Optical system, image projection device, and imaging device

Abstract

An optical system according to the present disclosure has a reduction conjugate surface on a reduction side and an enlargement conjugate surface on an enlargement side, and internally has an intermediate image that is conjugate to each of the reduction conjugate surface and the enlargement conjugate surface. The optical system comprises a first sub-optical system and a second sub-optical system arranged in order from the reduction side to the enlargement side. The first sub-optical system has a plurality of lens elements. The second sub-optical system has a prism and an enlargement-side lens element disposed on an enlargement side of the prism. The prism has a first transmission surface positioned on the reduction side, a second transmission surface positioned on the enlargement side, and one or more reflection surfaces positioned on an optical path from the first transmission surface to the second transmission surface. At least a part of an intermediate image formed at an intermediate imaging position is located inside the prism. The enlargement-side lens element condenses a divergent light flux, among light fluxes emitted from the prism, onto the enlargement conjugate surface.

Description

Optical system, image projection device, and imaging device

[0007]

[0001] The present disclosure relates to an optical system that forms an intermediate image. The present disclosure also relates to an image projection device and an imaging device using such an optical system.

[0002] Patent Document 1 discloses an optical system in which a first reflecting surface and a second reflecting surface are arranged close to each other. The optical system described in Patent Document 1 includes a first optical element and a second optical element arranged on the reduction side of the first optical element. The first optical element has a concave first reflecting surface, and the second optical element has a first transmission surface, a second reflecting surface arranged on the reduction side of the first transmission surface, and a second transmission surface arranged on the reduction side of the second reflecting surface. The first optical axis of the first reflecting surface is parallel to the second optical axis of the first transmission surface, and at least one of the first transmission surface, the second reflecting surface, and the second transmission surface has power.

[0003] Japanese Patent Application Laid-Open No. 2023-84787

[0004] The present disclosure provides an optical system that can be miniaturized while realizing a low f-number. The present disclosure also provides an image projection device and an imaging device using such an optical system.

[0005] An optical system according to an aspect of the present disclosure is an optical system having a reduction conjugate surface on the reduction side and an enlargement conjugate surface on the enlargement side, and having an intermediate image conjugate with the reduction conjugate surface and the enlargement conjugate surface inside, and includes a first sub-optical system and a second sub-optical system arranged in order from the reduction side to the enlargement side. The first sub-optical system has a plurality of lens elements, and the second sub-optical system has a prism and an enlargement-side lens element arranged on the enlargement side of the prism. The prism has a first transmission surface located on the reduction side, a second transmission surface located on the enlargement side, and one or more reflecting surfaces located on the optical path from the first transmission surface to the second transmission surface. At least a part of the intermediate image formed at the intermediate image position is located inside the prism, and the enlargement-side lens element condenses the diverging light beam among the light beams emitted from the prism onto the enlargement conjugate surface.

[0006] An image projection device according to the present disclosure includes the above optical system and an image forming element that generates an image to be projected onto a screen via the optical system.

[0007] Furthermore, the imaging device according to this disclosure comprises the optical system described above and an image sensor that receives the optical image formed by the optical system and converts it into an electrical image signal.

[0008] The optical system, image projection device, and imaging device described herein can be miniaturized while achieving a low throw ratio.

[0009] 1. Arrangement diagram showing the optical system of Example 1. Explanatory diagram showing the usage of an image projection device using the optical system of Example 1. Transverse aberration diagram in the optical system of Example 1. Transverse aberration diagram in the optical system of Example 1. Enlarged partial view showing the second sub-optical system in the optical system of Example 1. Arrangement diagram showing the optical system of Example 2. Transverse aberration diagram in the optical system of Example 2. Transverse aberration diagram in the optical system of Example 2. Arrangement diagram showing the optical system of Example 3. Transverse aberration diagram in the optical system of Example 3. Transverse aberration diagram in the optical system of Example 3. Arrangement diagram showing the optical system of Example 4. Transverse aberration diagram in the optical system of Example 4. Transverse aberration diagram in the optical system of Example 4. Arrangement diagram showing the optical system of Example 5. Transverse aberration diagram in the optical system of Example 5. Transverse aberration diagram in the optical system of Example 5. Block diagram showing an example of an image projection device according to this disclosure. Block diagram showing an example of an imaging device according to this disclosure.

[0010] (Background to this disclosure) In optical systems using prisms, it is known that intermediate images are formed inside or near the prism in order to miniaturize the prism. In such a configuration, in order to achieve a low throw ratio, it is conceivable to increase the curvature of the prism's exit surface, that is, the surface on the widest side of the prism. However, increasing the curvature of the prism's exit surface increases the inclination angle of the prism's exit surface with respect to the optical axis, which can result in a shape that is difficult to realize.

[0011] On the other hand, reducing the curvature of the prism's exit surface presents problems such as the prism becoming larger or the throw ratio increasing.

[0012] Therefore, in order to solve the above problem, the present inventors have found an optical system that focuses the light beam emitted by a magnifying lens element placed on the magnifying side of a prism, and have come to the following disclosure.

[0013] The embodiments will be described in detail below, with reference to the drawings as appropriate. However, unnecessarily detailed explanations may be omitted. For example, detailed explanations of already well-known matters or redundant explanations of substantially identical configurations may be omitted. This is to avoid the following explanation becoming unnecessarily verbose and to facilitate understanding for those skilled in the art.

[0014] The applicant provides the accompanying drawings and the following description so that a person skilled in the art can fully understand the disclosure, and not to limit the subject matter described in the claims.

[0015] Furthermore, in this specification, terms such as "first," "second," etc., are used solely for descriptive purposes and should not be understood as expressing or implying relative importance or ranking of technical features. Features designated as "first" and "second" express or imply that they include one or more such features.

[0016] The following describes various embodiments of the optical system according to this disclosure. In each embodiment, the case in which the optical system is used in a projector (an example of an image projection device) that projects image light of an original image S, which is obtained by spatially modulating incident light using an image forming element such as a liquid crystal or a DMD (digital micromirror device) based on an image signal, onto a screen will be described. That is, the optical system according to this disclosure can be used to enlarge an original image S on an image forming element located on the reduction side and project it onto a screen by placing a screen (not shown) on the extension of the enlargement side.

[0017] Furthermore, the optical system according to this disclosure can also be used to collect light emitted from an object located on the extension of the magnification side and to form an optical image of the object on the imaging surface of an image sensor located on the reduction side.

[0018] (Embodiment 1) Hereinafter, Embodiment 1 of the present disclosure will be described with reference to Figures 1 to 17.

[0019] Figures 1, 6, 9, 12, and 15 are arrangement diagrams showing the optical system 1 of Examples 1 to 5, respectively. In each figure, the reducing image position (i.e., the reducing conjugate plane) is located on the left side. In Figures 1, 9, 12, and 15, the enlargement image position (i.e., the enlargement conjugate plane) is located further to the left than shown in the figure, and in Figure 6, the enlargement image position (i.e., the enlargement conjugate plane) is located further to the right than shown in the figure. In each figure, the optical system 1 is shown as viewed from a direction perpendicular to the Y-Z plane (meridional plane), with the optical axis in the Z direction in the X-Y-Z Cartesian coordinate system. In each figure, for clarity, we show a ray passing through the center of the original image S in the X direction and the lowest point in the Y direction (normalized height Y = 0.0 on the reduction conjugate plane), a ray passing through the center of the original image S in the X direction and the middle part in the Y direction (normalized height Y = 0.5 on the reduction conjugate plane), and a ray passing through the center of the original image S in the X direction and the highest point in the Y direction (normalized height Y = 1.0 on the reduction conjugate plane). In each figure, the straight line drawn on the most reduced side represents the position of the original image S, and the optical element P is located on the enlarged side of the original image S. The optical element P represents optical elements such as a TIR (total internal reflection) prism, prisms for color separation and color synthesis, optical filters, parallel plate glass, quartz low-pass filters, and infrared cut filters. The optical element P has two parallel and flat transmitting surfaces.

[0020] The optical systems 1 of Examples 1 to 5 have a reduction conjugate plane on the reduction side and an enlargement conjugate plane on the enlargement side, and internally have intermediate imaging positions MI that are conjugate to the reduction conjugate plane and the enlargement conjugate plane, respectively. The optical systems 1 of Examples 1 to 5 include a first sub-optical system OP1 and a second sub-optical system OP2, in order from the reduction side to the enlargement side.

[0021] In Examples 1 to 4, the first sub-optical system OP1 includes a plurality of lens elements L1 to L9 and an aperture ST.

[0022] Multiple lens elements L1 to L9 are arranged in the first sub-optical system OP1 in order from the reduction side to the magnification side. The aperture ST is located between lens element L4 and lens element L5.

[0023] In Example 5, the first sub-optical system OP1 includes a plurality of lens elements L21 to L32 and an aperture ST.

[0024] Multiple lens elements L21 to L32 are arranged in the first sub-optical system OP1 in order from the reduction side to the magnification side. The aperture ST is located between lens element L25 and lens element L26.

[0025] In Examples 1 to 5, the second sub-optical system OP2 includes a prism PM and a magnifying lens element L10. In Example 4, the second sub-optical system OP2 further includes a magnifying lens element L11.

[0026] The prism PM has a first transmission surface T1 located on the reduction side, a second transmission surface T2 located on the expansion side, and one or more reflective surfaces R1, R2 located in the optical path from the first transmission surface T1 to the second transmission surface T2.

[0027] The prism PM is formed, for example, from glass or synthetic resin.

[0028] The magnifying lens elements L10 and L11 are positioned on the magnifying side of the prism PM in the second sub-optical system OP2. In Examples 1 to 3 and 5, the magnifying lens element L10 is positioned on the most magnified side of the second sub-optical system OP2. In Example 4, the magnifying lens element L11 is positioned on the most magnified side of the second sub-optical system OP2.

[0029] The magnifying lens elements L10 and L11 focus the diverging light beam from the prism PM onto the magnifying conjugate plane. In other words, the magnifying lens elements L10 and L11 have the power to conjugate the diverging light beam from the prism PM onto the magnifying conjugate plane.

[0030] The intermediate imaging position MI is located at the prism PM of the second sub-optical system OP2. At least a portion of the intermediate image formed at the intermediate imaging position MI is located inside the prism PM.

[0031] Figure 2 is an explanatory diagram showing how to use the image projection device using the optical system 1 of Example 1. The image projection device including the optical system 1 is placed horizontally on a support base such as a table, or on the floor. The screen SC is installed vertically above at a relatively short horizontal distance from the support base, for example, 0.5 m away. The screen SC is a single plane (magnification conjugate plane) located at the conjugate point on the magnification side. Light generated from the optical system 1 is projected diagonally upward and backward, achieving short-focus and large-screen projection. Note that Figure 2 shows an example of rearward projection of the optical system 1 of Example 1, but the same applies to the optical systems 1 of Examples 3 to 5. The optical system 1 of Example 2 differs in that it projects forward. Light generated from the optical system 1 of Example 2 is projected diagonally upward and forward, achieving short-focus and large-screen projection.

[0032] Figures 3-4, 7-8, 10-11, 13-14, and 16-17 are transverse aberration diagrams for the optical system 1 of Examples 1-5, respectively. (A) to (I) in each figure show the transverse aberration diagrams of the tangential (meridional) plane and sagittal plane at positions shifted from the center in the X and Y directions, respectively.

[0033] (Example 1) Figure 1 is a layout diagram showing the optical system 1 according to Example 1. The surface data for Example 1 is shown in the numerical example 1 described later.

[0034] In the first sub-optical system OP1 of Embodiment 1, a plurality of lens elements L1 to L9 are arranged in order from the reduction side to the magnification side. Lens element L1 has a biconvex shape. Lens element L2 has a biconvex shape. Lens element L3 has a biconcave shape. Lens element L4 has a biconvex shape. Lens element L5 has a positive meniscus shape with its convex surface facing the magnification side. Lens element L6 has a positive meniscus shape with its convex surface facing the magnification side. Lens element L7 has a positive meniscus shape with its convex surface facing the reduction side. Lens element L8 has a negative meniscus shape with its convex surface facing the magnification side. Lens element L9 has a negative meniscus shape with its convex surface facing the magnification side.

[0035] In the second sub-optical system OP2 of Example 1, the prism PM has a first transmission surface T1, a second transmission surface T2, and a reflective surface R1. In the second sub-optical system OP2, the first transmission surface T1, the reflective surface R1, and the second transmission surface T2 are arranged in order from the reduction side to the expansion side.

[0036] The first transmission surface T1 is located on the reduction side of the prism PM. The first transmission surface T1 has a free-form shape with its convex surface facing the lens element L9 side of the first sub-optical system OP1.

[0037] The second transmission surface T2 is located on the magnifying side of the prism PM. The second transmission surface T2 has a free-form shape with its convex side facing the magnifying lens element L10.

[0038] The reflective surface R1 is located in the optical path from the first transmitting surface T1 to the second transmitting surface T2. The reflective surface R1 has a freeform surface shape in which the concave surface is oriented in the direction in which the light rays incident on the reflective surface R1 from the first transmitting surface T1 are reflected toward the second transmitting surface T2.

[0039] In the second sub-optical system OP2 of Example 1, the magnifying lens element L10 has a negative meniscus shape with a convex surface facing the magnifying side.

[0040] In Example 1, the entire intermediate image formed at the intermediate imaging position MI is located inside the prism PM.

[0041] In Example 1, variable intervals SP1 to SP5 are set. Variable interval SP1 is the interval between the optical element P and the lens element L1. Variable interval SP2 is the interval between the aperture ST and the lens element L5. Variable interval SP3 is the interval between the lens element L5 and the lens element L6. Variable interval SP4 is the interval between the lens element L9 and the first transmission surface T1. Variable interval SP5 is the interval between the screen SC and the magnifying lens element L10.

[0042] (Example 2) Figure 6 is a layout diagram showing the optical system 1 according to Example 2. The surface data for Example 2 is shown in the numerical example 2 described later.

[0043] In the first sub-optical system OP1 of Example 2, a plurality of lens elements L1 to L9 are arranged in order from the reduction side to the enlargement side. The lens element L1 has a biconvex shape. The lens element L2 has a biconvex shape. The lens element L3 has a biconcave shape. The lens element L4 has a biconvex shape. The lens element L5 has a positive meniscus shape with the convex surface facing the enlargement side. The lens element L6 has a positive meniscus shape with the convex surface facing the enlargement side. The lens element L7 has a positive meniscus shape with the convex surface facing the reduction side. The lens element L8 has a negative meniscus shape with the convex surface facing the enlargement side. The lens element L9 has a negative meniscus shape with the convex surface facing the enlargement side.

[0044] In the second sub-optical system OP2 of Example 2, the prism PM has a first transmission surface T1, a second transmission surface T2, a first reflection surface R1, and a second reflection surface R2. In the second sub-optical system OP2, the first transmission surface T1, the first reflection surface R1, the second reflection surface R2, and the second transmission surface T2 are arranged in order from the reduction side to the enlargement side.

[0045] The first transmission surface T1 is arranged on the reduction side of the prism PM. The first transmission surface T1 has a free-form surface shape with the concave surface facing the lens element L9 side of the first sub-optical system OP1.

[0046] The second transmission surface T2 is arranged on the enlargement side of the prism PM. The second transmission surface T2 has a free-form surface shape with the convex surface facing the enlargement-side lens element L10.

[0047] The first reflection surface R1 is located on the optical path from the first transmission surface T1 to the second transmission surface T2 and is arranged on the reduction side of the second reflection surface. The first reflection surface R1 is arranged at the position farthest from the first sub-optical system OP1 in the prism PM. The first reflection surface R1 has a free-form surface shape with the concave surface facing in the direction in which the light rays incident from the first transmission surface T1 to the first reflection surface R1 are reflected toward the second reflection surface R2.

[0048] The second reflection surface R2 is located on the optical path from the first transmission surface T1 to the second transmission surface T2 and is arranged on the enlargement side of the first reflection surface. The second reflection surface R2 has a flat surface shape or a surface shape close to flat.

[0049] In the second sub-optical system OP2 of Example 2, the magnifying lens element L10 has a negative meniscus shape with a convex surface facing the magnifying side.

[0050] In Example 2, the entire intermediate image formed at the intermediate imaging position MI is located inside the prism PM.

[0051] (Example 3) Figure 9 is a layout diagram showing the optical system 1 according to Example 3. The surface data for Example 3 is shown in the numerical example 3 described later.

[0052] In the first sub-optical system OP1 of Embodiment 3, a plurality of lens elements L1 to L9 are arranged in order from the reduction side to the magnification side. Lens element L1 has a biconvex shape. Lens element L2 has a biconvex shape. Lens element L3 has a biconcave shape. Lens element L4 has a biconvex shape. Lens element L5 has a positive meniscus shape with its convex surface facing the magnification side. Lens element L6 has a positive meniscus shape with its convex surface facing the magnification side. Lens element L7 has a positive meniscus shape with its convex surface facing the reduction side. Lens element L8 has a biconcave shape. Lens element L9 has a negative meniscus shape with its convex surface facing the magnification side.

[0053] In the second sub-optical system OP2 of Example 3, the prism PM includes a first transmission surface T1, a second transmission surface T2, and a reflective surface R1. In the second sub-optical system OP2, the first transmission surface T1, the reflective surface R1, and the second transmission surface T2 are arranged in order from the reduction side to the expansion side.

[0054] The first transmission surface T1 is located on the reduction side of the prism PM. The first transmission surface T1 has a free-form shape with its convex surface facing the lens element L9 side of the first sub-optical system OP1.

[0055] The second transmission surface T2 is located on the magnifying side of the prism PM. The second transmission surface T2 has a free-form shape with its convex side facing the magnifying lens element L10.

[0056] The reflective surface R1 is located in the optical path from the first transmitting surface T1 to the second transmitting surface T2. The reflective surface R1 has a freeform surface shape in which the concave surface is oriented in the direction in which the light rays incident on the reflective surface R1 from the first transmitting surface T1 are reflected toward the second transmitting surface T2.

[0057] In the second sub-optical system OP2 of Example 3, the magnifying lens element L10 has a negative meniscus shape with a convex surface facing the magnifying side.

[0058] In Example 3, a portion of the intermediate image formed at the intermediate imaging position MI is located inside the prism PM. That is, a portion of the intermediate image formed at the intermediate imaging position MI is located outside the prism PM.

[0059] (Example 4) Figure 12 is a layout diagram showing the optical system 1 according to Example 4. The surface data for Example 4 is shown in the numerical example 4 described later.

[0060] In the first sub-optical system OP1 of Embodiment 4, a plurality of lens elements L1 to L9 are arranged in order from the reduction side to the magnification side. Lens element L1 has a biconvex shape. Lens element L2 has a biconvex shape. Lens element L3 has a biconcave shape. Lens element L4 has a biconvex shape. Lens element L5 has a positive meniscus shape with its convex surface facing the magnification side. Lens element L6 has a positive meniscus shape with its convex surface facing the magnification side. Lens element L7 has a positive meniscus shape with its convex surface facing the reduction side. Lens element L8 has a biconcave shape. Lens element L9 has a negative meniscus shape with its convex surface facing the magnification side.

[0061] In the second sub-optical system OP2 of Example 4, the prism PM includes a first transmission surface T1, a second transmission surface T2, and a reflective surface R1. In the second sub-optical system OP2, the first transmission surface T1, the reflective surface R1, and the second transmission surface T2 are arranged in order from the reduction side to the expansion side.

[0062] The first transmission surface T1 is located on the reduction side of the prism PM. The first transmission surface T1 has a free-form shape with its convex surface facing the lens element L9 side of the first sub-optical system OP1.

[0063] The second transmission surface T2 is located on the magnifying side of the prism PM. The second transmission surface T2 has a free-form shape with its convex side facing the magnifying lens element L10.

[0064] The reflective surface R1 is located in the optical path from the first transmitting surface T1 to the second transmitting surface T2. The reflective surface R1 has a freeform surface shape in which the concave surface is oriented in the direction in which the light rays incident on the reflective surface R1 from the first transmitting surface T1 are reflected toward the second transmitting surface T2.

[0065] The second sub-optical system OP2 of Example 4 has a plurality of magnifying lens elements L10 and L11. The magnifying lens element L10 has a negative meniscus shape with a convex surface facing the magnifying side. The magnifying lens element L11 has a negative meniscus shape with a convex surface facing the magnifying side.

[0066] In Example 4, the entire intermediate image formed at the intermediate imaging position MI is located inside the prism PM.

[0067] In Example 4, variable intervals SP1 to SP5 are set. Variable interval SP1 is the interval between the optical element P and the lens element L1. Variable interval SP2 is the interval between the aperture ST and the lens element L5. Variable interval SP3 is the interval between the lens element L5 and the lens element L6. Variable interval SP4 is the interval between the lens element L9 and the first transmission surface T1. Variable interval SP5 is the interval between the screen SC and the magnifying lens element L11.

[0068] (Example 5) Figure 15 is a layout diagram showing the optical system 1 according to Example 5. The surface data for Example 5 is shown in the numerical example 5 described later.

[0069] In the first sub-optical system OP1 of Embodiment 5, a plurality of lens elements L21 to L32 are arranged in order from the reduction side to the magnification side. Lens element L21 has a biconvex shape. Lens element L22 has a biconvex shape. Lens element L23 has a negative meniscus shape with its convex surface facing the magnification side. Lens element L24 has a biconcave shape. Lens element L25 has a biconvex shape. Lens element L26 has a biconcave shape. Lens element L27 has a biconvex shape. Lens element L28 has a positive meniscus shape with its convex surface facing the reduction side. Lens element L29 has a positive meniscus shape with its convex surface facing the reduction side. Lens element L30 has a biconcave shape. Lens element L31 has a positive meniscus shape with its convex surface facing the magnification side. Lens element L32 has a biconcave shape.

[0070] In the second sub-optical system OP2 of Example 5, the prism PM includes a first transmission surface T1, a second transmission surface T2, and a reflective surface R1. In the second sub-optical system OP2, the first transmission surface T1, the reflective surface R1, and the second transmission surface T2 are arranged in order from the reduction side to the expansion side.

[0071] The first transmission surface T1 is located on the reduction side of the prism PM. The first transmission surface T1 has a free-form shape with its convex surface facing the lens element L32 of the first sub-optical system OP1.

[0072] The second transmission surface T2 is located on the magnifying side of the prism PM. The second transmission surface T2 has a free-form shape with its convex side facing the magnifying lens element L10.

[0073] The reflective surface R1 is located in the optical path from the first transmitting surface T1 to the second transmitting surface T2. The reflective surface R1 has a freeform surface shape in which the concave surface is oriented in the direction in which the light rays incident on the reflective surface R1 from the first transmitting surface T1 are reflected toward the second transmitting surface T2.

[0074] The second sub-optical system OP2 of Example 5 has a magnifying lens element L10. The magnifying lens element L10 has a negative meniscus shape with a convex surface facing the magnifying side.

[0075] In Example 5, the entire intermediate image formed at the intermediate imaging position MI is located inside the prism PM.

[0076] In Example 5, variable intervals SP1 to SP5 are set. Variable interval SP1 is the interval between the optical element P and the lens element L21. Variable interval SP2 is the interval between the aperture ST and the lens element L26. Variable interval SP3 is the interval between the lens elements L27 and L28. Variable interval SP4 is the interval between the lens element L32 and the first transmission surface T1. Variable interval SP5 is the interval between the screen SC and the magnifying lens element L10.

[0077] Thus, the optical system 1 according to this disclosure has the following features: (i) at least a portion of the intermediate image formed at the intermediate imaging position MI is located inside the prism PM; and (ii) magnifying lens elements L10 and L11, which are positioned on the magnifying side of the prism PM, focus the diverging light beam from the light beam emitted from the prism PM onto the magnifying conjugate plane. These features (i) and (ii) enable miniaturization of the prism PM while achieving a low throw ratio. Furthermore, since the curvature of the emission surface of the prism PM can be reduced, it becomes easier to realize the shape and manufacturing costs can also be reduced.

[0078] Next, the conditions that the optical system according to this disclosure can satisfy will be explained. Note that multiple conditions are specified for the optical system according to each embodiment, and it is possible to satisfy all of these conditions, or to satisfy individual conditions to obtain the corresponding effects.

[0079] Figure 5 is a magnified partial view showing the second sub-optical system OP2 in the optical system 1 of Example 1. Figure 5 shows the optical system 1 of Example 1 as an example of the conditions that the optical system 1 according to this disclosure can satisfy.

[0080] Referring to Figure 5, the optical system 1 according to this disclosure may satisfy the following condition (1): 1 < L1a / L2a < 10 ... (1) where, L1a: maximum optical path length in the optical path from the second transmission surface T2 to the magnifying lens element L10 L2a: minimum optical path length in the optical path from the second transmission surface T2 to the magnifying lens element L10.

[0081] This configuration allows for miniaturization of the magnifying lens element L10. Furthermore, by setting L1a / L2a < 5, the magnifying lens element L10 can be made even smaller.

[0082] The prism PM may be formed from a single prism.

[0083] This configuration can suppress ghosting or flare compared to configurations made up of multiple prisms.

[0084] The entire intermediate image formed at the intermediate imaging position MI may be located inside the prism PM.

[0085] This configuration prevents the intermediate image from crossing the surface of the prism PM, thereby suppressing pixel defects or brightness reduction and improving image quality. However, if the intermediate image does cross the surface of the prism PM, the footprint on the magnified side becomes even larger, making it more susceptible to the effects of polishing marks on the transmission or reflection surface, which can degrade image quality.

[0086] The optical system 1 according to this disclosure may satisfy the following condition (2): θ1 ≤ 60° ... (2) where, θ1: the maximum incident angle of light rays incident on the magnifying lens element L10.

[0087] This configuration allows for maintaining the peripheral light ratio.

[0088] The optical system 1 according to this disclosure may satisfy the following condition (3): θ2 ≤ 130° ... (3) where, θ2 is the angle between the first normal G1 at the first position of the first transmission surface T1 through which the outermost luminous beam of the first sub-optical system OP1 passes, and the second normal G2 at the second position of the second transmission surface T2 through which the outermost luminous beam passes.

[0089] This configuration simplifies the shapes of the first and second transmission surfaces T1 and T2 of the prism PM, making it easier to manufacture the prism PM. This reduces manufacturing costs.

[0090] The second transmission surface T2 of the prism PM may be convex toward the magnifying lens element L10, and the surface of the magnifying lens element L10 toward the second transmission surface T2 may be concave.

[0091] This configuration can reduce aberrations.

[0092] The magnifying lens element L10 may focus 75% or more of the light beam emitted from the prism PM onto the magnifying conjugate surface.

[0093] This configuration allows for miniaturization of the prism PM and simplification of its shape.

[0094] The light beam focused by the magnifying lens element L10 may include a light beam directed toward the center of the magnifying conjugate plane.

[0095] This configuration allows for a smaller prism PM and a simpler shape for the prism PM.

[0096] At least one of the incident surface and the exit surface of the magnifying lens element L10 may have an aspherical shape.

[0097] This configuration allows for improved image quality and alignment of the image plane.

[0098] The prism PM may have a reflective surface R1 located in the optical path from the first transmission surface T1 to the second transmission surface T2.

[0099] This configuration allows for a simplification of the prism PM's shape.

[0100] In a prism PM, the first transmission surface T1 and the second transmission surface T2 may be defined as having the same surface shape.

[0101] This configuration simplifies the shapes of the first and second transmission surfaces T1 and T2 of the prism PM, making it easier to manufacture the prism PM. This reduces manufacturing costs.

[0102] The prism PM may have two reflective surfaces located in the optical path from the first transmission surface T1 to the second transmission surface T2. The two reflective surfaces may include a first reflective surface R1 and a second reflective surface R2 located on the magnified side of the first reflective surface R1.

[0103] This configuration allows for miniaturization of the prism PM.

[0104] The magnifying lens element L10 may have a rotationally symmetric shape with respect to the optical axis of the first sub-optical system OP1. The line connecting the vertices of the multiple lens elements L1 to L9 that constitute the first sub-optical system OP1 is defined as the "optical axis of the first sub-optical system OP1".

[0105] This configuration makes it easier to manufacture the magnifying lens element L10.

[0106] The first reflective surface R1 may be positioned in the prism PM at the position furthest from the first sub-optical system OP1 in the direction of the optical axis of the first sub-optical system OP1.

[0107] This configuration allows for miniaturization of the prism PM.

[0108] In Embodiment 1, an embodiment with one or two magnifying lenses was described, but three or more magnifying lenses (magnifying lens group) may be used. Each of the three or more magnifying lens elements has a negative meniscus shape with a convex surface facing the magnifying side. By using two or more magnifying lenses, image quality can be improved, peripheral image height aberrations can be reduced, and the design flexibility of the magnifying lenses can be increased.

[0109] (Numerical Example 1) For the optical system of Numerical Example 1 (corresponding to Example 1), surface data is shown in Table 1, field of view data in Table 2, variable interval data in Table 3, aspherical shape data of the lens in Table 4, and freeform surface shape data of the prism in Tables 5 to 7. Note that "DAR" in the tables stands for Decenter & Return.

[0110]

[0111]

[0112]

[0113]

[0114]

[0115]

[0116]

[0117] (Numerical Example 2) For the optical system of Numerical Example 2 (corresponding to Example 2), the surface data is shown in Table 8, the field of view data is shown in Table 8, the aspherical shape data of the lens is shown in Table 9, and the free-form surface shape data of the prism is shown in Tables 10 to 12.

[0118]

[0119]

[0120]

[0121]

[0122]

[0123]

[0124] (Numerical Example 3) For the optical system of Numerical Example 3 (corresponding to Example 3), surface data is shown in Table 14, field of view data is shown in Table 15, aspherical shape data of the lens is shown in Table 16, and free-form surface shape data of the prism is shown in Tables 17 to 19.

[0125]

[0126]

[0127]

[0128]

[0129]

[0130]

[0131] (Numerical Example 4) For the optical system of Numerical Example 4 (corresponding to Example 4), surface data is shown in Table 20, field of view data in Table 21, variable interval data in Table 22, aspherical shape data of the lens in Table 23, and freeform surface shape data of the prism in Tables 24 to 26.

[0132]

[0133]

[0134]

[0135]

[0136]

[0137]

[0138]

[0139] (Numerical Example 5) For the optical system of Numerical Example 5 (corresponding to Example 5), surface data is shown in Table 27, field of view data in Table 28, variable interval data in Table 29, aspherical shape data of the lens in Table 30, and freeform surface shape data of the prism in Tables 31 to 33.

[0140]

[0141]

[0142]

[0143]

[0144]

[0145]

[0146]

[0147] Table 34 shows the conditions in the optical systems for Numerical Examples 1 to 5 (corresponding to Examples 1 to 5).

[0148]

[0149] (Embodiment 2) Hereinafter, Embodiment 2 of the present disclosure will be described with reference to Figure 18. Figure 18 is a block diagram showing an example of an image projection device according to the present disclosure. The image projection device 100 includes the optical system 1 disclosed in Embodiment 1, an image forming element 101, a light source 102, a control unit 110, etc. The image forming element 101 is composed of liquid crystal, DMD, etc., and generates an image to be projected onto the screen SC via the optical system 1. The light source 102 is composed of an LED (light-emitting diode), laser, etc., and supplies light to the image forming element 101. The control unit 110 is composed of a CPU or MPU, etc., and controls the entire device and each component. The optical system 1 may be configured as an interchangeable lens that can be detachably attached to the image projection device 100. In this case, the device obtained by removing the optical system 1 from the image projection device 100 is an example of the main device.

[0150] The image projection device 100 described above, with the optical system 1 according to Embodiment 1, can achieve a wide-angle zoom function while reducing costs.

[0151] (Embodiment 3) Hereinafter, Embodiment 3 of the present disclosure will be described with reference to Figure 19. Figure 19 is a block diagram showing an example of an imaging device according to the present disclosure. The imaging device 200 includes the optical system 1 disclosed in Embodiment 1, an image sensor 201, a control unit 210, etc. The image sensor 201 is composed of a CCD (charge-coupled device) image sensor, a CMOS image sensor, etc., and receives the optical image of an object OBJ formed by the optical system 1 and converts it into an electrical image signal. The control unit 110 is composed of a CPU or MPU, etc., and controls the entire device and each component. The optical system 1 may be configured as an interchangeable lens that can be detachably attached to the imaging device 200. In this case, the device obtained by removing the optical system 1 from the imaging device 200 is an example of the main device.

[0152] The imaging device 200 described above, with the optical system 1 according to Embodiment 1, can achieve a wide-angle zoom function while reducing costs.

[0153] As described above, embodiments have been explained as part of the technical disclosure in this disclosure. For this purpose, accompanying drawings and a detailed description have been provided.

[0154] Therefore, the components described in the attached drawings and detailed descriptions may include not only components essential for solving the problem, but also components that are not essential for solving the problem, provided that they illustrate the technology described above. For this reason, the mere presence of such non-essential components in the attached drawings or detailed descriptions should not be immediately assumed to mean that these non-essential components are essential.

[0155] Furthermore, since the embodiments described above are for illustrative purposes of the technology described herein, various modifications, substitutions, additions, omissions, etc., can be made within the scope of the claims or their equivalents.

[0156] This disclosure is applicable to image projection devices such as projectors and head-up displays, and imaging devices such as digital still cameras, digital video cameras, surveillance cameras in surveillance systems, webcams, and in-vehicle cameras. In particular, this disclosure is applicable to optical systems that require high image quality, such as projectors, digital still camera systems, and digital video camera systems.

[0157] 1. Optical System: L1-L9, L21-L32; Lens Elements: L10, L11; Magnifying Lens Elements: R1, R2; Reflecting Surfaces: T1, T2; Transmitting Surfaces: SP1-SP5; Variable Interval: ST; Aperture: P; Optical Element: PM; Prism: S; Original Image: SC; Screen:

Claims

1. An optical system having a reducing conjugate surface on the reducing side and an expanding conjugate surface on the expanding side, and having an intermediate imaging position internally that is conjugate to the reducing conjugate surface and the expanding conjugate surface, respectively, comprising a first sub-optical system and a second sub-optical system arranged sequentially from the reducing side to the expanding side, wherein the first sub-optical system has a plurality of lens elements, the second sub-optical system has a prism and an expanding lens element positioned on the expanding side of the prism, the prism has a first transmitting surface located on the reducing side, a second transmitting surface located on the expanding side, and one or more reflecting surfaces located in the optical path from the first transmitting surface to the second transmitting surface, at least a portion of the intermediate image formed at the intermediate imaging position is located inside the prism, and the expanding lens element focuses the diverging light beam from the light beam emitted from the prism onto the expanding conjugate surface.

2. The optical system according to claim 1, wherein the prism is formed from a single prism.

3. The optical system according to claim 1, wherein the entire intermediate image formed at the intermediate imaging position is located inside the prism.

4. The optical system according to any one of claims 1 to 3, wherein the second transmission surface is convex toward the magnifying lens element, and the surface of the magnifying lens element toward the second transmission surface is concave.

5. The optical system according to claim 4, satisfying the following condition (1): 1 < L1a / L2a < 10 ... (1) where, L1a: maximum optical path length in the optical path from the second transmission surface to the magnifying lens element L2a: minimum optical path length in the optical path from the second transmission surface to the magnifying lens element.

6. The optical system according to any one of claims 1 to 3, wherein the magnifying lens element focuses 75% or more of the light beam emitted from the prism onto the magnifying conjugate surface.

7. The optical system according to claim 6, wherein the light beam focused by the magnifying lens element includes a light beam directed toward the center of the magnifying conjugate plane.

8. An optical system according to any one of claims 1 to 3 that satisfies the following condition (2): θ1 ≤ 60° ... (2) where, θ1: the maximum incident angle of light rays incident on the magnifying lens element.

9. The optical system according to any one of claims 1 to 3, wherein at least one of the incident surface and the exit surface of the magnifying lens element has an aspherical shape.

10. The optical system according to any one of claims 1 to 3, wherein the one or more reflective surfaces is a single reflective surface.

11. The optical system according to claim 10, satisfying the following condition (3): θ2 ≤ 130° ... (3) where, θ2: the angle between the first normal to the first position of the first transmission surface through which the outermost luminous beam of the first sub-optical system passes, and the second normal to the second position of the second transmission surface through which the outermost luminous beam passes.

12. The optical system according to claim 10, wherein the first transmission surface and the second transmission surface are defined by the same surface shape.

13. The optical system according to any one of claims 1 to 3, wherein the one or more reflective surfaces include a first reflective surface and a second reflective surface located on the magnified side of the first reflective surface.

14. The optical system according to claim 13, wherein the magnifying lens element has a rotationally symmetric shape with respect to the optical axis of the first sub-optical system.

15. The optical system according to claim 13, wherein the first reflective surface is located in the prism at the position furthest from the first sub-optical system in the optical axis direction of the first sub-optical system.

16. An image projection device comprising: an optical system according to any one of claims 1 to 15; and an image forming element that generates an image to be projected onto a screen via the optical system.

17. An imaging device comprising: an optical system according to any one of claims 1 to 15; and an image sensor that receives an optical image formed by the optical system and converts it into an electrical image signal.

Images