Optical system

Abstract

The present application discloses an optical system, which sequentially includes a first lens, a reflective polarizing element, a first quarter-wave plate, a second lens, a third lens, a partial reflection element, a second quarter-wave plate, a polarizer, and a fourth lens along the optical axis from the first side to the second side; the first lens has a positive optical power, and its first side is a convex surface; the second lens has a negative optical power, its first side is a flat surface, and its second side is a concave surface; the second side of the third lens is a convex surface; the first side of the fourth lens is a flat surface; wherein, the effective focal length f1 of the first lens and the effective focal length f2 of the second lens satisfy: -0.7 < f1 / f2 < -0.15; the combined focal length fz2 of the second quarter-wave plate, the polarizer, and the fourth lens and the curvature radius R8 of the second side of the fourth lens satisfy: -2.0 ≤ fz2 / R8 ≤ -1.5.

Description

Technical Field

[0001] This application relates to the field of optical devices, and particularly to a catadioptric optical system. Background Art

[0002] The optical systems of virtual reality devices or augmented reality devices are mainly divided into three types: optical systems using aspherical lenses, optical systems using Fresnel lenses, and catadioptric optical systems. Among them, the catadioptric optical system is a major innovation in the optical system itself and reserves space for the overall design of virtual reality devices or augmented reality devices, and has become the mainstream trend of research and development.

[0003] 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 improving the user experience. However, the existing catadioptric optical systems usually use two lenses, which results in a relatively blurred image and poor imaging quality of the catadioptric optical system. Summary of the Invention

[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, this application provides such an optical system that sequentially includes a first lens, a second lens, a third lens, and a fourth lens along the optical axis from the first side to the second side. The first lens has a positive optical power, and its first side is a convex surface. The second lens has a negative optical power, its first side is a plane, and its second side is a concave surface. The third lens has an optical power, and its second side is a convex surface. The fourth lens has an optical power, and its first side is a plane. Among them, the optical system further includes a first quarter-wave plate, a reflective polarizing element, a partial reflection element, a polarizer, and a second quarter-wave plate; the first quarter-wave plate is disposed on the first side of the second lens; the reflective polarizing element is disposed on the first side of the first quarter-wave plate; the partial reflection element is disposed on the second side of the third lens; the polarizer is disposed on the first side of the fourth lens; the second quarter-wave plate is disposed on the first side of the polarizer. The effective focal length f1 of the first lens and the effective focal length f2 of the second lens satisfy: -0.7 < f1 / f2 < -0.15; the combined focal length fz2 of the second quarter-wave plate, the polarizer, and the fourth lens and the radius of curvature R8 of the second side of the fourth lens satisfy: -2.0 ≤ fz2 / R8 ≤ -1.5.

[0006] According to an exemplary embodiment of the present application, the refractive index NR of the reflective polarizing element, the refractive index NQ1 of the first quarter-wave plate, and the refractive index N2 of the second lens satisfy: 1.6 < (NR + NQ1) / N2 < 1.75.

[0007] According to an exemplary embodiment of the present application, the refractive index NQ2 of the second quarter-wave plate, the refractive index NL of the polarizer, and the refractive index N4 of the fourth lens satisfy: 1.75 < (NQ2 + NL) / N4 < 2.05.

[0008] According to an exemplary embodiment of the present application, 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: 5.7 < CT4 / (CTQ2 + CTL) ≤ 9.1.

[0009] According to an exemplary embodiment of the present application, the central thickness CTR of the reflective polarizing element on the optical axis, the central thickness CTQ1 of the first quarter-wave plate on the optical axis, the central thickness CT2 of the second lens on the optical axis, and the axial distance SAG22 between the intersection of the second side surface of the second lens and the optical axis and the vertex of the effective semi-aperture of the second side surface of the second lens satisfy: 3.6 < (CTR + CTQ1 + CT2) / SAG22 < 4.6.

[0010] According to an exemplary embodiment of the present application, the effective focal length f1 of the first lens, the axial 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, and the axial distance SAG12 between the intersection of the second side surface of the first lens and the optical axis and the vertex of the effective semi-aperture of the second side surface of the first lens satisfy: 4.9 < f1 / (SAG11 + SAG12) < 8.2.

[0011] According to an exemplary embodiment of the present application, the edge thickness ET1 of the first lens and the edge thickness ET3 of the third lens satisfy: 4.4 < ET3 / ET1 < 5.2.

[0012] According to an exemplary embodiment of the present application, the refractive index N1 of the first lens and the Abbe number V1 of the first lens satisfy: 40 < V1 / N1 < 44; the refractive index N2 of the second lens and the Abbe number V2 of the second lens satisfy: 12.8 < V2 / N2 < 20.

[0013] According to an exemplary embodiment of the present application, the combined focal length fz1 of the reflective polarizing element, the first quarter-wave plate, and the second lens and the total effective focal length f of the optical system satisfy: -1.0 < f / fz1 < -0.1.

[0014] 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 central thickness CT1 of the first lens on the optical axis satisfy: 2.2 < R1 / CT1 < 4.2.

[0015] According to an exemplary embodiment of the present application, the central thickness CTQ2 of the second quarter-wave plate on the optical axis, the central thickness CTL of the polarizer on the optical axis, and the axial distance SAG42 between the intersection of the second side surface of the fourth lens and the optical axis and the vertex of the effective semi-aperture of the second side surface of the fourth lens satisfy: 0.3 < (CTQ2 + CTL) / |SAG42| < 1.4.

[0016] According to an exemplary embodiment of the present application, the radius of curvature R4 of the second side surface of the second lens and the radius of curvature R6 of the second side surface of the third lens satisfy: -2.1 ≤ R4 / R6 < 0.

[0017] According to an exemplary embodiment of the present application, the optical system further includes an aperture disposed between the first side and the first lens; wherein, the axial distance TD from the first side surface of the first lens to the second side surface of the fourth lens and the axial distance SR from the aperture to the first side surface of the first lens satisfy: 1.2 < TD / SR < 1.3.

[0018] The optical system provided by the present application uses four lenses, reasonably configuring the optical powers of the four lenses and making the optical system satisfy "-0.7 < f1 / f2 < -0.15", which is beneficial to improving the imaging quality of the optical system; at the same time, by restricting the ratio of the combined focal length of the second quarter-wave plate, the polarizer and the fourth lens to the radius of curvature of the second side surface of the fourth lens, it is beneficial to provide a wider viewing angle, enabling the user to see more display content, enhancing the user's immersion and experience, and also being able to reduce or eliminate optical problems such as distortion and aberration, and improving the clarity and accuracy of the image formed by the optical system. Description of the Drawings

[0019] Other features, objects and advantages of the present application will become more apparent by reading the detailed description of the non-limiting embodiments made with reference to the following drawings. Among them:

[0020] Figure 1 Shows a schematic structural diagram of the optical system according to Embodiment 1 of the present application;

[0021] Figures 2A to 2D Respectively show the axial chromatic aberration curve, astigmatism curve, distortion curve and modulation transfer function (MTF) curve of the optical system according to Embodiment 1 of the present application;

[0022] Figure 3 Shows a schematic structural diagram of the optical system according to Embodiment 2 of the present application;

[0023] Figures 4A to 4DThe on-axis chromatic aberration curve, astigmatism curve, distortion curve, and modulation transfer function curve of the optical system according to Embodiment 2 of this application are shown respectively.

[0024] Figure 5 A schematic diagram of the structure of the optical system according to Embodiment 3 of this application is shown;

[0025] Figures 6A to 6D The on-axis chromatic aberration curve, astigmatism curve, distortion curve, and modulation transfer function curve of the optical system according to Embodiment 3 of this application are shown respectively.

[0026] Figure 7 A schematic diagram of the structure of the optical system according to Embodiment 4 of this application is shown; and

[0027] Figures 8A to 8D The on-axis chromatic aberration curve, astigmatism curve, distortion curve, and modulation transfer function curve of the optical system according to Embodiment 4 of this application are shown respectively. Detailed Implementation

[0028] To better understand this application, various aspects of this application will be described in more detail with reference to the accompanying drawings. It should be understood that these detailed descriptions are merely illustrative of exemplary embodiments of this application and are not intended to limit the scope of this application in any way. Throughout the specification, the same reference numerals refer to the same elements.

[0029] It should be noted that in this specification, the terms "first," "second," etc., are used only to distinguish one feature from another and do not imply any limitation on the features. Therefore, without departing from the teachings of this application, the first lens discussed below may also be referred to as the second lens.

[0030] In the accompanying drawings, the thickness, size, and shape of the lenses have been slightly exaggerated for ease of illustration. Specifically, the shapes of the spherical or aspherical surfaces shown in the drawings are illustrated by way of example. That is, the shapes of the spherical or aspherical surfaces are not limited to those shown in the drawings. The drawings are for illustrative purposes only and are not drawn strictly to scale.

[0031] In this paper, the paraxial region refers to the region near the optical axis. If the lens surface is convex and the location of the convexity 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 location of the concaveness 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 (e.g., the human eye side) is called the first side surface of the lens, and the surface of each lens closest to the second side (e.g., the display screen side) is called the second side surface of the lens.

[0032] It should also be understood that the terms "comprising," "including," "having," "containing," and / or "comprising" as used in this specification indicate 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. Furthermore, when describing embodiments of this application, the word "may" is used to mean "one or more embodiments of this application." And the term "exemplary" is intended to refer to an example or illustration.

[0033] Unless otherwise specified, all terms used herein (including technical and scientific terms) shall have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. It should also be understood that terms (e.g., those defined in common dictionaries) shall be interpreted as having the meaning consistent with their meaning in the context of the relevant art and shall not be interpreted in an idealized or overly formalized sense, unless expressly so specified herein.

[0034] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0035] The features, principles and other aspects of this application are described in detail below.

[0036] refer to Figure 1 , Figure 3 , Figure 5 and Figure 7 The first aspect of this application provides an optical system that may include a first lens, a second lens, a third lens and a fourth lens arranged sequentially along an optical axis from a first side to a second side.

[0037] In an exemplary embodiment, the first lens may have positive optical power. The second lens may have negative optical power. The third lens may have either positive or negative optical power. The fourth lens may have either positive or negative optical power. Properly configuring the optical power of each lens is beneficial for improving the imaging quality of the optical system.

[0038] In an exemplary embodiment, the first side surface of the first lens is convex, and the second side surface is either convex or concave.

[0039] In an exemplary embodiment, the first side of the second lens is a plane, and the second side is a concave surface.

[0040] In an exemplary embodiment, the first side of the third lens is a convex or concave surface, and the second side is a convex surface.

[0041] In an exemplary embodiment, the first side of the fourth lens is a plane, and the second side is a convex or concave surface.

[0042] In an exemplary embodiment, the optical system may further include a reflective polarizing element and a first quarter-wave plate. The first quarter-wave plate may be disposed on a first side of the second lens. The reflective polarizing element may be disposed on the first side of the first quarter-wave plate.

[0043] In an exemplary embodiment, the first side surface of the second lens is a plane. A reflective polarizing element and a first quarter-wave plate are bonded and attached to the first side surface of the second lens, wherein the first quarter-wave plate is closer to the second lens than the reflective polarizing element. By combining the reflective polarizing element and the first quarter-wave plate together and then attaching them to the first side surface of the second lens, the bonding process difficulty can be reduced, the bonding quality improved, and thus the performance of the optical system enhanced.

[0044] In an exemplary embodiment, the optical system may further include a partially reflective element. The partially reflective element may be disposed on the second side of the third lens. The partially reflective element has a semi-transmissive and semi-reflective effect on light. By disposing a partially reflective element on the second side of the third lens, and combining it with a reflective polarizing element and a first quarter-wave plate, light can be refracted multiple times, effectively reducing the overall length of the optical system.

[0045] In an exemplary embodiment, the optical system may further include a second quarter-wave plate and a polarizer. The polarizer may be disposed on a first side of the fourth lens. The second quarter-wave plate may be disposed on a first side of the polarizer. The polarizer is used to convert natural light emitted from the display screen on the second side into linearly polarized light, and the second quarter-wave plate is used to convert the linearly polarized light from the polarizer into circularly polarized light. By using the second quarter-wave plate and the polarizer, the natural light emitted from the display screen can be converted into circularly polarized light, thereby reducing the material stress effect of the components between the display screen and the polarizer and improving the contrast of the optical system.

[0046] In an exemplary embodiment, the first side surface of the fourth lens is planar. A second quarter-wave plate and a polarizer are bonded and attached to the first side surface of the fourth lens, wherein the polarizer is closer to the fourth lens than the second quarter-wave plate. By combining the second quarter-wave plate and the polarizer before attaching them to the first side surface of the fourth lens, the bonding process difficulty can be reduced, the bonding quality improved, and thus the performance of the optical system enhanced.

[0047] In an exemplary embodiment, the optical system may further include an aperture stop, which may be disposed between the first side and the first lens. Image light from the second side is finally projected onto the user's eye on the first side after multiple refractions and reflections through a fourth lens, a polarizer, a second quarter-wave plate, a third lens, a second lens, a first quarter-wave plate, a reflective polarizing element, and the first lens.

[0048] In an exemplary embodiment, the first side can be, for example, the side facing the human eye, and the second side can be, for example, the side facing the display screen. Correspondingly, the first side surfaces of each element (the first lens, the second lens, the third lens, the fourth lens, the first quarter-wave plate, the second quarter-wave plate) can be referred to as the near-eye side surfaces, and the second side surfaces can be referred to as the near-screen side surfaces.

[0049] In an exemplary embodiment, an image plane can be provided on the second side of the optical system. A display screen can be provided on the image plane. Image light from the display screen can sequentially pass through the fourth lens, the polarizer, the second quarter-wave plate, the third lens, the second lens, the first quarter-wave plate, reach the reflective polarizing element, and then be reflected at the reflective polarizing element to form the first reflected image light. The first reflected image light passes through the first quarter-wave plate, the second lens, the third lens and reaches the partial reflection element on the second side surface of the third lens, and then is reflected at the partial reflection element to form the 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 and finally projects into the user's eyes. The optical system provided in the present application folds the required optical path in a way that combines light reflection and refraction without affecting the projection quality, effectively shortening the body length of the optical system.

[0050] In an exemplary embodiment, the effective focal length f1 of the first lens and the effective focal length f2 of the second lens can satisfy: -0.7 < f1 / f2 < -0.15; the combined focal length fz2 of the second quarter-wave plate, the polarizer and the fourth lens and the curvature radius R8 of the second side surface of the fourth lens can satisfy: -2.0 ≤ fz2 / R8 ≤ -1.5. By controlling the optical system to satisfy "-0.7 < f1 / f2 < -0.15", it is beneficial to improve the imaging quality of the optical system; at the same time, by restricting the ratio of the combined focal length of the second quarter-wave plate, the polarizer and the fourth lens to the curvature radius of the second side surface of the fourth lens, it is beneficial to provide a wider viewing angle, enabling the user to see more display content, enhancing the user's immersion and experience, 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.

[0051] In an exemplary embodiment, the refractive index NR of the reflective polarizing element, the refractive index NQ1 of the first quarter-wave plate, and the refractive index N2 of the second lens may satisfy: 1.6 < (NR + NQ1) / N2 < 1.75. By controlling the ratio of the sum of the refractive indices of the reflective polarizing element and the first quarter-wave plate to the refractive index of the second lens, it is possible to avoid total internal reflection of light caused by excessive differences in the refractive indices of the reflective polarizing element, the first quarter-wave plate, and the second lens, reduce light reflection and light refraction losses in the optical system, improve the light transmission efficiency, and at the same time, it is also beneficial to improve the dispersion effect of the optical system.

[0052] In an exemplary embodiment, the refractive index NQ2 of the second quarter-wave plate, the refractive index NL of the polarizer, and the refractive index N4 of the fourth lens may satisfy: 1.75 < (NQ2 + NL) / N4 < 2.05. By controlling the ratio of the sum of the refractive indices of the second quarter-wave plate and the polarizer to the refractive index of the fourth lens, it is possible to avoid total internal reflection of light caused by excessive differences in the refractive indices of the second quarter-wave plate, the polarizer, and the fourth lens, reduce light reflection and light refraction losses in the optical system, improve the light transmission efficiency, and at the same time, it is also beneficial to improve the dispersion effect of the optical system.

[0053] In an exemplary embodiment, 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 may satisfy: 5.7 < CT4 / (CTQ2 + CTL) ≤ 9.1. By controlling the ratio of the central thickness of the fourth lens to the sum of the central thicknesses of the second quarter-wave plate and the polarizer, it is possible to shorten the body length of the optical system and at the same time facilitate the attachment of the second quarter-wave plate and the polarizer.

[0054] In an exemplary embodiment, the central thickness CTR of the reflective polarizing element on the optical axis, the central thickness CTQ1 of the first quarter-wave plate on the optical axis, the central thickness CT2 of the second lens on the optical axis, and the axial distance SAG22 between the intersection of the second side surface of the second lens and the optical axis and the vertex of the effective semi-aperture of the second side surface of the second lens may satisfy: 3.6 < (CTR + CTQ1 + CT2) / SAG22 < 4.6. By controlling the above conditional expression, it is possible to achieve a compact design of the optical system, thereby reducing the volume and weight of the electronic device including the optical system, improving the convenience of wearing the electronic device, and at the same time, it is also possible to avoid the thickness of the second lens being too thin and reduce the difficulty of processing, forming, and assembling the second lens.

[0055] In an exemplary embodiment, the effective focal length f1 of the first lens, the axial 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, and the axial distance SAG12 between the intersection of the second side surface of the first lens and the optical axis and the vertex of the effective semi-aperture of the second side surface of the first lens may satisfy: 4.9 < f1 / (SAG11 + SAG12) < 8.2. By controlling the above conditional expression, it is possible to constrain the effective focal length of the first lens and the sagittal heights of the first side surface and the second side surface of the first lens, reduce the axial distance ratio between adjacent lenses, thereby reducing the generation of aberrations and improving the clarity and accuracy of the image formed by the optical system.

[0056] In an exemplary embodiment, the edge thickness ET1 of the first lens and the edge thickness ET3 of the third lens may satisfy: 4.4 < ET3 / ET1 < 5.2. By controlling the ratio of the edge thickness of the third lens to the edge thickness of the first lens, a compact design of the optical system can be achieved, thereby reducing the volume and weight of the electronic device including the optical system, improving the convenience of wearing the electronic device, and at the same time avoiding the edge thickness of the first lens and the third lens being too thin, reducing the difficulty of processing, forming, and assembling the first lens and the third lens, and also helping to reduce the risk of optical system failures and increase the service life of the optical system.

[0057] In an exemplary embodiment, the refractive index N1 of the first lens and the Abbe number V1 of the first lens may satisfy: 40 < V1 / N1 < 44; the refractive index N2 of the second lens and the Abbe number V2 of the second lens may satisfy: 12.8 < V2 / N2 < 20. By controlling the ratio of the Abbe number to the refractive index of the first lens and the ratio of the Abbe number to the refractive index of the second lens, the dispersion characteristics of the first lens and the second lens can be optimized, the color reproduction ability and imaging quality of the optical system can be improved, and at the same time, it is beneficial to reduce the aberrations that may occur in the optical system, reduce the distortion and image blurring of the optical system.

[0058] In an exemplary embodiment, the combined focal length fz1 of the reflective polarizing element, the first quarter-wave plate, and the second lens and the total effective focal length f of the optical system may satisfy: -1.0 < f / fz1 < -0.1. By controlling the ratio of the total effective focal length of the optical system to the combined focal length of the reflective polarizing element, the first quarter-wave plate, and the second lens, the imaging quality of the optical system can be improved, the focusing ability of light can be enhanced, and the distortion can be reduced.

[0059] 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 may satisfy: 2.2 < R1 / CT1 < 4.2. By controlling 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, it is possible to reduce aberration, improve the image quality and overall optical characteristics of the optical system. At the same time, it is also beneficial to enhance the stability and reliability of the design of the first lens, better constrain the optical characteristics of the first lens, and reduce the possibility of unexpected optical behaviors or performance problems.

[0060] In an exemplary embodiment, the central thickness CTQ2 of the second quarter-wave plate on the optical axis, the central thickness CTL of the polarizer on the optical axis, and the axial distance SAG42 between the intersection of the second side surface of the fourth lens and the optical axis and the vertex of the effective semi-aperture of the second side surface of the fourth lens may satisfy: 0.3 < (CTQ2 + CTL) / |SAG42| < 1.4. During the use of the optical system, it is vulnerable to vibration, which may cause the formed image to be blurred or distorted. By controlling the ratio of the sum of the central thicknesses of the second quarter-wave plate and the polarizer to the absolute value of the sagitta of the second side surface of the fourth lens, it is possible to optimize the structure and stability of the fourth lens, improve the anti-vibration ability of the optical system, and make the formed image more stable and clear.

[0061] In an exemplary embodiment, the radius of curvature R4 of the second side surface of the second lens and the radius of curvature R6 of the second side surface of the third lens may satisfy: -2.1 ≤ R4 / R6 < 0. By controlling the ratio of the radius of curvature of the second side surface of the second lens to the radius of curvature of the second side surface of the third lens, it is beneficial to reduce or eliminate the aberration that may occur in the optical system, improve the imaging quality and clarity of the optical system. At the same time, it is also beneficial to reduce the manufacturing cost and improve the production efficiency.

[0062] In an exemplary embodiment, the axial distance TD from the first side surface of the first lens to the second side surface of the fourth lens and the axial distance SR from the aperture stop to the first side surface of the first lens may satisfy: 1.2 < TD / SR < 1.3. By controlling the above conditional formula, it is beneficial to reduce the aberration of the optical system, improve the clarity and accuracy of the formed image, and achieve higher-quality image output. At the same time, it is also beneficial to reduce the fluctuations and instabilities of the optical system and ensure the long-term stable operation of the optical system.

[0063] The optical system according to the above embodiments of this application can employ multiple lenses, such as the four lenses described above. By rationally allocating the parameters of the reflective polarizing element, the first quarter-wave plate, the second quarter-wave plate, the polarizer, and each lens, the overall length of the optical system can be reduced, the imaging quality of the optical system can be improved, and the user's immersion and experience can be enhanced. The optical system configured as described above features miniaturization and good imaging quality, and can well meet the usage needs of various portable electronic products in projection scenarios.

[0064] In embodiments of this application, at least one of the surfaces of the third and fourth lenses is an aspherical surface. An aspherical lens is characterized by a continuously changing curvature from its center to its periphery. Unlike a spherical lens, which has a constant curvature from its center to its periphery, an aspherical lens has superior curvature radius characteristics, offering advantages in improving distortion and astigmatism. By employing an aspherical lens, aberrations occurring during imaging can be eliminated as much as possible, thereby improving image quality.

[0065] refer to Figure 1 , Figure 3 , Figure 5 and Figure 7 The second aspect of this application provides an optical system comprising, sequentially from a first side to a second side along an optical axis, a first lens, a second lens, a third lens, and a fourth lens. The first lens has positive optical power and its first side is convex. The second lens has negative optical power, its first side is planar, and its second side is concave. The third lens has optical power and its second side is convex. The fourth lens has optical power and its first side is planar. The optical system further includes a first quarter-wave plate, a reflective polarizing element, a partial reflective element, a polarizer, and a second quarter-wave plate; the first quarter-wave plate is disposed on the first side of the second lens; the reflective polarizing element is disposed on the first side of the first quarter-wave plate; the partial reflective element is disposed on the second side of the third lens; the polarizer is disposed on the first side of the fourth lens; and the second quarter-wave plate is disposed on the first side of the polarizer.

[0066] Among them, the effective focal length f1 of the first lens and the effective focal length f2 of the second lens satisfy: -0.7 < f1 / f2 < -0.15; the refractive index NR of the reflective polarizing element, the refractive index NQ1 of the first quarter-wave plate, and the refractive index N2 of the second lens satisfy: 1.6 < (NR + NQ1) / N2 < 1.75. The optical system provided by this application uses four lenses, rationally configuring the optical power of the four lenses and making the optical system satisfy "-0.7 < f1 / f2 < -0.15", which is beneficial to improving the imaging quality of the optical system; at the same time, by restricting the ratio of the sum of the refractive indices of the reflective polarizing element and the first quarter-wave plate to the refractive index of the second lens, it is possible to avoid total internal reflection of light caused by excessive differences in the refractive indices of the reflective polarizing element, the first quarter-wave plate, and the second lens, reduce light reflection and light refraction losses in the optical system, improve the light transmission efficiency, and is also beneficial to improving the dispersion effect of the optical system.

[0067] However, those skilled in the art should understand that without departing from the technical solution claimed in this application, the number of lenses constituting the optical system can be changed to obtain the various results and advantages described in this specification.

[0068] The following further describes specific embodiments of the optical system applicable to the above embodiments with reference to the accompanying drawings.

[0069] Example 1

[0070] The following refers to Figure 1 、 Figure 2A 、 Figure 2B 、 Figure 2C and Figure 2D describe the optical system of Embodiment 1 of this application.

[0071] As Figure 1 shown, the optical system may include 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 second quarter-wave plate QWP2, a polarizer LP, and a fourth lens E4 arranged in sequence along the optical axis from the first side to the second side. The aperture stop STO may be 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 surfaces of each element are all referred to as the near-human-eye side surfaces, and the second side surfaces are all referred to as the near-screen side surfaces.

[0072] ​​The first lens E1 has positive optical power, with its eye-facing side S1 being convex and its screen-facing side S2 being concave. The second lens E2 has negative optical power, with its eye-facing side S3 being planar and its screen-facing side S4 being concave. The third lens E3 has positive optical power, with its eye-facing side S5 being convex and its screen-facing side S6 being convex. The fourth lens E4 has positive optical power, with its eye-facing side S7 being planar and its screen-facing side S8 being convex. A reflective polarizing element RP and a first quarter-wave plate QWP1 are attached to the eye-facing side S3 of the second lens E2. A partially reflective element BS is attached to the screen-facing side S6 of the third lens E3. A second quarter-wave plate QWP2 and a polarizer LP are attached to the eye-facing side S7 of the fourth lens E4. It should be noted that surfaces S1-S8 are... Figure 1 Not shown in the image.

[0073] In this example, an image plane IMG can be provided on the second side of the optical system, and the image plane IMG can, for example, be a display screen. Image light from the image plane IMG passes sequentially through the fourth lens E4, polarizer LP, second quarter-wave plate QWP2, third lens E3, second lens E2, and first quarter-wave plate QWP1, and reaches the reflective polarizing element RP, where it undergoes a first reflection. The light after the first reflection passes through the first quarter-wave plate QWP1, second lens E2, and third lens E3, and reaches the partial reflective element BS located near the screen side of the third lens E3, where it undergoes a second reflection. The light after the second reflection passes sequentially through the third lens E3, second lens E2, first quarter-wave plate QWP1, reflective polarizing element RP, and first lens E1 to the aperture stop and is finally projected into the user's eye. For example, the light from this optical system after two reflections is finally projected into the user's eye. A protective glass (not shown) can also be provided between the image plane IMG and the fourth lens E4.

[0074] Table 1 shows the basic parameters of the optical system of Embodiment 1, where the units for radius of curvature and thickness / distance are millimeters (mm). Image light from the image plane IMG passes through each element in the order of number 23 to number 1 and is finally projected into the human eye.

[0075]

[0076] Table 1

[0077] In this embodiment, the near-eye side S5 and near-screen side S6 of the third lens E3, and the near-screen side S8 of the fourth lens E4 are all aspherical. The surface shape x of each aspherical lens can be defined using, but is not limited to, the following aspherical formula:

[0078]

[0079] Where x is the distance vector from the vertex of the aspherical surface at a height of h along the optical axis; 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 i-th order correction coefficient of the aspherical surface. Table 2 gives the higher-order coefficients A4, A6, A8, A14, A25, A36, A46, A58 that can be used for the aspherical surfaces S5, S6, and S8 in Example 1. 10 A 12 A 14 A 16 A 18 and A 20 .

[0080] Face number A4 A6 A8 A10 A12 A14 A16 A18 A20 S5 -1.7321E-01 3.7503E-01 6.9162E-02 1.0327E-02 2.2502E-03 2.7641E-04 -2.1806E-04 0.0000E+00 0.0000E+00 S6 3.8033E-01 1.7550E-01 2.6809E-02 -6.0262E-03 -6.3487E-03 -2.4129E-03 -4.5348E-04 0.0000E+00 0.0000E+00 S8 -1.3963E-01 1.8549E-02 5.0906E-04 -5.5609E-04 1.8651E-04 -3.0061E-04 -6.7872E-05 0.0000E+00 0.0000E+00

[0081] Table 2

[0082] Figure 2A The on-axis chromatic aberration curve of the optical system of Embodiment 1 is shown, which represents the deviation of the focal point of light of different wavelengths after passing through the optical system. Figure 2B The astigmatism curves of the optical system of Example 1 are shown, which represent the meridional image plane curvature and sagittal image plane curvature corresponding to different field of view angles. Figure 2C The distortion curves of the optical system of Example 1 are shown, which represent the distortion magnitude values ​​corresponding to different field of view angles. Figure 2D The modulation transfer function curve of the optical system in Example 1 is shown. According to... Figures 2A to 2D It can be seen that the optical system given in Example 1 can achieve good imaging quality.

[0083] Example 2

[0084] The following is for reference Figure 3 , Figure 4A , Figure 4B , Figure 4C and Figure 4D The optical system of Embodiment 2 of this application is described.

[0085] like Figure 3 As shown, the optical system may include 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 reflective element BS, a second quarter-wave plate QWP2, a polarizer LP, and a fourth lens E4, arranged sequentially along the optical axis from the first side to the second side. An aperture stop STO may be 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 of each element is referred to as the near-human eye side, and the second side is referred to as the near-screen side.

[0086] The first lens E1 has positive optical power, with its eye-facing side S1 being convex and its screen-facing side S2 being convex. The second lens E2 has negative optical power, with its eye-facing side S3 being planar and its screen-facing side S4 being concave. The third lens E3 has positive optical power, with its eye-facing side S5 being convex and its screen-facing side S6 being convex. The fourth lens E4 has negative optical power, with its eye-facing side S7 being planar and its screen-facing side S8 being concave. A reflective polarizing element RP and a first quarter-wave plate QWP1 are attached to the eye-facing side S3 of the second lens E2. A partially reflective element BS is attached to the screen-facing side S6 of the third lens E3. A second quarter-wave plate QWP2 and a polarizer LP are attached to the eye-facing side S7 of the fourth lens E4. It should be noted that surfaces S1-S8 are... Figure 1 Not shown in the image.

[0087] In this example, an image plane IMG can be provided on the second side of the optical system, and the image plane IMG can, for example, be a display screen. Image light from the image plane IMG passes sequentially through the fourth lens E4, polarizer LP, second quarter-wave plate QWP2, third lens E3, second lens E2, and first quarter-wave plate QWP1, and reaches the reflective polarizing element RP, where it undergoes a first reflection. The light after the first reflection passes through the first quarter-wave plate QWP1, second lens E2, and third lens E3, and reaches the partial reflective element BS located near the screen side of the third lens E3, where it undergoes a second reflection. The light after the second reflection passes sequentially through the third lens E3, second lens E2, first quarter-wave plate QWP1, reflective polarizing element RP, and first lens E1 to the aperture stop and is finally projected into the user's eye. For example, the light from this optical system after two reflections is finally projected into the user's eye. A protective glass (not shown) can also be provided between the image plane IMG and the fourth lens E4.

[0088] Table 3 shows the basic parameters of the optical system of Embodiment 2, where the units for radius of curvature and thickness / distance are millimeters (mm). Image light from the image plane IMG passes through each element in the order of number 23 to number 1 and is finally projected into the human eye.

[0089]

[0090] Table 3

[0091] In this embodiment, the near-eye side S5 and near-screen side S6 of the third lens E3, and the near-screen side S8 of the fourth lens E4 are both aspherical surfaces. Table 4 shows the higher-order coefficients A4, A6, A8, and A6 of the aspherical surfaces S5, S6, and S8 that can be used in Embodiment 2. 10 A 12 A 14A 16 A 18 and A 20 .

[0092] Face number A4 A6 A8 A10 A12 A14 A16 A18 A20 S5 -7.1874E-01 7.2814E-01 2.7264E-01 8.7554E-02 2.8686E-02 5.9606E-03 2.2679E-04 0.0000E+00 0.0000E+00 S6 1.0574E+00 3.4208E-01 -1.1471E-01 -1.6160E-01 -8.2154E-02 -2.3484E-02 -3.1671E-03 0.0000E+00 0.0000E+00 S8 -1.8584E-01 -3.6156E-03 -2.2890E-04 3.2741E-04 -8.0570E-04 -3.3659E-04 -3.6592E-04 0.0000E+00 0.0000E+00

[0093] Table 4

[0094] Figure 4A The on-axis chromatic aberration curve of the optical system of Embodiment 2 is shown, which represents the deviation of the focal point of light of different wavelengths after passing through the optical system. Figure 4B The astigmatism curves of the optical system of Example 2 are shown, which represent the meridional image plane curvature and sagittal image plane curvature corresponding to different field of view angles. Figure 4C The distortion curves of the optical system of Example 2 are shown, which represent the distortion magnitude values ​​corresponding to different field of view angles. Figure 4D The modulation transfer function curve of the optical system in Example 2 is shown. According to... Figures 4A to 4D It can be seen that the optical system given in Example 2 can achieve good imaging quality.

[0095] Example 3

[0096] The following is for reference Figure 5 , Figure 6A , Figure 6B , Figure 6C and Figure 6D The optical system of Embodiment 3 of this application is described.

[0097] like Figure 5 As shown, the optical system may include 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 reflective element BS, a second quarter-wave plate QWP2, a polarizer LP, and a fourth lens E4, arranged sequentially along the optical axis from the first side to the second side. An aperture stop STO may be 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 of each element is referred to as the near-human eye side, and the second side is referred to as the near-screen side.

[0098] The first lens E1 has positive optical power, with its eye-facing side S1 being convex and its screen-facing side S2 being concave. The second lens E2 has negative optical power, with its eye-facing side S3 being planar and its screen-facing side S4 being concave. The third lens E3 has positive optical power, with its eye-facing side S5 being convex and its screen-facing side S6 being convex. The fourth lens E4 has positive optical power, with its eye-facing side S7 being planar and its screen-facing side S8 being convex. A reflective polarizing element RP and a first quarter-wave plate QWP1 are attached to the eye-facing side S3 of the second lens E2. A partially reflective element BS is attached to the screen-facing side S6 of the third lens E3. A second quarter-wave plate QWP2 and a polarizer LP are attached to the eye-facing side S7 of the fourth lens E4. It should be noted that surfaces S1-S8 are... Figure 1 Not shown in the image.

[0099] In this example, an image plane IMG can be provided on the second side of the optical system, and the image plane IMG can, for example, be a display screen. Image light from the image plane IMG passes sequentially through the fourth lens E4, polarizer LP, second quarter-wave plate QWP2, third lens E3, second lens E2, and first quarter-wave plate QWP1, and reaches the reflective polarizing element RP, where it undergoes a first reflection. The light after the first reflection passes through the first quarter-wave plate QWP1, second lens E2, and third lens E3, and reaches the partial reflective element BS located near the screen side of the third lens E3, where it undergoes a second reflection. The light after the second reflection passes sequentially through the third lens E3, second lens E2, first quarter-wave plate QWP1, reflective polarizing element RP, and first lens E1 to the aperture stop and is finally projected into the user's eye. For example, the light from this optical system after two reflections is finally projected into the user's eye. A protective glass (not shown) can also be provided between the image plane IMG and the fourth lens E4.

[0100] Table 5 shows the basic parameters of the optical system of Embodiment 3, where the units for radius of curvature and thickness / distance are millimeters (mm). Image light from the image plane IMG passes through each element in the order of number 23 to number 1 and is finally projected into the human eye.

[0101]

[0102]

[0103] Table 5

[0104] In this embodiment, the near-eye side S5 and near-screen side S6 of the third lens E3, and the near-screen side S8 of the fourth lens E4 are both aspherical surfaces. Table 6 shows the higher-order coefficients A4, A6, A8, and A6 of the aspherical surfaces S5, S6, and S8 that can be used in Embodiment 3.10 A 12 A 14 A 16 A 18 and A 20 .

[0105] Face number A4 A6 A8 A10 A12 A14 A16 A18 A20 S5 -1.1464E-01 2.2587E-01 -4.8393E-03 -1.4819E-02 -6.3860E-03 -2.1304E-03 -5.0213E-04 0.0000E+00 0.0000E+00 S6 2.7153E-01 1.1637E-01 1.4852E-02 -1.5439E-03 -2.1630E-03 -9.0144E-04 -1.9510E-04 0.0000E+00 0.0000E+00 S8 -4.7634E-02 1.0500E-02 -5.1612E-04 8.0158E-05 -2.4031E-06 -3.7978E-05 2.5588E-05 0.0000E+00 0.0000E+00

[0106] Table 6

[0107] Figure 6A The on-axis chromatic aberration curve of the optical system of Embodiment 3 is shown, which represents the deviation of the focal point of light of different wavelengths after passing through the optical system. Figure 6B The astigmatism curves of the optical system of Example 3 are shown, which represent the meridional image plane curvature and sagittal image plane curvature corresponding to different field of view angles. Figure 6C The distortion curves of the optical system of Example 3 are shown, which represent the distortion magnitude values ​​corresponding to different field of view angles. Figure 6D The modulation transfer function curve of the optical system in Example 3 is shown. According to... Figures 6A to 6D It can be seen that the optical system given in Example 3 can achieve good imaging quality.

[0108] Example 4

[0109] The following is for reference Figure 7 , Figure 8A , Figure 8B , Figure 8C and Figure 8D The optical system of Embodiment 4 of this application is described.

[0110] like Figure 7 As shown, the optical system may include 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 reflective element BS, a second quarter-wave plate QWP2, a polarizer LP, and a fourth lens E4, arranged sequentially along the optical axis from the first side to the second side. An aperture stop STO may be 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 of each element is referred to as the near-human eye side, and the second side is referred to as the near-screen side.

[0111] The first lens E1 has positive optical power, with its eye-facing side S1 being convex and its screen-facing side S2 being concave. The second lens E2 has negative optical power, with its eye-facing side S3 being planar and its screen-facing side S4 being concave. The third lens E3 has negative optical power, with its eye-facing side S5 being concave and its screen-facing side S6 being convex. The fourth lens E4 has positive optical power, with its eye-facing side S7 being planar and its screen-facing side S8 being convex. A reflective polarizing element RP and a first quarter-wave plate QWP1 are attached to the eye-facing side S3 of the second lens E2. A partially reflective element BS is attached to the screen-facing side S6 of the third lens E3. A second quarter-wave plate QWP2 and a polarizer LP are attached to the eye-facing side S7 of the fourth lens E4. It should be noted that surfaces S1-S8 are... Figure 1 Not shown in the image.

[0112] In this example, an image plane IMG can be provided on the second side of the optical system, and the image plane IMG can, for example, be a display screen. Image light from the image plane IMG passes sequentially through the fourth lens E4, polarizer LP, second quarter-wave plate QWP2, third lens E3, second lens E2, and first quarter-wave plate QWP1, and reaches the reflective polarizing element RP, where it undergoes a first reflection. The light after the first reflection passes through the first quarter-wave plate QWP1, second lens E2, and third lens E3, and reaches the partial reflective element BS located near the screen side of the third lens E3, where it undergoes a second reflection. The light after the second reflection passes sequentially through the third lens E3, second lens E2, first quarter-wave plate QWP1, reflective polarizing element RP, and first lens E1 to the aperture stop and is finally projected into the user's eye. For example, the light from this optical system after two reflections is finally projected into the user's eye. A protective glass (not shown) can also be provided between the image plane IMG and the fourth lens E4.

[0113] Table 7 shows the basic parameters of the optical system of Embodiment 4, where the units for radius of curvature and thickness / distance are millimeters (mm). Image light from the image plane IMG passes through each element in the order of number 23 to number 1 and is finally projected into the human eye.

[0114]

[0115]

[0116] Table 7

[0117] In this embodiment, the near-eye side S5 and near-screen side S6 of the third lens E3, and the near-screen side S8 of the fourth lens E4 are both aspherical surfaces. Table 8 shows the higher-order coefficients A4, A6, A8, and A6 of the aspherical surfaces S5, S6, and S8 that can be used in Embodiment 4.10 A 12 A 14 A 16 A 18 and A 20 .

[0118] Face number A4 A6 A8 A10 A12 A14 A16 A18 A20 S5 -2.6123E-02 1.5122E-01 -1.8531E-01 -9.4805E-02 -4.0745E-02 -1.2081E-02 -1.9036E-03 0.0000E+00 0.0000E+00 S6 8.6423E-01 3.7529E-01 4.6176E-02 -1.6842E-02 -1.9169E-02 -7.7663E-03 -1.4327E-03 0.0000E+00 0.0000E+00 S8 -6.9149E-02 2.4710E-02 -2.7986E-03 -2.4106E-04 9.0018E-04 -7.1260E-04 6.8650E-05 0.0000E+00 0.0000E+00

[0119] Table 8

[0120] Figure 8A The on-axis chromatic aberration curve of the optical system of Embodiment 4 is shown, which represents the deviation of the focal point of light of different wavelengths after passing through the optical system. Figure 8B The astigmatism curves of the optical system of Example 4 are shown, which represent the meridional image plane curvature and sagittal image plane curvature corresponding to different field of view angles. Figure 8C The distortion curves of the optical system of Example 4 are shown, representing the distortion magnitude values ​​corresponding to different field of view angles. Figure 8D The modulation transfer function curve of the optical system in Example 4 is shown. According to... Figures 8A to 8D It can be seen that the optical system given in Example 4 can achieve good imaging quality.

[0121] Table 9 provides the basic parameters for each embodiment in Examples 1 to 4, such as the values ​​of f, f1, f2, f3, f4, SR, TD, fz1, fz2, SAG11, SAG12, SAG22, SAG42, ET1, and ET3. The unit of the parameters in Table 9 is millimeters (mm).

[0122] Parameters / Examples 1 2 3 4 f 42.00 42.00 42.00 42.00 f1 44.89 30.25 54.54 51.08 f2 -68.55 -43.96 -115.25 -306.52 f3 96.19 69.52 145.02 -797.62 f4 472.95 -120.79 220.00 51.91 SR 20.00 20.00 20.00 20.00 TD 25.39 25.20 24.87 25.39 fz1 -68.55 -43.96 -115.25 -306.52 fz2 472.95 -120.79 220.00 51.91 SAG11 5.55 6.32 5.12 6.72 SAG12 0.93 -0.17 1.59 1.84 SAG22 1.38 1.72 0.93 0.33 SAG42 -0.20 0.19 -0.20 -0.82 ET1 1.30 1.30 1.30 1.30 ET3 6.53 6.47 6.68 5.76

[0123] Table 9

[0124] In summary, Table 10 shows the values ​​of the conditional expressions for each of the embodiments in Examples 1 to 4.

[0125] Conditional / Example 1 2 3 4 f1 / f2 -0.65 -0.69 -0.47 -0.17 fz2 / R8 -1.70 -2.00 -1.50 -1.61 (NR+NQ1) / N2 1.71 1.69 1.74 1.62 (NQ2+NL) / N4 1.89 2.00 1.80 1.85 f / fz1 -0.61 -0.96 -0.36 -0.14 R1 / CT1 3.21 2.27 4.15 2.87 CT4 / (CTQ2+CTL) 5.78 9.10 5.77 8.14 (CTR+CTQ1+CT2) / SAG22 3.96 3.61 3.67 4.59 f1 / (SAG11+SAG12) 6.92 4.92 8.13 5.97 ET3 / ET1 5.02 4.98 5.14 4.43 V1 / N1 41.79 40.23 40.82 43.97 V2 / N2 19.96 19.41 16.91 12.82 (CTQ2+CTL) / |SAG42| 1.28 1.38 1.30 0.32 R4 / R6 -0.29 -0.07 -0.49 -2.10 TD / SR 1.27 1.26 1.24 1.27

[0126] Table 10

[0127] This application also provides an optical device, which can be a standalone projection device such as a projector, or a projection module integrated into a mobile electronic device such as a virtual reality device. The optical device is equipped with the optical system described above.

[0128] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. Optical system, characterized in that In order from the first side to the second side along the optical axis, the optical system comprises: a first lens with positive refractive power, a first side of which is convex; a second lens with negative refractive power, a first side of which is flat and a second side of which is concave; a third lens with positive refractive power or negative refractive power, a second side of which is convex; and a fourth lens with positive refractive power or negative refractive power, a first side of which is flat; wherein the optical system further comprises: a first quarter-wave plate arranged on the first side of the second lens; a reflective polarizing element arranged on the first side of the first quarter-wave plate; a partially reflective element arranged on the second side of the third lens; a polarizer arranged on the first side of the fourth lens; and a second quarter-wave plate arranged on the first side of the polarizer; the optical system has four lenses with refractive power; an effective focal length f1 of the first lens and an effective focal length f2 of the second lens satisfy: -0.69≤f1 / f2≤-0.17; a combined focal length fz2 of the second quarter-wave plate, the polarizer and the fourth lens and a radius of curvature R8 of the second side of the fourth lens satisfy: -2.0≤fz2 / R8≤-1.

5.

2. The optical system of claim 1, wherein, a refractive index NR of the reflective polarizing element, a refractive index NQ1 of the first quarter-wave plate and a refractive index N2 of the second lens satisfy: 1.6<(NR+NQ1) / N2<1.

75.

3. The optical system of claim 1, wherein, a refractive index NQ2 of the second quarter-wave plate, a refractive index NL of the polarizer and a refractive index N4 of the fourth lens satisfy: 1.80≤(NQ2+NL) / N4≤2.

00.

4. The optical system of claim 1, wherein, a central thickness CT4 of the fourth lens on the optical axis, a central thickness CTQ2 of the second quarter-wave plate on the optical axis and a central thickness CTL of the polarizer on the optical axis satisfy: 5.77≤CT4 / (CTQ2+CTL)≤9.

1.

5. The optical system of claim 1, wherein, a central thickness CTR of the reflective polarizing element on the optical axis, a central thickness CTQ1 of the first quarter-wave plate on the optical axis, a central thickness CT2 of the second lens on the optical axis and an on-axis distance SAG22 between an intersection of the second side of the second lens and the optical axis and an effective semi-aperture vertex of the second side of the second lens satisfy: 3.6<(CTR+CTQ1+CT2) / SAG22<4.

6.

6. The optical system of claim 1, wherein, an effective focal length f1 of the first lens, an on-axis distance SAG11 between an intersection of a first side of the first lens and the optical axis and an effective semi-aperture vertex of the first side of the first lens and an on-axis distance SAG12 between an intersection of a second side of the first lens and the optical axis and an effective semi-aperture vertex of the second side of the first lens satisfy: 4.9<f1 / (SAG11+SAG12)≤8.

13.

7. The optical system of claim 1, wherein, an edge thickness ET1 of the first lens and an edge thickness ET3 of the third lens satisfy: 4.4<ET3 / ET1≤5.

14.

8. The optical system of claim 1, wherein, The Abbe number V1 of the first lens and the refractive index N1 of the first lens satisfy: 40.23≤V1 / N1<44; the Abbe number V2 of the second lens and the refractive index N2 of the second lens satisfy: 12.8<V2 / N2<20.

9. The optical system of any one of claims 1-8, wherein, The combined focal length fz1 of the reflective polarizing element, the first quarter-wave plate and the second lens and the total effective focal length f of the optical system satisfy: -1.0<f / fz1<-0.

1.

10. The optical system of any one of claims 1-8, wherein, The curvature radius R1 of the first side surface of the first lens and the central thickness CT1 of the first lens on the optical axis satisfy: 2.27≤R1 / CT1≤4.

15.

11. The optical system of any one of claims 1-8, wherein, The central thickness CTQ2 of the second quarter-wave plate on the optical axis, the central thickness CTL of the polarizing plate on the optical axis and the on-axis distance SAG42 between the intersection of the second side surface of the fourth lens and the optical axis and the effective semi-aperture vertex of the second side surface of the fourth lens satisfy: 0.3<(CTQ2+CTL) / |SAG42|<1.

4.

12. The optical system of any one of claims 1-8, wherein, The curvature radius R4 of the second side surface of the second lens and the curvature radius R6 of the second side surface of the third lens satisfy: -2.1≤R4 / R6≤-0.

07.

13. The optical system of any one of claims 1-8, wherein, The optical system further comprises a diaphragm arranged between the first side and the first lens; 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 on-axis distance SR from the diaphragm to the first side surface of the first lens satisfy: 1.2<TD / SR<1.3.

Images