n 71 ≤1.95,1.45≤n 72 ≤1.55, 1.55≤n8≤1.65, 1.85≤n9≤1.95.

[0008] Further, the center thickness of the first lens is d1, the center thickness of the second lens is d2, the center thickness of the third lens is d3, the center thickness of the fourth lens is d4, the center thickness of the fifth lens is d5, and the center thickness of the sixth lens is d 61 , the center thickness of the seventh lens is d 62 , the central thickness of the eighth lens is d 63 , the center thickness of the ninth lens is d 71 , the center thickness of the tenth lens is d 72 , the center thickness of the eleventh lens is d8, and the center thickness of the twelfth lens is d9; wherein: 2.0mm≤d1≤2.4mm, 2.3mm≤d2≤2.7mm, 5.5mm≤d3≤5.9mm, 5.4mm≤d4≤5.8mm, 4.2mm≤d5≤4.6mm, 6.1mm≤d 61 ≤6.5mm, 0.9mm≤d 62 ≤0.13mm, 4.3mm≤d 63 ≤4.7mm, 1.1mm≤d 71 ≤1.5mm, 4.5mm≤d 72 ≤4.9mm, 5.8mm≤d8≤6.2mm, 3.0mm≤d9≤3.4mm.

[0009] Furthermore, the distance between the reflective bowl and the first lens is between 55mm and 65mm; the distance between the first lens and the second lens on the optical axis is between 7mm and 10mm; the distance between the second lens and the third lens on the optical axis is between 18mm and 22mm; the distance between the third lens and the fourth lens on the optical axis is between 1mm and 2mm; the distance between the fourth lens and the fifth lens on the optical axis is between 1.5mm and 3.5mm; the distance between the fifth lens and the triplet lens on the optical axis is between 0mm and 1mm; the distance between the triplet lens and the doublet lens on the optical axis is between 0mm and 1mm; the distance between the doublet lens and the eleventh lens on the optical axis is between 0mm and 1mm; the distance between the eleventh lens and the twelfth lens on the optical axis is between 0mm and 1mm; the distance between the twelfth lens and the protective glass on the optical axis is between 2mm and 5mm; the distance between the TIR prism and the display chip on the optical axis is between 2mm and 4mm.

[0010] Furthermore, the eleventh lens establishes a Cartesian rectangular coordinate system O-xyz with the two surface vertices as the origin O. Based on the O-xyz coordinate system, both surfaces can be expressed as the following formula: , in, is the radial distance of the aspherical axis, c is the surface curvature, k is the cone coefficient, α1, α2, α3, α4, α5, α6, α7, and α8 are r respectively. 2 、r 4 、r 6 、r 8 、r 10 、r 12 、r 14 、r 16 The coefficient of .

[0011] The embodiments of the present invention have the following technical effects: The present application sets twelve lenses. First, the meniscus lens converges the light received from the display chip, and the third aspheric lens further converges the light and eliminates aberrations. The double cemented lens and the triple cemented lens correct the image chromatic aberration to make the image clear. The second spherical convex lens converges the light beam, and the spherical concave lens further corrects the aberration. Finally, the first aspheric lens and the second aspheric lens magnify the image, focus and reflect it through the reflection bowl to form an enlarged image. This application achieves short focal length projection and ensures imaging clarity by setting the lens arrangement and lens shape; The present application further improves the imaging quality and reduces the overall volume of the system by setting the focal length, refractive index, center thickness of the lens, and the spacing between lenses. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0013] Figure 1 is a structural schematic diagram of an ultra-short-throw projection system provided by an embodiment of the present invention; Figure 2 is a light fan diagram provided by an embodiment of the present invention; 11 pairs of graphs respectively represent 11 normalized fields of view, and the two graphs in each field of view respectively represent the aberration in the x-axis direction and the aberration in the y-axis direction symmetrical with the optical axis as the center of the projection lens system; the horizontal axis direction in each graph is the pupil height position under the field of view condition, and the vertical axis direction is the error between each wavelength of light and the main light; Figure 3 is a curve showing the relationship between the modulus and frequency of the optical transfer function provided by an embodiment of the present invention; Figure 4 3 is a schematic diagram of TV distortion provided by an embodiment of the present invention. The horizontal coordinate represents the magnitude of field curvature in mm, and the vertical coordinate represents the normalized image height.

[0014] In the figure, 1, the first lens; 2, the second lens; 3, the third lens; 4, the fourth lens; 5, the fifth lens; 6, the sixth lens; 7, the seventh lens; 8, the eighth lens; 9, the ninth lens; 10, the tenth lens; 11, the eleventh lens; 12, the twelfth lens; 13, the display chip; 14, the reflection bowl; 15, the aperture; 16, the TIR prism; 17, the protective glass. DETAILED DESCRIPTION

[0015] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention. Example

[0016] Figure 1 is a structural diagram of an ultra-short-throw projection system provided by an embodiment of the present invention. Figure 1 , specifically including: The system is provided with a display chip 13, a lens group and a reflection bowl 14 in sequence along the optical path; the display chip 13 is used to convert image data into a visible image and transmit it, such as a DMD chip; the light emitted by the DMD chip is amplified and focused by the lens group, and this process directly affects the clarity, brightness and contrast of the image; the reflection bowl is used to further amplify, reflect and focus the light received from the lens group, forming an amplified image in the reflection direction, thereby improving the utilization rate and brightness of the light.

[0017] The lens group includes a plurality of lenses arranged on the same optical axis, which are, from the side of the reflection bowl 14 to the side of the display chip 13, the first lens 1, the second lens 2, the third lens 3, the fourth lens 4, the fifth lens 5, the sixth lens 6, the seventh lens 7, the eighth lens 8, the ninth lens 9, the tenth lens 10, the eleventh lens 11, and the twelfth lens 12; The first lens 1 is a first aspheric lens, the second lens 2 is a second aspheric lens, the third lens 3 is a first spherical convex lens, the fourth lens 4 is a spherical concave lens, the fifth lens 5 is a second spherical convex lens, the sixth lens 6, the seventh lens 7 and the eighth lens 8 are combined into a triplet lens, the ninth lens 9 and the tenth lens 10 are combined into a doublet lens, the eleventh lens 11 is a third aspheric lens, and the twelfth lens 12 is a meniscus lens; An aperture 15 is provided between the fourth lens 4 and the fifth lens 5 , and a TIR prism 16 is provided between the display chip 13 and the ninth lens 9 .

[0018] Wherein, the first aspheric lens and the second aspheric lens are both made of plastic material, and are used to amplify the projected image received and eliminate the aberration caused by the imaging system; The first spherical convex lens is made of glass and is used to converge the light beam; The spherical concave lens is made of glass and is used to diverge the light beam; the second spherical convex lens is made of glass and is used to converge the light beam; A triplet lens is made of three glass materials with different curvatures, thicknesses and brands glued together; a doublet lens is also made of two glass materials with different curvatures, thicknesses and brands glued together. The doublet lens can correct chromatic aberration of multiple wavelengths, while the triplet lens performs more sophisticated chromatic aberration correction, making the image clearer; the combination of doublet and triplet lenses can more effectively control aberrations, improve imaging quality, and further improve the magnification and resolution of the entire system.

[0019] The function of the third aspherical lens is to converge light and eliminate aberrations; the meniscus lens is made of glass and is also used to converge light.

[0020] In addition, an aperture 15 is provided between the fourth lens 4 and the fifth lens 5, that is, between the spherical concave lens and the second spherical convex lens. The aperture 15 is provided to ensure that only light within a specific range can enter the spherical concave lens to adapt to different lighting conditions. A TIR prism 16 is provided between the display chip 13 and the twelfth lens 12, that is, the meniscus lens, to reduce the refraction and scattering of the tube and reduce the loss of light.

[0021] In summary, by setting the above lens arrangement and lens shape, short focal length projection is achieved and imaging clarity is guaranteed.

[0022] Furthermore, a protective glass 17 is provided between the TIR prism 16 and the twelfth lens 12 to prevent dust and isolate water vapor.

[0023] In a specific implementation, the focal length, refractive index, etc. of each lens are set accordingly: The focal length of the first lens 1 is f1, the focal length of the second lens 2 is f2, the focal length of the third lens 3 is f3, the focal length of the fourth lens 4 is f4, and the focal length of the fifth lens 5 is f5; the focal length of the triplet lens is f6, the focal length of the doublet lens is f7, the focal length of the eleventh lens 11 is f8, and the focal length of the twelfth lens 12 is f9; Among them: -53mm≤f1≤-63mm, -20mm≤f2≤-30mm, 53mm≤f3≤63mm, -69mm≤f4≤-79mm, 31mm≤f5≤41mm, 61mm≤f6≤71mm, -15mm≤f7≤-25mm, 17mm≤f8≤27mm, 51mm≤f9≤61mm; The focal length f of the reflector bowl 14 10 Range: 10mm≤f 10 ≤20mm.

[0024] The refractive index of the first lens 1 is n1, the refractive index of the second lens 2 is n2, the refractive index of the third lens 3 is n3, the refractive index of the fourth lens 4 is n4, the refractive index of the fifth lens 5 is n5, and the refractive index of the sixth lens 6 is n 61 , the refractive index of the seventh lens 7 is n 62 , the refractive index of the eighth lens 8 is n 63 , the refractive index of the ninth lens 9 is n 71 , the refractive index of the tenth lens 10 is n 72 , the refractive index of the eleventh lens 11 is n8, and the refractive index of the twelfth lens 12 is n9; wherein: 1.50≤n1≤1.60, 1.50≤n2≤1.60, 1.85≤n3≤1.95, 1.65≤n4≤1.75, 1.80≤n5≤1.90,1.45≤n 61 ≤1.55, 2.00≤n 62 ≤2.10,1.40≤n 63 ≤1.50, 1.85≤n 71 ≤1.95,1.45≤n 72 ≤1.55, 1.55≤n8≤1.65, 1.85≤n9≤1.95.

[0025] The center thickness of the first lens 1 is d1, the center thickness of the second lens 2 is d2, the center thickness of the third lens 3 is d3, the center thickness of the fourth lens 4 is d4, the center thickness of the fifth lens 5 is d5, and the center thickness of the sixth lens 6 is d 61 , the center thickness of the seventh lens 7 is d 62 , the center thickness of the eighth lens 8 is d 63 , the center thickness of the ninth lens 9 is d 71 , the center thickness of the tenth lens 10 is d 72 , the center thickness of the eleventh lens 11 is d8, and the center thickness of the twelfth lens 12 is d9; wherein: 2.0mm≤d1≤2.4mm, 2.3mm≤d2≤2.7mm, 5.5mm≤d3≤5.9mm, 5.4mm≤d4≤5.8mm, 4.2mm≤d5≤4.6mm, 6.1mm≤d 61 ≤6.5mm, 0.9mm≤d 62 ≤0.13mm, 4.3mm≤d 63 ≤4.7mm, 1.1mm≤d 71 ≤1.5mm, 4.5mm≤d 72≤4.9mm, 5.8mm≤d8≤6.2mm, 3.0mm≤d9≤3.4mm.

[0026] The distance between the reflection bowl 14 and the first lens 1 is between 55mm and 65mm; the distance between the first lens 1 and the second lens 2 on the optical axis is between 7mm and 10mm; the distance between the second lens 2 and the third lens 3 on the optical axis is between 18mm and 22mm; the distance between the third lens 3 and the fourth lens 4 on the optical axis is between 1mm and 2mm; the distance between the fourth lens 4 and the fifth lens 5 on the optical axis is between 1.5mm and 3.5mm; the distance between the fifth lens 5 and the triplet lens ... third lens 3 and the fourth lens 4 on the optical axis is between 1.5mm and 3.5mm; the distance between the fifth lens 5 and the triplet lens on the optical axis is between 1.5mm and 3.5mm; the distance between the third lens 3 and the fourth lens 4 on the optical axis is between 1.5mm and 3.5mm; the distance between the fifth lens 5 and the triplet lens on the optical axis is between 1. The spacing between the triplet lens and the doublet lens on the optical axis is between 0mm and 1mm; the spacing between the doublet lens and the eleventh lens 11 on the optical axis is between 0mm and 1mm; the spacing between the eleventh lens 11 and the twelfth lens 12 on the optical axis is between 0mm and 1mm; the spacing between the twelfth lens 12 and the protective glass 17 on the optical axis is between 2mm and 5mm; the spacing between the TIR prism 16 and the display chip 13 on the optical axis is between 2mm and 4mm.

[0027] By limiting the focal length, refractive index and center thickness of each lens, the imaging quality is further improved; by limiting the optical axis spacing between each element, the overall volume of the system is further reduced. Example

[0028] Based on the content of Example 1, this application provides a specific implementation method: The parameters of each component are set as shown in Table 1 and Table 2, and the focal length and the distance between each lens only need to meet the range in Example 1.

[0029] Table 1 Some parameter settings of ultra short throw projection system

[0030] Table 2 Some parameter settings of ultra short throw projection system (continued)

[0031] It should be noted that the center thickness of -243.41mm corresponding to the imaging surface in the above table represents the distance from the imaging surface to the reflection bowl; the front surface of each lens is the side facing the reflection bowl, and the rear surface is the side facing away from the reflection bowl; the surface type is the formula type satisfied by each surface, where the standard surface is a plane. Obviously, this application can achieve a smaller projection distance; the center thickness corresponding to the front surface of each lens is the thickness of the lens, and the center thickness corresponding to the rear surface of each lens is the distance from the rear surface of each lens to the front surface of the next lens on the optical axis.

[0032] For further information, see Figure 1 The concave side of the reflection bowl 14, the two surfaces of the first lens 1, and the two surfaces of the second lens 2 satisfy the following aspheric formula: , The formulas of each lens surface respectively establish a Cartesian rectangular coordinate system O-xyz with each surface vertex as the origin O. In the present application, the directions of the x-axis, y-axis and z-axis of the coordinate system of each lens surface formula are the same, and only the position of the coordinate origin is different. The z-axis is parallel to the optical axis, and the direction from the reflection bowl 14 to the display chip 13 is the positive direction of the z-axis; wherein, r' is the radial distance of the aspheric axis, and the specific solution method is not described in detail in this application, c' is the surface curvature, k' is the cone coefficient, for The corresponding aspheric coefficients, N is the order, is the radial coordinate constant.

[0033] The relevant parameters are shown in Tables 3 to 5 below: Table 3 Parameter settings of reflection bowl Table 4 Parameter settings of the first lens Table 5 Parameter settings of the second lens

[0034] See also Figure 1 , the eleventh lens 11 establishes a Cartesian rectangular coordinate system O-xyz with the two surface vertices as the origin O. Based on the O-xyz coordinate system, both surfaces can be expressed as the following formula: , in, is the radial distance, c is the surface curvature, c is the inverse of the radius of curvature, k is the cone coefficient, α1, α2, α3, α4, α5, α6, α7, and α8 are r respectively. 2 、r 4 、r 6 、r 8 、r 10 、r 12 、r 14 、r 16 The coefficient of .

[0035] The specific parameter settings are as shown in Table 6: Table 6 Parameter settings

[0036] Three representative light beams with different wavelengths were set, and green light was selected as the main wavelength. The three light beams had wavelengths of 0.45um, 0.55um, and 0.62um, respectively. These three light beams were passed through the above-mentioned ultra-short-focus projection system, and the imaging effects were verified. Figures 2 to 4 , conduct relevant analysis based on the content of the diagram: Figure 2 It shows the aberration values ​​between the three kinds of light and the main wavelength light on the x-axis and y-axis respectively under normalized field of view conditions. OBJ represents the projected image. It can be seen that the aberrations under different wavelengths of light are very small.

[0037] Figure 3 The larger the modulus of the optical transfer function, the stronger the resolution, and the lens can restore the details and contrast of the object more clearly. Figure 3 It indicates that the resolution of the projection lens is greater than 0.5@66lp / mm. 0.5@66lp / mm means that the resolution of 66 line pairs / millimeter is 0.5.

[0038] Figure 4 This indicates that there is little difference in image quality between the center and the surrounding areas during imaging.

[0039] In summary, the ultra-short-focus projection system provided in the present application realizes short-focus projection and ensures imaging clarity.

[0040] It should be noted that the terms used in the present invention are only for describing specific embodiments, rather than limiting the scope of the present application. As shown in the present specification, unless the context clearly indicates an exception, the words "one", "a", "a kind of" and / or "the" do not specifically refer to the singular, but may also include the plural. The terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, method or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method or device. In the absence of more restrictions, the elements defined by the sentence "include one..." do not exclude the presence of other identical elements in the process, method or device including the elements.

[0041] It should also be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. Unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", etc. should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be a connection between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the technical solutions of the embodiments of the present invention.

Claims

1. An ultra-short-throw projection system, characterized in that: The system is provided with a display chip (13), a lens group and a reflection bowl (14) in sequence along the optical path; The lens group comprises a plurality of lenses arranged on the same optical axis, which are, from the reflection bowl (14) side to the display chip (13) side, a first lens (1), a second lens (2), a third lens (3), a fourth lens (4), a fifth lens (5), a sixth lens (6), a seventh lens (7), an eighth lens (8), a ninth lens (9), a tenth lens (10), an eleventh lens (11), and a twelfth lens (12); The first lens (1) is a first aspheric lens, the second lens (2) is a second aspheric lens, the third lens (3) is a first spherical convex lens, the fourth lens (4) is a spherical concave lens, the fifth lens (5) is a second spherical convex lens, the sixth lens (6), the seventh lens (7) and the eighth lens (8) are combined into a triplet lens, the ninth lens (9) and the tenth lens (10) are combined into a doublet lens, the eleventh lens (11) is a third aspheric lens, and the twelfth lens (12) is a meniscus lens; An aperture (15) is provided between the fourth lens (4) and the fifth lens (5), and a TIR prism (16) is provided between the display chip (13) and the twelfth lens (12).

2. The ultra short throw projection system according to claim 1, characterized in that: A protective glass (17) is provided between the TIR prism (16) and the twelfth lens (12).

3. The ultra short throw projection system according to claim 1, characterized in that: The focal length of the first lens (1) is f1, the focal length of the second lens (2) is f2, the focal length of the third lens (3) is f3, the focal length of the fourth lens (4) is f4, and the focal length of the fifth lens (5) is f5; the focal length of the triplet lens is f6, the focal length of the doublet lens is f7, the focal length of the eleventh lens (11) is f8, and the focal length of the twelfth lens (12) is f9; Among them: -53mm≤f1≤-63mm, -20mm≤f2≤-30mm, 53mm≤f3≤63mm, -69mm≤f4≤-79mm, 31mm≤f5≤41mm, 61mm≤f6≤71mm, -15mm≤f7≤-25mm, 17mm≤f8≤27mm, 51mm≤f9≤61mm; The focal length f of the reflection bowl (14) 10 The value range is: 10mm≤f 10 ≤20mm.

4. The ultra short throw projection system according to claim 1, characterized in that: The refractive index of the first lens (1) is n1, the refractive index of the second lens (2) is n2, the refractive index of the third lens (3) is n3, the refractive index of the fourth lens (4) is n4, the refractive index of the fifth lens (5) is n5, and the refractive index of the sixth lens (6) is n 61 , the refractive index of the seventh lens (7) is n 62 , the refractive index of the eighth lens (8) is n 63 , the refractive index of the ninth lens (9) is n 71 The refractive index of the tenth lens (10) is n 72 , the refractive index of the eleventh lens (11) is n8, and the refractive index of the twelfth lens (12) is n9; wherein: 1.50≤n1≤1.60, 1.50≤n2≤1.60, 1.85≤n3≤1.95, 1.65≤n4≤1.75, 1.80≤n5≤1.90,1.45≤n 61 ≤1.55,2.00≤n 62 ≤2.10,1.40≤n 63 ≤1.50, 1.85≤n 71 ≤1.95,1.45≤n 72 ≤1.55,1.55≤n8≤1.65,1.85≤n9≤1.95。 5. The ultra short throw projection system according to claim 1, characterized in that: The center thickness of the first lens (1) is d1, the center thickness of the second lens (2) is d2, the center thickness of the third lens (3) is d3, the center thickness of the fourth lens (4) is d4, the center thickness of the fifth lens (5) is d5, and the center thickness of the sixth lens (6) is d 61 The central thickness of the seventh lens (7) is d 62 , the central thickness of the eighth lens (8) is d 63 , the center thickness of the ninth lens (9) is d 71 The central thickness of the tenth lens (10) is d 72 , the center thickness of the eleventh lens (11) is d8, and the center thickness of the twelfth lens (12) is d9; wherein: 2.0mm≤d1≤2.4mm, 2.3mm≤d2≤2.7mm, 5.5mm≤d3≤5.9mm, 5.4mm≤d4≤5.8mm,4.2mm≤d5≤4.6mm,6.1mm≤d 61 ≤6.5mm, 0.9mm≤d 62 ≤0.13mm,4.3mm≤d 63 ≤4.7mm,1.1mm≤d 71 ≤1.5mm, 4.5mm≤d 72 ≤4.9mm,5.8mm≤d8≤6.2mm,3.0mm≤d9≤3.4mm。 6. The ultra short throw projection system according to claim 2, characterized in that: The distance between the reflection bowl (14) and the first lens (1) is between 55 mm and 65 mm; The distance between the first lens (1) and the second lens (2) on the optical axis is between 7 mm and 10 mm; The distance between the second lens (2) and the third lens (3) on the optical axis is between 18 mm and 22 mm; The distance between the third lens (3) and the fourth lens (4) on the optical axis is between 1 mm and 2 mm; The distance between the fourth lens (4) and the fifth lens (5) on the optical axis is between 1.5 mm and 3.5 mm; The distance between the fifth lens (5) and the triplet lens on the optical axis is between 0 mm and 1 mm; The distance between the triplet lens and the doublet lens on the optical axis is between 0 mm and 1 mm; The distance between the doublet lens and the eleventh lens (11) on the optical axis is between 0 mm and 1 mm; The distance between the eleventh lens (11) and the twelfth lens (12) on the optical axis is between 0 mm and 1 mm; The distance between the twelfth lens (12) and the protective glass (17) on the optical axis is between 2 mm and 5 mm; The distance between the TIR prism (16) and the display chip (13) on the optical axis is between 2 mm and 4 mm.

7. The ultra short throw projection system according to claim 1, characterized in that: The eleventh lens (11) establishes a Cartesian rectangular coordinate system O-xyz with the two surface vertices as the origin O. Based on the O-xyz coordinate system, the two surfaces can be expressed as the following formula: ， in, is the radial distance, c is the surface curvature, k is the cone coefficient, α1, α2, α3, α4, α5, α6, α7, and α8 are r respectively. 2 、r 4 、r 6 、r 8 、r 10 、r 12 、r 14 、r 16 The coefficient of .

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