Ultra-short-throw projection system

Abstract

The present invention relates to the field of projection display technology in an optical imaging system, and discloses an ultra-short-focus 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 with the same optical axis, and the first lens to the twelfth lens are arranged in sequence 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 an 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. The advantages of the present invention are: short-focus projection is realized, and imaging clarity is guaranteed.

Description

Technical Field

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

[0002] With the advancement of optical technology, projectors are becoming increasingly widespread, and their potential for automotive applications is becoming increasingly significant. However, current automotive projectors on the market generally face challenges such as bulk, limited installation locations, interference with the driver's field of view, limited passenger seating, and insufficient clarity. These issues severely hinder the widespread adoption of automotive projectors and the improvement of user experience. Therefore, there is an urgent need to develop a projection system that can address these issues. 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 reflective bowl in sequence along an optical path;

[0005] The lens group includes several lenses arranged on the same optical axis, including a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, a seventh lens, an eighth lens, a ninth lens, a tenth lens, an eleventh lens, and a twelfth lens from the reflector 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. A stop is provided between the fourth lens and the fifth lens, and a TIR prism is provided between the display chip and the twelfth lens.

[0006] Furthermore, a protective glass is provided between the TIR prism and the twelfth lens.

[0007] Furthermore, 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;

[0008] 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;

[0009] The focal length f of the reflector bowl 10 The value range is: 10mm≤f 10 ≤20mm.

[0010] 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:

[0011] 1.50≤n1≤1.60, 1.50≤n2≤1.60, 1.85≤n3≤1.95, 1.65≤n4≤1.75,

[0012] 1.80≤n5≤1.90,1.45≤n 61 ≤1.55,2.00≤n 62 ≤2.10,1.40≤n 63 ≤1.50,

[0013] 1.85≤n 71 ≤1.95, 1.45≤n 72 ≤1.55, 1.55≤n8≤1.65, 1.85≤n9≤1.95.

[0014] Furthermore, 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 d72 , the center thickness of the eleventh lens is d8, and the center thickness of the twelfth lens is d9; wherein:

[0015] 2.0mm≤d1≤2.4mm, 2.3mm≤d2≤2.7mm, 5.5mm≤d3≤5.9mm,

[0016] 5.4mm≤d4≤5.8mm, 4.2mm≤d5≤4.6mm, 6.1mm≤d 61 ≤6.5mm,

[0017] 0.9mm≤d 62 ≤0.13mm, 4.3mm≤d 63 ≤4.7mm, 1.1mm≤d 71 ≤1.5mm,

[0018] 4.5mm≤d 72 ≤4.9mm, 5.8mm≤d8≤6.2mm, 3.0mm≤d9≤3.4mm.

[0019] 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; and the distance between the TIR prism and the display chip on the optical axis is between 2mm and 4mm.

[0020] Furthermore, the eleventh lens establishes a Cartesian 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:

[0021] ,

[0022] in, is the radial distance of the aspheric axis, c is the surface curvature, k is the cone coefficient, α1, α2, α3, α4, α5, α6, α7, and α8 are r2 、r 4 、r 6 、r 8 、r 10 、r 12 、r 14 、r 16 The coefficient of .

[0023] The embodiments of the present invention have the following technical effects:

[0024] The present application sets up twelve lenses. First, the meniscus lens converges the light received from the display chip. The third aspheric lens further converges the light and eliminates aberrations. The doublet and triplet lenses correct the image chromatic aberration to make the image clear. The light beam is then converged by the second spherical convex lens. The spherical concave lens further corrects the aberration. Finally, the first aspheric lens and the second aspheric lens magnify the image, focus it through the reflective bowl, and reflect it out to form an enlarged image.

[0025] This application achieves short focal length projection and ensures image clarity by setting the lens arrangement and lens shape;

[0026] This 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

[0027] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0028] Figure 1 1 is a schematic structural diagram of an ultra-short-throw projection system provided by an embodiment of the present invention;

[0029] Figure 2 is a ray fan diagram provided by an embodiment of the present invention; the 11 pairs of graphs 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 of the projection lens system, which are symmetrical about the optical axis. The horizontal axis in each graph represents the pupil height position under the conditions of the field of view, and the vertical axis represents the error between each wavelength of light and the chief ray;

[0030] 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;

[0031] Figure 43 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.

[0032] In the figure, 1 is the first lens; 2 is the second lens; 3 is the third lens; 4 is the fourth lens; 5 is the fifth lens; 6 is the sixth lens; 7 is the seventh lens; 8 is the eighth lens; 9 is the ninth lens; 10 is the tenth lens; 11 is the eleventh lens; 12 is the twelfth lens; 13 is the display chip; 14 is the reflection bowl; 15 is the aperture; 16 is the TIR prism; 17 is the protective glass. DETAILED DESCRIPTION

[0033] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention are described clearly and completely below. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are also within the scope of protection of the present invention. Example

[0034] Figure 1 This is a structural diagram of an ultra-short-throw projection system provided by an embodiment of the present invention. Figure 1 , specifically including:

[0035] The system is equipped with a display chip 13, a lens group and a reflective 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 reflective 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.

[0036] The lens group includes several lenses arranged along the optical axis, including, from the reflective 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.

[0037] 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;

[0038] 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 .

[0039] The first aspheric lens and the second aspheric lens are both made of plastic material and are used to amplify the projected image and eliminate the aberration caused by the imaging system.

[0040] The first spherical convex lens is made of glass and is used to converge the light beam;

[0041] 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;

[0042] 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 precise chromatic aberration correction, making the image clearer; the combination of doublet and triplet lenses can more effectively control aberrations, improve imaging quality, and further increase the magnification and resolution of the entire system.

[0043] The function of the third aspheric lens is to converge light and eliminate aberrations; the meniscus lens is made of glass and is also used to converge light.

[0044] In addition, an aperture 15 is located between the fourth lens 4 and the fifth lens 5, that is, between the spherical concave lens and the second spherical convex lens. This aperture 15 ensures that only a specific range of light can enter the spherical concave lens to accommodate varying lighting conditions. A TIR prism 16 is located between the display chip 13 and the twelfth lens 12, or meniscus lens, to reduce refraction and scattering in the tube, thereby minimizing light loss.

[0045] In summary, by setting the above lens arrangement and lens shape, short focal length projection is achieved and imaging clarity is guaranteed.

[0046] Furthermore, a protective glass 17 is provided between the TIR prism 16 and the twelfth lens 12 to prevent dust and isolate moisture.

[0047] In a specific embodiment, the focal length, refractive index, etc. of each lens are set accordingly:

[0048] 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;

[0049] 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;

[0050] The focal length f of the reflector bowl 14 10 Range: 10mm≤f 10 ≤20mm.

[0051] 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:

[0052] 1.50≤n1≤1.60, 1.50≤n2≤1.60, 1.85≤n3≤1.95, 1.65≤n4≤1.75,

[0053] 1.80≤n5≤1.90,1.45≤n 61 ≤1.55,2.00≤n 62 ≤2.10,1.40≤n 63 ≤1.50,

[0054] 1.85≤n 71 ≤1.95, 1.45≤n 72 ≤1.55, 1.55≤n8≤1.65, 1.85≤n9≤1.95.

[0055] 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:

[0056] 2.0mm≤d1≤2.4mm, 2.3mm≤d2≤2.7mm, 5.5mm≤d3≤5.9mm,

[0057] 5.4mm≤d4≤5.8mm, 4.2mm≤d5≤4.6mm, 6.1mm≤d 61 ≤6.5mm,

[0058] 0.9mm≤d 62 ≤0.13mm, 4.3mm≤d 63 ≤4.7mm, 1.1mm≤d 71 ≤1.5mm,

[0059] 4.5mm≤d 72 ≤4.9mm, 5.8mm≤d8≤6.2mm, 3.0mm≤d9≤3.4mm.

[0060] The distance between the reflective 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 1 mm and 2 mm. The spacing between the triplet lens and the doublet lens on the optical axis is between 0 mm and 1 mm; the spacing between the doublet lens and the eleventh lens 11 on the optical axis is between 0 mm and 1 mm; the spacing between the eleventh lens 11 and the twelfth lens 12 on the optical axis is between 0 mm and 1 mm; the spacing between the twelfth lens 12 and the protective glass 17 on the optical axis is between 2 mm and 5 mm; the spacing between the TIR prism 16 and the display chip 13 on the optical axis is between 2 mm and 4 mm.

[0061] 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

[0062] Based on the content of Example 1, this application provides a specific implementation method:

[0063] 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.

[0064] Table 1 Some parameter settings of ultra-short-throw projection system

[0065]

[0066] Table 2 Some parameter settings of ultra-short-throw projection system (continued)

[0067]

[0068] It should be noted that the center thickness of the imaging surface in the table above, -243.41mm, represents the distance from the imaging surface to the reflective bowl. The front surface of each lens is the side facing the reflective bowl, and the rear surface is the side facing away from the reflective bowl. The surface type is the formula type satisfied by each surface, where a standard surface is a plane. Clearly, this application can achieve a smaller projection distance. The center thickness of each lens's front surface is the thickness of that lens, while the center thickness of each lens's rear surface is the distance from the rear surface of each lens to the front surface of the next lens on the optical axis.

[0069] Further, see Figure 1 The concave side of the reflecting bowl 14, the two surfaces of the first lens 1, and the two surfaces of the second lens 2 satisfy the following aspheric formula:

[0070] ,

[0071] The formulas for each lens surface establish a Cartesian coordinate system O-xyz with the vertex of each surface as the origin O. In this application, the x-axis, y-axis, and z-axis directions 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 reflective 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 explained in detail in this application, c' is the surface curvature, k' is the cone coefficient, for The corresponding aspheric coefficient, N is the order, is the radial coordinate constant.

[0072] The relevant parameters are shown in Tables 3 to 5 below:

[0073] Table 3 Parameter settings of reflection bowl

[0074]

[0075] Table 4 Parameter settings of the first lens

[0076]

[0077] Table 5 Parameter settings of the second lens

[0078]

[0079] See also Figure 1 , the eleventh lens 11 establishes a Cartesian 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:

[0080] ,

[0081] in, is the radial distance, c is the surface curvature, c is the inverse of the curvature radius, k is the cone coefficient, α1, α2, α3, α4, α5, α6, α7, and α8 are r 2 、r 4 、r 6 、r 8 、r 10 、r 12 、r 14 、r 16 The coefficient of .

[0082] The specific parameter settings are as shown in Table 6:

[0083] Table 6 Parameter settings

[0084]

[0085] 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-throw projection system, and the imaging effects were verified. Figures 2 to 4 , conduct relevant analysis based on the content of the diagram:

[0086] 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 aberration under different wavelengths of light is very small.

[0087] 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 resolving power of the projection lens is greater than 0.5@66lp / mm. 0.5@66lp / mm means that the resolving power of 66 line pairs per millimeter is 0.5.

[0088] Figure 4 This indicates that the difference in image quality between the center and the surrounding areas is small.

[0089] In summary, the ultra-short-focus projection system provided in this application realizes short-focus projection and ensures imaging clarity.

[0090] It should be noted that the terms used in the present invention are only for describing specific embodiments and are not intended to limit the scope of this 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 and may also include the plural. The terms "comprise", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method or device comprising 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 further restrictions, the elements defined by the sentence "comprise a..." do not exclude the presence of other identical elements in the process, method or device comprising the elements.

[0091] It should also be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations 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 an indirect connection through an intermediate medium, or it can be a communication between the internal parts of 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.

[0092] 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 above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with 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 front and rear surfaces of the first lens (1) are both aspherical lenses, the front and rear surfaces of the second lens (2) are both aspherical lenses, the front and rear surfaces of the third lens (3) are both spherical lenses, the third lens (3) is a convex lens with its front and rear surfaces convex toward the reflection bowl (14), the front and rear surfaces of the fourth lens (4) are both spherical lenses, the fourth lens (4) is a concave lens with its front and rear surfaces convex toward the display chip (13), the front and rear surfaces of the fifth lens (5) are both spherical lenses, the fifth lens (5) is a convex lens with its front and rear surfaces convex toward the reflection bowl (14), 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 aspherical 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); Wherein, 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 reflecting bowl (14) 10 The value range is: 10mm≤f 10 ≤20mm.

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 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。 4. 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。 5. 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.

6. 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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