Optical system
By adopting a four-piece lens foldback optical system, combined with reasonable power distribution and lens thickness and radius of curvature configuration, the problem of poor imaging quality in the prior art is solved, and higher imaging quality and focus ability are achieved.
Patent Information
- Application Number
- CN202421863163.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-08-02
- Publication Date
- 2025-06-24
- Estimated Expiration
- 2034-08-02
AI Technical Summary
The existing fold-trans optics are not ideal in virtual reality devices, resulting in blurred pictures.
A foldback optical system with four lenses is adopted. By reasonably allocating the system's power, and reasonably configuring the thickness and curvature radius of the lens, an appropriate filming method is used to improve the imaging quality.
It achieves better imaging quality, enhances the optical system's focus ability to light, reduces distortion, and reduces process difficulty and cost.
Smart Images
Figure CN223022466U_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of optical devices, and more particularly to an optical system. Background Art
[0002] Virtual reality technology has broad prospects and great potential in the market. With the continuous development and popularization of technology, virtual reality technology has gradually moved out of the field of game entertainment and began to be applied in various fields such as education, medical treatment, tourism, and real estate. In the future, with the continuous improvement of hardware devices and the gradual decline of costs, virtual reality technology will become more popular and become an indispensable part of people's lives and work. The advantage of virtual reality technology is that it can provide an immersive experience, allowing users to feel the virtual world as if they were there, which is incomparable to traditional flat screens.
[0003] Virtual reality devices using catadioptric optical systems are known. The catadioptric optical system shortens the body length of the optical system by refracting the optical path, thereby shifting the center of gravity of the virtual reality device or augmented reality device backward and enhancing the user experience. However, existing catadioptric optical systems usually use two lenses, resulting in a relatively blurred image and unsatisfactory imaging quality in the catadioptric optical system. Summary of the Utility Model
[0004] This application provides an optical system that can at least solve or partially solve at least one problem or other problems existing in the prior art.
[0005] On the one hand, the present application provides an optical system which sequentially includes, from the first side to the second side along the optical axis: a first lens with positive optical power, whose first side is convex and the second side is flat; a reflective polarizing element placed on the second side of the first lens and at least partially adhered to the second side of the first lens; a first quarter-wave plate placed on the second side of the reflective polarizing element and at least partially adhered to the second side of the reflective polarizing element; a second lens with positive optical power; a third lens with negative optical power, whose first side is concave; a partial reflection element; a fourth lens with optical power, whose second side is flat; a second quarter-wave plate placed on the second side of the fourth lens and at least partially adhered to the second side of the fourth lens; and a polarizer placed on the second side of the second quarter-wave plate and at least partially adhered to the second side of the second quarter-wave plate. The optical system satisfies: 1.1 < f2 / f < 1.7, -1.1 < f / f3 < -0.45, and 6.1 < fz1 / (CT1 + CTR + CTQ1) < 6.7, where f2 is the effective focal length of the second lens, f is the total effective focal length of the optical system, f3 is the effective focal length of the third lens, fz1 is the combined focal length of the first lens, the reflective polarizing element, and the first quarter-wave plate, CT1 is the central thickness of the first lens on the optical axis, CTR is the central thickness of the reflective polarizing element on the optical axis, and CTQ1 is the central thickness of the first quarter-wave plate on the optical axis.
[0006] The optical system provided by the present application is a catadioptric optical system using four lenses. By reasonably distributing the optical power of the system, reasonably setting the thicknesses of the first lens, the reflective polarizing element, and the first quarter-wave plate, and adopting an appropriate film pasting method, it is beneficial to achieve better imaging quality and reduce the process difficulty and cost. Specifically, on the premise that f2 / f and f / f3 are set within a reasonable range, satisfying 6.1 < fz1 / (CT1 + CTR + CTQ1) < 6.7 helps to improve the imaging quality of the optical system, enhance the light focusing ability of the optical system, and reduce distortion. Film pasting on the flat second side of the fourth lens and the flat second side of the first lens can effectively reduce the film pasting difficulty, simplify the manufacturing process of the optical system, and reduce the process difficulty and manufacturing cost of the optical system.
[0007] On the other hand, the present application provides an optical system which sequentially includes, along the optical axis from the first side to the second side: a first lens with a positive focal power, whose first side is convex and second side is flat; a reflective polarizing element placed on the second side of the first lens and at least partially adhered to the second side of the first lens; a first quarter-wave plate placed on the second side of the reflective polarizing element and at least partially adhered to the second side of the reflective polarizing element; a second lens with a positive focal power; a third lens with a negative focal power, whose first side is concave; a partially reflective element; a fourth lens with a focal power, whose second side is flat; a second quarter-wave plate placed on the second side of the fourth lens and at least partially adhered to the second side of the fourth lens; and a polarizer placed on the second side of the second quarter-wave plate and at least partially adhered to the second side of the second quarter-wave plate. The optical system satisfies: 1.1 < f2 / f < 1.7, -1.1 < f / f3 < -0.45, and 0.15 < f23 / R6 < 1.05, where f2 is the effective focal length of the second lens, f is the total effective focal length of the optical system, f3 is the effective focal length of the third lens, f23 is the combined focal length of the second lens and the third lens, and R6 is the radius of curvature of the second side of the third lens.
[0008] The optical system provided by the present application is a catadioptric optical system using four lenses. By reasonably distributing the system focal power, reasonably configuring the radius of curvature of the second side of the third lens, and adopting an appropriate film pasting method, it is beneficial to improve the imaging clarity and accuracy of the optical system and reduce the process difficulty and cost. Specifically, on the premise that f2 / f and f / f3 are set within a reasonable range, satisfying 0.15 < f23 / R6 < 1.05 is beneficial in providing a larger field of view angle for the optical system on the one hand, enabling users to see more virtual or augmented reality content, thereby enhancing the user's immersion and optimizing the experience, and on the other hand, being able to effectively reduce or eliminate the distortion or aberration generated by the optical system, improving the imaging clarity and accuracy. In addition, by pasting a film on the second flat side of the fourth lens and the second flat side of the first lens, the film pasting difficulty can be effectively reduced, the manufacturing process of the optical system can be simplified, and the process difficulty and manufacturing cost of the optical system can be reduced.
[0009] According to an exemplary embodiment of the present application, the refractive index N1 of the first lens, the dispersion coefficient V1 of the first lens, and the central thickness CT1 of the first lens on the optical axis satisfy: 6.9mm -1 <(V1 / N1) / CT1 < 7.65mm -1 。
[0010] According to an exemplary embodiment of the present application, the radius of curvature R1 of the first side of the first lens and the central thickness CT1 of the first lens on the optical axis satisfy: 3.05 < R1 / CT1 < 3.4.
[0011] According to an exemplary embodiment of the present application, the effective focal length f3 of the third lens, the refractive index N3 of the third lens, and the dispersion coefficient V3 of the third lens satisfy: -7.2 mm < f3 / (V3 / N3) ≤ -1.6 mm.
[0012] According to an exemplary embodiment of the present application, the on-axis distance T34 from the second side surface of the third lens to the first side surface of the fourth lens, the central thickness CT4 of the fourth lens on the optical axis, the central thickness CTQ2 of the second quarter-wave plate on the optical axis, and the central thickness CTL of the polarizer on the optical axis satisfy: 9.4 < (T34 + CT4) / (CTQ2 + CTL) < 17.8.
[0013] According to an exemplary embodiment of the present application, the radius of curvature R1 of the first side surface of the first lens and the radius of curvature R5 of the first side surface of the third lens satisfy: -1.0 < R1 / R5 < -0.15.
[0014] According to an exemplary embodiment of the present application, the effective focal length f1 of the first lens and the effective focal length f4 of the fourth lens satisfy: 0.35 < f1 / |f4| < 2.3.
[0015] According to an exemplary embodiment of the present application, the on-axis distance T23 from the second side surface of the second lens to the first side surface of the third lens, the central thickness CT3 of the third lens on the optical axis, and the effective focal length f3 of the third lens satisfy: -0.2 < (T23 + CT3) / f3 < -0.05.
[0016] According to an exemplary embodiment of the present application, the on-axis distance SAG31 between the intersection point of the first side surface of the third lens and the optical axis and the vertex of the effective semi-aperture of the first side surface of the third lens and the central thickness CT3 of the third lens on the optical axis satisfy: -0.5 < SAG31 / CT3 < -0.1.
[0017] According to an exemplary embodiment of the present application, the on-axis distance SAG41 between the intersection point of the first side surface of the fourth lens and the optical axis and the vertex of the effective semi-aperture of the first side surface of the fourth lens, the central thickness CTQ2 of the second quarter-wave plate on the optical axis, and the central thickness CTL of the polarizer on the optical axis satisfy: 2.6 < |SAG41| / (CTQ2 + CTL) < 6.55.
[0018] According to an exemplary embodiment of the present application, the combined focal length f23 of the second lens and the third lens and the radius of curvature R6 of the second side surface of the third lens satisfy: 0.15 < f23 / R6 < 1.05.
[0019] According to an exemplary embodiment of the present application, the total effective focal length f of the optical system, the on-axis distance T12 from the second side of the first lens to the first side of the second lens, and the central thickness CT2 of the second lens on the optical axis satisfy: 4.55 ≤ f / (T12 + CT2) < 5.6.
[0020] According to an exemplary embodiment of the present application, the optical system further includes a diaphragm; wherein, the on-axis distance SR from the diaphragm to the first side of the first lens and the on-axis distance SAG11 between the intersection of the first side of the first lens and the optical axis and the vertex of the effective semi-aperture of the first side of the first lens satisfy: 4.0 < SR / SAG11 < 4.3.
[0021] According to an exemplary embodiment of the present application, the on-axis distance TD from the first side of the first lens to the second side of the fourth lens and the entrance pupil diameter EPD of the optical system satisfy: 0.95 < TD / EPD < 1.05. Description of the Drawings
[0022] Other features, objects, and advantages of the present application will become more apparent by reading the detailed description of the non-limiting embodiments with reference to the following drawings. In the drawings:
[0023] Figure 1 A schematic structural diagram of the optical system according to Embodiment 1 of the present application is shown;
[0024] Figures 2A to 2D The axial chromatic aberration curve, astigmatism curve, distortion curve, and modulation transfer function curve of the optical system according to Embodiment 1 of the present application are shown;
[0025] Figure 3 A schematic structural diagram of the optical system according to Embodiment 2 of the present application is shown;
[0026] Figures 4A to 4D The axial chromatic aberration curve, astigmatism curve, distortion curve, and modulation transfer function curve of the optical system according to Embodiment 2 of the present application are shown;
[0027] Figure 5 A schematic structural diagram of the optical system according to Embodiment 3 of the present application is shown;
[0028] Figures 6A to 6D The axial chromatic aberration curve, astigmatism curve, distortion curve, and modulation transfer function curve of the optical system according to Embodiment 3 of the present application are shown;
[0029] Figure 7 A schematic structural diagram of the optical system according to Embodiment 4 of the present application is shown;
[0030] Figures 8A to 8DShows the axial chromatic aberration curve, astigmatism curve, distortion curve, and modulation transfer function curve of the optical system according to Embodiment 4 of the present application. Detailed implementation
[0031] To better understand the present application, more detailed descriptions of various aspects of the present application will be made with reference to the accompanying drawings. It should be understood that these detailed descriptions are only descriptions of exemplary embodiments of the present application and do not limit the scope of the present application in any way. Throughout the specification, the same reference numerals refer to the same elements.
[0032] It should be noted that in this specification, the expressions such as first and second are only used to distinguish one feature from another feature and do not represent any limitation on the feature. Therefore, without departing from the teachings of the present application, the first lens discussed below may also be referred to as the second lens.
[0033] In the drawings, for ease of illustration, the thickness, size, and shape of the lens have been slightly exaggerated. Specifically, the shape of the spherical or aspherical surface 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 spherical or aspherical shape shown in the drawings. The drawings are only for illustration and are not drawn to an exact scale.
[0034] In this article, the paraxial region refers to the region near the optical axis. If the lens surface is convex and the position of the convex surface is not defined, it means that the lens surface is convex at least in the paraxial region; if the lens surface is concave and the position of the concave surface is not defined, it means that the lens surface is concave at least in the paraxial region. The surface of each lens closest to the first side (such as the human eye side) is called the first side surface of the lens, and the surface of each lens closest to the second side (such as the display screen side) is called the second side surface of the lens.
[0035] It should also be understood that the terms "comprising", "including", "having", "containing" and / or "including", when used in this specification, mean the presence of the stated features, elements and / or components, but do not exclude the presence or addition of one or more other features, elements, components and / or combinations thereof. In addition, when describing the embodiments of the present application, the use of "may" means "one or more embodiments of the present application". And the term "exemplary" is intended to refer to an example or illustration.
[0036] Unless otherwise defined, all terms (including 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. It should also be understood that terms (such as those defined in a common dictionary) should be interpreted as having a meaning consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
[0037] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments may be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.
[0038] The features, principles and other aspects of the present application will be described in detail below.
[0039] Referring to Figure 1 , a first aspect of the present application provides an optical system, which includes a first lens, a reflective polarizing element, a first quarter-wave plate, a second lens, a third lens, a partial reflection element, a fourth lens, a second quarter-wave plate, and a polarizer arranged in sequence along the optical axis from the first side to the second side.
[0040] In an exemplary embodiment, the reflective polarizing element is placed on the second side surface of the first lens and at least partially adheres to the second side surface of the first lens. The first quarter-wave plate is placed on the second side surface of the reflective polarizing element and at least partially adheres to the second side surface of the reflective polarizing element. The second quarter-wave plate is placed on the second side surface of the fourth lens and at least partially adheres to the second side surface of the fourth lens. The polarizer is placed on the second side surface of the second quarter-wave plate and at least partially adheres to the second side surface of the second quarter-wave plate.
[0041] In an exemplary embodiment, the first side may be, for example, the human eye side, and the second side may be, for example, the display screen side. Correspondingly, the first side surfaces of the respective elements (such as the first lens, the second lens, the third lens, the fourth lens, the first quarter-wave plate, and the second quarter-wave plate) may be referred to as the near-human-eye side surfaces, and the second side surfaces may be referred to as the near-screen side surfaces.
[0042] In an exemplary embodiment, an image plane may be provided on the second side of the optical system, and a display screen may be provided on the image plane. The image light from the display screen may sequentially pass through the polarizer, the second quarter-wave plate, the fourth lens, the third lens, the second lens, and the first quarter-wave plate, reach the reflective polarizing element, and then be reflected at the reflective polarizing element to form a first reflected image light. The first reflected image light passes through the first quarter-wave plate, the second lens, and the third lens and reaches the partial reflection element on the second side of the third lens, and then is reflected at the partial reflection element to form a second reflected image light. The second reflected image light sequentially passes through the third lens, the second lens, the first quarter-wave plate, the reflective polarizing element, the first lens to the aperture stop and finally projects into the user's eyes. The optical system provided by the present application folds the required optical path by a combination of light reflection and refraction without affecting the projection quality, effectively shortening the body length of the optical system.
[0043] In an exemplary embodiment, the second side surface of the first lens is a plane, and the second side surface of the fourth lens is a plane. The reflective polarizing element and the second quarter-wave plate are respectively attached to the second side surface of the first lens and the second side surface of the fourth lens. By laminating the planar sides of the first lens and the fourth lens, the lamination difficulty can be effectively reduced, the manufacturing process of the optical system can be simplified, and the process difficulty and manufacturing cost of the optical system can be reduced. Further, by combining the reflective polarizing element and the first quarter-wave plate together and then attaching them to the second planar side of the first lens, the lamination process difficulty can be reduced, the lamination quality can be improved, and thus the imaging performance of the optical system can be improved. By combining the second quarter-wave plate and the polarizer together and then attaching them to the second side surface of the fourth lens, the lamination process difficulty can be reduced, the lamination quality can be improved, and thus the imaging performance of the optical system can be improved.
[0044] In an exemplary embodiment, the first lens has a positive optical power, the second lens has a positive optical power, the third lens has a negative optical power, and the fourth lens has a positive or negative optical power.
[0045] In an exemplary embodiment, the optical system may further include a diaphragm, and the diaphragm is disposed between the first side and the first lens.
[0046] In an exemplary embodiment, the effective focal length f2 of the second lens and the total effective focal length f of the optical system satisfy: 1.1 < f2 / f < 1.7; the total effective focal length f of the optical system and the effective focal length f3 of the third lens satisfy: -1.1 < f / f3 < -0.45; the combined focal length fz1 of the first lens, the reflective polarizing element, and the first quarter-wave plate, the central thickness CTR of the reflective polarizing element on the optical axis, and the central thickness CTQ1 of the first quarter-wave plate on the optical axis satisfy: 6.1 < fz1 / (CT1 + CTR + CTQ1) < 6.7. When controlling the optical system to satisfy "1.1 < f2 / f < 1.7" and "-1.1 < f / f3 < -0.45", further controlling the relationship between the combined focal length of the first lens, the reflective polarizing element, and the first quarter-wave plate, the central thickness of the first lens on the optical axis, the central thickness of the reflective polarizing element on the optical axis, and the central thickness of the first quarter-wave plate on the optical axis within a certain range can effectively improve the imaging quality of the optical system, is beneficial to enhancing the light focusing ability of the optical system, and reducing distortion.
[0047] In an exemplary embodiment, the refractive index N1 of the first lens, the dispersion coefficient V1 of the first lens, and the central thickness CT1 of the first lens on the optical axis satisfy: 6.9mm -1 <(V1 / N1) / CT1 < 7.65mm -1By controlling the relationship between the refractive index of the first lens, the dispersion coefficient of the first lens, and the central thickness of the first lens on the optical axis within a certain range, the dispersion characteristics of the first lens can be effectively optimized, the color reproduction ability of the optical system can be improved, and the imaging quality of the optical system can be enhanced. At the same time, it is beneficial to reduce the aberrations that may occur in the optical system and reduce the generation of distortion and blur.
[0048] In an exemplary embodiment, the radius of curvature R1 of the first side surface of the first lens and the central thickness CT1 of the first lens on the optical axis satisfy: 3.05 < R1 / CT1 < 3.4. By reasonably configuring the ratio of the radius of curvature of the first side surface of the first lens to the central thickness of the first lens on the optical axis, the weight of the optical system can be reduced, the wearing comfort can be improved, and the lightweight design of the optical system can be achieved. The lightweight design can effectively relieve the pressure and discomfort when the user wears it. By controlling the radius of curvature and the central thickness of the first lens within a certain range, the manufacturing cost of the optical system can be reduced, and the production process of the optical system can be simplified.
[0049] In an exemplary embodiment, the effective focal length f3 of the third lens, the refractive index N3 of the third lens, and the dispersion coefficient V3 of the third lens satisfy: -7.2 mm < f3 / (V3 / N3) ≤ -1.6 mm. By reasonably configuring the relationship between the effective focal length of the third lens, the refractive index of the third lens, and the dispersion coefficient of the third lens, on the one hand, it is beneficial to achieve the convergence of light rays by the optical system, and then control the degree of dispersion, enabling the optical system to have appropriate dispersion characteristics in different wavelength ranges; on the other hand, it is beneficial to reduce the influence of the dispersion effect on imaging and improve the color accuracy and consistency of the optical system. At the same time, it is beneficial to enable the optical system to cover a wider spectral range, thereby meeting the application requirements of different wavelengths.
[0050] In an exemplary embodiment, the on-axis distance T34 from the second side surface of the third lens to the first side surface of the fourth lens, the central thickness CT4 of the fourth lens on the optical axis, the central thickness CTQ2 of the second quarter-wave plate on the optical axis, and the central thickness CTL of the polarizer on the optical axis satisfy: 9.4 < (T34 + CT4) / (CTQ2 + CTL) < 17.8. By reasonably configuring the relationship between the on-axis distance from the second side surface of the third lens to the first side surface of the fourth lens, the central thickness of the fourth lens on the optical axis, the central thickness of the second quarter-wave plate on the optical axis, and the central thickness of the polarizer on the optical axis, the compact design of the optical system can be effectively achieved, the volume and weight of the optical system can be effectively reduced, thereby improving the wearing convenience, and it can also effectively avoid the optical elements such as lenses from being too thin, which is beneficial to improving the adhesion of the second quarter-wave plate and reducing the difficulty of processing, forming, and assembling the optical system.
[0051] In an exemplary embodiment, the radius of curvature R1 of the first side surface of the first lens and the radius of curvature R5 of the first side surface of the third lens satisfy: -1.0 < R1 / R5 < -0.15. Reasonably configuring the ratio of the radius of curvature of the first side surface of the first lens to the radius of curvature of the first side surface of the third lens is beneficial to reducing or eliminating the aberration that may occur in the optical system, improving the imaging quality and clarity of the optical system, and at the same time is beneficial to reducing the manufacturing cost of the optical system, thereby improving production efficiency.
[0052] In an exemplary embodiment, the effective focal length f1 of the first lens and the effective focal length f4 of the fourth lens satisfy: 0.35 < f1 / |f4| < 2.3. Reasonably configuring the ratio of the effective focal length of the first lens to the effective focal length of the fourth lens can effectively optimize the imaging quality of the optical system, enhance the light focusing ability and reduce the distortion performance.
[0053] In an exemplary embodiment, the on-axis distance T23 from the second side surface of the second lens to the first side surface of the third lens, the central thickness CT3 of the third lens on the optical axis, and the effective focal length f3 of the third lens satisfy: -0.2 < (T23 + CT3) / f3 < -0.05. By controlling the relationship between the on-axis distance from the second side surface of the second lens to the first side surface of the third lens, the central thickness of the third lens on the optical axis, and the effective focal length of the third lens within a certain range, the axial distance ratio between the lenses can be reduced, thereby reducing the generation of aberration and improving the imaging quality and accuracy of the optical system.
[0054] In an exemplary embodiment, the on-axis distance SAG31 between the intersection point of the first side surface of the third lens and the optical axis and the vertex of the effective semi-aperture of the first side surface of the third lens and the central thickness CT3 of the third lens on the optical axis satisfy: -0.5 < SAG31 / CT3 < -0.1. Reasonably configuring the ratio of the on-axis distance between the intersection point of the first side surface of the third lens and the optical axis and the vertex of the effective semi-aperture of the first side surface of the third lens to the central thickness of the third lens on the optical axis can effectively optimize the optical performance in the optical system, ensure that the optical system has high imaging quality and imaging clarity. At the same time, controlling the total length and volume of the optical system is beneficial to realizing the portability and convenience of the optical system, and improving the convenience of users to carry and wear.
[0055] In an exemplary embodiment, the axial distance SAG41 between the intersection point of the first side surface of the fourth lens and the optical axis and the vertex of the effective semi-aperture of the first side surface of the fourth lens, the central thickness CTQ2 of the second quarter-wave plate on the optical axis, and the central thickness CTL of the polarizer on the optical axis satisfy: 2.6 < |SAG41| / (CTQ2 + CTL) < 6.55. By controlling the relationship between the axial distance between the intersection point of the first side surface of the fourth lens and the optical axis and the vertex of the effective semi-aperture of the first side surface of the fourth lens, the central thickness of the second quarter-wave plate on the optical axis, and the central thickness of the polarizer on the optical axis within a certain range, the optical performance in the optical system can be effectively optimized, ensuring that the optical system has high imaging quality and imaging clarity. At the same time, by controlling the total length and volume of the optical system, it is beneficial to achieve the portability and convenience of the optical system, improving the convenience for users to carry and wear.
[0056] In an exemplary embodiment, the combined focal length f23 of the second lens and the third lens and the radius of curvature R6 of the second side surface of the third lens satisfy: 0.15 < f23 / R6 < 1.05. Reasonably configuring the ratio of the combined focal length of the second lens and the third lens to the radius of curvature of the second side surface of the third lens is beneficial to providing a wider field of view angle, enabling users to see more display content, enhancing the immersion and experience of users, and also being able to reduce or eliminate optical problems such as distortion and aberration, improving the clarity and accuracy of the image formed by the optical system.
[0057] In an exemplary embodiment, the total effective focal length f of the optical system, the axial distance T12 from the second side surface of the first lens to the first side surface of the second lens, and the central thickness CT2 of the second lens on the optical axis satisfy: 4.55 ≤ f / (T12 + CT2) < 5.6. By controlling the relationship between the total effective focal length of the optical system, the axial distance from the second side surface of the first lens to the first side surface of the second lens, and the central thickness of the second lens on the optical axis within a certain range, the axial distance ratio between the lenses can be reduced, thereby reducing the generation of aberration and improving the imaging quality and clarity of the optical system.
[0058] In an exemplary embodiment, the optical system further includes a diaphragm; wherein, the on-axis distance SR from the diaphragm to the first side surface of the first lens and the on-axis distance SAG11 between the intersection of the first side surface of the first lens and the optical axis and the vertex of the effective semi-aperture of the first side surface of the first lens satisfy: 4.0 < SR / SAG11 < 4.3. In order to ensure an appropriate distance between the optical system and the human eye to avoid the eyelashes touching the lens and thus ensure the wearing comfort, it is necessary to reasonably configure the ratio of the on-axis distance from the diaphragm to the first side surface of the first lens to the on-axis distance between the intersection of the first side surface of the first lens and the optical axis and the vertex of the effective semi-aperture of the first side surface of the first lens. On the one hand, it is beneficial to improve the user experience, and on the other hand, it can effectively reduce or eliminate optical problems such as distortion and aberration in the optical system, thereby improving the clarity and accuracy of the imaging of the optical system.
[0059] In an exemplary embodiment, the on-axis distance TD from the first side surface of the first lens to the second side surface of the fourth lens and the entrance pupil diameter EPD of the optical system satisfy: 0.95 < TD / EPD < 1.05. Reasonably configuring the ratio of the on-axis distance from the first side surface of the first lens to the second side surface of the fourth lens to the entrance pupil diameter of the optical system is beneficial to realizing the compact design of the optical system, reducing the volume and size of the optical system, so as to facilitate the integration and application of the optical system. At the same time, it is beneficial to weaken the sensitivity of the optical system to the thickness change of the lens and the change of the incident light, and can effectively optimize the performance and stability of the optical system.
[0060] The optical system according to the above embodiment of the present application can adopt multiple lenses, such as the four lenses above. By reasonably allocating the parameters of the reflective polarizing element, the first quarter-wave plate, the partial reflection element, the second quarter-wave plate, the polarizer and each lens, the body length of the optical system can be effectively reduced, and the user's immersion and experience can be improved. The optical system configured as above has the characteristics of miniaturization and good imaging quality, and can well meet the use requirements of various portable electronic products in the projection scenario.
[0061] In an embodiment of the present application, at least one of the surfaces of the second lens to the fourth lens is an aspherical surface. The characteristics of an aspherical lens are that the curvature changes continuously from the center of the lens to the periphery of the lens. Different from a spherical lens with a constant curvature from the center of the lens to the periphery of the lens, an aspherical lens has better curvature radius characteristics and has the advantages of improving distortion aberration and improving astigmatism aberration. After using an aspherical lens, the aberration that appears during imaging can be eliminated as much as possible, thereby improving the imaging quality.
[0062] However, those skilled in the art should understand that without departing from the technical solutions claimed in the present application, the number of lenses constituting the optical system can be changed to obtain the various results and advantages described in this specification.
[0063] A specific embodiment of an optical system applicable to the above-described embodiments will be further described below with reference to the accompanying drawings.
[0064] Example 1
[0065] The following refers to Figures 1 to 2D Describe the optical system according to Embodiment 1 of the present application.
[0066] As Figure 1 shown, the optical system sequentially includes a first lens E1, a reflective polarizing element RP, a first quarter-wave plate QWP1, a second lens E2, a third lens E3, a partial reflection element BS, a fourth lens E4, a second quarter-wave plate QWP2, and a polarizer LP along the optical axis from the object side to the image side. The aperture stop STO is disposed between the first side and the first lens E1. In this embodiment, the first side refers to the human eye side, and the second side refers to the display screen side. The first side surface of each element is also referred to as the near-eye side surface, and the second side surface is also referred to as the near-screen side surface.
[0067] The first lens E1 has a positive optical power, its first side surface S1 is convex, and its second side surface S2 is flat. The second lens E2 has a positive optical power, its first side surface S3 is convex, and its second side surface S4 is convex. The third lens E3 has a negative optical power, its first side surface S5 is concave, and its second side surface S6 is concave. The fourth lens E4 has a negative optical power, its first side surface S7 is concave, and its second side surface S8 is flat. The first quarter-wave plate QWP1 and the reflective polarizing element RP are attached to the second side surface S2 of the first lens E1. The partial reflection element BS is attached to the second side surface S6 of the third lens E3. The second quarter-wave plate QWP2 and the polarizer LP are attached to the second side surface S8 of the fourth lens E4. It should be noted that the surfaces S1 to S8 are not shown in Figure 1 shown.
[0068] In this example, an image plane IMG may be provided on the second side of the optical system, and a display screen may be provided on the image plane IMG. Image light from the display screen may sequentially pass through a polarizer LP, a second quarter-wave plate QWP2, a fourth lens E4, a third lens E3, a second lens E2, a first quarter-wave plate QWP1, reach a reflective polarizing element RP, and then be reflected at the reflective polarizing element RP to form first reflected image light. The first reflected image light passes through the first quarter-wave plate QWP1, the second lens E2, the third lens E3 and reaches a partial reflection element BS on the second side S6 of the third lens E3, and then is reflected at the partial reflection element BS to form second reflected image light. The second reflected image light sequentially passes through the third lens E3, the second lens E2, the first quarter-wave plate QWP1, the reflective polarizing element RP, a first lens E1 to an aperture STO and is finally projected into the user's eyes. For example, the light after two reflections of the optical system is finally projected into the user's eyes. A protective glass may also be provided between the image plane IMG and the polarizer LP.
[0069] Table 1 shows the basic parameter table of the optical system of Example 1, where the units of the radius of curvature, thickness / distance, and focal length are all millimeters (mm). Image light from the display screen passes through each element in the order from No. 28 to No. 1 and is finally projected into the human eye.
[0070]
[0071]
[0072] Table 1
[0073] In this embodiment, the first side S3 and the second side S4 of the second lens E2 and the first side S7 of the fourth lens E4 are all aspherical surfaces. The surface profile x of each aspherical lens can be defined by, but not limited to, the following aspherical formula:
[0074]
[0075] where x is the sagitta, the distance from the vertex of the aspherical surface at the position with a height of h along the optical axis direction; c is the paraxial curvature of the aspherical surface, c = 1 / R (i.e., the paraxial curvature c is the reciprocal of the radius of curvature R in Table 1 above); k is the conic coefficient; Ai is the correction coefficient of the i-th order of the aspherical surface. Table 2 gives the higher-order term coefficients A4, A6, A8, A 10 、A 12 、A 14 、A 16 、A 18 、and A 20 .
[0076] Surface number A4 A6 A8 A10 A12 A14 A16 A18 A20 S3 -1.8064E-05 -3.1946E-08 1.6169E-11 8.8927E-14 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 S4 -6.1703E-06 -5.1619E-09 1.0730E-10 -1.7912E-13 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 S7 2.2471E-01 -2.0151E-02 4.3479E-04 -3.0171E-03 -9.1056E-04 -4.3575E-04 2.7962E-06 1.5287E-04 0.0000E+00
[0077] Table 2
[0078] Figure 2A shows the axial chromatic aberration curve of the optical system of Example 1, which represents the deviation of the focus points of light rays with different wavelengths after passing through the optical system. Figure 2B shows the astigmatism curve of the optical system of Example 1, which represents the meridional image plane curvature and sagittal image plane curvature corresponding to different field angles. Figure 2C shows the distortion curve of the optical system of Example 1, which represents the distortion magnitude values corresponding to different field angles. Figure 2D shows the modulation transfer function curve of the optical system of Example 1. According to Figures 2A to 2D it can be seen that the optical system given in Example 1 can achieve good imaging quality.
[0079] Example 2
[0080] The following refers to Figures 3 to 4D to describe the optical system according to Embodiment 2 of the present application.
[0081] As Figure 3 shown, the optical system sequentially includes a first lens E1, a reflective polarizing element RP, a first quarter-wave plate QWP1, a second lens E2, a third lens E3, a partial reflection element BS, a fourth lens E4, a second quarter-wave plate QWP2, and a polarizer LP along the optical axis from the object side to the image side. The aperture stop STO is disposed between the first side and the first lens E1. In this embodiment, the first side refers to the human eye side, and the second side refers to the display screen side. The first side surface of each element is also referred to as the near-eye side surface, and the second side surface is also referred to as the near-screen side surface.
[0082] The first lens E1 has a positive optical power, its first side surface S1 is a convex surface, and its second side surface S2 is a plane. The second lens E2 has a positive optical power, its first side surface S3 is a convex surface, and its second side surface S4 is a concave surface. The third lens E3 has a negative optical power, its first side surface S5 is a concave surface, and its second side surface S6 is a concave surface. The fourth lens E4 has a negative optical power, its first side surface S7 is a concave surface, and its second side surface S8 is a plane. The first quarter-wave plate QWP1 and the reflective polarizing element RP are attached to the second side surface S2 of the first lens E1. The partial reflection element BS is attached to the second side surface S6 of the third lens E3. The second quarter-wave plate QWP2 and the polarizer LP are attached to the second side surface S8 of the fourth lens E4. It should be noted that the surfaces S1 to S8 are not shown in Figure 3 it.
[0083] In this example, an image plane IMG may be provided on the second side of the optical system, and a display screen may be provided on the image plane IMG. Image light from the display screen may sequentially pass through a polarizer LP, a second quarter-wave plate QWP2, a fourth lens E4, a third lens E3, a second lens E2, a first quarter-wave plate QWP1, reach a reflective polarizing element RP, and then be reflected at the reflective polarizing element RP to form first-reflected image light. The first-reflected image light passes through the first quarter-wave plate QWP1, the second lens E2, the third lens E3 and reaches a partial reflection element BS on the second side S6 of the third lens E3, and then is reflected at the partial reflection element BS to form second-reflected image light. The second-reflected image light sequentially passes through the third lens E3, the second lens E2, the first quarter-wave plate QWP1, the reflective polarizing element RP, a first lens E1 to an aperture STO and is finally projected into the user's eyes. For example, the light rays after two reflections of the optical system are finally projected into the user's eyes. A protective glass may also be provided between the image plane IMG and the polarizer LP.
[0084] Table 3 shows the basic parameter table of the optical system of Embodiment 2, where the units of the radius of curvature, thickness / distance, and focal length are all millimeters (mm). Image light from the display screen passes through each element in the order from No. 28 to No. 1 and is finally projected into the human eye.
[0085]
[0086]
[0087] Table 3
[0088] In this embodiment, the first side S3 and the second side S4 of the second lens E2 and the first side S7 of the fourth lens E4 are all aspherical surfaces. Table 4 gives the higher-order term coefficients A4, A6, A8, A 10 , A 12 , A 14 , A 16 , A 18 , and A 20 that can be used for the aspherical mirror surfaces S3, S4, and S7 in Embodiment 2.
[0089] Surface number A4 A6 A8 A10 A12 A14 A16 A18 A20 S3 -1.9842E-05 -7.2404E-08 -9.3795E-10 -4.0783E-12 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 S4 -1.1313E-05 -4.3936E-08 -1.3554E-09 -4.0187E-13 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 S7 4.2492E-01 -1.4597E-02 3.5082E-03 -2.0801E-03 -8.0062E-04 -7.0088E-04 -4.1859E-04 -2.8031E-06 0.0000E+00
[0090] Table 4
[0091] Figure 4A shows the axial chromatic aberration curve of the optical system of Embodiment 2, which represents the deviation of the focusing points of light rays of different wavelengths after passing through the optical system. Figure 4B shows the astigmatism curve of the optical system of Embodiment 2, which represents the meridional image plane curvature and sagittal image plane curvature corresponding to different field angles.Figure 4C The distortion curve of the optical system of Embodiment 2 is shown, which represents the distortion magnitude values corresponding to different field angles of view. Figure 4D The modulation transfer function curve of the optical system of Embodiment 2 is shown. According to Figures 4A to 4D it can be known that the optical system given in Embodiment 2 can achieve good imaging quality.
[0092] Example 3
[0093] The following refers to Figures 5 to 6D describe the optical system according to Embodiment 3 of the present application.
[0094] As Figure 5 shown, the optical system sequentially includes a first lens E1, a reflective polarizing element RP, a first quarter-wave plate QWP1, a second lens E2, a third lens E3, a partial reflection element BS, a fourth lens E4, a second quarter-wave plate QWP2, and a polarizer LP along the optical axis from the object side to the image side. The aperture stop STO is disposed between the first side and the first lens E1. In this embodiment, the first side refers to the human eye side, and the second side refers to the display screen side. The first side surface of each element is also referred to as the near-eye side surface, and the second side surface is also referred to as the near-screen side surface.
[0095] The first lens E1 has a positive optical power, its first side surface S1 is convex, and its second side surface S2 is flat. The second lens E2 has a positive optical power, its first side surface S3 is concave, and its second side surface S4 is convex. The third lens E3 has a negative optical power, its first side surface S5 is concave, and its second side surface S6 is convex. The fourth lens E4 has a positive optical power, its first side surface S7 is convex, and its second side surface S8 is flat. The first quarter-wave plate QWP1 and the reflective polarizing element RP are attached to the second side surface S2 of the first lens E1. The partial reflection element BS is attached to the second side surface S6 of the third lens E3. The second quarter-wave plate QWP2 and the polarizer LP are attached to the second side surface S8 of the fourth lens E4. It should be noted that the surfaces S1 to S8 are not shown in Figure 5 it.
[0096] In this example, an image plane IMG may be provided on the second side of the optical system, and a display screen may be provided on the image plane IMG. Image light from the display screen may sequentially pass through a polarizer LP, a second quarter-wave plate QWP2, a fourth lens E4, a third lens E3, a second lens E2, a first quarter-wave plate QWP1, reach a reflective polarizing element RP, and then be reflected at the reflective polarizing element RP to form first-reflected image light. The first-reflected image light passes through the first quarter-wave plate QWP1, the second lens E2, the third lens E3 and reaches a partial reflection element BS on the second side S6 of the third lens E3, and then is reflected at the partial reflection element BS to form second-reflected image light. The second-reflected image light sequentially passes through the third lens E3, the second lens E2, the first quarter-wave plate QWP1, the reflective polarizing element RP, a first lens E1 to a stop STO and is finally projected into the user's eyes. For example, the light rays after two reflections by the optical system are finally projected into the user's eyes. A protective glass may also be provided between the image plane IMG and the polarizer LP.
[0097] Table 5 shows the basic parameter table of the optical system of Embodiment 3, where the units of the radius of curvature, thickness / distance, and focal length are all millimeters (mm). Image light from the display screen passes through each element in the order from No. 28 to No. 1 and is finally projected into the human eye.
[0098]
[0099]
[0100] Table 5
[0101] In this embodiment, the first side S3 of the second lens E2 to the first side S7 of the fourth lens E4 are all aspherical surfaces. Table 6 gives the higher-order term coefficients A4, A6, A8, A 10 , A 12 , A 14 , A 16 , A 18 , and A 20 that can be used for each aspherical mirror surface S3 to S7 in Embodiment 3.
[0102] Surface number A4 A6 A8 A10 A12 A14 A16 A18 A20 S3 3.2030E-05 1.2526E-08 -7.4935E-10 2.2518E-12 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 S4 1.6866E-04 -8.3155E-07 1.7344E-09 1.3820E-12 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 S5 6.3892E-05 -7.8509E-07 5.9444E-09 -1.3170E-11 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 S6 -2.5017E-05 1.5251E-07 -6.6248E-11 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 S7 2.4650E-01 -1.5904E-02 -3.2258E-03 -1.8287E-04 2.6187E-04 2.0432E-06 -3.4679E-05 -5.2321E-08 0.0000E+00
[0103] Table 6
[0104] Figure 6A shows the axial chromatic aberration curve of the optical system of Embodiment 3, which represents the deviation of the convergence points of light rays of different wavelengths after passing through the optical system. Figure 6B shows the astigmatism curve of the optical system of Embodiment 3, which represents the meridional image plane curvature and sagittal image plane curvature corresponding to different field angles. Figure 6CThe distortion curve of the optical system of Embodiment 3 is shown, which represents the distortion magnitude values corresponding to different field angles of view. Figure 6D The modulation transfer function curve of the optical system of Embodiment 3 is shown. According to Figures 6A to 6D it can be known that the optical system given in Embodiment 3 can achieve good imaging quality.
[0105] Example 4
[0106] The following refers to Figures 7 to 8D describe the optical system according to Embodiment 4 of the present application.
[0107] As Figure 7 shown, the optical system sequentially includes a first lens E1, a reflective polarizing element RP, a first quarter-wave plate QWP1, a second lens E2, a third lens E3, a partial reflection element BS, a fourth lens E4, a second quarter-wave plate QWP2, and a polarizer LP along the optical axis from the object side to the image side. The aperture stop STO is disposed between the first side and the first lens E1. In this embodiment, the first side refers to the human eye side, and the second side refers to the display screen side. The first side surface of each element is also referred to as the near-eye side surface, and the second side surface is also referred to as the near-screen side surface.
[0108] The first lens E1 has a positive focal power, its first side surface S1 is convex, and its second side surface S2 is flat. The second lens E2 has a positive focal power, its first side surface S3 is concave, and its second side surface S4 is convex. The third lens E3 has a negative focal power, its first side surface S5 is concave, and its second side surface S6 is concave. The fourth lens E4 has a negative focal power, its first side surface S7 is concave, and its second side surface S8 is flat. The first quarter-wave plate QWP1 and the reflective polarizing element RP are attached to the second side surface S2 of the first lens E1. The partial reflection element BS is attached to the second side surface S6 of the third lens E3. The second quarter-wave plate QWP2 and the polarizer LP are attached to the second side surface S8 of the fourth lens E4. It should be noted that the surfaces S1 to S8 are not shown in Figure 7 this figure.
[0109] In this example, an image plane IMG may be provided on the second side of the optical system, and a display screen may be provided on the image plane IMG. Image light from the display screen may sequentially pass through a polarizer LP, a second quarter-wave plate QWP2, a fourth lens E4, a third lens E3, a second lens E2, a first quarter-wave plate QWP1, reach a reflective polarizing element RP, and then be reflected at the reflective polarizing element RP to form first reflected image light. The first reflected image light passes through the first quarter-wave plate QWP1, the second lens E2, the third lens E3 and reaches a partial reflection element BS on the second side S6 of the third lens E3, and then is reflected at the partial reflection element BS to form second reflected image light. The second reflected image light sequentially passes through the third lens E3, the second lens E2, the first quarter-wave plate QWP1, the reflective polarizing element RP, a first lens E1 to a stop STO and finally projects into the user's eyes. For example, the light after two reflections by the optical system finally projects into the user's eyes. A protective glass may also be provided between the image plane IMG and the polarizer LP.
[0110] Table 7 shows the basic parameter table of the optical system of Embodiment 4, where the units of the radius of curvature, thickness / distance, and focal length are all millimeters (mm). Image light from the display screen passes through each element in the order from No. 28 to No. 1 and finally projects into the human eye.
[0111]
[0112] Table 7
[0113] In this embodiment, the first side S3 and the second side S4 of the second lens E2 and the first side S7 of the fourth lens E4 are all aspherical surfaces. Table 8 gives the high-order term coefficients A4, A6, A8, A 10 , A 12 , A 14 , A 16 , A 18 , and A 20 that can be used for the aspherical mirror surfaces S3, S4, and S7 in Embodiment 4.
[0114] Surface number A4 A6 A8 A10 A12 A14 A16 A18 A20 S3 -3.3358E-05 -4.4330E-08 4.9884E-11 -3.3312E-13 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 S4 -1.6301E-05 -4.7698E-09 3.4362E-11 -2.8834E-13 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 0.0000E+00 S7 1.8468E-01 -2.4371E-02 -1.2344E-03 -3.5291E-03 -2.0958E-03 -7.1887E-04 -2.9361E-04 6.2643E-05 0.0000E+00
[0115] Table 8
[0116] Figure 8A shows the axial chromatic aberration curve of the optical system of Embodiment 4, which represents the deviation of the focusing points of light rays of different wavelengths after passing through the optical system. Figure 8B shows the astigmatism curve of the optical system of Embodiment 4, which represents the meridional image plane curvature and sagittal image plane curvature corresponding to different field angles. Figure 8CThe distortion curve of the optical system of Embodiment 4 is shown, which represents the distortion magnitude values corresponding to different field angles of view. Figure 8D The modulation transfer function curve of the optical system of Embodiment 4 is shown. According to Figures 8A to 8D it can be known that the optical system given in Embodiment 4 can achieve good imaging quality.
[0117] Table 9 shows the values of the parameters f, f1, f2, f3, f4, EPD, TD, fz1, f23, SAG11, SAG31, SAG41, and SR for each of Embodiments 1 - 4.
[0118] Example parameters 1 2 3 4 f (mm) 42.00 42.00 42.00 42.00 f1 (mm) 42.93 42.93 42.93 42.93 f2 (mm) 50.80 69.20 47.78 60.68 f3 (mm) -53.63 -91.10 -39.86 -71.87 f4 (mm) -25.52 -19.06 115.12 -24.15 EPD (mm) 25.00 25.00 25.00 25.00 TD (mm) 25.23 24.05 24.62 24.92 fz1 (mm) 42.93 42.93 42.93 42.93 f23 (mm) 620.35 241.17 -272.51 395.68 SAG11 (mm) 4.70 4.77 4.97 4.72 SAG31 (mm) -1.36 -0.56 -2.54 -1.09 SAG41 (mm) -1.48 -1.70 0.66 -1.44 SR (mm) 20.00 20.00 20.00 20.00
[0119] Table 9
[0120] Table 10 shows the values of the conditional expressions for each of Embodiments 1 - 4.
[0121] Condition formula / Example 1 2 3 4 f2 / f 1.21 1.65 1.14 1.44 f / f3 -0.78 -0.46 -1.05 -0.58 fz1 / (CT1 + CTR + CTQ1) 6.12 6.69 6.52 6.69 (T34 + CT4) / (CTQ2 + CTL) 12.35 17.78 9.43 12.23 (V1 / N1) / CT1 6.94 7.61 7.41 7.63 TD / EPD 1.01 0.96 0.98 1.00 R1 / R5 -0.48 -0.20 -0.96 -0.35 f / (T12 + CT2) 4.70 5.57 4.96 4.55 f1 / |f4| 1.68 2.25 0.37 1.78 (T23 + CT3) / f3 -0.12 -0.06 -0.19 -0.09 f23 / R6 0.18 0.82 1.00 0.20 SR / SAG11 4.26 4.19 4.03 4.24 SAG31 / CT3 -0.22 -0.12 -0.49 -0.18 R1 / CT1 3.09 3.39 3.30 3.39 |SAG41| / (CTQ2 + CTL) 5.68 6.53 2.63 5.53 f3 / (V3 / N3) -2.91 -7.15 -1.60 -4.35
[0122] Table 10
[0123] This application also provides an optical device, which can be an independent projection device such as a projector, or a projection module integrated on a mobile electronic device such as a virtual reality device. This optical device is equipped with the optical system described above.
[0124] The above description is only for the preferred embodiments of this application and the explanation of the applied technical principles. Those skilled in the art should understand that the scope of the application involved in this application is not limited to the technical solutions formed by the specific combination of the above technical features, and should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the application concept. For example, the technical solutions formed by mutually replacing the above features with the (but not limited to) technical features with similar functions disclosed in this application.
Claims
1. An optical system, characterized in that In order from the first side to the second side along the optical axis: A first lens with a positive optical power, whose first side is convex and the second side is flat; A reflective polarizing element placed on the second side of the first lens and at least partially attached to the second side of the first lens; A first quarter-wave plate placed on the second side of the reflective polarizing element and at least partially attached to the second side of the reflective polarizing element; A second lens with a positive optical power; A third lens with a negative optical power, whose first side is concave; A partial reflection element; A fourth lens with an optical power, whose second side is flat; A second quarter-wave plate placed on the second side of the fourth lens and at least partially attached to the second side of the fourth lens; And A polarizer placed on the second side of the second quarter-wave plate and at least partially attached to the second side of the second quarter-wave plate; Among them, the number of lenses with optical power in the optical system is four; The optical system satisfies: 1.1 < f2 / f < 1.7, -1.1 < f / f3 < -0.45, and 6.1 < fz1 / (CT1 + CTR + CTQ1) < 6.7, where f2 is the effective focal length of the second lens, f is the total effective focal length of the optical system, f3 is the effective focal length of the third lens, fz1 is the combined focal length of the first lens, the reflective polarizing element and the first quarter-wave plate, CT1 is the central thickness of the first lens on the optical axis, CTR is the central thickness of the reflective polarizing element on the optical axis, and CTQ1 is the central thickness of the first quarter-wave plate on the optical axis.
2. The optical system according to claim 1, characterized in that The refractive index N1 of the first lens, the dispersion coefficient V1 of the first lens and the center thickness CT1 of the first lens on the optical axis satisfy: 6.9 mm -1 <(V1 / N1) / CT1<7.65mm -1 .
3. The optical system according to claim 1, characterized in that The radius of curvature R1 of the first side of the first lens and the central thickness CT1 of the first lens on the optical axis satisfy: 3.05 < R1 / CT1 < 3.
4.
4. The optical system according to claim 1, characterized in that The effective focal length f3 of the third lens, the refractive index N3 of the third lens and the dispersion coefficient V3 of the third lens satisfy: -7.2mm < f3 / (V3 / N3) ≤ -1.6mm.
5. The optical system according to claim 1, characterized in that The on-axis distance T34 from the second side of the third lens to the first side of the fourth lens, the central thickness CT4 of the fourth lens on the optical axis, the central thickness CTQ2 of the second quarter-wave plate on the optical axis and the central thickness CTL of the polarizer on the optical axis satisfy: 9.4 < (T34 + CT4) / (CTQ2 + CTL) < 17.
8.
6. The optical system according to claim 1, characterized in that The radius of curvature R1 of the first side of the first lens and the radius of curvature R5 of the first side of the third lens satisfy: -1.0 < R1 / R5 < -0.
15.
7. The optical system according to claim 1, characterized in that The effective focal length f1 of the first lens and the effective focal length f4 of the fourth lens satisfy: 0.35 < f1 / |f4| < 2.
3.
8. The optical system according to claim 1, characterized in that The on-axis distance T23 from the second side of the second lens to the first side of the third lens, the central thickness CT3 of the third lens on the optical axis and the effective focal length f3 of the third lens satisfy: -0.2 < (T23 + CT3) / f3 < -0.
05.
9. The optical system according to claim 1, characterized in that The axial distance SAG31 between the intersection of the first surface of the third lens and the optical axis and the vertex of the effective semi-aperture of the first surface of the third lens and the central thickness CT3 of the third lens on the optical axis satisfy: -0.5 < SAG31 / CT3 < -0.
1.
10. The optical system according to claim 1, characterized in that The axial distance SAG41 between the intersection of the first surface of the fourth lens and the optical axis and the vertex of the effective semi-aperture of the first surface of the fourth lens, the central thickness CTQ2 of the second quarter-wave plate on the optical axis and the central thickness CTL of the polarizer on the optical axis satisfy: 2.6 < |SAG41| / (CTQ2 + CTL) < 6.
55.
11. The optical system according to any one of claims 1 to 10, characterized in that The combined focal length f23 of the second lens and the third lens and the radius of curvature R6 of the second surface of the third lens satisfy: 0.15 < f23 / R6 < 1.
05.
12. The optical system according to any one of claims 1 to 10, characterized in that The total effective focal length f of the optical system, the axial distance T12 from the second surface of the first lens to the first surface of the second lens and the central thickness CT2 of the second lens on the optical axis satisfy: 4.55 ≤ f / (T12 + CT2) < 5.
6.
13. The optical system according to any one of claims 1 to 10, characterized in that The optical system further includes a diaphragm; wherein, the axial distance SR from the diaphragm to the first surface of the first lens and the axial distance SAG11 between the intersection of the first surface of the first lens and the optical axis and the vertex of the effective semi-aperture of the first surface of the first lens satisfy: 4.0 < SR / SAG11 < 4.
3.
14. The optical system according to any one of claims 1 to 10, characterized in that The axial distance TD from the first surface of the first lens to the second surface of the fourth lens and the entrance pupil diameter EPD of the optical system satisfy: 0.95 < TD / EPD < 1.
05.
15. An optical system, characterized in that In sequence along the optical axis from the first side to the second side: A first lens, having a positive optical power, with its first surface being convex and its second surface being flat; A reflective polarizing element, disposed on the second surface of the first lens and at least partially adhered to the second surface of the first lens; A first quarter-wave plate, disposed on the second surface of the reflective polarizing element and at least partially adhered to the second surface of the reflective polarizing element; A second lens, having a positive optical power; A third lens, having a negative optical power, with its first surface being concave; A partial reflection element; A fourth lens, having an optical power, with its second surface being flat; A second quarter-wave plate, disposed on the second surface of the fourth lens and at least partially adhered to the second surface of the fourth lens; A polarizer, disposed on the second surface of the second quarter-wave plate and at least partially adhered to the second surface of the second quarter-wave plate; wherein, the number of lenses with optical power in the optical system is four; The optical system satisfies: 1.1 < f2 / f < 1.7, -1.1 < f / f3 < -0.45, and 0.15 < f23 / R6 < 1.05, Wherein, f2 is the effective focal length of the second lens, f is the total effective focal length of the optical system, f3 is the effective focal length of the third lens, f23 is the combined focal length of the second lens and the third lens, and R6 is the radius of curvature of the second side surface of the third lens.