Projection lens

Abstract

The invention belongs to the technical field of projection optical lenses, and discloses a projection lens which can form a lens structure with a long back focal length through three lens groups which are respectively used for focusing, zooming and fixing, can obtain higher brightness and contrast through the lens structure with the long back focal length, and is more beneficial to heat dissipation. On the basis, continuous zooming can be achieved through the first zoom lens set, the second zoom lens set and the third zoom lens set which independently move along the optical axis, and meanwhile under the condition that the back focal length is long or the length of the lens is fixed, through the design in the aspects of back focal length control, lens materials and / or lens gluing and the like, continuous zooming can be achieved. The problems of chromatic aberration and difficult light correction caused by a long back focal length lens structure can be solved in the aspects of aberration, chromatic aberration and the like, the contrast ratio and the brightness are better improved, and the purposes of long back focal length, high brightness, low chromatic aberration, low distortion, large aperture and high imaging quality of the projection lens are finally achieved.

Description

Technical Field

[0001] This invention belongs to the field of projection optical lens technology, and specifically relates to a projection lens. Background Technology

[0002] Projection displays are now widely used in near-eye displays (AR-Glass), home projection, and commercial projection. Existing projection technologies include DLP, LCOS, LCD, and LBS. LCOS display is a new type of reflective display technology that organically combines LCD and CMOS integrated circuits. As a new type of display device, LCOS has many advantages such as large screen, high brightness, high resolution, and energy saving. Compared to DLP projection technology, LCOS selects light through its own polarization characteristics, and its contrast ratio can now reach thousands or even tens of thousands. Regarding brightness, which is a key concern, significant progress has been made by processing monochromatic light for each chip before combining the light. However, incorporating the light combining system into the lens design increases the back focal length, requiring more design space for the entire lens. Furthermore, to meet higher design requirements and ensure clear full-frame imaging and uniform illumination, the lens design becomes increasingly complex. Market feedback indicates that zoom lenses, which can change the image size without moving the camera, are very popular.

[0003] In summary, in order to obtain machines with higher contrast and higher brightness, how to solve the problems of complex structure, excessive length and large size of long back focal length projection lenses, while achieving continuous zoom, has become a technical challenge that needs to be solved by those skilled in the art. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a projection lens to solve the problems of excessive lens length, low contrast and low brightness in existing continuously zoomable long back focal length projection lenses.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A projection lens includes a first lens group, a second lens group, and a third lens group arranged from the magnification side to the reduction side. The first lens group is used for focusing and has a negative optical power. The second lens group is a zoom group and has a positive optical power. The third lens group is a fixed lens group and has a positive optical power. The second lens group includes a zoom lens group one, a zoom lens group two, and a zoom lens group three, each independently movable along a first optical axis arranged from the magnification side to the reduction side. The zoom lens group three is provided with an aperture stop.

[0007] A reflective element is provided between the third lens group and the second lens group. Light emitted from the third lens group is deflected and guided by the reflective element to be emitted from the second lens group and the first lens group.

[0008] BFL / TTL > 0.2, where BFL is the back focal length of the projection lens and TTL is the total length of the projection lens;

[0009] The projection lens also satisfies at least one of the following:

[0010] The projection ratio of the projection lens is continuously variable between 1.3 and 2.1. When the projection ratio is 1.3, TTL / EFL ≥ 20, and when the projection ratio is 2.1, TTL / EFL ≤ 18, where TTL is the total length of the projection lens and EFL is the effective focal length of the projection lens.

[0011] The zoom ratio of the projection lens is greater than 1.5;

[0012] In the projection lens, there are 1-3 lenses with positive optical power and an Abbe number greater than 80;

[0013] The projection lens includes cemented triplet lenses and cemented doublet lenses. The number of cemented triplet lenses is 'a' and the number of cemented doublet lenses is 'b', where 1 < a < 4 and 2 < b < 5.

[0014] In a possible implementation, the reflective element, the second lens group, and the first lens group are rotatable relative to the third lens group as a whole to project in different directions.

[0015] In possible implementations, the focal lengths of the first lens group, zoom lens group one, zoom lens group two, zoom lens group three, and the third lens group are related to the focal length of the projection lens as follows:

[0016] -2.5 <EFL1 / EFL<-1;

[0017] 3 <EFL2 / EFL<8;

[0018] 5 <EFL3 / EFL<12;

[0019] 13 <EFL4 / EFL<27;

[0020] 2 <EFL5 / EFL<7;

[0021] Wherein, EFL1 is the focal length of the first lens group, EFL2 is the focal length of the first zoom lens group, EFL3 is the focal length of the second zoom lens group, EFL4 is the focal length of the third zoom lens group, EFL5 is the focal length of the third lens group, and EFL is the focal length of the projection lens.

[0022] In a possible implementation, the projection lens is a lens architecture one, wherein the first lens group includes a first lens with negative optical power, a second lens with negative optical power, a third lens with positive optical power, and a fourth lens with negative optical power, arranged from the magnification side to the reduction side; the second lens group includes a fifth lens with positive optical power, a sixth lens with negative optical power, a seventh lens with positive optical power, an eighth lens with positive optical power, a ninth lens with negative optical power, a tenth lens with positive optical power, an aperture stop, an eleventh lens with negative optical power, and an optical power sensor, arranged from the magnification side to the reduction side. The zoom lens group consists of a negative 12th lens, a positive 13th lens, a negative 14th lens, and a positive 15th lens. The fifth lens forms zoom lens group one; the sixth, seventh, and eighth lenses form zoom lens group two; and the ninth, tenth, and diaphragm lenses, along with the 11th, 12th, 13th, 14th, and 15th lenses, form zoom lens group three. The third lens group includes a negative 16th lens, a positive 17th lens, and a positive 18th lens, arranged from the magnification side to the reduction side.

[0023] Alternatively, the projection lens may be a second lens architecture, wherein the first lens group includes a first lens with negative optical power, a second lens with negative optical power, and a third lens with positive optical power, arranged from the magnification side to the reduction side; the second lens group includes a zoom lens group one with a fourth lens with positive optical power, a fifth lens with negative optical power, and a sixth lens with positive optical power, arranged from the magnification side to the reduction side; the zoom lens group two includes a seventh lens with negative optical power, an eighth lens with positive optical power, and a ninth lens with positive optical power, arranged from the magnification side to the reduction side; the zoom lens group three includes a tenth lens with negative optical power, an eleventh lens with positive optical power, an aperture stop, a twelfth lens with negative optical power, a thirteenth lens with negative optical power, a fourteenth lens with positive optical power, a fifteenth lens with negative optical power, and a sixteenth lens with positive optical power, arranged from the magnification side to the reduction side; and the third lens group includes a seventeenth lens with negative optical power, an eighteenth lens with positive optical power, and a nineteenth lens with positive optical power.

[0024] In a possible implementation, the first lens group includes at least one set of cemented lens groups formed by cementing together two or three adjacent lenses;

[0025] The zoom lens group three includes at least one cemented lens group formed by cementing together two or three adjacent lenses;

[0026] The third lens group includes a cemented lens group formed by cementing together two or three adjacent lenses.

[0027] In one possible implementation, in lens architecture one, the second, third, and fourth lenses are cemented together to form a cemented triplet lens one, where the refractive index of the second lens is less than that of the third and fourth lenses; the ninth and tenth lenses are cemented together to form a cemented doublet lens one; the twelfth, thirteenth, and fourteenth lenses are cemented together to form a cemented triplet lens two, where the refractive index of the thirteenth lens is less than that of the twelfth and fourteenth lenses; and the sixteenth and seventeenth lenses are cemented together to form a cemented doublet lens two, where the refractive index of the sixteenth lens is greater than that of the seventeenth lens.

[0028] Alternatively, in lens architecture two, the second lens and the third lens are combined to form a cemented doublet lens group one, where the refractive index of the second lens is lower than that of the third lens; the fourth lens and the fifth lens are combined to form a cemented doublet lens group two; the tenth lens and the eleventh lens are combined to form a cemented doublet lens group three; the thirteenth lens, the fourteenth lens, and the fifteenth lens are combined to form a triplet lens group one, where the refractive index of the fourteenth lens is lower than that of the thirteenth and fifteenth lenses; and the seventeenth lens and the eighteenth lens are combined to form a cemented doublet lens group four, where the refractive index of the seventeenth lens is higher than that of the eighteenth lens.

[0029] In one possible implementation, the first lens is a meniscus aspherical lens.

[0030] In one possible implementation, the projection lens has at least two lenses with a refractive index greater than 1.8 in the lens on the aperture reduction side.

[0031] In a possible implementation, the projection lens on the aperture reduction side includes 1 to 4 lenses with positive optical power, and the material of the lenses satisfies dn / dt < 0, where dn / dt represents the derivative of the refractive index n with respect to temperature t.

[0032] In a possible implementation, the ratio of the back focal length to the effective focal length of the projection lens satisfies BFL / EFL≧3, where BFL is the back focal length of the projection lens and EFL is the effective focal length of the projection lens.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The projection lens of this invention, through three lens groups used for focusing, zooming, and fixing respectively, can form a lens structure with a long back focal length. The long back focal length lens structure can achieve higher brightness and contrast, and is also more conducive to heat dissipation. On this basis, through zoom lens group one, zoom lens group two, and zoom lens group three, which move independently along the optical axis, continuous zoom can be achieved. At the same time, when the long back focal length or lens length is constant, through the design of back focal length control, lens materials and / or lens bonding, the problems of chromatic aberration and light correction difficulties caused by the long back focal length lens structure can be solved, thereby improving contrast and brightness. Ultimately, the projection lens achieves the goals of long back focal length, high brightness, low chromatic aberration, low distortion, large aperture, and high image quality.

[0035] Moreover, by setting a reflective element between the third lens group and the second lens group, the lens structure can form an L-shaped folding architecture. On the one hand, it can avoid structural limitations, reduce the space occupied in the axis, and give more room for structural design. On the other hand, the folding design can make a rotating mechanism at the reflective element to realize multi-directional projection, and the projection direction selection is more flexible and diverse. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the structure of a projection lens using a lens architecture in a wide-angle state.

[0037] Figure 2 This is a schematic diagram of the structure of a projection lens using a lens architecture in a telephoto state.

[0038] Figure 3 A schematic diagram of the structure of another projection lens using lens architecture two in the wide-angle state;

[0039] Figure 4 This is a schematic diagram of the structure of another projection lens using lens architecture two in the telephoto state.

[0040] In the diagram: L1 - First lens; L2 - Second lens; L3 - Third lens; L4 - Fourth lens; L5 - Fifth lens; L6 - Sixth lens; L7 - Seventh lens; L8 - Eighth lens; L9 - Ninth lens; L10 - Tenth lens; L11 - Eleventh lens; L12 - Twelfth lens; L13 - Thirteenth lens; L14 - Fourteenth lens; L15 - Fifteenth lens; L16 - Sixteenth lens; L17 - Seventeenth lens; L18 - Eighteenth lens; G1 - First lens group; G2 - Second lens group; G21 - Zoom lens group one; G22 - Zoom lens group two; G23 - Zoom lens group three; G3 - Third lens group. Detailed Implementation

[0041] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to specific embodiments.

[0042] Please refer to Figure 1 and Figure 2 As shown, a projection lens includes a first lens group G1, a second lens group G2, and a third lens group G3 arranged from the magnification side to the reduction side. The first lens group G1 is used for focusing and has a negative optical power, the second lens group G2 is a zoom group and has a positive optical power, and the third lens group G3 is a fixed lens group and has a positive optical power.

[0043] The projection lens's first lens group G1, second lens group G2, and third lens group G3 form a negative-positive-positive lens architecture. This, combined with the first lens group G1 for focusing, the second lens group G2 for zooming, and the third lens group G3 (which is a fixed lens group), facilitates a reduction in the overall lens length. Furthermore, it allows the second lens group G2 to perform continuous zooming within a long back focal length lens structure. Since the first lens group G1 and the third lens group G3 are relatively fixed, the long back focal length or lens length remains constant. This allows for improved lens performance, and even a reduction in overall lens length, through the design of the lens groups and lenses, without increasing the lens length. The back focal length is defined as the distance of light from the rear principal plane of the lens to the image plane, or the distance from the last lens element to the chip.

[0044] In an embodiment of this application, the second lens group G2 includes a zoom lens group one G21, a zoom lens group two G22, and a zoom lens group three G23, each independently movable along the first optical axis from the magnification side to the reduction side, and the zoom lens group three G23 is provided with an aperture stop.

[0045] The second lens group G2 mainly includes zoom lens group one G21, zoom lens group two G22, and zoom lens group three G23. Each of the three zoom lens groups can move along the optical axis, enabling continuous zooming. Furthermore, the aperture stop can limit or adjust the size of the light beam passing through the lens while the second lens group G2 is zooming, thus facilitating changes to image parameters such as exposure, depth of field, and resolution. The projection lens is a zoom lens, and focusing is achieved through front-group focusing. That is, when the projection distance (i.e., the distance to the object surface projection side) changes to obtain different image sizes, focusing can be adjusted by changing the interval between the first lens group G1 and the second lens group G2.

[0046] In lens structures based on long back focal lengths, the requirement of long back focal lengths results in a large overall lens length, making it difficult to arrange the structural components in space, and the stacking of structures is prone to interference problems.

[0047] To solve this problem, in the embodiments of this application, a reflective element is provided between the third lens group G3 and the second lens group G2, and the light emitted from the third lens group G3 is deflected and guided by the reflective element to be emitted from the second lens group L2 and the first lens group G1.

[0048] By using reflective elements, the optical path structure of the lens can be altered, creating a folding structure, such as an L-shaped folding architecture. In this way, light emitted from the third lens group G3 can be folded and guided by the reflective elements to the second lens group L2 and the first lens group G1 for emission. This folding design solves spatial arrangement problems while maintaining the same back focal length and design performance requirements, making the structure more flexible and allowing for more diverse projection directions.

[0049] The projection lens in this embodiment satisfies: BFL / TTL > 0.2, where BFL is the back focal length of the projection lens and TTL is the total length of the projection lens.

[0050] The projection lens satisfies BFL / TTL > 0.2. Since the projection ratio range of the projection lens in this embodiment is larger and more lenses are used, the total length will increase. This makes the ratio of back focal length to total lens length smaller and greater than 0.2, which is a feature of this lens structure. However, through the lens folding design, the space occupied can be reduced and the problem of the lens being too long in the axial direction can be avoided.

[0051] In addition, the projection lens may also satisfy at least one of the following:

[0052] The projection ratio of the projection lens is continuously variable between 1.3 and 2.1; when the projection ratio is 1.3, TTL / EFL ≥ 20; when the projection ratio is 2.1, TTL / EFL ≤ 18; where TTL is the total length of the projection lens and EFL is the effective focal length of the projection lens.

[0053] The zoom ratio of the projection lens is greater than 1.5;

[0054] In the projection lens, there are 1-3 lenses with positive optical power and an Abbe number greater than 80;

[0055] The projection lens includes cemented triplet lenses and cemented doublet lenses. The number of cemented triplet lenses is 'a' and the number of cemented doublet lenses is 'b', where 1 < a < 4 and 2 < b < 5.

[0056] The aforementioned throw ratio reflects the range of focal length that the projection lens can achieve. A larger throw ratio means that, with a fixed total lens length, a shorter focal length results in a larger TTL / EFL. A throw ratio of 1.3 indicates a wide-angle, short-focal-length projection. Figure 1 When the projection ratio is 2.1, it is in a telecentric telephoto state, such as... Figure 2With a fixed total length, the longer the focal length, the smaller the TTL / EFL. By utilizing this projection ratio and the effective focal length to lens ratio range, continuous zoom with a large zoom ratio can be achieved. A projection lens with a zoom ratio greater than 1.5 requires a larger back focal length, resulting in a longer and more difficult-to-control lens length. However, a folding design can solve the problem of excessive axial space occupation while also achieving a larger zoom ratio and better projection effect. Lenses with positive optical power and an Abbe number greater than 80 point to a type of material characterized by a negative temperature coefficient of refractive index (dn / dt), while most materials have a positive dn / dt. For materials with negative dn / dt, the focal length increases with temperature, while for materials with positive dn / dt, the focal length decreases. Because there is more material with positive dn / dt in the system, thermal defocusing is more likely to occur. Thermal defocusing often manifests as a decrease in the system's focal length, shifting the optimal imaging plane forward. Therefore, it is necessary to add material with negative dn / dt to compensate for thermal defocusing. However, to maintain system thermal defocusing balance, too much material with negative dn / dt should be added; 1-3 elements are recommended. This helps to solve the thermal defocusing problem present in long back focal length structures. Meanwhile, the projection lens includes cemented triplet lenses and cemented doublet lenses. Cemented triplet lenses and cemented doublet lenses are formed by cementing two or three adjacent lenses together. This allows the use of different materials, refractive indices, and / or positive and negative combinations between different lenses to compensate for the dispersion of various materials, thereby reducing the overall chromatic aberration. Furthermore, reasonable material refractive indices and positive and negative combinations can also help improve aberrations such as spherical aberration and coma of the system. Therefore, cemented lenses can improve the optical performance of the system to a certain extent compared to single lenses. Since the projection lens has a larger zoom ratio and a longer total lens length, the number of cemented doublet lenses and cemented triplet lenses needs to be greater, preferably 1 < a < 4, 2 < b < 5.

[0057] Through the above technical solution, three lens groups used for focusing, zooming, and fixing can form a lens structure with a long back focal length. The long back focal length lens structure can achieve higher brightness and contrast, and is also more conducive to heat dissipation. On this basis, continuous zoom can be achieved by using zoom lens group 1 G21, zoom lens group 2 G22, and zoom lens group 3 G23, which move independently along the optical axis. At the same time, when the long back focal length or lens length is fixed, by designing aspects such as back focal length control, lens materials, and / or lens bonding, the problems of chromatic aberration and light correction difficulties caused by the long back focal length lens structure can be solved, thereby improving contrast and brightness. This is conducive to achieving the goals of long back focal length, high brightness, low chromatic aberration, low distortion, large aperture, and high image quality of the projection lens. Moreover, by setting a reflective element between the third lens group G3 and the second lens group G2, the lens structure can form an L-shaped folding architecture. On the one hand, it can avoid structural limitations, reduce the space occupied in the axis, and give more room for structural design. On the other hand, the folding design can make a rotating mechanism at the reflective element to realize multi-directional projection, and the projection direction selection is more flexible and diverse.

[0058] In one embodiment, the reflective element, the second lens group G2, and the first lens group G1 are rotatable relative to the third lens group G3 to project in different directions.

[0059] In this way, under the folding structure with the reflective element as the dividing line, the reflective element, the second lens group G2 and the first lens group G1 rotate as a whole or as a module relative to the third lens group G3, and projection in different directions can be achieved by rotating.

[0060] Based on this, in order to achieve rotational drive of the projection direction, a rotation mechanism can also be set up. The rotation mechanism drives the module, which consists of the reflective element, the second lens group G2, and the first lens group G1 as a whole, to rotate relative to the third lens group G3. For example, the housing of the projection lens can be divided into housing one, which is equipped with the reflective element, the second lens group G2, and the first lens group G1, and housing two, which is equipped with the third lens group G3. Housing one is perpendicular to housing two and can rotate relative to each other. A rotation mechanism is set on the outside. The rotation mechanism is driven by a motor, and the motor achieves rotational drive through gear meshing with gears set outside housing one. In this way, the projection direction can be selected according to the needs, which is more convenient.

[0061] Furthermore, the focal lengths of the first lens group G1, zoom lens group one G21, zoom lens group two G22, zoom lens group three G23, and the third lens group G3 are related to the focal length of the projection lens as follows:

[0062] -2.5 <EFL1 / EFL<-1;

[0063] 3 <EFL2 / EFL<8;

[0064] 5 <EFL3 / EFL<12;

[0065] 13 <EFL4 / EFL<27;

[0066] 2 <EFL5 / EFL<7;

[0067] Wherein, EFL1 is the focal length of the first lens group G1, EFL2 is the focal length of the zoom lens group one G21, EFL3 is the focal length of the zoom lens group two G22, EFL4 is the focal length of the zoom lens group three G23, EFL5 is the focal length of the third lens group G3, and EFL is the focal length of the projection lens.

[0068] The focal length ratios of the aforementioned groups reflect the overall focal length distribution of the projection lens system. This focal length distribution allows for a smaller overall length, better system aberration correction, and superior imaging quality while maintaining a long back focal length. In essence, the entire projection lens is divided into five zoom groups: Zoom1 is the front focusing group, i.e., the first lens group G1, which achieves clear imaging at the screen end at a given projection distance; Zoom2 / ZOOM3 / ZOOM4 together form the zoom group, namely zoom lens group one G21, zoom lens group two G22, and zoom lens group three G23, respectively, enabling different image sizes at the same object distance; Zoom5 forms the rear fixed group, i.e., the third lens group G3, which can refract light through reflective elements and further compensate for aberrations in the entire system.

[0069] In the first embodiment of this application, the projection lens is a lens architecture one, and the first lens group G1 includes a first lens L1 with negative optical power, a second lens L2 with negative optical power, a third lens L3 with positive optical power and a fourth lens L4 with negative optical power, arranged from the magnification side to the reduction side.

[0070] The second lens group G2 includes, from the magnification side to the reduction side, a fifth lens L5 with positive optical power, a sixth lens L6 with negative optical power, a seventh lens L7 with positive optical power, an eighth lens L8 with positive optical power, a ninth lens L9 with negative optical power, a tenth lens L10 with positive optical power, an aperture stop, an eleventh lens L11 with negative optical power, a twelfth lens L12 with negative optical power, a thirteenth lens L13 with positive optical power, a fourteenth lens L14 with negative optical power, and a fifteenth lens L15 with positive optical power. Among them, the fifth lens L5 constitutes zoom lens group one G21, the sixth lens L6, the seventh lens L7, and the eighth lens L8 constitute zoom lens group two G22, and the ninth lens L9, the tenth lens L10, the aperture stop, the eleventh lens L11, the twelfth lens L12, the thirteenth lens L13, the fourteenth lens L14, and the fifteenth lens L15 constitute zoom lens group three G23.

[0071] The third lens group G3 includes a sixteenth lens L16 with negative optical power, a seventeenth lens L17 with positive optical power, and an eighteenth lens L18 with positive optical power, arranged from the magnification side to the reduction side.

[0072] By configuring the positive and negative lenses of each group as described above, in a lens architecture with a long back focal length, the focusing function of the first lens group G1, the zooming function of the second lens group G2, and the fixed group function of the third lens group G3 can be achieved. This enables the projection of a large-size image, ensuring a larger projection ratio and a long back focal length, while guaranteeing image quality and low distortion.

[0073] Based on this, the first lens group G1 includes at least one cemented lens group formed by cementing together two or three adjacent lenses; the zoom lens group G23 includes at least one cemented lens group formed by cementing together two or three adjacent lenses; and the third lens group G3 includes a cemented lens group formed by cementing together two or three adjacent lenses. By cementing together double or triplet lens groups in each lens group, the overall chromatic aberration of the entire projection lens can be reduced more evenly, aberrations such as spherical aberration and coma can be improved, and the optical performance of the system can be further enhanced to a certain extent.

[0074] In the specific implementation process, in the above-mentioned lens structure one, the second lens L2, the third lens L3, and the fourth lens L4 are cemented together to form a cemented triplet lens one, and the refractive index of the second lens L2 is less than that of the third lens L3 and the fourth lens L4; the ninth lens L9 and the tenth lens L10 are cemented together to form a cemented doublet lens one; the twelfth lens L12, the thirteenth lens L13, and the fourteenth lens L14 are cemented together to form a cemented triplet lens two, and the refractive index of the thirteenth lens L13 is less than that of the twelfth lens L12 and the fourteenth lens L14; the sixteenth lens L16 and the seventeenth lens L17 are cemented together to form a cemented doublet lens two, and the refractive index of the sixteenth lens L16 is greater than that of the seventeenth lens L17. In the first lens group G1, a cemented triplet lens is formed by cementing the second lens L2, the third lens L3, and the fourth lens L4, creating a negative-positive-negative combination. Furthermore, by using a low-refractive-index second lens L2, a high-refractive-index second lens L2, and a high-refractive-index third lens L3 (i.e., a low-refractive-index, high-refractive-index, and high-refractive-index combination), a lens combination more conducive to reducing chromatic aberration can be formed. In the second lens group G2, a cemented doublet lens is formed by cementing the ninth lens L9 and the tenth lens L10, creating a lens group with a negative-positive combination and a high-refractive-index, high-refractive-index combination. In addition, a cemented triplet lens is formed by cementing the twelfth lens L12, the thirteenth lens L13, and the fourteenth lens L14 together. This cemented triplet lens is a combination of negative and positive lenses, with high refractive index and low refractive index, and high refractive index. This combination of two cemented lenses in the second lens group G2 can better reduce chromatic aberration during zooming. In the third lens group G3, a cemented doublet lens is formed by cementing the sixteenth lens L16 and the seventeenth lens L17 together. This cemented doublet lens is a combination of negative and positive lenses, with high refractive index and low refractive index, and can correct chromatic aberration in the third lens group G3. Therefore, the cemented lenses with the above combination can better correct the overall chromatic aberration of the projection lens, and further achieve better optical performance in a long back focal length architecture.

[0075] It is understandable that a refractive index above 1.7 is generally considered to be a high refractive index, while a refractive index below 1.7 is considered a low refractive index. However, in other lens architectures, it is not ruled out that 1.6 may be used as a threshold, and the configuration can be selected according to the actual situation or needs.

[0076] In one embodiment, the first lens L1 is a meniscus aspherical lens.

[0077] In this way, aberrations and system distortions can be effectively corrected by using a meniscus aspherical lens on the magnifying side.

[0078] Specifically, the meniscus aspherical lens can be a meniscus negative power resin aspherical lens.

[0079] To further improve image quality, the projection lens further includes at least two lenses with a refractive index greater than 1.8 in the lens on the aperture reduction side. By using two or more lenses with a refractive index greater than 1.8, light can be focused or dispersed more effectively, thereby improving image quality.

[0080] Specifically, lenses with a refractive index greater than 1.8 are positive lenses.

[0081] Meanwhile, the projection lens on the narrowing side of the aperture includes 1 to 4 lenses with positive optical power. The material used to manufacture these lenses satisfies dn / dt < 0, where dn / dt represents the derivative of the refractive index n with respect to temperature t. Since the lenses on the narrowing side of the aperture are closer to the illumination part, using positive lenses made of a material with negative dn / dt can effectively provide temperature compensation, ensuring that the image quality is not significantly affected within a certain temperature range.

[0082] Specifically, in the third lens group G3, the last lens is a positive lens. Positive lenses facilitate the convergence of light spots and also help to narrow the principal ray angle, resulting in a smaller ray angle, better coordination with the illumination section, and higher light source efficiency.

[0083] Preferably, the first lens L1 is a meniscus negative power aspherical lens, the second lens L2 is a biconcave lens, the third lens L3 is a biconvex lens, the fourth lens L4 is a biconcave lens, the fifth lens L5 is a biconvex lens, the sixth lens L6 is a biconcave lens, the seventh lens L7 is a biconvex lens, the eighth lens L8 is a biconvex lens, the ninth lens L9 is a biconcave lens, the tenth lens L10 is a biconvex lens, the eleventh lens L11 is a biconcave lens, the twelfth lens L12 is a meniscus lens convex towards the magnification side, the thirteenth lens L13 is a biconvex lens, the fourteenth lens L14 is a meniscus lens convex towards the reduction side, the fifteenth lens L15 is a biconvex lens, the sixteenth lens L16 is a meniscus lens convex towards the reduction side, the seventeenth lens L17 is a biconvex lens, and the eighteenth lens L18 is a biconvex lens.

[0084] The thirteenth lens is a lens with a positive optical power and an Abbe number greater than 80.

[0085] In the embodiments of this application, the ratio of the back focal length to the effective focal length of the projection lens satisfies BFL / EFL≧3, where BFL is the back focal length of the projection lens and EFL is the effective focal length of the projection lens.

[0086] With a long back focal length lens architecture, the projection lens can simultaneously satisfy BFL / EFL≧3. That is, the back focal length is not increased by increasing the focal length. At a certain focal length, the above lens structure can make the projection lens have a longer back focal length, and higher brightness and contrast can be obtained through the long back focal length.

[0087] In one embodiment, the projection lens is applied to a projection device, which may further include an illumination section, a beam-splitting device (also known as a PBS), an LCOS liquid crystal module, a prism, and a TSP galvanometer. The beam-splitting device and the LCOS liquid crystal module are disposed in the outgoing light path of the illumination section. The image light modulated by the LCOS liquid crystal module passes through the beam-splitting device, the prism, and the TSP galvanometer and enters the projection lens from the narrowed side of the projection lens.

[0088] During projection, light enters the projection lens group from the reduced side, i.e., the LCOS image plane side, through the PBS, prism, and galvanometer, and finally exits the projection lens to project onto the projection surface, thus obtaining the projection imaging effect.

[0089] In this embodiment, the LCOS liquid crystal module includes an LCOS chip with a physical resolution of 1181p / mm.

[0090] In addition, in order to cooperate with the focusing drive, zoom drive and jitter drive of the projection lens, the projection lens may also include a drive motor 1 for focusing drive of the first lens group G1, a drive motor 2 for zoom drive of the second lens group G2, and a drive motor 3 connected to the TSP galvanometer to drive the jitter of the TSP galvanometer.

[0091] In practice, the LCOS chip is offset to ensure that the projected image is tilted upwards during projection, so that the projected beam is higher than the projection lens and the projected image is not obstructed by the lens. The overall lens aperture is small, with all lenses having a diameter of less than 42mm.

[0092] In summary, the principle by which a projection lens in this application can improve brightness is that: Fno = effective focal length of the lens / aperture diameter. When the focal length of the lens remains unchanged, the larger the aperture diameter, the larger the light passage, and the more light can be received, so the higher the brightness.

[0093] This application provides a zoom projection lens with an aperture of F2.5, distortion less than 0.5%, and a back focal length to effective focal length ratio (BFL / EFL) ≥ 3. This lens has a precise structure, enabling a low-cost, compact design. The projection lens creates a continuous diagonal image variation of 78 to 126 inches at a position of 2390mm. 2390mm corresponds to the projection distance of a 126-inch image at a throw ratio of 1.3, which can be understood as the distance between the lens and the projection screen. The continuous diagonal image variation of 78 to 126 inches is achieved through continuous zooming of the lens at throw ratios of 1.3 to 2.1. This application is based on the principle of optical imaging. It uses optical design software to repeatedly optimize the curvature radius, material, thickness, air gap of each lens in the projection lens, as well as one plastic aspherical lens, one glass molded aspherical lens, and four cemented lenses. The goal is to achieve small aberrations, high resolution, long back focal length, small overall length, simple structure, ingenious design, high manufacturability, and easy mass production.

[0094] Moreover, by designing the projection lens as a folding L-shape, interference problems caused by structural stacking can be avoided. The folding L-shape design allows the lens to rotate and project in different directions according to actual usage needs.

[0095] The specific parameters of a projection lens for lens architecture 1 described above are shown in Table 1.

[0096] Table 1

[0097]

[0098]

[0099]

[0100] Among them, the first lens and the fifteenth lens are aspherical lenses, and the remaining lenses are spherical lenses. The aspherical polynomial formula is:

[0101]

[0102] In the formula, z represents the distance sag of the aspherical surface from the fixed point of the aspherical surface at a height r along the optical axis, c is the curvature corresponding to the radius, r is the radial height of the lens, k is the conic conic coefficient, and α1 to α8 are the aspherical coefficients corresponding to the second to sixteenth orders, respectively. The aspherical coefficients of the first lens and the fifteenth lens are shown in Table 2.

[0103] When the coefficient k is less than -1, the surface profile of the lens is a hyperbola;

[0104] When the coefficient k equals -1, the surface profile of the lens is a parabola;

[0105] When the k coefficient is between -1 and 0, the surface curve of the lens is an ellipse;

[0106] When the k coefficient is equal to 0, the surface curve of the lens is circular;

[0107] When the coefficient k is greater than 0, the surface shape curve of the lens is an oval.

[0108] Table 2

[0109] k <![CDATA[α2]]> <![CDATA[α3]]> <![CDATA[α4]]> <![CDATA[α5]]> <![CDATA[α6]]> <![CDATA[α7]]> <![CDATA[α8]]> S1 0 5.71E-05 -4.66E-07 3.09E-09 -1.52E-11 5.26E-14 -1.21E-16 1.78E-19 S2 0 5.95E-05 -4.14E-07 1.08E-09 1.57E-11 -2.19E-13 1.29E-15 -4.07E-18 S25 0 3.84E-07 2.67E-08 -2.28E-10 4.68E-12 -8.25E-14 1.16E-15 -9.49E-18 S26 0 2.56E-06 -6.23E-10 6.07E-10 -1.42E-11 1.92E-13 -1.47E-15 6.09E-18

[0110] In Embodiment 1, the lens material of the projection lens is arranged as 1P17G, where P represents plastic and G represents glass.

[0111] Example 2

[0112] like Figure 3 and Figure 4 As shown, the main difference from Embodiment 1 is that the projection lens adopts Lens Architecture 2. The first lens group G1 includes 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, arranged from the magnification side to the reduction side. More specifically, the first lens L1 is a meniscus lens convex to the magnification side, the second lens L2 is a biconcave lens, and the third lens L3 is a meniscus lens convex to the magnification side. The second lens L2 and the third lens L3 are combined to form a cemented doublet lens group 1. The refractive index of the second lens L2 is lower than that of the third lens L3.

[0113] The zoom lens group G21 in the second lens group G2 includes a fourth lens L4 with positive optical power, a fifth lens L5 with negative optical power, and a sixth lens L6 with positive optical power, arranged from the magnification side to the reduction side. The fourth lens L4 is a biconvex lens, the fifth lens L5 is a biconcave lens, and the sixth lens L6 is a biconvex lens. The fourth lens L4 and the fifth lens L5 are combined to form a cemented doublet lens group two. Both the fourth lens L4 and the fifth lens L5 are made of high refractive index material. G22 includes a negative seventh lens L7, a positive eighth lens L8, and a positive ninth lens L9, arranged from the magnification side to the reduction side. The seventh lens L7 is a biconcave lens, the eighth lens L8 is a meniscus lens convex towards the reduction side, and the ninth lens L9 is a biconvex lens. G23 includes a negative tenth lens L10, a positive eleventh lens L11, an aperture stop, and a negative twelfth lens, arranged from the magnification side to the reduction side. Lens L12, the thirteenth lens with negative optical power L13, the fourteenth lens with positive optical power L14, the fifteenth lens with negative optical power L15, and the sixteenth lens with positive optical power L16. Among these, the tenth lens L10 is a biconcave lens, the eleventh lens L11 is a biconvex lens, the twelfth lens L12 is a meniscus lens convex towards the reduction side, the thirteenth lens L13 is a meniscus lens convex towards the magnification side, the fourteenth lens L14 is a biconvex lens, and the fifteenth lens L15 is a meniscus lens convex towards the reduction side. The moon lens, the sixteenth lens L16 is a biconvex lens, and the tenth lens L10 and the eleventh lens L11 are combined to form a cemented doublet lens group three. Both the tenth lens L10 and the eleventh lens L11 are made of high refractive index material. The thirteenth lens L13, the fourteenth lens L14 and the fifteenth lens L15 are combined to form a cemented triplet lens group one. The refractive index of the fourteenth lens L14 is lower than that of the thirteenth lens L13 and the fifteenth lens L15, thus forming a high-low-high refractive index combination structure.

[0114] The third lens group G3 includes a seventeenth lens L17 with negative optical power, an eighteenth lens L18 with positive optical power, and a nineteenth lens L19 with positive optical power. The seventeenth lens L17 is a biconcave lens, the eighteenth lens L18 is a biconvex lens, and the nineteenth lens L19 is a biconvex lens. The seventeenth lens L17 and the eighteenth lens L18 are combined to form a cemented doublet lens group four. The refractive index of the seventeenth lens L17 is higher than that of the eighteenth lens L18.

[0115] The fourteenth lens is a lens with a positive optical power and an Abbe number greater than 80.

[0116] The specific parameters of one type of projection lens in lens architecture two described above are shown in Table 3.

[0117] Table 3

[0118]

[0119]

[0120] Among them, the first lens and the sixteenth lens are aspherical lenses, and the remaining lenses are spherical lenses. The aspherical polynomial formula is:

[0121]

[0122] In the formula, z represents the distance sag of the aspherical surface from the fixed point of the aspherical surface at a height r along the optical axis, c is the curvature corresponding to the radius, r is the radial height of the lens, k is the conic conic coefficient, and α1 to α8 are the aspherical coefficients corresponding to the second to sixteenth orders, respectively. The aspherical coefficients of the first lens and the sixteenth lens are shown in Table 4.

[0123] When the coefficient k is less than -1, the surface profile of the lens is a hyperbola;

[0124] When the coefficient k equals -1, the surface profile of the lens is a parabola;

[0125] When the k coefficient is between -1 and 0, the surface curve of the lens is an ellipse;

[0126] When the k coefficient is equal to 0, the surface curve of the lens is circular;

[0127] When the coefficient k is greater than 0, the surface shape curve of the lens is an oval.

[0128] Table 4

[0129] k <![CDATA[α2]]> <![CDATA[α3]]> <![CDATA[α4]]> <![CDATA[α5]]> <![CDATA[α6]]> <![CDATA[α7]]> <![CDATA[α8]]> S1 0 8.20E-05 -8.84E-07 6.96E-09 -3.93E-11 1.55E-13 -4.13E-16 7.10E-19 S2 0 8.20E-05 -8.30E-07 4.35E-09 3.22E-12 -2.39E-13 1.79E-15 -6.70E-18 S27 0 -7.65E-08 1.20E-07 -3.32E-09 6.09E-11 -6.86E-13 5.02E-15 -2.39E-17 S28 0 1.44E-06 7.06E-08 -1.55E-09 2.04E-11 -1.22E-13 1.21E-16 2.00E-18

[0130] In Embodiment 2, the lens material of the projection lens is arranged as 1P18G, where P represents plastic and G represents glass.

[0131] The above are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be considered as limitations on the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims. For those skilled in the art, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A projection lens characterized in that, The projection lens comprises a first lens group, a second lens group and a third lens group arranged from the magnifying side to the reducing side, the first lens group is used for focusing and has negative optical power, the second lens group is a zoom group and has positive optical power, the third lens group is a fixed lens group and has positive optical power, the second lens group comprises zoom lens group one, zoom lens group two and zoom lens group three each independently movable along a first optical axis and arranged from the magnifying side to the reducing side, and a diaphragm is arranged in the zoom lens group three; A reflecting element is arranged between the third lens group and the second lens group, and light emitted from the third lens group is guided to the second lens group and the first lens group by the reflecting element; BFL / TTL>0.2, wherein BFL is the back focal length of the projection lens, and TTL is the total length of the projection lens; And / or, the projection lens further satisfies at least one of the following: The projection ratio of the projection lens is continuously variable between 1.3-2.1, TTL / EFL≥20 when the projection ratio is 1.3, and TTL / EFL≤18 when the projection ratio is 2.1, wherein TTL is the total length of the projection lens, and EFL is the effective focal length of the projection lens; The zoom ratio of the projection lens is greater than 1.5; Among the lenses of the projection lens, there are 1-3 lenses with positive optical power and an Abbe number greater than 80; The projection lens comprises three cemented lenses and double cemented lenses, the number of the three cemented lenses is a, and the number of the double cemented lenses is b, wherein 1 2. The projection lens of claim 1, wherein, The reflecting element, the second lens group and the first lens group can be rotated as a whole relative to the third lens group to project in different directions.

3. The projection lens of claim 1, wherein, The focal lengths of the first lens group, the zoom lens group one, the zoom lens group two, the zoom lens group three and the third lens group are related to the focal length of the projection lens as follows: -2.5<EFL1 / EFL<-1; 3<EFL2 / EFL<8; 5<EFL3 / EFL<12; 13<EFL4 / EFL<27; 2<EFL5 / EFL<7; Wherein EFL1 is the focal length of the first lens group, EFL2 is the focal length of the zoom lens group one, EFL3 is the focal length of the zoom lens group two, EFL4 is the focal length of the zoom lens group three, EFL5 is the focal length of the third lens group, and EFL is the focal length of the projection lens.

4. The projection lens of claim 1, wherein, The projection lens is lens architecture one, wherein the first lens group comprises a first lens with negative focal power, a second lens with negative focal power, a third lens with positive focal power and a fourth lens with negative focal power arranged from the magnification side to the reduction side; the second lens group comprises a fifth lens with positive focal power, a sixth lens with negative focal power, a seventh lens with positive focal power, an eighth lens with positive focal power, a ninth lens with negative focal power, a tenth lens with positive focal power, a diaphragm, an eleventh lens with negative focal power, a twelfth lens with negative focal power, a thirteenth lens with positive focal power, a fourteenth lens with negative focal power and a fifteenth lens with positive focal power arranged from the magnification side to the reduction side, wherein the fifth lens constitutes a first zoom lens group, the sixth lens, the seventh lens and the eighth lens constitute a second zoom lens group, and the ninth lens, the tenth lens, the diaphragm, the eleventh lens, the twelfth lens, the thirteenth lens, the fourteenth lens and the fifteenth lens constitute a third zoom lens group; the third lens group comprises a sixteenth lens with negative focal power, a seventeenth lens with positive focal power and an eighteenth lens with positive focal power arranged from the magnification side to the reduction side; Or, the projection lens is lens architecture two, wherein the first lens group comprises a first lens with negative focal power, a second lens with negative focal power and a third lens with positive focal power arranged from the magnification side to the reduction side; the first zoom lens group in the second lens group comprises a fourth lens with positive focal power, a fifth lens with negative focal power and a sixth lens with positive focal power arranged from the magnification side to the reduction side; the second zoom lens group comprises a seventh lens with negative focal power, an eighth lens with positive focal power and a ninth lens with positive focal power arranged from the magnification side to the reduction side; the third zoom lens group comprises a tenth lens with negative focal power, an eleventh lens with positive focal power, a diaphragm, a twelfth lens with negative focal power, a thirteenth lens with negative focal power, a fourteenth lens with positive focal power, a fifteenth lens with negative focal power, a sixteenth lens with positive focal power arranged from the magnification side to the reduction side; and the third lens group comprises a seventeenth lens with negative focal power, an eighteenth lens with positive focal power and a nineteenth lens with positive focal power.

5. A projection lens as claimed in claim 4, characterized in that At least one cemented lens group formed by cementing two or three adjacent lenses is arranged in the first lens group; At least one cemented lens group formed by cementing two or three adjacent lenses is arranged in the third zoom lens group; A cemented lens group formed by cementing two or three adjacent lenses is arranged in the third lens group.

6. The projection lens of claim 4, wherein, In the lens architecture one, the second lens, the third lens and the fourth lens are cemented to form a three-cemented lens one, the refractive index of the second lens is less than the refractive index of the third lens and the fourth lens; the ninth lens and the tenth lens are cemented to form a two-cemented lens one, the twelfth lens, the thirteenth lens and the fourteenth lens are cemented to form a three-cemented lens two, the refractive index of the thirteenth lens is less than the refractive index of the twelfth lens and the fourteenth lens; the sixteenth lens and the seventeenth lens are cemented to form a two-cemented lens two, the refractive index of the sixteenth lens is greater than the refractive index of the seventeenth lens; Or, in the lens architecture two, the second lens and the third lens are combined to form a two-cemented lens group one, the refractive index of the second lens is lower than the refractive index of the third lens; the fourth lens and the fifth lens are combined to form a two-cemented lens group two; the tenth lens and the eleventh lens are combined to form a two-cemented lens group three; the thirteenth lens, the fourteenth lens and the fifteenth lens are combined to form a three-cemented lens group one, the refractive index of the fourteenth lens is lower than the refractive index of the thirteenth lens and the fifteenth lens; The seventeenth lens and the eighteenth lens are combined to form a two-cemented lens group four, the refractive index of the seventeenth lens is higher than the refractive index of the eighteenth lens.

7. The projection lens of claim 4, wherein, The first lens is a meniscus aspherical lens.

8. The projection lens of claim 1, wherein, There are at least two lenses with a refractive index greater than 1.8 in the lenses on the aperture stop reducing side of the projection lens.

9. The projection lens of claim 1, wherein, The lenses on the aperture stop reducing side of the projection lens include 1-4 lenses with positive optical power, and the manufacturing material of the lenses satisfies dn / dt<0, wherein dn / dt represents the derivative of the refractive index n with respect to the temperature t.

10. The projection lens of claim 1, wherein, The ratio of the back focal length of the projection lens to the effective focal length satisfies BFL / EFL>3, wherein BFL is the back focal length of the projection lens, and EFL is the effective focal length of the projection lens.

Images