Lens system and projection device

Abstract

The lens system comprises a first lens group, a diaphragm, a second lens group, a Fresnel lens and a modulation device which are sequentially arranged along the optical axis from the image side to the object side, the first lens group comprises a first lens and a second lens, the focal power of the first lens is negative and used for diverging light, the focal power of the second lens is positive and used for diverging light, and the focal power of the second lens is negative and used for diverging light. The lens is used for converging light; the second lens group comprises a third lens and a fourth lens, the third lens has positive focal power and is used for converging light, and the fourth lens has negative focal power and is used for diverging light; the diaphragm is arranged between the second lens and the third lens; the Fresnel surface of the Fresnel lens is close to the object side direction. The diffraction loss of incident light can be reduced, and the light line transmittance and the imaging contrast ratio can be improved. The lens system provided by the invention is beneficial to improving the distortion of the lens system and improving the edge imaging quality.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical technology, in particular to a lens system and a projection device. BACKGROUND

[0002] The starry sky atmosphere lamp device on the market uses LED lamp beads as a light source, and a film with a starry sky pattern is close to the light source. After the light passes through the film, it is enlarged by a convex lens and projected, so as to form a static or slowly rotating starry sky image on a wall or a ceiling, presenting a soft starry sky effect to improve the environment atmosphere of a family or a gathering.

[0003] The existing starry sky atmosphere lamp device usually needs a certain projection distance to achieve the projection area required by the user. For a space-limited environment, the existing starry sky atmosphere lamp device will affect the visual effect. For example, when the user needs to enlarge the starry sky image, the device needs to be moved away from the projection surface. However, when the distance exceeds a certain distance, such as 1.5 meters, the starry sky image will be distorted and blurred due to light diffusion. When the user wants to reduce the pattern, the device needs to be moved close to the projection surface. At this time, the starry sky image is too small, and the atmosphere is poor. Therefore, there is an urgent need for a new lens system and a projection device. SUMMARY

[0004] The lens system provided by the embodiments of the present application can have an optical axis. In the direction from the image side to the object side along the optical axis, the lens system can include a first lens group, a diaphragm, a second lens group, and a Fresnel lens arranged in sequence. The first lens group can include a first lens and a second lens. The focal power of the first lens can be negative, used for diverging light. The focal power of the second lens can be positive, used for converging light. The second lens group can include a third lens and a fourth lens. The focal power of the third lens can be positive, used for converging light. The focal power of the fourth lens can be negative, used for diverging light. The diaphragm can be arranged between the second lens and the third lens. The Fresnel surface of the Fresnel lens is close to the object side.

[0005] Further, the focal power range of the first lens group is -0.004 < φ1 < -0.003; and / or the focal power range of the second lens group is 0.0255 < φ2 < 0.0355; and / or the focal power range of the Fresnel lens is 0.0245 < φ3 < 0.0345.

[0006] Further, the object side surface of the first lens is a concave surface, the object side surface of the second lens is a spherical surface, the image side surface of the third lens is a spherical surface, and the image side surface of the fourth lens is a concave surface.

[0007] Furthermore, the equivalent focal length f of the lens system is in the range of 21.375mm≤f≤23.625mm, the diagonal field of view of the lens system is ≥ 95°, and the lens system also includes a modulation device, the thickness of the object side of the modulation device to the image side of the first lens group is ≤ 65mm.

[0008] Furthermore, the distance L1 between the image side of the first lens group and the object side of the second lens group is 29.60 mm, and the distance L2 between the aperture stop and the object side of the fourth lens is 13.92 mm.

[0009] Furthermore, the distance L3 between the object side of the fourth lens and the image side of the Fresnel lens is 20.816 mm to 21.571 mm, and the distance L4 between the image side of the first lens and the object side of the fourth lens is 29.02 mm.

[0010] Furthermore, the modulation device is located on the object side of the Fresnel lens, and the distance L5 between the Fresnel surface of the Fresnel lens and the modulation device is 8.91mm to 9.51mm.

[0011] Furthermore, the diameter Φ1 of the first lens group is 36.54 mm; and / or the diameter Φ2 of the first lens is 31.50 mm; and / or the diameter Φ3 of the fourth lens is 27.00 mm.

[0012] Furthermore, the lens system is designed with the image side telecentric.

[0013] This application also provides a projection device, including the lens system described in any of the above embodiments.

[0014] The lens system provided in this application, along the optical axis from the image side to the object side, includes a first lens group, an aperture stop, a second lens group, and a Fresnel lens arranged sequentially. The first lens group includes a first lens and a second lens. The first lens has a negative optical power and is used to diverge light, while the second lens has a positive optical power and is used to converge light. The second lens group includes a third lens and a fourth lens. The third lens has a positive optical power and is used to converge light, while the fourth lens has a negative optical power and is used to diverge light. The aperture stop is located between the second and third lenses. The Fresnel surface of the Fresnel lens is closer to the object side. The Fresnel lens can reduce diffraction loss of incident light, improve light transmittance and imaging contrast. The lens system can effectively shorten the optical path length, and with fewer lenses, it can reduce the overall size and weight of the lens system. The negative-positive-positive-negative optical power symmetrical structure of the second and first lens groups, and the aperture stop located between the second and third lenses, are beneficial for correcting distortion. The lens system provided in this application is beneficial for improving lens system distortion and enhancing edge imaging quality. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 A schematic diagram of one structure of the lens system of this application is shown;

[0017] Figure 2 Another schematic diagram of the lens system of this application is shown;

[0018] Figure 3 Another structural schematic diagram of the lens system of this application is shown.

[0019] Figure 4 A schematic diagram of the optical path of the lens system of this application is shown;

[0020] Figure 5 This paper shows a point diagram illustrating the RMS spot size distribution under the sampling field of view of the lens system of this application;

[0021] Figure 6 The field curvature and distortion curves of the lens system of this application are shown.

[0022] Figure Labels

[0023] 100. Lens system;

[0024] 110. First lens group; 111. First lens; 112. Second lens;

[0025] 120. Aperture;

[0026] 130. Second lens group; 131. Third lens; 132. Fourth lens;

[0027] 140. Fresnel lens;

[0028] 150. Modulation device;

[0029] O, optical axis; A, image side; B, object side;

[0030] φ1, the optical power of the first lens group;

[0031] φ2, the optical power of the second lens group;

[0032] φ3, the optical power of the Fresnel lens;

[0033] L1 is the distance between the image-side surface of the first lens group and the object-side surface of the second lens group.

[0034] L2, the distance between the aperture stop and the side surface of the fourth lens;

[0035] L3, the distance between the object side of the fourth lens and the image side of the Fresnel lens;

[0036] L4, the distance between the image-side surface of the first lens and the object-side surface of the fourth lens;

[0037] L5, the distance between the Fresnel surface of the Fresnel lens and the modulation device;

[0038] Φ1, the diameter of the first lens group;

[0039] Φ2, the diameter of the first lens;

[0040] Φ3, the diameter of the fourth lens. Detailed Implementation

[0041] To make the above-described objects, features, and advantages of this disclosure more apparent and understandable, specific embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a full understanding of this disclosure. However, this disclosure can be implemented in many other alternative ways different from those described herein, and those skilled in the art can make similar modifications to achieve the same or similar functional effects without departing from the spirit of this disclosure. Therefore, this disclosure is not limited to the specific embodiments disclosed below.

[0042] In the description of this disclosure, it should be understood that if terms such as “center,” “longitudinal,” “transverse,” “length,” “width,” “thickness,” “upper,” “lower,” “front,” “rear,” “left,” “right,” “vertical,” “horizontal,” “top,” “bottom,” “inner,” “outer,” “clockwise,” “counterclockwise,” “axial,” “radial,” “circumferential,” and “oblique” appear, the orientation or positional relationship indicated by these terms can be understood based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this disclosure and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this disclosure.

[0043] Furthermore, where the terms "first" and "second" appear, these terms are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this disclosure, where the term "multiple" appears, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0044] Furthermore, unless explicitly specified and limited, the descriptive terms indicating actions such as "installation," "connection," "linking," "fixing," "fitting," "setting," and "positioning" used in this disclosure should be interpreted broadly in conjunction with the inventive concept of this disclosure. For example, they should at least be understood as implementation methods such as direct implementation, indirect implementation, fixed implementation, and movable implementation. Taking "connection" as an example, it can be understood as a direct connection and an indirect connection, such as through a third-party component, as well as a fixed connection and a movable connection. A movable connection can be, for example, a hinge. Similarly, "fixing" can be understood at least as two methods: non-removable fixing and detachable fixing.

[0045] Please refer to the reference. Figure 1 and Figure 4 The lens system 100 provided in this application may have an optical axis O. Along the optical axis O from the image side A to the object side B, the lens system 100 may include a first lens group 110, an aperture stop 120, a second lens group 130, and a Fresnel lens 140 arranged sequentially. The image side A refers to the side closer to the projection surface, i.e., the side where the image is formed, and the object side B refers to the side where the original object to be imaged is located, which is the starting side where light enters the optical system. Since the light emitted by the light source is divergent, if this divergent light is not controlled by the lens, it will cause image distortion in the subsequent imaging process, making it difficult to form a clear image.

[0046] The lens system 100 also includes a modulation device 150. As light passes through the lens system 100, it first passes through the modulation device 150, which filters and controls the light, converting it into a light signal carrying image information. Specifically, the modulation device 150 can be a thin-film transistor liquid crystal display panel (TFT-LCD panel). The thin-film transistor array of the modulation device 150 is equivalent to equipping each pixel with a dedicated switch, independently controlling the deflection angle of the liquid crystal molecules, thereby adjusting the light transmittance of that pixel. Through pixel-level precise light control, the modulation device 150 converts white light into color image light. The light then passes sequentially through the second lens group 130, the aperture 120, and the first lens group 110 to form an image.

[0047] The first lens group 110 may include a first lens 111 and a second lens 112. The object-side B-plane of the first lens 111 may be concave, and the overall optical power may be negative, used to diverge light rays. The object-side B-plane of the second lens 112 may be spherical, and the overall optical power may be positive, used to converge light rays. The second lens group 130 may include a third lens 131 and a fourth lens 132. The image-side A-plane of the third lens 131 may be spherical, and the overall optical power may be positive, used to converge light rays. The image-side A-plane of the fourth lens 132 may be concave, and the overall optical power may be negative, used to diverge light rays. An aperture stop 120 is disposed between the second lens 112 and the third lens 131. The Fresnel surface of the Fresnel lens 140 is closer to the object-side B direction.

[0048] The modulation device 150 is a surface light source. Surface light sources emit light in all directions, which can lead to excessively large light angles, wasted edge light, and difficulty in light entering the lens of the lens system. The Fresnel lens 140, however, compresses its refractive surface onto a thin, serrated surface. This allows it to organize and initially converge the light emitted from the modulation device 150, gathering and controlling some edge-oriented, high-angle light rays within the usable beam range. It adjusts and directs the light angle, improving light efficiency and reducing light loss. The Fresnel lens 40 can also reduce the focal length, enabling the lens system 100 to achieve ultra-short throw (UST), allowing light to diffuse into a large image without long-distance projection.

[0049] Furthermore, the overall thinness of the Fresnel lens 140 can significantly reduce the thickness of the lens system 100 and its weight, making the lens system 100 thinner and lighter, and allowing users to use the device with the lens system 100 provided in this application to be more portable.

[0050] After passing through Fresnel lens 140, the light rays are emitted to fourth lens 132. Fourth lens 132 disperses the light rays and readjusts the direction of light rays that still have a certain angular error after being converged by Fresnel lens 140. Thus, after the light rays enter third lens 131, third lens 131 can more uniformly and effectively converge the light rays and correct aberrations. Aperture stop 120 is used to constrain the angle of the transmitted light rays and control the effective aperture of lens system 100. It can eliminate high-angle stray light and edge beams that deviate from the optical axis O, thereby helping to correct the distortion problem at the edge of the final image pattern and making the light brightness at the edge of the pattern more uniform. The light rays pass through aperture stop 120 to second lens 112. Second lens 112 further precisely controls the direction of the light rays and optimizes the distribution of the light rays, making the light rays converge more consistently. The light rays then pass through first lens 111 for aberration optimization and field-of-view unification processing, thereby improving the overall sharpness and image quality of the light rays output from image side A.

[0051] The fourth lens 132 has a negative optical power, the third lens 131 has a positive optical power, the second lens 112 has a positive optical power, and the first lens 111 has a negative optical power. This negative-positive-positive-negative optical power symmetrical structure is beneficial for correcting distortion and makes the correction degrees of freedom of the lens system 100 more balanced. After the light rays are converged by the Fresnel lens 140, they are diverged by the fourth lens 132, then converged again by the third lens 131 and the second lens 112, and finally diverged by the first lens 111. The light rays are projected after passing through the Fresnel lens 140, the negative optical power lens, the two positive optical power lenses, and the negative optical power lens in sequence, which helps to improve the distortion of the ultra-short focal length lens system 100 and improve the quality of edge imaging.

[0052] In an optional embodiment, the lens system 100 is designed to be image-side telecentric, with the exit pupil of the lens system located at image-side infinity. The principal rays of each field of view are approximately parallel to the optical axis in image-side space and incident on the projection surface in an approximately normal direction. The image-side telecentric design can make the brightness of the projected image and the overall light better consistent and the color difference smaller, which can improve the edge illumination uniformity and geometric accuracy of the projected image of the projection device using the lens system 100 of this application.

[0053] In an optional embodiment, the optical power range of the first lens group 110 is -0.004 < φ1 < -0.003; and / or the optical power range of the second lens group 130 is 0.0255 < φ2 < 0.0355; and / or the optical power range of the Fresnel lens 140 is 0.0245 < φ < 0.0345. A lens optical power φ greater than 0 is positive, and a lens with positive optical power can converge light, while a lens optical power φ less than 0 is negative, and a lens with negative optical power can diverge light. The optical powers of the first lens 111 and the second lens 112 are negative and positive, respectively, but the optical power of the first lens group 110 formed by their combination is negative. That is to say, the first lens group 110 as a whole acts to diverge light, projecting the image over a shorter distance and correcting edge distortion of the image. The optical powers of the third lens 131 and the fourth lens 132 are positive and negative, respectively, but the optical power of the second lens group 130 formed by their combination is positive. This means that the second lens group 130 as a whole acts as a converging agent for light. The Fresnel lens 140 also has a positive optical power and acts as a converging agent for light. Please refer to the reference section. Figure 5 and Figure 6The RMS across the entire field of view is ≤ 0.085 mm, and it does not change much with the field of view, resulting in relatively uniform image quality. After light passes through the lens system 100 provided in this application, the optical distortion is less than 2%, and the geometric distortion within the field of view is controlled within 2%, thereby ensuring that the projected image will not exhibit obvious barrel or pincushion distortion, and the TV distortion is less than 1%. The geometric errors of the image in the horizontal and vertical directions are strictly suppressed, which is beneficial to improving the geometric fidelity and visual experience of the projected image.

[0054] In an optional embodiment, the equivalent focal length f of the lens system 100 ranges from 21.375mm to 23.625mm. If the focal length is too short, the tilt angle of the edge rays will increase, making vignetting and distortion more difficult to control, and edge aberrations will be more prone to instability; if the focal length is too long, the image size will be smaller, making it difficult to meet the requirements of ultra-short-throw projection. Therefore, the lens system 100 with an equivalent focal length f in the range of 21.375mm to 23.625mm can achieve a good balance between short-throw projection and image clarity. Under ultra-short-throw projection conditions, the lens system 100 can cover a large field of view while controlling image aberrations and distortions, thereby obtaining better clarity and optical performance.

[0055] Optionally, the lens system 100, with a diagonal field of view (FOV) ≥ 95°, can effectively cover the maximum beam angle range within the image-side A space, enabling the acquisition of a large-size projected image at a shorter projection distance. The lens system 100 provided in this application can be used in projection devices to achieve ultra-short-throw projection. The lens system 100 also includes a mechanical support and a focusing structure. The mechanical support supports and positions the first lens group 110, the aperture 120, the second lens group 130, and the Fresnel lens 140. The focusing structure can adjust the distance between the lenses. The projection distance of the lens system 100 can be adjusted within the range of 0.9m to 3m, and the throw ratio can be 0.46. This results in a smaller projection distance required for the same image width, making it more suitable for use in space-constrained scenarios. The thickness from the object-side B surface of the modulation device 150 to the image-side A surface of the first lens group 110 is ≤ 65mm. The lens system 100 provided in this application has a more compact and integrated structure.

[0056] In an optional embodiment, the maximum imaging circle diameter of the lens system 100 is 53mm. Under conditions of wide field of view and ultra-short focal length, the lens system 100 can achieve complete and low-distortion imaging within an imaging circle with a diameter of 53mm. The images of the modulation device 150 within the entire effective image plane can be completely and accurately transmitted to the image side A without any adverse phenomena such as image cropping, edge vignetting, or information loss.

[0057] Please refer to the reference. Figure 2Optionally, the distance L1 between the image-side A surface of the first lens group 110 and the object-side B surface of the second lens group 130 is 29.60 mm, and the distance L2 between the aperture stop 120 and the object-side B surface of the fourth lens 132 is 13.92 mm. The distance L3 between the object-side B surface of the fourth lens 132 and the image-side A surface of the Fresnel lens 140 is 20.82 mm, and the distance L4 between the image-side A surface of the first lens 111 and the object-side B surface of the fourth lens 132 is 29.02 mm. The lens system 100 has a compact overall structure and small size.

[0058] Optionally, the lens system 100 also includes a modulation device 150, wherein the distance L5 between the Fresnel surface of the Fresnel lens 140 and the modulation device 150 is 8.91 mm to 9.51 mm.

[0059] Optionally, the diameter Φ1 of the first lens group 110 is 36.54 mm, and / or the diameter Φ2 of the first lens 111 is 31.50 mm; and / or the diameter Φ3 of the fourth lens 132 is 27.00 mm. By limiting the diameter of the lens system 100, sufficient effective light-passing aperture can be provided under large field of view conditions, reducing vignetting caused by lens edge occlusion, thereby improving the uniformity of image edge illumination.

[0060] Optionally, the first lens group 110, the second lens group 130, and the Fresnel lens 140 are all plastic lenses. Plastic lenses can effectively reduce the cost and size of the lens system 100, facilitating its integration and further reducing the overall size of the projection device. Specifically, injection molding can be used for mass production, thereby enhancing the advantages of this application in terms of cost, weight, and integration. Furthermore, plastic materials are easier to use to achieve complex surface shapes such as aspherical surfaces, better meeting aberration correction requirements, reducing manufacturing costs, and improving assembly efficiency.

[0061] Compared with existing starry sky ambient lights, this application, through the combined design of the first lens group 110, aperture 120, second lens group 130, and Fresnel lens 140, with the optical power of the first lens 111, second lens 112, third lens 131, and fourth lens 132 being negative, positive, positive, and negative respectively, can achieve a large field of view and low geometric distortion with ultra-short focal length. At the same time, by using image-side telecenty, the angle of the emitted beam is kept consistent, thereby improving the brightness uniformity and geometric accuracy of the projected image.

[0062] Please refer to the reference. Figure 3 Table 1 lists the lens design parameters of the lens system 100. Figure 3 The numbers in the table indicate the surface shape, radius of curvature, thickness, refractive index, and Abbe number of the object-side B-plane and image-side A-plane of the lens, as detailed in Table 1. Number 0 indicates the projection reference plane.

[0063] Serial number Surface type Curvature radius Thickness Refractive index Abbe number 0 Spherical Infinite T / / 1 Aspherical 298.40 1.5 1.531 56 2 Aspherical 10.449 2.58 / / 3 Aspherical 14.083 4.55 1.492 57.5 4 Spherical 138.35 6.46 / / Stop Spherical Infinite 4.36 / / 5 Spherical 107.49 7.95 1.492 57.5 6 Aspherical -7.040 0.10 / / 7 Aspherical -7.524 1.5 1.531 56 8 Aspherical -17.19 L3 / / 9 Spherical Infinite 1.6 1.492 57.5 10 Fresnel surface -16.63 L5 / / 11 Spherical Infinite 0.7 1.52 62.3 12 Spherical Infinite 0 / /

[0064] In Table 1, the surfaces that constitute aspherical and Fresnel surfaces satisfy the following equations: Where c is the reciprocal of the radius of curvature R, r is the radial distance to a point on the surface, k is the quadratic surface constant, and Ai is the coefficient of higher-order terms. Aspherical surfaces can be optimized using conic constants and higher-order coefficients to reduce aberrations such as spherical aberration and improve edge image quality. The lens system provided in this application sets the lens as an aspherical surface, which can improve the texture of the image while maintaining low distortion.

[0065] The lens system 100, when used in a projection device, can be adjusted within a projection distance T of 0.9m to 3m. The projection ratio of the projection device is 0.46, calculated as projection distance T / screen width W, with W ranging from 1.96m to 6.52m. The lens system 100 provided in this application enables ultra-short throw projection, allowing users to project a large screen even in small rooms. The short light propagation path and minimal light loss of the ultra-short throw projection device alleviate the limitations of long-throw projection devices that require light shielding. The lens system 100 provided in this application offers greater flexibility in application scenarios and a wider range of uses, allowing users to enjoy a large-screen viewing experience even in limited spaces. When the projection distance T is 0.9m, L3 is 21.571mm; when T is 2.0m, L3 is 20.963mm; and when the projection distance T is 3.0m, L3 is 20.816mm.

[0066] On the other hand, this application also provides a projection device, including the lens system 100 provided in any embodiment of this application. When equipped with the lens system 100 provided in this application, the projection device can achieve ultra-short throw, clear projection surface edges, and minimal distortion. Furthermore, due to the good overall integration of the lens system 100, the size of the projection device can be reduced to a certain extent, making the projection device easier to carry and thus improving its multi-scenario application.

[0067] It should be understood that the above embodiments are only used to illustrate the principles and preferred implementations of this application, and it should be understood that this application is not limited to the specific details described above. Without departing from the spirit of this application, those skilled in the art can make various modifications, combinations, and variations to this solution, and all such variations should be covered within the protection scope of this application.

[0068] The embodiments and technical features described above can be reasonably combined to obtain similar or other technical solutions without obvious conflicts. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described; however, any combination of these technical features that does not contradict each other should be considered within the scope of this specification.

[0069] The embodiments described above are merely illustrative of several implementations of this disclosure, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this disclosure, and these all fall within the scope of protection of this disclosure. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A lens system having an optical axis, characterized in that, Along the optical axis from the image side to the object side, the lens system includes a first lens group, an aperture stop, a second lens group, and a Fresnel lens arranged sequentially. The first lens group includes a first lens and a second lens. The first lens has a negative optical power and is used to diverge light rays, while the second lens has a positive optical power and is used to converge light rays. The second lens group includes a third lens and a fourth lens. The third lens has a positive optical power and is used to converge light rays, while the fourth lens has a negative optical power and is used to diverge light rays. The aperture is positioned between the second lens and the third lens; the Fresnel surface of the Fresnel lens is close to the object side.

2. The lens system according to claim 1, characterized in that, The optical power range of the first lens group is -0.004 < φ1 < -0.003; and / or the optical power range of the second lens group is 0.0255 < φ2 < 0.0355; and / or the optical power range of the Fresnel lens is 0.0245 < φ3 < 0.0345.

3. The lens system according to claim 1, characterized in that, The object-side surface of the first lens is concave, the object-side surface of the second lens is spherical, the image-side surface of the third lens is spherical, and the image-side surface of the fourth lens is concave.

4. The lens system according to claim 1, characterized in that, The equivalent focal length f of the lens system is in the range of 21.375mm≤f≤23.625mm, the diagonal field of view of the lens system is ≥95°, and the lens system also includes a modulation device, the thickness of the object side of the modulation device to the image side of the first lens group is ≤65mm.

5. The lens system according to claim 4, characterized in that, The distance L1 between the image side of the first lens group and the object side of the second lens group is 29.60 mm, and the distance L2 between the aperture and the object side of the fourth lens is 13.92 mm.

6. The lens system according to claim 5, characterized in that, The distance L3 between the object side of the fourth lens and the image side of the Fresnel lens is 20.816 mm to 21.571 mm, and the distance L4 between the image side of the first lens and the object side of the fourth lens is 29.02 mm.

7. The lens system according to claim 6, characterized in that, The modulation device is located on the object side of the Fresnel lens, and the distance L5 between the Fresnel surface of the Fresnel lens and the modulation device is 8.91mm to 9.51mm.

8. The lens system according to claim 1, characterized in that, The diameter Φ1 of the first lens group is 36.54 mm; and / or the diameter Φ2 of the first lens is 31.50 mm; and / or the diameter Φ3 of the fourth lens is 27.00 mm.

9. The lens system according to any one of claims 1-8, characterized in that, The lens system is designed with an image-side telecentric orientation.

10. A projection device, characterized in that, Includes the lens system as described in any one of claims 1-9.

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