Optical system, image projection device, and imaging device

Abstract

To provide an optical system that allows projection or imaging with a short focus on a large screen by using a small-sized prism.SOLUTION: An optical system according to the present disclosure comprises a first sub optical system and a second sub optical system in order from a reduction side toward an enlargement side. The second sub optical system includes a prism having a first transmission surface, a first reflection surface, a second reflection surface, and a second transmission surface in order from the reduction side. The first reflection surface has a shape in which a concave surface is directed in a direction in which an incident light beam is reflected. The second reflection surface is located between the first reflection surface and a first optical surface located on the most enlargement side of the first sub optical system, in a first direction from the reduction side to the enlargement side in the first sub optical system. When a surface including a position where a principal ray passing through the center of a direction of a predetermined side in a rectangular area of reduction conjugate points is reflected on the first reflection surface, as a Y cross section, a curvature shape of the first reflection surface is set so that, when seen from a direction perpendicular to the Y cross section, parts of the plurality of principal rays passing through the reduction conjugate points intersect on an optical path between the first reflection surface and the second transmission surface.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Patent Document 1 discloses a zoom optical system that employs off-axial optical elements arranged eccentrically. This bends the optical path within the zoom optical system into a desired shape and shortens the overall length of the zoom optical system.

[0003] Patent Document 2 discloses an imaging optical system including a plurality of eccentric prisms. Specifically, two eccentric prisms each having a rotationally asymmetric reflecting surface are arranged on both sides of the aperture, and the medium of the eccentric prism 10 before the aperture and the medium of the eccentric prism 20 after the aperture have different optical properties.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present disclosure provides an optical system that enables short-focus and large-screen projection or imaging using a small prism. The present disclosure also provides an image projection device and an imaging device using such an imaging optical system.

Means for Solving the Problems

[0006] It should be noted that there is an error in the original text where "

発明が解決しようとする課題

課題を解決するための手段

発明が解決しようとする課題

Problems to be Solved by the Invention

[0007] Another aspect of the present disclosure includes an image projection device comprising the optical system and an image forming element that generates an image to be projected onto a screen via the optical system.

[0008] Another aspect of the present disclosure of an imaging device comprises the optical system and an image sensor that receives the optical image formed by the optical system and converts it into an electrical image signal. [Effects of the Invention]

[0009] According to the optical system described herein, multiple principal rays intersect in the optical path between the first reflective surface and the second transmissive surface of the prism in both the Y and X cross-sections. This makes it possible to project or image a large image with a short focal length using a small prism. [Brief explanation of the drawing]

[0010] [Figure 1] Layout diagram showing the optical system according to Example 1 [Figure 2] Figure 2(a) is a Y-section view showing the optical path through which the principal ray passes in the optical system according to Example 1. Figure 2(b) is an X-section view of the optical system as seen from above. [Figure 3]Explanatory diagram showing the usage mode of an image projection apparatus using the optical system according to Example 1 [Figure 4] Graph showing the relative positional relationship between the reflecting surface, the intermediate image in the Y direction, and the intermediate image in the X direction in the optical system 1 according to Example 1 [Figure 5] Layout diagram showing the optical system according to Example 2 [Figure 6] Fig. 6(a) is a Y cross-sectional view showing the optical path through which the principal ray passes in the optical system according to Example 2. Fig. 6(b) is an X cross-sectional view when the optical system is viewed from above [Figure 7] Explanatory diagram showing the usage mode of an image projection apparatus using the optical system according to Example 2 [Figure 8] Graph showing the relative positional relationship between the reflecting surface, the intermediate image in the Y direction, and the intermediate image in the X direction in the optical system according to Example 2 [Figure 9] Layout diagram showing the optical system according to Example 3 [Figure 10] Fig. 10(a) is a Y cross-sectional view showing the optical path through which the principal ray passes in the optical system according to Example 3. Fig. 10(b) is an X cross-sectional view when the optical system is viewed from above [Figure 11] Explanatory diagram showing the usage mode of an image projection apparatus using the optical system according to Example 3 [Figure 12] Graph showing the relative positional relationship between the reflecting surface, the intermediate image in the Y direction, and the intermediate image in the X direction in the optical system according to Example 3 [Figure 13] Layout diagram showing the optical system according to Example 4 [Figure 14] Fig. 14(a) is a Y cross-sectional view showing the optical path through which the principal ray passes in the optical system according to Example 4. Fig. 14(b) is an X cross-sectional view when the optical system is viewed from above [Figure 15] Explanatory diagram showing the usage mode of an image projection apparatus using the optical system according to Example 4 [Figure 16] Graph showing the relative positional relationship between the reflecting surface, the intermediate image in the Y direction, and the intermediate image in the X direction in the optical system according to Example 4 [Figure 17] Diagram schematically showing the three-dimensional shape of the prism PM according to Example 1 [Figure 18] It is an explanatory diagram showing an example of an image area at the reduction conjugate point [Figure 19] It is an explanatory diagram showing the definitions of the imaging magnification at the intermediate imaging position and the imaging magnification at the enlarged conjugate point. [Figure 20] It is a Y-direction cross-sectional view showing various examples of the stepped structure of the prism. [Figure 21] Block diagram showing an example of an image projection apparatus according to the present disclosure [Figure 22] Block diagram showing an example of an imaging apparatus according to the present disclosure

Embodiments for Carrying out the Invention

[0011] Hereinafter, embodiments will be described in detail with reference to the drawings as appropriate. However, a more detailed description than necessary may be omitted. For example, detailed descriptions of well-known matters or duplicate descriptions of substantially the same configuration may be omitted. This is to avoid making the following description unnecessarily redundant and to facilitate the understanding of those skilled in the art.

[0012] Note that the applicant provides the accompanying drawings and the following description for those skilled in the art to fully understand the present disclosure, and does not intend to limit the subject matter described in the claims by these.

[0013] [[ID=I27]]Hereinafter, each embodiment of the optical system according to the present disclosure will be described. In each embodiment, a case where the optical system is used in a projector (an example of an image projection apparatus) that projects the image light of the original image SA obtained by spatially modulating incident light by an image forming element such as a liquid crystal or a DMD (Digital Micro-Mirror Device) based on an image signal onto a screen will be described. That is, the optical system according to the present disclosure can be used to project the original image S on the image forming element arranged on the reduction side onto the screen by arranging a screen (not shown) on the extension line on the enlargement side. However, the projection surface is not limited to the screen. It also includes the walls, ceilings, floors, and windows of houses, stores, or vehicles and aircraft used in mobile transportation means.

[0014] 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.

[0015] (Embodiment 1) The optical system according to Embodiment 1 of this disclosure will be described below with reference to Figures 1 to 20.

[0016] (Example 1) Figure 1 is a diagram showing the optical system 1 according to Embodiment 1. The optical system 1 comprises a first sub-optical system including an aperture diaphragm ST and a second sub-optical system including a prism PM. In Figure 1, the reduction conjugate point, which is the image formation position on the reduction side, is located on the left, and the enlargement conjugate point, which is the image formation position on the enlargement side, is located on the right. The second sub-optical system is provided on the enlargement side of the first sub-optical system.

[0017] Figure 18 is an explanatory diagram showing an example of an image region at a reduced conjugate point. The image region at a reduced conjugate point is defined as a rectangular region having a longitudinal direction (X direction) and a transverse direction (Y direction), and has an imaging relationship that is optically conjugate to the image region at an enlarged conjugate point. Light rays travel along the normal direction (Z direction) of this rectangular region. This rectangular region has aspect ratios such as 3:2, 4:3, 16:9, and 256:135, and in the case of an image projection device, it corresponds to the image display area of ​​the image forming element, and in the case of an imaging device, it corresponds to the imaging area of ​​the image sensor.

[0018] Furthermore, within the optical system 1, there are intermediate imaging positions that are conjugate to the reduction conjugate point and the expansion conjugate point, respectively. These intermediate imaging positions are shown as the Y-direction intermediate image IMy in Figure 1, but the X-direction intermediate image IMx is not shown and will be described later in relation to Figure 4.

[0019] The first sub-optical system includes optical elements PA and lens elements L1 to L14, arranged in order from the reduction side to the enlargement side. Optical elements PA represent optical elements such as TIR (total internal reflection) prisms, prisms for color separation and color synthesis, optical filters, parallel plate glass, quartz low-pass filters, and infrared cut filters. The original image SA is placed on the reduction-side end face of optical element PA (face 1). For face numbers, please refer to the numerical examples described later.

[0020] The optical element PA has two parallel and flat transmission surfaces (surfaces 2, 3). The lens element L1 has a positive meniscus shape with its convex surface facing the reduction side (surfaces 4, 5). The lens element L2 has a negative meniscus shape with its convex surface facing the reduction side (surfaces 6, 7). The lens element L3 has a biconvex shape (surfaces 7, 8). The lens element L4 has a negative meniscus shape with its convex surface facing the enlargement side (surfaces 8, 9). Lens elements L2 to L4 are joined together to form a composite lens. The lens element L5 has a biconcave shape (surfaces 10, 11). The lens element L6 has a biconvex shape (surfaces 11, 12). Lens elements L5 and L6 are joined together to form a composite lens.

[0021] Lens element L7 has a biconvex shape (surfaces 14, 15). Lens element L8 has a negative meniscus shape with its convex surface facing the magnification side (surfaces 16, 17). Lens element L9 has a positive meniscus shape with its convex surface facing the magnification side (surfaces 17, 18). Lens elements L8 and L9 are joined together to form a composite lens. Lens element L10 has a biconvex shape (surfaces 19, 20). Lens element L11 has a biconvex shape (surfaces 21, 22). Lens element L12 has a biconcave shape (surfaces 22, 23). Lens elements L11 and L12 are joined together to form a composite lens. Lens element L13 has a negative meniscus shape with its convex surface facing the reduction side (surfaces 24, 25). Lens element L14 has a positive meniscus shape with its convex surface facing the magnification side (surfaces 26, 27).

[0022] Figure 17 schematically shows the three-dimensional shape of the prism PM according to Example 1, where Figure 17(a) is a rear view, Figure 17(b) is a front view, Figure 17(c) is a top view, Figure 17(d) is a bottom view, and Figure 17(e) is a side view.

[0023] The second sub-optical system includes a prism PM formed from a transparent medium, such as glass or synthetic resin. The prism PM has a transmission surface A located on the reduction side, a transmission surface B located on the expansion side, and two reflective surfaces R1 and R2 located on the optical path between transmission surface A and transmission surface B. Transmission surface A has a free-form shape with a concave surface facing the reduction side (surface 28). Reflective surface R1 has a free-form shape with a concave surface facing the direction in which light rays incident on reflective surface R1 are reflected (surface 29). Reflective surface R2 has a planar shape (surface 30). Transmission surface B has a free-form shape with a convex surface facing the expansion side (surface 31).

[0024] The aperture diaphragm ST defines the range through which the light beam passes through the optical system 1 and is positioned between the reduced conjugate point and the intermediate imaging position described above. As an example, the aperture diaphragm ST is located between lens elements L6 and L7 (plane 13).

[0025] The intermediate images formed at the intermediate imaging position, namely the Y-direction intermediate image IMy and the X-direction intermediate image IMx, are positioned, in whole or in part, within the medium of the prism PM. Furthermore, when the longitudinal direction of the rectangular region of the reduced conjugate point is defined as the X direction, the transverse direction as the Y direction, and the normal direction as the Z direction, the plane containing the position where the principal ray passing through the center in the X direction is reflected by the reflective surface R1 is defined as the Y cross-section, and the cross-section perpendicular to the Y cross-section is defined as the X cross-section. The light beam passing through the first sub-optical system has different intermediate imaging positions in the Y cross-section and the X cross-section, that is, the intermediate image IMy in the Y direction and the intermediate image IMx in the X direction are formed at different positions. This reduces the impact on image quality due to disturbances such as dust and dirt.

[0026] Figure 2(a) is a Y-section view showing the optical path through which the principal ray passes in the optical system 1 according to Embodiment 1, and Figure 2(b) is an X-section view of the optical system 1 as seen from above. Note that in Figure 2(b), the middle portion of the optical system 1 is omitted, and only the optical path inside the prism PM is schematically shown.

[0027] Figure 2(a) shows, for clarity, the principal rays passing through the center of the original image SA in the X direction and the lowest point in the Y direction (normalized height Y=0.0 at the reduction conjugate point), and the principal rays passing through the center of the original image SA in the X direction and the highest point in the Y direction (normalized height Y=1.0 at the reduction conjugate point). Both principal rays pass through the first sub-optical system, through the transmission surface A, into the interior of the prism PM, are subsequently reflected by the reflection surface R1, and intersect in the region CRy, indicated by the dashed circle, just before reaching the reflection surface R2.

[0028] Figure 2(b) shows, for clarity, the principal rays passing through the left edge of the original image SA in the X direction and the principal rays passing through the right edge of the original image SA in the X direction. Both principal rays pass through the first sub-optical system, through the transmission surface A, into the interior of the prism PM, are subsequently reflected by the reflective surface R1, and intersect in the region CRx shown by the dashed circle just before reaching the reflective surface R2.

[0029] In this disclosure, as shown in Figure 2(a), the curvature shape of the free-form surface of the reflecting surface R1 is set such that, when viewed from a direction perpendicular to the Y cross-section, some of the principal rays passing through the reduced conjugate point intersect in the optical path between the reflecting surface R1 and the transmitting surface B, and as shown in Figure 2(b), when viewed from a direction perpendicular to the X cross-section, some of the principal rays passing through the reduced conjugate point intersect in the optical path between the reflecting surface R1 and the transmitting surface B. With this configuration, the second sub-optical system can be miniaturized using a small prism, and projection or imaging of a short focal length and large screen becomes possible.

[0030] Figure 3 is an explanatory diagram showing how an image projection device using the optical system 1 according to Embodiment 1 is used. 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 the support base at a relatively short horizontal distance, for example, 0.5 m away. The light generated from the optical system 1 is projected diagonally upward and forward, achieving short-focus and large-screen projection.

[0031] Figure 4 is a graph showing the relative positional relationship between the reflective surface R1 and the intermediate image IMy in the Y direction and the intermediate image IMx in the X direction in the optical system 1 according to Example 1, viewed from a direction perpendicular to the Y cross-section. The horizontal axis represents the relative position in the Z direction (unit: mm) with respect to IMx, which is formed by a ray passing through the center of the original image SA in the X direction and at the bottom of the Y direction. The vertical axis represents the relative position in the Y direction (unit: mm) with respect to IMx, which is formed by a ray passing through the center of the original image SA in the X direction and at the bottom of the Y direction. The diamond marks indicate the intermediate image IMx in the X direction, the square marks indicate the intermediate image IMy in the Y direction, and the triangle marks indicate the curvature shape of the reflective surface R1. The intermediate image IMx in the X direction is a state in which the light beam passing through the optical system 1 is focused only in the X direction and not in the Y direction. The intermediate image IMy in the Y direction is a state in which the light beam passing through the optical system 1 is focused only in the Y direction and not in the X direction.

[0032] Looking at the graph, the Y-direction intermediate image IMy is distributed obliquely to the Z-direction from around coordinate (-2.5,0) to around coordinate (-19.5,-14.5). The X-direction intermediate image IMx is distributed obliquely to the Z-direction from around coordinate (0,0) to around coordinate (-13,-15), with a concave shape facing the reduced optical path side. The reflective surface R1 is distributed obliquely to the Z-direction from around coordinate (9,0) to around coordinate (0.5,-17), with a concave shape facing the reduced optical path side.

[0033] In this disclosure, the reflective surface R1 may have a shape in which a concave surface faces toward the reduced optical path side along the intermediate imaging position in the X direction parallel to the X cross-section of the light ray passing through the center of the longitudinal direction of the rectangular region. This can suppress image distortion on the screen SC.

[0034] (Example 2) Figure 5 is a diagram showing the optical system 1 according to Embodiment 2. This optical system 1 has a similar configuration to Embodiment 1, but the first sub-optical system includes lens elements L1 to L13, and the second sub-optical system, which includes a prism PM, projects diagonally downwards and forwards in the case of an image projection device. The following explanation will be omitted as it overlaps with Embodiment 1.

[0035] Lens element L1 has a positive meniscus shape with its convex surface facing the reduction side (surfaces 4, 5). Lens element L2 has a negative meniscus shape with its convex surface facing the reduction side (surfaces 6, 7). Lens element L3 has a biconvex shape (surfaces 7, 8). Lens element L4 has a negative meniscus shape with its convex surface facing the enlargement side (surfaces 8, 9). Lens elements L2 to L4 are joined together to form a composite lens. Lens element L5 has a biconcave shape (surfaces 10, 11). Lens element L6 has a biconvex shape (surfaces 11, 12). Lens elements L5 and L6 are joined together to form a composite lens.

[0036] Lens element L7 has a biconvex shape (surfaces 14, 15). Lens element L8 has a negative meniscus shape with the convex surface facing the magnification side (surfaces 16, 17). Lens element L9 has a biconvex shape (surfaces 18, 19). Lens element L10 has a biconvex shape (surfaces 20, 21). Lens element L11 has a biconcave shape (surfaces 21, 22). Lens elements L10 and L11 are joined together to form a composite lens. Lens element L12 has a negative meniscus shape with the convex surface facing the reduction side (surfaces 23, 24). Lens element L13 has a biconvex shape (surfaces 25, 26).

[0037] The prism PM has a transmissive surface A located on the reduction side, a transmissive surface B located on the expansion side, and two reflective surfaces R1 and R2 located on the optical path between transmissive surface A and transmissive surface B. Transmissive surface A has a freeform surface shape with a concave surface facing the reduction side (surface 27). Reflective surface R1 has a freeform surface shape with a concave surface facing the direction in which the light ray incident on reflective surface R1 is reflected (surface 28). Reflective surface R2 has a planar shape (surface 29). Transmissive surface B has a freeform surface shape with a convex surface facing the expansion side (surface 30).

[0038] Figure 6(a) is a Y-section view showing the optical path through which the principal ray passes in the optical system 1 according to Example 2, and Figure 6(b) is an X-section view of the optical system 1 as seen from above.

[0039] Figure 6(a) shows, for clarity, the principal rays passing through the center of the original image SA in the X direction and the lowest point in the Y direction (normalized height Y=0.0 at the reduction conjugate point), and the principal rays passing through the center of the original image SA in the X direction and the highest point in the Y direction (normalized height Y=1.0 at the reduction conjugate point). Both principal rays pass through the first sub-optical system, through the transmission surface A, into the interior of the prism PM, are subsequently reflected by the reflection surface R1, and intersect in the region CRy, indicated by the dashed circle, just before reaching the reflection surface R2.

[0040] Figure 6(b) shows, for clarity, the principal rays passing through the left edge of the original image SA in the X direction and the principal rays passing through the right edge of the original image SA in the X direction. Both principal rays pass through the first sub-optical system, through the transmission surface A, into the interior of the prism PM, are subsequently reflected by the reflective surface R1, and intersect in the region CRx shown by the dashed circle just before reaching the reflective surface R2.

[0041] Figure 7 is an explanatory diagram showing how an image projection device using the optical system 1 according to Embodiment 2 is used. 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 horizontally in front of the support base at a relatively short vertical distance, for example, 0.3 m away. The light generated from the optical system 1 is projected diagonally downward and forward, achieving short-focus and large-screen projection.

[0042] Figure 8 is a graph showing the relative positional relationship between the reflective surface R1 and the intermediate image IMy in the Y direction and the intermediate image IMx in the X direction in the optical system 1 according to Example 2, and is viewed from a direction perpendicular to the Y cross-section.

[0043] Looking at the graph, the Y-direction intermediate image IMy is distributed obliquely to the Z-direction from around coordinate (-3.5,0) to around coordinate (-17,-10). The X-direction intermediate image IMx is distributed obliquely to the Z-direction from around coordinate (0,0) to around coordinate (-12,-10), with a concave shape facing the reduced optical path side. The reflective surface R1 is distributed obliquely to the Z-direction from around coordinate (5.5,0) to around coordinate (-2,-11), with a concave shape facing the reduced optical path side.

[0044] In this disclosure, the reflective surface R1 may have a shape in which a concave surface faces toward the reduced optical path side along the intermediate imaging position in the X direction parallel to the X cross-section of the light ray passing through the center of the longitudinal direction of the rectangular region. This can suppress image distortion on the screen SC.

[0045] (Example 3) Figure 9 is a diagram showing the optical system 1 according to Embodiment 3. This optical system 1 has a similar configuration to Embodiment 1, but the first sub-optical system includes lens elements L1 to L14, and the second sub-optical system, which includes a prism PM, projects diagonally upward and backward in the case of an image projection device. The following explanation will be omitted as it overlaps with Embodiment 1.

[0046] Lens element L1 has a positive meniscus shape with its convex surface facing the reduction side (surfaces 4, 5). Lens element L2 has a negative meniscus shape with its convex surface facing the reduction side (surfaces 6, 7). Lens element L3 has a biconvex shape (surfaces 7, 8). Lens element L4 has a negative meniscus shape with its convex surface facing the enlargement side (surfaces 8, 9). Lens elements L2 to L4 are joined together to form a composite lens. Lens element L5 has a biconcave shape (surfaces 10, 11). Lens element L6 has a biconvex shape (surfaces 11, 12). Lens elements L5 and L6 are joined together to form a composite lens.

[0047] Lens element L7 has a biconvex shape (surfaces 14, 15). Lens element L8 has a negative meniscus shape with its convex surface facing the magnification side (surfaces 16, 17). Lens element L9 has a positive meniscus shape with its convex surface facing the magnification side (surfaces 17, 18). Lens elements L8 and L9 are joined together to form a composite lens. Lens element L10 has a biconvex shape (surfaces 19, 20). Lens element L11 has a biconvex shape (surfaces 21, 22). Lens element L12 has a biconcave shape (surfaces 22, 23). Lens elements L11 and L12 are joined together to form a composite lens. Lens element L13 has a negative meniscus shape with its convex surface facing the reduction side (surfaces 24, 25). Lens element L14 has a positive meniscus shape with its convex surface facing the magnification side (surfaces 26, 27).

[0048] The prism PM has a transmissive surface A located on the reduction side, a transmissive surface B located on the expansion side, and a reflective surface R1 located in the optical path between transmissive surface A and transmissive surface B. Transmissive surface A has a freeform surface shape with a concave surface facing the reduction side (surface 28). Reflective surface R1 has a freeform surface shape with a concave surface facing the direction in which the light ray incident on reflective surface R1 is reflected (surface 29). Transmissive surface B has a freeform surface shape with a convex surface facing the expansion side (surface 30).

[0049] Figure 10(a) is a Y-section view showing the optical path through which the principal ray passes in the optical system 1 according to Embodiment 3, and Figure 10(b) is an X-section view of the optical system 1 as seen from above.

[0050] Figure 10(a) shows, for clarity, the principal rays passing through the center of the original image SA in the X direction and the lowest point in the Y direction (normalized height Y=0.0 at the reduction conjugate point), and the principal rays passing through the center of the original image SA in the X direction and the highest point in the Y direction (normalized height Y=1.0 at the reduction conjugate point). Both principal rays pass through the first sub-optical system, through the transmission surface A, into the interior of the prism PM, are subsequently reflected by the reflection surface R1, and intersect in the region CRy, indicated by the dashed circle, just before reaching the transmission surface B.

[0051] Figure 10(b) shows, for clarity, the principal rays passing through the left edge of the original image SA in the X direction and the principal rays passing through the right edge of the original image SA in the X direction. Both principal rays pass through the first sub-optical system, enter the interior of the prism PM through the transmission surface A, are subsequently reflected by the reflection surface R1, and intersect in the region CRx shown by the dashed circle just before reaching the transmission surface B.

[0052] Figure 11 is an explanatory diagram showing how an image projection device using the optical system 1 according to Embodiment 3 is used. 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, for example, 0.6 m, behind the support base. The light generated from the optical system 1 is projected diagonally upward and backward, achieving short-focus and large-screen projection.

[0053] Figure 12 is a graph showing the relative positional relationship between the reflective surface R1 and the intermediate image IMy in the Y direction and the intermediate image IMx in the X direction in the optical system 1 according to Example 3, and is viewed from a direction perpendicular to the Y cross-section.

[0054] Looking at the graph, the Y-direction intermediate image IMy is distributed obliquely to the Z-direction from around coordinate (-2,0) to around coordinate (-19,-14.5). The X-direction intermediate image IMx is distributed obliquely to the Z-direction from around coordinate (0,0) to around coordinate (-12.5,-15), with a concave shape facing the reduced optical path side. The reflective surface R1 is distributed obliquely to the Z-direction from around coordinate (9,0) to around coordinate (1,-17), with a concave shape facing the reduced optical path side.

[0055] In this disclosure, the reflective surface R1 may have a shape in which a concave surface faces toward the reduced optical path side along the intermediate imaging position in the X direction parallel to the X cross-section of the light ray passing through the center of the longitudinal direction of the rectangular region. This can suppress image distortion on the screen SC.

[0056] (Example 4) Figure 13 is a diagram showing the optical system 1 according to Embodiment 4. This optical system 1 has a similar configuration to Embodiment 1, but the first sub-optical system includes lens elements L1 to L3 and prism PF, and the second sub-optical system, which includes prism PM, projects diagonally upward and backward in the case of an image projection device. The following explanation will be omitted as it overlaps with Embodiment 1.

[0057] Lens element L1 has a biconvex shape (surfaces 2, 3). Lens element L2 has a negative meniscus shape with the convex surface facing the magnification side (surfaces 4, 5). Lens element L3 has a negative meniscus shape with the convex surface facing the magnification side (surfaces 6, 7).

[0058] Prism PF, like prism PM, is formed from a transparent medium, such as glass or synthetic resin. Prism PF has a transmissive surface P located on the contraction side, a transmissive surface Q located on the expansion side, and three reflective surfaces K1, K2, and K3 located on the optical path between transmissive surface P and transmissive surface Q. Transmissive surface P has a free-form surface shape with a concave surface facing the contraction side (surface 9). Reflective surface K1 has a free-form surface shape with a concave surface facing both the contraction and expansion sides (surface 10). Reflective surface K2 has a free-form surface shape with a convex surface facing both the contraction and expansion sides (surface 11). Reflective surface K3 has a free-form surface shape with a concave surface facing both the contraction and expansion sides (surface 12). Transmissive surface Q has a free-form surface shape with a convex surface facing the contraction side (surface 13).

[0059] The prism PM has a transmissive surface A located on the reduction side, a transmissive surface B located on the expansion side, and two reflective surfaces R1 and R2 located on the optical path between transmissive surface A and transmissive surface B. Transmissive surface A has a freeform surface shape with a convex surface facing the reduction side (surface 14). Reflective surface R1 has a freeform surface shape with a concave surface facing both the reduction and expansion sides (surface 15). Reflective surface R2 has a freeform surface shape with a convex surface facing the direction in which the light ray incident on reflective surface R1 is reflected (surface 16). Transmissive surface B has a freeform surface shape with a convex surface facing the expansion side (surface 17).

[0060] The aperture diaphragm ST defines the range through which the light beam passes through the optical system 1 and is positioned between the reduced conjugate point and the intermediate imaging position described above. As an example, the aperture diaphragm ST is located between the lens element L3 and the transmission surface P of the prism PM (surface 8).

[0061] Figure 14(a) is a Y-section view showing the optical path through which the principal ray passes in the optical system 1 according to Embodiment 4, and Figure 14(b) is an X-section view of the optical system 1 as seen from above.

[0062] Figure 14(a) shows, for clarity, the principal rays passing through the center of the original image SA in the X direction and the lowest point in the Y direction (normalized height Y=0.0 at the reduction conjugate point), and the principal rays passing through the center of the original image SA in the X direction and the highest point in the Y direction (normalized height Y=1.0 at the reduction conjugate point). Both principal rays pass through the first sub-optical system, through the transmission surface A, into the interior of the prism PM, are subsequently reflected by the reflection surface R1, and intersect in the region CRy, indicated by the dashed circle, just before reaching the reflection surface R2.

[0063] Figure 14(b) shows, for clarity, the principal rays passing through the left edge of the original image SA in the X direction and the principal rays passing through the right edge of the original image SA in the X direction. Both principal rays pass through the first sub-optical system, through the transmission surface A, into the interior of the prism PM, are subsequently reflected by the reflective surface R1, and intersect in the region CRx shown by the dashed circle just before reaching the reflective surface R2.

[0064] Figure 15 is an explanatory diagram showing how an image projection device using the optical system 1 according to Embodiment 4 is used. 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, for example, 0.2 m, behind the support base. Light generated from the optical system 1 is projected diagonally upward and backward, achieving short-focus and large-screen projection.

[0065] Figure 16 is a graph showing the relative positional relationship between the reflective surface R1 and the intermediate image IMy in the Y direction and the intermediate image IMx in the X direction in the optical system 1 according to Example 4, and is viewed from a direction perpendicular to the Y cross-section.

[0066] Looking at the graph, the Y-direction intermediate image IMy is distributed obliquely to the Z-direction from around coordinate (-1,0) to around coordinate (12,-5.7). The X-direction intermediate image IMx is distributed obliquely to the Z-direction from around coordinate (0,0) to around coordinate (7.5,-6), with a concave shape facing the reduced optical path. The reflective surface R1 is distributed obliquely to the Z-direction from around coordinate (-4.5,-0.5) to around coordinate (-0.8,-6.8), with a concave shape facing the reduced optical path.

[0067] In this disclosure, the reflective surface R1 may have a shape in which a concave surface faces toward the reduced optical path side along the intermediate imaging position in the X direction parallel to the X cross-section of the light ray passing through the center of the longitudinal direction of the rectangular region. This can suppress image distortion on the screen SC. In the optical system 1 according to Example 4, if the prism PF and prism PM are composed of media having different refractive indices and Abbe numbers, the correction of chromatic aberration is more effective than if they are composed of the same medium.

[0068] Next, the conditions that the optical system according to this embodiment can satisfy will be described. Note that multiple conditions are defined 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.

[0069] The optical system according to this embodiment has a reduction conjugate point on the reduction side and an expansion conjugate point on the expansion side, and has an intermediate imaging position inside that is conjugate to the reduction conjugate point and the expansion conjugate point, respectively. The aforementioned reduced conjugate point has an imaging relationship in a rectangular region having a longitudinal direction and a transverse direction. The optical system 1 includes a first sub-optical system which includes an aperture diaphragm ST that defines the range through which the light beam passes, It comprises a second sub-optical system provided on the magnifying side of the first sub-optical system and including a prism PM formed of a transparent medium, The prism PM has a transmissive surface A located on the reduction side, a transmissive surface B located on the expansion side, and at least one reflective surface R1 located on the optical path between the transmissive surface A and the transmissive surface B. The aperture diaphragm ST is positioned between the reduced conjugate point and the intermediate imaging position, A portion or all of the intermediate images IMx, IMy formed at the intermediate imaging position are positioned inside the medium of the prism PM. The reflective surface R1 closest to the intermediate imaging position has a shape in which the concave surface faces the direction in which the light ray incident on the reflective surface R1 is reflected. The aforementioned transparent surface B has a shape with a convex surface facing the magnification side, When the longitudinal direction of the rectangular region of the reduced conjugate point is the X direction, the transverse direction is the Y direction, and the normal direction is the Z direction, the Y section is defined as the plane containing the position where the principal ray passing through the center in the X direction is reflected by the reflective surface R1, and the X section is defined as the cross section perpendicular to the Y section, the curvature shape of the reflective surface R1 may be set such that, when viewed from a direction perpendicular to the Y section, a portion of the multiple principal rays passing through the reduced conjugate point intersect in the optical path between the reflective surface R1 and the transmissive surface B, and when viewed from a direction perpendicular to the X section, a portion of the multiple principal rays passing through the reduced conjugate point intersect in the optical path between the reflective surface R1 and the transmissive surface B.

[0070] In this configuration, multiple principal rays intersect in the optical path between the reflective surface R1 and the transmitting surface B of the prism, with respect to both the Y and X cross-sections. Therefore, by using a small prism, the second sub-optical system can be miniaturized, and projection or imaging of a short focal length and large screen becomes possible.

[0071] In the optical system according to this embodiment, the reflective surface R1 may have a shape in which a concave surface faces toward the reduced optical path side along the intermediate imaging position in the X direction parallel to the X cross-section of the light ray passing through the center of the longitudinal direction of the rectangular region.

[0072] This configuration allows for the suppression of image distortion on the screen SC.

[0073] In the optical system according to this embodiment, the light beam passing through the first sub-optical system may include different intermediate imaging positions in the Y cross-section and the X cross-section.

[0074] This configuration allows for independent setting of the image magnification in the X and Y directions, increasing design flexibility.

[0075] Figure 19 is an explanatory diagram showing the definitions of imaging magnifications MX, MY at the intermediate imaging position and imaging magnifications MMX, MMY at the magnification conjugate point. In the optical system 1 according to this disclosure, the reduction conjugate point, the intermediate imaging position, and the magnification conjugate point are optically conjugate to each other.

[0076] With respect to the Y direction, the length ΔY1 at the reduction conjugate point, the length ΔY2 at the intermediate imaging position in the Y direction, and the length ΔY3 at the expansion conjugate point are imaged at predetermined magnifications. In this case, the imaging magnification MY at the intermediate imaging position in the Y direction parallel to the Y cross-section relative to the reduction conjugate point, and the Y-direction imaging magnification MMY at the expansion conjugate point relative to the reduction conjugate point are given by the following equations. MY = |ΔY2 / ΔY1| MMY = |ΔY3 / ΔY1|

[0077] Similarly, in the X direction, the length ΔX1 at the reduction conjugate point, the length ΔX2 at the intermediate imaging position in the X direction, and the length ΔX3 at the expansion conjugate point are imaged at predetermined magnifications. In this case, the imaging magnification MX at the intermediate imaging position in the X direction parallel to the X cross-section relative to the reduction conjugate point, and the X-direction imaging magnification MMX at the expansion conjugate point relative to the reduction conjugate point are given by the following equations. MX = |ΔX² / ΔX¹| MMX = |ΔX3 / ΔX1|

[0078] The optical system according to this embodiment may satisfy either condition (1a) or condition (1b) below. 0<|MX|<10 ···(1a) 0<|MY|<10 ···(1b) Here, MX: Imaging magnification at the intermediate imaging position in the X direction parallel to the X cross-section relative to the reduced conjugate point. MY: Imaging magnification at an intermediate imaging position in the Y direction parallel to the Y cross-section relative to the reduced conjugate point. That is the case.

[0079] This configuration allows for appropriate setting of the intermediate imaging position, suppressing image distortion on the screen SC while maintaining a compact second sub-optical system. Furthermore, within the above range, the difference between the X-direction imaging magnification and the Y-direction imaging magnification on the screen SC can be minimized. If the upper limit of condition (1a) or condition (1b) is exceeded, the intermediate image formed in the second sub-optical system becomes larger, making it difficult to maintain miniaturization. It is desirable to set the imaging magnifications MX and MY at the intermediate imaging position so that they gradually decrease from the normalization height Y=0 to Y=1 at the reduction conjugate point. By doing so, the field curvature at the intermediate imaging position can be set to the under-side (reduction optical path side), making it possible to keep the field curvature on the screen SC within a good range.

[0080] Furthermore, the above effects can be made more effective by satisfying the following conditions (1c) or (1d). 0.5 < |MX| < 7.5 ···(1c) 0.5 < |MY| < 7.5 ···(1d)

[0081] Furthermore, the above effects can be made more effective by satisfying the following conditions (1e) or (1f). 0.6 < |MX| < 5.0 ···(1e) 0.6 < |MY| < 5.0 ···(1f)

[0082] The optical system according to this embodiment may satisfy the following condition (2). |MX|>|MY| ···(2) Here, MX: Magnification of imaging in the X direction MY: Magnification of imaging in the Y direction That is the case.

[0083] This configuration minimizes the difference between the X-direction imaging magnification and the Y-direction imaging magnification on the screen SC. If condition (2) is not met, a difference will occur between the X-direction imaging magnification and the Y-direction imaging magnification on the screen SC, making it difficult to maintain appropriate optical performance.

[0084] In the optical system according to this embodiment, an intermediate imaging position in the X direction may exist between the intermediate imaging position in the Y direction and the reflective surface R1.

[0085] This configuration allows for minimizing the difference between the X-axis imaging magnification and the Y-axis imaging magnification on the screen SC.

[0086] The optical system according to this embodiment may satisfy the following condition (3). Σ(|OPLY|-|OPLX|)>0 ···(3) Here, OPLX: Optical path length between the intermediate imaging position in the X direction and the reflective surface R1 OPLY: Optical path length between the intermediate imaging position in the Y direction and the reflective surface R1 Σ(|OPLY|-|OPLX|): The sum of the differences between the absolute value of the optical path length OPLX and the absolute value of the optical path length OPLY for the three principal rays passing through normalized heights Y=0.0, 0.5, and 1.0 at the contracted conjugate point. That is the case.

[0087] This configuration allows the difference between the X-direction imaging magnification and the Y-direction imaging magnification on the screen SC to be minimized. If it falls below the lower limit of condition (3), the Y-direction imaging magnification on the screen SC becomes smaller than the X-direction imaging magnification, making it difficult to properly reproduce the original image SA.

[0088] Furthermore, the above effects can be made more effective by satisfying the following condition (3a). Σ(|OPLY|-|OPLX|)>2.5 ···(3a)

[0089] Furthermore, the above effects can be made more effective by satisfying the following condition (3b). Σ(|OPLY|-|OPLX|)>5.0 ···(3b)

[0090] The optical system according to this embodiment may satisfy the following condition (4). |2×(MMX-MMY) / (MMX+MMY)|<0.30 ···(4) Here, MMX: X-direction imaging magnification at the enlarged conjugate point relative to the reduced conjugate point. MMY: Y-direction imaging magnification at the enlarged conjugate point relative to the reduced conjugate point. That is the case.

[0091] This configuration suppresses image distortion on the screen SC and minimizes the difference between the X-direction imaging magnification and the Y-direction imaging magnification. If the upper limit of condition (4) is exceeded, the Y-direction imaging magnification differs from the X-direction imaging magnification on the screen SC, making it difficult to properly reproduce the original image SA. Condition (4) defines the range in which the original image SA can be properly reproduced on the screen SC.

[0092] Furthermore, the above effects can be made more effective by satisfying the following condition (4a). |2×(MMX-MMY) / (MMX+MMY)|<0.15 ···(4a)

[0093] Furthermore, the above effects can be made more effective by satisfying the following condition (4b). |2×(MMX-MMY) / (MMX+MMY)|<0.08 ···(4b)

[0094] The optical system according to this embodiment may satisfy the following condition (5). |θi|<50 ···(5) Here, θi: The angle of incidence (in degrees) of the normal to the transmission surface B at the position where the principal ray enters the transmission surface B of the medium when the principal ray passes through the transmission surface B. That is the case.

[0095] With this configuration, reflected light from the transmissive surface B as it passes through can be suppressed, reducing the loss of transmitted light and thus suppressing the decrease in the light intensity of the projected image.

[0096] In the optical system according to this embodiment, among the transmitting surface A, the transmitting surface B, and the at least one reflecting surface R1, the transmitting surface B may have the largest effective area.

[0097] This configuration allows for a uniform amount of light in the projected image.

[0098] In the optical system according to this embodiment, the aperture diaphragm ST may be positioned between the reduced conjugate point and the transmission surface A.

[0099] This configuration allows for miniaturization of the prism PM.

[0100] In the optical system according to this embodiment, all of the principal rays passing through the reduced conjugate point may intersect in the optical path between the reflective surface R1 and the transmitting surface B.

[0101] This configuration allows for the miniaturization of the second sub-optical system using a small prism, and enables projection or imaging of a large screen with a short focal length.

[0102] In this embodiment, the optical system may have either the entrance pupil or the exit pupil, which corresponds to the aperture diaphragm, positioned within the prism. The entrance pupil is the image of the aperture diaphragm as viewed from the reduction side, and the exit pupil is the image of the aperture diaphragm as viewed from the expansion side.

[0103] This configuration allows for the miniaturization of the second sub-optical system using a small prism, and enables projection or imaging of a large screen with a short focal length.

[0104] In the optical system according to this embodiment, the intermediate imaging position may be positioned at a distance from the reflective surface R1 toward the reduction side.

[0105] This configuration allows for the suppression of image distortion on the screen SC.

[0106] Figures 20(a) to (d) are cross-sectional views in the Y direction showing various examples of stepped structures of the prism PM. The various lens elements and prisms constituting the optical system 1 are generally mounted inside the lens barrel 50 using adhesive, metal fittings, etc. In this case, a highly precise mounting structure is required to faithfully reproduce the various dimensions of the optical design.

[0107] The prism PM is provided with, for example, an end face PMa and an inner corner PMb that serve as mounting references. On the other hand, the lens barrel 50 is provided with an end face 50a and an outer corner 50b that correspond to the shapes of the end face PMa and the inner corner PMb. During mounting, the prism PM can be fixed to the lens barrel 50 with high precision and stability by ensuring that the end face PMa and the end face 50a are aligned and that the inner corner PMb and the outer corner 50b are aligned.

[0108] In this embodiment, the optical system may have a stepped structure formed on the outer periphery of the prism PM.

[0109] This configuration allows the prism to be mounted to the external housing with high precision and stability.

[0110] In this embodiment, the optical system may also be an imaging optical system.

[0111] This configuration allows for miniaturization of the second sub-optical system and enables projection or imaging of a large screen with a short focal length.

[0112] The following describes numerical examples of the optical systems for Examples 1 to 4. In each numerical example, the unit of length in the table is "mm" and the unit of field of view is "°". In each numerical example, the radius of curvature, interplanar spacing, Nd (refractive index for the d line), vd (Abbe number for the d line), N550 (refractive index at a wavelength of 550 nm), and eccentricity data (displacement amount X, Y, Z of the prism surface relative to the previous surface of the optical system, and the normal direction α, β, γ of the prism surface relative to the previous surface). When the interplanar spacing is indicated as "variable", it means that it can be changed according to the image size at the magnified conjugate point (100" (inches), 80", 60", etc.), as shown in the table below. In each numerical example, the shape of the aspherical surface is defined by the following formula. Note that only coefficients other than the conic coefficient k are listed for the aspherical coefficients.

[0113]

number

[0114] Here, z: Sag amount of a plane parallel to the z axis, r: Radial distance (=√(x 2 +y 2 )), c: Curvature at the face vertex k: Conic coefficient, A~H: 4th to 18th order coefficients of r That is the case.

[0115] Furthermore, the shape of a freeform surface is defined in a local Cartesian coordinate system (x,y,z) with its vertices as the origin. It is defined by the following equation using .

[0116]

number

[0117]

number

[0118] In the following data, the i-th order x and j-th order y terms, which are the free surface coefficients in the polynomial, are denoted as x**i*y**j. For example, "X**2*Y" indicates that these are the free surface coefficients of the quadratic x and first-order y terms in the polynomial.

[0119] (Numerical Example 1) For the optical system of Numerical Example 1 (corresponding to Example 1), the lens data is shown in Table 1, the aspherical shape data of the lens is shown in Table 2, and the free-form surface shape data of the prism is shown in Table 3.

[0120] [Table 1]

[0121] [Table 2]

[0122] [Table 3]

[0123] (Numerical Example 2) For the optical system of Numerical Example 2 (corresponding to Example 2), the lens data is shown in Table 4, the aspherical shape data of the lens is shown in Table 5, and the free-form surface shape data of the prism is shown in Table 6.

[0124] [Table 4]

[0125] [Table 5]

[0126] [Table 6]

[0127] (Numerical Example 3) For the optical system of Numerical Example 3 (corresponding to Example 3), the lens data is shown in Table 7, the aspherical shape data of the lens is shown in Table 8, and the free-form surface shape data of the prism is shown in Table 9.

[0128] [Table 7]

[0129] [Table 8]

[0130] [Table 9]

[0131] (Numerical Example 4) For the optical system of Numerical Example 4 (corresponding to Example 4), the lens data is shown in Table 10, and the free-form surface shape data of the prism is shown in Table 11. Only in Example 4, the lens data is in absolute coordinates relative to the first surface.

[0132] [Table 10]

[0133] [Table 11]

[0134] Tables 12 to 15 below show the corresponding values ​​for each conditional expression (1) to (4) in each numerical example 1 to 4.

[0135] [Table 12]

[0136] [Table 13]

[0137] [Table 14]

[0138] [Table 15]

[0139] Table 16 below shows the corresponding values ​​for conditional equation (5) in each of the numerical examples 1 to 4.

[0140] [Table 16]

[0141] (Embodiment 2) Embodiment 2 of this disclosure will be described below with reference to Figure 21. Figure 21 is a block diagram showing an example of an image projection device according to this 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, and the like. The image forming element 101 is composed of liquid crystal, a 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), a 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, or as a built-in lens integrated into the image projection device 100.

[0142] The image projection device 100 described above, with the optical system 1 according to Embodiment 1, enables projection of a large screen with a short focal length using a compact device.

[0143] (Embodiment 3) Embodiment 3 of this disclosure will be described below with reference to Figure 22. Figure 22 is a block diagram showing an example of an imaging device according to this 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, or as a built-in lens integrated into the imaging device 200.

[0144] The imaging device 200 described above, with the optical system 1 according to Embodiment 1, enables imaging of a large screen with a short focal length in a compact device.

[0145] 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.

[0146] 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.

[0147] 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 claims or their equivalents. [Industrial applicability]

[0148] 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. [Explanation of Symbols]

[0149] 1 Optical system SA Original Image PA optical elements L1~L14 Lens Elements ST aperture diaphragm PM, PF prism R1,R2,K1,K2,K3 Reflective surface A,B,P,Q Transparent surface SC Screen 100 Image projection device 200 Imaging device

Claims

1. In an optical system comprising a first sub-optical system and a second sub-optical system, arranged in order from the reduction side to the enlargement side, The second sub-optical system comprises a prism having, in order from the reduction side, a first transmission surface, a first reflection surface, a second reflection surface, and a second transmission surface. The first reflective surface has a shape in which the concave surface is oriented in the direction in which the incident light ray is reflected. The second reflective surface is positioned in a first direction from the reduction side to the magnification side of the first sub-optical system, at a position in the first direction relative to the first surface on the magnification side of the first lens located furthest towards the magnification side of the first sub-optical system, and at a position where light rays reflected in the opposite direction to the first direction by the first reflective surface are incident. The second transmissive surface is positioned in the first direction relative to the second reflective surface, An optical system in which the curvature shape of the first reflecting surface is set such that, when viewed from a direction perpendicular to the Y-section, a portion of the multiple principal rays passing through the reduced conjugate point intersects in the optical path between the first reflecting surface and the second transmitting surface, and when viewed from a direction perpendicular to the X-section, a portion of the multiple principal rays passing through the reduced conjugate point intersects in the optical path between the first reflecting surface and the second transmitting surface.

2. The optical system according to claim 1, wherein the second reflective surface is positioned in the first direction relative to the first transmissive surface in the first direction.

3. The optical system according to claim 1, wherein in the first direction, the first transmitting surface and the second reflecting surface are positioned on the side of the prism opposite to the first direction, and the first reflecting surface and the second transmitting surface are positioned on the side of the prism in the first direction.

4. The optical system according to claim 3, wherein the first reflective surface and the second transmissive surface have different curvatures.

5. The optical system according to claim 3, wherein the first transmission surface and the second reflection surface have different curvatures.

6. The optical system according to claim 1, wherein in a second direction perpendicular to the first direction, the first transmitting surface and the first reflecting surface are positioned on the second direction side of the prism, and the second reflecting surface and the second transmitting surface are positioned on the opposite side of the second direction of the prism.

7. The optical system according to claim 6, wherein the second reflective surface is not positioned at the same location as the first reflective surface in the second direction.

8. The optical system according to claim 7, wherein a portion of the second reflective surface is positioned in the same location as a portion of the second transmissive surface in the second direction.

9. The optical system according to claim 8, wherein a portion of the first reflective surface is positioned in the same location as a portion of the first transmissive surface in the second direction.

10. In the first direction, the first transparent surface is positioned facing the opposite direction to the first direction, and the second transparent surface is positioned facing the first direction, In the first direction, the first transmitting surface receives light rays emitted from the first sub-optical system from the opposite side of the first direction, and the second transmitting surface emits light rays reflected by the first reflecting surface and the second reflecting surface toward the first direction. The optical system according to claim 1.

11. The optical system according to claim 1, wherein the first transmissive surface has a different shape from the second transmissive surface, and the first transmissive surface and the second transmissive surface are spaced apart from each other.

12. The optical system according to claim 1, wherein the second reflective surface has a shape in which a convex surface is oriented in the direction in which light rays incident on the first reflective surface are reflected, and the first reflective surface and the second reflective surface have a non-planar curvature.

13. The optical system according to claim 1, wherein in the first direction, the second transmission surface is positioned on the first direction side of the prism.

14. The optical system according to claim 1, wherein the first reflective surface is positioned in the first direction from the first transmissive surface and in the opposite direction from the magnified conjugate point of the optical system.

15. The optical system according to claim 1, wherein the direction of the predetermined side is the longitudinal direction of the rectangular region of the reduced conjugate point.

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

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

Images