A ground projection lens with a large depth of field and off-axis

Abstract

The present invention provides a ground projection lens with a large depth of field and off-axis, which sequentially includes, from the image source to the imaging side: a projection picture plane, a first group of lenses with positive optical power, a diaphragm, a second group of lenses with positive optical power, a beam splitter, a protective glass, and an imaging plane. The beam splitter is a beam splitting prism. The ground projection lens with a large depth of field and off-axis provided by the present invention can match the optical characteristic group lenses of a large aperture and a large image plane, solve the disadvantage of insufficient depth of field of this type of projection objective lens, and has the advantages of balancing the projection working range, image quality, optical compatibility, manufacturing factors, simple structure, excellent aberration balance, and reasonable tolerances.

Description

Technical Field

[0001] The present invention relates to the technical field of optical lenses, and particularly to a ground projection lens with a large depth of field and off-axis characteristics. Background Art

[0002] A projection lens is a core component of a projection device. After light passes through a reflective or projective light modulation device, it is then projected onto a projection screen through the projection lens to form an image.

[0003] With the development of technology, projection devices are applied in more and more fields, including home audio and video, automotive entertainment, projection advertising, industrial inspection, 3D printing, etc. More and more devices need to embed a micro-projection system, and the requirements for projection devices are also getting higher and higher, such as smaller size, higher imaging quality, lower cost, etc.

[0004] With the popularization of projection devices, higher requirements are also placed on the technical indicators of projectors: clearer picture quality, larger projection frame size, wider projection working distance, etc. In a projector, due to the actual application scenario, the projection lens is required to have a higher off-axis ratio. When the off-axis ratio reaches 100%, the projection optical machine can be directly placed on any platform for projection without considering the problem of insufficient space under the projector. Therefore, to obtain a more immersive viewing experience, a larger projection frame size is required, and at the same time, a sufficient depth of field is needed to balance the comfort of viewing. The existing lens projects a rectangular frame, and when the frame is tilted, the depth of field is seriously insufficient and the imaging becomes blurred. Therefore, it is very necessary to design a ground projection lens with a large depth of field and off-axis characteristics. Summary of the Invention

[0005] The purpose of the present invention is to provide a ground projection lens with a large depth of field and off-axis characteristics, which can match the optical characteristic group lens with a large aperture and large image plane, solve the disadvantage of insufficient depth of field of this type of projection objective lens, and has the advantages of balancing the projection working range, image quality, optical compatibility, manufacturing factors, simple structure, excellent aberration balance, reasonable tolerance, etc.

[0006] To achieve the above purpose, the present invention provides the following solution:

[0007] A ground projection lens with a large depth of field and off-axis characteristics includes, in sequence from the image source to the imaging side: a projection frame, a first group lens with positive optical power, a diaphragm, a second group lens with positive optical power, a beam splitter, a protective glass, and an imaging surface, and the beam splitter is a beam splitting prism;

[0008] The ground projection lens satisfies 0.9 < T L / f / IH < 0.95, where T LIt represents the total optical length of the ground projection lens, f represents the effective focal length of the ground projection lens, and IH represents the actual half-image height of the ground projection lens;

[0009] The ground projection lens satisfies 3.2mm<IH / tanθ<3.6mm, where θ represents the half field angle of the ground projection lens;

[0010] The ground projection lens satisfies 0.25<tanθ1 / tanθ2<0.35, where θ1 is the tilt angle between the projection frame and the optical axis, and θ2 is the tilt angle between the imaging plane and the optical axis;

[0011] The terrestrial projection lens satisfies CRA<2°, where CRA represents the incident angle of the chief ray of the terrestrial projection lens on the imaging plane;

[0012] The first lens group includes, from the image source to the image side, a first lens G01, a second lens GM02, a third lens G03, a fourth lens G04, and a fifth lens G05;

[0013] The second lens group includes, from the image source to the image side, the sixth lens G06, the seventh lens G07, the eighth lens G08 and the ninth lens GM09;

[0014] The ratio of the focal length f1 of the first lens group to the effective focal length f of the ground projection lens is 0.753;

[0015] The ratio of the focal length f2 of the second lens group to the effective focal length f of the ground projection lens is 1.138.

[0016] Optionally, the first lens G01 is a biconcave lens with negative power, the second lens GM02 is a meniscus lens with negative power, the third lens G03 is a meniscus lens with positive power, the fourth lens G04 is a meniscus lens with positive power, and the fifth lens G05 is a meniscus lens with positive power.

[0017] Optionally, the sixth lens G06 is a biconcave lens with negative power, the seventh lens G07 and the eighth lens G08 are a cemented lens with negative power, and the ninth lens GM09 is a biconvex aspheric lens with positive power.

[0018] Optionally, the focal length f of the second lens GM02 is GM02 The focal length f of the ninth lens GM09 is GM09 The ratio is -2.54;

[0019] The focal length f of the first lens G01 is G01 The ratio to the effective focal length f of the ground projection lens is -1.072;

[0020] The focal length f of the second lens GM02 GM02 has a ratio of -2.616 to the effective focal length f of the ground projection lens;

[0021] The focal length f of the third lens G03 G03 has a ratio of 1.994 to the effective focal length f of the ground projection lens;

[0022] The focal length f of the fourth lens G04 G04 has a ratio of 1.871 to the effective focal length f of the ground projection lens;

[0023] The focal length f of the fifth lens G05 G05 has a ratio of 1.478 to the effective focal length f of the ground projection lens;

[0024] The focal length f of the sixth lens G06 G06 has a ratio of -1.723 to the effective focal length f of the ground projection lens;

[0025] The focal length f of the seventh lens G07 G07 and the focal length f of the eighth lens G08 G08 has a ratio of -1.479 to the effective focal length f of the ground projection lens;

[0026] The focal length f of the ninth lens GM09 GM09 has a ratio of 1.030 to the effective focal length f of the ground projection lens.

[0027] Optionally, the first group of lenses with positive optical power, the aperture stop, the second group of lenses with positive optical power, the beam splitter device, and the protective glass are all made of glass.

[0028] Optionally, the angle between the projection picture plane and the optical axis is 10°, and the angles between the protective glass and the imaging plane and the optical axis are 87°.

[0029] According to the specific embodiments provided by the present invention, the following technical effects are disclosed: The large depth-of-field off-axis ground projection lens provided by the present invention includes, in sequence from the image source to the imaging side: a projection picture plane, a first group of lenses with positive optical power, an aperture stop, a second group of lenses with positive optical power, a beam splitter device, a protective glass, and an imaging plane. The beam splitter device is a beam splitter prism. When working in a horizontal position, it can project a clear picture on the ground plane. The picture has characteristics such as a very long depth-of-field range, clear image quality, and an isosceles trapezoid shape. The projection system reasonably balances imaging brightness, cost, image quality, and resolution, and fully considers the actual application scenario. It has a series of advantages such as being easy to manufacture, having reasonable tolerances, low cost, and high imaging quality, and can match the optical characteristic group lenses with a large aperture and a large image plane, solving the drawback of insufficient depth-of-field of this type of projection objective lens. Description of the Drawings

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for use in the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained based on these drawings.

[0031] Figure 1 Schematic structural diagram of a ground projection lens with a large depth of field and off-axis for an embodiment of the present invention;

[0032] Figure 2 Spatial frequency MTF diagram;

[0033] Figure 3 Axial chromatic aberration diagram;

[0034] Figure 4 Relative illumination diagram;

[0035] Figure 5 Principal ray incident angle diagram for each field of view of the lens.

[0036] Reference numerals: 1, projection picture plane; 2, first group of lenses; 3, aperture stop; 4, second group of lenses; 5, anamorphic prism; 6, protective glass; 7, imaging plane. Detailed implementation manners

[0037] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0038] The object of the present invention is to provide a ground projection lens with a large depth of field and off-axis, which can match the optical characteristic group of lenses with a large aperture and large image plane, solve the shortcoming of insufficient depth of field of this type of projection objective lens, and has the advantages of balancing the projection working range, image quality, optical compatibility, manufacturing factors, simple structure, excellent aberration balance, and reasonable tolerances.

[0039] In order to make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0040] Such as Figure 1As shown in the figure, the large depth-of-field off-axis ground projection lens provided by the embodiment of the present invention includes, in sequence from the image source to the imaging side: a projection picture plane 1, a first group of lenses 2 with positive optical power, a diaphragm 3, a second group of lenses 4 with positive optical power, a beam splitting device, a protective glass 6, and an imaging surface 7. The beam splitting device is a beam splitting prism 5;

[0041] A 0.3-inch display chip is adopted, and the off-axis ratio reaches 120%;

[0042] The ground projection lens satisfies 0.9 < T L / f / IH < 0.95. In the formula, T L represents the total optical length of the ground projection lens, f represents the effective focal length of the ground projection lens, and IH represents the actual semi-image height of the ground projection lens;

[0043] The ground projection lens satisfies 3.2mm < IH / tanθ < 3.6mm. In the formula, θ represents the semi-field angle of the ground projection lens;

[0044] The ground projection lens satisfies 0.25 < tanθ1 / tanθ2 < 0.35. In the formula, θ1 is the tilt angle between the projection picture plane and the optical axis, and θ2 is the tilt angle between the imaging surface and the optical axis;

[0045] The ground projection lens satisfies CRA < 2°. In the formula, CRA represents the main ray incident angle of the ground projection lens on the imaging surface;

[0046] The first group of lenses 2 includes, in sequence from the image source to the imaging side: a first lens G01, a second lens GM02, a third lens G03, a fourth lens G04, and a fifth lens G05;

[0047] The second group of lenses 4 includes, in sequence from the image source to the imaging side: a sixth lens G06, a seventh lens G07, an eighth lens G08, and a ninth lens GM09;

[0048] The ratio of the focal length f1 of the first group of lenses 2 to the effective focal length f of the ground projection lens is 0.753;

[0049] The ratio of the focal length f2 of the second group of lenses 4 to the effective focal length f of the ground projection lens is 1.138.

[0050] The first lens G01 is a biconcave lens with negative optical power, the second lens GM02 is a concave-convex lens with negative optical power, the third lens G03 is a convex-concave lens with positive optical power, the fourth lens G04 is a convex-concave lens with positive optical power, and the fifth lens G05 is a convex-concave lens with positive optical power.

[0051] The sixth lens G06 is a biconcave lens with a negative focal power, the seventh lens G07 and the eighth lens G08 are cemented lenses with a negative focal power, and the ninth lens GM09 is a biconvex aspherical lens with a positive focal power.

[0052] The focal length f of the second lens GM02 GM02 and the focal length f of the ninth lens GM09 GM09 have a ratio of -2.54;

[0053] The focal length f of the first lens G01 G01 and the effective focal length f of the ground projection lens have a ratio of -1.072;

[0054] The focal length f of the second lens GM02 GM02 and the effective focal length f of the ground projection lens have a ratio of -2.616;

[0055] The focal length f of the third lens G03 G03 and the effective focal length f of the ground projection lens have a ratio of 1.994;

[0056] The focal length f of the fourth lens G04 G04 and the effective focal length f of the ground projection lens have a ratio of 1.871;

[0057] The focal length f of the fifth lens G05 G05 and the effective focal length f of the ground projection lens have a ratio of 1.478;

[0058] The focal length f of the sixth lens G06 G06 and the effective focal length f of the ground projection lens have a ratio of -1.723;

[0059] The focal length f of the seventh lens G07 G07 and the focal length f of the eighth lens G08 G08 and the effective focal length f of the ground projection lens have a ratio of -1.479;

[0060] The focal length f of the ninth lens GM09 GM09 and the effective focal length f of the ground projection lens have a ratio of 1.030.

[0061] The first group of lenses with positive focal power, the aperture stop, the second group of lenses with positive focal power, the beam splitter, and the protective glass are all made of glass.

[0062] The angle between the projection picture plane and the optical axis is 10°, and the angles between the protective glass and the imaging plane and the optical axis are 87°.

[0063] Among them, the specific parameter table of the ground projection lens is shown in Table 1. The surface serial numbers are S0 - S23 in sequence from the image source to the imaging side. Nd is the refractive index, and vd is the Abbe number;

[0064] Table 1 Specific Parameter Table of the Ground Projection Lens

[0065]

[0066]

[0067] The coefficients of each order of the second lens GM02 and the ninth lens GM09 are shown in Table 2;

[0068] Table 2 Coefficients of Each Order of the Second Lens GM02 and the Ninth Lens GM09

[0069]

[0070] An embodiment of the present invention is to obtain a projection lens according to the above technical solution and conduct MTF evaluation on it. Among them, the MTF (English name: Modulation Transfer Function) index is the most accurate and scientific evaluation standard for lenses at present. The vertical coordinate is the contrast, and the closer it is to 1, the better the lens imaging. The horizontal coordinate represents the resolution, with the unit of line pairs per millimeter.

[0071] The pixel size of the image source adopted in the embodiment of the present invention is 7.637μm, and the corresponding design resolution is 65 line pairs per millimeter. Generally, the projection lens requires that the MTF values of each field of view reach above 0.3 at the design resolution. After testing, the MTF values of each field of view in the embodiment of the present invention are all above 0.5, having extremely excellent imaging quality. The spatial frequency MTF diagram of the present invention is as Figure 2 shown;

[0072] The lateral chromatic aberration diagram is as Figure 3 shown. The vertical coordinate is the image height field of view value size, and the horizontal coordinate is the numerical value size, with the unit of micrometers. In the figure, based on the main wavelength, the chromatic aberration values of each field of view between blue light, red light, and green light (main wavelength) are respectively plotted. Generally, the projection lens requires that the chromatic aberration value is within one image source pixel size. The lateral chromatic aberration of the embodiment of the present invention is controlled within 2.2μm, which is less than 0.3 pixel sizes (pixel size 7.637μm);

[0073] The relative illumination diagram is as Figure 4 shown. The relative illumination refers to the ratio of the illuminance at different coordinate points on the image plane to the illuminance at the center point. The vertical coordinate represents the normalized illuminance value, and the horizontal coordinate represents the field of view angle of the lens. Under the same conditions, the smoother the transition of the relative illumination curves of each field of view represents the uniform illuminance within the projection frame, and the closer the relative illumination values of each field of view are to 1, the higher the final projection brightness;

[0074] The principal ray angle of incidence diagram for each field of view of the lens is as Figure 5 shown. The smaller the principal ray angle of incidence for each field of view, the higher the optical system efficiency, the smaller the energy loss. Generally, when the full field of view CRA is within 3°, it belongs to an excellent level, while in the embodiments of the present invention, the full field of view is within 1.6°, belonging to a very excellent level;

[0075] According to the embodiments, when the working distance is set to 1100 mm, the MTF (Modulation Transfer Function) of the low, medium, and high frequencies of the lens is very good, and it can be analyzed that it has a high resolution effect. The focal length of the entire objective lens system is 10.37 mm, the DMD is adapted to 0.3 inches, the corresponding offset reaches 120%, the tilt amount of the projection surface reaches 80° (relative to the vertical projection surface), the tilt amount of the DMD image surface is about 3° (relative to the vertical image surface), and the depth of field is relatively deep, and clear imaging can be achieved within the entire frame range.

[0076] In this embodiment, the ground projection lens satisfies 0.9 < T L / f / IH < 0.95. In the formula, T L represents the total optical length of the ground projection lens, f represents the effective focal length of the ground projection lens, and IH represents the actual semi-image height of the ground projection lens. When this formula is satisfied, the relationship between the total length of the lens and the resolution ability can be reasonably balanced. When the value of T L / f / IH exceeds the upper limit, the overall total length of the lens is too large (the volume of the imaging system is too large). If the total length is scaled proportionally or forced to be compressed, the image height will be insufficient. When the value of T L / f / IH is lower than the lower limit, due to the excessive optical power of each lens, it is difficult to correct the lens aberration, and the resolution ability drops significantly;

[0077] The ground projection lens satisfies 3.2 mm < IH / tanθ < 3.6 mm. In the formula, θ represents the half field of view angle of the ground projection lens. When this formula is satisfied, the distortion of the optical lens can be reasonably limited, and the difficulty of distortion correction can be reduced. When the value of IH / tanθ exceeds the lower limit, the distortion of the lens will increase in the negative direction. When the value of IH / tanθ exceeds the upper limit, the distortion of the lens will increase in the positive direction. At the same time, the field of view size can be limited, and then the size of the projection frame can be controlled;

[0078] The ground projection lens satisfies 0.25 < tanθ1 / tanθ2 < 0.35. In the formula, θ1 is the tilt angle between the projection frame surface and the optical axis, and θ2 is the tilt angle between the imaging surface and the optical axis. When this formula is satisfied, the size of the depth of field of the projection surface can be reasonably controlled. When tanθ1 / tanθ2 exceeds the upper limit, the overall depth of field is relatively large, and the corresponding aberration correction is more difficult. When tanθ1 / tanθ2 exceeds the lower limit, the overall depth of field is relatively small, and the system aberration is relatively easy to correct;

[0079] The ground projection lens satisfies CRA < 2°, where CRA represents the principal ray incident angle of the ground projection lens on the imaging surface. When this formula is satisfied, it can well match the DMD chip and achieve a good projection effect.

[0080] The large-depth-of-field off-axis ground projection lens provided by the present invention sequentially includes, from the image source to the imaging side: a projection picture plane, a first group of lenses with positive optical power, a diaphragm, a second group of lenses with positive optical power, a beam splitter device, a protective glass, and an imaging surface. The beam splitter device is a beam splitter prism. When working horizontally, it can project a clear picture on the ground plane. The picture has characteristics such as a very long depth-of-field range, clear image quality, and an isosceles trapezoid shape. The projection system reasonably and evenly balances imaging brightness, cost, image quality, and resolution, and fully considers the actual application scenario. It has a series of advantages such as being easy to manufacture, having reasonable tolerances, low cost, and high imaging quality. It can match the optical characteristic group lenses with a large aperture and a large image surface, and solve the shortcoming of insufficient depth of field of this type of projection objective lens.

[0081] In this article, specific examples are used to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A ground projection lens with a large depth of field and off-axis, characterized in that, From the image source to the imaging side, it successively includes: a projection picture plane, a first group of lenses with positive optical power, a diaphragm, a second group of lenses with positive optical power, a beam splitter device, a protective glass, and an imaging surface, and the beam splitter device is a beam splitter prism; The ground projection lens satisfies 0.9 < T L / f / IH < 0.95, where T L represents the total optical length of the ground projection lens, f represents the effective focal length of the ground projection lens, and IH represents the actual semi-image height of the ground projection lens; The ground projection lens satisfies 3.2mm < IH / tanθ < 3.6mm, where θ represents the half field angle of the ground projection lens; The ground projection lens satisfies 0.25 < tanθ1 / tanθ2 < 0.35, where θ1 is the tilt angle between the projection picture plane and the optical axis, and θ2 is the tilt angle between the imaging surface and the optical axis; The ground projection lens satisfies CRA < 2°, where CRA represents the principal ray incident angle of the ground projection lens on the imaging surface; The first group of lenses successively includes a first lens G01, a second lens GM02, a third lens G03, a fourth lens G04, and a fifth lens G05 from the image source to the imaging side; The second group of lenses successively includes a sixth lens G06, a seventh lens G07, an eighth lens G08, and a ninth lens GM09 from the image source to the imaging side; The ratio of the focal length f1 of the first group of lenses to the effective focal length f of the ground projection lens is 0.753; The ratio of the focal length f2 of the second group of lenses to the effective focal length f of the ground projection lens is 1.

138.

2. The off-axis ground projection lens with a large depth of field according to claim 1, characterized in that, The first lens G01 is a biconcave lens with negative optical power, the second lens GM02 is a meniscus lens with negative optical power, the third lens G03 is a meniscus lens with positive optical power, the fourth lens G04 is a convex meniscus lens with positive optical power, and the fifth lens G05 is a convex meniscus lens with positive optical power.

3. The off-axis ground projection lens with large depth of field according to claim 2, wherein The sixth lens G06 is a biconcave lens with negative optical power, the seventh lens G07 and the eighth lens G08 are cemented lenses with negative optical power, and the ninth lens GM09 is a biconvex aspherical lens with positive optical power.

4. The off-axis ground projection lens with a large depth of field according to claim 3, characterized in that The focal length f of the second lens GM02 GM02 and the focal length f of the ninth lens GM09 GM09 are in a ratio of -2.54; The focal length f of the first lens G01 G01 is -1.072 times the effective focal length f of the ground projection lens; The focal length f of the second lens GM02 GM02 has a ratio of -2.616 to the effective focal length f of the ground projection lens; The focal length f of the third lens G03 G03 is 1.994 times the effective focal length f of the ground projection lens; The focal length f of the fourth lens G04 G04 is 1.871 times the effective focal length f of the ground projection lens; The focal length f of the fifth lens G05 G05 is 1.478 times the effective focal length f of the ground projection lens; The focal length f of the sixth lens G06 G06 has a ratio of -1.723 to the effective focal length f of the ground projection lens; The focal length f of the seventh lens G07 G07 and the focal length f of the eighth lens G08 G08 has a ratio of -1.479 to the effective focal length f of the ground projection lens; The focal length f of the ninth lens GM09 GM09 is 1.030 times the effective focal length f of the ground projection lens.

5. The off-axis ground projection lens with large depth of field according to claim 1, characterized in that, The first group of lenses with positive optical power, the diaphragm, the second group of lenses with positive optical power, the beam splitter device, and the protective glass are all made of glass.

6. The off-axis ground projection lens with large depth of field according to claim 1, characterized in that The angle between the projection picture plane and the optical axis is 10°, and the angles between the protective glass and the imaging surface and the optical axis are 87°.

Images