Projection lens

Abstract

The invention belongs to the 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 difficulty also increases accordingly. Market feedback indicates that zoom lenses, which can change the image size without moving the camera, are highly favored by the market.

[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 the optical axis arranged from the magnification side to the reduction side. The element closest to the magnification side in the zoom lens group three is an aperture stop.

[0007] The projection lens satisfies BFL / TTL≥0.3, where BFL is the back focal length of the projection lens and TTL is the total length of the projection lens.

[0008] The projection lens is a lens architecture one, wherein the first lens group includes 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 an eighth lens with positive optical power, a ninth lens with negative optical power and a tenth lens with positive optical power arranged from the magnification side to the reduction side; the third lens group includes a thirteenth lens with negative optical power and a fourteenth lens with positive optical power arranged from the magnification side to the reduction side; wherein the second lens and the third lens are cemented together to form a cemented doublet lens one; the eighth lens, the ninth lens and the tenth lens are cemented together to form a triplet lens one; and the thirteenth lens and the fourteenth lens are cemented together to form a cemented doublet lens two.

[0009] Alternatively, the projection lens can be a lens architecture two, wherein the first lens group includes a third lens with positive optical power, a fourth lens with negative optical power, and a fifth lens with positive optical power, arranged from the magnification side to the reduction side; the second lens group includes a ninth lens with negative optical power and a tenth lens with positive optical power, arranged from the magnification side to the reduction side; the third lens group includes a twelfth lens with negative optical power, a thirteenth lens with positive optical power, a fourteenth lens with negative optical power, a sixteenth lens with negative optical power, and a seventeenth lens with positive optical power, arranged from the magnification side to the reduction side; the third lens, the fourth lens, and the fifth lens are combined to form a cemented triplet lens group one; the ninth lens and the tenth lens are combined to form a cemented doublet lens group one; the twelfth lens, the thirteenth lens, and the fourteenth lens are combined to form a cemented triplet lens group two; and the sixteenth lens and the seventeenth lens are combined to form a cemented doublet lens group two.

[0010] In possible implementations, the projection lens contains 1-3 lenses with positive Abbe numbers greater than 80.

[0011] Alternatively, the projection ratio of the projection lens is continuously variable from 1.2 to 1.5; when the projection ratio is 1.2, TTL / EFL ≥ 18; when the projection ratio is 1.5, TTL / EFL ≤ 15; where TTL is the total length of the projection lens and EFL is the effective focal length of the projection lens.

[0012] In one possible implementation, within lens architecture one, the focal lengths of the first lens group, zoom lens group one, zoom lens group two, zoom lens group three, and third lens group are related to the focal length of the projection lens as follows:

[0013] -3 <EFL1 / EFL<-0.8;

[0014] 3 <EFL2 / EFL<7;

[0015] 4 <EFL3 / EFL<9;

[0016] 7 <EFL4 / EFL<15;

[0017] 2 <EFL5 / EFL<7;

[0018] Alternatively, in lens architecture two, the focal lengths of the first lens group, zoom lens group one, zoom lens group two, zoom lens group three, and third lens group are related to the focal length of the projection lens as follows: -3 <EFL1 / EFL<-0.8;

[0019] -5 <EFL2 / EFL<-3;

[0020] 2 <EFL3 / EFL<5;

[0021] 60 <EFL4 / EFL<85;

[0022] 2 <EFL5 / EFL<7;

[0023] 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.

[0024] In a possible implementation, the first lens group in the lens architecture one further includes a first lens with negative optical power disposed on the magnification side of the second lens, and a fourth lens with negative optical power and a fifth lens with positive optical power disposed on the reduction side of the third lens along the direction from magnification side to reduction side; the second lens group further includes a sixth lens with positive optical power disposed on the magnification side of the eighth lens, a seventh lens with positive optical power disposed on the magnification side of the eighth lens, and an eleventh lens with negative optical power and a twelfth lens with positive optical power disposed on the reduction side of the tenth lens along the direction from magnification side to reduction side, wherein the sixth lens constitutes zoom lens group one, the seventh lens constitutes zoom lens group two, and the eighth, ninth, tenth, eleventh, and twelfth lenses constitute zoom lens group three; the third lens group further includes a fifteenth lens with positive optical power disposed on the reduction side of the fourteenth lens.

[0025] Alternatively, the projection lens is a second lens architecture, wherein the first lens group further includes a first lens with negative optical power and a second lens with negative optical power, both disposed along the direction from the magnification side to the reduction side of the third lens; the second lens group further includes a sixth lens with negative optical power, a seventh lens with positive optical power, an eighth lens with positive optical power, and an aperture stop disposed along the direction from the magnification side to the reduction side of the ninth lens, wherein the sixth lens constitutes a zoom lens group one, the seventh and eighth lenses constitute a zoom lens group two, and the ninth, tenth lenses, and the aperture stop constitute a zoom lens group three; the third lens group further includes an eleventh lens with positive optical power disposed along the magnification side of the twelfth lens, a fifteenth lens with positive optical power disposed between the fourteenth and fifteenth lenses, and an eighteenth lens with positive optical power disposed along the reduction side of the seventeenth lens.

[0026] In one possible implementation, in the first lens architecture, the refractive index of the eighth and ninth lenses is higher than that of the tenth lens, and the refractive index of the thirteenth lens is higher than that of the fourteenth lens.

[0027] Alternatively, in the second lens architecture, the refractive index of the fourth lens is higher than that of the third and fifth lenses, the refractive index of the thirteenth lens is lower than that of the twelfth and fourteenth lenses, and the refractive index of the sixteenth lens is higher than that of the seventeenth lens.

[0028] In one possible implementation, the first lens is a meniscus aspherical lens.

[0029] In a possible implementation, the third lens group may have at least two lenses with a refractive index greater than 1.8.

[0030] In a possible implementation, the third lens group includes at least one positive lens with a refractive index greater than 1.8.

[0031] In a possible implementation, the projection lens includes 1 to 4 lenses with positive optical power in the lens on the aperture reduction side, and the material of the lens is used to satisfy 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≧4, 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. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the structure of a projection lens using a lens architecture in a wide-angle state.

[0036] Figure 2 This is a schematic diagram of the structure of a projection lens using a lens architecture in a telephoto state.

[0037] Figure 3 A schematic diagram of the structure of another projection lens using lens architecture two in the wide-angle state;

[0038] Figure 4 This is a schematic diagram of the structure of another projection lens using lens architecture two in the telephoto state.

[0039] In the diagram: L01 - Cemented doublet lens 1; L02 - Cemented triplet lens 1; L03 - Cemented doublet lens 2; 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; G1 - First lens group; G2 - Second lens group; G21 - Zoom lens group 1; G22 - Zoom lens group 2; G23 - Zoom lens group 3; G3 - Third lens group. Detailed Implementation

[0040] 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.

[0041] Please refer to Figure 1 and Figure 2As 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.

[0042] 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.

[0043] 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 optical axis from the magnification side to the reduction side. The element closest to the magnification side in the zoom lens group three G23 is the aperture stop.

[0044] 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, by placing the aperture stop closest to the magnification side, the size of the light beam passing through the lens can be limited or adjusted 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 done via the front group focusing mechanism. 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 achieved by adjusting the interval between the first lens group G1 and the second lens group G2.

[0045] In a lens structure based on a long back focal length, the projection lens satisfies BFL / TTL ≥ 0.3, where BFL is the back focal length of the projection lens and TTL is the total length of the projection lens. This ratio range allows for a long back focal length lens structure, which is also a design feature of the embodiments of this application. Under the same constraints, the longer the back focal length, the longer the distance in front of the imaging plane where no lens is involved in aberration correction, making it more difficult to correct system aberrations.

[0046] Therefore, to address the difficulty of aberration correction in lens structures with long back focal lengths, in the embodiments of this application, the projection lens further satisfies at least one of the following:

[0047] In the projection lens, there are 1-3 lenses with positive optical power and an Abbe number greater than 80.

[0048] 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 ≤ 3 and 2 ≤ b ≤ 4.

[0049] Among them, lenses with positive optical power and an Abbe number greater than 80 point to a type of material. This type of material is characterized by a negative temperature coefficient of refractive index (dn / dt), while most materials have a positive dn / dt. When the temperature of materials with negative dn / dt increases, the focal length of the lens will increase, and when the temperature of materials with positive dn / dt increases, the focal length of the lens will decrease. Because there are more materials with positive dn / dt in the system, thermal defocusing is likely to occur. Thermal defocusing is mostly manifested as a decrease in the system's focal length and the optimal imaging plane being in front. Therefore, it is necessary to add materials with negative dn / dt to compensate for the thermal defocusing of the system. However, for the sake of system thermal defocusing balance, too many materials with negative dn / dt should not be added. It is advisable to add 1-3 lenses, for example, adding 1-3 lenses with positive optical power and an Abbe number greater than 80 in the second lens group and / or the third lens group. This can help solve the thermal defocusing problem in long back focal length structures. Meanwhile, the projection lens includes cemented triplet lenses and cemented doublet lenses, which can be distributed in different lens groups. 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 in the system. Therefore, cemented lenses can improve the optical performance of the system to a certain extent compared to single lenses.

[0050] In one embodiment of this application, taking a lens architecture as an example, namely lens architecture one, the first lens group G1 includes 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. The second lens group G2 includes an eighth lens L8 with positive optical power, a ninth lens L9 with negative optical power and a tenth lens L10 with positive optical power arranged from the magnification side to the reduction side. The third lens group G3 includes a thirteenth lens L13 with negative optical power and a fourteenth lens L14 with positive optical power arranged from the magnification side to the reduction side. The second lens L2 and the third lens L3 are cemented together to form a cemented doublet lens one. The eighth lens L8, the ninth lens L9 and the tenth lens L10 are cemented together to form a triplet lens one. The thirteenth lens L13 and the fourteenth lens L14 are cemented together to form a cemented doublet lens two.

[0051] Chromatic aberration is mainly caused by the differences in dispersion and refractive index of light of different wavelengths in lens materials, causing light of different wavelengths to converge at different focal points. Chromatic aberration can be eliminated by combining cemented lenses. The principle is mainly through the cementation design of different lens materials, which allows the dispersion of the lenses to compensate for each other due to the different materials, thereby reducing the overall chromatic aberration. Furthermore, by designing cemented doublet or cemented triplet lenses in each lens group, the overall chromatic aberration of the entire projection lens can be reduced more evenly, and aberrations such as spherical aberration and coma can be improved, which can further enhance the optical performance of the system to a certain extent.

[0052] The above technical solution, using three lens groups for focusing, zooming, and fixing respectively, forms a lens structure with a long back focal length. This long back focal length lens structure can achieve higher brightness and contrast, and is also more conducive to heat dissipation. Based on this, continuous zoom can be achieved through 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, with a fixed back focal length or lens length, 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. Ultimately, this achieves the goal of a projection lens with a long back focal length, high brightness, low chromatic aberration, low distortion, large aperture, and high image quality.

[0053] In one embodiment, the projection ratio of the projection lens is continuously variable from 1.2 to 1.5;

[0054] When the projection ratio is 1.2, TTL / EFL ≥ 18; when the projection ratio is 1.5, TTL / EFL ≤ 15.

[0055] Where TTL is the total length of the projection lens and EFL is the effective focal length of the projection lens.

[0056] The throw ratio reflects the range of focal lengths achievable by the projection lens. With a fixed total lens length, a shorter focal length results in a higher TTL / EFL. A throw ratio of 1.2 indicates a wide-angle, short-focal-length projection. Figure 1 When the projection ratio is 1.5, it is in a telecentric telephoto state, such as... Figure 2 With a fixed total length, the longer the focal length, the smaller the TTL / EFL. By using this projection ratio and the effective focal length to lens ratio range, continuous zoom with a large zoom ratio can be achieved.

[0057] 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:

[0058] -3 <EFL1 / EFL<-0.8;

[0059] 3 <EFL2 / EFL<7;

[0060] 4 <EFL3 / EFL<9;

[0061] 7 <EFL4 / EFL<15;

[0062] 2 <EFL5 / EFL<7;

[0063] 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.

[0064] 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 under a given object 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; and Zoom5 forms the rear fixed group, i.e., the third lens group G3, which further compensates for aberrations in the entire system.

[0065] In one embodiment of this application, taking a lens architecture (i.e., lens architecture one) as an example, the first lens group G1 in the lens architecture one further includes a first lens L1 with negative optical power disposed on the magnification side of the second lens L2, and a fourth lens L4 with negative optical power and a fifth lens L5 with positive optical power disposed on the reduction side of the third lens L3 along the direction from magnification side to reduction side; the second lens group G2 further includes a sixth lens L6 with positive optical power disposed on the magnification side of the eighth lens L8 along the direction from magnification side to reduction side, a seventh lens L7 with positive optical power and a fifth lens L5 with negative optical power disposed on the magnification side of the eighth lens L8, and a fifth lens L5 with positive optical power disposed on the magnification side of the eighth lens L8 along the direction from magnification side to reduction side. Along the direction from the magnification side to the reduction side, an eleventh lens L11 with negative optical power and a twelfth lens L12 with positive optical power are disposed on the reduction side of the tenth lens L10. The sixth lens L6 constitutes zoom lens group one G21, the seventh lens L7 constitutes zoom lens group two G22, and the eighth lens L8, ninth lens L9, tenth lens L10, eleventh lens L11, and twelfth lens L12 constitute zoom lens group three G23. The third lens group G3 also includes a fifteenth lens L15 with positive optical power disposed on the reduction side of the fourteenth lens L14.

[0066] By configuring the positive and negative lenses of each group as described above, in a lens architecture with a long back focal length, it is possible to achieve 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. This enables the projection of a large-size image while ensuring image quality and low distortion.

[0067] In the specific implementation process, in the lens architecture described above, the refractive indices of the eighth lens L8 and the ninth lens L9 are higher than those of the tenth lens L10, and the refractive index of the thirteenth lens L13 is higher than that of the fourteenth lens L14. By using appropriate material refractive indices and a combination of positive and negative values, it is also helpful to improve aberrations such as spherical aberration and coma in the system. Therefore, cemented lenses can improve the optical performance of the system to a certain extent compared to single lenses.

[0068] In this architecture, the second lens L2 and the third lens L3 are cemented together to form a cemented doublet lens L01, the eighth lens L8, the ninth lens L9 and the tenth lens L10 are cemented together to form a cemented triplicate lens L02, the refractive index of the eighth lens L8 and the ninth lens L9 is higher than the refractive index of the tenth lens L10, and the thirteenth lens L13 and the fourteenth lens L14 are cemented together to form a cemented doublet lens L03, the refractive index of the thirteenth lens L13 is greater than the refractive index of the fourteenth lens L14. By cementing the second lens L2 and the third lens L3 to form a cemented doublet L01, a negative-positive paired cemented doublet L01 can be formed. Furthermore, by using the high-refractive-index second lens L2 and the third lens L3 (i.e., a high-refractive-index combination), a lens combination that is more conducive to reducing chromatic aberration can be formed. The eighth lens L8, the ninth lens L9, and the tenth lens L10 are also cemented to form a cemented triplet, creating a negative-positive-negative paired lens assembly with a high-refractive-index combination. This combination can better reduce chromatic aberration during zooming within the second lens group G2. Simultaneously, the thirteenth lens L13 and the fourteenth lens L14 are cemented to form a second cemented doublet L03. This second cemented doublet L03 is a negative-positive paired, high-refractive-index, low-refractive-index lens combination, which can correct chromatic aberration within the third lens group G3. Therefore, cemented lenses with the above-described combination can better correct the overall chromatic aberration of the projection lens, further achieving better optical performance in a long back focal length architecture.

[0069] 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.

[0070] In one embodiment, the first lens L1 may be a meniscus aspherical lens.

[0071] In this way, aberrations and system distortions can be effectively corrected by using a meniscus aspherical lens on the magnifying side.

[0072] Specifically, the meniscus aspherical lens can be a meniscus negative power resin aspherical lens.

[0073] To further improve image quality, the third lens group G3 further includes at least two lenses with a refractive index greater than 1.8. By employing two or more lenses with a refractive index greater than 1.8, light can be focused or dispersed more effectively, thereby improving image quality.

[0074] Furthermore, the third lens group G3 includes at least one positive lens with a refractive index greater than 1.8. This high-refractive-index positive lens facilitates light spot convergence and also helps to narrow the principal ray angle, resulting in a smaller ray angle, better coordination with the illumination section, and higher light source efficiency.

[0075] Meanwhile, the projection lens includes 1 to 4 lenses with positive optical power in the lens on the aperture reduction side. 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. Since the lens behind the aperture is closer to the illumination part, by using positive lenses made of a material with negative dn / dt, temperature compensation can be effectively provided, ensuring that the image quality is not significantly affected within a certain temperature range.

[0076] 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.

[0077] 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 meniscus lens convex towards the reduction side, the sixth lens L6 is a biconvex lens, the seventh lens L7 is a biconvex lens, the eighth lens L8 is a meniscus lens convex towards the reduction side, the ninth lens L9 is a biconcave lens, the tenth lens L10 is a biconvex lens, the eleventh lens L11 is a plano-concave lens, the twelfth lens L12 is a biconvex lens, the thirteenth lens L13 is a biconcave lens, the fourteenth lens L14 is a biconvex lens, and the fifteenth lens L15 is a biconvex lens.

[0078] Among them, the tenth lens L10 and the fourteenth lens L14 are lenses with positive optical power and an Abbe number greater than 80.

[0079] 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≧4, where BFL is the back focal length of the projection lens and EFL is the effective focal length of the projection lens.

[0080] With a long back focal length lens architecture, the projection lens can simultaneously satisfy BFL / EFL≧4. 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. The longer back focal length can obtain higher brightness and contrast. Thus, the total length of the lens can be reduced or even increased to obtain a longer back focal length.

[0081] 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.

[0082] During projection, light enters the projection lens group from the reduced side, i.e., the LCOS image plane side, through the PBS, prism, and TSP galvanometer, and finally exits the projection lens to project onto the projection surface, thus obtaining the projection imaging effect.

[0083] In this embodiment, the LCOS liquid crystal module includes an LCOS chip with a physical resolution of 1181p / mm.

[0084] 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 galvanometer to drive the galvanometer to jitter.

[0085] In practice, the LCOS chip is offset to ensure that the projected image is upwardly offset 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 30mm.

[0086] 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.

[0087] 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) ≥ 4. This lens has a precise structure, enabling a low-cost, compact design. The projection lens creates a continuous diagonal image range of 72-90 inches at a position of 2390mm. 2390mm corresponds to the projection distance of a 90-inch image at a throw ratio of 1.2, which can be understood as the distance between the lens and the projection screen. The continuous diagonal image range of 72-90 inches is achieved through continuous zooming of the lens at throw ratios of 1.5 to 1.2. This application is based on optical imaging principles. Optical design software is used to repeatedly optimize the curvature radius, material, thickness, and air gap of each lens element, as well as one plastic aspherical lens, one glass molded aspherical lens, and three cemented lenses. This achieves the goals of low aberration, high resolution, long back focal length, small overall length, simple structure, ingenious design, high manufacturability, and ease of mass production.

[0088] The specific parameters of one embodiment of the projection lens described above are shown in Table 1.

[0089] Table 1

[0090]

[0091]

[0092] Among them, the first lens and the twelfth lens are aspherical lenses, and the remaining lenses are spherical lenses. The aspherical polynomial formula is:

[0093]

[0094] 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 twelfth lens are shown in Table 2.

[0095] When the coefficient k is less than -1, the surface profile of the lens is a hyperbola;

[0096] When the coefficient k equals -1, the surface profile of the lens is a parabola;

[0097] When the k coefficient is between -1 and 0, the surface curve of the lens is an ellipse;

[0098] When the k coefficient is equal to 0, the surface curve of the lens is circular;

[0099] When the coefficient k is greater than 0, the surface shape curve of the lens is an oval.

[0100] Table 2

[0101] k <![CDATA[α2]]> <![CDATA[α3]]> <![CDATA[α4]]> <![CDATA[α5]]> <![CDATA[α6]]> <![CDATA[α7]]> <![CDATA[α8]]> S1 0 1.12E-04 -7.06E-07 4.81E-09 -2.94E-11 1.45E-13 -5.22E-16 1.26E-18 S2 0 1.03E-04 -6.91E-07 4.76E-09 -3.87E-11 2.82E-13 -1.58E-15 5.86E-18 S21 0 -2.40E-05 1.20E-07 -4.35E-09 1.34E-10 -2.62E-12 3.25E-14 -2.44E-16 S22 0 6.60E-06 4.25E-08 -1.22E-09 2.35E-11 -2.14E-13 1.42E-17 1.86E-17

[0102] In Embodiment 1, the lens material arrangement of the projection lens is 1P1GM13G, where P represents plastic, G represents glass, and GM represents aspherical.

[0103] Example 2

[0104] like Figure 3 and Figure 4 As shown, the main difference from Embodiment 1 is that the projection lens adopts a different lens architecture (i.e., 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, a third lens L3 with positive optical power, a fourth lens L4 with negative optical power, and a fifth lens L5 with positive optical power, arranged from the magnification side to the reduction side. The first lens L1 is a meniscus lens convex towards the magnification side, the second lens L2 is a biconcave lens, the third lens L3 is a biconvex lens, the fourth lens L4 is a biconcave lens, and the fifth lens L5 is a biconvex lens. The third lens L3, the fourth lens L4, and the fifth lens L5 are combined to form a three-cement lens group 1. The refractive index of the fourth lens L4 is higher than that of the third lens L3 and the fifth lens L5, forming a low-high-low refractive index combination structure.

[0105] The zoom lens group one G21 in the second lens group G2 includes a sixth lens L6 with negative optical power, which is a biconcave lens; the zoom lens group two G22 includes a seventh lens L7 and an eighth lens L8 with positive optical power, arranged from the magnification side to the reduction side, wherein the seventh lens L7 is a plano-convex lens and the eighth lens L8 is a biconvex lens; the zoom lens group three G23 includes a ninth lens L9 with negative optical power, a tenth lens L10 with positive optical power, and an aperture stop, arranged from the magnification side to the reduction side, wherein the ninth lens L9 is a biconcave lens and the tenth lens L10 is a biconvex lens, and the ninth lens L9 and the tenth lens L10 are combined to form a cemented doublet lens group one, and both the ninth lens L9 and the tenth lens L10 use low refractive index.

[0106] The third lens group G3 includes, from the magnification side to the reduction side, an eleventh lens L11 with positive 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, a fifteenth lens L15 with positive optical power, 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. The eleventh lens L11 is a meniscus lens convex towards the reduction side, the twelfth lens L12 is a biconcave lens, the thirteenth lens L13 is a biconvex lens, and the fourteenth lens L17... 14 is a meniscus lens convex towards the narrowing side. The fifteenth lens L15 is a biconvex lens, the sixteenth lens L16 is a biconcave lens, the seventeenth lens L17 is a biconvex lens, and the eighteenth lens L18 is a biconvex lens. Furthermore, the twelfth lens L12, the thirteenth lens L13, and the fourteenth lens L14 are combined to form a cemented doublet lens group two. The refractive index of the thirteenth lens L13 is lower than that of the twelfth lens L12 and the fourteenth lens L14. The sixteenth lens L16 and the seventeenth lens L17 are combined to form a cemented doublet lens group two. The refractive index of the sixteenth lens L16 is greater than that of the seventeenth lens L17.

[0107] In the lens architecture two described above, the thirteenth lens L13 is a lens with positive optical power and an Abbe number greater than 80.

[0108] 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:

[0109] -3 <EFL1 / EFL<-0.8;

[0110] -5 <EFL2 / EFL<-3;

[0111] 2 <EFL3 / EFL<5;

[0112] 60 <EFL4 / EFL<85;

[0113] 2 <EFL5 / EFL<7;

[0114] 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.

[0115] The specific parameters of a projection lens are shown in Table 3.

[0116] Table 3

[0117]

[0118]

[0119] The first lens is an aspherical lens, and the remaining lenses are spherical lenses. The aspherical polynomial formula is:

[0120]

[0121] 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 are shown in Table 4.

[0122] When the coefficient k is less than -1, the surface profile of the lens is a hyperbola;

[0123] When the coefficient k equals -1, the surface profile of the lens is a parabola;

[0124] When the k coefficient is between -1 and 0, the surface curve of the lens is an ellipse;

[0125] When the k coefficient is equal to 0, the surface curve of the lens is circular;

[0126] When the coefficient k is greater than 0, the surface shape curve of the lens is an oval.

[0127] Table 4

[0128] k <![CDATA[α2]]> <![CDATA[α3]]> <![CDATA[α4]]> <![CDATA[α5]]> <![CDATA[α6]]> <![CDATA[α7]]> <![CDATA[α8]]> S1 0 1.99E-04 -2.06E-06 2.40E-08 -2.36E-10 1.78E-12 -9.50E-15 3.37E-17 S2 0 1.25E-04 -7.21E-07 5.56E-09 -4.21E-11 2.77E-13 -1.68E-15 4.66E-18

[0129] In Embodiment 2, the lens material of the projection lens is arranged as 1P17G, where P represents plastic and G represents glass.

[0130] 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, and 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 the optical axis and arranged from the magnifying side to the reducing side, and the element closest to the magnifying side in the zoom lens group three is a diaphragm; The projection lens satisfies BFL / TTL≥0.3, wherein BFL is the back focal length of the projection lens, and TTL is the total length of the projection lens; The projection lens is lens architecture one, wherein the first lens group comprises a second lens with negative optical power and a third lens with positive optical power arranged from the magnifying side to the reducing side, the second lens group comprises an eighth lens with positive optical power, a ninth lens with negative optical power and a tenth lens with positive optical power arranged from the magnifying side to the reducing side, and the third lens group comprises a thirteenth lens with negative optical power and a fourteenth lens with positive optical power arranged from the magnifying side to the reducing side, wherein the second lens and the third lens are cemented to form a double-cemented lens one, the eighth lens, the ninth lens and the tenth lens are cemented to form a triple-cemented lens one, and the thirteenth lens and the fourteenth lens are cemented to form a double-cemented lens two; Or, the projection lens is lens architecture two, wherein the first lens group comprises a third lens with positive optical power, a fourth lens with negative optical power and a fifth lens with positive optical power arranged from the magnifying side to the reducing side, the second lens group comprises a ninth lens with negative optical power and a tenth lens with positive optical power arranged from the magnifying side to the reducing side, and the third lens group comprises a twelfth lens with negative optical power, a thirteenth lens with positive optical power, a fourteenth lens with negative optical power, a sixteenth lens with negative optical power and a seventeenth lens with positive optical power arranged from the magnifying side to the reducing side, the third lens, the fourth lens and the fifth lens are combined to form a triple-cemented lens group one, the ninth lens and the tenth lens are combined to form a double-cemented lens group one, the twelfth lens, the thirteenth lens and the fourteenth lens are combined to form a triple-cemented lens group two, and the sixteenth lens and the seventeenth lens are combined to form a double-cemented lens group two.

2. The projection lens of claim 1, wherein, In the lenses of the projection lens, there are 1-3 lenses with positive optical power and an Abbe number greater than 80; Or, the projection ratio of the projection lens is continuously variable at 1.2-1.5, TTL / EFL≥18 when the projection ratio is 1.2, and TTL / EFL≤15 when the projection ratio is 1.5, wherein TTL is the total length of the projection lens, and EFL is the effective focal length of the projection lens.

3. The projection lens of claim 1, wherein, In lens architecture one, 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: -3<EFL1 / EFL<-0.8; 3<EFL2 / EFL<7; 4<EFL3 / EFL<9; 7<EFL4 / EFL<15; 2<EFL5 / EFL<7; Or, in the second lens architecture, the focal lengths of the first lens group, the first zoom lens group, the second zoom lens group, the third zoom lens group and the third lens group are related to the focal length of the projection lens as follows: -3<EFL1 / EFL<-0.8; -5<EFL2 / EFL<-3; 2<EFL3 / EFL<5; 60<EFL4 / EFL<85; 2<EFL5 / EFL<7; 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.

4. The projection lens of claim 1, wherein, The first lens group in the first lens architecture further comprises a first lens with negative refractive power arranged on the magnification side of the second lens, and a fourth lens with negative refractive power, a fifth lens with positive refractive power, which are both arranged on the demagnification side of the third lens; the second lens group further comprises a sixth lens with positive refractive power, a seventh lens with positive refractive power, which are both arranged on the magnification side of the eighth lens, and an eleventh lens with negative refractive power, a twelfth lens with positive refractive power, which are both arranged on the demagnification side of the tenth lens, wherein the sixth lens constitutes the first zoom lens group, the seventh lens constitutes the second zoom lens group, and the eighth lens, the ninth lens, the tenth lens, the eleventh lens and the twelfth lens constitute the third zoom lens group; the third lens group further comprises a fifteenth lens with positive refractive power arranged on the demagnification side of the fourteenth lens. Or, the projection lens is a second lens architecture, wherein the first lens group further comprises a first lens with negative refractive power and a second lens with negative refractive power, which are both arranged on the magnification side of the third lens; the second lens group further comprises a sixth lens with negative refractive power, a seventh lens with positive refractive power, an eighth lens with positive refractive power, which are all arranged on the magnification side of the ninth lens, and a diaphragm arranged on the demagnification side of the tenth lens, wherein the sixth lens constitutes the first zoom lens group, the seventh lens and the eighth lens constitute the second zoom lens group, and the ninth lens, the tenth lens and the diaphragm constitute the third zoom lens group; the third lens group further comprises an eleventh lens with positive refractive power arranged on the magnification side of the twelfth lens, a fifteenth lens with positive refractive power arranged between the fourteenth lens and the fifteenth lens, and an eighteenth lens with positive refractive power arranged on the demagnification side of the seventeenth lens.

5. The projection lens of claim 1, wherein, In the first lens architecture, the refractive index of the eighth lens and the ninth lens is higher than that of the tenth lens, and the refractive index of the thirteenth lens is higher than that of the fourteenth lens; Or, in the second lens architecture, the refractive index of the fourth lens is higher than that of the third lens and the fifth lens, the refractive index of the thirteenth lens is lower than that of the twelfth lens and the fourteenth lens, and the refractive index of the sixteenth lens is higher than that of the seventeenth lens.

6. The projection lens of claim 4, wherein, The first lens is a meniscus aspheric lens.

7. The projection lens of claim 1, wherein, The third lens group has at least one lens with a refractive index greater than 1.

8.

8. The projection lens of claim 7, wherein, The third lens group has at least one positive lens with a refractive index greater than 1.

8.

9. The projection lens of claim 1, wherein, The projection lens comprises 1-4 lenses with positive refractive power in the lens on the side of the aperture stop, and the material of the lens 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>=4, wherein BFL is the back focal length of the projection lens, and EFL is the effective focal length of the projection lens.

Images