External lens and projection module

Abstract

The invention provides an external lens and a projection module. The external lens sequentially comprises a first lens group with negative focal power and a second lens group with positive focal power from the first side to the second side, the first lens group and the second lens group are arranged in a non-coaxial mode, the first lens group comprises at least one lens with negative focal power, and the second lens group comprises at least one lens with positive focal power. The second lens group comprises at least one lens with positive focal power. The problem that an external lens in the prior art is large in size is solved.

Description

Technical Field

[0001] This invention relates to the field of optical projection equipment technology, and more specifically, to an external lens and a projection module. Background Technology

[0002] With the continuous development of the optical projection field and the advancement of technology, various projection lenses are gradually entering people's lives. Currently, projection lenses are usually fixed-focus lenses. Common fixed-focus lenses cannot achieve zoom functionality to achieve larger magnification ratios, requiring external lenses to achieve different magnification ratios. However, current external lenses use more elements and have a larger overall size, making it difficult to achieve good projection effects when used in conjunction with projection lenses.

[0003] In other words, existing external lenses suffer from large size issues. Summary of the Invention

[0004] The main objective of this invention is to provide an external lens and projection module to solve the problem of large size of external lenses in the prior art.

[0005] To achieve the above objectives, according to one aspect of the present invention, an external lens is provided, comprising, from a first side to a second side, a first lens group having negative optical power and a second lens group having positive optical power, wherein the first lens group and the second lens group are non-coaxially arranged, wherein the first lens group includes at least one lens having negative optical power and the second lens group includes at least one lens having positive optical power.

[0006] Furthermore, at least one lens in the first lens group and the second lens group is an aspherical lens, and the refractive index of the aspherical lens is greater than or equal to 1.48 and less than or equal to 1.8.

[0007] Furthermore, the external lens consists of two to six lenses. The first lens group consists of one or more lenses with negative optical power and at least one lens with positive optical power. The second lens group consists of one or more lenses with positive optical power and at least one lens with negative optical power. When the first lens group consists of one lens with negative optical power and the second lens group consists of one lens with positive optical power, the external lens includes two spherical lenses or at least one non-spherical lens. Spherical lens; when the first lens group consists of two lenses with negative optical power and the second lens group consists of one lens with positive optical power, at least one of the two lenses in the first lens group has a refractive index greater than 1.7, and / or the external lens has at least two aspherical lenses; when the first lens group consists of two lenses with negative optical power and one lens with positive optical power and the second lens group consists of two lenses with positive optical power, at least one of the three lenses in the first lens group has a refractive index greater than 1.8, and / or the external lens has at least two aspherical lenses.

[0008] Furthermore, the focal length F1 of the first lens group and the total focal length Fs of the external lens satisfy the following condition: 10≤Fs / F1≤40, the focal length F2 of the second lens group and the total focal length Fs of the external lens satisfy the following condition: -29≤Fs / F2≤-5; and / or the total focal length Fs of the external lens satisfies the following condition: -1200mm≤Fs≤0mm.

[0009] According to another aspect of the present invention, a projection module is provided, comprising, from a first side to a second side, the following: an external lens as described above; a projection lens, wherein the external lens and the projection lens are non-coaxially arranged, and the projection lens includes multiple lenses, a galvanometer, a prism, and a DMD chip; the projection lens and the external lens satisfy one or more of the following: the projection ratio TR1 of the external lens and the projection ratio TR of the projection lens satisfy: 1.0≤TR / TR1≤6.0; the aperture ΦL1 of the first lens of the external lens and the aperture ΦG1 of the first lens of the projection lens satisfy: 1.0≤ΦL1 / ΦG1≤2.6; the aperture ΦL1 of the first lens of the external lens and the F-number F# of the projection lens satisfy: 10≤ΦL1 / F#≤26; the total focal length Fs of the external lens and the total focal length F0 of the projection lens satisfy: -160≤Fs / F0≤-10.

[0010] Furthermore, the distance H1 between the optical axis of the first lens group of the external lens and the optical axis of the projection lens and the distance H2 between the optical axis of the second lens group of the external lens and the optical axis of the projection lens satisfy the following condition: 1.0 ≤ H1 / H2 ≤ 2.0.

[0011] Furthermore, the distance H2 between the optical axis of the second lens group of the external lens and the optical axis of the projection lens satisfies the following condition with respect to the image plane height H_image of the projection lens: 1.0≤H2 / H_image≤2.5.

[0012] Furthermore, the optical total length TTL1 of the external lens and the optical total length TTL of the projection lens satisfy the following condition: 0.7≤TTL1 / TTL≤1.

[0013] Furthermore, the total optical length TTL1 of the external lens and the total focal length F0 of the projection lens satisfy the following condition: 3≤TTL1 / F0≤8.

[0014] Furthermore, the multiple lenses, from the first side to the second side, sequentially include a first lens with negative optical power, a second lens with positive optical power, a third lens with optical power, a fourth lens with optical power, and a fifth lens with positive optical power, wherein the optical powers of the third lens and the fourth lens are opposite in sign.

[0015] According to the technical solution of the present invention, the external lens sequentially includes a first lens group with negative optical power and a second lens group with positive optical power from the first side to the second side. The first lens group and the second lens group are not coaxially arranged. The first lens group includes at least one lens with negative optical power, and the second lens group includes at least one lens with positive optical power.

[0016] By setting the first lens group to have negative optical power, it magnifies the angle of light, thereby enlarging the projected image and helping to correct distortion. By setting the second lens group to have positive optical power, it converges the light from the projection lens, while also correcting chromatic aberration and controlling the beam aperture. By setting the first and second lens groups to be non-coaxial, it is beneficial to reduce the diameter and weight of the external lens, thus enabling a smaller size and lower cost. Attached Figure Description

[0017] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0018] Figure 1 A schematic diagram of the projection module according to Embodiment 1 of the present invention is shown;

[0019] Figure 2 A schematic diagram of the projection module according to Embodiment 2 of the present invention is shown;

[0020] Figure 3 A schematic diagram of the projection module according to Embodiment 3 of the present invention is shown.

[0021] The above figures include the following reference numerals:

[0022] 100. External lens; 200. Projection lens; G1. First lens; G2. Second lens; 10. Aperture stop; G3. Third lens; G4. Fourth lens; G5. Fifth lens; G6. Galvanometer; G7. Prism; G8. Protective glass; 20. DMD chip; 30. Projection screen; L1. First lens; L2. Second lens; L3. Third lens; L4. Fourth lens; L5. Fifth lens. Detailed Implementation

[0023] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0024] It should be noted that, unless otherwise specified, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0025] In this invention, unless otherwise stated, directional terms such as "upper," "lower," "top," and "bottom" are generally used in relation to the direction shown in the accompanying drawings, or in relation to the vertical, perpendicular, or gravitational direction of the component itself; similarly, for ease of understanding and description, "inner" and "outer" refer to the inner and outer contours of each component itself, but the above directional terms are not intended to limit this invention.

[0026] It should be noted that in this specification, the terms "first," "second," "third," etc., are used only to distinguish one feature from another and do not imply any limitation on the feature.

[0027] In this paper, the paraxial region refers to the region near the optical axis. If the lens surface is convex and the location of the convexity is not defined, it means that the lens surface is convex at least in the paraxial region; if the lens surface is concave and the location of the concaveness is not defined, it means that the lens surface is concave at least in the paraxial region. The surface of each lens closest to the first side is called the first side surface of the lens, and the surface of each lens closest to the second side is called the second side surface of the lens. The surface shape in the paraxial region can be determined according to the judgment method commonly known in the field, using the R value (R refers to the radius of curvature of the paraxial region, usually the R value in the lens database of optical software) to determine concavity or convexity. For the first side surface, when the R value is positive, it is determined to be convex, and when the R value is negative, it is determined to be concave; for the second side surface, when the R value is positive, it is determined to be concave, and when the R value is negative, it is determined to be convex.

[0028] In this application, the left side of the external lens is designated as the first side, and the right side as the second side. In a specific embodiment of this application, the first side of the external lens is the projection screen side, and the second side is the DMD chip side, or it can be the projection lens side.

[0029] To address the issue of large size in existing external lenses, this invention provides an external lens and a projection module.

[0030] like Figures 1 to 3 As shown, the external lens includes, from the first side to the second side, a first lens group with negative optical power and a second lens group with positive optical power. The first lens group and the second lens group are not coaxially arranged. The first lens group includes at least one lens with negative optical power, and the second lens group includes at least one lens with positive optical power.

[0031] By setting the first lens group to have negative optical power, it magnifies the angle of light, thereby enlarging the projected image and helping to correct distortion. By setting the second lens group to have positive optical power, it converges the light from the projection lens, corrects chromatic aberration, and controls the beam aperture, which is beneficial for achieving a small aperture. The non-coaxial arrangement of the first and second lens groups helps to reduce the diameter and weight of the external lens, contributing to a smaller size and lower cost. Furthermore, the combination of the second and first lens groups helps to cancel out chromatic aberration.

[0032] In one optional embodiment of this application, an aspherical lens may not be provided in the external lens. In another optional embodiment of this application, at least one lens in the first lens group and the second lens group is an aspherical lens or a spherical lens. When an aspherical lens is provided in the first lens group, it is beneficial for correcting distortion, reducing weight, and improving manufacturing stability, thereby further improving the overall performance of the external lens. When an aspherical lens is provided in the second lens group, it is beneficial for reducing weight and the aperture of the lens in the middle part of the external lens, while also improving manufacturing stability and making the light convergence smoother, which can effectively improve performance stability.

[0033] It should be noted that the non-coaxial arrangement between the first lens group and the second lens group mentioned above means that the optical axes of the first lens group and the second lens group are not located on the same straight line, and that they are parallel to each other and have a gap between them.

[0034] Specifically, the external lens of this application features a certain degree of aberration correction capability, light weight, low cost, miniaturization, and high image quality. It can be used in conjunction with a projection lens, positioned on the first side of the projection lens to alter its projection ratio, achieving a zoom effect and shortening the focal length. The projection lens, in conjunction with the external lens, can support a projection ratio reduction of 1 to 5 times; that is, at the same distance, the original image size can be enlarged by 1 to 5 times while maintaining a certain level of projection quality. For example, a projection image of 40 to 250 inches can be achieved at a distance of 1.6 meters.

[0035] In different embodiments of this application, the external lens may consist of two to six lenses. In a preferred embodiment of this application, the external lens may consist of two, three, or five lenses. The first lens group consists of one or more lenses with negative optical power and at least one lens with positive optical power, and the second lens group consists of one or more lenses with positive optical power and at least one lens with negative optical power.

[0036] Specifically, in one embodiment of this application, the external lens consists of two lenses: a first lens group consisting of a lens with negative optical power and a second lens group consisting of a lens with positive optical power. Both lenses can be spherical lenses or at least one can be an aspherical lens. Using an aspherical lens in the two-element lens design significantly reduces weight and size while effectively ensuring high performance. In another embodiment of this application, the external lens can consist of three lenses: a first lens group consisting of two lenses with negative optical power and a second lens group consisting of a lens with positive optical power. This three-element design allows the front two lenses to amplify light more smoothly, thus reducing the aperture; furthermore, the two lenses in the first lens group can perform chromatic aberration correction. In another embodiment of this application, the external lens may consist of five lenses. The first lens group comprises two lenses with negative optical power and one lens with positive optical power. The first lens group includes three lenses, including a set of positive and negative lenses with a near-cemented distribution, which effectively improves chromatic aberration. The second lens group consists of two lenses with positive optical power. By rationally configuring the lens composition of the first and second lens groups of the external lens, the overall size of the external lens can be effectively reduced, achieving a higher magnification and a lower projection ratio. By rationally increasing the number of lenses, a smaller projection ratio is obtained. Simultaneously, as the number of lenses increases, the shift distance decreases, thereby reducing the overall size of the external lens.

[0037] Specifically, the refractive index of an aspherical lens should be greater than or equal to 1.48 and less than or equal to 1.8. Aspherical lenses can be appropriately selected for the first and second lens groups, which helps improve distortion and astigmatism. When the second lens group uses aspherical lenses, it improves edge resolution and enhances overall performance.

[0038] In this application, the focal length F1 of the first lens group and the total focal length Fs of the external lens satisfy the following relationship: 10 ≤ Fs / F1 ≤ 40; the focal length F2 of the second lens group and the total focal length Fs of the external lens satisfy the following relationship: -29 ≤ Fs / F2 ≤ -5; the total focal length Fs of the external lens satisfies the following relationship: -1200mm ≤ Fs ≤ 0mm. This arrangement facilitates a reasonable allocation of the focal lengths of the first and second lens groups, ensuring their rationality, which helps eliminate chromatic aberration and guarantees imaging performance. In different optional embodiments of this application, Fs / F1 = 10, 20, 23, 25, 30, 34, 40, and Fs / F2 = -29, -25, -20, -15, -10, -5.

[0039] This application also provides a projection module, which includes, from the first side to the second side, the aforementioned external lens and projection lens. The external lens and projection lens are not coaxially arranged. The projection lens includes multiple lenses, a galvanometer, a prism, and a DMD chip. The projection lens and the external lens satisfy one or more of the following:

[0040] The projection ratio TR1 of the external lens and the projection ratio TR of the projection lens satisfy the following condition: 1.0 ≤ TR / TR1 ≤ 6.0;

[0041] The aperture ΦL1 of the first lens of the external lens and the aperture ΦG1 of the first lens of the projection lens satisfy the following condition: 1.0≤ΦL1 / ΦG1≤2.6;

[0042] The aperture ΦL1 of the first lens of the external lens and the F-number F# of the projection lens satisfy the following condition: 10≤ΦL1 / F#≤26;

[0043] By constraining the ratio between the aperture of the external lens and the F# of the projection lens, we can prevent the external lens aperture from being too large when the F# is small. This can increase the lens's manufacturability or reduce the processing difficulty.

[0044] The total focal length Fs of the external lens and the total focal length F0 of the projection lens satisfy the following condition: -160≤Fs / F0≤-10.

[0045] The throw ratio TR1 of the external lens and the throw ratio TR of the projection lens are constrained to satisfy the following condition: 1.0 ≤ TR / TR1 ≤ 6.0. This throw ratio is defined as the ratio of the projection distance to the width of the projected image, and it also balances the relationship between the throw ratio and the length of the external lens. This setting helps ensure that the external lens has a small throw ratio, enabling the conversion from telephoto to medium-telephoto, short-telephoto, or ultra-short-telephoto. In different optional embodiments of this application, TR / TR1 = 1.0, 1.7, 3.2, 4.0, 4.5, and 6.0.

[0046] The aperture ΦL1 of the first lens of the external lens and the aperture ΦG1 of the first lens element of the projection lens satisfy the following condition: 1.0 ≤ ΦL1 / ΦG1 ≤ 2.6. This setting helps ensure that the size of the external lens matches the size of the projection lens, facilitates reducing the aperture of the external lens, maintains a small aperture, and balances the throw ratio and the length of the external lens. It should be noted that the first lens of the external lens refers to the lens closest to the projection screen, and the first lens element of the projection lens refers to the lens closest to the projection screen. In different optional embodiments of this application, ΦL1 / ΦG1 = 1.0, 1.5, 2.0, and 2.6.

[0047] The aperture ΦL1 of the first lens of the external lens is constrained to satisfy the following relationship with the F-number F# of the projection lens: 10 ≤ ΦL1 / F# ≤ 26. This setting helps to ensure the small aperture characteristic of the external lens while balancing the projection ratio and the length of the external lens. In different optional embodiments of this application, ΦL1 / F# = 10, 15, 20, 23, 26.

[0048] The total focal length Fs of the external lens and the total focal length F0 of the projection lens are constrained to satisfy: -160 ≤ Fs / F0 ≤ -10. This setting helps ensure that the external lens can reduce the focal length of the projection lens, thereby achieving a zoom effect. It can convert a telephoto lens into a medium telephoto or short telephoto lens, and can also balance the relationship between the projection ratio and the length of the external lens. In different optional embodiments of this application, Fs / F0 = -160, -130, -100, -90, -60, -40, -20, -10.

[0049] Specifically, the distance H2 between the optical axis of the second lens group of the external lens and the optical axis of the projection lens satisfies the following condition with respect to the image plane height H_image of the projection lens: 1.0 ≤ H2 / H_image ≤ 2.5. Constraining this condition facilitates matching between the external lens and the projection lens, ensuring that the external lens can change the projection ratio of the projection lens. It also helps to determine the tilt-shift distance, avoiding excessively large tilt-shift distances, thus achieving a smaller overall size and balancing the relationship between the projection ratio and the length of the external lens. In different optional embodiments of this application, H2 / H_image = 1.0, 1.3, 1.5, 2.2, and 2.5.

[0050] Specifically, the distance H1 between the optical axis of the first lens group of the external lens and the optical axis of the projection lens, and the distance H2 between the optical axis of the second lens group of the external lens and the optical axis of the projection lens, satisfy the following condition: 1.0 ≤ H1 / H2 ≤ 2.0. It should be noted that H1 is the vertical distance between the optical axes of the first lens group and the projection lens, and H2 is the vertical distance between the optical axes of the second lens group and the projection lens. That is, the optical axes of the first lens group and the projection lens are not on the same straight line, and the optical axes of the second lens group and the projection lens are also not on the same straight line. Furthermore, in this invention, as the length or number of lenses of the external lens increases, the light path becomes smoother, resulting in a smaller axis-shift distance, i.e., a smaller H1 / H2 value. Simultaneously, a smoother light path can improve the lens aperture and performance. Controlling the H1 / H2 ratio can balance parameters such as the number of lenses and the length of the external lens. In different optional embodiments of this application, H1 / H2 = 1.0, 1.4, 1.6, and 2.0. By constraining this condition, the relationship between the projection ratio and the length of the external lens can be balanced.

[0051] Specifically, the total optical length TTL1 of the external lens and the total optical length TTL of the projection lens satisfy the following condition: 0.7 ≤ TTL1 / TTL ≤ 1. This setting is beneficial for compressing the total optical length of the external lens, which in turn helps to reduce the overall size of the external lens, thus achieving miniaturization. It also balances the relationship between the projection ratio and the length of the external lens. In different optional embodiments of this application, TTL1 / TTL = 0.7, 0.8, 0.9, and 1.

[0052] Specifically, the total optical length TTL1 of the external lens and the total focal length F0 of the projection lens satisfy the following relationship: 3 ≤ TTL1 / F0 ≤ 8. This setting helps ensure the miniaturization of the external lens and guarantees its compact structure. With a fixed focal length of the projection lens, increasing the length of the external lens or the number of lenses in the external lens can achieve a smaller projection ratio; influenced by one or more of the constraints above, the relationship between the projection ratio and the length of the external lens can be balanced. Using this external lens can effectively improve the projection ratio of the projection lens, achieve short-throw projection, improve chromatic aberration, and suppress distortion to a certain extent; the entire external lens has advantages such as miniaturization, small aperture, light weight, and low cost, while ensuring certain imaging performance. In different embodiments of this application, TTL1 / F0 = 3, 5, 7, and 8.

[0053] The following is combined with Figures 1 to 3 The projection module of this application will be described in detail with reference to specific embodiments. Figures 1 to 3 Three different embodiments of the projection module of this application are described respectively. Figures 1 to 3 In all three embodiments, the projection module consists of a non-coaxial external lens 100 and a projection lens 200. The external lens 100 is positioned on the projection side of the projection lens 200 and is located between the projection screen 30 and the projection lens 200. Figures 1 to 3 In the three embodiments, the projection lens 200 has the same structural composition, while the external lens 100 has a different structural composition.

[0054] like Figures 1 to 3 In the three embodiments shown, the projection lens 200 is composed of a first lens G1, a second lens G2, an aperture 10, a third lens G3, a fourth lens G4, a fifth lens G5, a galvanometer G6, a prism G7, a protective glass G8, and a DMD chip 20, arranged sequentially from the first side to the second side. The third lens G3 and the fourth lens G4 are cemented together to form a cemented lens. The lenses in the projection lens 200 can be made of either plastic or glass.

[0055] exist Figures 1 to 3 In the three embodiments, the first lens G1 has a convex first side and a concave second side. The second lens G2 has a convex first side and a convex second side. The third lens G3 has a concave first side and a convex second side. The fourth lens G4 has a concave first side and a convex second side. The fifth lens G5 has a convex first side and a convex second side. The first lens G1 is an aspherical lens with negative optical power. The second lens G2 is a spherical or aspherical lens with positive optical power. The third lens G3 has negative optical power and the fourth lens G4 has positive optical power, or the third lens G3 has positive optical power and the fourth lens G4 has negative optical power. The fifth lens G5 is an aspherical lens with positive optical power.

[0056] Table 1 below shows the basic structural parameters of the projection lens 200 in Embodiments 1 to 3.

[0057]

[0058] Table 1

[0059] The surface shape of each aspherical lens can be defined using, but is not limited to, the following aspherical formulas:

[0060]

[0061] In the formula, z represents the surface sagitta; c is the curvature; r is the radial coordinate; k is the quadratic coefficient; and α is the coefficient.

[0062] The values ​​of α in the formulas corresponding to the aspherical surfaces in Table 1 are shown in Table 2 below:

[0063] The first side of the first lens G1 The second side of the first lens G1 The first side of the fifth lens G5 The second side of the fifth lens G5 <![CDATA[α1]]> -0.00028 0.000486 -4.50E-05 3.06E-06 <![CDATA[α2]]> 3.50E-06 -1.01E-05 5.41E-08 -8.13E-08 <![CDATA[α3]]> -5.6E-08 2.39E-07 3.01E-13 -8.27E-11 <![CDATA[α4]]> 2.14E-10 -3.83E-09 3.11E-13 4.37E-12 <![CDATA[α5]]> -2.21E-14 -3.98E-14 -4.23E-14 -3.98E-14 <![CDATA[α6]]> 1.7E-15 -4.20E-13 6.14E-16 7.44E-16 <![CDATA[α7]]> -2.19E-18 6.35E-16 -7.88E-18 -6.55E-19 <![CDATA[α8]]> 0 0 0 0

[0064] Table 2

[0065] The following is combined with Figures 1 to 3 The external lens 100 of different embodiments is further described. The lens in the external lens 100 can be made of plastic or glass.

[0066] Example 1

[0067] like Figure 1 As shown, the projection module of Embodiment 1 is described.

[0068] like Figure 1 As shown, the external lens 100 of the projection module consists of two lenses. The first lens group consists of a first lens L1 with negative optical power, and the second lens group consists of a second lens L2 with positive optical power. The first lens L1 and the second lens L2 are sequentially arranged along a direction away from the projection screen 30, and the first lens L1 and the second lens L2 are not coaxially arranged, nor are they coaxially arranged with the projection lens 200.

[0069] In this embodiment, the first lens L1 serves to diverge light and correct distortion. The second lens L2 serves to collect light and control the beam aperture. The first side surface of the first lens L1 is concave, and the second side surface is concave. The first side surface of the second lens L2 is convex, and the second side surface is convex. By appropriately setting the surface shape of the lenses, chromatic aberration can be corrected. By adjusting the minimum distance between the optical axes of the first lens L1, the second lens L2, and the optical axis of the projection lens 200, the optical axes can be kept at the center of the lens, ensuring good resolution in the center of the image. The first lens L1 and the second lens L2 can be selectively set as aspherical lenses. By setting aspherical lenses, the local light correction capability can be enhanced, and the resolution can be improved. When both the first lens L1 and the second lens L2 are aspherical lenses, the cost, weight, and volume can be reduced, while the overall resolution can be improved.

[0070] In this embodiment, the total focal length Fs of the external lens 100 satisfies: -1200mm≤Fs≤0mm, preferably -900mm≤Fs≤-600mm. This setting helps to ensure that the total focal length of the external lens 100 is negative, thereby ensuring the effect of the external lens 100 in reducing the projection ratio of the projection lens 200.

[0071] Table 3 below shows the basic structural parameters of the external lens 100 in Embodiment 1.

[0072] surface Radius of curvature (mm) Thickness (mm) The first side surface of the first lens L1 -45 3.9 The second side surface of the first lens L1 20 12 The first side surface of the second lens L2 30 10 The second side surface of the second lens L2 -70 14

[0073] Table 3

[0074] Example 2

[0075] like Figure 2 As shown, the projection module of Embodiment 2 is described.

[0076] like Figure 2 As shown, the external lens 100 of the projection module consists of three lenses. The first lens group comprises a first lens L1 with negative optical power and a second lens L2 with negative optical power, arranged coaxially. The second lens group comprises a third lens L3 with positive optical power. The first lens L1, second lens L2, and third lens L3 are arranged sequentially along a direction away from the projection screen 30. Furthermore, the first and second lens groups are not coaxially arranged, and both the first and second lens groups are not coaxially arranged with the projection lens 200.

[0077] In this embodiment, the first lens L1 and the second lens L2 serve to diverge light and correct distortion. The third lens L3 serves to collect light and control the beam aperture. The first side of the first lens L1 is concave, and the second side is concave. The first side of the second lens L2 is concave, and the second side is convex. The second lens L2 is designed as a meniscus, which can work with the first lens L1 to more effectively adjust chromatic aberration. The first side of the third lens L3 is convex, and the second side is convex. Both the first lens L1 and the third lens L3 can be set to aspherical lenses, which is beneficial for improving edge resolution. Since the first lens L1 can diverge light to a certain extent, the aperture of the first lens L1 can be effectively adjusted, thereby effectively reducing the aperture and volume of the entire external lens 100.

[0078] In this embodiment, the first lens group consists of two lenses with negative optical power and the second lens group consists of one lens with positive optical power. At least one of the two lenses in the first lens group has a refractive index greater than 1.7.

[0079] In this embodiment, the total focal length Fs of the external lens 100 satisfies: -1200mm≤Fs≤0mm, preferably -400mm≤Fs≤-100mm. This setting helps to ensure that the total focal length of the external lens 100 is negative, thereby ensuring the effect of the external lens 100 in reducing the projection ratio of the projection lens 200.

[0080] Table 4 below shows the basic structural parameters of the external lens 100 in Embodiment 2.

[0081]

[0082]

[0083] Table 4

[0084] Example 3

[0085] like Figure 3 As shown, the projection module of Embodiment 3 is described.

[0086] like Figure 3 As shown, the external lens 100 of the projection module consists of five lenses. The first lens group comprises a first lens L1 with negative optical power, a second lens L2 with negative optical power, and a third lens L3 with positive optical power, all coaxially arranged. The second lens group comprises a fourth lens L4 with positive optical power and a fifth lens L5 with positive optical power, both coaxially arranged. The first lens L1, second lens L2, third lens L3, fourth lens L4, and fifth lens L5 are arranged sequentially along a direction away from the projection screen 30. Furthermore, the first and second lens groups are not coaxially arranged, and both the first and second lens groups are not coaxially arranged with the projection lens 200.

[0087] In this embodiment, the first lens L1, the second lens L2, and the third lens L3 serve to diverge light and correct distortion. The fourth lens L4 and the fifth lens L5 serve to collect light and control the beam aperture. Because the second lens group has two positive lenses, it has a strong beam-gathering ability, which helps to reduce the distance between the optical axes of the second lens group and the first lens group. This embodiment increases the number of lenses compared to embodiments one and two. With the increase in the number of lenses, it is beneficial to reduce the distance between the optical axes of the two lens groups, and thus to reduce the overall size of the external lens 100. At the same time, due to the increased number of lenses, the magnification capability of the external lens 100 is enhanced, meaning the projection ratio will increase.

[0088] In this embodiment, the first lens L1 has a convex first side and a concave second side. The second lens L2 has a concave first side and a concave second side. The third lens L3 has a convex first side and a convex second side. The fourth lens L4 has a convex first side and a concave second side. The fifth lens L5 has a convex first side and a convex second side. The second lens L2 and the third lens L3 can be cemented together to form a cemented lens, which can better correct chromatic aberration and simultaneously reduce the distance between the optical axes of the first lens group and the second lens group.

[0089] In this embodiment, at least two aspherical lenses are provided among the first lens L1 to the fifth lens L5. The first lens group in this embodiment consists of two lenses with negative optical power and one lens with positive optical power, and the second lens group consists of two lenses with positive optical power. In this case, at least one of the three lenses in the first lens group has a refractive index greater than 1.8. By providing a lens made of a high-refractive-index material in the first lens group, it helps to reduce the overall aperture of the external lens 100.

[0090] In this embodiment, the total focal length Fs of the external lens 100 satisfies: -1200mm≤Fs≤0mm, preferably -600mm≤Fs≤-300mm. This setting helps to ensure that the total focal length of the external lens 100 is negative, thereby ensuring the effect of the external lens 100 in reducing the projection ratio of the projection lens 200.

[0091] Table 5 below shows the basic structural parameters of the external lens 100 in Embodiment 3.

[0092] surface Radius of curvature (mm) Thickness (mm) The first side surface of the first lens L1 120 2.1 The second side surface of the first lens L1 16 7.5 The first side surface of the second lens L2 -30 6.2 The second side surface of the second lens L2 140 0.3 The first side of the third lens L3 70 6.1 The second side of the third lens L3 -190 2.5 The first side of the fourth lens L4 46 3.2 The second side of the fourth lens L4 170 0.3 The first side of the fifth lens L5 55 3.6 The second side of the fifth lens L5 -205 14

[0093] Table 5

[0094] In summary, Examples 1 to 3 satisfy the relationships shown in Table 6 below.

[0095] Example 1 Example 2 Example 3 1.5 ≤ H2 / H_image ≤ 2.5 1.3 ≤ H2 / H_image ≤ 2.2 1.0 ≤ H2 / H_image ≤ 1.5 1.6 ≤ H1 / H2 ≤ 2.0 1.4 ≤ H1 / H2 ≤ 1.6 1.0 ≤ H1 / H2 ≤ 2.0 1.0 ≤ TR / TR1 ≤ 4.0 1.0≤TR / TR1≤4.5 1.0 ≤ TR / TR1 ≤ 6.0 25≤Fs / F1≤40 10≤Fs / F1≤20 20≤Fs / F1≤34 -29≤Fs / F2≤-15 -15≤Fs / F2≤-5 -20≤Fs / F2≤-10 -160≤Fs / F0≤-90 -60≤Fs / F0≤-10 -100≤Fs / F0≤-50 1.0≤ΦL1 / ΦG1≤2.6 1.0≤ΦL1 / ΦG1≤2.0 1.0≤ΦL1 / ΦG1≤2.0 10≤ΦL1 / F#≤26 10≤ΦL1 / F#≤23 10≤ΦL1 / F#≤20 0.7≤TTL1 / TTL≤1 0.7≤TTL1 / TTL≤1 0.7≤TTL1 / TTL≤1

[0096] Table 6

[0097] Obviously, the embodiments described above are merely some, not all, embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0098] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0099] It should be noted that the terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in sequences other than those illustrated or described herein.

[0100] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An external lens, characterized in that, From the first side to the second side, it sequentially includes a first lens group with negative optical power and a second lens group with positive optical power, wherein the first lens group and the second lens group are not coaxially arranged. The first lens group includes at least one lens with negative optical power, and the second lens group includes at least one lens with positive optical power.

2. The external lens according to claim 1, characterized in that, At least one lens in the first lens group and the second lens group is an aspherical lens, and the refractive index of the aspherical lens is greater than or equal to 1.48 and less than or equal to 1.

8.

3. The external lens according to claim 1, characterized in that, The external lens consists of two to six lenses. The first lens group consists of one or more lenses with negative optical power and at least one lens with positive optical power. The second lens group consists of one or more lenses with positive optical power and at least one lens with negative optical power. When the first lens group consists of a lens with negative optical power and the second lens group consists of a lens with positive optical power, the external lens includes two spherical lenses or at least one aspherical lens. When the first lens group consists of two lenses with negative optical power and the second lens group consists of one lens with positive optical power, at least one of the two lenses in the first lens group has a refractive index greater than 1.7, and / or the external lens has at least two aspherical lenses. When the first lens group consists of two lenses with negative optical power and one lens with positive optical power, and the second lens group consists of two lenses with positive optical power, at least one of the three lenses in the first lens group has a refractive index greater than 1.8, and / or the external lens has at least two aspherical lenses.

4. The external lens according to claim 1, characterized in that, The focal length F1 of the first lens group and the total focal length Fs of the external lens satisfy the following condition: 10≤Fs / F1≤40; the focal length F2 of the second lens group and the total focal length Fs of the external lens satisfy the following condition: -29≤Fs / F2≤-5; and / or the total focal length Fs of the external lens satisfies the following condition: -1200mm≤Fs≤0mm.

5. A projection module, characterized in that, From the first side to the second side, the following are included in sequence: External lens as described in any one of claims 1 to 4; The projection lens is non-coaxially arranged with the external lens and the projection lens. The projection lens includes multiple lenses, a galvanometer, a prism, and a DMD chip. The projection lens and the external lens satisfy one or more of the following: The projection ratio TR1 of the external lens and the projection ratio TR of the projection lens satisfy the following condition: 1.0 ≤ TR / TR1 ≤ 6.0; The aperture ΦL1 of the first lens of the external lens and the aperture ΦG1 of the first lens of the projection lens satisfy the following condition: 1.0≤ΦL1 / ΦG1≤2.6; The aperture ΦL1 of the first lens of the external lens and the F-number F# of the projection lens satisfy the following relationship: 10 ≤ ΦL1 / F#≤26; The total focal length Fs of the external lens and the total focal length F0 of the projection lens satisfy the following condition: -160≤Fs / F0≤-10.

6. The projection module according to claim 5, characterized in that, The distance H1 between the optical axis of the first lens group of the external lens and the optical axis of the projection lens and the distance H2 between the optical axis of the second lens group of the external lens and the optical axis of the projection lens satisfy the following condition: 1.0 ≤ H1 / H2 ≤ 2.

0.

7. The projection module according to claim 5, characterized in that, The distance H2 between the optical axis of the second lens group of the external lens and the optical axis of the projection lens satisfies the following condition with respect to the image plane height H_image of the projection lens: 1.0 ≤ H2 / H_image ≤ 2.

5.

8. The projection module according to claim 5, characterized in that, The optical total length TTL1 of the external lens and the optical total length TTL of the projection lens satisfy the following condition: 0.7≤TTL1 / TTL≤1.

9. The projection module according to claim 5, characterized in that, The total optical length TTL1 of the external lens and the total focal length F0 of the projection lens satisfy the following condition: 3≤TTL1 / F0≤8.

10. The projection module according to claim 5, characterized in that, The plurality of lenses, from the first side to the second side, sequentially include a first lens with negative optical power, a second lens with positive optical power, a third lens with optical power, a fourth lens with optical power, and a fifth lens with positive optical power, wherein the optical power of the third lens and the fourth lens are opposite in sign.

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