Optical system

Abstract

Disclosed in the present invention is an optical system, consisting of an image surface, a fourth lens, a third lens, a second lens, and a first lens, which are sequentially arranged from a front side to a rear side. A polarizing reflective film is provided between the first lens and the second lens, a quarter-wave plate is provided between the second lens and the third lens, and the first lens, the second lens and the third lens are sequentially cemented to form a composite lens. In the optical system of the present invention, by rationally setting the radius of curvature of a lens on the side close to a screen, it is possible to better match the divergence angle of light emitted from the image surface, thereby improving energy utilization and the uniformity of display brightness in the optical system. In addition, by rationally designing the focal lengths of the composite lens and the fourth lens, the field of view angle of the optical system can be increased, and by rationally allocating the axial thickness of each lens, the thickness of the optical system can be reduced, resulting in a compact structure and achieving a lightweight and thin design for the optical system, thus effectively reducing the sensitivity and improving the imaging performance of the optical system.

Description

Optical system Technical Field

[0001] The present invention relates to the field of optical technology, and in particular to an optical system. Background Technology

[0002] In VR optical devices, the optical system often adopts a pancake design. This design reduces the overall optical length of the optical module by folding the optical path, making the optical module thinner and lighter, and has advantages such as high-quality imaging, low image distortion and adjustable diopter.

[0003] However, current VR optical systems using the pancake design still suffer from problems such as poor imaging quality and high sensitivity.

[0004] Summary of the Invention

[0005] The purpose of this invention is to provide an optical system that can effectively reduce its sensitivity and improve the imaging effect of the optical system.

[0006] To solve the above-mentioned technical problems, the present invention provides an optical system comprising an image surface for emitting light, a fourth lens, a third lens, a second lens, and a first lens arranged sequentially from front to back; a polarizing reflective film is provided between the first lens and the second lens, and a quarter-wave plate is provided between the second lens and the third lens; the first lens, the second lens, and the third lens are cemented together to form a combined lens, the focal length of the combined lens is f1_2_3, the focal length of the fourth lens is f4, the focal length of the optical system is f, the radius of curvature of the front surface of the fourth lens is R8, the on-axis thicknesses of the first lens, the second lens, and the third lens are d1, d3, and d5, respectively, and the maximum half-aperture (MSD) of the lens of the optical system is MSD, satisfying the following relationships: 5.50≤f4 / f1_2_3≤8.00; 0.04≤f / R8≤0.14; 0.20≤d1 / (d1+d3+d5)≤0.37; MSD≥24.00mm.

[0007] The beneficial effects of this invention are as follows: By rationally setting the radius of curvature of the lens near the screen, the divergence angle of the light emitted from the image surface can be better matched, improving energy utilization and enhancing the uniformity of the display brightness of the optical system. Furthermore, by rationally designing the focal lengths of the combined lens and the fourth lens, the field of view of the optical system can be increased. By rationally distributing the on-axis thickness of each lens, the thickness of the optical system can be reduced, making the structure of the optical system compact and achieving a thinner and lighter design. This effectively reduces its sensitivity, improves the imaging effect of the optical system, and meets the thinner and lighter requirements of electronic devices equipped with this optical system. Attached Figure Description

[0008] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments of the present invention will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0009] Figure 1 is a schematic diagram of the optical system according to the first embodiment of the present invention;

[0010] Figure 2 is a schematic diagram of the field curvature and distortion of the optical system shown in Figure 1;

[0011] Figure 3 is a schematic diagram of axial aberrations in the optical system shown in Figure 1;

[0012] Figure 4 is a point array schematic diagram of the optical system shown in Figure 1;

[0013] Figure 5 is a schematic diagram of the optical system according to the second embodiment of the present invention;

[0014] Figure 6 is a schematic diagram of the field curvature and distortion of the optical system shown in Figure 5;

[0015] Figure 7 is a schematic diagram of axial aberrations in the optical system shown in Figure 5;

[0016] Figure 8 is a point array diagram of the optical system shown in Figure 5. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the various embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been presented in the various embodiments of the present invention to enable the reader to better understand the present invention. However, the technical solutions claimed in the present invention can be implemented even without these technical details and various changes and modifications based on the following embodiments.

[0018] In embodiments of the present invention, the terms "upper," "lower," "left," "right," "front," "rear," "top," "bottom," "inner," "outer," "middle," "vertical," "horizontal," "lateral," and "longitudinal" indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings. These terms are primarily for the purpose of better describing the present invention and its embodiments, and are not intended to limit the indicated devices, elements, or components to having a specific orientation, or to be constructed and operated in a specific orientation.

[0019] Furthermore, in addition to indicating direction or positional relationship, some of the aforementioned terms may also have other meanings. For example, the term "above" may also be used in certain situations to indicate a dependency or connection. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.

[0020] Furthermore, the terms "installation," "setting," "equipped with," "opening," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral structure; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium, or an internal connection between two devices, components, or parts. Those skilled in the art can understand the specific meaning of these terms in this invention according to the specific circumstances.

[0021] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes said element.

[0022] Please refer to the accompanying drawings. The technical solution of the present invention provides an optical system 10, 20, which is composed of an image surface Si for emitting light, a fourth lens L4, a third lens L3, a second lens L2, and a first lens L1 arranged sequentially from the front to the rear. A polarizing reflective film RP is provided between the first lens L1 and the second lens L2, and a quarter-wave plate QWP is provided between the second lens L2 and the third lens L3. The first lens L1, the second lens L2, and the third lens L3 are cemented together in sequence to form a composite lens. The focal length of the composite lens is f1_2_3, the focal length of the fourth lens L4 is f4, the focal lengths of the optical systems 10 and 20 are f, the radius of curvature of the front surface of the fourth lens L4 is R8, the on-axis thicknesses of the first lens L1, the second lens L2, and the third lens L3 are d1, d3, and d5, respectively, and the maximum half-aperture of the optical system is MSD, satisfying the following relationships: 5.50≤f4 / f1_2_3≤8.00 (1) 0.04≤f / R8≤0.14 (2) 0.20≤d1 / (d1+d3+d5)≤0.37 (3) MSD≥24.00mm (4)

[0023] Condition (1) specifies the range of the ratio of the focal length f4 of the fourth lens L4 to the focal length f1_2_3 of the combined lens. By reasonably designing the focal length f4 of the fourth lens L4 and the focal length f1_2_3 of the combined lens, the field of view of the optical systems 10 and 20 can be increased, their sensitivity can be effectively reduced, the image imaging effect can be improved, and the thickness of the optical systems 10 and 20 can be reduced to meet the requirements of the thin and light design of electronic devices equipped with the optical systems 10 and 20.

[0024] Condition (2) specifies the shape of the radius of curvature R8 of the lens (i.e. the fourth lens L4) on the side closer to the image surface Si in the optical systems 10 and 20. This can better match the divergence angle of the light emitted from the image surface Si, improve energy utilization, and enhance the uniformity of the display brightness of the optical systems 10 and 20.

[0025] Condition (3) specifies the on-axis thickness of each lens in the optical systems 10 and 20. By reasonably allocating the on-axis thickness of each lens, the sensitivity of the optical systems 10 and 20 can be reduced and the production yield of the optical systems 10 and 20 can be improved. At the same time, the structure of the optical systems 10 and 20 can be made compact, realizing the ultra-thin design of the optical systems 10 and 20.

[0026] Condition (4) specifies the range of the maximum half-aperture diameter (MSD) of the lenses of the optical systems 10 and 20, which is conducive to the miniaturization design of the optical systems 10 and 20.

[0027] In this solution, by rationally setting the radius of curvature of the lens near the screen, the divergence angle of the light emitted from the image surface Si can be better matched, improving energy utilization and enhancing the uniformity of display brightness of optical systems 10 and 20. Furthermore, by rationally designing the focal length of the combined lens and the fourth lens L4, the field of view of optical systems 10 and 20 can be increased. By rationally allocating the on-axis thickness of each lens, the thickness of optical systems 10 and 20 can be reduced, making their structure compact and achieving a thinner and lighter design. This effectively reduces their sensitivity, improves the imaging effect of optical systems 10 and 20, and meets the thinner and lighter requirements of electronic devices equipped with these optical systems 10 and 20.

[0028] Furthermore, the front side of the third lens L3 is provided with a beam splitter BS, which is used to properly project and reflect light from the image plane Si. Additionally, the rear side of the image plane Si is provided with a polarizer POL, which polarizes the light emitted from the image plane Si.

[0029] It should be noted that in this invention, the front side is the image surface side and the rear side is the human eye side. The front side refers to the surface facing the image surface side in the optical axis direction, and the rear side refers to the surface facing the human eye side in the optical axis direction.

[0030] It is understood that the image surface Si is a display screen, and the light emitted from the display screen is circularly polarized light. After passing through the polarizer POL, it forms left-handedly polarized light LCP. The left-handedly polarized light LCP enters the fourth lens L4 from its front side and exits from its rear side, illuminating the beam splitter BS. A portion of the left-handedly polarized light LCP is reflected by the beam splitter BS, and the other portion is transmitted to the third lens L3. It then enters the third lens L3 from its front side and exits from its rear side to the quarter-wave plate QWP. Afterward, the left-handedly polarized light LCP passes through the quarter-wave plate QWP, forming linearly polarized light S. The linearly polarized light S illuminates the polarizing reflective film RP. Since the polarizing reflective film RP has the characteristic of reflecting both linearly polarized light S and projecting linearly polarized light P, the linearly polarized light S illuminating the polarizing reflective film RP is reflected back to the second lens L2.

[0031] The reflected linearly polarized S-light enters the second lens L2 from its rear side and exits from its front side. After passing through the quarter-wave plate QWP for the second time, it forms left-handedly polarized LCP light, which then enters the third lens L3 via its rear side and exits from its front side to the beam splitter BS. The left-handedly polarized LCP light is reflected by the beam splitter BS to form right-handedly polarized RCP light, which again enters the third lens L3 via its front side. The right-handedly polarized RCP light exits from the rear side of the third lens L3, passes through the quarter-wave plate QWP, and forms linearly polarized P-light. The linearly polarized P-light light enters the second lens L2 via its front side and exits from its rear side. Upon exiting the polarizing reflective film RP, the linearly polarized P-light light passes through the polarizing reflective film RP and enters the first lens L1, exiting from its rear side and propagating to the human eye.

[0032] For example, the axial distance from the image plane Si to the rear side of the first lens L1 is dL, and the thickness is dL, and the following relationship is satisfied: dL≤23.00mm (5)

[0033] Condition (5) specifies the on-axis thickness dL of the combined lens. Within this range, it is beneficial to reduce the overall on-axis thickness of the optical systems 10 and 20, thereby achieving the ultra-thin design of the optical systems 10 and 20.

[0034] For example, the total optical length of the optical systems 10 and 20 is TTL, and satisfies the following relationship: TTL≤38.00mm (6)

[0035] Condition (6) limits the total optical length TTL of the optical systems 10 and 20. By reasonably limiting the total optical length TTL of the optical systems 10 and 20, the ultra-thin design of the optical systems 10 and 20 can be achieved while achieving high imaging quality.

[0036] For example, the total optical length TTL of the optical systems 10 and 20 also satisfies the following relationship: TTL / f≤1.95 (7)

[0037] Condition (7) limits the range of the ratio of the total optical length TTL to the focal length f of the optical systems 10 and 20. Within this range, it helps to maintain a small volume of the optical systems 10 and 20 and achieve miniaturization of the optical systems 10 and 20.

[0038] For example, the field of view of the optical systems 10 and 20 is FOV, and satisfies the following relationship: 75.00°≤FOV≤85.00° (8)

[0039] Condition (8) specifies the field of view (FOV) of the optical systems 10 and 20. Within this range, it can be ensured that the field of view (FOV) of the optical systems 10 and 20 effectively covers the display screen, so that the user can fully receive the display content of the display screen.

[0040] For example, the front side of the third lens L3 is provided with a semi-reflective and semi-transparent film HRHT, the transmittance of the semi-reflective and semi-transparent film HRHT is t1, the reflectance of the semi-reflective and semi-transparent film HRHT is r, and the following relationships are satisfied: 40.00% ≤ t1 ≤ 60.00% (9) 40.00% ≤ r ≤ 60.00% (10)

[0041] Conditions (9) and (10) respectively specify the range of values ​​for the transmittance t1 and reflectance r of the semi-reflective and semi-transparent film HRHT. Within this range, the light emitted by the display screen can have a reasonable light intensity when it is imaged on the human eye after passing through the lens group, avoiding excessive light intensity that may cause eye discomfort to the user, while enabling the user to clearly receive the display content of the display screen.

[0042] For example, the transmittance of the polarizing reflective film RP is t2, and satisfies the following relationship: t2≥95.00% (11)

[0043] Condition (11) specifies the range of transmittance t2 of the polarizing reflective film RP. Within this range, sufficient light can pass through the polarizing reflective film RP and be emitted to the human eye, avoiding insufficient imaging light and ensuring the user's experience.

[0044] For example, the chromatic difference between the optical systems 10 and 20 is |LC|, and satisfies the following relationship: |LC|≤75.00μm (12)

[0045] Condition (12) specifies the chromatic difference range of the optical systems 10 and 20, which can reduce the color distortion of the optical systems 10 and 20 and ensure that the optical systems 10 and 20 have good imaging effects.

[0046] For example, the optical distortion of the optical system is OD, and satisfies the following relationship: OD≤24.00% (13)

[0047] Condition (13) specifies the range of optical distortion of the optical systems 10 and 20. Within the range of the condition, the degree of imaging distortion of the optical systems 10 and 20 can be reduced, ensuring that the optical systems 10 and 20 have good imaging effects.

[0048] For example, the eye box size of the optical systems 10 and 20 is EYEBOX, and satisfies the following relationship: EYEBOX ≥ 12.00 mm (14)

[0049] Conditional equation (14) defines the range of values ​​for the eye box size of the optical systems 10 and 20. In this invention, the position of the aperture ST simulates the position of the human eye surface, the diameter of the aperture ST is EPD = 4.00 mm, the eye box size of the optical systems 10 and 20 is EYEBOX, and the range of human eye movement is EYESHIFT. Therefore, EYEBOX = EPD + EYESHIFT, where EYESHIFT is the movement of the field of vision caused by the rotation of the human eye. Let EYESHIFT = ±4.00 mm, that is, the maximum distance that the human eye can move in two opposite directions is 4.00 mm, then EYEBOX = 12.00 mm. Therefore, the human eye can see a clear image when moving within a range of 12.00 mm in diameter, so that the user can see the best display effect in the optimal position without complicated adjustments.

[0050] For example, the axial distance from the human eye to the rear side of the first lens L1 is EYERELIF, and satisfies the following relationship: EYERELIF≤15.00mm (15)

[0051] Condition (15) defines the axial distance between the human eye and the rear side of the first lens L1 when the optical systems 10 and 20 are in use. In this invention, the aperture ST simulates the position of the human eye, and the diameter EPD of the aperture ST is the entrance pupil diameter ENPD of the optical systems 10 and 20. The aperture ST is located on one side of the rear side of the first lens L1, and the axial distance from the aperture ST to the rear side of the first lens L1 is EYERELIF. Other structures, such as mechanical structures and eyeglasses, can be placed within this distance. Within this range, the smoothness of the eye's observation of the display screen can be satisfied, and the overall system length of the optical systems 10 and 20 can be made smaller, which is beneficial for miniaturization design.

[0052] For example, the screen size SS satisfies the following relationship: 1 inch ≤ SS ≤ 1.3 inches (16)

[0053] Condition (16) limits the size of the display screen in the optical systems 10 and 20, which is beneficial to the miniaturization of the optical systems.

[0054] In one embodiment, the first lens L1 has positive refractive power, and the rear surface of the first lens L1 is convex near the axis, as are the front surface of the first lens L1. In other feasible embodiments, the first lens may also have negative refractive power, and the front and rear surfaces of the first lens L1 may be configured with other surface shapes.

[0055] For example, the radius of curvature of the rear side of the first lens L1 is R1, the radius of curvature of the front side of the first lens L2 is R2, the on-axis thickness of the first lens L1 is d1, the total optical length of the optical systems 10 and 20 is TTL, and the focal length of the first lens L1 is f1, and the following relationships are satisfied: -0.26≤(R1+R2) / (R1-R2)≤0.43 (17) 0.04≤d1 / TTL≤0.20 (18) 2.73≤f1 / f≤13.92 (19)

[0056] Condition (17) specifies the shape of the first lens L1. Within this range, the degree of refraction of light after passing through the first lens L1 can be mitigated, effectively reducing aberrations. In addition, the relationship -0.16≤(R1+R2) / (R1-R2)≤0.35 can be satisfied. Condition (18) specifies the on-axis thickness d1 of the first lens L1. Within this range, it is conducive to the ultra-thin design of the optical systems 10 and 20. In addition, the relationship 0.06≤d1 / TTL≤0.16 can be satisfied. Condition (19) specifies the range of the ratio of the focal length f1 of the first lens L1 to the focal length f of the optical systems 10 and 20. Within the above range, it is conducive to reducing aberrations and improving image quality. In addition, the relationship 4.37≤f1 / f≤11.14 can be satisfied.

[0057] In one embodiment, the second lens L2 has negative refractive power, with a flat front surface and a concave rear surface near the axis. It is understood that making the front surface of the second lens L2 flat reduces the manufacturing difficulty of the second lens L2 and the difficulty of setting the quarter-wave plate (QWP) on its front surface. In other feasible embodiments, the second lens L2 may also have positive refractive power, and its front and rear surfaces may be configured with other surface shapes.

[0058] For example, the on-axis thickness of the second lens L2 is d3, and the total optical length of the optical systems 10 and 20 is TTL; the focal length of the second lens L2 is f2, and the focal length of the optical systems 10 and 20 is f, and they satisfy the following relationships: 0.02≤d3 / TTL≤0.13 (20) -28.72≤f2 / f≤-6.88 (21)

[0059] Condition (20) specifies the range of values ​​for the on-axis thickness d3 of the second lens L2, which helps to achieve the miniaturization design of the optical systems 10 and 20. In addition, it can also satisfy the relationship 0.03≤d3 / TTL≤0.10. Condition (21) specifies the focal length f2 of the second lens L2. By reasonably configuring the focal length f2 of the second lens L2, it helps to improve the optical performance of the optical systems 10 and 20. In addition, it can also satisfy the relationship -18.00≤f2 / f≤-8.60.

[0060] For example, the front surface of the first lens L1 and the rear surface of the second lens L2 are aspherical.

[0061] In one embodiment, the third lens L3 has positive refractive power, with its front surface being convex near the axis and its rear surface being flat. It is understood that setting the rear surface of the third lens L3 to be flat reduces the manufacturing difficulty of the third lens L3 and also reduces the difficulty of attaching the rear surface of the third lens L3 to the front surface of the quarter-wave plate (QWP). In other feasible embodiments, the third lens L3 may also have negative refractive power, and its front and rear surfaces may be configured with other surface shapes.

[0062] For example, the on-axis thickness of the third lens L3 is d5, and the total optical length of the optical systems 10 and 20 is TTL; the focal length of the third lens L3 is f3, and the focal length of the optical systems 10 and 20 is f, and they satisfy the following relationships: 0.10≤d5 / TTL≤0.30 (22) 2.51≤f3 / f≤7.64 (23)

[0063] Condition (22) specifies the range of values ​​for the on-axis thickness d5 of the third lens L3, which helps to achieve the miniaturization design of the optical systems 10 and 20. In addition, it can also satisfy the relationship 0.16≤d5 / TTL≤0.24. Condition (23) specifies the focal length f3 of the third lens L3, which helps to reduce aberrations and improve imaging quality. In addition, it can also satisfy the relationship 4.02≤f3 / f≤6.11.

[0064] In one embodiment, the fourth lens L4 has positive refractive power, with its front surface being concave near the axis and its rear surface being convex near the axis. In other feasible embodiments, the fourth lens L4 may also have negative refractive power, and its front and rear surfaces may be configured with other surface shapes.

[0065] For example, the radius of curvature of the rear side of the fourth lens L4 is R7, the radius of curvature of the front side of the fourth lens L4 is R8, the on-axis thickness of the fourth lens is d7, the total optical length of the optical system 10 and 20 is TTL, and the focal length of the fourth lens L4 is f4, and the following relationships are satisfied: -4.39≤(R7+R8) / (R7-R8)≤-0.84 (24) 0.05≤d7 / TTL≤0.17 (25) 2.94≤f4 / f≤12.14 (26)

[0066] Condition (24) specifies the shape of the fourth lens L4, which can reduce the spherical aberration of the optical systems 10 and 20. In addition, it can also satisfy the relationship -2.74≤(R7+R8) / (R7-R8)≤-1.05. Condition (25) specifies the on-axis thickness d7 of the fourth lens L4. Within this range, it is beneficial to realize the ultra-thin design of the optical systems 10 and 20. In addition, it can also satisfy the relationship 0.09≤d7 / TTL≤0.13. Condition (26) specifies the focal length f4 of the fourth lens L4, which helps to reduce aberrations and improve image quality. In addition, it can also satisfy the relationship 4.71≤f4 / f≤9.71.

[0067] Furthermore, the focal length of the combined lens consisting of the first lens L1, the second lens L2, and the third lens L3 is f1_2_3, and satisfies the following relationship: 0.52≤f1_2_3 / f≤1.60 (27)

[0068] Condition (27) specifies the focal length f123 of the combined lens, which helps to control the light path between the lenses and improve the optical performance of the optical systems 10 and 20. In addition, it can also satisfy the relation 0.84≤f1_2_3 / f≤1.28.

[0069] The optical systems 10 and 20 of this invention utilize a combination of a polarizer (POL), a quarter-wave plate (QWP), and a polarizing reflective film (RP) in a solid-line optical path folding structure to reduce the volume of the optical systems 10 and 20. Specifically, the use of a combined lens, consisting of a first lens L1, a second lens L2, and a third lens L3 cemented together, in the folded optical path significantly reduces the total optical length (TTL) of the optical systems 10 and 20, lowering the assembly difficulty and contributing to the miniaturization and weight reduction of electronic devices. Furthermore, due to the large size of the eyebox, users can achieve the best display effect from the optimal position without frequent adjustments, with a maximum field of view (FOV) of 85°. Even at the edge of the eyebox (EYESHIFT = ±4mm), the full-field performance of the optical systems 10 and 20 is excellent, improving the user's display experience when the position is not ideal. The lenses in the optical systems 10 and 20 of this invention use aspherical design to adjust the image's focus position, thereby reducing chromatic aberration and distortion of the displayed image and improving image quality.

[0070] The optical system 10 of the present invention will be described below with examples. The symbols described in each example are shown in Table [1], and the units for focal length, on-axis distance, radius of curvature, and on-axis thickness are millimeters.

[0071] TTL: Total optical length (axial distance from the object surface of the first lens L1 to the image surface), in millimeters.

[0072] First implementation method:

[0073] In this embodiment, the first lens L1 has positive refractive power, its rear side surface is convex near the axis, and its front side surface is convex near the axis.

[0074] The second lens L2 has negative refractive power, its rear side is concave near the axis, and its front side is flat near the axis;

[0075] The third lens L3 has positive refractive power, its rear side is flat near the axis, and its front side is convex near the axis;

[0076] The fourth lens L4 has positive refractive power, its rear side is convex near the axis, and its front side is concave near the axis.

[0077] Figure 1 is a schematic diagram of the optical system 10 in the first embodiment. The design data of the optical system 10 in the first embodiment of the present invention are shown below.

[0078] Table 1 lists the radius of curvature R, axial thickness of the lenses, axial distance d between the lenses, refractive index nd, and Abbe number vd of the object-side and image-side surfaces of the first lens L1 to the sixth lens L6 constituting the optical system 10 in the first embodiment of the present invention. Table 2 shows the conic coefficient k and aspherical coefficient of the optical system 10. It should be noted that in this embodiment, the units of distance, radius, and thickness are all millimeters (mm).

[0079] Table 1

[0080] The meanings of the symbols in the table above are as follows.

[0081] R: Radius of curvature of the optical surface; for lenses, it is the central radius of curvature.

[0082] ST: Aperture;

[0083] R1: Radius of curvature of the rear surface of the first lens L1;

[0084] R2: Radius of curvature of the front surface of the first lens L1;

[0085] R3: Radius of curvature of the rear surface of the second lens L2;

[0086] R4: Radius of curvature of the front surface of the second lens L2;

[0087] R5: Radius of curvature of the rear side surface of the third lens L3;

[0088] R6: Radius of curvature of the front surface of the third lens L3;

[0089] R7: Radius of curvature of the rear side surface of the fourth lens L4;

[0090] R8: Radius of curvature of the front surface of the fourth lens L4;

[0091] d: Axial thickness of the lens, axial distance between lenses;

[0092] EYERELIF: The on-axis distance from the aperture ST to the rear side of the first lens L1;

[0093] d1: On-axis thickness of the first lens L1;

[0094] d3: On-axis thickness of the second lens L2;

[0095] d5: On-axis thickness of the third lens L3;

[0096] d6: The on-axis distance from the front surface of the third lens L3 to the rear surface of the fourth lens L4;

[0097] d7: On-axis thickness of the fourth lens L4;

[0098] d8: The on-axis distance from the front surface of the fourth lens L4 to the image plane Si;

[0099] nd: Refractive index of the d-line;

[0100] nd1: Refractive index of the first lens L1;

[0101] nd2: Refractive index of the second lens L2;

[0102] nd3: Refractive index of the third lens L3;

[0103] nd4: Refractive index of the fourth lens L4;

[0104] vd: Abbe number;

[0105] vd1: Abbe number of the first lens L1;

[0106] vd2: Abbe number of the second lens L2;

[0107] vd3: Abbe number of the third lens L3;

[0108] vd4: Abbe number of the fourth lens L4.

[0109] Table 2

[0110] It should be noted that the aspherical surfaces of each lens in this embodiment are aspherical surfaces as shown in the following conditional expression (28). However, the specific form of the following conditional expression (28) is only an example. In fact, the present invention is not limited to the aspherical polynomial form represented in conditional expression (28). z=(c 2 / r) / {1+[1-(k+1)(c 2 / r 2 )] 1 / 2}+A4r 4 +A6r 6 +A8r 8 +A10r 10 (28)

[0111] Where k is the conic coefficient, and A4, A6, A8, and A10 are aspheric coefficients. c is the curvature at the center of the optical surface, r is the perpendicular distance between a point on the aspheric curve and the optical axis, and z is the aspheric depth (the perpendicular distance between a point r on the aspheric surface at a distance r from the optical axis and a tangent plane at the vertex of the aspheric optical axis).

[0112] In addition, Table 5 below lists the values ​​of various parameters in the first embodiment and the parameters specified in the conditional expressions.

[0113] Figure 2 shows a schematic diagram of field curvature and distortion of light with a wavelength of 540 nm after passing through the optical system 10 of the first embodiment. In Figure 2, the field curvature S is the field curvature in the sagittal direction, and T is the field curvature in the meridional direction. Figure 3 shows a schematic diagram of axial aberrations of light with wavelengths of 470 nm, 540 nm, and 630 nm after passing through the optical system 10 of the first embodiment. Figure 4 shows a dot plot of light with wavelengths of 470 nm, 540 nm, and 630 nm after passing through the optical system 10 of the first embodiment.

[0114] As shown in Table 5, the first embodiment satisfies all the conditional expressions.

[0115] In this embodiment, the focal length f1 of the first lens L1 is 182.044 mm, the focal length f2 of the second lens L2 is -281.721 mm, the focal length f3 of the third lens L3 is 99.881 mm, the focal length f4 of the fourth lens L4 is 158.803 mm, the entrance pupil diameter ENPD of the optical system 10 is 4.00 mm, the full field of view image height IH is 12.50 mm, the field of view FOV in the diagonal direction is 79.99°, and the total optical length TTL is 36.09 mm. Its on-axis and off-axis chromatic aberrations are fully corrected. The optical system 10 has a compact structure, which enables the optical system 10 to be thin and light, and has excellent optical characteristics.

[0116] Second implementation method:

[0117] Figure 5 is a schematic diagram of the optical system 20 in the second embodiment. The second embodiment is basically the same as the first embodiment, and the symbols have the same meanings as in the first embodiment. Only the differences are listed below.

[0118] Tables 3 and 4 show the design data of the optical system 20 according to the second embodiment of the present invention.

[0119] Table 3

[0120] Table 4

[0121] In addition, Table 5 below lists the values ​​of various parameters in the second embodiment and the parameters specified in the conditional expressions.

[0122] Figure 6 shows a schematic diagram of field curvature and distortion of light with a wavelength of 540 nm after passing through the optical system 20 of the second embodiment. In Figure 6, the field curvature S is the field curvature in the sagittal direction, and T is the field curvature in the meridional direction. Figure 7 shows a schematic diagram of axial aberrations of light with wavelengths of 470 nm, 540 nm, and 630 nm after passing through the optical system 20 of the second embodiment. Figure 8 shows a dot plot of light with wavelengths of 470 nm, 540 nm, and 630 nm after passing through the optical system 20 of the second embodiment.

[0123] As shown in Table 5, the second embodiment satisfies all the conditional expressions.

[0124] In this embodiment, the focal length f1 of the first lens L1 is 105.396 mm, the focal length f2 of the second lens L2 is -199.354 mm, the focal length f3 of the third lens L3 is 97.120 mm, the focal length f4 of the fourth lens L4 is 113.649 mm, the entrance pupil diameter ENPD of the optical system 20 is 4.00 mm, the full field of view image height IH is 12.50 mm, the diagonal field of view FOV is 79.99°, and the total optical length TTL is 36.09 mm. Its on-axis and off-axis chromatic aberrations are fully corrected. The optical system 10 has a compact structure, which enables the optical system 10 to be thin and light, and has excellent optical characteristics.

[0125] Table 5

[0126] The optical system provided in the embodiments of the present invention has been described in detail above. Specific examples have been used to illustrate the principles and embodiments of the present invention. The description of the above embodiments is only for the purpose of helping to understand the idea of ​​the present invention. There may be changes in specific embodiments and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

An optical system comprises, from front to back, an image surface for emitting light, a fourth lens, a third lens, a second lens, and a first lens; a polarizing reflective film is provided between the first lens and the second lens, and a quarter-wave plate is provided between the second lens and the third lens; the first lens, the second lens, and the third lens are cemented together to form a composite lens, the focal length of the composite lens is f1_2_3, the focal length of the fourth lens is f4, the focal length of the optical system is f, the radius of curvature of the front surface of the fourth lens is R8, the on-axis thicknesses of the first lens, the second lens, and the third lens are d1, d3, and d5, respectively, and the maximum half-aperture of the lens in the optical system is MSD, satisfying the following relationship: 5.50≤f4 / f1_2_3≤8.00; 0.04≤f / R8≤0.14; 0.20≤d1 / (d1+d3+d5)≤0.37; MSD ≥ 24.00 mm. The optical system according to claim 1, wherein, The axial distance from the image plane to the rear side of the first lens is dL, and satisfies the following relationship: dL≤23.00mm. The optical system according to claim 1, wherein, The total optical length of the optical system is TTL, and satisfies the following relationship: TTL≤38.00mm. The optical system according to claim 3, wherein, It also satisfies the following relationship: TTL / f≤1.

95. The optical system according to claim 1, wherein, The field of view of the optical system is FOV, and it satisfies the following relationship: 75.00°≤FOV≤85.00°. The optical system according to claim 1, wherein, The front surface of the third lens is provided with a semi-reflective and semi-transparent film. The transmittance of the semi-reflective and semi-transparent film is t1, and the reflectance of the semi-reflective and semi-transparent film is r, which satisfy the following relationship: 40.00％≤t1≤60.00％； 40.00％≤r≤60.00％。 The optical system according to claim 1, wherein, The transmittance of the polarizing reflective film is t2, and it satisfies the following relationship: t2≥95.00％。 The optical system according to claim 1, wherein, The chromatic difference of the optical system is |LC|, and satisfies the following relationship: |LC|≤75.00μm. The optical system according to claim 1, wherein, The optical distortion of the optical system is OD, and satisfies the following relationship: OD ≤ 24%. The optical system according to claim 1, wherein, The front surface of the first lens and the rear surface of the second lens are aspherical. The optical system according to claim 1, wherein, The front surface of the second lens and the rear surface of the third lens are flat. The optical system according to claim 1, wherein, The eyebox size of the optical system is EYEBOX, and satisfies the following relationship: EYEBOX ≥ 12.00 mm. The optical system according to claim 1, wherein, The axial distance from the human eye to the rear surface of the first lens is EYERELIF, and satisfies the following relationship: EYERELIF≤15.00mm. The optical system according to claim 1, wherein, The image surface is a display screen with a size of 1.00-1.30 inches.

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