A projection lens

Abstract

This invention relates to the field of projection device technology, and more particularly to a projection lens, comprising a front lens group, an aperture, and a rear lens group arranged from the magnification side to the reduction side. Aspherical lenses are respectively disposed in the front and rear lens groups. The projection lens of this invention has a simple and compact structure, fewer lenses, small footprint, and light weight. It has a large clear imaging range, supports tilt-shift, is highly adaptable to various usage scenarios, ensures clear full-frame imaging, uniform screen illumination, and improves image quality.

Description

Technical Field

[0001] This invention relates to the field of projection device technology, and more particularly to a projection lens. Background Technology

[0002] Projectors are becoming increasingly widely used, and the projection lens is a core component, leading to ever-higher requirements for them. Current projectors typically use a fixed-direction projection method, meaning the projected image is fixed and cannot be adjusted horizontally or vertically relative to the projector. This means traditional projector lenses cannot be tilt-shifted, which limits their application scenarios. Tilt-shift lenses allow for a wider range of image movement and adjustment, flexibly meeting user needs. Tilt-shift lenses usually require large apertures and support for wide field-of-view imaging to ensure clear full-frame imaging and uniform illumination. This results in a complex structure with numerous lenses, leading to a large size, weight, and high cost for existing projector lenses. Summary of the Invention

[0003] The technical problem to be solved and the technical task proposed by the present invention is to improve the existing technology and provide a projection lens that solves the problems of complex structure, large number of lenses, large size, heavy weight and high cost of the projection lens in the current technology.

[0004] To solve the above technical problems, the technical solution of the present invention is as follows:

[0005] A projection lens includes a front lens group, an aperture, and a rear lens group arranged from the magnification side to the reduction side. The front lens group includes a negative diopter front lens 1, a negative diopter front subgroup, a positive diopter front lens 2, and a positive diopter front lens 3, all arranged from the magnification side to the reduction side. The rear lens group includes a negative diopter rear lens 1, a positive diopter rear lens 2, a negative diopter rear lens 3, a positive diopter rear lens 4, a positive diopter rear lens 5, and a positive diopter rear lens 6, all arranged from the magnification side to the reduction side. The projection lens of this invention has a simple and compact structure, fewer lenses, small footprint, and light weight. It has a large clear imaging range, supports tilt-shift, is highly adaptable to various usage scenarios, ensures clear full-frame imaging, uniform screen illumination, and improves image quality.

[0006] Furthermore, the front subgroup is composed of a single sub-lens or a combination of two sub-lens. This design is simple, compact, and space-saving, which is beneficial for lens structure design, easy to implement, and low in cost.

[0007] Furthermore, when the front subgroup consists of only a single sub-lens, the sub-lens is a biconcave negative lens, which has a simple structure, a small number of lenses, is easy to implement, and has a low cost.

[0008] Alternatively, the front subgroup may include a first sub-lens and a second sub-lens arranged from the magnification side to the reduction side. The first sub-lens is a biconcave negative lens, and the second sub-lens is a meniscus negative lens convex towards the magnification side. Combining the two sub-lenses forms the front subgroup, which flexibly meets the requirements and facilitates lens assembly.

[0009] Furthermore, the front lens group contains at least one aspherical lens, and the rear lens group contains at least one aspherical lens. The aspherical lenses in the front and rear lens groups satisfy the relationship -2 ≤ f_asp1 / f_asp2 ≤ 1.0, where f_asp1 is the focal length of the aspherical lens in the front lens group, and f_asp2 is the focal length of the aspherical lens in the rear lens group. By reasonably optimizing the aspherical coefficient, the aspherical lens in the front lens group can be used to improve the field of view of the system, effectively correct off-axis aberrations and system distortion, and the aspherical lens in the rear lens group can be used to correct spherical aberration and field curvature of the system, thereby improving the optical MTF performance of the lens.

[0010] Furthermore, the first front lens is a meniscus aspherical lens convex towards the magnification side, and the fifth rear lens is a biconvex aspherical lens. Both sides of the first front lens are even-order aspherical surfaces. By reasonably optimizing the aspherical coefficient, system distortion and off-axis aberrations are effectively corrected. The biconvex aspherical lens used in the fifth rear lens is made of glass, which improves the molding processability and component precision of the aspherical element, and also makes it more suitable for mass production and reduces costs. The fifth rear lens is located at the position of the principle aperture, and the outer diameter of the fifth rear lens can be reduced and controlled, reducing the sensitivity to the aspherical element itself, and allowing for a more relaxed processing specification for the aspherical surface, thus reducing costs.

[0011] Furthermore, the second front lens is an aspherical lens, with both sides of the second front lens being even-order aspherical surfaces. By optimizing the aspherical coefficient, the system distortion and off-axis aberrations can be better corrected.

[0012] Furthermore, the first rear lens element can be a biconcave lens or a meniscus lens convex towards the magnification side. When the first rear lens element is a meniscus lens convex towards the magnification side, the back focal length of the lens is small.

[0013] Furthermore, the second, third, and fourth rear lenses are connected to form a cemented triplet lens. The refractive indices of the second and fourth rear lenses are lower than that of the third rear lens. The second and fourth rear lenses are made of materials with a negative Dn / Dt ratio, where Dn / Dt represents the trend of refractive index change with temperature. The cemented triplet lens uses a combination of high and low refractive indices to effectively correct system chromatic aberration. The lens also features a positive-negative-positive diopter configuration. The second and fourth rear lenses use low refractive indices, and their refractive indices decrease with increasing temperature for thermal compensation.

[0014] Furthermore, the focal length of the front lens group satisfies 10 mm ≤ f1 ≤ 50 mm, the focal length of the front sub-group satisfies -50 mm ≤ f1a ≤ -10 mm, and the focal length of the rear lens group satisfies 10 mm ≤ f2 ≤ 100 mm. This enables the lens to have a short effective focal length, a small projection ratio for short-distance projection, and achieve a low-cost, small-size compact lens.

[0015] Furthermore, the effective focal length satisfies 2.5 mm ≤ EFL ≤ 5.5 mm, the relative aperture F-number satisfies 1.5 ≤ FNO ≤ 3.0, the projection ratio satisfies 0.6 ≤ TR ≤ 0.7, and the imaging image circle diameter satisfies 0 ≤ φ ≤ 15.605 mm.

[0016] Furthermore, the ratio of the total lens length to the focal length satisfies 20 ≤ TTL / EFL ≤ 30, the ratio of the back focal length to the effective focal length satisfies 3.5 ≤ BFL / EFL ≤ 4.5, the telecentric angle satisfies TA ≤ 1.14°, the total lens length TTL ≤ 118.4 mm, the system field angle FOV ≥ 100.7°, the aperture is set at the focal position of the rear lens group, the front air spacing of the aperture satisfies 5 mm < T1 < 28 mm, and the lens is adapted to a spectral range of 450 - 650 nm.

[0017] Compared with the prior art, the advantages of the present invention are as follows:

[0018] The projection lens described in the present invention has a simple and compact structure, few lens elements, small occupied volume, light weight, is easy to implement and mass-produce, has a low cost, small system distortion, small aberration, high resolution, has a large clear imaging range, supports shift, for a 0.23-inch DMD, the longitudinal shift range supported is -200% to +200%, the focusing distance range is 0.5 - 3.5 m, has strong adaptability to the use scenario, ensures clear imaging of the full frame, uniform picture illumination, and improves the imaging quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic structural diagram of a projection lens according to Embodiment 1 of the present invention;

[0020] Figure 2 It is a schematic structural diagram of a projection lens according to Embodiment 2 of the present invention;

[0021] Figure 3 It is a schematic structural diagram of a projection lens according to Embodiment 3 of the present invention;

[0022] Figure 4 It is a schematic structural diagram of a projection lens according to Embodiment 4 of the present invention.

[0023] In the figure:

[0024] Front lens group G1, aperture 10, rear lens group G2, front lens 1 11, front subgroup G11, sub-lens 1 111, sub-lens 2 112, front lens 2 12, front lens 3 13, rear lens 1 21, rear lens 2 22, rear lens 3 23, rear lens 4 24, rear lens 5 25, rear lens 6 26, galvanometer 2, prism 3, DMD chip 4. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0026] The projection lens disclosed in this invention has a small number of lenses, a compact structure, a small footprint, light weight, and low cost, while ensuring good imaging effect, having a large clear imaging range, supporting a wide range of tilt shift, and being highly adaptable to various usage scenarios.

[0027] Example 1

[0028] like Figure 1 As shown, a projection lens mainly includes a front lens group G1, an aperture 10, and a rear lens group G2 arranged sequentially from the magnification side to the reduction side. The front lens group G1 includes a front lens 11 with negative refractive power, a front subgroup G11 with negative refractive power, a front lens 2 12 with positive refractive power, and a front lens 3 13 with positive refractive power, arranged sequentially from the magnification side to the reduction side. The rear lens group G2 includes a rear lens 21 with negative refractive power, a rear lens 2 22 with positive refractive power, a rear lens 3 23 with negative refractive power, a rear lens 4 24 with positive refractive power, a rear lens 5 25 with positive refractive power, and a rear lens 6 26 with positive refractive power, arranged sequentially from the magnification side to the reduction side.

[0029] In this embodiment, at least one aspherical lens is provided in the front lens group G1, and at least one aspherical lens is provided in the rear lens group G2. The focal length range of the aspherical lens in the front lens group G1 is -50mm≤f_asp1≤-10mm, and the focal length range of the aspherical lens in the rear lens group G2 is -100mm≤f_asp2≤100mm. Furthermore, the aspherical lens in the front lens group G1 and the aspherical lens in the rear lens group G2 satisfy the relationship -2≤f_asp1 / f_asp2≤1.0. Further, the focal length of the front lens group G1 is 10mm≤f1≤50mm, the focal length of the front subgroup G11 is -50mm≤f1a≤-10mm, and the focal length of the rear lens group G2 is 10mm≤f2≤100mm. This achieves short-distance wide-angle projection, low chromatic aberration, low distortion, large aperture 10, low cost, and high imaging quality.

[0030] Specifically, the front lens 11 is a meniscus aspherical negative lens convex to the magnification side, made of resin. The radius of curvature of the magnification side surface of the front lens 11 is 50mm to 150mm, and the radius of curvature of the reduction side surface is 7mm to 15mm. Both the magnification side surface and the reduction side surface are even-order aspherical. The aspherical lens in the front lens group G1 can be used to improve the field of view of the system. By reasonably optimizing the aspherical coefficient, the distortion and off-axis aberration of the system can be effectively corrected.

[0031] In this embodiment, the front subgroup G11 is composed of two sub-lenses, specifically including sub-lens 111 and sub-lens 112 arranged from the magnification side to the reduction side. Sub-lens 111 is a biconcave negative lens, and sub-lens 112 is a meniscus negative lens convex towards the magnification side. The structure is simple, the number of lenses is small, it is easy to implement, low in cost, and facilitates lens assembly. The radius of curvature of the magnification side surface of sub-lens 111 is -80mm to -30mm, and the radius of curvature of the reduction side surface of sub-lens 111 is 15mm to 40mm. The radius of curvature of the magnification side surface of sub-lens 112 is 40mm to 100mm, and the radius of curvature of the reduction side surface is 15mm to 50mm.

[0032] The second front lens 12 is a plano-convex positive lens, with a flat surface on the magnifying side and a radius of curvature of -50mm to -20mm on the reducing side.

[0033] The third front lens 13 is a convex-concave positive lens, with a radius of curvature of 20mm to 50mm on the magnifying side surface and a radius of curvature of 200mm to 400mm on the reducing side surface. The second and third front lenses 12 and 13 together serve to gather light and reduce the aperture.

[0034] The aperture 10 is adjustable in size and can be continuously adjusted to meet the application needs of different scenarios. When high brightness is required, the aperture 10 can be adjusted to its maximum size. When using in a darker environment and wanting less brightness, the aperture 10 can be appropriately reduced. The aperture 10 is located at the focal position of the rear lens group G2, and the air gap in front of the aperture 10 is 5mm. <T1<28mm。

[0035] The rear lens 21 is a meniscus negative lens convex to the magnification side, with a radius of curvature of 50mm to 200mm on the magnification side surface and a radius of curvature of 8mm to 30mm on the reduction side surface of L6.

[0036] The rear lens 22, rear lens 3, and rear lens 4 are connected to form a cemented triplet lens. The refractive index of the rear lens 22 and rear lens 4 is lower than that of the rear lens 3. The rear lens 22 and rear lens 4 are made of a material with a negative Dn / Dt ratio, where Dn / Dt represents the trend of refractive index change with temperature. The rear lens 22 is a biconvex positive lens with a radius of curvature of 10mm to 30mm on its magnifying side and -30mm to -5mm on its reducing side. The rear lens 3 is a biconcave negative lens with a radius of curvature of -30mm to -5mm on its magnifying side and 10mm to 30mm on its reducing side. The rear lens 4 is a biconvex positive lens with a radius of curvature of 10mm to 30mm on its magnifying side and -200mm to -50mm on its reducing side. The rear lens 22 and rear lens 4 24 in the cemented triplet lens are made of low refractive index, high Abbe number and negative dn / dt material, combined with the biconcave, high refractive index and low Abbe number material of the rear lens 3 23. This combination allows for achromatic design, ensuring minimal chromatic aberration in the entire optical system while also compensating for thermal aberration. This system is compatible with illumination bands of 450-660nm, with a shorter blue wavelength and a longer red wavelength. The cemented triplet lens effectively corrects chromatic aberration caused by the increased spectral bandwidth.

[0037] The rear lens five 25 is a biconvex positive aspherical lens. The radius of curvature of its magnifying side surface is 25 mm to 150 mm, and the radius of curvature of the side surface near the DMD reduction side of L10 is -30 mm to -10 mm. Both its magnifying side surface and reduction side surface are even aspherical surfaces. The biconvex aspherical lens used for the rear lens five 25 is made of glass material. The selected glass material for the rear lens five 25 has a refractive index in the range of 1.50 to 1.60 and an Abbe number in the range of 55 to 75. By designing appropriate curvatures, intervals, and aspherical parameters, the spherical aberration and field curvature of the system can be effectively corrected to improve the optical MTF performance of the lens. Moreover, the aspherical lens designed as a biconvex positive lens structure can improve the molding processability and component accuracy of the aspherical element, is more suitable for mass production, reduces costs. The rear lens five 25 is located at a position far from the aperture 10, and the outer diameter of the rear lens five 25 can be controlled to shrink, reducing the sensitivity to the aspherical element itself, appropriately relaxing the processing specifications for the aspherical surface, and reducing costs.

[0038] The rear lens six 26 is a biconvex lens with a positive diopter. The radius of curvature of its magnifying side surface is 50 mm to 150 mm, and the radius of curvature of the side surface near the DMD reduction side of L11 is -80 mm to -20 mm.

[0039] The projection lens described in this embodiment can effectively improve the chromatic aberration of the system and suppress the occurrence of system distortion by adopting the above lens structure. Under the design of the image circle target surface of 10.17 mm, the number of entire optical lenses used is less, the structure is simplified, the focal length is small, the field angle is large, the projection ratio is small, the aperture 10 diameter is large, the distortion is low, the cost is low, and high-performance MTF values can be ensured at high temperatures.

[0040] This embodiment provides a shiftable projection lens with a short focal length, a small projection ratio, a large field of view, and a large aperture, realizing short-distance wide-angle projection, low chromatic aberration, low distortion, a large aperture of aperture 10, low cost, and high imaging quality for the projection lens. Specifically, the effective focal length of the projection lens is 2.5 mm ≤ EFL ≤ 5.5 mm, the relative aperture number of aperture 10 is 1.5 ≤ FNO ≤ 3.0, Fno = effective focal length of the lens / diameter of aperture 10. When the focal length of the lens remains unchanged, the larger the diameter of aperture 10, the larger the light passing aperture, and the more light rays can be received, so the brightness is higher. The projection ratio is 0.6 ≤ TR ≤ 0.7, and the imaging image circle diameter is 0 ≤ φ ≤ 15.605 mm; the ratio of the total lens length to the focal length is 20 ≤ TTL / EFL ≤ 30, the ratio of the back focal length of the lens to the effective focal length is 3.5 ≤ BFL / EFL ≤ 4.5, the telecentric angle is TA ≤ 1.14°, the total lens length TTL ≤ 118.4 mm, the system field angle FOV ≥ 100.7°, the aperture is set at the focal position of the rear lens group, the front air spacing of aperture 10 is 5 mm < T1 < 28 mm, and the lens is adapted to a spectrum of 450 to 650 nm, with a relatively wider spectrum, a shorter blue wave, and a longer red wave.

[0041] Furthermore, the projection system using the aforementioned projection lens also includes a galvanometer 2, a prism 3, a protective glass, and a DMD chip 4, arranged sequentially along the magnification side to the reduction side on the reduction side of the rear lens 6 26. The physical resolution of the DMD chip 4 is 93 lp / mm. Light enters the projection lens after passing through the prism 3 and the galvanometer 2 from the DMD chip 4, and finally exits from the projection lens onto the projection surface to achieve projection imaging. The aperture 10 is adjusted by a drive mechanism to adapt to the needs of different scenarios. The galvanometer 2 is driven by a drive device to vibrate, allowing the projection system to simultaneously obtain the size of the DMD chip 4 when the galvanometer 2 is stationary. With its high resolution even when the galvanometer 2 is jittery, and a 0.23-inch DMD chip 4, it can project a 228.6cm (80-inch) image at a working distance of 1417mm. It supports a vertical tilt-shift range of -200% to +200% for the 0.23-inch DMD and a focus distance range of 0.5 to 3.5m. When the optical axis of the projection lens shifts, the projected image will move in the same direction. During the lens movement, the image remains clear and stable except for the movement of the image. The projection lens has good MTF performance at a spatial frequency of 93lp / mm and in the visible light range of 450nm to 655nm, with low distortion, simple structure, and good image quality.

[0042] The specific parameters of a projection system are shown in Table 1.

[0043] Table 1

[0044]

[0045]

[0046] Among them, the front lens 11 and the rear lens 525 are aspherical lenses, and the remaining lenses are spherical lenses. The aspherical polynomial formula is:

[0047]

[0048] 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, as shown in Table 2.

[0049] When the coefficient k is less than -1, the surface profile of the lens is a hyperbola;

[0050] When the coefficient k equals -1, the surface profile of the lens is a parabola;

[0051] When the k coefficient is between -1 and 0, the surface curve of the lens is an ellipse;

[0052] When the k coefficient is equal to 0, the surface curve of the lens is circular;

[0053] When the coefficient k is greater than 0, the surface shape curve of the lens is an oval.

[0054] Table 2

[0055] k <![CDATA[α2]]> <![CDATA[α3]]> <![CDATA[α4]]> <![CDATA[α5]]> <![CDATA[α6]]> <![CDATA[α7]]> <![CDATA[α8]]> S1 -15.0 3.1E-05 -7.4E-08 4.9E-10 -2.7E-12 8.1E-15 -1.2E-17 6.9E-21 S2 -0.3 -6.2E-06 2.7E-07 -8.5E-09 1.5E-10 -1.4E-12 5.7E-15 -9.2E-18 S20 1.3 8.4E-05 3.0E-07 1.3E-07 6.7E-09 1.8E-10 2.4E-12 1.3E-14 S21 -7.4 -1.5E-04 1.1E-06 9.6E-09 -3.0E-10 3.1E-12

[0056] This embodiment provides a projection lens with an aperture of F1.7, distortion of less than 0.4%, focal length of 4.21mm, and a back focal length to effective focal length ratio of 3.5 ≤ BFL / EFL ≤ 4.5. The lens has a precise structure, achieving low cost, small size, low aberration, high resolution, simple structure, supports tilt-shift, and has a large imaging clarity range. Supporting a wide range of tilt-shift allows users to have more setting options and stronger adaptability to usage scenarios.

[0057] Example 2

[0058] like Figure 2 As shown, the main difference from Embodiment 1 is that the front subgroup G11 is composed of a single sub-lens, which is a biconcave negative lens. The number of lenses is small, the structure is more compact, the space occupied is small, and the implementation cost is low.

[0059] Specifically, the front lens 11 of the front lens group G1 is set as an aspherical lens with negative refractive power and the lens material is resin. The front lens 11 includes a magnifying side surface and a reducing side surface. Both the magnifying side surface and the reducing side surface are even-order aspherical. By reasonably optimizing the aspherical coefficient, the system distortion and off-axis aberrations are effectively corrected. The front lens 12 is a plano-convex lens with positive refractive power, and the front lens 13 is a convex-plano lens with positive refractive power.

[0060] The rear lens group G2 has a rear lens 1 (21) that is a convex meniscus negative lens facing the magnification side. The rear lenses 2 (22), 3 (23), and 4 (24) are connected to form a triplet lens. The refractive powers of the rear lenses 2 (22), 3 (23), and 4 (24) are positive, negative, and positive, respectively. The Abbe numbers of the rear lenses 2 (22) and 4 (24) are both greater than 81. The rear lens 5 (25) is a biconvex positive aspherical lens, and the rear lens 6 (26) is a biconvex lens with positive refractive power.

[0061] The specific parameters of the projection system using the above-mentioned projection lens are shown in Table 3.

[0062] Table 3

[0063]

[0064]

[0065] Furthermore, the aspherical coefficients corresponding to orders 2 to 16, such as α1 to α8, in the aspherical polynomial formula are shown in Figure 4.

[0066] Table 4

[0067] k <![CDATA[α2]]> <![CDATA[α3]]> <![CDATA[α4]]> <![CDATA[α5]]> <![CDATA[α6]]> <![CDATA[α7]]> <![CDATA[α8]]> <![CDATA[α9]]> <![CDATA[α 10 ]]> S1 3.2 2.5E-05 3.9E-07 -5.1E-09 3.1E-11 -1.0E-13 2.1E-16 -2.4E-19 1.2E-22 0.00 S2 -1.0 6.2E-05 -9.0E-07 7.2E-08 -1.7E-09 2.3E-11 -1.8E-13 8.4E-16 -2.2E-18 2.6E-21 S18 -0.7 -2.7E-05 2.8E-06 -2.8E-07 2.0E-08 -8.2E-10 1.9E-11 -2.4E-13 1.3E-15 0.00 S19 -23.9 -1.1E+00 2.2E-05 2.2E-08 1.6E-08 -2.1E-10 2.2E-12 0.00 0.00 0.00

[0068] This embodiment provides a projection lens with an aperture of F1.7, an effective focal length (EFL) of 4.2mm, a back focal length (BFL) of 15.2mm, and a system field of view (FOV) of 100.95.

[0069] Example 3

[0070] like Figure 3 As shown, the main difference compared to Embodiment 1 is that the rear lens 21 in the rear lens group G2 is a biconcave lens, and the lens back focal size is small.

[0071] Specifically, the front lens 11 of the front lens group G1 is set as an aspherical lens with negative refractive power and the lens material is resin. The front lens 11 includes a magnifying side surface and a reducing side surface. Both the magnifying side surface and the reducing side surface are even-order aspherical. By reasonably optimizing the aspherical coefficient, the system distortion and off-axis aberrations are effectively corrected.

[0072] The front subgroup G11 is composed of two sub-lenses, specifically including sub-lens 111 and sub-lens 112 arranged from the magnification side to the reduction side. Sub-lens 111 is a biconcave negative lens, and sub-lens 112 is a meniscus negative lens convex to the magnification side.

[0073] The second front lens 12 is a plano-convex lens with positive diopter, and the third front lens 13 is a convex-plano lens with positive diopter.

[0074] The rear lens group G2 consists of rear lens 22, rear lens 3, and rear lens 4, which are connected to form a triplet lens. The refractive powers of rear lens 22, rear lens 3, and rear lens 4 are positive, negative, and positive, respectively. The Abbe numbers of rear lens 22 and rear lens 4 are both greater than 81. Rear lens 5 is a biconvex positive aspherical lens, and rear lens 6 is a biconvex lens with positive refractive power.

[0075] The specific parameters of the projection system using the above-mentioned projection lens are shown in Table 5.

[0076] Table 5

[0077]

[0078]

[0079] Furthermore, the aspherical coefficients corresponding to orders 2 to 16, such as α1 to α8, in the aspherical polynomial formula are shown in Figure 6.

[0080] Table 6

[0081] k <![CDATA[α2]]> <![CDATA[α3]]> <![CDATA[α4]]> <![CDATA[α5]]> <![CDATA[α6]]> <![CDATA[α7]]> <![CDATA[α8]]> S1 -13.9 5.4E-05 -3.0E-07 1.8E-09 -7.5E-12 1.9E-14 -2.5E-17 1.4E-20 S2 -1.0 6.5E-05 3.6E-07 -1.4E-08 2.4E-10 -1.9E-12 7.4E-15 -1.1E-17 S20 -12.3 5.3E-05 -7.2E-07 7.2E-08 -3.2E-09 8.8E-11 -1.2E-12 7.0E-15 S21 -20.4 -7.5E-05 1.6E-06 -1.3E-08 1.5E-10 1.2E-13

[0082] This embodiment provides a projection lens with an aperture of F1.7001, an effective focal length (EFL) of 4.21mm, a back focal length (BFL) of 15.2mm, and a system field of view (FOV) of 100.76.

[0083] Example 4

[0084] like Figure 4 As shown, the main difference from Embodiment 1 is that the front subgroup G11 is composed of a single sub-lens, which is a biconcave negative lens. The number of lenses is small, the structure is more compact, the space occupied is small, and the implementation cost is low. The second front lens 12 is an aspherical lens, and the second front lens 12 is a meniscus positive lens convex to the reduction side. The magnification side surface and the reduction side surface of the second front lens 12 are both even-order aspherical. By reasonably optimizing the aspherical coefficient, the system distortion and off-axis aberrations are effectively corrected. The third front lens 13 is a biconvex lens with positive refractive power.

[0085] More specifically, the front lens 11 of the front lens group G1 is set as an aspherical lens with negative refractive power and the lens material is resin. The front lens 11 includes a magnifying side surface and a reducing side surface. Both the magnifying side surface and the reducing side surface are even-order aspherical. By reasonably optimizing the aspherical coefficient, the system distortion and off-axis aberrations are effectively corrected.

[0086] The rear lens group G2 has a rear lens 1 (21) that is a convex meniscus negative lens facing the magnification side. The rear lenses 2 (22), 3 (23), and 4 (24) are connected to form a triplet lens. The refractive powers of the rear lenses 2 (22), 3 (23), and 4 (24) are positive, negative, and positive, respectively. The Abbe numbers of the rear lenses 2 (22) and 4 (24) are both greater than 81. The rear lens 5 (25) is a biconvex positive aspherical lens, and the rear lens 6 (26) is a biconvex lens with positive refractive power.

[0087] The specific parameters of the projection system using the above-mentioned projection lens are shown in Table 7.

[0088] Table 7

[0089]

[0090]

[0091] Furthermore, the aspherical coefficients corresponding to orders 2 to 16, such as α1 to α8, in the aspherical polynomial formula are shown in Figure 8.

[0092] Table 8

[0093] k <![CDATA[α2]]> <![CDATA[α3]]> <![CDATA[α4]]> <![CDATA[α5]]> <![CDATA[α6]]> <![CDATA[α7]]> <![CDATA[α8]]> <![CDATA[α9]]> <![CDATA[α 10 ]]> S1 2.8 -1.1E-05 7.2E-07 -6.3E-09 2.8E-11 -6.3E-14 2.6E-17 1.9E-19 -4.0E-22 2.6E-25 S2 -1.0 -6.7E-06 -3.5E-07 4.7E-08 -9.2E-10 8.7E-12 -4.5E-14 1.3E-16 -2.0E-19 1.3E-22 S5 0.0 -2.9E-05 -2.4E-07 6.6E-09 -7.4E-11 4.5E-13 -1.6E-15 2.9E-18 0.0 0.0 S6 0.1 -1.6E-05 -1.7E-07 4.6E-09 -5.5E-11 3.7E-13 -1.4E-15 2.5E-18 0.0 0.0 S18 0.0 -1.2E-04 7.1E-06 -7.2E-07 4.4E-08 -1.7E-09 4.0E-11 -5.9E-13 4.7E-15 -1.6E-17 S19 0.0 -6.2E-05 3.7E-07 -1.7E-08 2.6E-10 -5.9E-13 -8.7E-15 3.7E-17 0.0 0.0

[0094] This embodiment provides a projection lens with an aperture of F1.7, an effective focal length (EFL) of 4.22mm, a back focal length (BFL) of 17.2mm, and a system field of view (FOV) of 100.67.

[0095] 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, It includes a front lens group, an aperture, and a rear lens group arranged in the direction from the magnification side to the reduction side. The front lens group includes a first front lens with a negative diopter, a front sub-group with a negative diopter, a second front lens with a positive diopter, and a third front lens with a positive diopter arranged in the direction from the magnification side to the reduction side. The rear lens group includes a first rear lens with a negative diopter, a second rear lens with a positive diopter, a third rear lens with a negative diopter, a fourth rear lens with a positive diopter, a fifth rear lens with a positive diopter, and a sixth rear lens with a positive diopter arranged in the direction from the magnification side to the reduction side; The ratio of the total lens length to the focal length is 20 ≤ TTL / EFL ≤ 30, the ratio of the back focal length to the effective focal length of the lens is 3.5 ≤ BFL / EFL ≤ 4.5, and the total lens length TTL ≤ 118.4 mm.

2. The projection lens according to claim 1, characterized in that The front sub-group is composed of a single sub-lens or a combination of two sub-lenses.

3. The projection lens according to claim 2, characterized in that When the front sub-group is only a single sub-lens, the sub-lens is a biconcave negative lens; Or, the front sub-group includes a first sub-lens and a second sub-lens arranged in the direction from the magnification side to the reduction side. The first sub-lens is a biconcave negative lens, and the second sub-lens is a meniscus negative lens convex toward the magnification side.

4. The projection lens according to claim 1, characterized in that, At least one aspherical lens is provided in the front lens group, and at least one aspherical lens is provided in the rear lens group. The aspherical lens in the front lens group and the aspherical lens in the rear lens group satisfy the relationship -2 ≤ f_asp1 / f_asp2 ≤ 1.0, where f_asp1 is the focal length of the aspherical lens in the front lens group, and f_asp2 is the focal length of the aspherical lens in the rear lens group.

5. The projection lens of claim 1, wherein, The first front lens is a meniscus aspherical lens convex toward the magnification side, and the fifth rear lens is a biconvex aspherical lens.

6. The projection lens of claim 5, wherein, The second front lens is an aspherical lens.

7. The projection lens of claim 1, wherein, The first rear lens is a biconcave lens or a meniscus lens convex toward the magnification side.

8. The projection lens of claim 1, wherein, The second rear lens, the third rear lens, and the fourth rear lens are connected as a three-piece cemented lens. The refractive indices of the second rear lens and the fourth rear lens are lower than that of the third rear lens. The second rear lens and the fourth rear lens are made of a material with a negative Dn / Dt, where Dn / Dt is the trend of the refractive index changing with temperature.

9. The projection lens of claim 1, wherein, The focal length of the front lens group is 10 mm ≤ f1 ≤ 50 mm, the focal length of the front sub-group is -50 mm ≤ f1a ≤ -10 mm, and the focal length of the rear lens group is 10 mm ≤ f2 ≤ 100 mm.

10. The projection lens of claim 1, wherein, The effective focal length is 2.5 mm ≤ EFL ≤ 5.5 mm, the relative aperture f-number is 1.5 ≤ FNO ≤ 3.0, the projection ratio is 0.6 ≤ TR ≤ 0.7, and the imaging image circle diameter is 0 ≤ φ ≤ 15.605 mm.

11. The projection lens of claim 1, wherein, The telecentric angle is TA ≤ 1.14°, the system field of view FOV ≥ 100.7°, the aperture is set at the focal position of the rear lens group, the front air spacing of the aperture is 5 mm < T1 < 28 mm, and the lens is adapted to the spectral range of 450~650 nm.

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