4k short focus projection optical system

Abstract

The application discloses a 4K short-focus projection optical system, comprising, from the object side to the image side, a first lens group, which is a fixed group and has a negative focal length; a second lens group, which is movable along the optical axis and has a negative focal length, and is used for focusing on different object distances; a third lens group, which is movable along the optical axis and has a negative focal length, and is used for focusing on different object distances; a fourth lens group, which is a fixed group and has a positive focal length; and a fifth lens group, which is a fixed group and has a positive focal length. The 4K short-focus projection optical system has the advantages of an ultra-short projection ratio, a large aperture, high resolution, an image far from the center, low distortion and high relative luminance, and realizes an ultra-short focal length without using a non-spherical reflecting bowl, and the manufacturing feasibility is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical systems, in particular to a 4K short-focus projection optical system. BACKGROUND

[0002] The projection systems in the current market are divided into micro projectors, engineering projectors, cinema projectors, etc. The micro projectors are small in size but low in brightness, and the engineering projectors and the cinema projectors are high in brightness but large in size. In view of the above background, a small-size high-resolution light valve engineering projector with medium-high brightness emerges as the times require, but there is a lack of a matching projection optical system. The projection ratio of similar products is large, the relative luminance is low, the displacement is small, and the cost is high. SUMMARY

[0003] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application provides a 4K short-focus projection optical system for solving the problems of large projection ratio, low relative luminance, small displacement, and high cost of high-brightness engineering projection lenses in the prior art.

[0004] According to the 4K short-focus projection optical system of the embodiment of the present application, from the object side to the image side, there are sequentially arranged: a first lens group, which is a fixed group and has a negative focal power; a second lens group, which is movable along the optical axis and has a negative focal power, and is used for focusing on different object distances; a third lens group, which is movable along the optical axis and has a positive focal power, and is used for focusing on different object distances; a fourth lens group, which is a fixed group and has a positive focal power; an equivalent prism group; and a light valve.

[0005] Each lens group satisfies the following formula:

[0006] -5.0 < f1 / f < -1;

[0007] -30 < f2 / f < -10;

[0008] 2.0 < f3 / f < 8.0;

[0009] 1.0 < f4 / f < 5.0;

[0010] 14 < PTLA < 20;

[0011] Wherein, f is the effective focal length of the 4K short-focus projection optical system, f1 is the focal length of the first lens group, f2 is the focal length of the second lens group, f3 is the focal length of the third lens group, f4 is the focal length of the fourth lens group, and PTLA is the equivalent air length of the equivalent prism group.

[0012] The 4K short-focus projection optical system according to the embodiment of the present application has at least the following beneficial effects: the present application has the advantages of 4K resolution, ultra-short projection ratio, large aperture, high resolution, telecentricity in the image plane, low distortion, high relative luminance, and small highlight by reasonably distributing the lens power and matching the optical materials to balance and correct the optical aberrations at all levels.

[0013] According to some embodiments of the present application, the first lens group comprises at least one negative lens and at least one aspherical lens; the second lens group comprises at least one negative lens; and the fourth lens group comprises at least one cemented lens.

[0014] According to some embodiments of the present application, the equivalent prism group is a galvanometer, a TIR prism or an X prism.

[0015] According to some embodiments of the present application, the light valve is a DMD digital micromirror, an LCD liquid crystal display or an LCOS reflective liquid crystal.

[0016] According to some embodiments of the present application, during the focusing process in which the projection distance gradually increases, the air gap between the second lens group and the first lens group gradually decreases, and the air gap between the third lens group and the fourth lens group gradually increases.

[0017] According to some embodiments of the present application, the fourth lens group comprises at least one lens of optical material with negative temperature characteristics.

[0018] According to some embodiments of the present application, a protective glass is arranged between the equivalent prism group and the light valve.

[0019] According to some embodiments of the present application, the light valve is a 0.47-inch light valve chip with a resolution of 3840x2160, a pixel pitch of 5.4um and a Nyquist frequency of 93lP / mm.

[0020] According to some embodiments of the present application, the light valve is arranged to be offset from the optical axis, and the offset displacement supports ±110% up and down and ±45% left and right.

[0021] According to some embodiments of the present application, the 4K short-focus projection optical system has a focal length f=5.8mm and an Fno=1.8.

[0022] Additional aspects and advantages of the present application will be in part apparent and in part pointed out hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0023] The above and / or additional aspects and advantages of the present application will become apparent and be readily understood from the following description, taken in conjunction with the accompanying drawings, in which:

[0024] Figure 1 System structure diagram of an embodiment of the present application;

[0025] Figure 2 Middle end spherical aberration, astigmatism, and field curvature graph of an embodiment of the present application;

[0026] Figure 3 Near end spherical aberration, astigmatism, and field curvature graph of an embodiment of the present application;

[0027] Figure 4 Far end spherical aberration, astigmatism, and field curvature graph of an embodiment of the present application;

[0028] Figure 5 Middle end ray aberration graph of an embodiment of the present application;

[0029] Figure 6 Near end ray aberration graph of an embodiment of the present application;

[0030] Figure 7 Far end ray aberration graph of an embodiment of the present application;

[0031] Figure 8 Middle end MTF graph of an embodiment of the present application;

[0032] Figure 9 Near end MTF graph of an embodiment of the present application;

[0033] Figure 10 Far end MTF graph of an embodiment of the present application. DETAILED DESCRIPTION

[0034] Embodiments of the present application are described in detail below with reference to the attached drawings, which show by way of example, embodiments in which the same or similar elements have the same or similar reference numbers and wherein:

[0035] In the description of the present application, it should be understood that, in relation to the orientation description, for example, the orientation or position relationship indicated by the up, down, front, back, left, right, etc. is based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application.

[0036] In the description of the present application, unless otherwise explicitly limited, the words such as setting, installing, connecting, etc. should be broadly understood, and the person skilled in the art can reasonably determine the specific meaning of the above words in the present application in combination with the specific content of the technical solution.

[0037] ReferenceFigure 1 As shown in the figure, it is a 4K short-focus projection optical system, comprising, from the object side to the image side, in sequence:

[0038] The first lens group G1 is a fixed group and has a negative focal power; in this embodiment, the first lens group G1 is composed of the first lens L1, the second lens L2 and the third lens L3;

[0039] The second lens group G2 is movable along the optical axis and has a negative focal power, used for focusing at different object distances; in this embodiment, the second lens group G2 is composed of the fourth lens L4 and the fifth lens L5;

[0040] The third lens group G3 is movable along the optical axis and has a positive focal power, used for focusing at different object distances; in this embodiment, the third lens group G3 is composed of the sixth lens L6, the seventh lens L7 and the eighth lens L8;

[0041] The fourth lens group G4 is a fixed group and has a positive focal power; in this embodiment, the fourth lens group G4 is composed of the ninth lens L9, the tenth lens L10, the eleventh lens L11, the twelfth lens L12, the thirteenth lens L13, the fourteenth lens L14, the fifteenth lens L15, the sixteenth lens L16 and the seventeenth lens L17;

[0042] The equivalent prism group Prism;

[0043] The light valve IMG;

[0044] Each lens group satisfies the following formula:

[0045] -5.0 < f1 / f < -1;

[0046] -30 < f2 / f < -10;

[0047] 2.0 < f3 / f < 8.0;

[0048] 1.0 < f4 / f < 5.0;

[0049] 14 < PTLA < 20;

[0050] Wherein, f is the effective focal length of the 4K short-focus projection optical system, f1 is the focal length of the first lens group G1, f2 is the focal length of the second lens group G2, f3 is the focal length of the third lens group G3, f4 is the focal length of the fourth lens group G4, and PTLA is the equivalent air length of the equivalent prism group Prism.

[0051] In the focusing process of gradually increasing projection distance, the air gap between the second lens group G2 and the first lens group G1 is constantly reduced, and the air gap between the third lens group G3 and the fourth lens group G4 is constantly increased, and the total length of the optical system (the front surface of the first optical lens to the rear surface of the last optical lens) remains unchanged during the focusing process. The optimal imaging target surface supported by the above-mentioned optical system is 16.2mm (half image height 8.1mm), and using the target surface, the present embodiment has the advantages of 4K resolution, ultra-short projection ratio, large aperture, high resolution, telecentricity, low distortion, high relative luminance, and small highlight body by reasonably allocating the lens power and matching the optical material to balance and correct the optical aberration at each level.

[0052] In some embodiments of the present application, the first lens group G1 includes at least one negative lens and at least one aspheric lens, and the shape of the aspheric lens includes but is not limited to M type, C type, etc., which is beneficial to improve the field of view of the optical system and balance and correct optical distortion and off-axis aberration.

[0053] The above-mentioned 4K short-focus projection optical system includes but is not limited to being used in a 0.47-inch digital micromirror DMD chip, and the light modulator chip within the image height range of the optical system is applicable.

[0054] In addition, the second lens group G2 includes at least one negative lens; the fourth lens group G4 includes at least one cemented lens, which is a three-cemented lens group, which is beneficial to correct the chromatic aberration of the system. The fourth projection group G4 includes at least one negative temperature characteristic optical material lens, which is beneficial to correct the thermal defocus phenomenon in the high-brightness projection system.

[0055] The specific parameters of the present embodiment are as follows:

[0056]

[0057] Table 1

[0058] Further, in some embodiments of the present application, the light valve IMG is preferably a 0.47-inch digital micromirror chip for projection, which has a display resolution of 3840x2160, a pixel pitch of 5.4um, a Nyquist frequency of 93lp / mm, a focal length EFL=5.8mm, an Fno=1.8, a projection ratio TR=0.55, and an optical distortion of less than 0.5%. The short-focus projection lens, the light valve can be placed offset from the optical axis, so that the projection picture can be shifted up, down, left and right, and the maximum offset displacement supports up and down ±110%, left and right ±45%.

[0059] In some embodiments of the present application, a protective glass is arranged between the equivalent prism group Prism and the light valve IMG, which can protect the light valve IMG from direct damage by external force.

[0060] In some embodiments of the present application, the equivalent prism Prism is a galvanometer, a TIR prism or an X prism, but is not limited to the above-mentioned light valves (signal modulation devices).

[0061] In some embodiments of the present application, the light valve IMG is a DMD digital micro-mirror, an LCD liquid crystal display or an LCOS reflective liquid crystal, but is not limited to the above-mentioned optical devices equivalent to parallel flat plates.

[0062] In the embodiment, the total length of the lens remains unchanged during zooming. The following table is the focusing interval data of the embodiment:

[0063]

[0064] Table 2

[0065] The embodiment of the present application adopts a pure transmission type 4K short focus projection optical system, which uses optical elements with perfect processing technology under the premise of realizing ultra-short projection ratio, greatly improving the processing and manufacturing feasibility.

[0066] The aspherical curve driving equation of the above-mentioned embodiment is as follows:

[0067]

[0068] In the formula, c is the aspherical curvature, r is the radial coordinate, k is the conic coefficient of the quadratic surface, and AR1..30 is the aspherical coefficient of each order. The specific aspherical parameters are as follows:

[0069]

[0070] Table 3

[0071] *Note: The aspherical coefficients of other orders not given are all 0.

[0072] The embodiment of the present application reasonably allocates optical power, uses only one aspherical surface under the premise of realizing 4K high resolution optical performance, has good tolerance tolerance, greatly reduces the cost, improves the processing and manufacturing feasibility and the assembly process yield.

[0073] Figures 2 to 10 The optical evaluation diagram of the embodiment of the present application is shown in the following figure: Figure 2 、 Figure 3 、 Figure 4 The spherical aberration field curve diagram of the embodiment of the present application under different projection object distances is shown in the following figure. It can be seen that the red-green axial chromatic aberration is corrected and the second-order spectrum is small, the optical distortion is less than 0.5%, the degree of picture distortion is small, and the axial chromatic aberration and optical distortion under different object distances are almost unchanged. Figure 5 、 Figure 6 、 Figure 7The light aberration diagram of the embodiment of the present application at different projection object distances is balanced and corrected well, the magnification chromatic aberration is about half a pixel, and the color difference effect of the actual projection picture is good. Figure 8 、 Figure 9 、 Figure 10 The MTF diagram of the embodiment of the present application at different projection object distances is less changed in the Near-Far focusing process, and the global MTF is greater than 0.45 at the Nyquist frequency under the F1.8 large aperture.

[0074] In the description of the present specification, the description referring to the terms "one embodiment", "some embodiments", "exemplary embodiment", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the exemplary description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0075] Although the embodiments of the present application have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, replacements and variations can be made to the embodiments without departing from the principles and purposes of the present application, the scope of the present application is defined by the claims and their equivalents, for example, the positive and negative lenses with small air gap and small difference in radius of curvature are glued, which should be regarded as a proper extension of the present patent and within the protection scope of the present patent.

Claims

1.A 4K short-throw projection optical system, characterized by comprising, in order from an object side to an image side: a first lens group (G1) which is a fixed group and has a negative refractive power; a second lens group (G2) which is movable in an optical axis direction and has a negative refractive power, and is used for focusing on different object distances; a third lens group (G3) which is movable in an optical axis direction and has a positive refractive power, and is used for focusing on different object distances; a fourth lens group (G4) which is a fixed group and has a positive refractive power; an equivalent prism group (Prism); and an image valve (IMG); each lens group satisfies the following formulae: -5.0 < f1 / f < -1; -30 < f2 / f < -10; 2.0 < f3 / f < 8.0; 1.0 < f4 / f < 5.0; and 14 < PTLA < 20; wherein f is an effective focal length of the 4K short-throw projection optical system, f1 is a focal length of the first lens group (G1), f2 is a focal length of the second lens group (G2), f3 is a focal length of the third lens group (G3), f4 is a focal length of the fourth lens group (G4), and PTLA is an equivalent air length of the equivalent prism group (Prism). The first lens group (G1) comprises at least one negative lens and at least one aspheric lens. The second lens group (G2) comprises at least one negative lens. The fourth lens group (G4) comprises at least one cemented lens. The equivalent prism group (Prism) is a galvanometer, a TIR prism or an X prism. The image valve (IMG) is a DMD digital micro-mirror, an LCD liquid crystal display or an LCOS reflective liquid crystal. ​ ​ ​ ​ 2.The 4K short focal length projection optical system according to claim 1, characterized by: ​ ​ 3.The 4K short focal length projection optical system according to claim 1, characterized by: ​ 4.The 4K short focal length projection optical system according to claim 1, characterized by: ​

Images