Projection lens

Abstract

The invention relates to the technical field of projection optical devices, in particular to a projection lens which adopts a framework with two lens groups and eight lenses. The projection lens is simple in structure, small in lens number, good in light weight, small in occupied size, large in imaging clear range, small in aberration, small in distortion, high in resolution, large in aperture number, telecentric in image space and high in brightness, and the imaging quality is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of projection optical devices, and in particular to a projection lens. Background Art

[0002] The application of projectors is becoming more and more extensive, and the requirements for their core components - projection lenses are also getting higher and higher. LCD projection display technology is one of the commonly used display technologies for projectors. LCD projection display products have the characteristics of high image contrast, clear imaging, and high color gamut. These remarkable characteristics have gradually made LCD projection display technology another mainstream development direction in the market. Large-size LCD screens usually use Fresnel lenses as field lenses, but the Fresnel lens itself has a poor impact on the quality of the projected image. The existing projection lenses have poor adaptability to LCD projection display systems, complex structures, and poor imaging quality. Summary of the invention

[0003] The technical problem to be solved and the technical task proposed by the present invention are to improve the existing technology and provide a projection lens to solve the problems of poor adaptability of the projection lens to the LCD projection display system, complex structure and poor imaging quality in the current technology.

[0004] In order to solve the above technical problems, the technical solution of the present invention is:

[0005] A projection lens comprises a lens group 1 arranged from the magnification side to the reduction side, an aperture and a lens group 2, wherein the lens group 1 comprises a first lens, a second lens and a third lens arranged from the magnification side to the reduction side, wherein the refractive power of the first lens is negative, and the refractive power of the second lens is positive, and the lens group 1 comprises a fourth lens, a fifth lens, a sixth lens, a seventh lens and an eighth lens arranged from the magnification side to the reduction side, wherein the refractive power of the fifth lens is negative, the refractive power of the sixth lens is positive, the refractive power of the seventh lens is positive, and the refractive power of the eighth lens is positive. The projection lens of the present invention has a simple and compact structure, a small number of lenses, adopts a two-lens group, eight-lens structure, occupies a small volume, is light in weight, and can achieve high brightness, low chromatic aberration, low distortion, a large aperture, low cost, and high imaging quality.

[0006] Furthermore, the first lens is an aspherical lens, and one of the second lens and the third lens is an aspherical lens with positive refractive power. Aspherical lenses can improve the field of view of the lens system, and can well correct off-axis aberrations, system distortion, astigmatism and sine difference. The two aspherical lenses in the lens group 1 use positive and negative focal lengths to achieve mutual compensation when the temperature changes, thereby reducing the impact of the temperature rise on the performance of the lens.

[0007] Furthermore, the two aspherical mirrors satisfy the relationship -1.3≤f_asp1 / f_asp2≤0.7, wherein f_asp1 is the focal length of the aspherical mirror on the magnification side, and f_asp2 is the focal length of the aspherical mirror on the reduction side, thereby ensuring the optical MTF performance at different temperatures.

[0008] Furthermore, the focal length range of the two aspherical mirrors is -200mm≤f_asp1≤-50mm, 50mm≤f_asp2≤200mm. By reasonably optimizing the aspherical coefficient, the aspherical lens in the front lens group can be used to increase the field of view of the system and to correct off-axis aberrations and system distortion.

[0009] Furthermore, the focal length of the lens group 1 is 50mm≤f1≤200mm, and the focal length of the lens group 2 is 50mm≤f2≤100mm, so that the lens has a longer effective focal length and a larger projection ratio.

[0010] Furthermore, the fifth lens and the sixth lens are connected to form a double-cemented lens, the refractive index of the fifth lens is greater than the refractive index of the sixth lens, the refractive index of the sixth lens is between 1.43 and 1.5, the Abbe number is between 70 and 95, and Dn / Dt is a negative number, and Dn / Dt is the trend of the refractive index changing with temperature. The double-cemented lens adopts a combination of high and low refractive indices to effectively correct system chromatic aberration, and adopts a bonding structure with negative and positive diopters. The material with negative Dn / Dt has a lower refractive index as the temperature rises, and can perform thermal compensation.

[0011] Furthermore, the refractive power of the third lens is negative, and the refractive power of the fourth lens is negative;

[0012] Alternatively, the refractive power of the third lens is positive, and the refractive power of the fourth lens is positive. The lenses can be flexibly matched according to needs, the structure is simple and compact, and the implementation cost is low.

[0013] Furthermore, the first lens is a meniscus lens convex to the magnification side, the second lens is a meniscus lens convex to the magnification side, the third lens is a meniscus lens convex to the magnification side, the fourth lens is a meniscus lens convex to the reduction side, the fifth lens is a double concave lens, the sixth lens is a double convex lens, the seventh lens is a meniscus lens convex to the reduction side, and the eighth lens is a double convex lens. It can effectively improve the chromatic aberration of the system and suppress the occurrence of system distortion, with a simplified structure, a large field of view, a large aperture, low distortion, and low cost.

[0014] Furthermore, the first lens and the second lens are plastic lenses, which are relatively low in cost, and use a positive and negative combination of refractive power to offset part of the thermal problem. The remaining lenses are made of glass, which has good thermal stability and solves the problem of thermal defocusing.

[0015] Furthermore, the effective focal length is 60 mm ≤ EFL ≤ 80 mm, the relative aperture number is 2.0 ≤ FNO ≤ 3.0, the projection ratio is 1.1 ≤ TR ≤ 1.3, and the imaging circle diameter is 0 ≤ φ ≤ 75.4 mm.

[0016] Furthermore, the total length to focal length ratio of the lens is 2.85≤TTL / EFL≤5, the ratio of the back focal length of the lens to the effective focal length is 0.5≤BFL / EFL≤2.5, the telecentric angle is TA≤2.4°, the total length of the lens is TTL≤200mm, the half field of view angle is ≥56.1°, and the ratio of the imaging circle diameter to the total length of the lens is 0.2≤φ / TTL≤0.5.

[0017] Furthermore, the entire projection lens or part of the lenses in the projection lens can be tilted and adjusted relative to the optical axis. In a side projection scene, the entire projection lens or part of the lenses in the projection lens can be tilted and adjusted, which effectively improves the out-of-focus condition during side projection and allows the projection image to achieve a better resolution effect.

[0018] Compared with the prior art, the present invention has the advantages of:

[0019] The projection lens of the present invention has a large imaging clarity range, small aberration, small distortion, high resolution, large aperture number, image telecentricity, high brightness, improved imaging quality, simple structure, small number of lenses, good lightness, small occupied volume, easy implementation, low cost, and high mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural schematic diagram of a projection lens of the present invention;

[0021] Figure 2 It is a schematic structural diagram of another projection lens of the present invention.

[0022] In the figure:

[0023] A first lens 1 , a second lens 2 , a third lens 3 , a fourth lens 4 , a fifth lens 5 , a sixth lens 6 , a seventh lens 7 , an eighth lens 8 , an aperture 10 , a galvanometer 11 , a prism 12 , a protective glass 13 , and a light valve 14 . DETAILED DESCRIPTION

[0024] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0025] A projection lens disclosed in an embodiment of the present invention realizes clear imaging over a wide range, a large aperture number, image telecentricity, high brightness, a large field of view, low distortion, ensures high performance MTF value at high temperature, improves imaging quality, has a simple structure, a small number of lenses, and low implementation cost.

[0026] Embodiment 1

[0027] like Figure 1 As shown, a projection lens mainly includes a lens group 1, an aperture 10 and a lens group 2 arranged from the magnification side to the reduction side, the lens group 1 includes a first lens 1, a second lens 2 and a third lens 3 arranged from the magnification side to the reduction side, wherein the refractive power of the first lens 1 is negative, the refractive power of the second lens 2 is positive, and the refractive power of the third lens 3 is positive, the lens group 1 includes a fourth lens 4, a fifth lens 5, a sixth lens 6, a seventh lens 7 and an eighth lens 8 arranged from the magnification side to the reduction side, wherein the refractive power of the fourth lens 4 is positive, the refractive power of the fifth lens 5 is negative, the refractive power of the sixth lens 6 is positive, the refractive power of the seventh lens 7 is positive, and the refractive power of the eighth lens 8 is positive.

[0028] Specifically, the first lens 1 is a negative meniscus lens convex to the magnifying side, the second lens 2 is a positive meniscus lens convex to the magnifying side, and the first lens 1 and the second lens 2 are aspherical lenses, the surface of the first lens 1 on the magnifying side and the surface on the reducing side are both even-order aspherical surfaces, the radius of curvature of the surface of the first lens 1 on the magnifying side is 30mm~150mm, and the radius of curvature of the surface on the reducing side is 10mm~50mm, the surface of the second lens 2 on the magnifying side and the surface on the reducing side are both even-order aspherical surfaces, the radius of curvature of the surface of the second lens 2 on the magnifying side is 10mm~50mm, and the radius of curvature of the surface on the reducing side is 40mm~90mm, the aspherical lens can improve the field of view of the lens system, and correct the off-axis aberration, system distortion, astigmatism and sine difference well, and effectively correct the system astigmatism and coma by reasonably optimizing the aspherical coefficient, the first lens 1 and the second lens 2 adopt positive and negative focal lengths to achieve mutual compensation and offset when the temperature changes, thereby reducing the influence of the temperature rise on the performance of the lens. The third lens 3 is a positive meniscus lens convex toward the magnification side. The curvature radius of the surface of the third lens 3 on the magnification side is 20 mm to 60 mm, and the curvature radius of the surface on the reduction side is 50 mm to 200 mm.

[0029] Furthermore, the two aspherical mirrors satisfy the relationship -1.3≤f_asp1 / f_asp2≤0.7. In the present embodiment, f_asp1 is the focal length of the first lens 1, and f_asp2 is the focal length of the second lens 2, ensuring the optical MTF performance at different temperatures. Specifically, the focal length range of the two aspherical mirrors is -200mm≤f_asp1≤-50mm, 50mm≤f_asp2≤200mm.

[0030] The fourth lens 4 is a positive meniscus lens convex to the reduction side, which has a better effect on the field curvature and astigmatism of the system. The curvature radius of the surface of the fourth lens 4 on the magnification side is -80mm~-20mm, and the curvature radius of the surface on the reduction side is -50mm~-15mm. The fifth lens 5 is a double concave negative lens. The curvature radius of the surface of the fifth lens 5 on the magnification side is -50mm~-15mm, and the curvature radius of the surface on the reduction side is 10mm~500mm. The sixth lens 6 is a double convex positive lens. The curvature radius of the surface of the sixth lens 6 on the magnification side is -50mm~-15mm, and the curvature radius of the surface on the reduction side is 10mm~500mm. The curvature radius of the surface on the reduction side is 100mm~500mm, and the curvature radius of the surface on the reduction side is -60mm~-20mm. The seventh lens 7 is a meniscus positive lens convex toward the reduction side. The curvature radius of the surface of the seventh lens 7 on the magnification side is less than -300mm, and the curvature radius of the surface on the reduction side is -100mm~-50mm. The eighth lens 8 is a double convex positive lens. The curvature radius of the surface of the eighth lens 8 on the magnification side is 80mm~205mm, and the curvature radius of the surface on the reduction side is -300mm~-100mm.

[0031] Among them, the fifth lens 5 and the sixth lens 6 are connected to form a double-cemented lens, the refractive index of the fifth lens 5 is greater than the refractive index of the sixth lens 6, and a high and low refractive index combination is used to form a double-cemented lens to effectively correct chromatic aberration, and the double-cemented lens adopts a negative and positive refractive power bonding structure, wherein the refractive index of the sixth lens 6, which is a positive lens, is between 1.43 and 1.5, the Abbe number is between 70 and 95, and Dn / Dt is a negative number, and Dn / Dt is a trend of the refractive index changing with temperature, which can perform thermal compensation on the optical system.

[0032] Among them, the first lens 1 and the second lens 2 are plastic lenses, which use a positive and negative combination of refractive power to offset part of the thermal problem. The remaining lenses are made of glass material with good thermal stability, which solves the problem of thermal defocusing and ensures imaging performance under high temperature changes.

[0033] The focal length of the lens group 1 in the projection lens is 50 mm ≤ f1 ≤ 200 mm, the focal length of the lens group 2 is 50 mm ≤ f2 ≤ 100 mm, the aperture 10 is arranged near the focal position of the lens group 2, the effective focal length is 60 mm ≤ EFL ≤ 80 mm, the relative aperture number is 2.0 ≤ FNO ≤ 3.0, the projection ratio is 1.1 ≤ TR ≤ 1.3, and the imaging circle diameter is 0 ≤ φ ≤ 75.4 mm; the total length-to-focal length ratio of the lens is 2.85 ≤ TTL / EFL ≤ 5, the ratio of the lens back focal length to the effective focal length is 0.5 ≤ BFL / EFL ≤ 2.5, the telecentric angle is TA ≤ 2.4°, the total length of the lens is TTL ≤ 200 mm, the half field of view angle is ≥ 56.1°, and the ratio of the imaging circle diameter to the total length of the lens is 0.2 ≤ φ / TTL ≤ 0.5. The above-mentioned projection lens can effectively improve the chromatic aberration of the system and suppress the occurrence of system distortion. While meeting the design of 75.4mm image target surface, the number of optical lenses used is relatively small, the structure is simplified, the field of view angle is large, the aperture diameter is large, the distortion is low, the cost is low, and the high performance MTF value can be ensured at high temperature.

[0034] The projection system using the above-mentioned projection lens also includes a galvanometer 11, a prism 12, a protective glass 13 and a light valve 14 which are arranged in sequence on the reduction side of the eighth lens 8 along the direction from the magnification side to the reduction side. The light valve 14 is specifically an LCD panel. During projection, light enters the projection lens from the reduction end side from the light valve 14 through the prism 12, and finally leaves the projection lens and is emitted to the projection surface to realize projection imaging. By setting the galvanometer 11 with a jitter of 2.5mm, the projection lens can simultaneously obtain the resolution inherent in the size of the LCD panel itself when the galvanometer 11 is stationary and the 4K resolution when the working jitter amplitude angle of the galvanometer 11 is 1.2 degrees. The prism 12 can be used to increase the brightness of the system by increasing the light source. With a 2.6-inch LCD panel, a 228.6cm (90-inch) screen can be projected at a working distance of 2390mm. It supports unidirectional longitudinal offset adjustment of the 2.6-inch LCD panel from -50% to +50%. The projection lens has excellent MTF performance at the spatial limit frequency of 17lp / mm and in the visible light range of 450nm to 630nm, with small distortion, simple structure, good imaging quality, and a large imaging clarity range. It ensures that the output image is biased upward during projection, so that the output light beam is higher than the projection lens position, and the projection image will not be blocked by the projection lens.

[0035] Specific parameters of a projection system are shown in Table 1.

[0036] Table 1

[0037]

[0038]

[0039] Among them, the first lens 1 and the second lens 2 are aspherical lenses, and the remaining lenses are spherical lenses. The aspherical polynomial formula is:

[0040]

[0041] In the formula, z represents the distance vector height of the aspheric surface from the fixed point of the aspheric surface when the aspheric surface is at a height r along the optical axis, the parameter c is the curvature corresponding to the radius, r is the radial height of the lens, k is the conic constant coefficient (ConicConstant), and α1~α8 are the aspheric coefficients corresponding to the 20th to 16th orders, as shown in Table 2.

[0042] When the k coefficient is less than -1, the surface curve of the lens is a hyperbola;

[0043] When the k coefficient is equal to -1, the surface curve of the lens is a parabola;

[0044] When the k coefficient is between -1 and 0, the surface curve of the lens is an ellipse;

[0045] When the k coefficient is equal to 0, the surface curve of the lens is circular;

[0046] When the k coefficient is greater than 0, the surface curve of the lens is an oblate circle.

[0047] Table 2

[0048] k <![CDATA[α 2 ]]> <![CDATA[α 3 ]]> <![CDATA[α 4 ]]> <![CDATA[α 5 ]]> <![CDATA[α 6 ]]> <![CDATA[α 7 ]]> <![CDATA[α 8 ]]> <![CDATA[α 9 ]]> <![CDATA[α 10 ]]> S1 0.0E+00 -3.6E-05 7.6E-08 -1.2E-10 1.3E-13 -1.1E-16 5.9E-20 -2.0E-23 2.9E-27 0.0E+00 S2 -1.0E+00 -4.7E-05 1.2E-07 -2.8E-10 5.8E-13 -9.1E-16 8.9E-19 -4.7E-22 9.9E-26 0.0E+00 S3 0.0E+00 -8.8E-07 1.4E-08 -5.9E-11 1.9E-13 -3.2E-16 2.8E-19 -9.7E-23 0.0E+00 0.0E+00 S4 0.0E+00 4.3E-06 1.5E-08 -4.8E-11 9.0E-14 -1.1E-16 6.1E-20 -1.5E-23 0.0E+00 0.0E+00

[0049] The physical resolution of the LCD panel is 17lp / mm. The projection system also includes a drive motor 1 for adjusting the position of the projection lens to meet the requirements of different screen sizes. The projection system also includes a drive motor 2 connected to the galvanometer 11 to drive the galvanometer 11 to vibrate.

[0050] This embodiment provides a fixed-focus projection lens with an aperture number of F2.4, a distortion of less than 2.0%, and a ratio of back focal length to effective focal length of 0.5≤BFL / EFL≤2.5. This lens has a precise structure and is low-cost. The projection lens forms a 90-inch diagonal screen at a position of 2390mm. Based on the principle of optical imaging, the curvature radius, material, thickness, air spacing, etc. of each lens of the projection lens are designed, and multiple aspherical lenses are set, with small aberration, high resolution, simple structure, and easy mass production.

[0051] LCD projectors generally have the problem that the side projection angle they support is significantly smaller than that of DLP projectors, which greatly limits the application of LCD projectors. The main reason is that the size of the LCD panel used in LCD projectors is significantly larger than that of the DMD chip used in DLP projectors, resulting in a huge difference in the NA angle at the projection screen end. The side projection resolution is limited by the NA angle at the projection screen end. When the side projection angle increases, it will be out of focus, resulting in a significant decrease in resolution, affecting the quality of the projected image.

[0052] In order to solve the above problems, the entire projection lens or part of the lenses in the projection lens can be tilted relative to the optical axis, and the projection effect can be optimized by tilting the entire projection lens or part of the lenses in the projection lens during side projection. The principle of tilting the entire projection lens or part of the lenses in the projection lens to improve the image quality is based on Sham's law, which means that a clear image can be obtained when the film surface, the objective lens plane and the image receiving surface intersect in the same straight line. The LCD panel in the projection device corresponds to the film surface, the projection lens corresponds to the objective lens plane, and the screen corresponds to the image receiving surface, so that a clear projection picture can be obtained by adjusting the entire projection lens or part of the lenses in the projection lens to achieve Sham's law, thereby solving the problem of defocusing and reduced resolution when the side projection angle is large, and effectively improving the quality of the projection picture.

[0053] Specifically, the rotation axis of the entire projection lens is perpendicular to and passes through the optical axis when the tilt adjustment is performed. The specific position of the rotation axis can be at the end of the projection lens on the magnification side, at the end of the projection lens on the reduction side, at the middle of the projection lens along the optical axis, etc. As long as the conditions of Sham's law can be met, the out-of-focus problem can be solved during side projection, the resolution of the projection picture can be improved, the image quality loss can be avoided, the projection picture effect can be improved, and the viewing experience can be guaranteed.

[0054] Part of the lenses in the projection lens can be tilted relative to the optical axis, specifically, a single lens or a single lens group in the projection lens can be tilted relative to the optical axis, and the rotation axis is perpendicular to and passes through the optical axis. The plane of the entire projection lens can also be adjusted to meet Sham's law, specifically, the first lens can be tilted, or the eighth lens can be tilted, or the lens group 2 can be tilted as a whole, etc.

[0055] Embodiment 2

[0056] like Figure 2As shown, a projection lens mainly includes a lens group 1 arranged from the magnification side to the reduction side, an aperture 10 and a lens group 2, wherein the lens group 1 includes a first lens 1, a second lens 2 and a third lens 3 arranged from the magnification side to the reduction side, and the lens group 1 includes a fourth lens 4, a fifth lens 5, a sixth lens 6, a seventh lens 7 and an eighth lens 8 arranged from the magnification side to the reduction side. The difference from the embodiment 1 is that the refractive power of the first lens 1 is negative, the refractive power of the second lens 2 is positive, the refractive power of the third lens 3 is negative, the refractive power of the fourth lens 4 is negative, the refractive power of the fifth lens 5 is negative, the refractive power of the sixth lens 6 is positive, the refractive power of the seventh lens 7 is positive, and the refractive power of the eighth lens 8 is positive.

[0057] More specifically, the first lens 1 is a negative meniscus lens convex to the magnification side, the second lens 2 is a positive meniscus lens convex to the magnification side, the third lens 3 is a negative meniscus lens convex to the magnification side, the first lens 1 and the third lens 3 are aspherical lenses, the second lens 2 is a spherical lens, the surface of the first lens 1 on the magnification side and the surface on the reduction side are both even-order aspherical surfaces, and the surface of the third lens 3 on the magnification side and the surface on the reduction side are both even-order aspherical surfaces.

[0058] The fourth lens 4 is a meniscus negative lens convex toward the reduction side, which is beneficial to the improvement of the field curvature and astigmatism correction of the system, the fifth lens 5 is a double concave negative lens, the sixth lens 6 is a double convex positive lens, the seventh lens 7 is a meniscus positive lens convex toward the reduction side, and the eighth lens 8 is a double convex positive lens, wherein the fifth lens 5 and the sixth lens 6 are connected to form a double cemented lens.

[0059] Specific parameters of a projection system using the above-mentioned projection lens are shown in Table 3.

[0060] Table 3

[0061]

[0062] Among them, the first lens 1 and the third lens 3 are aspherical lenses, and the remaining lenses are spherical lenses. The aspherical polynomial formula is:

[0063]

[0064] In the formula, z represents the distance vector height of the aspheric surface from the fixed point of the aspheric surface when the aspheric surface is at a height r along the optical axis, the parameter c is the curvature corresponding to the radius, r is the radial height of the lens, k is the conic constant coefficient (ConicConstant), and α1~α8 are the aspheric coefficients corresponding to the 20th to 16th orders, as shown in Table 4.

[0065] When the k coefficient is less than -1, the surface curve of the lens is a hyperbola;

[0066] When the k coefficient is equal to -1, the surface curve of the lens is a parabola;

[0067] When the k coefficient is between -1 and 0, the surface curve of the lens is an ellipse;

[0068] When the k coefficient is equal to 0, the surface curve of the lens is circular;

[0069] When the k coefficient is greater than 0, the surface curve of the lens is an oblate circle.

[0070] Table 4

[0071] k <![CDATA[α 2 ]]> <![CDATA[α 3 ]]> <![CDATA[α 4 ]]> <![CDATA[α 5 ]]> <![CDATA[α 6 ]]> <![CDATA[α 7 ]]> <![CDATA[α 8 ]]> S1 -1.0E+00 -9.4E-06 1.1E-09 1.4E-11 -1.9E-14 1.2E-17 -3.5E-21 4.3E-25 S2 -1.0E+00 -1.5E-05 6.0E-10 2.8E-11 -3.9E-14 2.5E-17 -6.2E-21 1.6E-25 S5 0.0E+00 -1.6E-05 -2.9E-08 -9.4E-11 1.0E-12 -3.4E-15 5.2E-18 -3.4E-21 S6 0.0E+00 -2.0E-05 -8.0E-08 2.7E-11 2.0E-12 -1.2E-14 3.1E-17 -3.5E-20

[0072] This embodiment provides a projection lens with an aperture number of F2.387, an effective focal length EFL of 70 mm, a lens back focal length BFL of 78.5, and a system field of view FOV of 56.1.

[0073] The above are only preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be regarded as limiting the present invention, and the protection scope of the present invention should be based on the scope defined by the claims. For ordinary technicians in this technical field, 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 regarded as the protection scope of the present invention.

Claims

1. A projection lens, characterized in that: The invention comprises a lens group 1 arranged from the magnification side to the reduction side, an aperture and a lens group 2, wherein the lens group 1 comprises a first lens, a second lens and a third lens arranged from the magnification side to the reduction side, wherein the refractive power of the first lens is negative, and the refractive power of the second lens is positive, and the lens group 1 comprises a fourth lens, a fifth lens, a sixth lens, a seventh lens and an eighth lens arranged from the magnification side to the reduction side, wherein the refractive power of the fifth lens is negative, the refractive power of the sixth lens is positive, the refractive power of the seventh lens is positive, and the refractive power of the eighth lens is positive.

2. The projection lens according to claim 1, characterized in that: The first lens is an aspherical lens, and one of the second lens and the third lens is an aspherical lens with positive refractive power.

3. The projection lens according to claim 2, characterized in that: The two aspherical mirrors satisfy the relationship -1.3≤f_asp1 / f_asp2≤0.7, where f_asp1 is the focal length of the aspherical mirror on the magnification side, and f_asp2 is the focal length of the aspherical mirror on the reduction side.

4. The projection lens according to claim 3, characterized in that: The focal length range of the two aspherical mirrors is -200mm≤f_asp1≤-50mm, 50mm≤f_asp2≤200mm.

5. The projection lens according to claim 1, wherein: The focal length of the lens group 1 is 50 mm ≤ f1 ≤ 200 mm, and the focal length of the lens group 2 is 50 mm ≤ f2 ≤ 100 mm.

6. The projection lens according to claim 1, wherein: The fifth lens and the sixth lens are connected to form a doublet lens, the refractive index of the fifth lens is greater than the refractive index of the sixth lens, the refractive index of the sixth lens is between 1.43 and 1.5, the Abbe number is between 70 and 95, and Dn / Dt is a negative number, and Dn / Dt is a trend of the refractive index changing with temperature.

7. The projection lens according to claim 1, wherein: The refractive power of the third lens is negative, and the refractive power of the fourth lens is negative; Alternatively, the refractive power of the third lens is positive, and the refractive power of the fourth lens is positive.

8. The projection lens according to claim 1, wherein: The first lens is a meniscus lens convex toward the magnification side, the second lens is a meniscus lens convex toward the magnification side, the third lens is a meniscus lens convex toward the magnification side, the fourth lens is a meniscus lens convex toward the reduction side, the fifth lens is a double concave lens, the sixth lens is a double convex lens, the seventh lens is a meniscus lens convex toward the reduction side, and the eighth lens is a double convex lens.

9. The projection lens according to claim 1, wherein: The first lens and the second lens are plastic lenses, and the remaining lenses are made of glass.

10. The projection lens according to claim 1, wherein: The effective focal length is 60mm≤EFL≤80mm, the relative aperture number is 2.0≤FNO≤3.0, the projection ratio is 1.1≤TR≤1.3, and the imaging circle diameter is 0≤φ≤75.4mm.

11. The projection lens according to claim 1, wherein: The total length to focal length ratio of the lens is 2.85≤TTL / EFL≤5, the ratio of the lens back focal length to the effective focal length is 0.5≤BFL / EFL≤2.5, the telecentric angle is TA≤2.4°, the total length of the lens is TTL≤200mm, the half field of view angle is ≥56.1°, and the ratio of the imaging circle diameter to the total length of the lens is 0.2≤φ / TTL≤0.

5.

12. The projection lens according to claim 1, wherein: The entire projection lens or a part of the lenses in the projection lens can be tilted and adjusted relative to the optical axis.

Images