Ultra-short-focus projection lens system applying free-form surface lens

Abstract

An image source chip, a prism, a plurality of lenses and a reflecting mirror are sequentially arranged, and through the configuration, the ultra-high degree of freedom of the free-form surface lens and specific combination distribution of the focal length of the lens, the refractive index, the thickness on the axis of the lens and the curvature radius of the lens are utilized; and astigmatism and curvature of field of the system are effectively corrected. On the premise that the structure of the ultra-short-focus projection lens is simple, the problems of low distortion, low astigmatism and high resolution under the condition of an ultra-large field of view can be solved.

Description

Technical Field

[0001] The invention belongs to the field of optical lenses, and in particular relates to an ultra-short-focus projection lens system using a free-form surface lens. Background Art

[0002] With the development of ultra-short-throw projection technology, ultra-short-throw projection lenses have been widely used in education, business, home entertainment and other fields. As the core component of the ultra-short-throw projection system, the ultra-short-throw projection lens determines the performance of the ultra-short-throw projection system, such as the projection ratio, image quality of the projection screen and system volume.

[0003] Currently, the commonly used ultra-short-throw projection lenses mainly adopt the structure of a refractive lens group plus a single reflector. For example, the transmission lens group in patent CN 109407288 A "A folding ultra-short-throw projection lens system" adopts a design of 16 lenses. The transmission lens group in patent CN 207181796 U "An ultra-short-throw projection lens" adopts a design of 15 lenses. The transmission lens group in patent CN 116107063 B "An ultra-short-throw projection lens and projection system" adopts a design of 15 lenses.

[0004] However, in order to achieve the requirements of large field of view, high definition and low TV distortion, these lens structures usually use aspherical surfaces for single reflectors, and the transmission lens group uses a combination of multiple aspherical lenses and spherical lenses. The entire system has a large number of lenses and a complex optical path structure, which makes installation and adjustment difficult and increases costs. Summary of the invention

[0005] In view of the above problems, an object of the present invention is to provide an ultra-short-throw projection lens system using a free-form surface lens, which can reduce the complexity of the system while achieving high imaging performance.

[0006] The specific technical solution for achieving the purpose of the present invention is:

[0007] An ultra-short-throw projection lens system using a free-form surface lens comprises an image source chip, a prism, a plurality of lenses and a reflector;

[0008] The lenses include a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens;

[0009] The image source chip, prism, first lens, second lens, third lens, fourth lens, fifth lens, sixth lens, seventh lens and reflector are arranged in sequence;

[0010] The first lens receives the light beam emitted by the image source chip, and forms a primary image after being refracted by the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens, and the seventh lens. The primary image forms a secondary image on the transmission image plane after passing through the reflector.

[0011] Further, when the image source chip is a DMD, the prism is a TIR prism, and when the image source chip is an LCOS, the prism is a polarization beam splitter prism;

[0012] The distance Ti between the projection image plane and the reflector on the optical axis satisfies: 350mm≤Ti≤550mm.

[0013] Furthermore, the first lens has positive power and is a biconvex aspheric lens, and the relationship between its focal length f1 and the total effective focal length f of the system satisfies: 6<f1 / f<7.

[0014] Furthermore, the second lens has negative optical power and is a triplet lens;

[0015] The relationship between the focal length f2 of the second lens and the focal length f1 of the first lens satisfies: -3.5<f2 / f1<-2.5.

[0016] Further, the second lens includes a first separate lens, a second separate lens and a third separate lens;

[0017] The first separate lens is a biconvex lens with an Abbe number v 2-1 >70; the second discrete lens is a biconcave lens with a refractive index of n 2-2 >1.8; The third discrete lens is a meniscus lens, the side of which close to the chip is convex, and the Abbe number is v 2-3 >70.

[0018] Furthermore, the third lens has negative optical focal length and is a meniscus lens, and its side close to the chip is concave; the fourth lens has positive optical focal length and is a meniscus lens, and its side close to the chip is concave; the fifth lens has positive optical focal length and is a meniscus lens, and its side close to the chip is concave.

[0019] Furthermore, the sixth lens has negative optical power and is a doublet lens;

[0020] The relationship between the focal length f6 of the sixth lens and the focal length f1 of the first lens satisfies: -20<f6 / f1<-18.

[0021] Further, the sixth lens includes a fourth separate lens and a fifth separate lens;

[0022] The fourth separate lens is a biconvex lens with an Abbe number v 6-1 >70; the fifth discrete lens is a biconcave lens with a refractive index of n 2-2>1.8.

[0023] Furthermore, the seventh lens is a free-form surface lens symmetric about the x-axis and satisfies the following equation:

[0024]

[0025] Wherein, z is the seventh lens sag, c is the seventh lens vertex curvature, r is the seventh lens radial coordinate, its unit is the same as the lens length unit, k is the cone coefficient, m and n are the indexes corresponding to x and y respectively, and the values ​​are positive integers between 0 and 10, C j is the free surface coefficient corresponding to different m and n orders, m+n=10, when m is an odd number, C j =0.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The solution of the present invention, through the configuration of the above-mentioned lenses, utilizes the ultra-high degree of freedom of the free-form surface lens and the specific combination of the lens focal length, refractive index, lens axial thickness and lens curvature radius, so that the ultra-short focus projection lens can solve the problems of low distortion, low astigmatism and high resolution in the case of ultra-large field of view with a simple structure.

[0028] The present invention is further described below in conjunction with specific implementation modes. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the structure of an ultra-short-throw projection lens system in an embodiment of the present invention.

[0030] Figure 2 Schematic diagram of the field curvature distortion curve in the +y direction of the ultra-short-throw projection lens in an embodiment of the present invention.

[0031] Figure 3 Schematic diagram of the full-field MTF distribution of the ultra-short-throw projection lens in an embodiment of the present invention.

[0032] Figure 4 Schematic diagram of full-field astigmatism distribution of an ultra-short-throw projection lens in an embodiment of the present invention. DETAILED DESCRIPTION

[0033] In order to clearly describe the technical solution and the effects achieved by the present invention, the technical solution of the present invention is clearly explained below in combination with the accompanying drawings and specific embodiments of the present invention, so that technical personnel in the field can implement the invention without performing creative work. The structure shown in the accompanying drawings is not the entire actual structure but only a part of the actual structure. It should be noted that all other embodiments made by ordinary technical personnel in the field on the basis of the embodiments of the present invention without performing creative work should fall within the protection scope of the present invention.

[0034] The following examples are only for better explanation of the present invention, but the content of the present invention is not limited to the application in the examples. Therefore, those skilled in the art can make non-essential modifications to the implementation scheme based on the above invention content and apply it to other embodiments, which is still within the protection scope of the present invention. In addition, the experimental methods without specific conditions in the following examples should be carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the expressions in the text are not specially explained, they are only used for distinction and have no other meanings.

[0035] Example

[0036] Combination Figure 1 , an ultra-short-throw projection lens system using a free-form surface lens, comprising an image source chip, a prism, a plurality of lenses and a reflector L8;

[0037] The lenses include a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5, a sixth lens L6, and a seventh lens L7;

[0038] The image source chip, prism, first lens L1, second lens L2, third lens L3, fourth lens L4, fifth lens L5, sixth lens L6, seventh lens L7 and reflector L8 are arranged in sequence;

[0039] The first lens L1 receives the light beam emitted by the image source chip, and forms a primary image after being refracted by the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5, the sixth lens L6, and the seventh lens L7. The primary image forms a secondary image on the transmission image plane after passing through the reflector L8.

[0040] In addition, when the image source chip is a DMD, the prism is a TIR prism, and when the image source chip is an LCOS, the prism is a polarization beam splitter prism;

[0041] The distance Ti between the projection image plane and the reflector L8 on the optical axis satisfies: 350mm≤Ti≤550mm.

[0042] Among them, the first lens L1 is connected to the image source chip through a TIR prism when the image source chip is a DMD or a polarization beam splitting prism when the image source chip is an LCOS; the projection image plane is located on the concave side of the reflector L8, and the interval Ti between the projection image plane and the reflector L8 on the optical axis satisfies: 350mm≤Ti≤550mm.

[0043] The interval T78 between the seventh lens L7 and the reflector L8 on the optical axis satisfies 80 mm ≤ Ti ≤ 100 mm. Within this range, it is beneficial to control the size of the reflector L8 to be within a reasonable range, which is beneficial to the production and processing of the reflector L8.

[0044] The interval T56 between the fifth lens L5 and the sixth lens L6 on the optical axis and the interval T67 between the sixth lens L6 and the seventh lens L7 on the optical axis satisfy: 1≤T56 / T67≤2. Within this range, it is beneficial for light of different fields to be divergently distributed on the seventh lens L7, which is beneficial for bringing into play the free surface degree of the seventh lens L7, thereby facilitating the correction of system astigmatism and field curvature.

[0045] By utilizing the ultra-high degree of freedom of free-form surfaces and reasonably setting the optical focal length, curvature radius, thickness, and refractive index Abbe number characteristics of each lens, the complexity of the system can be reduced, the aberration of the ultra-short-throw projection lens can be effectively balanced, and the tolerance sensitivity of the ultra-short-throw projection lens can be reduced.

[0046] The first lens L1 has positive power and is a biconvex aspheric lens. The relationship between its focal length f1 and the total effective focal length f of the system satisfies: 6<f1 / f<7, which is beneficial for the subsequent lens group to balance the spherical aberration, chromatic aberration and astigmatism generated by the first lens L1, and thus is beneficial for controlling the overall length of the lens;

[0047] The second lens L2 has negative optical power and is a triplet lens;

[0048] The relationship between the focal length f3 of the second lens L2 and the focal length f1 of the first lens satisfies: -3.5<f2 / f1<-2.5. Within this range, the focal length of the triplet lens can be reasonably controlled, which is beneficial to distortion correction and system miniaturization.

[0049] More specifically, the second lens L2 includes a first separate lens L2-1, a second separate lens L2-2 and a third separate lens L2-3;

[0050] The first discrete lens L2-1 is a biconvex lens with an Abbe number v 2-1 >70; the second discrete lens L2-2 is a biconcave lens with a refractive index n 2-2 >1.8; the third discrete lens L2-3 is a meniscus lens, the side of which close to the chip is convex, and the Abbe number v 2-3>70, within this range, the chromatic aberration correction capability of the triplet lens in the system can be effectively improved.

[0051] The third lens L3 has negative optical power and is a meniscus lens, and its side close to the chip is concave. The fourth lens L4 has positive optical power and is a meniscus lens, and its side close to the chip is concave. The fifth lens L5 has positive optical power and is a meniscus lens, and its side close to the chip is concave.

[0052] The sixth lens L6 has negative optical power and is a doublet lens;

[0053] The relationship between the focal length f6 of the sixth lens L6 and the focal length f1 of the first lens L1 satisfies: -20<f6 / f1<-18. Within this range, the focal length of the doublet lens can be reasonably controlled, which is beneficial to balancing the spherical aberration generated by the first lens L1, and can control the deflection angle of the light on the sixth lens L6 within a reasonable range, which is beneficial to controlling the tolerance sensitivity of the sixth lens L6;

[0054] More specifically, the sixth lens L6 includes a fourth separate lens L6-1 and a fifth separate lens L6-2;

[0055] The fourth separate lens L6-1 is a biconvex lens with an Abbe number v 6-1 >70; the fifth discrete lens L6-2 is a biconcave lens with a refractive index n 2-2 >1.8. Within this range, the chromatic aberration correction capability of the doublet lens in the system can be effectively improved.

[0056] The seventh lens L7 is a free-form surface lens symmetric about the x-axis and satisfies the following equation:

[0057]

[0058] Wherein, z is the sag height of the seventh lens L7, c is the vertex curvature of the seventh lens L7, r is the radial coordinate of the seventh lens L7, and its unit is the same as the unit of lens length, k is the cone coefficient, m and n are the indices corresponding to x and y respectively, and the values ​​are positive integers between 0 and 10, C j is the free surface coefficient corresponding to different m and n orders, m+n=10, when m is an odd number, C j = 0. This configuration can effectively improve the processability of the free-form surface lens while giving full play to the field curvature and astigmatism correction capability of the free-form surface.

[0059] The following table shows the design parameters of the ultra-short-throw projection lens in this embodiment, wherein the units of the curvature radius, thickness and focal length are all millimeters (mm).

[0060] Table 1 Ultra short throw projection lens parameters

[0061]

[0062]

[0063] Table 2 lists the aspheric coefficients.

[0064] Table 2 Aspheric coefficients of ultra short-throw projection lenses

[0065] Face number conic <![CDATA[X 4 ]]> <![CDATA[X 6 ]]> <![CDATA[X 8 ]]> <![CDATA[X 10 ]]> S2 -0.74 6.368E-7 -1.81E-10 3.702E-14 -3.299E-18 S19 -5.37 -1.284E-5 3.913E-8 -3.35E-11 0 S20 -0.65 -3.396E-5 5.899E-8 -5.074E-11 0

[0066] Table 3 lists the free-form surface coefficients.

[0067] Table 3 Free-form surface coefficients of ultra-short-throw projection lenses

[0068]

[0069] In this example, the total effective focal length f of the ultra short-throw projection lens is 3.9 mm, the total length TTL is 256 mm, the projection ratio is <0.25, the aperture value Fno is 2.0, and it can match a 0.65-inch DMD chip and a 0.69-inch LCOS chip.

[0070] Figure 2 : is the field curvature distortion curve of the ultra short focus projection lens in the +y direction in this embodiment. The field curvature represents the meridional image curvature and the sagittal image curvature, and the distortion represents the size of the distortion value corresponding to different image heights. Figure 3 : is a full field distribution diagram of the ultra short focus projection lens in this embodiment at 90lp / mm. Figure 4 : is the full-field astigmatism distribution diagram of the ultra-short-throw projection lens in this embodiment.

[0071] according to Figures 2 to 4 It can be seen that the ultra-short-throw projection lens provided in this embodiment achieves the design goals of low distortion, low astigmatism, and high resolution.

[0072] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. 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 application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. An ultra-short-throw projection lens system using a free-form surface lens, characterized in that: It includes an image source chip, a prism, a plurality of lenses and a reflector (L8); The lenses include a first lens (L1), a second lens (L2), a third lens (L3), a fourth lens (L4), a fifth lens (L5), a sixth lens (L6), and a seventh lens (L7); The image source chip, the prism, the first lens (L1), the second lens (L2), the third lens (L3), the fourth lens (L4), the fifth lens (L5), the sixth lens (L6), the seventh lens (L7) and the reflector (L8) are arranged in sequence; The first lens (L1) receives the light beam emitted by the image source chip, and forms a primary image after being refracted by the first lens (L1), the second lens (L2), the third lens (L3), the fourth lens (L4), the fifth lens (L5), the sixth lens (L6), and the seventh lens (L7). The primary image forms a secondary image on the transmission image plane after passing through a reflector (L8).

2. The ultra-short-throw projection lens system using a free-form surface lens according to claim 1, characterized in that: When the image source chip is a DMD, the prism is a TIR prism; when the image source chip is an LCOS, the prism is a polarization beam splitter prism; The distance Ti between the projection image plane and the reflector (L8) on the optical axis satisfies: 350mm≤Ti≤550mm.

3. The ultra-short-throw projection lens system using a free-form surface lens according to claim 1, characterized in that: The first lens (L1) has positive refractive power and is a biconvex aspheric lens. The relationship between its focal length f1 and the total effective focal length f of the system satisfies: 6<f1 / f<7.

4. The ultra-short-throw projection lens system using a free-form surface lens according to claim 1, characterized in that: The second lens (L2) has negative optical power and is a triplet lens; The relationship between the focal length f2 of the second lens (L2) and the focal length f1 of the first lens satisfies: -3.5<f2 / f1<-2.

5.

5. The ultra-short-throw projection lens system using a free-form surface lens according to claim 4, characterized in that: The second lens (L2) includes a first separate lens (L2-1), a second separate lens (L2-2) and a third separate lens (L2-3); The first separate lens (L2-1) is a biconvex lens with an Abbe number v 2-1 >70; the second discrete lens (L2-2) is a biconcave lens with a refractive index of n 2-2 >1.8; the third discrete lens (L2-3) is a meniscus lens, the side of which close to the chip is convex, and the Abbe number is v 2-3 >70.

6. The ultra-short-throw projection lens system using a free-form surface lens according to claim 4, characterized in that: The third lens (L3) has negative optical power and is a meniscus lens, and its side close to the chip is concave. The fourth lens (L4) has positive optical power and is a meniscus lens, and its side close to the chip is concave. The fifth lens (L5) has positive optical power and is a meniscus lens, and its side close to the chip is concave.

7. The ultra-short-throw projection lens system using a free-form surface lens according to claim 1, characterized in that: The sixth lens (L6) has negative optical power and is a doublet lens; The relationship between the focal length f6 of the sixth lens (L6) and the focal length f1 of the first lens satisfies: -20<f6 / f1<-18.

8. The ultra-short-throw projection lens system using a free-form surface lens according to claim 7, characterized in that: The sixth lens (L6) includes a fourth separate lens (L6-1) and a fifth separate lens (L6-2); The fourth separate lens (L6-1) is a biconvex lens with an Abbe number v 6-1 >70; the fifth separate lens (L6-2) is a biconcave lens with a refractive index of n 2-2 >1.

8.

9. The ultra-short-throw projection lens system using a free-form surface lens according to claim 1, characterized in that: The seventh lens (L7) is a free-form surface lens symmetric about the x-axis and satisfies the following equation: Wherein, z is the seventh lens (L7) sag height, c is the seventh lens (L7) vertex curvature, r is the seventh lens (L7) radial coordinate, its unit is the same as the lens length unit, k is the cone coefficient, m and n are the indexes corresponding to x and y respectively, and the values ​​are positive integers between 0 and 10, C j is the free surface coefficient corresponding to different m and n orders, m+n=10, when m is an odd number, C j =0.

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