Small long-focus projection imaging system

Abstract

The invention relates to the technical field of optical imaging systems, and discloses a small long-focus projection imaging system which comprises a light valve, a prism, an image bias lens and a projection lens. The projection lens is sequentially provided with a rear lens group and a front lens group on the same optical axis from light incidence to light emergence, the rear lens group comprises a first lens with positive focal power which is a glass aspheric lens, a second lens with positive focal power which is a glass spherical lens, a third lens with negative focal power which is a glass spherical lens, and a fourth lens with negative focal power which is a glass spherical lens. The front lens group comprises a fourth lens which has positive focal power and is a glass spherical lens, and a fifth lens which has negative focal power and is a plastic aspheric lens; a diaphragm is arranged between the front lens group and the rear lens group; the second lens and the third lens are combined into a doublet lens; the aspheric lens is adopted to optimize the exit pupil position of the lens and correct distortion and astigmatism, meanwhile, a compact structure is adopted, the manufacturing cost of the lens is reduced, and the size of the lens is successfully reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of optical imaging systems, and in particular to a small telephoto projection imaging system. Background Art

[0002] With the development of science and technology, society has entered the multimedia information age. As the main carrier of images and sounds, projection technology has been widely used in the fields of home, military, transportation, office, aerospace, etc. In projection technology, lens design is one of the key links, and it undertakes the core functions of imaging quality and projection effect. However, lens design faces many challenges. On the premise of ensuring imaging quality, it is necessary to control costs and take into account miniaturization. At the same time, ensuring high resolution when imaging in large sizes, thus improving product performance has become a major difficulty.

[0003] The long-focus projection products currently on the market face the following two main problems: 1. Complexity of optical design and high cost: Telephoto projection lenses usually have complex structural designs, involving a large number of lens combinations, especially the widely used spherical glass lenses. This design not only leads to a significant increase in manufacturing costs, but also makes the lens bulky, increasing the difficulty of carrying. This complex lens structure requires not only precise processing and assembly, but also strict quality control to ensure that the optical performance of each lens meets the standards. Therefore, the price of the final product is often high, which to a certain extent limits its market competitiveness.

[0004] 2. Poor imaging quality: The existing telephoto fixed-focus lenses are generally not ideal in terms of aberration correction, especially when performing large-size imaging, where distortion is particularly obvious. This distortion not only affects the intuitive effect of the image, but also reduces the image restoration, making it difficult for the projection effect to meet user expectations. In addition, since the lens design fails to effectively control various optical aberrations, the overall optical imaging quality often cannot meet the needs of high-demand application scenarios (such as professional displays, education and training, etc.), further affecting the user experience.

[0005] Therefore, there is an urgent need for a small telephoto projection imaging system to reduce the size of the lens and improve the imaging quality. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a small telephoto projection imaging system that can use a very small number of lenses to achieve high-quality imaging while adopting a compact structure, reducing the lens manufacturing cost and reducing the lens size.

[0007] The present invention provides a small telephoto projection imaging system, which includes: a light valve, a prism, an image biasing mirror and a projection lens in order from the incident direction of light to the exit direction of light; The projection lens is provided with a rear lens group and a front lens group in sequence on the same optical axis from the incident direction of the light to the exit direction of the light, the rear lens group includes a first lens with positive focal power, a second lens with positive focal power, and a third lens with negative focal power, and the front lens group includes a fourth lens with positive focal power and a fifth lens with negative focal power; An aperture is provided between the front lens group and the rear lens group; The second lens and the third lens are combined into a doublet lens.

[0008] Furthermore, the first lens is a glass aspheric lens, and the fifth lens is a plastic aspheric lens; The plastic aspherical lens of the fifth lens is a meniscus lens bent toward the light source.

[0009] Furthermore, the second lens, the third lens and the fourth lens are all glass spherical lenses.

[0010] Furthermore, the glass spherical lens of the second lens is biconvex, and the glass spherical lens of the third lens is biconcave.

[0011] Furthermore, the Abbe number of the first lens is in the range of (75, 85).

[0012] Furthermore, the difference in Abbe numbers between the second lens and the third lens is in the range of (40, 50).

[0013] Furthermore, the Abbe number range of the fourth lens is (20, 30); the refractive index of the fourth lens is greater than 1.6; and the thickness of the fourth lens is less than 2.2 mm.

[0014] Furthermore, the Abbe number of the fifth lens is greater than 60, and the refractive index of the fifth lens is less than 1.6.

[0015] Furthermore, the light valve, the prism, the image biasing mirror and the projection lens form a projection system, the length of the lens system is L2, L2<55mm, and the length of the projection lens is L1, L1<40mm; The distance from the light valve to the first lens is a back working distance BFL, and BFL satisfies the condition: 0.05<BFL / L1<1.

[0016] Furthermore, the total focal length of the projection lens is F, the focal length of the front lens group is F1, and the focal length of the rear lens group is F2, satisfying the following conditions: 1<F1 / F2<3; 0.18<F / F1<1.

[0017] The embodiments of the present invention have the following technical effects: 1. By optimizing the lens structure, the number of lenses required is significantly reduced, which not only simplifies the production process but also reduces production costs. In addition, the simple assembly process further improves production efficiency and reduces the input of manpower and time, making the market price of the product more competitive. At the same time, the compact design makes the lens smaller and lighter, which improves the convenience of carrying and meets the user's demand for portable devices.

[0018] 2. By introducing aspherical lenses, the distortion and astigmatism problems in traditional lens design are effectively corrected, and the deviation of the optimal focal plane is reduced. By optimizing the exit pupil position of the lens, aspherical lenses can achieve clearer images when imaging large sizes, significantly improving optical performance. In addition, the use of double-cemented lenses to correct chromatic aberration makes color reproduction more accurate, further improving imaging quality. This improvement ensures high-quality projection effects in various application scenarios, enhancing the user's visual experience and satisfaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 is a structural schematic diagram of a small telephoto projection imaging system provided by an embodiment of the present invention; Figure 2 Schematic diagram of optical distortion of an imaging screen of a small telephoto projection imaging system provided by an embodiment of the present invention; Figure 3 It is a light spot array diagram of a small telephoto projection imaging system under different field of view conditions provided by an embodiment of the present invention; Figure 4 It is a schematic diagram of the aberration values ​​between the three different wavelengths of light provided by an embodiment of the present invention and the main wavelength light on the x-axis and y-axis under normalized fields of view; Figure 5 It is a light modulation transfer function MTF diagram of a small telephoto projection imaging system provided by an embodiment of the present invention; Figure 6 It is an MTF diagram of a small telephoto projection imaging system provided by an embodiment of the present invention at a frequency of 93 Hz and a defocus range of -0.05 to 0.05. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0022] Figure 1 is a structural schematic diagram of a small telephoto projection imaging system provided by an embodiment of the present invention, see Figure 1 A small telephoto projection imaging system in the present invention includes, from the direction of light incidence to the direction of light emission, a light valve, a prism, an image biasing mirror and a projection lens 1; The projection lens 1 is provided with a rear lens group and a front lens group in sequence on the same optical axis from the incident direction of the light to the emitting direction of the light, the rear lens group includes a first lens GM1 with positive focal power, a second lens G2 with positive focal power, and a third lens G3 with negative focal power, and the front lens group includes a fourth lens G4 with positive focal power and a fifth lens P5 with negative focal power; An aperture is provided between the front lens group and the rear lens group; The second lens G2 and the third lens G3 are combined into a doublet lens.

[0023] Furthermore, the light valve is used to provide a high-resolution image beam; the prism is used to increase the brightness and contrast of the image beam; and the image biasing mirror is used to adjust the direction and position of the image.

[0024] Further, the first lens GM1 is a glass aspherical lens, and the Abbe number of the first lens GM1 is in the range of (75, 85); The design of the first lens GM1 aims to improve the performance of the lens in chromatic aberration correction and optical imaging by adopting high-performance aspherical shapes and high-quality high Abbe number materials. This design can ensure clearer and more accurate images in the projection system.

[0025] Furthermore, the second lens G2, the third lens G3 and the fourth lens G4 are all glass spherical lenses.

[0026] Furthermore, the glass spherical lens of the second lens G2 is biconvex, and the glass spherical lens of the third lens G3 is biconcave; the difference in Abbe numbers between the second lens G2 and the third lens G3 is in the range of (40, 50).

[0027] Specifically, the second lens G2 and the third lens G3 form a double-cemented lens. With the bonding of double convex and double concave, this combination can not only control the focusing and divergence of light, but also optimize the overall optical performance. The optical power of the double-cemented lens is negative, which means that it is mainly used to diverge light. The double-cemented lens is matched with the first lens GM1 with positive optical power to reduce the spherical aberration, coma, chromatic aberration and other aberrations of the lens, and achieve the overall optical power balance of the system.

[0028] In some embodiments, when selecting the materials of the second lens G2 and the third lens G3, selecting lenses with a large difference in refractive index and Abbe number can effectively correct chromatic aberration, spherical aberration and balance the system temperature. Chromatic aberration is caused by the different degrees of refraction of light in the lens. A larger difference can better disperse the deflection of light of different wavelengths, which helps to achieve better color reproduction in imaging. Spherical aberration is caused by the different refractive powers of different parts of the lens. Reasonable selection of materials and design of lens shape can effectively control and reduce spherical aberration. Different materials may respond differently to temperature changes. Through reasonable material selection, the impact of temperature changes on imaging performance can be reduced to a certain extent, ensuring that the system can maintain stable optical performance in different working environments.

[0029] Furthermore, the Abbe number of the fourth lens G4 is in the range of (20, 30); the refractive index of the fourth lens G4 is greater than 1.6; and the thickness of the fourth lens G4 is less than 2.2 mm.

[0030] A lower Abel number can effectively control dispersion, reduce chromatic aberration, and ensure that the focusing positions of light of each wavelength are close during imaging, thereby improving the color reproduction effect of the image. A reasonable Abel number helps reduce the impact of temperature changes (temperature drift) on lens performance and improves the stability of the lens. Selecting materials with higher refractive indexes can achieve stronger focusing capabilities with thinner lens designs. The thickness requirement of the fourth lens G4 should be less than 2.2mm. Selecting a thinner design can effectively suppress the low transmittance caused by high refractive index materials, while also reducing the weight and overall volume of the lens to meet the needs of compact design.

[0031] Furthermore, the fifth lens P5 is a plastic aspheric lens; the plastic aspheric lens of the fifth lens P5 is a meniscus lens bent toward the light source; the Abbe number of the fifth lens P5 is greater than 60, and the refractive index of the fifth lens P5 is less than 1.6.

[0032] Specifically, the shape of the fifth lens P5 is a meniscus lens that bends toward the light source. This design shape enables it to effectively diffuse the incident light beam; the lens is located far away from the light valve, usually in a low temperature environment, so a plastic lens is used; since the lens is located at the exit pupil position of the lens, in order to achieve a projection size with a specific magnification ratio, its aperture is designed to be larger, which allows more light to pass through the lens, thereby improving the light convergence ability and imaging brightness; the use of an aspheric surface can effectively correct the distortion and astigmatism in the imaging; in order to control costs, the refractive index of the lens should be selected to be less than 1.6, and in order to effectively correct chromatic aberration, the Abel number should be less than 60.

[0033] Furthermore, the light valve, the prism, the image biasing mirror and the projection lens 1 form a projection system, the length of the lens system is L2, L2<55mm, and the length of the projection lens 1 is L1, L1<40mm; Furthermore, the distance from the light valve to the first lens GM1 is a back working distance BFL, and BFL satisfies the condition: 0.05<BFL / L1<1.

[0034] Furthermore, the total focal length of the projection lens 1 is F, the focal length of the front lens group is F1, and the focal length of the rear lens group is F2, satisfying the following conditions: 1<F1 / F2<3; 0.18<F / F1<1.

[0035] Exemplarily, the aperture diaphragm is controlled at about 4.6 mm; Parameters of the first lens GM1, the second lens G2, the third lens G3, the fourth lens G4 and the fifth lens P5 are shown in Table 1: Table 1 Lens parameters Figure 2 FIG. 1 is a schematic diagram of optical distortion of an imaging screen of a small telephoto projection imaging system provided by an embodiment of the present invention. Figure 2 As shown in the left coordinate system, the horizontal coordinate represents the magnitude of the field curvature, in mm; the vertical coordinate represents the normalized image height, without unit; Figure 2 It can be seen that the black solid line represents the 0 position reference line, the solid line represents the field area data of the projection system provided by this embodiment, and the dotted line represents the theoretical expected field curvature data. The solid line and the dotted line are close, proving that the field curvature in the horizontal direction of the projection system provided by this embodiment is effectively controlled, that is, when imaging, the difference between the image quality in the center and the image quality in the periphery is small; the blue, green, and red lines represent 0.45μm, 0.54μm, and 0.61μm wavelength light, respectively. In the right coordinate system, the horizontal coordinate represents the size of the distortion, in %; the vertical coordinate represents the normalized image height, without units; Figure 2 It can be seen that the imaging distortion of the projection system provided in this embodiment in the horizontal direction is controlled.

[0036] Figure 3 It shows the light spot array of three wavelengths (0.45μm, 0.54μm, 0.61μm) on the imaging screen under different field of view conditions. The figure shows the normalized light spot array under different field of view conditions, which shows the influence of different wavelengths on the imaging effect; 0.45μm light: short wavelength light, small spot, showing higher resolution; 0.54μm light: medium wavelength light, spot size is between short wavelength and long wavelength light; 0.61μm light: long wavelength light, large spot, showing lower resolution.

[0037] Figure 4 It is a rayfan diagram, which shows the aberration values ​​between the three wavelengths of light (0.45um, 0.54um, 0.61um) and the main wavelength light on the x-axis and y-axis respectively under normalized field conditions. The figure contains 10 different groups of charts, each group of charts corresponds to a normalized field condition; the two charts in each field of view are the x-axis and y-axis symmetrical with the optical axis as the center in the projection lens system; the horizontal axis in each chart is the pupil height position under the field of view condition, and the vertical axis is the error between each wavelength of light and the main light.

[0038] Figure 5 The modulation transfer function (mtf) of light with different wavelengths (0.45μm, 0.54μm, 0.61μm) is shown. The vertical coordinate values ​​of the three different wavelengths of light in the figure are all greater than or close to 0.5, and the imaging quality of the system is very clear.

[0039] Figure 6 This is the MTF diagram of the projection system of this embodiment at a frequency of 93Hz. The defocus range in the figure is from -0.05 to 0.05, which indicates the deviation between the focal length of the system and the ideal focal length. Within the defocus range of -0.05 to 0.05, the change in the MTF value can be used to analyze the impact of the focus position on the image quality. Usually, at the best focus position (0 defocus), the MTF value will reach the highest, indicating the best image quality.

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

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

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

Claims

1. A small telephoto projection imaging system, characterized in that: From the direction of light incidence to the direction of light emission, they are: light valve, prism, image biasing mirror and projection lens (1); The projection lens (1) comprises a rear lens group and a front lens group arranged in sequence on the same optical axis from the incident direction of the light to the exit direction of the light, the rear lens group comprising a first lens (GM1) having a positive focal power, a second lens (G2) having a positive focal power, and a third lens (G3) having a negative focal power, and the front lens group comprising a fourth lens (G4) having a positive focal power, and a fifth lens (P5) having a negative focal power; An aperture is provided between the front lens group and the rear lens group; The second lens (G2) and the third lens (G3) are combined into a doublet lens.

2. The small telephoto projection imaging system according to claim 1, characterized in that: The first lens (GM1) is a glass aspheric lens, and the fifth lens (P5) is a plastic aspheric lens; The plastic aspherical lens of the fifth lens (P5) is a meniscus lens that bends toward the light source.

3. The small telephoto projection imaging system according to claim 1, characterized in that: The second lens (G2), the third lens (G3) and the fourth lens (G4) are all glass spherical lenses.

4. The small telephoto projection imaging system according to claim 1, characterized in that: The glass spherical lens of the second lens (G2) is biconvex, and the glass spherical lens of the third lens (G3) is biconcave.

5. The small telephoto projection imaging system according to claim 1, characterized in that: The Abbe number of the first lens (GM1) is in the range of (75, 85).

6. The small telephoto projection imaging system according to claim 1, characterized in that: The difference between the Abbe numbers of the second lens (G2) and the third lens (G3) is in the range of (40, 50).

7. The small telephoto projection imaging system according to claim 1, characterized in that: The Abbe number of the fourth lens (G4) is in the range of (20, 30); the refractive index of the fourth lens (G4) is greater than 1.6; and the thickness of the fourth lens (G4) is less than 2.2 mm.

8. The small telephoto projection imaging system according to claim 1, characterized in that: The Abbe number of the fifth lens (P5) is greater than 60, and the refractive index of the fifth lens (P5) is less than 1.

6.

9. The small telephoto projection imaging system according to claim 1, characterized in that: The light valve, the prism, the image biasing mirror and the projection lens (1) form a projection system, the length of the projection system is L2, L2<55 mm, and the length of the projection lens (1) is L1, L1<40 mm; The distance from the light valve to the first lens (GM1) is a back working distance BFL, and BFL satisfies the condition: 0.05<BFL / L1<1.

10. The small telephoto projection imaging system according to claim 1, characterized in that: The total focal length of the projection lens (1) is F, the focal length of the front lens group is F1, and the focal length of the rear lens group is F2, satisfying the condition: 1<F1 / F2<3; 0.18<F / F1<1.

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