Projection optical system unit, projection optical system, and projection optical apparatus

A projection optical system satisfies θ1≥15 (deg) and 3<EP/Ym<7. θ1 is a maximum inclination angle of the reflective surface of each of the micromirrors with respect to the line normal to the image display surface; EP is an entrance pupil distance of the projection optical system; and Ym is a maximum distance in a plane from an optical axis to a point on the image display surface, the plane being a plane in which a light ray propagating from a center of the image display surface toward the projection surface through a center of an aperture stop of the projection optical system exists, the optical axis being an axis shared by a largest number of the plurality of lenses of the projection optical system, the point corresponding to an image on the projection surface.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application No. 2018-050356, filed on Mar. 19, 2018 in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein.

BACKGROUND

Technical Field

Embodiments of the present disclosure relate to a projection optical system unit, a projection optical system, and a projection optical apparatus.

Description of the Related Art

In recent years, image display elements that project an image generated by a digital micromirror device (DMD) or a liquid crystal panel onto a screen are widely used. In particular, recently, demand for front-projection projectors that can display a large image at a short projection distance has been increasing.

In order to achieve a very short projection distance with a small size, projectors employing a curved mirror have been proposed. Some of the projectors can achieve a very short projection distance by employing a curved mirror in combination with a refractive optical system.

SUMMARY

However, existing technologies have a problem in that, even if it is possible to realize a very short projection distance with a projection optical system, reduction in size and increase in brightness (increase in efficiency) of a very short projection distance projector do not sufficiently proceed.

The embodiments of the present disclosure have been made in consideration of the above circumstances, and an object of the present invention is to provide a projection optical system, a projection optical system unit, and a projection optical apparatus, each of which has a very short projection distance, a small size, and high efficiency.

A projection optical system according to a first aspect of the invention, for use in a projection optical apparatus, includes a reflective image display element that includes a plurality of micromirrors. The image display element has an image display surface on which the plurality of micromirrors are two-dimensionally arranged and is configured to change an angle of a reflective surface of each of the micromirrors with respect to a line normal to the image display surface to form an image. The projection optical system includes a plurality of lenses and an aperture stop and is configured to magnify and project an image formed by the image display element onto a projection surface. The projection optical system satisfies θ1≥15 (deg) and 3<EP/Ym<7, where θ1 is a maximum inclination angle of the reflective surface of each of the micromirrors with respect to the line normal to the image display surface; EP is an entrance pupil distance of the projection optical system; and Ym is a maximum distance in a plane from an optical axis to a point on the image display surface, the plane being a plane in which a light ray propagating from a center of the image display surface toward the projection surface through a center of the aperture stop of the projection optical system exists, the optical axis being an axis shared by a largest number of the plurality of lenses of the projection optical system, the point corresponding to an image on the projection surface.

A projection optical system unit according to a second aspect of the invention includes: a reflective image display element that includes a plurality of micromirrors, the image display element having an image display surface on which the plurality of micromirrors are two-dimensionally arranged and being configured to change an angle of a reflective surface of each of the micromirrors with respect to a line normal to the image display surface to form an image; and the projection optical system according to the first aspect.

A projection optical apparatus according to a third aspect of the invention, for magnifying and projecting an image onto a screen, includes the projection optical system according to the first aspect.

DETAILED DESCRIPTION

Hereinafter, embodiments of a projection optical system unit, a projection optical system, and a projection optical apparatus will be described in detail with reference to the drawings.

In order to realize a smaller optical system having high efficiency (high brightness), it is effective to reduce the F-number of a projection optical system and to make the projection optical system into a non-telecentric optical system. It is possible to use a non-telecentric optical system as a projection optical system by using a digital micromirror device (DMD) as an image display element. However, the following problems occur in a case of realizing reduction in size and increase in efficiency of a very short projection distance projector.

First, a DMD operates in such a way that micromirrors of pixels are inclined as the pixels are switched between ON and OFF and light reflected by micromirrors in the ON-state is guided to the projection optical system. However, by simply reducing the F-number of the projection optical system in order to realize increase in efficiency, light reflected by micromirrors in the OFF-state is also guided to the projection optical system when the inclination angles of the micromirrors are small, and a problem arises in that the contrast of a projected image considerably decreases.

Second, the size of the projection optical system can be further reduced by reducing the entrance pupil distance of a pupil on the DMD side. However, regarding increase in efficiency, by simply increasing the inclination angles of micromirrors to solve the first problem, the incident angle of illumination light on a cover glass of the DMD increases, transmittance considerably decreases, and efficiency decreases.

The inventors have focused on the relationship between the inclination angles of micromirrors and the entrance pupil distance in realizing reduction in size and increase in efficiency (increase in brightness) of an optical system. The inventors have examined this relationship in various ways and found appropriate settings that have not been disclosed as existing technology. Hereinafter, the structure of an optical system including the appropriate settings will be described.

First Embodiment

Specific structures of a projection optical system unit according to a first embodiment will be described.

FIGS. 1A and 1Billustrate an example of a projection optical system unit according to the first embodiment.FIG. 1Aillustrates an example of the structure of a projection optical system unit1including an image display element10and a projection optical system25.FIG. 1Bis an enlarged view of the image display element10illustrated inFIG. 1Aand a plurality of lenses11included in a refractive optical system21of the projection optical system25. The image display element10includes an image forming portion LV, which is, for example, a light valve such as a DMD, a transmissive liquid crystal panel, or a reflective liquid crystal panel. The image forming portion LV is a “portion that forms an image to be projected”. If the image display element10is an element that does not emit light, such as a DMD, image information formed in the image forming portion LV is illuminated with illumination light from an illumination optical system. Specific structures of the illumination optical system will be described below.

Hereinafter, it is supposed that the image display element10is a DMD, and an “element that does not have a function of emitting light” will be described. A projection optical system unit according to the present embodiment is not limited to a unit of this type. A “self-luminous element that has a function of causing a generated image to emit light” or a light valve other than a DMD may be used. As long as the projection optical system unit includes a combination of the image display element10and the projection optical system25, the combination may further include an illumination device, a mirror, a dustproof glass, and the like, which will be described below.

As illustrated inFIGS. 1A and 1B, a parallel plate CG is disposed near the image forming portion LV (seeFIG. 1B) of the image display element10. The parallel plate CG is a light transmissive plate and is a cover glass (seal glass) of the image forming portion LV. The projection optical system25(seeFIG. 1A) magnifies an image formed by the image forming portion LV and projects the image onto a screen. The projection optical system25includes, in order from the image forming portion LV (reduction side) toward the screen (magnification side), the refractive optical system21, including the plurality of lenses11, and a reflective optical system24, including a reflective surface having power. The plurality of lenses11illustrated inFIGS. 1A and 1Bhave an aperture stop S. Light from the image forming portion LV (including an upper ray101and a chief ray102), which has passed through the parallel plate CG, passes through the plurality of lenses11along a light path whose example is illustrated inFIGS. 1A and 1B. Then, the light passes through the refractive optical system21and is projected onto a screen via the reflective optical system24that includes a reflecting mirror22and a curved mirror23. The projection optical system unit according to the embodiment has an entrance pupil T at a position illustrated inFIGS. 1A and 1B.

It is desirable that the aperture stop S be interposed between at least two lenses. By disposing the aperture stop S in this way, a back focus can be reduced while maintaining a sufficient pupil distance, and the reduction in back focus contributes to reduction is size. By disposing a lens on the image display element10side of the aperture stop S, the upper ray101can controlled, and correction of aberration, such as coma correction, can be efficiently performed.

The meanings of symbols used in the present embodiment are as follows.

R: radius of curvature (for an aspheric surface, paraxial radius of curvature)

D: surface distance

K: conic constant of aspheric surface

Here, a relational expression for an aspheric shape and a relational expression for a free surface shape will be described. An aspheric shape is represented by the following known formula:

where X is the aspheric amount in the optical axis direction, C is the reciprocal of the paraxial radius of curvature (paraxial curvature), H is the height from the optical axis, K is the conic constant, and Ai is the i-th order aspheric constant.

The aspheric shape is specified by giving the paraxial radius of curvature, the conic constant, and the aspheric coefficients to this formula.

The free-form surface shape is represented by the following known formula:

where X is the free-form surface amount in the optical axis direction, C is the reciprocal of the paraxial radius of curvature (paraxial curvature), H is the height from the optical axis, K is the conic constant, and Cj is the free-form surface coefficient.

The free-form surface shape is specified by giving the paraxial radius of curvature, the conic constant, and the free-form surface coefficients to this formula.

InFIGS. 1A and 1B, a Z-axis, a Y-axis, and an X-axis are set. The Z-axis extends in a direction normal to the image forming portion LV. The Z-axis is parallel to an axis (referred to as the “optical axis”) that is shared by a large number of optical devices (the majority of axially symmetric lenses) of the refractive optical system including the plurality of lenses11. The X-axis, the Y-axis, and the Z-axis are perpendicular to each other. A rotational direction illustrated inFIG. 1Bwill be referred to as the +α direction.

FIG. 2is a schematic view of the image display element10. A large number of micromirrors are disposed in the image forming portion LV of the image display element10. The micromirrors are two-dimensionally and regularly arranged on a flat surface (image display surface) of the image display element10. Each of the micromirrors creates an ON-state or an OFF-state in accordance with the inclination of the micromirror. That is, the image display element10is a reflective image display element that forms an image by operating the micromirrors.

FIG. 2is an enlarged view of a micromirror100, which is one of a large number of micromirrors. InFIG. 2, the maximum inclination angle θ1 of the micromirror100is defined as the maximum angle of an axis B with respect to an axis A, where the axis A is an axis extending in a direction normal to the image display surface of the image forming portion LV (normal line axis), and the axis B is an axis extending in a direction normal to the reflective surface of the micromirror100. That is, the maximum inclination angle θ1 is the maximum inclination angle of the axis B with respect to the axis A when the micromirror is in the ON-state.

The inventors have found by experiment that it is desirable that the maximum inclination angle θ1 satisfy the following conditional expression.
θ1≥15[deg]  (1)

The conditional expression (1) represents the optimal range of the maximum inclination angle θ1 of each micromirror. If the maximum inclination angle θ1 is smaller than the lower limit of the conditional expression (1), it is not possible to reduce the F-number of the projection optical system and to efficiently use light from a light source. Therefore, the optimal range of the maximum inclination angle θ1 is given by the conditional expression (1).

Next, conditions on EP/Ym will be described. The image forming portion LV is shifted in the Y-axis direction with respect to the optical axis that is shared by the plurality of lenses11of the refractive optical system.

FIG. 3illustrates the positional relationship between the image forming portion and the optical axis.FIG. 3illustrates an XY-plane (defined as “plane C”) in which a light ray propagating from the center LV0of the image forming portion LV (accordingly, the center of the image display surface) through the center of the aperture stop S toward a projection surface exists. Ym denotes the maximum distance from the optical axis to a point on the image display surface corresponding to an image on the projection surface.

As illustrated inFIG. 1B, a pupil of the projection optical system25on the image forming portion LV side is the entrance pupil T, and EP denotes the distance from the image forming portion LV to the entrance pupil T along the optical axis.

FIG. 4is a graph representing an example of the relationship between EP/Ym and the maximum incident angle of a light ray on the parallel plate CG. Values of the data change in accordance with conditions such as evenness of illumination on the image forming portion LV, the shift amount of each micromirror100, and the like. Therefore,FIG. 4illustrates an example the relationship between these. When a general antireflection film is used for the parallel plate CG, transmittance of light sharply decreases as the incident angle of light on the parallel plate CG exceeds 65 degrees (deg). Therefore, it is desirable to set EP/Ym at a value such that the incident angle becomes 65 deg or smaller. Based on the data represented inFIG. 4and the like, the inventors have found that it is desirable that EP/Ym satisfy the following conditional expression.
3<EP/Ym<7  (2)

The conditional expression (2) represents an appropriate range of the entrance pupil distance. If EP/Ym becomes smaller than the lower limit value of the conditional expression (2), the incident angle of light from each micromirror100to the parallel plate CG increases, reflectance at the surface of the parallel plate CG increases, and efficiency decreases. If EP/Ym becomes larger than the upper limit value, although efficiency increases because the incident angle of illumination light on the parallel plate CG decreases, the size of the projection optical system increases.

Thus, when the conditional expressions (1) and (2) are simultaneously satisfied, a small and high-efficiency projection optical apparatus can be realized, and it is possible to reduce size and increase efficiency even if the projection distance is very short.

It is more desirable that the range of EP/Y satisfy the following conditional expression.
4<EP/Y<7  (2′)

Second Embodiment

Next, a projection optical apparatus according to a second embodiment will be described. The projection optical apparatus includes the projection optical system unit according to the first embodiment. Therefore, in the second embodiment, descriptions of portions that are same as those of the first embodiment will be omitted, as appropriate, and, differences from the first embodiment will be mainly described.

FIG. 5illustrates an example of a projection optical apparatus according to the second embodiment.FIG. 5illustrates the internal structure of the projection optical apparatus.

A projection optical apparatus2illustrated inFIG. 5includes, in a housing20, an illumination optical system LS, the image display element10, the parallel plate CG, the projection optical system25, and a dustproof glass26. The projection optical system25includes the refractive optical system21, and the reflective optical system24including a plane mirror (reflective surface)22and a concave mirror23. In the refractive optical system21, a lens arrangement in a case of projecting a 100-inch image is illustrated, and a light path in this case is illustrated.

Referring toFIGS. 6 to 8, an incident direction of illumination light on the image forming portion LV of the image display element10will be described. As described in the first embodiment, the optical elements of the refractive optical system21share the optical axis, and the position of the image forming portion LV is shifted in the Y-axis direction as viewed from the optical axis (seeFIG. 3). The direction of illumination light with respect to the image forming portion LV is considered to be as follows.

FIG. 6illustrates an example of the incident direction of illumination light with respect to the image forming portion LV in the XY-plane.FIG. 6illustrates the structure of a so-called “bottom illumination” structure, with which illumination light is incident in a direction perpendicular to a long side LV1of the image forming portion LV.

FIG. 7illustrates another example of the incident direction of illumination light with respect to the image forming portion LV in the XY-plane.FIG. 7illustrates a so-called “side illumination” structure, with which illumination light is incident in a direction parallel to the long side LV1of the image forming portion LV.

FIG. 8illustrates an incident direction of illumination light in the YZ-plane. A surface vertex Q is defined as a vertex of a surface, which is nearest to the image forming portion LV side, of an optical element of the illumination optical system LS having power. θ2 is defined as the angle between a straight line connecting the surface vertex Q and the center LV0of the image forming portion LV and the axis A in the direction normal to the image forming portion LV.

The inventors have found by experiment that it is further desirable that θ2 satisfy the following conditional expression.
θ2>30[deg]  (3)

When illumination light that illuminates the image forming portion LV is incident in a direction perpendicular to or parallel to the long side LV1of the image forming portion LV, if the angle θ2 satisfies the conditional expression (3), light reflected by each micromirror in the ON-state can be efficiently made to enter the entrance pupil T. For example, the size of the entirety of the optical system can be reduced, by allowing illumination light to be incident in the direction perpendicular to the long side LV1of the image forming portion LV. The thickness of the entirety of the optical system can be reduced, by allowing illumination light to be incident in the direction parallel to the long side LV1of the image forming portion LV.

The inventors have found by experiment that it is further desirable that the following conditional expression be satisfied:
0.35<U/BF<0.85  (4)

where BF is the distance between the vertex of a lens surface that is nearest to the image forming portion LV and the image forming portion LV along the optical axis (seeFIG. 9), and U is the outside diameter of a lens that has the lens surface nearest to the image forming portion LV.

If the value of U/BF is smaller than the lower limit of the conditional expression (4), the amount of light reflected by the lens barrel increases, efficiency decreases, evenness of brightness on the screen SC is impaired, and temperature characteristics deteriorate because the lens barrel is heated. If the value of U/BF is larger than the upper limit of the conditional expression (4), although the amount of light taken into the image forming portion increases, interference between illumination light and the lens barrel becomes inevitable, efficiency decreases, and evenness of brightness on the screen SC is impaired. Therefore, it is desirable that the value of U/BF satisfy the conditional expression (4). It is more desirable that the value of U/BF satisfy the following conditional expression.
0.5<U/BF<0.8  (4′)

The inventors have found by experiment that it is desirable that the following conditional expression be satisfied.
NA>0.17  (5)

Light emitted from a light source propagates by way of the illumination optical system LS, is reflected by the image forming portion LV, passes through the parallel plate CG, and enters the entrance pupil T in the refractive optical system21. It is desirable that the entrance pupil T be located away from the image forming portion LV by a lens. By increasing the distance between the entrance pupil T and the image forming portion LV, the incident angle of light on the parallel plate CG can be reduced, and decrease of efficiency can be suppressed. It is also possible to reduce the lens diameter.

It is more desirable that the value of NA satisfy the following condition.
NA>0.18  (5′)

By increasing the numerical aperture of the projection optical system as in this conditional expression, light from the light source can be efficiently guided to the screen SC.

Because the present embodiment includes, in order from the image forming portion LV side, the refractive optical system21and at least one mirror having power, it is possible to project a large image at a very short distance.

The inventors have found by experiment that it is more desirable that the following conditional expression be satisfied:
TR<0.5  (6)

where TR (=(projection distance)/(lateral width W)), where the projection distance is defined as the distance from an optical surface that is nearest to the magnification side to the screen SC as illustrated inFIG. 5and the lateral width W is defined as the lateral width of the screen SC as illustrated inFIG. 10.

If the value of TR satisfies the conditional expression (6), it is possible to perform projection from a very short distance. It is more desirable that the value of TR satisfy the following conditional expression.
TR<0.35  (6′)

It is further desirable that the mirror having power be a concave mirror. By using a concave mirror, it is possible to perform projection from a very short distance.

It is further desirable that the concave mirror have a free-form surface shape. When the concave mirror has a free-form surface shape, it is possible to increase freedom in design and to reduce size.

It is further desirable that the dustproof glass26be disposed between the mirror having power and the screen SG, and reflection characteristics with respect to the incident angle on a coat of the dustproof glass26differ among regions. In this case, transmittance of light that is to reach a lower part of the screen is improved.

The inventors have found by experiment that it is further desirable that the following conditional expression be satisfied:
0.5<Lcg/Lm<1.8  (7)

where, as illustrated inFIG. 11, Lcg is the length of the dustproof glass26in the X-axis direction, and Lm is the length of the reflective surface having power in the X-axis direction.

If the value of Lcg/Lm is larger than the upper limit of the conditional expression (7), although it becomes easy to make the characteristics of the coat differ among regions, the size of the optical system increases. If the value of Lcg/Lm is smaller than the lower limit of the conditional expression (7), although the size of the optical system can be reduced, it becomes difficult to make the characteristics of the coat differ among regions. Therefore, it is desirable that the value of Lcg/Lm satisfy the conditional expression (7).

The projection optical apparatus includes at least one reflective surface between the refractive optical system21and the reflective surface having power. By bending the light path in this say, it is possible to make the light path to overlap, to alleviate conditions for interference between a light ray and an optical member, and to reduce size.

It is further desirable that a lens group, which is nearest to the image forming portion LV side, of the refractive optical system21have positive refractive power.

In the projection optical apparatus2, although the refractive optical system21, one plane mirror22, and one concave mirror23are included in a system, it possible to further increase mirrors. Increasing mirrors makes the structure complex and leads to increase in size and costs. Therefore, in consideration of reduction in size and costs, it is desirable to keep the number of mirrors small.

In the projection optical apparatus2, the micromirror100of the image display element10each enter the ON-state or the OFF-state based on image information to two-dimensionally modulate the intensity of illumination light from the illumination optical system LS. The light from the micromirrors100passes through the parallel plate CG and forms a projection light beam of object light. The projection light beam passes the refractive optical system21, the reflective surface22, the concave mirror23, and the dustproof glass26in this order and forms an image, and a magnified projection image is projected onto the screen SC.

The projection light beam, which has passed through the refractive optical system21, is magnified and projected onto the screen SC while receiving, for example, the following effect. An intermediate image that is conjugate to an image formed in the image forming portion LV is formed as a spatial image on a light path on the image forming portion LV side of the concave mirror23. Although the intermediate image is formed as a curved image in the present structure, the intermediate image may be formed as a planar image in accordance with the structure. The intermediate image is magnified and projected by the concave mirror23, which is disposed nearest to the magnification side, and is projected onto the screen SC as a projection image.

In the present embodiment, the plane mirror22is disposed between the reflective surface having power (the concave mirror23) and the refractive optical system21to form an optical system in which the light path is bent. In such an optical system, it is desirable to avoid interference between light reflected from the plane mirror22and the refractive optical system21. Because a lens is disposed on the image forming portion LV side of the aperture stop S, the upper ray101can be cut, interference between light reflected by the plane mirror22and the refractive optical system21can be avoided, and size can be further reduced.

In the present embodiment, the concave mirror23having a free-form surface is used as an example. The term “free-form surface” refers to an anamorphic surface such that curvature in the X-axis direction differs among points whose Y coordinates are the same and curvature in the Y-axis direction differs among points whose X coordinates are the same. Although the intermediate image includes field curvature and distortion, it is possible to correct field curvature and distortion by using the concave mirror23having a free-form surface. Use of the concave mirror23having a free-form surface reduces load of aberration correction on the lens system, increases freedom in design, and is advantages for reduction in size.

In the present embodiment, the dustproof glass26is disposed between the concave mirror23having a free-form surface and the screen SC as an example. On the surface of the dustproof glass26, a coat having transmission characteristics that differ among regions through which light passes is formed. The dustproof glass26, which is planar glass, may have curvature or may be an optical element having power, such as a lens. The angle of the dustproof glass26may be any angle. For example, the dustproof glass26may be disposed perpendicular to the optical axis of the refractive optical system21or may be inclined with respect to the optical axis.

Next, an example of the lens structure of the refractive optical system21and main parameters of the projection optical apparatus will be described.

FIG. 12illustrates an example of the lens structure of the refractive optical system21and an example of the lens arrangement in accordance with a focus.FIG. 12illustrates a lens arrangement (200) when focusing on the long-distance side (100 inches) is performed, and a lens arrangement (201) when focusing on the short-distance side (80 inches) is performed.FIG. 12also illustrates the image display element10in order to illustrate the positional relationship between the image display element10and the lenses of the refractive optical system21.

The refractive optical system21illustrated inFIG. 12includes, in order from the image forming portion LV side of the image display element10toward the image magnification side, a first lens group (I) having positive refractive power, a second lens group (II) having positive refractive power, a third lens group (III) having negative refractive power, and a fourth lens group (IV) having negative refractive power.

In order to perform focusing in response to variation in projection distance, for example, when focusing from the long-distance side toward the short-distance side, the positive second lens group (II), the negative third lens group (III), and the negative fourth lens group (IV) move toward the image forming portion LV side. The first lens group (I) is fixed in place relative to the image forming portion LV.

The positive first lens group (I) includes the following lenses, in order from the image forming portion LV side: a biaspheric biconvex lens211whose convex surface having a stronger power faces the image forming portion LV side, a negative meniscus lens212whose convex surface faces the image forming portion LV side, an aperture stop S, a cemented lens including a negative meniscus lens213whose convex surface faces the image forming portion LV side and a biconvex lens214whose convex surface having a stronger power faces the image forming portion LV side, a negative meniscus lens215whose convex surface faces the image forming portion LV side, a biaspheric biconvex lens216whose convex surface having a stronger power faces the magnification side, a biconcave lens217whose concave surface having a stronger power faces the magnification side, a cemented lens including a positive meniscus lens218whose convex surface faces the magnification side and a negative meniscus lens219whose convex surface faces the magnification side, a biconcave lens220whose concave surface having a stronger power faces the image forming portion LV side, and a biconvex lens221whose convex surface having a stronger power faces the magnification side.

The positive second lens group (II) includes one biconvex lens231whose convex surface having a stronger power faces the image forming portion LV side.

The negative third lens group (III) includes a negative meniscus lens241whose convex surface faces the magnification side, and a biaspheric negative meniscus resin lens242whose convex surface faces the image forming portion LV side.

The negative fourth lens group (IV) includes a biaspheric negative meniscus resin lens251whose convex surface faces the magnification side.

The first lens group (I), the second lens group (II), the third lens group (III), and the fourth lens group (1V) are included in the refractive optical system21. The curvature of the concave mirror23, having a free-form surface, of the projection optical apparatus2(seeFIG. 5) is 0.

Data tables are presented below. The tables present data in order of surface numbers from the image forming portion LV side. Surface numbers with “*” indicate aspheric surfaces, and a surface number with “**” indicates a free-form surface.

Table 7 presents the positional coordinates of the concave mirror23having a free-form surface from the vertex of a lens that is positioned nearest to the reflective surface22in an in-focus state in which a projected image is the largest. Rotation is represented by the angle between a surface normal and the optical axis.

First Modification of Second Embodiment

A modification of the second embodiment will be described. In the following description, differences from the second embodiment will be mainly described, and elements common to the second embodiment and the modification will not be illustrated and described, as appropriate.

FIG. 13illustrates an example of a projection optical apparatus according to a first modification of the second embodiment.FIG. 13illustrates the internal structure of the projection optical apparatus. In the refractive optical system21, a lens arrangement and a light path in a case of 100 inches are illustrated. The first modification differs from the projection optical apparatus according to the second embodiment in the lens structure of the refractive optical system21.

FIG. 14illustrates an example of the lens structure of the refractive optical system21according to the first modification and an example of the lens arrangement in accordance with a focus.FIG. 14illustrates a lens arrangement200when focusing on the long-distance side (100 inches) is performed, and a lens arrangement201when focusing on the short-distance side (80 inches) is performed.

The lens structure illustrated inFIG. 14, including a positive first lens group (I), a positive second lens group (II), a negative third lens group (III), and a negative fourth lens group (IV), will be described.

The positive first lens group (I) includes the following lenses, in order from the image forming portion LV side: a biaspheric biconvex lens311whose convex surface having a stronger power faces the image forming portion LV side, a negative meniscus lens312whose convex surface faces the image forming portion LV side, an aperture stop S, a cemented lens including a negative meniscus lens313whose convex surface faces the image forming portion LV side and a plano-convex lens314whose convex surface faces the image forming portion LV side, a negative meniscus lens315whose convex surface faces the image forming portion LV side, a biaspheric biconvex lens316whose convex surface having a stronger power faces the magnification side, a negative meniscus lens317whose convex surface faces the image forming portion LV side, a cemented lens including a negative meniscus lens318whose convex surface faces the magnification side and a negative meniscus lens319whose convex surface faces the magnification side, a biconcave lens320whose concave surface having a stronger power faces the image forming portion LV side, and a biconvex lens321whose convex surface having a stronger power faces the magnification side.

The positive second lens group (II) includes one biconvex lens331whose convex surface having a stronger power faces the image forming portion LV side.

The negative third lens group (III) includes a negative meniscus lens341whose convex surface faces the magnification side, and a biaspheric negative meniscus resin lens342whose convex surface faces the image forming portion LV side.

The negative fourth lens group (IV) includes a biaspheric negative meniscus resin lens351whose convex surface faces the magnification side.

The curvature of the concave mirror23, having a free-form surface, of the projection optical apparatus2(seeFIG. 13) is 0.

Data tables are presented below. The tables present data in order of surface numbers from the image forming portion LV side. Surface numbers with “*” indicate aspheric surfaces, and a surface number with “**” indicates a free-form surface.

Table 14 presents the positional coordinates of the concave mirror23having a free-form surface from the vertex of a lens that is positioned nearest to the reflective surface22in an in-focus state in which a projected image is the largest. Rotation is represented by the angle between a surface normal and the optical axis.

Second Modification of Second Embodiment

Another modification of the second embodiment will be described.

FIG. 15illustrates an example of a projection optical apparatus according to a second modification of the second embodiment.FIG. 16illustrates an example of the lens structure of the refractive optical system21according to the second modification and an example of the lens arrangement in accordance with a focus. The second modification differs from the first modification in the lens diameter of the refractive optical system21of the projection optical apparatus.

InFIG. 16, the positive first lens group (I) includes the following lenses, in order from the image forming portion LV side: a biaspheric biconvex lens411whose convex surface having a stronger power faces the image forming portion LV side, a negative meniscus lens412whose convex surface faces the image forming portion LV side, an aperture stop S, a cemented lens including a negative meniscus lens413whose convex surface faces the image forming portion LV side and a plano-convex lens414whose convex surface faces the image forming portion LV side, a negative meniscus lens415whose convex surface faces the image forming portion LV side, a biaspheric biconvex lens416whose convex surface having a stronger power faces the magnification side, a negative meniscus lens417whose convex surface faces the image forming portion LV side, a cemented lens including a negative meniscus lens418whose convex surface faces the magnification side and a negative meniscus lens419whose convex surface faces the magnification side, a biconcave lens420whose concave surface having a stronger power faces the image forming portion LV side, and a biconvex lens421whose convex surface having a stronger power faces the magnification side.

The positive second lens group (II) includes one biconvex lens431whose convex surface having a stronger power faces the image forming portion LV side.

The negative third lens group (III) includes a negative meniscus lens441whose convex surface faces the magnification side, and a biaspheric negative meniscus resin lens442whose convex surface faces the image forming portion LV side.

The negative fourth lens group (IV) includes a biaspheric negative meniscus resin lens451whose convex surface faces the magnification side.

In the figures, the NA of the refractive optical system21is 0.238, and the outside diameters of lenses are changed in accordance with the NA. In other respects, the second modification is the same as the first modification of the second embodiment. Further descriptions of the second modification, which are the same as those of the first modification of the second embodiment, will be omitted.

Table 15 presents examples of the values of parameters in the second embodiment, the first modification, and the second modification. Table 16 presents the values of the conditional expressions when these values of the parameters are input.

The values of the conditional expressions (1) to (7) for the second embodiment, the first modification, and the second modification, which are listed in Table 16, are within the ranges of the conditional expressions (1) to (7) described above. Accordingly, by setting the parameters at the values presented in Table 15, it is possible to reduce size and increase efficiency. Tables 16 and 15 also include values to be set for a projection optical unit and a projection optical system. By setting the projection optical unit and the projection optical system as listed in Table 15, it is possible to reduce size and increase efficiency.

As described above, when an appropriate pupil distance and inclination of micromirrors satisfy the conditional expressions in the projection optical system unit, the projection optical system, and the projection optical apparatus described in the embodiments and the modifications, it is possible to reduce size and increase efficiency.

The embodiments and the modifications are examples of a projection optical system unit, a projection optical system, and a projection optical apparatus. The structures of a projection optical system unit, a projection optical system, and a projection optical apparatus are not limited to these examples.

In particular, the shapes of elements and values are examples, and may be changed, as appropriate, within the gist described in the embodiments and the modifications.