CN117331201A

CN117331201A - Projection system and AR projection device

Info

Publication number: CN117331201A
Application number: CN202311506759.2A
Authority: CN
Inventors: 谢检来; 明玉生; 汪杰; 陈远
Original assignee: Ningbo Sunny Olai Technology Co ltd
Current assignee: Ningbo Sunny Olai Technology Co ltd
Priority date: 2023-11-13
Filing date: 2023-11-13
Publication date: 2024-01-02

Abstract

The invention provides a projection system and an AR projection device. The projection system comprises a diaphragm, a first lens group, a second lens group and an imaging module, wherein the first lens group comprises a first lens and a prism, the first lens has positive focal power, the second lens group comprises a third lens, a fourth lens, a fifth lens and a sixth lens, and the third lens has positive focal power; the fourth lens has negative focal power, and the image side surface of the fourth lens is a concave surface; the fifth lens has positive focal power, and the image side surface of the fifth lens is a convex surface; the sixth lens is an aspheric lens, the object side surface of the sixth lens is a convex surface, and the image side surface of the sixth lens is a concave surface; the on-axis distance TTL from the object side surface of the first lens to the image source, the focal length f of the projection system and the use field angle FOV of the projection system satisfy the following conditions: 3.0mm < TTL/(f tan (FOV)) <4.0mm. The invention solves the problem that the miniaturization and high definition of the projection system in the prior art are difficult to be simultaneously compatible.

Description

Projection system and AR projection device

Technical Field

The invention relates to the technical field of optical projection equipment, in particular to a projection system and an AR projection device.

Background

With rapid development and wide popularization of portable electronic products, augmented Reality (AR) devices have wide application prospects in the fields of industry, education, medical treatment, outdoor exercises, navigation and the like. In both head-mounted AR display devices and vehicle-mounted head-up display devices, projection systems are a critical component, which is a core component for implementing electronic image visualization.

With the continued improvement of augmented reality technology and the increasing consumer demand for lightweight, miniaturized devices, the high definition, miniaturization, and weight saving of projection systems have become a necessary trend of development. However, in the conventional optical projection technology, it is often difficult to achieve good compatibility in terms of high definition and miniaturization. For example, it is difficult to achieve high contrast of images while pursuing miniaturization, because non-rotationally symmetrical, non-coaxial structural supports are often very tolerant, making it difficult to achieve high precision assembly.

That is, the projection system of the related art has a problem that it is difficult to achieve both miniaturization and high definition.

Disclosure of Invention

The invention mainly aims to provide a projection system and an AR projection device, so as to solve the problem that the miniaturization and high definition of the projection system in the prior art are difficult to be simultaneously combined.

In order to achieve the above objective, the present invention provides a projection system, which sequentially includes, from an object side to an image source, a diaphragm, a first lens group, a second lens group, and an imaging module, wherein the first lens group includes a first lens and a prism, the first lens has positive focal power, and an object side surface of the first lens is a convex surface; the second lens group comprises a third lens, a fourth lens, a fifth lens and a sixth lens, wherein the third lens has positive focal power, the object side surface of the third lens is a convex surface, and the image side surface of the third lens is a concave surface; the fourth lens has negative focal power, and the image side surface of the fourth lens is a concave surface; the fifth lens has positive focal power, and the image side surface of the fifth lens is a convex surface; the sixth lens is an aspheric lens, the object side surface of the sixth lens is a convex surface, and the image side surface of the sixth lens is a concave surface; a total of five lenses having optical curves in the projection system; the on-axis distance TTL from the object side surface of the first lens to the image source, the focal length f of the projection system and the use field angle FOV of the projection system satisfy the following conditions: 3.0mm < TTL/(f tan (FOV)) <4.0mm.

Further, the field of view FOV of the projection system is used to satisfy: 29 ° < FOV <31 °.

Further, the on-axis distance TTL from the object side of the first lens to the image source and the effective aperture SD21 of the object side of the prism satisfy: 2.3< TTL/SD21<3; and/or the on-axis distance TTL from the object side of the first lens to the image source and the effective aperture SD22 of the image side of the prism satisfy: 2.6< TTL/SD22<2.92.

Further, the effective caliber SD21 of the object side surface of the prism, the thickness CT2 of the prism on the optical axis, and the image source side half image height ImgH corresponding to the use field angle of the projection system satisfy: 10.8< SD21×CT2/ImgH <14.5.

Further, the focal length f of the projection system, the image source side half image height ImgH corresponding to the use field angle of the projection system, and the effective clear aperture EPD of the diaphragm satisfy: 2.748< f.imgh/EPD <2.782.

Further, the on-axis distance TTL from the object side of the first lens to the image source, the image source side half image height ImgH corresponding to the use field angle of the projection system, and the effective clear aperture EPD of the diaphragm satisfy: 4.945< ttl > imgh/EPD <6.269.

Further, the focal length f1 of the first lens and the focal length f of the projection system satisfy: 1.6< f1/f <2.96; the focal length f1 of the first lens and the radius of curvature R11 of the object side surface of the first lens satisfy: 0.97< f1/R11<1.78.

Further, the combined focal length f56 of the fifth lens and the sixth lens and the focal length f of the projection system satisfy: 0.552< f56/f <0.783.

Further, the combined focal length f123 from the first lens to the third lens and the focal length f of the projection system satisfy: 0.691< f123/f <1.046.

Further, the aperture has the same size as the coupling opening of the optical waveguide located outside the projection system.

Further, the optical waveguide is one of an array optical waveguide, a geometric optical waveguide and a diffraction optical waveguide.

According to another aspect of the present invention, there is also provided an AR projection apparatus, including the above projection system.

By applying the technical scheme of the invention, the projection system sequentially comprises a diaphragm, a first lens group, a second lens group and an imaging module from the object side to the image source, wherein the first lens group comprises a first lens and a prism, the first lens has positive focal power, and the object side of the first lens is a convex surface; the second lens group comprises a third lens, a fourth lens, a fifth lens and a sixth lens, wherein the third lens has positive focal power, the object side surface of the third lens is a convex surface, and the image side surface of the third lens is a concave surface; the fourth lens has negative focal power, and the image side surface of the fourth lens is a concave surface; the fifth lens has positive focal power, and the image side surface of the fifth lens is a convex surface; the sixth lens is an aspheric lens, the object side surface of the sixth lens is a convex surface, and the image side surface of the sixth lens is a concave surface; a total of five lenses having optical curves in the projection system; the on-axis distance TTL from the object side surface of the first lens to the image source, the focal length f of the projection system and the use field angle FOV of the projection system satisfy the following conditions: 3.0mm < TTL/(f tan (FOV)) <4.0mm.

The projection system comprises five lenses with optical curved surfaces and a prism with two planar side surfaces, the focal power and the surface type of each lens are reasonably planned, the on-axis distance TTL from the object side surface of the first lens to an image source is restrained, the relation between the focal length f of the projection system and the use angle FOV of the projection system is in the range of 3.0mm to 4.0mm, the overall length of the optical system is favorably considered when the focal length of the projection system and the use angle are used, the distortion control improvement and miniaturization of the system are important, the influence of distortion can be reduced while the high-definition projection effect is realized under the condition that the relation is satisfied, the overall length of the optics is kept in a range, and the maximum size of the system is favorably restrained from being too large, and the processing difficulty of the lens is also not too small.

In addition, the direction from the object side to the image source side of the prism is consistent with the direction from the object side to the image source side of the projection system, when the direction of transmitted light and reflected light generated after the light from illumination enters the prism is inconsistent with the direction of the diaphragm, the phenomenon that the transmitted part in the illumination light directly exits from the diaphragm to interfere with the normal projection image is avoided, and therefore the contrast ratio of the projection image is improved; the third lens to the sixth lens are sequentially arranged along the optical axis, and as the lenses are all on the same optical axis and can be processed into a rotationally symmetrical structure, the lens is favorable for being independently designed as a lens group when a lens assembly scheme is designed, and the high-precision assembly mode of the mobile phone lens is utilized for packaging assembly and splicing, so that the high-precision and high-yield assembly of the projection system is realized. The projection system has the advantages of miniaturization, light weight and high projection quality, and has higher assembly tolerance so as to facilitate mass production.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention. In the drawings:

FIG. 1 is a schematic diagram of a projection system according to a first embodiment of the present invention;

FIGS. 2-5 illustrate, respectively, a spherical aberration curve, a field curvature curve, a distortion curve, and a chromatic aberration curve of the projection system of FIG. 1;

FIG. 6 is a schematic diagram of a projection system according to a second embodiment of the present invention;

fig. 7 to 10 show a spherical aberration curve, a field curvature curve, a distortion curve, and a chromatic aberration curve, respectively, of the projection system of fig. 6;

FIG. 11 is a schematic diagram showing the structure of a projection system according to a third embodiment of the present invention;

fig. 12 to 15 show a spherical aberration curve, a field curvature curve, a distortion curve, and a chromatic aberration curve, respectively, of the projection system of fig. 11.

Wherein the above figures include the following reference numerals:

101. a diaphragm; 101. a first lens; L1S1, an object side surface of the first lens; L1S2, the image side of the first lens; 103. a prism; L2S1, the object side surface of the prism; L2S2, the image side of the prism; 104. a third lens; L3S1, object side of the third lens; L3S2, the image side of the third lens; 105. a fourth lens; L4S1, object side of the fourth lens; L4S2, the image side of the fourth lens; 106. a fifth lens; L5S1, object side of the fifth lens; L5S2, the image side of the fifth lens; 107. a sixth lens; L6S1, object side of the sixth lens; L6S2, the image side of the sixth lens; 108. a protective glass; 109. an image source plane.

Detailed Description

It should be noted that, in the case of no conflict, the embodiments and features in the embodiments may be combined with each other. The invention will be described in detail below with reference to the drawings in connection with embodiments.

It is noted that all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs unless otherwise indicated.

In the present invention, unless otherwise indicated, terms of orientation such as "upper, lower, top, bottom" are used generally with respect to the orientation shown in the drawings or with respect to the component itself in the vertical, upright or gravitational direction; also, for ease of understanding and description, "inner and outer" refers to inner and outer relative to the profile of each component itself, but the above-mentioned orientation terms are not intended to limit the present invention.

It should be noted that in the present specification, the expressions of first, second, third, etc. are only used to distinguish one feature from another feature, and do not represent any limitation on the feature. Accordingly, a first lens discussed below may also be referred to as a second lens or a third lens without departing from the teachings of the present application.

In the drawings, the thickness, size, and shape of the lenses have been slightly exaggerated for convenience of explanation. Specifically, the spherical or aspherical shape shown in the drawings is shown by way of example. That is, the shape of the spherical or aspherical surface is not limited to the shape of the spherical or aspherical surface shown in the drawings. The figures are merely examples and are not drawn to scale.

Herein, the paraxial region refers to a region near the optical axis. If the lens surface is convex and the convex position is not defined, then the lens surface is convex at least in the paraxial region; if the lens surface is concave and the concave position is not defined, it means that the lens surface is concave at least in the paraxial region. The surface of each lens near the object side becomes the object side of the lens, and the surface of each lens near the image side is called the image side of the lens. The determination of the surface shape in the paraxial region can be performed by a determination method by a person skilled in the art by positive or negative determination of the concave-convex with R value (R means the radius of curvature of the paraxial region, and generally means the R value on a lens database (lens data) in optical software). In the object side surface, when the R value is positive, the object side surface is judged to be convex, and when the R value is negative, the object side surface is judged to be concave; in the image side, the concave surface is determined when the R value is positive, and the convex surface is determined when the R value is negative.

In order to solve the problem that the miniaturization and high definition of the projection system in the prior art are difficult to be simultaneously compatible, the invention provides a projection system and an AR projection device.

As shown in fig. 1 to 15, in an alternative embodiment of the present application, the projection system includes, in order from an object side to an image source, a diaphragm, a first lens group, a second lens group, and an imaging module, where the first lens group includes a first lens and a prism, the first lens has positive optical power, and an object side of the first lens is a convex surface; the second lens group comprises a third lens, a fourth lens, a fifth lens and a sixth lens, wherein the third lens has positive focal power, the object side surface of the third lens is a convex surface, and the image side surface of the third lens is a concave surface; the fourth lens has negative focal power, and the image side surface of the fourth lens is a concave surface; the fifth lens has positive focal power, and the image side surface of the fifth lens is a convex surface; the sixth lens is an aspheric lens, the object side surface of the sixth lens is a convex surface, and the image side surface of the sixth lens is a concave surface; a total of five lenses having optical curves in the projection system; the on-axis distance TTL from the object side surface of the first lens to the image source, the focal length f of the projection system and the use field angle FOV of the projection system satisfy the following conditions: 3.0mm < TTL/(f tan (FOV)) <4.0mm.

It should be noted that the imaging module at least includes a piece of protective glass.

It should be noted that the first lens is a positive focal power lens with a convex object side, which is beneficial to converging and coupling out system light rays and is beneficial to manufacturing structural support at the edge of the lens; the prism facilitates access to illumination when using an image source of a passive light source and acts as part of an illumination system; the third lens is a meniscus lens with positive focal power, which is favorable for correcting aberration of the system and improving imaging quality, and the third lens is matched with the first lens to realize converging and coupling out of light rays of an image source; the fourth lens is a negative focal power lens with a concave image side surface, has an important effect on correcting chromatic aberration of the system, and balances aberration of the system; the fifth lens is a positive focal power lens, plays a certain role in converging and converging divergent light rays from an image source, and reduces the maximum caliber of the whole projection light beam; the sixth lens is an aspheric lens, plays a role in correcting various levels of aberration on divergent light rays from an image source, and meanwhile, realizes the role of telecentric light beams of an image space by utilizing the characteristics of the aspheric surface, so that the coupling-out efficiency of the projection system on the light rays of the image source is improved.

In a specific embodiment of the present application, the field of view FOV of the projection system is used to satisfy: 29 ° < FOV <31 °. The view angle FOV is limited to be the range, so that the projection view angle can be limited to be in a range which gives consideration to the viewing effect of human eyes and the reasonable coupling angle of the optical waveguide, and the high-definition projection with small distortion is realized.

In the specific embodiment of the present application, the on-axis distance TTL from the object side of the first lens element to the image source and the effective aperture SD21 of the object side of the prism satisfy: 2.3< TTL/SD21<3; the on-axis distance TTL from the object side of the first lens element to the image source and the effective aperture SD22 of the image side of the prism satisfy: 2.6< TTL/SD22<2.92. The above relation is satisfied, which is beneficial to limiting the total optical length under the condition of determining the coupling outlet of the system, and is beneficial to limiting the size of the first lens under the condition of determining the total optical length, so that miniaturization is facilitated.

In the specific embodiment of the present application, the effective aperture SD21 of the object side surface of the prism, the thickness CT2 of the prism on the optical axis, and the image source side half image height ImgH corresponding to the use field angle of the projection system satisfy: 10.8< SD21×CT2/ImgH <14.5. The method meets the condition, is favorable for ensuring that the thickness and the height of the prism are in a relatively reasonable range under the condition of smaller half-image height, and is favorable for simultaneously considering the processability of the prism and the height and the total length of the system and simultaneously being favorable for connecting an illumination system into a illuminated image source system.

In a specific embodiment of the present application, the focal length f of the projection system, the image source side half image height ImgH corresponding to the use field angle of the projection system, and the effective clear aperture EPD of the diaphragm satisfy: 2.748< f.imgh/EPD <2.782. The method meets the conditional expression, is favorable for ensuring a smaller distortion and a larger coupling-out aperture of the projection system, and the larger coupling-out aperture is favorable for improving the light output of the projection system and the light coupling-in of the optical waveguide, so as to obtain a better projection effect.

In a specific embodiment of the present application, the on-axis distance TTL between the object side surface of the first lens element and the image source, the image source side half image height ImgH corresponding to the use field angle of the projection system, and the effective clear aperture EPD of the diaphragm satisfy: 4.945< ttl > imgh/EPD <6.269. The condition is satisfied, which is beneficial to limiting the total length of the system in a reasonable range while ensuring the coupling aperture and is beneficial to miniaturization of the projection system.

In a specific embodiment of the present application, the focal length f1 of the first lens and the focal length f of the projection system satisfy: 1.6< f1/f <2.96; the focal length f1 of the first lens and the radius of curvature R11 of the object side surface of the first lens satisfy: 0.97< f1/R11<1.78. The optical power of the first lens is in a reasonable range, so that light rays from the prism are smoothly received, converged and coupled out, and partial aberration is corrected; limiting the radius of curvature of the object-side surface of the first lens is beneficial to manufacturing the structural support of the first lens, and the problem that aberration is increased due to too small radius of curvature is avoided.

In a specific embodiment of the present application, the combined focal length f56 of the fifth lens and the sixth lens and the focal length f of the projection system satisfy: 0.552< f56/f <0.783. The lens has the advantages that the lens meets the relation, the larger focal power of the lens at the image source side is favorably maintained, the convergence capacity of the lens to telecentric divergent beams from the image source is improved, meanwhile, the problem of overlarge system caliber caused by outward diffusion of marginal rays is avoided, and the miniaturization of the system is favorably realized.

In a specific embodiment of the present application, the combined focal length f123 of the first lens to the third lens and the focal length f of the projection system satisfy: 0.691< f123/f <1.046. The relation is satisfied, so that the front part, close to the diaphragm, of the projection system has moderate combined focal power, and the focal power distribution of the front lens and the rear lens is facilitated, the whole system structure is more uniform, the chromatic aberration and the spherical aberration of the system are balanced, and the projection quality is improved.

In a specific embodiment of the present application, the aperture is the same size as the coupling opening of the optical waveguide located outside the projection system. Specifically, the diaphragm may be an effective aperture of the object side surface of the first lens, or an edge of the lens barrel, or a plate protection glass, or a coupling port of the optical waveguide.

In a specific embodiment of the present application, the optical waveguide is one of an arrayed optical waveguide, a geometric optical waveguide, and a diffractive optical waveguide. The array optical waveguide is a structure composed of a plurality of optical waveguides which are arranged in parallel, the geometric optical waveguide is a structure which realizes light refraction and reflection conduction by different refractive index distribution, and the diffraction optical waveguide is a structure which realizes image light beam expansion, coupling-in and coupling-out by using a diffraction grating.

The invention also provides an AR projection device, which comprises the projection system. The arrangement enables the whole size of the AR projection device to be compressed, is beneficial to being applied to miniaturization or head-mounted equipment, and achieves miniaturization while guaranteeing the quality of projection pictures.

Specifically, the lens in the projection system of the invention can be a spherical or aspherical glass lens, or can be a spherical or aspherical injection lens, and can be specifically set according to actual requirements.

In the present application, at least one of the mirrors of each lens is an aspherical mirror. The aspherical lens is characterized in that: the curvature varies continuously from the center of the lens to the periphery of the lens. Unlike a spherical lens having a constant curvature from the center of the lens to the periphery of the lens, an aspherical lens has a better radius of curvature characteristic, and has advantages of improving distortion aberration and improving astigmatic aberration. By adopting the aspherical lens, aberration occurring at the time of imaging can be eliminated as much as possible, thereby improving imaging quality.

In view of the fact that the aspheric surface is a structure obtained by rotating a curved surface in a meridian plane around an optical axis for one circle, the structure has rotational symmetry, and in an ideal optical system, aberration of the meridian plane and the sagittal plane can be well corrected; meanwhile, due to the unique lens model, enough space can be provided for subsequent relevant adjustment, so that relevant structures and assembly processes are more flexible and excessive imaging quality is not reduced.

Examples of specific facets, parameters, which may be suitable for use in the projection system of the above-described embodiments are further described below with reference to the accompanying drawings.

It should be noted that any one of the following examples one to three is applicable to all the embodiments of the present application.

Example 1

As shown in fig. 1 to 5, a projection system of the first embodiment is described. Fig. 1 shows a schematic configuration of a projection system according to a first embodiment.

As shown in fig. 1, the projection system sequentially includes, from an object side to an image source side along an optical axis: a diaphragm 101, a first lens 102, a prism 103, a third lens 104, a fourth lens 105, a fifth lens 106, a sixth lens 107, a cover glass 108, and an image source surface 109.

The first lens 102 has positive refractive power, wherein an object side surface L1S1 of the first lens is convex, and an image side surface L1S2 of the first lens is planar. The object side face L2S1 of the prism is a plane, and the image side face L2S2 of the prism is a plane. The third lens element 104 has positive refractive power, wherein an object-side surface L3S1 of the third lens element is convex, and an image-side surface L3S2 of the third lens element is concave. The fourth lens element 105 has negative refractive power, wherein an object-side surface L4S1 of the fourth lens element is concave, and an image-side surface L4S2 of the fourth lens element is concave. The fifth lens element 106 has positive refractive power, wherein an object-side surface L5S1 of the fifth lens element is concave, and an image-side surface L5S2 of the fifth lens element is convex. The sixth lens 107 has positive power, the object-side surface L6S1 of the sixth lens is convex, and the image-side surface L6S2 of the sixth lens is concave.

In this embodiment, the total effective focal length f of the projection system is 6.392mm, the total length TTL of the projection system is 13.030mm, the field angle FOV of use of the projection system is 30 degrees, and the f-number FNO of the projection system is 1.598.

Table 1 shows a basic structural parameter table of the projection system of the first embodiment, in which the unit of curvature radius, thickness/distance is millimeter (mm).

TABLE 1

In the first embodiment, the surface shape of each aspherical lens can be defined by, but not limited to, the following aspherical formula:

wherein x is the distance vector height from the vertex of the aspheric surface when the aspheric surface is at the position with the height h along the optical axis direction; c is the paraxial curvature of the aspheric surface, c=1/R (i.e., paraxial curvature c is the inverse of radius of curvature R in table 1 above); k is a conic coefficient; ai is the correction coefficient of the aspherical i-th order. The higher order coefficients A4, A6, A8, A10, A12, A14, A16, A18, A20 that can be used for each of the aspherical mirrors in example one are given in Table 2 below.

TABLE 2

Fig. 2 shows a spherical aberration curve of the projection system of the first embodiment. Fig. 3 shows a field curvature of a projection system of the first embodiment. Fig. 4 shows a distortion curve of the projection system of the first embodiment. Fig. 5 shows a color difference curve of the projection system of the first embodiment.

As can be seen from fig. 2 to 5, the projection system according to the first embodiment can achieve good imaging quality.

Example two

As shown in fig. 6 to 10, the projection system of the second embodiment is described. Fig. 6 shows a schematic configuration of a projection system according to the second embodiment.

As shown in fig. 6, the projection system includes, in order from an object side to an image source side along an optical axis: a diaphragm 101, a first lens 102, a prism 103, a third lens 104, a fourth lens 105, a fifth lens 106, a sixth lens 107, a cover glass 108, and an image source surface 109.

The first lens element 102 has positive refractive power, wherein an object-side surface L1S1 of the first lens element is convex, and an image-side surface L1S2 of the first lens element is concave. The object side face L2S1 of the prism is a plane, and the image side face L2S2 of the prism is a plane. The third lens element 104 has positive refractive power, wherein an object-side surface L3S1 of the third lens element is convex, and an image-side surface L3S2 of the third lens element is concave. The fourth lens element 105 has negative refractive power, wherein an object-side surface L4S1 of the fourth lens element is convex, and an image-side surface L4S2 of the fourth lens element is concave. The fifth lens element 106 has positive refractive power, wherein an object-side surface L5S1 of the fifth lens element is convex, and an image-side surface L5S2 of the fifth lens element is convex. The sixth lens 107 has negative power, the object-side surface L6S1 of the sixth lens is convex, and the image-side surface L6S2 of the sixth lens is concave.

In this embodiment, the total effective focal length f of the projection system is 6.460mm, the total length TTL of the projection system is 11.500mm, the field angle FOV of use of the projection system is 30 °, and the f-number FNO of the projection system is 1.61.

Table 3 shows a basic structural parameter table of the projection system of the second embodiment, in which the unit of radius of curvature, thickness/distance is millimeter (mm).

TABLE 3 Table 3

Table 4 shows the higher order coefficients that can be used for each aspherical mirror in embodiment two, where each aspherical surface profile can be defined by equation (1) given in embodiment one above.

TABLE 4 Table 4

Fig. 7 shows a spherical aberration curve of the projection system of the second embodiment. Fig. 8 shows a field curvature of the projection system of the second embodiment. Fig. 9 shows a distortion curve of the projection system of the second embodiment. Fig. 10 shows a color difference curve of the projection system of the second embodiment.

As can be seen from fig. 7 to fig. 10, the projection system according to the second embodiment can achieve good imaging quality.

Example III

As shown in fig. 11 to 15, the projection system of the third embodiment is described. Fig. 11 shows a schematic configuration of a projection system of the third embodiment.

As shown in fig. 11, the projection system includes, in order from an object side to an image source side along an optical axis: a diaphragm 101, a first lens 102, a prism 103, a third lens 104, a fourth lens 105, a fifth lens 106, a sixth lens 107, a cover glass 108, and an image source surface 109.

The first lens element 102 has positive refractive power, wherein an object-side surface L1S1 of the first lens element is convex, and an image-side surface L1S2 of the first lens element is convex. The object side face L2S1 of the prism is a plane, and the image side face L2S2 of the prism is a plane. The third lens element 104 has positive refractive power, wherein an object-side surface L3S1 of the third lens element is convex, and an image-side surface L3S2 of the third lens element is concave. The fourth lens element 105 has negative refractive power, wherein an object-side surface L4S1 of the fourth lens element is concave, and an image-side surface L4S2 of the fourth lens element is concave. The fifth lens element 106 has positive refractive power, wherein an object-side surface L5S1 of the fifth lens element is convex, and an image-side surface L5S2 of the fifth lens element is convex. The sixth lens 107 has negative power, the object-side surface L6S1 of the sixth lens is convex, and the image-side surface L6S2 of the sixth lens is concave.

In this embodiment, the total effective focal length f of the projection system is 6.469mm, the total length TTL of the projection system is 14.610mm, the field angle FOV of use of the projection system is 30 degrees, and the f-number FNO of the projection system is 1.61.

Table 5 shows a basic structural parameter table of the projection system of the third embodiment, in which the unit of radius of curvature, thickness/distance is millimeter (mm).

TABLE 5

Table 6 shows the higher order coefficients that can be used for each aspherical mirror in the third embodiment, wherein each aspherical surface profile can be defined by the formula (1) given in the above-described embodiment one.

TABLE 6

Fig. 12 shows a spherical aberration curve of the projection system of the third embodiment. Fig. 13 shows a field curvature of a projection system of the third embodiment. Fig. 14 shows a distortion curve of the projection system of the third embodiment. Fig. 15 shows a color difference curve of the projection system of the third embodiment.

As can be seen from fig. 12 to 15, the projection system according to the third embodiment can achieve good imaging quality.

In summary, examples one to three satisfy the relationships shown in table 7, respectively.

Condition/example	1	2	3
				TTL/(f*tan(FOV))	3.533	3.085	3.914
TTL/SD21	2.606	2.665	2.927
				TTL/SD22	2.606	2.665	2.927
SD21*CT2/ImgH	13.661	10.179	13.612
				f*ImgH/EPD	2.924	2.955	2.960
TTL*ImgH/EPD	5.961	5.245	6.654
				f1/f	2.522	1.596	2.958
f1/R11	1.785	1.682	0.975
				f56/f	0.783	0.719	0.552
f123/f	0.927	0.691	1.034

TABLE 7

Table 8 shows the effective focal lengths f of the projection systems of the first to third embodiments, the effective focal lengths f1, f3 to f6, etc. (unit: mm) of the respective lenses.

TABLE 8

It will be apparent that the embodiments described above are merely some, but not all, embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments in accordance with the present application. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the terms "comprises" and/or "comprising" when used in this specification are taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.

It should be noted that the terms "first," "second," and the like in the description and claims of the present application and the above figures are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged where appropriate such that embodiments of the present application described herein may be implemented in sequences other than those illustrated or described herein.

The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A projection system is characterized by sequentially comprising a diaphragm, a first lens group, a second lens group and an imaging module from an object side to an image source,

the first lens group comprises a first lens and a prism, wherein the first lens has positive focal power, and the object side surface of the first lens is a convex surface;

the second lens group comprises a third lens, a fourth lens, a fifth lens and a sixth lens, wherein the third lens has positive focal power, the object side surface of the third lens is a convex surface, and the image side surface of the third lens is a concave surface; the fourth lens has negative focal power, and the image side surface of the fourth lens is a concave surface; the fifth lens has positive focal power, and the image side surface of the fifth lens is a convex surface; the sixth lens is an aspheric lens, the object side surface of the sixth lens is a convex surface, and the image side surface of the sixth lens is a concave surface;

a total of five lenses with optical curved surfaces in the projection system; an on-axis distance TTL from an object side surface of the first lens to an image source, a focal length f of the projection system, and a field of view angle FOV of the projection system satisfy: 3.0mm < TTL/(f tan (FOV)) <4.0mm.

2. The projection system of claim 1 wherein the field of view FOV of the projection system is: 29 ° < FOV <31 °.

3. The projection system of claim 1 wherein the projection system comprises a projection system,

the on-axis distance TTL from the object side surface of the first lens to the image source and the effective caliber SD21 of the object side surface of the prism satisfy the following conditions: 2.3< TTL/SD21<3; and/or

The on-axis distance TTL from the object side surface of the first lens to the image source and the effective caliber SD22 of the image side surface of the prism satisfy the following conditions: 2.6< TTL/SD22<2.92.

4. A projection system according to claim 3, wherein the effective aperture SD21 of the object side of the prism, the thickness CT2 of the prism on the optical axis, and the image source side half image height ImgH corresponding to the field angle of use of the projection system satisfy: 10.8< SD21×CT2/ImgH <14.5.

5. The projection system of claim 1, wherein a focal length f of the projection system, an image source side half image height ImgH corresponding to a use field angle of the projection system, and an effective clear aperture EPD of the diaphragm satisfy: 2.748< f.imgh/EPD <2.782.

6. The projection system of claim 5, wherein an on-axis distance TTL from the object side of the first lens to the image source, an image source side half image height ImgH corresponding to a field of view of the projection system, and an effective clear aperture EPD of the diaphragm satisfy: 4.945< ttl > imgh/EPD <6.269.

7. The projection system of any of claims 1 to 6 wherein,

the focal length f1 of the first lens and the focal length f of the projection system satisfy the following conditions: 1.6< f1/f <2.96;

the focal length f1 of the first lens and the curvature radius R11 of the object side surface of the first lens satisfy: 0.97< f1/R11<1.78.

8. The projection system of any of claims 1 to 6, wherein a combined focal length f56 of the fifth lens and the sixth lens and a focal length f of the projection system satisfy: 0.552< f56/f <0.783.

9. The projection system of any of claims 1 to 6, wherein a combined focal length f123 of the first lens to the third lens and a focal length f of the projection system satisfy: 0.691< f123/f <1.046.

10. An AR projection device, characterized in that it comprises the projection system of any of claims 1 to 9.