A large-aperture long working distance objective system for micro-projection

Abstract

This invention provides a large-image-area, long-working-distance objective lens system for micro-projection, comprising: a first projection lens, a first lens group (1), a first aperture stop (3), a second lens group (2), a first beam splitter (4), a first protective glass (5), and a first imaging surface (6) arranged sequentially; light emitted from the first projection lens passes through the first lens group (1), the second lens group (2), the first beam splitter (4), the first protective glass (5), and the first imaging surface (6), and forms an image on the first imaging surface (6). This invention, by setting up the lens group and specifying the material and number of lenses, solves the problems of low image quality, imbalance between lens size and mass, and excessive cost caused by projection over long distances.

Description

Technical Field

[0001] This invention relates to the field of projection lens technology, and in particular to a large image plane and long working distance objective lens system for micro-projection. Background Technology

[0002] With the development of technology, projection equipment is being used in more and more fields, including home theater, projection advertising, industrial inspection, and 3D printing. More and more devices need to embed micro-projection systems, and the requirements for projection equipment are also getting higher and higher, such as smaller size, higher image quality, and lower cost.

[0003] To achieve a more immersive viewing experience, a larger projection screen is needed, along with a sufficiently long viewing distance (i.e., the lens projection working distance) to ensure viewing comfort. Current technologies for long-distance projection suffer from problems such as low image quality, an imbalance between lens size and mass, and excessively high costs. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, the purpose of this invention is to provide a large-image-area, long-working-distance objective lens system for micro-projection. This invention employs a lens group and specifies the material and number of lenses, thus solving the problems of low image quality, imbalance between lens size and mass, and excessive cost caused by projection over long distances.

[0005] To achieve the above objectives, the present invention provides the following solution: A large-image-plane, long-working-distance objective lens system for micro-projection includes: The first projection lens, the first lens group (1), the first aperture (3), the second lens group (2), the first beam splitter (4), the first protective glass (5), and the first imaging surface (6) are arranged in sequence. The light emitted by the first projection lens passes through the first lens group (1), the second lens group (2), the first beam splitter (4), the first protective glass (5) and the first imaging surface (6), and forms an image on the first imaging surface (6); The first lens group (1) is placed in front of the first aperture (3); The first lens group (1) consists of a first lens (P1), a second lens (G2), a third lens (G3), a fourth lens (G4), and a fifth lens (G5), wherein the first lens (P1) is a lens with negative optical power, the second lens (G2) is a lens with negative optical power, the third lens (G3) is a lens with negative optical power, the fourth lens (G4) is a lens with positive optical power, and the fifth lens (G5) is a lens with positive optical power. The second lens group (2) is placed behind the first aperture (3); The second lens group (2) consists of a sixth lens (G6), a seventh lens (G7), an eighth lens (G8), a ninth lens (G9), and a tenth lens (GM10). The sixth lens (G6) and the seventh lens (G7) are both cemented lenses with negative optical power, the eighth lens (G8) and the ninth lens (G9) are both cemented lenses with negative optical power, and the tenth lens (GM10) is a lens with positive optical power. The first lens (P1) is a plastic lens; the second lens (G2), the third lens (G3), the fourth lens (G4), the fifth lens (G5), the sixth lens (G6), the seventh lens (G7), the eighth lens (G8), the ninth lens (G9) and the tenth lens (GM10) are all glass lenses; The ratio of the focal length f1 of the first lens group (1) of the objective lens system to the focal length f of the objective lens system is 1.384; the ratio of the focal length f2 of the second lens group (2) of the objective lens system to the focal length f of the objective lens system is 1.417.

[0006] Preferably, both the first lens (P1) and the tenth lens (GM10) are aspherical lenses.

[0007] Preferably, the ratio of the focal length fG6G7 of the sixth lens (G6) and the seventh lens (G7) to the focal length fG8G9 of the eighth lens (G8) and the ninth lens (G9) is 1.056; the ratio of the focal length fP1 of the first lens (P1) to the focal length f of the objective lens system is -1.907; and the ratio of the focal length fGM10 of the tenth lens (GM10) to the focal length f of the objective lens system is 1.148.

[0008] Preferably, the MTF value of the field of view corresponding to the first projection lens is greater than 0.7; the color difference value of the first projection lens is less than 0.4 pixels.

[0009] A large-image-plane, long-working-distance objective lens system for micro-projection includes: The second projection lens, the third lens group (7), the second aperture (9), the fourth lens group (8), the second beam splitter (10), the second protective glass (11), and the second imaging surface (12) are arranged in sequence. The third lens group (7) is positioned in front of the second aperture (9); The light emitted by the second projection lens passes through the third lens group (7), the fourth lens group (8), the second beam splitter (10), the second protective glass (11), and the second imaging surface (12), and forms an image on the second imaging surface (12); The third lens group (7) consists of a first lens (G1'), a second lens (G2'), a third lens (G3'), a fourth lens (G4'), a fifth lens (G5'), and a sixth lens (G6'), wherein the first lens (G1') is a lens with negative optical power, the second lens (G2') is a lens with negative optical power, the third lens (G3') is a lens with negative optical power, the fourth lens (G4') is a lens with positive optical power, the fifth lens (G5') is a lens with positive optical power, and the sixth lens (G6') is a lens with positive optical power. The fourth lens group (8) is positioned behind the second aperture (9); The fourth lens group (8) consists of a seventh lens (G7'), an eighth lens (G8'), a ninth lens (G9'), a tenth lens (G10'), and an eleventh lens (GM11'). The seventh lens (G7') and the eighth lens (G8') are both cemented lenses with negative optical power, the ninth lens (G9') and the tenth lens (G10') are both cemented lenses with negative optical power, and the eleventh lens (GM11') is a lens with positive optical power. The lenses of the third lens group (7) and the lenses of the fourth lens group (8) are both made of glass; The ratio of the focal length f3 of the third lens group (7) of the objective lens system to the focal length f of the objective lens system is 1.239; the ratio of the focal length f4 of the fourth lens group (8) of the objective lens system to the focal length f of the objective lens system is 1.236.

[0010] Preferably, the eleventh lens (GM11') is an aspherical lens.

[0011] Preferably, the ratio of the focal length fG7'G8' of the seventh lens (G7') and the eighth lens (G8') to the focal length fG9'G10' of the ninth lens (G9') and the tenth lens (G10') is 1.560; the ratio of the focal length fGM11' of the eleventh lens (GM11) to the focal length f of the objective lens system is 1.025.

[0012] Preferably, the MTF value of the field of view corresponding to the second projection lens is greater than 0.65; the color difference value of the second projection lens is less than 0.4 pixels.

[0013] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects: This invention provides a large-image-area, long-working-distance objective lens system for micro-projection. By setting a first lens group, a second lens group, a third lens group, and a fourth lens group, and setting the material and number of lenses in each lens group, and determining the focal length ratio between the lenses, the light source emitted by the projection lens at a long distance is projected onto the imaging surface through the lens group to present a high-quality image. This invention also solves the problems of high cost of projection at long distances and the imbalance between the size and weight of the projection lens. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 An image of the objective lens system provided in Embodiment 1 of the present invention; Figure 2 This is a spatial frequency MTF diagram provided in Embodiment 1 of the present invention; Figure 3 This is the vertical axis color difference diagram provided in Embodiment 1 of the present invention; Figure 4 This is a relative illumination diagram provided in Embodiment 1 of the present invention; Figure 5 An image of the objective lens system provided in Embodiment 2 of the present invention; Figure 6 This is a spatial frequency MTF diagram provided in Embodiment 2 of the present invention; Figure 7 This is the vertical axis color difference diagram provided in Embodiment 2 of the present invention; Figure 8 An image of the objective lens system provided in Embodiment 2 of the present invention. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0018] The terms "first," "second," "third," and "fourth," etc., used in the specification, claims, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, including a series of steps, processes, methods, etc., is not limited to the steps listed, but may optionally include steps not listed, or may optionally include other steps inherent to these processes, methods, products, or devices.

[0019] The purpose of this invention is to provide a large-image-size, long-working-distance objective lens system for micro-projection. This invention sets up a lens group and sets the material and number of lenses, which solves the problems of low image quality, unbalanced lens size and mass, and excessive cost caused by projection at long distances.

[0020] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] Example 1: like Figure 1 As shown, this embodiment provides a large image plane and long working distance objective lens system for micro-projection, characterized in that it includes: The first projection lens, the first lens group (1), the first aperture (3), the second lens group (2), the first beam splitter (4), the first protective glass (5) and the first imaging surface (6) are arranged in sequence. The light emitted by the first projection lens passes through the first lens group (1), the second lens group (2), the first beam splitter (4), the first protective glass (5) and the first imaging surface (6), and forms an image on the first imaging surface (6); The first lens group (1) is placed in front of the first aperture (3); The first lens group (1) includes: a first lens (P1), a second lens (G2), a third lens (G3), a fourth lens (G4), and a fifth lens (G5), wherein the first lens (P1) is a lens with negative optical power, the second lens (G2) is a lens with negative optical power, the third lens (G3) is a lens with negative optical power, the fourth lens (G4) is a lens with positive optical power, and the fifth lens (G5) is a lens with positive optical power. The second lens group (2) is placed behind the first aperture (3); The second lens group (2) includes: a sixth lens (G6), a seventh lens (G7), an eighth lens (G8), a ninth lens (G9), and a tenth lens (GM10), wherein the sixth lens (G6) and the seventh lens (G7) are both cemented lenses with negative optical power, the eighth lens (G8) and the ninth lens (G9) are both cemented lenses with negative optical power, and the tenth lens (GM10) is a lens with positive optical power. It is matched to a display chip with a maximum image circle of 7.5 mm (i.e., 0.6 inches). Further, the first lens (P1) and the tenth lens (GM10) are both aspherical lenses. Further, the first lens (P1) is a plastic lens; the second lens (G2), the third lens (G3), the fourth lens (G4), the fifth lens (G5), the sixth lens (G6), the seventh lens (G7), the eighth lens (G8), the ninth lens (G9), and the tenth lens (GM10) are all glass lenses. Furthermore, the ratio of the focal length f1 of the first lens group (1) of the objective lens system to the focal length f of the objective lens system is 1.384; the ratio of the focal length f2 of the second lens group (2) of the objective lens system to the focal length f of the objective lens system is 1.417; the ratio of the focal length fG6G7 of the sixth lens (G6) and the seventh lens (G7) to the focal length fG8G9 of the eighth lens (G8) and the ninth lens (G9) is 1.056; the ratio of the focal length fP1 of the first lens (P1) to the focal length f of the objective lens system is -1.907; the ratio of the focal length fGM10 of the tenth lens (GM10) to the focal length f of the objective lens system is 1.148. The focal length of the objective lens system is the focal length of all optical lenses in the lens group, that is, the focal length of the entire system. Table 1 is a table of specific parameters of the objective lens system, as shown in Table 1.

[0022] Table 1. Specific parameters of the objective lens system

[0023] Table 2 shows the coefficients of each order of the aspherical lens P1\GM10. The coefficients of each order of the aspherical lens P1\GM10 are shown below.

[0024] Table 2. Coefficients of Aspherical Lenses Furthermore, the MTF value of the field of view corresponding to the first projection lens is greater than 0.7; the chromatic aberration value of the first projection lens is less than 0.4 pixels. Figure 2 As shown, MTF (Modulation Transfer Function) is currently the most accurate and scientific evaluation standard for lenses. The vertical axis represents contrast ratio; the closer to 1, the better the lens image quality. The horizontal axis represents resolution, measured in line pairs per millimeter. The image source pixel size used in this embodiment is 7.637 μm, corresponding to a design resolution of 65 line pairs per millimeter. Projection lenses generally require an MTF value of at least 0.3 for each field of view at the design resolution, while the MTF values ​​for each field of view in this embodiment are all above 0.7, exhibiting excellent image quality. Figure 3 The diagram shows the transverse chromatic aberration of the lens. The vertical axis represents the image height field of view value, and the horizontal axis represents the numerical value, in micrometers. The diagram plots the chromatic aberration values ​​for each field of view between blue, red, and green light (dominant wavelengths) based on the dominant wavelength. Projection lenses generally require the chromatic aberration value to be within one pixel size. In this embodiment, the transverse chromatic aberration is controlled within 2.8 μm, which is less than 0.4 pixels (pixel size 7.637 μm). Figure 4 As shown, relative illuminance refers to the ratio of illuminance at different coordinate points on the image plane to the illuminance at the center point. The vertical axis represents the normalized illuminance value, and the horizontal axis represents the field of view angle of the lens. Under the same conditions, a smooth transition of the relative illuminance curves for each field of view indicates uniform illuminance within the projection frame, and the closer the relative illuminance value for each field of view is to 1, the higher the final projection brightness.

[0025] Example 2: like Figure 5 As shown, this embodiment also provides a large image plane and long working distance objective lens system for micro-projection, including: The second projection lens, the third lens group (7), the second aperture (9), the fourth lens group (8), the second beam splitter (10), the second protective glass (11), and the second imaging surface (12) are arranged in sequence. The third lens group (7) is placed in front of the second aperture (9); The light emitted by the second projection lens passes through the third lens group (7), the fourth lens group (8), the second beam splitter (10), the second protective glass (11), and the second imaging surface (12), and forms an image on the second first imaging surface (6) 12; The third lens group (7) includes: a first lens (G1'), a second lens (G2'), a third lens (G3'), a fourth lens (G4'), a fifth lens (G5'), and a sixth lens (G6'), wherein the first lens (G1') is a lens with negative optical power, the second lens (G2') is a lens with negative optical power, the third lens (G3') is a lens with negative optical power, the fourth lens (G4') is a lens with positive optical power, the fifth lens (G5') is a lens with positive optical power, and the sixth lens (G6') is a lens with positive optical power. The fourth lens group (8) is positioned behind the second aperture (9); The fourth lens group (8) includes: a seventh lens (G7'), an eighth lens (G8'), a ninth lens (G9'), a tenth lens (G10'), and an eleventh lens (GM11'). The seventh lens (G7') and the eighth lens (G8') are both cemented lenses with negative optical power, the ninth lens (G9') and the tenth lens (G10') are both cemented lenses with negative optical power, and the eleventh lens (GM11') is a lens with positive optical power. Furthermore, the lenses of the third lens group (7) and the fourth lens group (8) are both made of glass. Furthermore, the eleventh lens (GM11') is an aspherical lens. Furthermore, the ratio of the focal length f3 of the third lens group (7) of the objective lens system to the focal length f of the objective lens system is 1.239; the ratio of the focal length f4 of the fourth lens group (8) of the objective lens system to the focal length f of the objective lens system is 1.236; the ratio of the focal length fG7'G8' of the seventh lens (G7') and the eighth lens (G8') to the focal length fG9'G10' of the ninth lens (G9') and the tenth lens (G10') is 1.560; the ratio of the focal length fGM11' of the (GM11) lens to the focal length f of the objective lens system is 1.025. Table 3 is a table of specific parameters of the objective lens system in the embodiment. The specific parameters of the objective lens system are as follows: Table 3 Specific parameters of the objective lens system

[0026] Table 4 shows the coefficients of each order for aspherical lenses P1 and GM10. The coefficients of each order for aspherical lenses P1 and GM10 are shown below: Table 4. Coefficients of each order for aspherical lenses P1 and GM10 Furthermore, the MTF value of the projection lens corresponding to the field of view is greater than 0.65; the chromatic aberration value of the second projection lens is less than 0.4 pixels. For example... Figure 6As shown, MTF (Modulation Transfer Function) is currently the most accurate and scientific evaluation standard for lenses. The vertical axis represents contrast ratio; the closer to 1, the better the lens image quality. The horizontal axis represents resolution, measured in line pairs per millimeter. The image source pixel size used in this embodiment is 7.637 μm, corresponding to a design resolution of 65 line pairs per millimeter. Projection lenses generally require an MTF value of at least 0.3 for each field of view at the design resolution, while the MTF values ​​for each field of view in this embodiment are all above 0.65, exhibiting excellent image quality. Figure 7 The diagram shows the transverse chromatic aberration of the lens. The vertical axis represents the image height field of view value, and the horizontal axis represents the numerical value, in micrometers. The diagram plots the chromatic aberration values ​​for each field of view between blue, red, and green light (dominant wavelengths) based on the dominant wavelength. Projection lenses generally require the chromatic aberration value to be within one pixel size. In this embodiment, the transverse chromatic aberration is controlled within the Airy disk size, less than 0.4 pixels (pixel size 7.637 μm). Figure 8 As shown, relative illuminance refers to the ratio of illuminance at different coordinate points on the image plane to the illuminance at the center point. The vertical axis represents the normalized illuminance value, and the horizontal axis represents the field of view angle of the lens. Under the same conditions, a smooth transition of the relative illuminance curves for each field of view indicates uniform illuminance within the projection frame, and the closer the relative illuminance value for each field of view is to 1, the higher the final projection brightness. From the two examples above, it can be seen that when the working distance is set to 20000mm, the lens exhibits very good MTF (modulation transfer function) at low, medium, and high frequencies, indicating that it possesses high resolution.

[0027] The above two embodiments also specifically disclose: The ratio of the combined focal length of the first lens group (1) to the combined optical power of the second lens group (2) is close to 1:1. The ratio of the combined focal length of the third lens group (7) to the combined optical power of the fourth lens group (8) is close to 1:1. The optical power ratio of the first aperture (3) is symmetrical and balanced.

[0028] The second lens group (2) and the fourth lens group (8) are located behind the first aperture stop (3). The two cemented lenses in the two example schemes have similar focal lengths, and the curvature directions of each lens surface are completely consistent. A triangular region can be drawn by connecting the points where the refractive index and Abbe number of each lens are distributed. This optical structure can significantly reduce second-order spectral chromatic aberration. The sequential arrangement and approximate optical power greatly reduce the introduction of spherical aberration and field curvature into the optical surfaces of the lens, thereby obtaining a low Seidel coefficient. The optical lens satisfies the following condition: The focal length of the first cemented lens / the focal length of the second cemented lens ≈ 1 (1) In this case, the sum of the refractive indices of the two glass materials in the first cemented lens is approximately equal to the sum of the refractive indices of the two glass materials in the er-th cemented lens. Optical lenses must meet the following conditions: The first cemented lens has its first surface bent away from the first aperture (3), its second surface bent towards the first aperture (3), and its third surface bent towards the first aperture (3); the second cemented lens has its first surface bent away from the first aperture (3), its second surface bent towards the first aperture (3), and its third surface bent away from the first aperture (3).

[0029] Optical lenses satisfy the following condition: Focal length of the first lens group (1) / Focal length of the second lens group (2) ≈ 1 (2) When condition (2) is satisfied, on-axis and off-axis aberrations of the system can be greatly controlled, reducing the difficulty of distortion correction. Optical lenses satisfy the following condition: CRA<2° (3) Wherein, CRA represents the principal ray incident angle of the optical lens on the first imaging plane (6). When condition (3) is satisfied, it can be well matched with the DMD chip, achieving a good projection effect. The beneficial effects of the present invention are as follows: (1) It solves the shortcomings of insufficient image quality and insufficient depth of focus of long-distance projection objects.

[0030] (2) It solves the problem of excessively high cost of long-distance projection objects. The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0031] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A large image plane, long working distance objective lens system for micro-projection, characterized in that, include: The first projection lens, the first lens group (1), the first aperture (3), the second lens group (2), the first beam splitter (4), the first protective glass (5), and the first imaging surface (6) are arranged in sequence. The light emitted by the first projection lens passes through the first lens group (1), the second lens group (2), the first beam splitter (4), the first protective glass (5) and the first imaging surface (6), and forms an image on the first imaging surface (6); The first lens group (1) is placed in front of the first aperture (3); The first lens group (1) consists of a first lens (P1), a second lens (G2), a third lens (G3), a fourth lens (G4), and a fifth lens (G5), wherein the first lens (P1) is a lens with negative optical power, the second lens (G2) is a lens with negative optical power, the third lens (G3) is a lens with negative optical power, the fourth lens (G4) is a lens with positive optical power, and the fifth lens (G5) is a lens with positive optical power. The second lens group (2) is placed behind the first aperture (3); The second lens group (2) consists of a sixth lens (G6), a seventh lens (G7), an eighth lens (G8), a ninth lens (G9), and a tenth lens (GM10). The sixth lens (G6) and the seventh lens (G7) are both cemented lenses with negative optical power, the eighth lens (G8) and the ninth lens (G9) are both cemented lenses with negative optical power, and the tenth lens (GM10) is a lens with positive optical power. The first lens (P1) is a plastic lens; the second lens (G2), the third lens (G3), the fourth lens (G4), the fifth lens (G5), the sixth lens (G6), the seventh lens (G7), the eighth lens (G8), the ninth lens (G9) and the tenth lens (GM10) are all glass lenses; The ratio of the focal length f1 of the first lens group (1) of the objective lens system to the focal length f of the objective lens system is 1.384; the ratio of the focal length f2 of the second lens group (2) of the objective lens system to the focal length f of the objective lens system is 1.

417.

2. The large image plane and long working distance objective lens system for micro-projection according to claim 1, characterized in that, Both the first lens (P1) and the tenth lens (GM10) are aspherical lenses.

3. The large image plane and long working distance objective lens system for micro-projection according to claim 1, characterized in that, The ratio of the focal length fG6G7 of the sixth lens (G6) and the seventh lens (G7) to the focal length fG8G9 of the eighth lens (G8) and the ninth lens (G9) is 1.056; the ratio of the focal length fP1 of the first lens (P1) to the focal length f of the objective lens system is -1.907; and the ratio of the focal length fGM10 of the tenth lens (GM10) to the focal length f of the objective lens system is 1.

148.

4. The large image plane and long working distance objective lens system for micro-projection according to claim 1, characterized in that, The MTF value of the field of view corresponding to the first projection lens is greater than 0.7; the color difference value of the first projection lens is less than 0.4 pixels.

5. A large image plane, long working distance objective lens system for micro-projection, characterized in that, include: The second projection lens, the third lens group (7), the second aperture (9), the fourth lens group (8), the second beam splitter (10), the second protective glass (11), and the second imaging surface (12) are arranged in sequence. The third lens group (7) is positioned in front of the second aperture (9); The light emitted by the second projection lens passes through the third lens group (7), the fourth lens group (8), the second beam splitter (10), the second protective glass (11), and the second imaging surface (12), and forms an image on the second imaging surface (12); The third lens group (7) consists of a first lens (G1'), a second lens (G2'), a third lens (G3'), a fourth lens (G4'), a fifth lens (G5'), and a sixth lens (G6'), wherein the first lens (G1') is a lens with negative optical power, the second lens (G2') is a lens with negative optical power, the third lens (G3') is a lens with negative optical power, the fourth lens (G4') is a lens with positive optical power, the fifth lens (G5') is a lens with positive optical power, and the sixth lens (G6') is a lens with positive optical power. The fourth lens group (8) is positioned behind the second aperture (9); The fourth lens group (8) consists of a seventh lens (G7'), an eighth lens (G8'), a ninth lens (G9'), a tenth lens (G10'), and an eleventh lens (GM11'). The seventh lens (G7') and the eighth lens (G8') are both cemented lenses with negative optical power, the ninth lens (G9') and the tenth lens (G10') are both cemented lenses with negative optical power, and the eleventh lens (GM11') is a lens with positive optical power. The lenses of the third lens group (7) and the lenses of the fourth lens group (8) are both made of glass; The ratio of the focal length f3 of the third lens group (7) of the objective lens system to the focal length f of the objective lens system is 1.239; the ratio of the focal length f4 of the fourth lens group (8) of the objective lens system to the focal length f of the objective lens system is 1.

236.

6. A large image plane, long working distance objective lens system for micro-projection according to claim 5, characterized in that, The eleventh lens (GM11') is an aspherical lens.

7. A large image plane, long working distance objective lens system for micro-projection according to claim 5, characterized in that, The ratio of the focal length fG7'G8' of the seventh lens (G7') and the eighth lens (G8') to the focal length fG9'G10' of the ninth lens (G9') and the tenth lens (G10') is 1.560; the ratio of the focal length fGM11' of the eleventh lens (GM11') to the focal length f of the objective lens system is 1.

025.

8. A large image plane, long working distance objective lens system for micro-projection according to claim 5, characterized in that, The MTF value of the field of view corresponding to the second projection lens is greater than 0.65; the color difference value of the second projection lens is less than 0.4 pixels.

Images