An ultra-short focus projection lens system using a free-form lens

Abstract

The application discloses an ultra-short-focus projection lens system using a free-form lens, wherein an image source chip, a prism, multiple lenses and a mirror are sequentially arranged, and the system chromatic aberration and field curvature are effectively corrected by using the ultra-high degree of freedom of the free-form lens and the specific combination distribution of the focal length, the refractive index, the thickness on the lens axis and the lens curvature radius of the lens. The ultra-short-focus projection lens can solve the problems of low distortion, low chromatic aberration and high resolution under the condition of an ultra-large field of view under the premise of simple structure.

Description

Technical Field

[0001] This invention belongs to the field of optical lenses, and specifically relates to an ultra-short-throw projection lens system that uses a freeform surface lens. Background Technology

[0002] With the development of ultra-short throw projection technology, ultra-short throw projection lenses have been widely used in education, business, and home entertainment. As a core component of an ultra-short throw projection system, the ultra-short throw projection lens determines the system's throw ratio, image quality, and overall system size.

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

[0004] However, in order to achieve the requirements of a large field of view, high definition and low TV distortion, these lens structures typically use aspherical surfaces for single reflectors and a combination of multiple aspherical and spherical lenses for transmission lens groups. The entire system has a large number of lenses and a complex optical path structure, which leads to difficulties in assembly and adjustment and increased costs. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide an ultra-short-throw projection lens system that utilizes a freeform surface lens, which can achieve high imaging performance while reducing system complexity.

[0006] The specific technical solution for achieving the objective of this invention is as follows:

[0007] An ultra-short-throw projection lens system using a freeform surface lens includes an image source chip, a prism, multiple 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 from the image source chip, which is refracted by the first lens, second lens, third lens, fourth lens, fifth lens, sixth lens and seventh lens to form a primary image. The primary image is then reflected by the mirror to form a secondary image on the transmission image surface.

[0011] Furthermore, 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 polarizing beam splitter.

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

[0013] Furthermore, the first lens has positive optical power and is a biconvex aspherical lens. Its focal length f1 is related to the total effective focal length f of the system by the following condition: 6 < f1 / f < 7.

[0014] Furthermore, the second lens has negative optical power and is a cemented 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] Furthermore, the second lens includes a first discrete lens, a second discrete lens, and a third discrete lens;

[0017] The first discrete 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 n 2-2 >1.8; The third discrete lens is a meniscus lens, with a convex surface on the side closest to the chip, and an Abbe number v. 2-3 >70.

[0018] Furthermore, the third lens has negative optical power and is a meniscus lens, with a concave surface on the side closest to the chip; the fourth lens has positive optical power and is a meniscus lens, with a concave surface on the side closest to the chip; and the fifth lens has positive optical power and is a meniscus lens, with a concave surface on the side closest to the chip.

[0019] Furthermore, the sixth lens has negative optical power and is a cemented 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] Furthermore, the sixth lens includes a fourth discrete lens and a fifth discrete lens;

[0022] The fourth discrete 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 n. 2-2>1.8.

[0023] Furthermore, the seventh lens is a freeform surface lens that is symmetrical about the x-axis, satisfying the following equation:

[0024]

[0025] Where z is the sagitta of the seventh lens, c is the vertex curvature of the seventh lens, r is the radial coordinate of the seventh lens (with the same unit as the lens length), k is the conic coefficient, m and n are the exponents corresponding to x and y respectively, and their values ​​are positive integers between 0 and 10. j For different orders m and n, C represents the freeform surface coefficients, where m + n = 10 and m is an odd number. j =0.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] The present invention, through the lens configuration described above, utilizes the ultra-high degree of freedom of freeform lenses and the specific combination and allocation of lens focal length, refractive index, on-axis thickness, and radius of curvature to enable ultra-short-throw projection lenses to solve the problems of low distortion, low astigmatism, and high resolution in ultra-large field of view under the premise of simple structure.

[0028] The present invention will be further described below with reference to specific embodiments. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the ultra-short-throw projection lens system in an embodiment of the present invention.

[0030] Figure 2 This is a 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 This is a schematic diagram of the full field-of-view MTF distribution of the ultra-short-throw projection lens in an embodiment of the present invention.

[0032] Figure 4 This is a schematic diagram of the full-field astigmatism distribution of the ultra-short-throw projection lens in an embodiment of the present invention. Detailed Implementation

[0033] To clearly describe the technical solution and effects achieved by the present invention, the technical solution of the present invention will be clearly explained below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can realize the invention without creative effort. The structure shown in the drawings is not the entirety of the actual structure but only a part of the actual structure. It should be noted that all other embodiments made by those skilled in the art based on the embodiments of the present invention without creative effort should fall within the protection scope of the present invention.

[0034] The following examples are merely illustrative of the invention, and the scope of the invention is not limited to the examples provided. Therefore, any non-essential modifications made by those skilled in the art to the embodiments described above, applied to other embodiments, are still within the scope of protection of this invention. Furthermore, experimental methods not specified in the following examples should be performed according to conventional or manufacturer-recommended conditions. Unless otherwise specified, expressions in the text are used for distinguishing purposes only and have no other meaning.

[0035] Example

[0036] Combination Figure 1 An ultra-short-throw projection lens system using a freeform surface lens includes an image source chip, a prism, multiple 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 from the image source chip, and 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, a primary image is formed. The primary image is then reflected by the mirror L8 to form a secondary image on the transmission image surface.

[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 polarizing beam splitter.

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

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

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

[0044] The optical axis spacing T56 between the fifth lens L5 and the sixth lens L6 and the optical axis spacing T67 between the sixth lens L6 and the seventh lens L7 satisfy: 1≤T56 / T67≤2. Within this range, it is beneficial for light rays from different fields of view to diverge on the seventh lens L7, which is beneficial for utilizing the freeformability of the seventh lens L7, thereby benefiting the correction of astigmatism and field curvature of the system.

[0045] By utilizing the ultra-high degree of freedom of freeform surfaces and by rationally setting the optical power, radius of curvature, thickness, and refractive index Abbe number characteristics of each lens, the complexity of the system can be reduced, the aberrations of ultra-short-throw projection lenses can be effectively balanced, and the tolerance sensitivity of ultra-short-throw projection lenses can be reduced.

[0046] The first lens L1 has positive optical power and is a biconvex aspherical lens. Its focal length f1 and the total effective focal length f of the system are related by the following condition: 6 < f1 / f < 7. This is beneficial for the subsequent lens group to balance the spherical aberration, chromatic aberration and astigmatism generated by the first lens L1, and thus helps to control the overall length of the lens.

[0047] The second lens L2 has negative optical power and is a cemented 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 cemented triplet lens can be reasonably controlled, which is beneficial for distortion correction and system miniaturization.

[0049] More specifically, the second lens L2 includes a first discrete lens L2-1, a second discrete lens L2-2, and a third discrete 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, with a convex surface on the side closest to the chip, and an Abbe number v. 2-3>70, within this range, the chromatic aberration correction capability of the three-layer composite lens in the system can be effectively improved.

[0051] The third lens L3 has negative optical power and is a meniscus lens, with a concave surface on the side closest to the chip; the fourth lens L4 has positive optical power and is a meniscus lens, with a concave surface on the side closest to the chip; the fifth lens L5 has positive optical power and is a meniscus lens, with a concave surface on the side closest to the chip.

[0052] The sixth lens L6 has negative optical power and is a cemented 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 cemented doublet lens can be reasonably controlled, which is beneficial to balancing the spherical aberration generated by the first lens L1. It can also control the deflection angle of 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 discrete lens L6-1 and a fifth discrete lens L6-2;

[0055] The fourth discrete 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 cemented doublet lens in the system can be effectively improved.

[0056] The seventh lens L7 is a freeform surface lens that is symmetrical about the x-axis and satisfies the following equation:

[0057]

[0058] Where z is the sagitta 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 (with the same units as the lens length), k is the conic coefficient, m and n are the exponents corresponding to x and y respectively, and their values ​​are positive integers between 0 and 10, C j For different orders m and n, C represents the freeform surface coefficients, where m + n = 10 and m is an odd number. j =0. This configuration effectively improves the manufacturability of freeform surface lenses while leveraging their ability to correct field astigmatism.

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

[0060] Table 1 Parameters of Ultra-Short Throw Projector Lenses

[0061]

[0062]

[0063] Table 2 lists the aspherical 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 freeform surface coefficients.

[0067] Table 3 Freeform Surface Coefficients of Ultra-Short Throw Projector Lenses

[0068]

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

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

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

[0072] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. An ultra-short-throw projection lens system using a freeform surface lens, characterized in that, Includes image source chip, prism, multiple lenses and reflector (L8); The lens is composed of 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, 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; The first lens (L1) receives the light beam emitted from the image source chip, and 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), a primary image is formed. The primary image is then reflected by the mirror (L8) to form a secondary image on the transmission image surface. The first lens (L1) has positive optical power and is a biconvex aspherical lens. Its focal length f1 and the total effective focal length f of the system are related by the following: 6 < f1 / f < 7l. The second lens (L2) has negative optical power and is a cemented 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; The third lens (L3) has negative optical power and is a meniscus lens, with a concave surface on the side closest to the chip; the fourth lens (L4) has positive optical power and is a meniscus lens, with a concave surface on the side closest to the chip; the fifth lens (L5) has positive optical power and is a meniscus lens, with a concave surface on the side closest to the chip. The sixth lens (L6) has negative optical power and is a cemented 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; The seventh lens (L7) is a freeform surface lens that is symmetrical about the x-axis and satisfies the following equation: ； Where z is the 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), with the same unit as the lens length, k is the conic coefficient, and m and n are the exponents corresponding to x and y, respectively, taking values ​​between 0 and 10 as positive integers. These are the freeform surface coefficients corresponding to different orders m and n, where m + n = 10, and m is an odd number. .

2. The ultra-short-throw projection lens system using a freeform 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 polarizing beam splitter. The distance Ti between the projection image plane and the reflecting mirror (L8) on the optical axis satisfies: 350mm≤Ti≤550mm.

3. The ultra-short-throw projection lens system using a freeform surface lens according to claim 1, characterized in that, The second lens (L2) includes a first discrete lens (L2-1), a second discrete lens (L2-2), and a third discrete lens (L2-3). 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, with a convex surface on the side closest to the chip, and an Abbe number v. 2-3 >70.

4. The ultra-short-throw projection lens system using a freeform surface lens according to claim 1, characterized in that, The sixth lens (L6) includes the fourth discrete lens (L6-1) and the fifth discrete lens (L6-2). The fourth discrete 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.

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