Optical system for projection and projection type display device

Abstract

To provide an optical system for projection constructed in a compact size and having excellent optical performance, and a projection type display device equipped with this optical system for projection.SOLUTION: The optical system for projection projects a reduction-side image to an expansion side and does not include a reflection plane having power, and comprises a first optical system and a second optical system in order from the expansion side to the reduction side along the optical path. An intermediate image is formed between the first optical system and the second optical system and the first optical system includes an optical path deflection plane for bending the optical path. When it is assumed that Imax represents the radius of a maximum effective image circle on the reduction side, and Ddef represents the distance on the optical axis from the lens surface on the most expansion side to the optical path deflection plane of the first optical system, the optical system for projection satisfies the relationship 0.2<Imax / Ddef<0.7.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The technology disclosed herein relates to a projection optical system and a projection display device. [Background technology]

[0002] An optical system described in Patent Document 1 below is known as an optical system that can be used in a projection display device. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2014-029392 A Summary of the Invention [Problem to be solved by the invention]

[0004] There is a demand for projection optical systems that are compact and have good optical performance, and the level of these requirements is increasing year by year.

[0005] The present disclosure has been made in consideration of the above circumstances, and provides a projection optical system that is compact and has good optical performance, and a projection display device that includes this projection optical system. [Means for solving the problem]

[0006] A first aspect of the present disclosure is a projection optical system that projects an image on a reduced side onto an enlarged side, the projection optical system not including a reflective surface having power, and including, in order along an optical path from the enlargement side to the reduction side, a first optical system and a second optical system, an intermediate image is formed between the first optical system and the second optical system, the first optical system including an optical path deflection surface that bends the optical path, 0.2 <Imax / Ddef<0.7 (1) This satisfies conditional expression (1) expressed by the following. In this disclosure, the symbols in the conditional expressions are defined as follows. The radius of the maximum effective image circle on the reduction side is defined as Imax. The distance on the optical axis from the lens surface on the most enlargement side of the first optical system to the optical path deflection surface is defined as Ddef. Note that when the projection optical system is a variable magnification optical system, Ddef is defined as the value at the wide-angle end.

[0007] A second aspect of the present disclosure is a projection optical system according to the first aspect, wherein the first optical system comprises, in order along the optical path from the enlargement side to the reduction side, a front group having negative power, an optical path deflection member including an optical path deflection surface, and a rear group having positive power.

[0008] A third aspect of the present disclosure is the projection optical system of the second aspect, wherein the front group includes one or more positive lenses.

[0009] A fourth aspect of the present disclosure is a projection optical system according to the second aspect, wherein the outermost periphery of the optically effective surface on the most enlargement side of the first optical system is located on the reduction side in the optical axis direction relative to the intersection of the optically effective surface and the optical axis.

[0010] A fifth aspect of the present disclosure provides a projection optical system according to the third aspect, in which, when the average Abbe number based on the d-line of all negative lenses included in the front group is denoted as νnave and the average Abbe number based on the d-line of all positive lenses included in the front group is denoted as νpave, 10<νnave-νpave<40 (2) The condition (2) expressed by the following formula (2) is satisfied.

[0011] A sixth aspect of the present disclosure provides a projection optical system according to the third aspect, in which, when the average value of the refractive index for the d-line of all negative lenses included in the front group is Nnave and the average value of the refractive index for the d-line of all positive lenses included in the front group is Npave, 0.15 <Npave-Nnave<0.45 (3) The condition (3) is satisfied.

[0012] A seventh aspect of the present disclosure is the projection optical system of the second aspect, wherein at least a part of the rear group moves during focusing.

[0013] An eighth aspect of the present disclosure is the projection optical system of the first aspect, wherein the second optical system includes two or more moving groups that move along the optical axis during magnification change.

[0014] A ninth aspect of the present disclosure is directed to the projection optical system of the eighth aspect, wherein, of the moving groups of the second optical system, the moving group closest to the enlargement side has positive power.

[0015] A tenth aspect of the present disclosure is a projection optical system according to the second aspect, in which, assuming that the air-equivalent distance on the optical axis from the surface of the front group closest to the reduction side to the surface of the rear group closest to the enlargement side is Dfr, and in the case where the projection optical system is a variable magnification optical system, Dfr is a value at the wide-angle end, 0.5 <Imax / Dfr<0.9 (4) The condition (4) is satisfied.

[0016] An eleventh aspect of the present disclosure is the projection optical system of the second aspect, wherein the optical path deflection surface is a prism surface.

[0017] A twelfth aspect of the present disclosure is a projection optical system according to the eleventh aspect, in which, assuming that the thickness of the prism along the optical axis is Dpr and the refractive index of the prism with respect to the d-line is Npr, 0.9 <Imax / (Dpr / Npr)<1.3 (5) The condition (5) is satisfied.

[0018] A thirteenth aspect of the present disclosure provides a projection optical system according to the first aspect, in which, assuming that the maximum effective radius of the lens surface on the most enlargement side of the first optical system is ERf and the maximum value of the maximum effective radii of all lens surfaces of the projection optical system is ERmax, 0 <ERf / ERmax<0.7 (6) Condition (6) expressed by the following formula (6) is satisfied.

[0019] A fourteenth aspect of the present disclosure provides a projection optical system according to the first aspect, in which, assuming that a maximum value of a height from an optical axis of an on-axis marginal ray on all lens surfaces of a first optical system is AH1, and a maximum value of a height from an optical axis of an on-axis marginal ray on all lens surfaces of a second optical system is AH2, 0 <AH1 / AH2<0.7 (7) Condition (7) expressed by the following formula (7) is satisfied.

[0020] A fifteenth aspect of the present disclosure relates to a projection optical system of the first aspect, which includes an aperture stop on the reduction side of the intermediate image, a real image of the aperture stop existing inside the first optical system, the position of the real image of the aperture stop in the optical axis direction being a first position, and the second position being the position farthest from the first position among the positions where a light ray originating from any point within the maximum effective image circle on the reduction side, heading toward the enlargement side and passing through the center of the aperture stop intersects with the optical axis on the enlargement side of the intermediate image, the intersection point between the optical path deflection surface and the optical axis is located within the range from the first position to the second position in the optical axis direction.

[0021] A sixteenth aspect of the present disclosure relates to a projection optical system according to the fifteenth aspect, in which k is a natural number from 1 to 10, a point on a maximum effective image circle on the reduction side whose height from the optical axis is k / s of the radius of the maximum effective image circle is a point PHk, a position where a light ray that starts from point PHk, travels toward the enlargement side, passes through the center of the aperture stop, and intersects with the optical axis on the enlargement side of the intermediate image is a position Pk, a position among the positions Pk where the air-equivalent distance on the optical axis from the first position is the longest is a third position, and the air-equivalent distance from the first position to the third position is DifP, and the sign of DifP is positive for the reduction-side distance and negative for the enlargement-side distance with respect to the first position, and when the projection optical system is a variable magnification optical system, when DifP is a value at the wide-angle end, -3 <DifP / Imax<-0.2 (8) The condition (8) is satisfied.

[0022] A seventeenth aspect of the present disclosure is a projection optical system according to the sixteenth aspect, wherein the first optical system comprises, in order along the optical path from the enlargement side to the reduction side, a front group, an optical path deflection member including an optical path deflection surface, and a rear group, and the air-equivalent distance on the optical axis from the surface of the front group closest to the reduction side to the surface of the rear group closest to the enlargement side is defined as Dfr, and when the projection optical system is a variable magnification optical system, Dfr is defined as a value at the wide-angle end, 0.4<|DifP / Dfr|<0.7 (9) Condition (9) expressed by the following formula (9) is satisfied.

[0023] An eighteenth aspect of the present disclosure is the projection optical system of the sixteenth aspect, wherein the optical path deflection surface is a prism surface.

[0024] A nineteenth aspect of the present disclosure provides a projection optical system according to the eighteenth aspect, in which, assuming that the thickness of the prism along the optical axis is Dpr and the refractive index of the prism with respect to the d-line is Npr, 0.7<|DifP / (Dpr / Npr)|<1.8 (10) Satisfies condition (10) expressed by:

[0025] A twentieth aspect of the present disclosure is a projection display device including the projection optical system according to any one of the first to nineteenth aspects.

[0026] In addition, in this specification, "consisting of" and "consisting of" are intended to mean that, in addition to the listed components, the following may be included: a lens having substantially no power (refractive power), optical elements other than lenses such as apertures, masks, filters, cover glasses, flat mirrors, and prisms, as well as mechanical parts such as lens flanges, lens barrels, image sensors, and image stabilization mechanisms.

[0027] In this specification, "group having positive power" and "group has positive power" mean that the group as a whole has positive power. Similarly, "group having negative power" and "group has negative power" mean that the group as a whole has negative power. In this specification, the "front group," "rear group," "focusing group," and "lens group" are not limited to configurations consisting of multiple lenses, and may be configurations consisting of only one lens.

[0028] A compound aspherical lens (a lens in which a lens (e.g. a spherical lens) and an aspherical film formed on the lens are integrally constructed and function as a single aspherical lens as a whole) is not considered a cemented lens, but is treated as a single lens. Unless otherwise specified, the power sign and surface shape of lenses including aspherical surfaces are those in the paraxial region. Unless otherwise specified, the "distance on the optical axis" used in the conditional expressions is a geometric distance. The "focal length" used in the conditional expressions is the paraxial focal length. The values ​​used in the conditional expressions are based on the d line.

[0029] The terms "d-line," "C-line," and "F-line" used in this specification are emission lines, and the wavelength of the d-line is treated as 587.56 nm (nanometers), the wavelength of the C-line is 656.27 nm (nanometers), and the wavelength of the F-line is 486.13 nm (nanometers). Effect of the Invention

[0030] According to the present disclosure, it is possible to provide a projection optical system that is compact and has good optical performance, and a projection display device that includes this projection optical system. [Brief description of the drawings]

[0031] [Figure 1] 2 is a cross-sectional view showing the configuration and light flux of a projection optical system according to one embodiment, which corresponds to the projection optical system of Example 1. FIG. [Diagram 2] FIG. 2 is a partially enlarged view of the projection optical system of FIG. [Diagram 3]2 is a cross-sectional view showing a configuration in which the optical path of the projection optical system in FIG. 1 is developed and a light beam. [Figure 4] FIG. 13 is a diagram for explaining a maximum effective radius. [Diagram 5] 2 is a diagram showing a ray of light that originates from a point within the maximum effective image circle on the reduction side, travels toward the enlargement side, and passes through the center of the aperture stop in the projection optical system of FIG. 1. [Figure 6] FIG. 6 is an enlarged view of a main part of FIG. 5. [Figure 7] 2 is a diagram showing a ray of light that originates from a point PHk on the reduction side, travels toward the enlargement side, and passes through the center of the aperture stop in the projection optical system of FIG. 1. [Figure 8] FIG. 8 is an enlarged view of a main part of FIG. [Figure 9] 3A to 3C are diagrams showing various aberrations in the projection optical system of the first embodiment. [Figure 10] 10 is a cross-sectional view showing the configuration and light beam of a projection optical system according to a second embodiment. [Figure 11] 11 is a cross-sectional view showing a developed configuration of the optical path of the projection optical system in FIG. 10 and a light beam. [Figure 12] 6A to 6C are diagrams showing various aberrations in the projection optical system according to the second embodiment. [Figure 13] 11 is a cross-sectional view showing the configuration and light beam of a projection optical system according to a third embodiment. [Figure 14] 14 is a cross-sectional view showing a configuration in which the optical path of the projection optical system in FIG. 13 is developed and a light beam. [Figure 15] 11A to 11C are diagrams showing various aberrations in the projection optical system according to the third embodiment. [Figure 16] 11 is a cross-sectional view showing the configuration and light beam of a projection optical system according to a fourth embodiment. [Figure 17] 17 is a cross-sectional view showing a configuration in which the optical path of the projection optical system in FIG. 16 is developed and a light beam. [Figure 18] 11A to 11C are diagrams showing various aberrations in the projection optical system according to the fourth embodiment. [Figure 19] 1 is a schematic configuration diagram of a projection display device according to an embodiment. [Figure 20] FIG. 11 is a schematic configuration diagram of a projection display device according to another embodiment. [Figure 21]FIG. 13 is a schematic configuration diagram of a projection display device according to yet another embodiment. [Figure 22] FIG. 13 is a schematic configuration diagram of a projection display device according to yet another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0033] Fig. 1 shows a cross-sectional view of a configuration of a projection optical system according to an embodiment of the present disclosure and light beams. In Fig. 1, an axial light beam B0 and light beams B1 and B2 at the maximum angle of view are shown as light beams. The example shown in Fig. 1 corresponds to the projection optical system of Example 1 described below. In Fig. 1, the upper left of the figure is the enlargement side, and the lower right of the figure is the reduction side.

[0034] FIG. 1 shows an example in which an optical member PP and a display surface Sim of a light valve are arranged on the reduction side of the projection optical system, assuming that the projection optical system is mounted on a projection display device. The light valve is a display element that outputs an optical image, and this optical image is displayed as an image on the display surface Sim. For example, a liquid crystal display element or an image display element such as a DMD (Digital Micromirror Device: registered trademark) can be used as the light valve. The optical member PP is a member assuming a filter, a cover glass, a color synthesis prism, etc. The optical member PP is a member that does not have power. The material, length, and number of parts of the optical member PP can be changed as appropriate, and a configuration in which the optical member PP is omitted is also possible.

[0035] The projection optical system is mounted on, for example, a projection display device, and enlarges and projects an image displayed on a display surface Sim of a display element on the reduction side onto a projection surface on the enlargement side. In the projection display device, a light beam given image information on the display surface Sim is incident on the projection optical system via an optical member PP, and is projected onto a screen (not shown) as a projection surface by the projection optical system. That is, the display surface Sim and the screen are in optically conjugate positions. The display surface Sim corresponds to the reduction side conjugate surface, and the screen corresponds to the enlargement side conjugate surface. In this specification, the "screen" means an object onto which a projection image formed by the projection optical system is projected. The screen may be a dedicated screen, or may be a wall, floor, or ceiling of a room, or an exterior wall of a building.

[0036] In the explanation of this specification, "enlargement side" means the screen side on the optical path, and "reduction side" means the display surface Sim side on the optical path. In this specification, "enlargement side" and "reduction side" are determined along the optical path. Furthermore, "adjacent" in relation to the arrangement of components means adjacent to each other in terms of the order on the optical path. In the following, to avoid redundant explanation, "in sequence from the enlargement side to the reduction side along the optical path" may be written as "in sequence from the enlargement side to the reduction side."

[0037] The projection optical system of the present disclosure is configured not to include a reflective surface having power. In the projection optical system, the center position of the image on the display surface Sim may be shifted from the optical axis Z of the projection optical system in a direction perpendicular to the optical axis Z. In the projection optical system including a reflective surface having power such as a concave mirror, the light flux is blocked by the projection display device in the vicinity of the optical axis Z of the image circle, and there is an area that cannot be used, so the amount of shift is often fixed. In contrast, the projection optical system not including a reflective surface having power as in the present disclosure does not have the above-mentioned problem of blocking, and the amount of shift can be changed within the image circle, so that it can be configured with a high degree of freedom.

[0038] The projection optical system of the present disclosure is composed of a first optical system G1 and a second optical system G2 in order along the optical path from the enlargement side to the reduction side, and an intermediate image MI is formed between the first optical system G1 and the second optical system G2. When shortening the focal length of the projection optical system to widen the angle, if one tries to achieve the required optical performance while ensuring the back focus required for the projection optical system, the lens on the enlargement side tends to become huge. By using a relay optical system in which the intermediate image MI is formed, it is possible to shorten the back focus of the optical system on the enlargement side from the intermediate image MI, and also to reduce the lens diameter on the enlargement side, which is advantageous for miniaturization.

[0039] The first optical system G1 is configured to include an optical path deflection surface that bends the optical path. By bending the optical path, the optical system can be configured compactly, which is advantageous for miniaturization.

[0040] As an example, the projection optical system in FIG. 1 is configured as follows. The first optical system G1 is composed of a front group G1F, a prism Pr, and a rear group G1R, in order from the enlargement side to the reduction side. The front group G1F is composed of lenses L1a to L1d, in order from the enlargement side to the reduction side. The rear group G1R is composed of lenses L1e to L1n, in order from the enlargement side to the reduction side. The second optical system G2 is composed of a lens L2a, a plane mirror Mr, lenses L2b to L2h, an aperture stop St, and lenses L2i to L2m, in order along the optical path from the enlargement side to the reduction side. Note that the aperture stop St shown in FIG. 1 does not indicate the size or shape, but indicates the position in the optical axis direction. This method of illustrating the aperture stop St is the same in other drawings. Also, in FIG. 1, the intermediate image MI is conceptually shown by a dotted line, and the shape of the intermediate image MI in FIG. 1 is not accurate.

[0041] FIG. 2 shows an enlarged view of the prism Pr and the lenses in the vicinity thereof in the projection optical system of FIG. 1. Note that in FIG. 2, only the axial light beam B0 is shown as the light beam. The prism Pr includes a reflecting surface Prs inside. The reflecting surface Prs is an example of a light path deflection surface that bends the light path of the present disclosure. The prism Pr is an example of a light path deflection member of the present disclosure. By using the surface of the prism Pr as the light path deflection surface, it is advantageous to ensure performance during assembly. Note that the surface of the prism on which a reflective film is formed may be used as the light path deflection surface, or the surface of the prism may be used as the light path deflection surface by using total reflection.

[0042] It is preferable that the outermost periphery of the optically effective surface on the most enlargement side of the first optical system G1 is located on the reduction side in the optical axis direction from the intersection of this optically effective surface and the optical axis Z. In this case, it is advantageous for correcting distortion aberration.

[0043] In the projection optical system of Fig. 1, the most enlarged optically effective surface of the first optical system G1 is on the enlargement side surface of the lens L1a. As an example, Fig. 2 shows point 2 on the outermost circumference of the most enlarged optically effective surface of the first optical system G1 and intersection point 4 between this optically effective surface and the optical axis Z. As shown in Fig. 2, point 2 is located on the reduction side of intersection point 4 in the optical axis direction.

[0044] The "optically effective surface" is usually a mirror-finished surface. In this specification, the "optically effective surface" of a lens includes a surface within an effective diameter through which light rays for imaging pass, and is a surface that extends radially outward with the same shape as the surface shape within this effective diameter. The same shape refers to a surface having a shape formed based on the same design data. "The same design data" means that in the case of a spherical shape, the radius of curvature is the same, in the case of an aspheric shape, the aspheric formula and the aspheric coefficient are the same, and in the case of a free-form surface shape, the free-form surface formula and the free-form surface coefficient are the same.

[0045] It is preferable that the power of the front group G1F is negative and the power of the rear group G1R is positive. By configuring the first optical system G1 to be composed of, in order from the enlargement side to the reduction side, a front group G1F having negative power, an optical path deflection member, and a rear group G1R having positive power, this is advantageous for achieving compactness while ensuring a wide angle of view.

[0046] It is preferable that the front group G1F includes one or more positive lenses, which is advantageous for correcting chromatic aberration and curvature of field.

[0047] It is preferable that at least a part of the rear group G1R moves along the optical axis Z during focusing. This configuration makes it possible to configure a projection optical system with a focusing function. In addition, in this case, the front group G1F is fixed during focusing, and a configuration can be made in which no focusing mechanism is provided in the front group G1F, which is advantageous for miniaturizing the lens on the most enlargement side. In the following, the group that moves during focusing is referred to as the focusing group. Focusing is performed by moving the focusing group along the optical axis Z.

[0048] In the example of Fig. 1, the focusing group is made up of lenses L1g to L1l. The brackets and double-headed arrows attached to the lenses L1g to L1l in Fig. 1 and Fig. 3 indicate that the lenses L1g to L1l are the focusing group. Fig. 3 is a cross-sectional view in which the optical path of the projection optical system in Fig. 1 is developed. Note that Fig. 3 omits illustration of the reflecting surface Prs, the plane mirror Mr, and the light beam B2 at the maximum angle of view.

[0049] It is preferable that the second optical system G2 includes two or more moving groups that move along the optical axis Z during magnification change. With this configuration, a projection optical system having a magnification change function can be configured. Also, by disposing the moving groups in the second optical system G2, which has a relatively small diameter, the load on the magnification change mechanism can be reduced. Furthermore, since the magnification change optical system can be configured within the range of a refractive optical system that does not include a folded optical path, it is easy to ensure mechanical precision.

[0050] Of the moving groups of the second optical system G2, it is preferable that the moving group on the most enlargement side has a positive power. In this case, it is advantageous to make the moving group on the reduction side smaller than the moving group on the most enlargement side. In addition, it is easy to ensure a long air gap on the reduction side of the intermediate image MI and on the enlargement side of the moving group on the most enlargement side. If a member that bends the optical path is arranged in this long air gap, the optical path can be bent two or more times in the entire projection optical system, which is more advantageous for miniaturization. In the second optical system G2 of FIG. 1, the optical path is bent by 90 degrees by the plane mirror Mr arranged in this long air gap.

[0051] It is preferable that the second optical system G2 includes a fixed group, which is composed of one positive lens and is fixed with respect to the display surface Sim during zooming, on the most reduction side. In this case, it is easy to ensure telecentricity on the reduction side.

[0052] As an example, the second optical system G2 in Fig. 1 includes, in order from the enlargement side to the reduction side, five lens groups, namely, a 2A lens group G2A, a 2B lens group G2B, a 2C lens group G2C, a 2D lens group G2D, and a 2E lens group G2E, as shown in Fig. 3. The lens groups in Fig. 3 are configured as follows. The 2A lens group G2A is made up of a lens L2a. The 2B lens group G2B is made up of lenses L2b to L2e. The 2C lens group G2C is made up of lenses L2f to L2h, an aperture stop St, and a lens L2i. The 2D lens group G2D is made up of lenses L2j to L2l. The 2E lens group G2E is made up of a lens L2m. During magnification change, the 2A lens group G2A and the 2E lens group G2E are fixed with respect to the display surface Sim, and the 2B lens group G2B, the 2C lens group G2C, and the 2D lens group G2D move along the optical axis Z while changing the spacing between adjacent lens groups. In Figure 3, parentheses and arrows indicating the general direction of movement of each lens group when changing magnification from the wide-angle end to the telephoto end are written under the lens groups that move during magnification change.

[0053] Next, preferred and possible configurations for the conditional expressions of the projection optical system of the present disclosure will be described. In the following description of the conditional expressions, in order to avoid redundant explanations, the same symbols are used for elements with the same definitions, and redundant explanations of the symbols are omitted. In addition, in the following, in order to avoid redundant explanations, the "projection optical system of the present disclosure" will also be simply referred to as the "projection optical system."

[0054] It is preferable that the projection optical system satisfies the following conditional formula (1). Here, the radius of the maximum effective image circle on the reduction side is Imax. The distance on the optical axis from the lens surface on the most enlargement side of the first optical system G1 to the optical path deflection surface is Ddef. Imax is the maximum image height on the reduction side. As an example, the above-mentioned radius Imax and distance Ddef are shown in FIG. 1. Note that, when the projection optical system is a variable magnification optical system, Ddef is the value at the wide-angle end. By making sure that the corresponding value of conditional formula (1) is not equal to or less than the lower limit, it is possible to prevent the lens on the most enlargement side from becoming large. By making sure that the corresponding value of conditional formula (1) is not equal to or more than the upper limit, it is advantageous to maintain good optical performance and specifications. 0.2 <Imax / Ddef<0.7 (1)

[0055] In order to obtain better characteristics, the lower limit of conditional formula (1) should more preferably be 0.25, and even more preferably be 0.3, and the upper limit of conditional formula (1) should more preferably be 0.6, and even more preferably be 0.5.

[0056] It is preferable that the projection optical system satisfies the following conditional formula (2). Here, the average value of the Abbe numbers based on the d-line of all the negative lenses included in the front group G1F is defined as νnave. The average value of the Abbe numbers based on the d-line of all the positive lenses included in the front group G1F is defined as νpave. Ensuring that the corresponding value of conditional formula (2) is not equal to or lower than the lower limit value is advantageous for correcting chromatic aberration. Ensuring that the corresponding value of conditional formula (2) is not equal to or higher than the upper limit value is advantageous for correcting secondary spectrum of chromatic aberration. 10<νnave-νpave<40 (2)

[0057] In order to obtain better characteristics, the lower limit of conditional formula (2) should more preferably be set to 12, and even more preferably to 15. In order to obtain better characteristics, the upper limit of conditional formula (2) should more preferably be set to 36, and even more preferably to 32.

[0058] It is preferable that the projection optical system satisfies the following conditional expression (3). Here, the average value of the refractive index for the d-line of all the negative lenses included in the front group G1F is designated as Nnave. The average value of the refractive index for the d-line of all the positive lenses included in the front group G1F is designated as Npave. Ensuring that the corresponding value of conditional expression (3) is not equal to or less than the lower limit value is advantageous for correcting curvature of field. Ensuring that the corresponding value of conditional expression (3) is not equal to or more than the upper limit value is advantageous for correcting spherical aberration. 0.15 <Npave-Nnave<0.45 (3)

[0059] In order to obtain better characteristics, the lower limit of condition (3) should more preferably be 0.18, and even more preferably be 0.2.In order to obtain better characteristics, the upper limit of condition (3) should more preferably be 0.36, and even more preferably be 0.3.

[0060] It is preferable that the projection optical system satisfies the following conditional formula (4). Here, Dfr is the air-equivalent distance on the optical axis from the surface of the front group G1F on the most reduction side to the surface of the rear group G1R on the most enlargement side. If the projection optical system is a variable magnification optical system, Dfr is the value at the wide-angle end. Conditional formula (4) is an equation that specifies the ratio between the maximum image height on the reduction side and the space for arranging the optical path deflector. Conditional formula (4) can suppress the light beam diameter in the optical path deflector. By making sure that the corresponding value of conditional formula (4) is not equal to or less than the lower limit, it is possible to suppress the size of the lens on the most enlargement side. By making sure that the corresponding value of conditional formula (4) is not equal to or more than the upper limit, it is possible to secure a space for passing the light beam whose optical path has been bent. 0.5 <Imax / Dfr<0.9 (4)

[0061] In order to obtain better characteristics, it is more preferable that the lower limit of conditional expression (4) be set to 0.6, and it is more preferable that the upper limit of conditional expression (4) be set to 0.8.

[0062] It is preferable that the projection optical system satisfies the following conditional formula (5). Here, the thickness of the prism Pr along the optical axis Z is defined as Dpr. The refractive index of the prism Pr with respect to the d-line is defined as Npr. As an example, the above thickness Dpr is shown in FIG. 3. The conditional formula (5) is an equation that specifies the ratio between the maximum image height on the reduction side and the thickness of the prism Pr converted into air. By making sure that the corresponding value of the conditional formula (5) is not equal to or less than the lower limit, it is possible to prevent the lens on the most enlargement side from becoming large. By making sure that the corresponding value of the conditional formula (5) is not equal to or more than the upper limit, it is possible to ensure a space for passing the light beam whose optical path has been bent. 0.9 <Imax / (Dpr / Npr)<1.3 (5)

[0063] In order to obtain better characteristics, it is more preferable that the lower limit value of conditional expression (5) be 1. In order to obtain even better characteristics, it is more preferable that the upper limit value of conditional expression (5) be 1.2.

[0064] It is preferable that the projection optical system satisfies the following conditional expression (6). Here, the maximum effective radius of the lens surface on the most enlargement side of the first optical system G1 is ERf. The maximum value of the maximum effective radii of all lens surfaces of the projection optical system is ERmax. The lower limit of conditional expression (6) is ERf>0 and ERmax>0, so ERf / ERmax>0. By ensuring that the corresponding value of conditional expression (6) is not equal to or greater than the upper limit, it is possible to prevent the lens on the most enlargement side from becoming large, or it is advantageous for correcting off-axis aberrations. 0 <ERf / ERmax<0.7 (6)

[0065] In order to obtain even better characteristics, it is more preferable to set the upper limit of condition (6) to 0.6.

[0066] The maximum effective radius will be described with reference to FIG. 4. FIG. 4 is an explanatory diagram. In FIG. 4, the left side is the enlarged side, and the right side is the reduced side. FIG. 4 shows an on-axis light beam Xa and an off-axis light beam Xb passing through a lens Lx. In the example of FIG. 4, a light beam Xb1, which is an upper light beam of the off-axis light beam Xb, is a light beam that passes through the outermost side. The "outside" here means the radial outside centered on the optical axis Z, that is, the side away from the optical axis Z. In this specification, the distance from the position Px of the intersection between the outermost light beam and the lens surface to the optical axis Z is the maximum effective radius ER of the lens surface. Note that in the example of FIG. 4, the upper light beam of the off-axis light beam Xb is a light beam that passes through the outermost side, but which light beam passes through the outermost side varies depending on the optical system.

[0067] In the example of Fig. 3, which satisfies conditional expression (6), the diameter of the lens on the most enlargement side is smaller than the diameter of the lens in the middle part of the projection optical system. Usually, in a projection optical system, the diameter of the lens on the most enlargement side is large, but in the example of Fig. 3, the diameter of the lens on the most enlargement side is preferably reduced.

[0068] It is preferable that the projection optical system satisfies the following conditional formula (7). Here, the maximum value of the height of the axial marginal ray B0m from the optical axis Z on all lens surfaces of the first optical system G1 is AH1. The maximum value of the height of the axial marginal ray B0m from the optical axis Z on all lens surfaces of the second optical system G2 is AH2. As an example, in the projection optical system of FIG. 1, the height of the axial marginal ray B0m from the optical axis Z on the enlargement side surface of the lens L1f is AH1, and the height of the axial marginal ray B0m from the optical axis Z on the reduction side surface of the lens L2c is AH2. FIG. 2 shows the above maximum value AH1, and FIG. 3 shows the above maximum value AH2. Note that, when the projection optical system is a variable magnification optical system, AH1 and AH2 are maximum values ​​in the entire variable magnification range. The lower limit of the conditional formula (7) is AH1>0 and AH2>0, so AH1 / AH2>0. By making sure that the corresponding value of conditional expression (7) is not equal to or greater than the upper limit, the increase in the light beam width near the optical path deflection surface can be suppressed, and therefore the size of the lens on the most enlarging side can be suppressed. 0 <AH1 / AH2<0.7 (7)

[0069] Next, a preferred position for arranging the optical path deflection surface will be described with reference to FIG. 5 and FIG. 6. FIG. 5 shows a diagram in which the optical path is expanded to become a linear optical path for ease of understanding. FIG. 6 shows an enlarged view of the prism Pr portion. When the projection optical system includes an aperture stop St on the reduction side of the intermediate image MI, and a real image of the aperture stop St exists inside the first optical system G1, it is preferred that the position of the optical path deflection surface is as follows. Here, the position of the real image of the aperture stop St in the optical axis direction is defined as position Pist. Among the positions at which a light ray originating from an arbitrary point in the maximum effective image circle on the reduction side, traveling toward the enlargement side and passing through the center of the aperture stop St intersects with the optical axis Z on the enlargement side of the intermediate image MI, the position furthest from position Pist is defined as position Pch. It is preferred that the intersection of the optical path deflection surface and the optical axis Z is located within the range from position Pist to position Pch in the optical axis direction. In this case, the optical path deflection surface can be arranged near the real image of the pupil. When the projection optical system is a variable magnification optical system, it is preferable that the intersection of the optical path deflection surface and the optical axis Z is located within the above range at the wide-angle end.

[0070] As an example, in Fig. 5 and Fig. 6, the position Pist in the projection optical system of Fig. 1 is shown by a two-dot chain line, the position Pch is shown by a short dashed line, and the position Pdef of the intersection between the optical path deflection surface and the optical axis Z is shown by a long dashed line. Note that Fig. 5 and Fig. 6 also show these positions in the optical axis direction. Fig. 5 and Fig. 6 also show a number of light rays Rys that originate from a number of points within the maximum effective image circle on the reduction side, proceed toward the enlargement side, and pass through the center of the aperture stop St. In the projection optical system of Fig. 1, the above three positions are all located within the prism Pr, which is the optical path deflection member.

[0071] In relation to the position Pist, it is preferable that the projection optical system satisfies the following conditional expression (8). Conditional expression (8) will be described with reference to FIG. 7 and FIG. 8. FIG. 7 shows a diagram in which the optical path is expanded to become a straight optical path for easy understanding. FIG. 8 shows an enlarged view of the prism Pr portion. Here, k is a natural number from 1 to 10. That is, k=1, 2, 3, 4, 5, 6, 7, 8, 9, 10. Point PHk is a point on the maximum effective image circle on the reduction side whose height from the optical axis Z is k times the radius Imax of the maximum effective image circle. Position Pk is a position where a light ray that emanates from point PHk toward the enlargement side and passes through the center of the aperture stop St intersects with the optical axis Z on the enlargement side of the intermediate image MI. Position Pmax is a position of positions Pk where the air-equivalent distance from position Pist is the longest. And, DifP is a distance on the optical axis from position Pist to position Pmax. The sign of DifP is positive for the distance on the reduction side and negative for the distance on the enlargement side with respect to the position Pist. If the projection optical system is a variable magnification optical system, DifP is the value at the wide-angle end. Conditional formula (8) is, so to speak, an equation that specifies the ratio between the pupil aberration and the maximum image height. By making sure that the corresponding value of conditional formula (8) is not equal to or less than the lower limit, it is possible to prevent the overall length of the optical system from becoming too long. By making sure that the corresponding value of conditional formula (8) is not equal to or more than the upper limit, it is possible to prevent the lens on the most enlargement side from becoming too large. -3 <DifP / Imax<-0.2 (8)

[0072] In order to obtain better characteristics, it is more preferable that the lower limit of conditional expression (8) be set to -2.5, and it is more preferable that the upper limit of conditional expression (8) be set to -0.5.

[0073] As an example, in Fig. 7 and Fig. 8, the position Pist in the projection optical system of Fig. 1 is indicated by a two-dot chain line, and the position Pmax is indicated by a dashed line. Note that Fig. 7 and Fig. 8 show these positions in the optical axis direction. Fig. 7 and Fig. 8 also show ten light rays Ry1, ..., Ry10 that originate from a point PHk, which is a point on the maximum effective image circle on the reduction side whose height from the optical axis Z is k times the radius Imax of the maximum effective image circle, and pass through the center of the aperture stop St toward the enlargement side. Note that in Fig. 7, only the points PH1 and PH10 of the point PHk are labeled to avoid complication of the figure. In the projection optical system of Fig. 1, the positions Pist and Pmax are located inside a prism Pr, which is an optical path deflection member.

[0074] Furthermore, in relation to the above-mentioned DifP, it is preferable that the projection optical system satisfies the following conditional expression (9). Conditional expression (9) is, so to speak, an expression that specifies the ratio between the pupil aberration and the space in which the optical path deflection member is disposed. Conditional expression (9) makes it possible to suppress the diameter of the light beam in the optical path deflection member. By making sure that the corresponding value of conditional expression (9) is not equal to or less than the lower limit, it is possible to suppress an increase in the size of the lens on the most enlargement side. By making sure that the corresponding value of conditional expression (9) is not equal to or more than the upper limit, it is possible to ensure a space for passing the light beam whose optical path has been bent. 0.4<|DifP / Dfr|<0.7 (9)

[0075] In order to obtain better characteristics, it is more preferable that the lower limit of condition (9) be set to 0.45, and it is more preferable that the upper limit of condition (9) be set to 0.6.

[0076] It is preferable that the projection optical system satisfies the following conditional expression (10). Conditional expression (10) is, so to speak, an expression that specifies the ratio between the pupil aberration and the thickness of the prism Pr converted into air. By making sure that the corresponding value of conditional expression (10) is not equal to or smaller than the lower limit, it is possible to prevent the lens on the most enlargement side from becoming large. By making sure that the corresponding value of conditional expression (10) is not equal to or larger than the upper limit, it is possible to ensure a space for passing the light beam whose optical path has been bent. 0.7<|DifP / (Dpr / Npr)|<1.8 (10)

[0077] In order to obtain better characteristics, it is more preferable that the lower limit of condition (10) be set to 0.75, and it is more preferable that the upper limit of condition (10) be set to 1.2.

[0078] Note that the example shown in Fig. 1 is just one example, and various modifications are possible within the scope of the gist of the technology of the present disclosure. For example, the number of lenses and the shape of the lenses included in each optical system may be different from those in the example of Fig. 1. In the example of Fig. 1, all optical elements having power are refractive elements, but the projection optical system of the present disclosure may include a diffractive optical element.

[0079] The light path deflection surface may be a surface of a reflecting mirror. In this case, it is advantageous for weight reduction. The reflecting mirror may be a metal mirror or a dielectric multilayer mirror. The number of light path deflection surfaces included in the projection optical system can be set arbitrarily. The angle at which the light path deflection surface bends the light path is advantageous in terms of manufacturing if it is 90 degrees, but it may be other than 90 degrees. Note that the above "90 degrees" includes an error that is practically acceptable in the technical field to which the technology of the present disclosure belongs. The error can be set to a range of, for example, -1 degree or more and +1 degree or less.

[0080] The above-mentioned preferable configurations and possible configurations, including the configurations relating to the conditional expressions, can be arbitrarily combined, and it is preferable that they are appropriately and selectively adopted according to the required specifications.

[0081] As an example, a preferred embodiment of the present disclosure is a projection optical system that projects an image on the reduced side onto the enlarged side, does not include a reflective surface having power, and is composed of, in order along an optical path from the enlargement side to the reduction side, a first optical system G1 and a second optical system G2, an intermediate image MI is formed between the first optical system G1 and the second optical system G2, the first optical system G1 includes an optical path deflection surface that bends the optical path, and satisfies the above conditional formula (1).

[0082] Next, examples of the projection optical system of the present disclosure will be described with reference to the drawings. Note that the reference symbols attached to the cross-sectional views of each example are used independently for each example to avoid the explanation and the drawings becoming complicated due to the increase in the number of digits of the reference symbols. Therefore, even if common reference symbols are attached in the drawings of different examples, they do not necessarily have the same configuration.

[0083] [Example 1] The configuration of the projection optical system of the first embodiment and a cross-sectional view of the light beam are shown in FIG. 1. The method of illustration and the configuration are as described above, so some of the overlapping explanations will be omitted here. The projection optical system of the first embodiment is composed of a first optical system G1 and a second optical system G2 in order along the optical path from the enlargement side to the reduction side, and an intermediate image MI is formed between the first optical system G1 and the second optical system G2. The first optical system G1 includes a prism Pr inside. The prism Pr has a reflecting surface Prs, which functions as an optical path deflection surface that bends the optical path by 90 degrees. The second optical system G2 includes five lens groups, and three of the lens groups move while changing the interval between the lens groups adjacent to each other when changing the magnification. The second optical system G2 includes a plane mirror Mr that bends the optical path by 90 degrees.

[0084] For the projection optical system of Example 1, basic lens data is shown in Tables 1A and 1B, specifications and variable surface spacing in Table 2, and aspheric coefficients in Table 3. In order to avoid making one table too long, the basic lens data is shown in two tables, Table 1A and Table 1B. Table 1A shows the first optical system G1, and Table 1B shows the second optical system G2.

[0085] The table of basic lens data is written as follows. The Sn column shows the surface numbers when the surface on the most enlargement side is the first surface and the numbers increase by one toward the reduction side. However, the surface number column for the surface corresponding to the reflecting surface Prs is filled in with "Prs", and the surface number column for the surface corresponding to the plane mirror Mr is filled in with "Mr". The surface number column for the surface corresponding to the aperture stop St is filled in with the surface number and "(St)". The R column shows the radius of curvature of each surface. The D column shows the surface distance on the optical axis between each surface and its adjacent surface on the reduction side. The Nd column shows the refractive index for the d-line of each component. The νd column shows the Abbe number of each component based on the d-line. The ER column shows the maximum effective radius of each surface. The AH column shows the height from the optical axis Z of the axial marginal ray B0m of each surface. The value shown in the AH column is the maximum value over the entire magnification range.

[0086] In the basic lens data table, the sign of the radius of curvature of the surface with a convex shape facing the enlargement side is positive, and the sign of the radius of curvature of the surface with a convex shape facing the reduction side is negative. In the basic lens data table, the symbol DD[ ] is used for the variable surface spacing when varying magnification, and the surface number on the enlargement side of this spacing is entered in the [ ] in the D column.

[0087] Table 2 shows the zoom ratio Zr, absolute focal length |f|, back focal length Bf in air equivalent distance, F-number FNo., maximum total angle of view 2ω, and variable surface spacing based on the d-line. [°] in the 2ω column indicates that the unit is degrees. In Table 2, the columns labeled "Wide" and "Tele" show the values ​​for the wide-angle end and telephoto end states, respectively.

[0088] In the basic lens data, the aspheric surface numbers are marked with an *, and the paraxial radius of curvature value is given in the aspheric radius of curvature column. In Table 3, the Sn row shows the aspheric surface numbers, and the KA and Am (m = 3, 4, 5, 6, ..., 20) rows show the numerical values ​​of the aspheric coefficients for each aspheric surface. The numerical values ​​of the aspheric coefficients in Table 3, "E±n" (n: integer), are expressed as "×10 ±n " KA and Am are aspheric coefficients in the aspheric equation expressed below. Zd = C × h 2 / {1+(1-KA×C 2 ×h 2 ) 1 / 2}+ΣAm×h m however, Zd: Aspheric depth (the length of the perpendicular line drawn from a point on the aspheric surface at height h to a plane perpendicular to the optical axis Z where the apex of the aspheric surface is in contact) h: Height (distance from optical axis Z to lens surface) C: Reciprocal of paraxial curvature radius KA, Am: Aspheric coefficients In the aspheric surface formula, Σ means the summation with respect to m.

[0089] In the data in each table, the angle unit is degrees and the length unit is mm (millimeters), but since the optical system can be used with proportional enlargement or reduction, other appropriate units can be used. Also, in each table shown below, values ​​are rounded to a certain number of decimal places.

[0090] [Table 1A]

[0091] [Table 1B]

[0092] [Table 2]

[0093] [Table 3]

[0094] FIG. 9 shows each aberration diagram of the projection optical system of Example 1 when the projection distance is 1.55 m (meters). The projection distance is the distance on the optical axis from the projection surface to the lens surface on the most enlarged side. From the left, FIG. 9 shows spherical aberration, astigmatism, distortion aberration, and lateral chromatic aberration. In the spherical aberration diagram, the aberrations related to the d-line, C-line, and F-line are shown by solid lines, long dashed lines, and short dashed lines, respectively. In the astigmatism diagram, the aberrations related to the d-line in the sagittal direction are shown by solid lines, and the aberrations related to the d-line in the tangential direction are shown by short dashed lines. In the distortion aberration diagram, the aberrations related to the d-line are shown by solid lines. In the lateral chromatic aberration diagram, the aberrations related to the C-line and F-line are shown by long dashed lines and short dashed lines, respectively. In the spherical aberration diagram, the value of the F-number is shown after "FNo.=". In the other aberration diagrams, the value of the maximum half angle of view is shown after "ω=".

[0095] The symbols, meanings, description methods, and illustration methods of each piece of data related to the above-mentioned Example 1 are basically the same in the following Examples unless otherwise specified, so duplicated explanations will be omitted below.

[0096] [Example 2] A cross-sectional view of the configuration of the projection optical system of Example 2 and the light beam is shown in Fig. 10. A cross-sectional view of the optical path of the projection optical system of Example 2 is shown in Fig. 11. The projection optical system of Example 2 is composed of a first optical system G1 and a second optical system G2, in that order along the optical path from the enlargement side to the reduction side, and an intermediate image MI is formed between the first optical system G1 and the second optical system G2.

[0097] The first optical system G1 is made up of, in order along the optical path from the enlargement side to the reduction side, a front group G1F, a prism Pr, and a rear group G1R. The front group G1F is made up of lenses L1a-L1d, in order along the optical path from the enlargement side to the reduction side. The rear group G1R is made up of lenses L1e-L1n, in order along the optical path from the enlargement side to the reduction side. The internal reflecting surface Prs of the prism Pr functions as an optical path deflection surface that bends the optical path by 90 degrees. The focusing group is made up of lenses L1g-L1l.

[0098] The second optical system G2 is composed of, in order from the enlargement side to the reduction side along the optical path, a second A lens group G2A, a plane mirror Mr, a second B lens group G2B, a second C lens group G2C, a second D lens group G2D, and a second E lens group G2E. The second A lens group G2A is composed of a lens L2a. The second B lens group G2B is composed of lenses L2b to L2e. The second C lens group G2C is composed of lenses L2f to L2h, an aperture stop St, and lenses L2i to L2j. The second D lens group G2D is composed of lenses L2k to L2m. The second E lens group G2E is composed of a lens L2n. During magnification change, the 2A lens group G2A and the 2E lens group G2E are fixed with respect to the display surface Sim, and the 2B lens group G2B, the 2C lens group G2C, and the 2D lens group G2D move along the optical axis Z while changing the spacing between adjacent lens groups. The plane mirror Mr functions as an optical path deflection surface that bends the optical path by 90 degrees.

[0099] For the projection optical system of Example 2, basic lens data is shown in Tables 4A and 4B, specifications and variable surface spacing are shown in Table 5, aspheric coefficients are shown in Table 6, and each aberration diagram is shown in Fig. 12. Each aberration diagram is for a projection distance of 1.55 m (meters).

[0100] [Table 4A]

[0101] [Table 4B]

[0102] [Table 5]

[0103] [Table 6]

[0104] [Example 3] A cross-sectional view of the configuration of the projection optical system of Example 3 and the light beam is shown in Fig. 13. A cross-sectional view of the optical path of the projection optical system of Example 3 is shown in Fig. 14. The projection optical system of Example 3 is composed of a first optical system G1 and a second optical system G2, in that order along the optical path from the enlargement side to the reduction side, and an intermediate image MI is formed between the first optical system G1 and the second optical system G2.

[0105] The first optical system G1 is made up of, in order along the optical path from the enlargement side to the reduction side, a front group G1F, a prism Pr, and a rear group G1R. The front group G1F is made up of lenses L1a-L1d, in order along the optical path from the enlargement side to the reduction side. The rear group G1R is made up of lenses L1e-L1n, in order along the optical path from the enlargement side to the reduction side. The internal reflecting surface Prs of the prism Pr functions as an optical path deflection surface that bends the optical path by 90 degrees. The focusing group is made up of lenses L1g-L1l.

[0106] The second optical system G2 is composed of, in order from the enlargement side to the reduction side along the optical path, a 2A lens group G2A, a plane mirror Mr, a 2B lens group G2B, a 2C lens group G2C, a 2D lens group G2D, a 2E lens group G2E, and a 2F lens group G2F. The 2A lens group G2A is composed of a lens L2a. The 2B lens group G2B is composed of lenses L2b to L2e. The 2C lens group G2C is composed of lenses L2f to L2g. The 2D lens group G2D is composed of a lens L2h, an aperture stop St, and lenses L2i to L2j. The 2E lens group G2E is composed of lenses L2k to L2m. The 2F lens group G2F is composed of a lens L2n. During magnification change, the 2A lens group G2A and the 2F lens group G2F are fixed with respect to the display surface Sim, and the 2B lens group G2B, the 2C lens group G2C, the 2D lens group G2D, and the 2E lens group G2E move along the optical axis Z while changing the intervals between adjacent lens groups. The plane mirror Mr functions as an optical path deflection surface that bends the optical path by 90 degrees.

[0107] For the projection optical system of Example 3, basic lens data is shown in Tables 7A and 7B, specifications and variable surface spacing is shown in Table 8, aspheric coefficients are shown in Table 9, and each aberration diagram is shown in Fig. 15. Each aberration diagram is for a projection distance of 1.55 m (meters).

[0108] [Table 7A]

[0109] [Table 7B]

[0110] [Table 8]

[0111] [Table 9]

[0112] [Example 4] A cross-sectional view of the configuration of the projection optical system of Example 4 and the light beam is shown in Fig. 16. A cross-sectional view of the optical path of the projection optical system of Example 4 is shown in Fig. 17. The projection optical system of Example 4 is composed of a first optical system G1 and a second optical system G2, in that order along the optical path from the enlargement side to the reduction side, and an intermediate image MI is formed between the first optical system G1 and the second optical system G2.

[0113] The first optical system G1 is made up of, in order along the optical path from the enlargement side to the reduction side, a front group G1F, a prism Pr, and a rear group G1R. The front group G1F is made up of lenses L1a-L1e along the optical path from the enlargement side to the reduction side. The rear group G1R is made up of lenses L1f-L1o along the optical path from the enlargement side to the reduction side. The internal reflecting surface Prs of the prism Pr functions as an optical path deflection surface that bends the optical path by 90 degrees. The focusing group is made up of lenses L1h-L1m.

[0114] The second optical system G2 is composed of, in order from the enlargement side to the reduction side along the optical path, a second A lens group G2A, a plane mirror Mr, a second B lens group G2B, a second C lens group G2C, a second D lens group G2D, and a second E lens group G2E. The second A lens group G2A is composed of a lens L2a. The second B lens group G2B is composed of lenses L2b to L2e. The second C lens group G2C is composed of lenses L2f to L2g, an aperture stop St, and lenses L2h to L2i. The second D lens group G2D is composed of lenses L2j to L2l. The second E lens group G2E is composed of a lens L2m. During magnification change, the 2A lens group G2A and the 2E lens group G2E are fixed with respect to the display surface Sim, and the 2B lens group G2B, the 2C lens group G2C, and the 2D lens group G2D move along the optical axis Z while changing the spacing between adjacent lens groups. The plane mirror Mr functions as an optical path deflection surface that bends the optical path by 90 degrees.

[0115] For the projection optical system of Example 4, basic lens data is shown in Tables 10A and 10B, specifications and variable surface spacing are shown in Table 11, aspheric coefficients are shown in Table 12, and each aberration diagram is shown in Figure 18. Each aberration diagram is for a projection distance of 1.55 m (meters).

[0116] [Table 10A]

[0117] [Table 10B]

[0118] [Table 11]

[0119] [Table 12]

[0120] Table 13 shows the values ​​corresponding to conditional expressions (1) to (10) and the values ​​of Imax and DifP for the projection optical systems of Examples 1 to 4. The corresponding values ​​of the Examples shown in Table 13 may be used as the upper or lower limits of the conditional expressions to set preferred ranges for the conditional expressions.

[0121] [Table 13]

[0122] The projection optical systems of Examples 1 to 4 have a wide angle of view, with a total angle of view of 100 degrees or more at the wide-angle end. The projection optical systems of Examples 1 to 4 have a small F-number of 2.3 or less at the wide-angle end. Furthermore, the projection optical systems of Examples 1 to 4 are compact, yet achieve high optical performance with various aberrations well corrected.

[0123] In general, projection optical systems are often required to project images with a wide angle of view, and recently, there is also a demand for the ability to project a large screen from close to the screen. For these reasons, the lens on the most enlarged side of the projection optical system has tended to become larger. In contrast, the projection optical system of the present disclosure makes it possible to reduce the size of the lens on the most enlarged side. In addition, the projection optical system of the present disclosure includes an optical path deflection surface, so that it can be configured compactly while having a high degree of freedom in installation.

[0124] Next, a projection display device according to an embodiment of the present disclosure will be described. FIG. 19 is a schematic diagram of a projection display device according to an embodiment of the present disclosure. The projection display device 100 shown in FIG. 19 has a projection optical system 10 according to an embodiment of the present disclosure, a light source 15, and transmissive display elements 11a to 11c as light valves that output optical images corresponding to each color light. The projection display device 100 also has dichroic mirrors 12 and 13 for color separation, a cross dichroic prism 14 for color synthesis, condenser lenses 16a to 16c, and total reflection mirrors 18a to 18c for deflecting the optical path. Note that the projection optical system 10 is shown in a schematic manner in FIG. 19. An integrator is disposed between the light source 15 and the dichroic mirror 12, but is not shown in FIG. 19.

[0125] White light from light source 15 is separated into three colored light beams (green light, blue light, red light) by dichroic mirrors 12 and 13, and then passes through condenser lenses 16a to 16c, where the colored light beams are incident on transmissive display elements 11a to 11c corresponding to the colored light beams, where they are modulated, and then color-synthesized by cross dichroic prism 14, before being incident on projection optical system 10. Projection optical system 10 projects an optical image based on the modulated light modulated by transmissive display elements 11a to 11c onto screen 105.

[0126] FIG. 20 is a schematic diagram of a projection display device according to another embodiment of the present disclosure. The projection display device 200 shown in FIG. 20 has a projection optical system 210 according to an embodiment of the present disclosure, a light source 215, and DMD (Digital Micromirror Device: registered trademark) elements 21a to 21c as light valves that output optical images corresponding to each color light. The projection display device 200 also has TIR (Total Internal Reflection) prisms 24a to 24c for color separation and color synthesis, and a polarization separation prism 25 that separates illumination light and projection light. Note that FIG. 20 shows a schematic diagram of the projection optical system 210. An integrator is disposed between the light source 215 and the polarization separation prism 25, but is not shown in FIG. 20.

[0127] White light from light source 215 is reflected by a reflecting surface inside polarization separation prism 25, and then separated into three colored light beams (green light, blue light, and red light) by TIR prisms 24a-24c. Each colored light beam after separation enters corresponding DMD elements 21a-21c and is modulated, travels again in the opposite direction through TIR prisms 24a-24c and is color-synthesized, then passes through polarization separation prism 25 and enters projection optical system 210. Projection optical system 210 projects an optical image based on the modulated light modulated by DMD elements 21a-21c onto screen 205.

[0128] FIG. 21 is a schematic diagram of a projection display device according to yet another embodiment of the present disclosure. The projection display device 300 shown in FIG. 21 has a projection optical system 310 according to an embodiment of the present disclosure, a light source 315, and reflective display elements 31a to 31c as light valves that output optical images corresponding to the respective color lights. The projection display device 300 also has dichroic mirrors 32 and 33 for color separation, a cross dichroic prism 34 for color synthesis, a total reflection mirror 38 for optical path deflection, and polarization separation prisms 35a to 35c. Note that FIG. 21 shows the projection optical system 310 in a schematic manner. An integrator is disposed between the light source 315 and the dichroic mirror 32, but is not shown in FIG. 21.

[0129] White light from the light source 315 is separated into three colored light beams (green light, blue light, and red light) by the dichroic mirrors 32 and 33. Each colored light beam after separation passes through the polarization separation prisms 35a to 35c, enters the reflective display elements 31a to 31c corresponding to each colored light beam, is modulated, is color-synthesized by the cross dichroic prism 34, and then enters the projection optical system 310. The projection optical system 310 projects an optical image based on the modulated light modulated by the reflective display elements 31a to 31c onto the screen 305.

[0130] Fig. 22 is a schematic diagram of a projection display device according to yet another embodiment of the present disclosure. The projection display device 600 shown in Fig. 22 has a projection optical system 66 according to an embodiment of the present disclosure, a light source 61, and a DMD element 64 as a light valve that outputs an optical image corresponding to each color light. The projection display device 600 also has a color wheel 62, a light guide optical system 63, and a TIR prism 65. Note that in Fig. 22, the projection optical system 66 is illustrated in a schematic manner.

[0131] The color wheel 62 has three color filters of green, blue, and red arranged on its circumference, and as the color wheel 62 rotates, the filters of each color are inserted in sequence onto the optical path. White light from the light source 61 is time-divided into three colored light beams (green light, blue light, and red light) by entering the rotating color wheel 62. After time-dividing, each colored light beam passes through a light-guiding optical system 63 and a TIR prism 65, enters a DMD element 64 and is modulated, and passes through the TIR prism 65 again to enter a projection optical system 66. The projection optical system 66 projects an optical image based on the modulated light modulated by the DMD element 64 onto a screen 67.

[0132] Although the technology of the present disclosure has been described above with reference to the embodiments and examples, the technology of the present disclosure is not limited to the above embodiments and examples, and various modifications are possible. For example, the radius of curvature, surface spacing, refractive index, Abbe number, aspheric coefficient, etc. of each lens are not limited to the values ​​shown in the above examples, and may take other values.

[0133] Furthermore, the projection display device according to the technology of the present disclosure is not limited to the above configuration, and for example, the optical members and light valves used for light beam separation or light beam synthesis can be modified in various ways. The light valve is not limited to a mode in which light from a light source is spatially modulated by an image display element and output as an optical image based on image data, and may be a mode in which light itself output from a self-luminous image display element is output as an optical image based on image data. Examples of the self-luminous image display element include an image display element in which light-emitting elements such as LEDs (Light Emitting Diodes) or OLEDs (Organic Light Emitting Diodes) are two-dimensionally arranged.

[0134] Regarding the above-mentioned embodiments and examples, the following supplementary notes are further disclosed. [Appendix 1] A projection optical system that projects a reduced-side image onto an enlarged side, Does not include a reflective surface having power, The optical system comprises, in order from the enlargement side to the reduction side along the optical path, a first optical system and a second optical system, an intermediate image is formed between the first optical system and the second optical system; the first optical system includes an optical path deflection surface that bends an optical path, The radius of the maximum effective image circle on the reduction side is Imax. The distance on the optical axis from the lens surface on the most enlargement side of the first optical system to the optical path deflection surface is defined as Ddef, When the projection optical system is a variable magnification optical system, Ddef is the value at the wide-angle end, 0.2 <Imax / Ddef<0.7 (1) A projection optical system that satisfies conditional expression (1) expressed as follows: [Appendix 2] The projection optical system described in Appendix 1, wherein the first optical system is composed of, in order along the optical path from the enlargement side to the reduction side, a front group having negative power, an optical path deflection member including the optical path deflection surface, and a rear group having positive power. [Appendix 3] 3. The projection optical system according to claim 2, wherein the front group includes one or more positive lenses. [Appendix 4] 4. The projection optical system according to claim 2, wherein the outermost periphery of the optically effective surface on the most enlarged side of the first optical system is located on the reduction side in the optical axis direction relative to the intersection of the optically effective surface and the optical axis. [Appendix 5] The average Abbe number based on the d-line of all the negative lenses included in the front group is ν When the average Abbe number of all the positive lenses included in the front group based on the d-line is denoted by νpave, 10<νnave-νpave<40 (2) 5. The projection optical system according to claim 2, which satisfies conditional expression (2) shown below. [Appendix 6] The average value of the refractive indexes for the d-line of all the negative lenses included in the front group is Nnave, When the average value of the refractive index for the d line of all the positive lenses included in the front group is Npave, 0.15 <Npave-Nnave<0.45 (3) 6. The projection optical system according to claim 2, which satisfies conditional expression (3) represented by: [Appendix 7] 7. The projection optical system according to claim 2, wherein at least a part of the rear group moves during focusing. [Appendix 8] 8. The projection optical system according to claim 1, wherein the second optical system includes two or more moving groups that move along the optical axis during magnification change. [Appendix 9] 9. The projection optical system according to claim 8, wherein the moving group of the second optical system, which is located closest to the enlargement side, has positive power. [Appendix 10] Dfr is the air-equivalent distance on the optical axis from the surface of the front group closest to the reduction side to the surface of the rear group closest to the enlargement side, When the projection optical system is a variable magnification optical system, Dfr is the value at the wide-angle end, 0.5 <Imax / Dfr<0.9 (4) 8. The projection optical system according to claim 2, which satisfies conditional expression (4) shown below. [Appendix 11] 11. The projection optical system according to claim 1, wherein the optical path deflection surface is a surface of a prism. [Appendix 12] The thickness of the prism along the optical axis is Dpr, If the refractive index of the prism for the d line is Npr, 0.9 <Imax / (Dpr / Npr)<1.3 (5) 12. The projection optical system according to claim 11, which satisfies conditional expression (5) shown below. [Appendix 13] The maximum effective radius of the lens surface on the most enlargement side of the first optical system is ERf. If the maximum value of the maximum effective radius of all the lens surfaces of the projection optical system is ERmax, 0 <ERf / ERmax<0.7 (6) 13. The projection optical system according to claim 1, which satisfies conditional expression (6) shown below. [Appendix 14] AH1 is a maximum value of the height from the optical axis of the on-axis marginal ray on all lens surfaces of the first optical system; When the maximum value of the height from the optical axis of the on-axis marginal ray on all the lens surfaces of the second optical system is AH2, 0 <AH1 / AH2<0.7 (7) 14. The projection optical system according to claim 1, which satisfies conditional expression (7) shown below. [Appendix 15] an aperture stop is included on the reduction side of the intermediate image; a real image of the aperture stop exists inside the first optical system, A position of the real image in the optical axis direction is defined as a first position, When a light ray originates from an arbitrary point within the maximum effective image circle on the reduction side, travels toward the enlargement side, passes through the center of the aperture stop, and intersects with the optical axis on the enlargement side of the intermediate image, the second position is the position farthest from the first position, 15. The projection optical system according to claim 1, wherein an intersection between the optical path deflection surface and the optical axis is located within a range from the first position to the second position in the optical axis direction. [Appendix 16] Let k be a natural number between 1 and 10. On the reduction side, a point PHk is defined as a point whose height from the optical axis is k times the radius of the maximum effective image circle. A position where a light ray originating from the point PHk toward the enlargement side and passing through the center of the aperture stop intersects with the optical axis on the enlargement side of the intermediate image is defined as a position Pk, Among the positions Pk, a position where the air-equivalent distance on the optical axis from the first position is the longest is defined as a third position; The air-equivalent distance from the first position to the third position is defined as DifP, The sign of DifP is such that the distance on the reduction side based on the first position is positive and the distance on the enlargement side is negative. When the projection optical system is a variable magnification optical system, DifP is the value at the wide-angle end, -3 <DifP / Imax<-0.2 (8) 16. The projection optical system according to claim 15, which satisfies conditional expression (8) shown below. [Appendix 17] the first optical system includes, in order along an optical path from the enlargement side to the reduction side, a front group, an optical path deflection member including the optical path deflection surface, and a rear group; Dfr is the air-equivalent distance on the optical axis from the surface of the front group closest to the reduction side to the surface of the rear group closest to the enlargement side, When the projection optical system is a variable magnification optical system, Dfr is the value at the wide-angle end, 0.4<|DifP / Dfr|<0.7 (9) 17. The projection optical system according to claim 16, which satisfies conditional expression (9) shown below. [Appendix 18] 17. The projection optical system according to claim 12, wherein the optical path deflection surface is a surface of a prism. [Appendix 19] The thickness of the prism along the optical axis is Dpr, If the refractive index of the prism for the d line is Npr, 0.7<|DifP / (Dpr / Npr)|<1.8 (10) 19. The projection optical system according to claim 18, which satisfies conditional expression (10) shown below. [Appendix 20] 20. A projection display device comprising the projection optical system according to any one of claims 1 to 19. [Explanation of symbols]

[0135] 2 points 4 intersection 10 Projection optical system 11a to 11c Transmissive display element 12 Dichroic mirror 13 Dichroic mirror 14 Cross dichroic prism 15 light source 16a~16c Condenser lenses 18a~18c Total reflection mirror 21a~21c DMD elements 24a~24c TIR Prism 25 Polarizing beam splitter prism 31a to 31c reflective display element 32 Dichroic mirror 33 Dichroic Mirror 34 Cross dichroic prism 35a~35c Polarizing beam splitter prism 38 Total Reflection Mirror 61 Light source 62 Color Wheel 63 Light guide optical system 64 DMD elements 65 TIR Prism 66 Projection Optical System 67 Screens 100 Projection display device 105 Screen 200 Projection display device 205 Screen 210 Projection optical system 215 Light source 300 Projection display device 305 Screen 310 Projection Optical Systems 315 Light source 600 Projection display device AH1 Maximum AH2 Maximum B0 On-axis luminous flux B0m Axial marginal ray B1 Maximum angle of view luminous flux B2 Light output at maximum angle of view Ddef Distance Dpr Thickness ER Maximum effective radius G1 1st optical system G1F front group G1R rear group G2 2nd optical system G2A 2A lens group G2B 2B lens group G2C 2C lens group G2D 2D lens group G2E 2E lens group G2F 2nd lens group Imax radius L1a~L2n lenses Lx Lens MI intermediate image Mr Plane Mirror PH1 point PH10 points PP Optical Components Pch position Pdef position Pist position Pmax position Pr Prism Prs reflective surface Px position Ry1 ray Ry10 ray Rys rays Sim display surface St Aperture Xa On-axis luminous flux Xb Off-axis luminous flux Xb1 ray Z optical axis

Claims

1. A projection optical system that projects a reduced-side image onto an enlarged side, Does not include a reflective surface having power, The optical system includes, in order from the enlargement side to the reduction side along the optical path, a first optical system and a second optical system, an intermediate image is formed between the first optical system and the second optical system; the first optical system includes an optical path deflection surface that bends an optical path, The radius of the maximum effective image circle on the reduction side is Imax, The distance on the optical axis from the lens surface on the most enlargement side of the first optical system to the optical path deflection surface is defined as Ddef, When the projection optical system is a variable magnification optical system, Ddef is the value at the wide-angle end, 0.2<Imax / Ddef<0.7 (1) A projection optical system that satisfies conditional expression (1) expressed by:

2. 2. The projection optical system according to claim 1, wherein the first optical system comprises, in order along the optical path from the enlargement side to the reduction side, a front group having negative power, an optical path deflection member including the optical path deflection surface, and a rear group having positive power.

3. 3. The projection optical system according to claim 2, wherein the front group includes one or more positive lenses.

4. 3. The projection optical system according to claim 2, wherein an outermost periphery of an optically effective surface on the most enlargement side of the first optical system is located on the reduction side in the optical axis direction from an intersection of the optically effective surface and the optical axis.

5. The average Abbe number based on the d-line of all the negative lenses included in the front group is νnave, When the average value of the Abbe numbers based on the d-line of all the positive lenses included in the front group is ν, 10<νnave−νpave<40 (2) 4. The projection optical system according to claim 3, which satisfies conditional expression (2) expressed as follows:

6. The average value of the refractive indexes for the d line of all the negative lenses included in the front group is Nnave, When the average value of the refractive index for the d line of all the positive lenses included in the front group is Npave, 0.15<Npave−Nnave<0.45 (3) 4. The projection optical system according to claim 3, which satisfies conditional expression (3) expressed as follows:

7. 3. The projection optical system according to claim 2, wherein at least a portion of the rear group moves during focusing.

8. The projection optical system according to claim 1 , wherein the second optical system includes two or more moving groups that move along the optical axis during magnification change.

9. 9. The projection optical system according to claim 8, wherein the moving group of the second optical system, which is located most on the enlargement side, has a positive power.

10. Dfr is the air-equivalent distance on the optical axis from the surface of the front group closest to the reduction side to the surface of the rear group closest to the enlargement side, In the case where the projection optical system is a variable magnification optical system, Dfr is the value at the wide-angle end, 0.5<Imax / Dfr<0.9 (4) 3. The projection optical system according to claim 2, which satisfies conditional expression (4) expressed as follows:

11. 3. The projection optical system according to claim 2, wherein the optical path deflecting surface is a surface of a prism.

12. The thickness of the prism along the optical axis is Dpr, When the refractive index of the prism with respect to the d line is Npr, 0.9<Imax / (Dpr / Npr)<1.3 (5) 12. The projection optical system according to claim 11, which satisfies conditional expression (5) expressed as follows:

13. The maximum effective radius of the lens surface on the most enlargement side of the first optical system is ERf, If the maximum value of the maximum effective radius of all the lens surfaces of the projection optical system is ERmax, 0<ERf / ERmax<0.7 (6) 2. The projection optical system according to claim 1, which satisfies conditional expression (6) expressed as follows:

14. AH1 is the maximum value of the height from the optical axis of the on-axis marginal ray on all the lens surfaces of the first optical system; When the maximum value of the height from the optical axis of the on-axis marginal ray on all the lens surfaces of the second optical system is AH2, 0<AH1 / AH2<0.7 (7) 2. The projection optical system according to claim 1, which satisfies conditional expression (7) expressed as follows:

15. an aperture stop is included on the reduction side of the intermediate image; a real image of the aperture stop exists inside the first optical system, A position of the real image in the optical axis direction is defined as a first position, When a light ray originates from an arbitrary point within the maximum effective image circle on the reduction side, travels toward the enlargement side, passes through the center of the aperture stop, and intersects with the optical axis on the enlargement side of the intermediate image, the second position is the position farthest from the first position, 2. The projection optical system according to claim 1, wherein the intersection of the optical path deflection surface and the optical axis is located within a range from the first position to the second position in the optical axis direction.

16. Let k be a natural number between 1 and 10. A point PHk is defined as a point on the maximum effective image circle on the reduction side whose height from the optical axis is k times the radius of the maximum effective image circle, A position where a light ray originating from the point PHk toward the enlargement side and passing through the center of the aperture stop intersects with the optical axis on the enlargement side of the intermediate image is defined as a position Pk. Among the positions Pk, a position where the air-equivalent distance on the optical axis from the first position is the longest is defined as a third position; An air-equivalent distance from the first position to the third position is defined as DifP, The sign of DifP is positive when the distance is reduced from the first position and negative when the distance is enlarged. When the projection optical system is a variable magnification optical system, DifP is the value at the wide-angle end, -3<DifP / Imax<-0.2 (8) 16. The projection optical system according to claim 15, which satisfies conditional expression (8) expressed as follows:

17. the first optical system includes, in order along an optical path from an enlargement side to a reduction side, a front group, an optical path deflection member including the optical path deflection surface, and a rear group; Dfr is the air-equivalent distance on the optical axis from the surface of the front group closest to the reduction side to the surface of the rear group closest to the enlargement side, In the case where the projection optical system is a variable magnification optical system, Dfr is the value at the wide-angle end, 0.4<|DifP / Dfr|<0.7 (9) 17. The projection optical system according to claim 16, which satisfies conditional expression (9) expressed as follows:

18. 17. The projection optical system according to claim 16, wherein the optical path deflecting surface is a surface of a prism.

19. The thickness of the prism along the optical axis is Dpr, When the refractive index of the prism with respect to the d line is Npr, 0.7<|DifP / (Dpr / Npr)|<1.8 (10) 19. The projection optical system according to claim 18, which satisfies conditional expression (10) expressed as follows:

20. A projection display device comprising the projection optical system according to any one of claims 1 to 19.

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