PROJECTION SYSTEM AND PROJECTOR

A projection system includes a first and second optical system arranged from a reduction side toward an enlargement side. The second optical system includes an optical element having a concave reflection surface and a first lens having negative power, the optical element and first lens arranged from reduction side toward enlargement side. The projection system satisfies the following expressions:  TR≤0.3   (1)  35≤(OAL/imy)×(LL/imy)×TR×(1/NA)≤60   (2) OAL represents an axial inter-surface spacing from an image formation device to the reflection surface, imy represents a first distance from an optical axis to the largest image height at the image formation device, LL represents the largest radius of the first lens, TR represents a throw ratio, and NA represents the numerical aperture of the image formation device.

The present application is based on, and claims priority from JP Application Serial Number 2022-006175, filed Jan. 19, 2022, the disclosure of which is hereby incorporated by reference herein in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to a projection system and a projector.

2. Related Art

JP-A-2020-34690 describes a projector in which a projection system enlarges a projection image displayed at an image display device and projects the enlarged projection image onto a screen. The projection system includes a first refractive optical system, a reflective optical system, and a second refractive optical system sequentially arranged from the reduction side toward the enlargement side. The first refractive optical system includes a plurality of refractive lenses. The reflective optical system includes a concave mirror and reflects beams from the first refractive optical system toward the side facing the image display device in directions that intersect with the optical axis of the first refractive optical system. The second refractive optical system is formed of a single refractive lens. The refractive lens is an enlargement-side lens located at a position closest to the enlargement side in the projection system. Beams from the concave mirror enter the enlargement-side lens in directions that intersect with the optical axis of the enlargement-side lens.

Out of the examples of the projection system disclosed in JP-A-2020-34690, the projection system having the shortest projection distance has a projection distance of 257.6 mm. The enlargement-side lens of the thus configured projection system has an effective radius of 79.7 mm. The thus configured projection system further has a throw ratio of 0.154.

A projector including a projection system having a smaller throw ratio has a shorter projection distance over which the projector projects an enlarged image having a predetermined size. A projection system incorporated in a projector used indoors or at similar locations therefore needs to have a short focal length that provides a throw ratio smaller than or equal to 0.3.

A projection system having a shorter focal length tends to produce larger amounts of aberrations at the enlargement side. It is therefore necessary to increase the effective radius of the enlargement-side lens, through which the beams from the concave mirror obliquely pass, to allow the enlargement-side lens to correct the beams on an image height basis. When the size of the enlargement-side lens is increased to provide a sufficient effective radius, however, the amount of protrusion by which the enlargement-side lens protrudes radially from the first optical axis of the first refractive optical system increases, resulting in an increase in the diameter of the entire projection system. The size of the projector that incorporates the projection system is therefore not reduced.

SUMMARY

To solve the problem described above, a projection system according to an aspect of the present disclosure is a projection system for enlarging a projection image formed by an image formation device disposed in a reduction-side conjugate plane and projecting the enlarged image in an enlargement-side conjugate plane. The projection system includes a first optical system and a second optical system sequentially arranged from the reduction side toward the enlargement side. The first optical system includes a diaphragm. The second optical system includes an optical element having a concave reflection surface and a first lens having negative power, the optical element and the first lens sequentially arranged from the reduction side toward the enlargement side. An intermediate image conjugate with the reduction-side conjugate plane and the enlargement-side conjugate plane is formed between the first optical system and the second optical system. A portion at the reduction side of the first optical system forms a telecentric portion. The projection system satisfies all Conditional Expressions (1) and (2) below,

where OAL represents an axial inter-surface spacing from the image formation device to the reflection surface, imy represents a first distance from an optical axis to a largest image height at the image formation device, LL represents a largest radius of the first lens, TR represents a throw ratio that is a quotient of division of a projection distance by a second distance from the optical axis to a largest image height of the enlarged image, and NA represents a numerical aperture of the image formation device.

A projector according to another aspect of the present disclosure includes the projection system described above and the image formation device that forms a projection image in the reduction-side conjugate plane of the projection system.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

An optical system and a projector according to an embodiment of the present disclosure will be described below with reference to the drawings.

Projector

FIG.1shows a schematic configuration of a projector including a projection system3according to the embodiment of the present disclosure. A projector1includes an image formation unit2, which generates a projection image to be projected onto a screen S, the projection system3, which enlarges the projection image and projects the enlarged image onto the screen S, and a controller4, which controls the operation of the image formation unit2, as shown inFIG.1.

Image Formation Unit and Controller

The image formation unit2includes a light source10, a first optical integration lens11, a second optical integration lens12, a polarization converter13, and a superimposing lens14. The light source10is formed, for example, of an ultrahigh-pressure mercury lamp or a solid-state light source. The first optical integration lens11and the second optical integration lens12each include a plurality of lens elements arranged in an array. The first optical integration lens11divides a luminous flux from the light source10into a plurality of luminous fluxes. The lens elements of the first optical integration lens11focus the luminous flux from the light source10in the vicinity of the lens elements of the second optical integration lens12.

The polarization converter13converts the light from the second optical integration lens12into predetermined linearly polarized light. The superimposing lens14superimposes images of the lens elements of the first optical integration lens11on one another in a display area of each of liquid crystal panels18R,18G, and18B, which will be described later, via the second optical integration lens12.

The image formation unit2further includes a first dichroic mirror15, a reflection mirror16, a field lens17R, and the liquid crystal panel18R. The first dichroic mirror15reflects R light, which is part of the beams incident via the superimposing lens14, and transmits G light and B light, which are part of the beams incident via the superimposing lens14. The R light reflected off the first dichroic mirror15travels via the reflection mirror16and the field lens17R and is incident on the liquid crystal panel18R. The liquid crystal panel18R is an image formation element. The liquid crystal panel18R modulates the R light in accordance with an image signal to form a red projection image.

The image formation unit2further includes a second dichroic mirror21, a field lens17G, and the liquid crystal panel18G. The second dichroic mirror21reflects the G light, which is part of the beams via the first dichroic mirror15, and transmits the B light, which is part of the beams via the first dichroic mirror15. The G light reflected off the second dichroic mirror21passes through the field lens17G and is incident on the liquid crystal panel18G. The liquid crystal panel18G is an image formation element. The liquid crystal panel18G modulates the G light in accordance with an image signal to form a green projection image.

The image formation unit2further includes a relay lens22, a reflection mirror23, a relay lens24, a reflection mirror25, a field lens17B, the liquid crystal panel18B, and a cross dichroic prism19. The B light having passed through the second dichroic mirror21travels via the relay lens22, the reflection mirror23, the relay lens24, the reflection mirror25, and the field lens17B and is incident on the liquid crystal panel18B. The liquid crystal panel18B is an image formation element. The liquid crystal panel18B modulates the B light in accordance with an image signal to form a blue projection image.

The liquid crystal panels18R,18G, and18B surround the cross dichroic prism19so as to face three sides of the cross dichroic prism19. The cross dichroic prism19is a prism for light combination and produces a projection image that is the combination of the light modulated by the liquid crystal panel18R, the light modulated by the liquid crystal panel18G, and the light modulated by the liquid crystal panel18B.

The projection system3enlarges the combined projection image from the cross dichroic prism19and projects the enlarged projection image onto the screen S.

The control unit4includes an image processor6, to which an external image signal, such as a video signal, is inputted, and a display driver7, which drives the liquid crystal panels18R,18G, and18B based on image signals outputted from the image processor6.

The image processor6converts the image signal inputted from an external apparatus into image signals each containing grayscales and other factors of a color corresponding to the image signal. The display driver7operates the liquid crystal panels18R,18G, and18B based on the color projection image signals outputted from the image processor6. The image processor6thus causes the liquid crystal panels18R,18G, and18B to display projection images corresponding to the image signals.

Projection System

The projection system3will next be described. The screen S is disposed in the enlargement-side conjugate plane of the projection system3, as shown inFIG.1. The liquid crystal panels18R,18G, and18B are disposed in the reduction-side conjugate plane of the projection system3.

Examples 1 to 4 will be described below as examples of the configuration of the projection system3incorporated in the projector1.

FIG.2is a beam diagram showing beams passing through a projection system3A according to Example 1. In the beam diagrams for the projection systems3according to Examples 1 to 4, the liquid crystal panels18R,18G, and18B are referred to as a liquid crystal panel18. The projection system3A according to the present example is formed of a first optical system31and a second optical system32sequentially arranged from the reduction side toward the enlargement side, as shown inFIG.2. The second optical system32is disposed on an optical axis N of the first optical system31.

In the following description, three axes perpendicular to one another are called axes X, Y, and Z for convenience. The axis Z coincides with the optical axis N of the first optical system31. The direction along the optical axis N is an axis-Z direction. The axis-Z direction toward the side where the first optical system31is located is called a first direction Z1, and the axis-Z direction toward the side where the second optical system32is located is called a second direction Z2. The axis Y extends along the screen S. The upward-downward direction is an axis-Y direction, with one side of the axis-Y direction called an upper side Y1and the other side of the axis-Y direction called a lower side Y2. The axis X extends in the width direction of the screen.

The first optical system31is a refractive optical system. The first optical system31is formed of 17 lenses L1to L17. The lenses L1to L17are arranged in the presented order from the reduction side toward the enlargement side. A diaphragm51is disposed between the lens L7and the lens L8.

The lens L6has aspherical shapes at opposite sides. The lens L9has aspherical shapes at opposite sides. The lens L16(third lens) has aspherical shapes at opposite sides. The lens L17(second lens) has aspherical shapes at opposite sides. The lens L2and the lens L3are bonded to each other into a cemented doublet L21. The lens L4and the lens L5are bonded to each other into a cemented doublet L22. The lens L11and the lens L12are bonded to each other into a cemented doublet L23. The lens L14and the lens L15are bonded to each other into a cemented doublet L24.

The second optical system32includes an optical element33and a first lens34. The optical element33and the first lens34are arranged in the presented order from the reduction side toward the enlargement side. The optical element33has a reflection surface40, which faces the reduction side. The reflection surface40has a concave shape recessed in the second direction Z2. The reflection surface40has an aspherical shape. The reflection surface40is located at the lower side Y2of the optical axis N, as shown inFIG.2. The reflection surface40is formed by providing the outer surface, in the first direction Z1, of the optical element33with a reflection coating layer (reflection layer). The reflection surface40reflects light at the surface, facing in the direction Z1, of the optical element33.

The first lens34is located at a position shifted from the optical element33in the first direction Z1and disposed at the upper side Y1of the optical axis N. The first lens34has negative power. The first lens34has a convex enlargement-side surface and a concave reduction-side surface. The first lens34has aspherical shapes at opposite sides.

The liquid crystal panel18of the image formation unit2is disposed in the reduction-side conjugate plane of the projection system3A. The screen S is disposed in the enlargement-side conjugate plane of the projection system3A.

The liquid crystal panel18forms a projection image in an image formation plane perpendicular to the optical axis N of the first optical system31. The liquid crystal panel18is disposed in a position offset from the optical axis N of the first optical system31toward the upper side Y1. The projection image is therefore formed in a position offset from the optical axis N toward the upper side Y1.

The beams from the liquid crystal panel18pass through the first optical system31and the second optical system32in the presented order. Between the first optical system31and the second optical system32, the beams pass through the lower side Y2of the optical axis N. The beams are therefore directed through the second optical system32toward the reflection surface40. The beams having reached the reflection surface40are deflected back in the first direction Z1towards the upper side Y1. The beams deflected back by the reflection surface40cross the optical axis N toward the upper side Y1and travels toward the first lens34. The beams passing through the first lens34are widened by the first lens34and reach the screen S.

The lens L17of the first optical system31is disposed between the reflection surface40and the first lens34in the direction of the optical axis N. An intermediate image30is formed between the lens L17and the reflection surface40.

In the projection system3A, the portion at the reduction side of the first optical system31is a telecentric portion. The term “telecentric” means that the central beam of each luminous flux traveling between the first optical system31and the liquid crystal panel18disposed in the reduction-side conjugate plane is parallel or substantially parallel to the optical axis of the projection system.

The projection system3A has a changeable projection distance. When the projection distance is changed, eight lenses of the first optical system31, the lenses L10to L17, are moved along the optical axis N for focusing. In the focusing, the lenses L10, L11, and L12are moved as a unit. In the focusing, the lenses L13, L14, and L15are moved also as a unit.

Data on the projection system3A are listed below,

NA0.3125imy11.7 mmscy1463 mmPD283.1 mmM125TR0.194OAL203 mmLL47.8 mm
where NA represents the numerical aperture of the liquid crystal panel18, imy represents a first distance from the optical axis N to the largest image height at the liquid crystal panel18, scy represents a second distance from the optical axis N to the largest image height of the enlarged image projected on the screen S, PD represents a projection distance that is the distance from the first lens34to the screen S, M represents a projection magnification that is the quotient of division of the second distance by the first distance, TR represents a throw ratio that is the quotient of division of the projection distance by the second distance, OAL represents the axial inter-surface spacing from the liquid crystal panel18to the reflection surface40, and LL represents the largest radius of the first lens34.

Data on the lenses of the projection system3A are listed below. The surfaces of the lenses are numbered sequentially from the reduction side toward the enlargement side. Reference characters are given to the liquid crystal panel, the dichroic prism, the lenses, the optical element, the first lens, and the screen. Data labeled with a surface number that does not correspond to any of the liquid crystal panel, the dichroic prism, the lenses, the optical element, the first lens, and the screen is dummy data. Reference character R represents the radius of curvature. Reference character D represents the axial inter-surface spacing. Reference character C represents the aperture radius, and twice the aperture radius is the diameter of the lens surface. Reference characters R, D, and C are each expressed in millimeters.

The projection system3A according to the present example has a changeable projection distance selected from a standard distance, a short distance shorter than the standard distance, and a long distance longer than the standard distance. When the projection distance is changed, eight lenses of the first optical system31, the lenses L10to L17, are moved along the optical axis N for focusing. When the focusing is performed so as to change the projection distance from the short distance to the long distance, the lenses L10, L11, and L12move along the optical axis N toward the enlargement side. In the same focusing operation, the lenses L13, L14, and L15move along the optical axis N toward the enlargement side. In the same focusing operation, the lens L16moves along the optical axis N toward the enlargement side. In the same focusing operation, the lens L17moves along the optical axis N toward the reduction side.

The table below shows the variable spacings 1, 2, 3, 4, 5, and 6 at the projection distances where the focusing is performed. The variable spacing 1 is the axial inter-surface spacing between the lens L9and the lens L10. The variable spacing 2 is the axial inter-surface spacing between the lens L12and the lens L13. The variable spacing 3 is the axial inter-surface spacing between the lens L15and the lens L16. The variable spacing 4 is the axial inter-surface spacing between the lens L16and the lens L17. The variable spacing 5 is the axial inter-surface spacing between the lens L17and the reflection surface40. The variable spacing 6 is the projection distance.

The aspherical coefficients are listed below.

The projection system3A according to the present example satisfies all Conditional Expressions (1) and (2) below,

where OAL represents the axial inter-surface spacing from the liquid crystal panel18to the reflection surface40, imy represents the first distance from the optical axis N to the largest image height at the liquid crystal panel18, LL represents the largest radius of the first lens34, TR represents the throw ratio, which is the quotient of division of the projection distance by the second distance from the optical axis N to the largest image height of the enlarged image projected on the screen S, and NA represents the numerical aperture of the liquid crystal panel18.

Furthermore, it is more preferable that the projection system3A satisfies all Conditional Expressions (1) and (2′) below.

In the present example, the values described above are listed below.

TR=0.194 is provided from the table shown above, so that Conditional Expression (1) is satisfied. (OAL/imy)×(LL/imy)×TR×(1/NA)=44 is satisfied, so that Conditional Expression (2) is satisfied.

Effects and Advantages

The projection system3A according to the present example enlarges a projection image formed by the liquid crystal panel18disposed in the reduction-side conjugate plane and projects the enlarged projection image in the enlargement-side conjugate plane. The projection system3A according to the present example includes the first optical system31and the second optical system32sequentially arranged from the reduction side toward the enlargement side. The first optical system31includes the diaphragm51. The second optical system32includes the optical element33, which has the concave reflection surface40, and the first lens34, which has negative power, sequentially arranged from the reduction side toward the enlargement side. The intermediate image30conjugate with the reduction-side conjugate plane and the enlargement-side conjugate plane is formed between the first optical system31and the second optical system32. The portion at the reduction side of the first optical system31form a telecentric portion.

The projection system3A according to the present example satisfies all Conditional Expressions (1) and (2) below,

where OAL represents the axial inter-surface spacing from the liquid crystal panel18to the reflection surface40, imy represents the first distance from the optical axis N to the largest image height at the liquid crystal panel18, LL represents the largest radius of the first lens34, TR represents the throw ratio, which is the quotient of division of the projection distance by the second distance from the optical axis N to the largest image height of the enlarged image projected on the screen S, and NA represents the numerical aperture of the liquid crystal panel18.

The projection system3A according to the present example satisfies Conditional Expression (1). The projection system3therefore has a short focal length. A projection system having a shorter focal length tends to produce larger amounts of aberrations at the enlargement side. It is therefore necessary to increase the effective radius of the enlargement-side lens, through which the beams from the concave mirror obliquely pass, to allow the enlargement-side lens to correct the beams on an image height basis. When the size of the enlargement-side lens is increased to provide a sufficient effective radius, however, the amount of protrusion by which the enlargement-side lens protrudes radially from the first optical axis of the first refractive optical system increase, resulting in an increase in the diameter of the entire projection system.

To solve the problem described above, the projection system3A according to the present example satisfies Conditional Expression (2). Suppression of the amount of protrusion by which the first lens34protrudes radially from the optical axis N can therefore suppress an increase in the diameter of the entire projection system, whereby the size of the projector that incorporates the projection system3A can be reduced. Furthermore, the effective diameter of the first lens34within which the beams can be corrected on an image height basis can be ensured, while the amount of protrusion by which the first lens34protrudes radially from the optical axis N is suppressed. That is, when (OAL/imy)×(LL/imy)×TR×(1/NA) in Conditional Expression (2) is smaller than the lower limit, the axial inter-surface spacing from the liquid crystal panel18to the reflection surface40and the lens diameter of the first lens34become too small relative to TR and 1/NA, so that it is difficult to correct the beams on an image height basis, and sufficient resolution of the projection system3A is unlikely to be provided. Even when a lens that can provide sufficient resolution can be designed, the lens has a problem of low mass producibility because the lens needs to be manufactured with high molding precision. When (OAL/imy)×(LL/imy)×TR×(1/NA) in Conditional Expression (2) is greater than the upper limit, the axial inter-surface spacing from the liquid crystal panel18to the reflection surface40and the lens diameter of the first lens34become excessively large. That is, the amount of protrusion by which the first lens34protrudes radially from the optical axis N increases, resulting in an increase in the diameter of the entire projection system. The size of the projector that incorporates the projection system therefore increases.

Example 3 described in JP-A-2020-34690, which is a related-art literature, will now be examined as Comparable Example. The projection system according to Comparable Example includes a first refractive optical system, a reflective optical system, and a second refractive optical system sequentially arranged from the reduction side toward the enlargement side. The first refractive optical system includes a plurality of refractive lenses. The reflective optical system includes a concave mirror and reflects beams from the first refractive optical system toward the side facing the image display device in directions that intersect with the optical axis of the first refractive optical system. The second refractive optical system is formed of a single refractive lens. The refractive lens is an enlargement-side lens located at a position closest to the enlargement side in the projection system. Beams from the concave mirror enter the enlargement-side lens in directions that intersect with the optical axis of the enlargement-side lens. Data on Comparable Example are listed below.

In Comparable Example, TR=0.154. The projection system according to Comparable Example therefore satisfies Conditional Expression (1). In Comparable Example, however, (OAL/imy)×(LL/imy)×TR×(1/NA)=72. The projection system according to Comparable Example therefore does not satisfy Conditional Expression (2). Therefore, when the throw ratio is fixed in the present example and Comparative Example, the effective radius of the enlargement-side lens of the projection system according to Comparative Example is greater than the effective radius of the first lens of the projection system3A according to the present example. That is, the entire projection system according to Comparative Example has a diameter greater than that of the entire projection system3A according to the present example.

In the projection system3A according to the present example, the reflection surface40is provided with a reflection coating layer (reflection layer). In the configuration in which the reflection surface is provided inside the optical element33, the accuracy of the shape of the enlargement-side lens surface, at which the reflection surface is provided, depends on the accuracy of the shape of the optical element33. That is, to improve the accuracy of the shape of the enlargement-side lens surface, the accuracy of the shape of the reduction-side lens surface also needs to be improved. In contrast, since the reflection surface40of the projection system3A according to the present example is provided at the outer surface of the optical element33, only the accuracy of the shape of the outer surface of the optical element33needs to be improved. The accuracy of the shape of the reflection surface40in the present example is therefore readily improved as compared with that in the configuration in which the reflection surface is provided inside the optical element33.

In the configuration in which the reflection surface is provided inside the optical element33, the optical element33is formed, and a reflection coating layer is then formed at the enlargement-side lens surface of the optical element33to form the reflection surface. In this process, a support film layer needs to be provided between the reflection coating layer and the enlargement-side lens surface. Although the thus provided support film layer causes the reflection coating layer to be unlikely to peel off the enlargement-side lens surface, the interposed support film layer tends to lower the optical performance of the reflection surface, so that the optical performance of the reflection surface tends to vary in the manufacturing process. In contrast, in the projection system3A according to the present example, the support film layer is provided on the side opposite from the reflection surface of the reflection coating layer, whereby the optical performance of the reflection surface40is unlikely to deteriorate. Stable optical performance of the reflection surface40is therefore likely to be achieved during the manufacture of the optical element33.

In the projection system3A according to the present example, the lens L17(second lens) disposed at a position closest to the enlargement side in the first optical system31is formed as a lens separate from the first lens34. The lens L17is disposed between the reflection surface40and the first lens34in the direction of the optical axis N. That is, the lens L17disposed at a position closest to the enlargement side in the first optical system31is disposed inside the second optical system32in the direction of the optical axis N, so that the distance between the lens L17and the reflection surface40decreases. The axial inter-surface spacing from the liquid crystal panel18to the reflection surface40can thus be shortened, whereby the size of the projection system3A can be reduced. Furthermore, the intermediate image30is formed between the lens L17of the first optical system31and the reflection surface40of the second optical system32. When the distance between the lens L17and the reflection surface40thus decreases, a variety of aberrations contained in the intermediate image30are readily corrected on an image height basis.

The first optical system31includes the lens L17(second lens) and the lens L16(third lens), which is disposed adjacent to the lens L17and shifted therefrom toward the reduction side. The lenses L16and L17each have an aspherical shape. In the projection system3A according to the present example, focusing that causes the projection distance to be changed from the short distance to the long distance is performed by moving the lenses L16and L17toward the enlargement side in the direction of the optical axis N. The projection system3A, in which the lenses L16and L17, which correct a variety of aberrations on an image height basis, are moved in the direction of the optical axis N, therefore allows suppression of occurrence of the variety of aberrations during focusing. Furthermore, in a configuration in which a lens having no aspherical shape is moved in the direction of the optical axis N for focusing, an aspherical lens that corrects a variety of aberrations needs to be separately prepared. In contrast, the present example, in which the lenses L16and L17, which move during focusing, each have an aspherical shape, allows reduction in the size of the entire projection system.

The first optical system31further includes the cemented doublets L23and L24at the enlargement side of the diaphragm51. The chromatic aberrations can therefore be corrected well.

FIG.3shows lateral aberrations produced by the projection system3A set at the standard distance.FIG.4shows the spherical aberration, astigmatism, and distortion produced by the projection system3A set at the standard distance.FIG.5shows the spherical aberration, astigmatism, and distortion produced by the projection system3A set at the short distance.FIG.6shows the spherical aberration, astigmatism, and distortion produced by the projection system3A set at the long distance. The projection system3A according to the present example produces an enlarged image having suppressed aberrations, as shown inFIGS.3to6.

FIG.7is a beam diagram showing beams passing through a projection system3B according to Example 2. The projection system3B according to the present example is formed of a first optical system31and a second optical system32sequentially arranged from the reduction side toward the enlargement side, as shown inFIG.7. The second optical system32is disposed on an optical axis N of the first optical system31.

The first optical system31is a refractive optical system. The first optical system31is formed of sixteen lenses L1to L16. The lenses L1to L16are arranged in the presented order from the reduction side toward the enlargement side. A diaphragm51is disposed between the lens L7and the lens L8.

The lens L6has aspherical shapes at opposite sides. The lens L9has aspherical shapes at opposite sides. The lens L15(third lens) has aspherical shapes at opposite sides. The lens L16(second lens) has aspherical shapes at opposite sides. The lens L2and the lens L3are bonded to each other into a cemented doublet L21. The lens L4and the lens L5are bonded to each other into a cemented doublet L22. The lens L10and the lens L11are bonded to each other into a cemented doublet L23. The lens L13and the lens L14are bonded to each other into a cemented doublet L24.

The second optical system32includes an optical element33and a first lens34. The optical element33and the first lens34are arranged in the presented order from the reduction side toward the enlargement side. The optical element33has a reflection surface40, which faces the reduction side. The reflection surface40has a concave shape recessed in the second direction Z2. The reflection surface40has an aspherical shape. The reflection surface40is located at the lower side Y2of the optical axis N, as shown inFIG.7. The reflection surface40is formed by providing the outer surface, in the first direction Z1, of the optical element33with a reflection coating layer (reflection layer). The reflection surface40reflects light at the surface, facing in the direction Z1, of the optical element33.

The first lens34is located at a position shifted from the optical element33in the first direction Z1and disposed at the upper side Y1of the optical axis N. The first lens34has negative power. The first lens34has a convex enlargement-side surface and a concave reduction-side surface. The first lens34has aspherical shapes at opposite sides.

The liquid crystal panel18of the image formation unit2is disposed in the reduction-side conjugate plane of the projection system3B. The screen S is disposed in the enlargement-side conjugate plane of the projection system3B.

The liquid crystal panel18forms a projection image in an image formation plane perpendicular to the optical axis N of the first optical system31. The liquid crystal panel18is disposed in a position offset from the optical axis N of the first optical system31toward the upper side Y1. The projection image is therefore formed in a position offset from the optical axis N toward the upper side Y1.

The beams from the liquid crystal panel18pass through the first optical system31and the second optical system32in the presented order. Between the first optical system31and the second optical system32, the beams pass through the lower side Y2of the optical axis N. The beams are therefore directed through the second optical system32toward the reflection surface40. The beams having reached the reflection surface40are deflected back in the first direction Z1towards the upper side Y1. The beams deflected back by the reflection surface40cross the optical axis N toward the upper side Y1and travel toward the first lens34. The beams passing through the first lens34are widened by the first lens34and reach the screen S.

The lens L16of the first optical system31is disposed between the reflection surface40and the first lens34in the direction of the optical axis N. An intermediate image30is formed between the lens L16and the reflection surface40.

In the projection system3B, the portion at the reduction side of the first optical system31is a telecentric portion.

The projection system3B has a changeable projection distance. When the projection distance is changed, seven lenses of the first optical system31, the lenses L10to L16, are moved along the optical axis N for focusing. In the focusing, the lenses L12, L13, and L14are moved as a unit.

Data on the projection system3B are listed below,

NA0.2778imy11.8 mmscy1462 mmPD288.6 mmM124TR0.197OAL189 mmLL36.5 mm
where NA represents the numerical aperture of the liquid crystal panel18, imy represents a first distance from the optical axis N to the largest image height at the liquid crystal panel18, scy represents a second distance from the optical axis N to the largest image height of the enlarged image projected on the screen S, PD represents a projection distance that is the distance from the first lens34to the screen S, M represents a projection magnification that is the quotient of division of the second distance by the first distance, TR represents a throw ratio that is the quotient of division of the projection distance by the second distance, OAL represents the axial inter-surface spacing from the liquid crystal panel18to the reflection surface40, and LL represents the largest radius of the first lens34.

Data on the lenses of the projection system3B are listed below. The surfaces of the lenses are numbered sequentially from the reduction side toward the enlargement side. Reference characters are given to the liquid crystal panel, the dichroic prism, the lenses, the optical element, the first lens, and the screen. Data labeled with a surface number that does not correspond to any of the liquid crystal panel, the dichroic prism, the lenses, the optical element, the first lens, and the screen is dummy data. Reference character R represents the radius of curvature. Reference character D represents the axial inter-surface spacing. Reference character C represents the aperture radius, and twice the aperture radius is the diameter of the lens surface. Reference characters R, D, and C are each expressed in millimeters.

The projection system3B according to the present example has a changeable projection distance selected from a standard distance, a short distance shorter than the standard distance, and a long distance longer than the standard distance. When the projection distance is changed, seven lenses of the first optical system31, the lenses L10to L16, are moved along the optical axis N for focusing. When the focusing is performed so as to change the projection distance from the short distance to the long distance, the lenses L10and L11move along the optical axis N toward the reduction side. In the same focusing operation, the lenses L12, L13, and L14move along the optical axis N toward the enlargement side. In the same focusing operation, the lens L15moves along the optical axis N toward the enlargement side. In the same focusing operation, the lens L16moves along the optical axis N toward the enlargement side.

The table below shows the variable spacings 1, 2, 3, 4, 5, and 6 at the projection distances where the focusing is performed. The variable spacing 1 is the axial inter-surface spacing between the lens L9and the lens L10. The variable spacing 2 is the axial inter-surface spacing between the lens L11and the lens L12. The variable spacing 3 is the axial inter-surface spacing between the lens L14and the lens L15. The variable spacing 4 is the axial inter-surface spacing between the lens L15and the lens L16. The variable spacing 5 is the axial inter-surface spacing between the lens L16and the reflection surface40. The variable spacing 6 is the projection distance.

The aspherical coefficients are listed below.

The projection system3B according to the present example satisfies all Conditional Expressions (1) and (2) below,

where OAL represents the axial inter-surface spacing from the liquid crystal panel18to the reflection surface40, imy represents the first distance from the optical axis N to the largest image height at the liquid crystal panel18, LL represents the largest radius of the first lens34, TR represents the throw ratio, which is the quotient of division of the projection distance by the second distance from the optical axis N to the largest image height of the enlarged image projected on the screen S, and NA represents the numerical aperture of the liquid crystal panel18.

Furthermore, it is more preferable that the projection system3B satisfies all Conditional Expressions (1) and (2′) below.

In the present example, the values described above are listed below.

TR=0.197 is provided from the table shown above, so that Conditional Expression (1) is satisfied. (OAL/imy)×(LL/imy)×TR×(1/NA)=35 is satisfied, so that Conditional Expression (2) is satisfied.

Effects and Advantages

In the projection system3B according to the present example, the reflection surface40is provided with a reflection coating layer (reflection layer). The projection system3B according to the present example can therefore provide the same effects and advantages as those provided by Example 1.

In the projection system3B according to the present example, the lens L16(second lens) disposed at a position closest to the enlargement side in the first optical system31is formed as a lens separate from the first lens34. The lens L16is disposed between the reflection surface40and the first lens34in the direction of the optical axis N. That is, the lens L16disposed at a position closest to the enlargement side in the first optical system31is disposed inside the second optical system32in the direction of the optical axis N, so that the distance between the lens L16and the reflection surface40decreases. The projection system3B according to the present example can therefore provide the same effects and advantages as those provided by Example 1.

The first optical system31includes the lens L16(second lens) and the lens L15(third lens), which is disposed adjacent to the lens L16and shifted therefrom toward the reduction side. The lenses L15and L16each have an aspherical shape. In the projection system3B according to the present example, focusing that causes the projection distance to be changed from the short distance to the long distance is performed by moving the lenses L15and L16toward the enlargement side in the direction of the optical axis N. The projection system3B, in which the lenses L15and L16, which correct a variety of aberrations on an image height basis, are moved in the direction of the optical axis N, therefore allows suppression of occurrence of the variety of aberrations during focusing. Furthermore, in a configuration in which a lens having no aspherical shape is moved in the direction of the optical axis N for focusing, an aspherical lens that corrects a variety of aberrations needs to be separately prepared. In contrast, the present example, in which the lenses L15and L16, which move during focusing, each have an aspherical shape, allows reduction in the size of the entire projection system.

The first optical system31further includes the cemented doublets L23and L24at the enlargement side of the diaphragm51. The chromatic aberrations can therefore be corrected well.

The projection system3B according to the present example, which satisfies Conditional Expressions (1) and (2), can provide the same effects and advantages as those provided by the projection system3A according to Example 1.FIG.8shows the lateral aberrations produced by the projection system3B set at the standard distance.FIG.9shows the spherical aberration, astigmatism, and distortion produced by the projection system3B set at the standard distance.FIG.10shows the spherical aberration, astigmatism, and distortion produced by the projection system3B set at the short distance.FIG.11shows the spherical aberration, astigmatism, and distortion produced by the projection system3B set at the long distance. The projection system3B according to the present example produces an enlarged image having suppressed aberrations, as shown inFIGS.8to11.

FIG.12is a beam diagram showing beams passing through a projection system3C according to Example 3. The projection system3C according to the present example is formed of a first optical system31and a second optical system32sequentially arranged from the reduction side toward the enlargement side, as shown inFIG.12. The second optical system32is disposed on an optical axis N of the first optical system31.

The first optical system31is a refractive optical system. The first optical system31is formed of thirteen lenses L1to L13. The lenses L1to L13are arranged in the presented order from the reduction side toward the enlargement side. A diaphragm51is disposed between the lens L6and the lens L7.

The lens L5has aspherical shapes at opposite sides. The lens L8has aspherical shapes at opposite sides. The lens L12(third lens) has aspherical shapes at opposite sides. The lens L13(second lens) has aspherical shapes at opposite sides. The lens L3and the lens L4are bonded to each other into a cemented doublet L21. The lens L10and the lens L11are bonded to each other into a cemented doublet L22.

The second optical system32includes an optical element33and a first lens34. The optical element33and the first lens34are arranged in the presented order from the reduction side toward the enlargement side. The optical element33has a reflection surface40, which faces the reduction side. The reflection surface40has a concave shape recessed in the second direction Z2. The reflection surface40has an aspherical shape. The reflection surface40is located at the lower side Y2of the optical axis N, as shown inFIG.12. The reflection surface40is formed by providing the outer surface, in the first direction Z1, of the optical element33with a reflection coating layer (reflection layer). The reflection surface40reflects light at the surface, facing in the direction Z1, of the optical element33.

The first lens34is located at a position shifted from the optical element33in the first direction Z1and disposed at the upper side Y1of the optical axis N. The first lens34has negative power. The first lens34has a convex enlargement-side surface and a concave reduction-side surface. The first lens34has aspherical shapes at opposite sides.

The liquid crystal panel18of the image formation unit2is disposed in the reduction-side conjugate plane of the projection system3C. The screen S is disposed in the enlargement-side conjugate plane of the projection system3C.

The liquid crystal panel18forms a projection image in an image formation plane perpendicular to the optical axis N of the first optical system31. The liquid crystal panel18is disposed in a position offset from the optical axis N of the first optical system31toward the upper side Y1. The projection image is therefore formed in a position offset from the optical axis N toward the upper side Y1.

The beams from the liquid crystal panel18pass through the first optical system31and the second optical system32in the presented order. Between the first optical system31and the second optical system32, the beams pass through the lower side Y2of the optical axis N. The beams are therefore directed through the second optical system32toward the reflection surface40. The beams having reached the reflection surface40are deflected back in the first direction Z1towards the upper side Y1. The beams deflected back by the reflection surface40cross the optical axis N toward the upper side Y1and travel toward the first lens34. The beams passing through the first lens34are widened by the first lens34and reach the screen S.

The lens L13of the first optical system31is disposed between the reflection surface40and the first lens34in the direction of the optical axis N. An intermediate image30is formed between the lens L13and the reflection surface40.

In the projection system3C, the portion at the reduction side of the first optical system31is a telecentric portion.

The projection system3C has a changeable projection distance. When the projection distance is changed, four lenses of the first optical system31, the lenses L9to L12, are moved along the optical axis N for focusing. In the focusing, the lenses L10and L11are moved as a unit.

Data on the projection system3C are listed below,

NA0.2084imy11.7 mmscy1462 mmPD378.0 mmM125TR0.259OAL172 mmLL37.8 mm
where NA represents the numerical aperture of the liquid crystal panel18, imy represents a first distance from the optical axis N to the largest image height at the liquid crystal panel18, scy represents a second distance from the optical axis N to the largest image height of the enlarged image projected on the screen S, PD represents a projection distance that is the distance from the first lens34to the screen S, M represents a projection magnification that is the quotient of division of the second distance by the first distance, TR represents a throw ratio that is the quotient of division of the projection distance by the second distance, OAL represents the axial inter-surface spacing from the liquid crystal panel18to the reflection surface40, and LL represents the largest radius of the first lens34.

Data on the lenses of the projection system3C are listed below. The surfaces of the lenses are numbered sequentially from the reduction side toward the enlargement side. Reference characters are given to the liquid crystal panel, the dichroic prism, the lenses, the optical element, the first lens, and the screen. Data labeled with a surface number that does not correspond to any of the liquid crystal panel, the dichroic prism, the lenses, the optical element, the first lens, and the screen is dummy data. Reference character R represents the radius of curvature. Reference character D represents the axial inter-surface spacing. Reference character C represents the aperture radius, and twice the aperture radius is the diameter of the lens surface. Reference characters R, D, and C are each expressed in millimeters.

The projection system3C according to the present example has a changeable projection distance selected from a standard distance, a short distance shorter than the standard distance, and a long distance longer than the standard distance. When the projection distance is changed, four lenses of the first optical system31, the lenses L9to L12, are moved along the optical axis N for focusing. When the focusing is performed so as to change the projection distance from the short distance to the long distance, the lens L9moves along the optical axis N toward the enlargement side. In the same focusing operation, the lenses L10and L11move along the optical axis N toward the enlargement side. In the same focusing operation, the lens L12moves along the optical axis N toward the enlargement side. In the projection system3C according to the present example, the lens L13is fixed.

The table below shows the variable spacings 1, 2, 3, 4, and 5 at the projection distances where the focusing is performed. The variable spacing 1 is the axial inter-surface spacing between the lens L8and the lens L9. The variable spacing 2 is the axial inter-surface spacing between the lens L9and the lens L10. The variable spacing 3 is the axial inter-surface spacing between the lens L11and the lens L12. The variable spacing 4 is the axial inter-surface spacing between the lens L12and the lens L13. The variable spacing 5 is the projection distance.

The aspherical coefficients are listed below.

The projection system3C according to the present example satisfies all Conditional Expressions (1) and (2) below,

where OAL represents the axial inter-surface spacing from the liquid crystal panel18to the reflection surface40, imy represents the first distance from the optical axis N to the largest image height at the liquid crystal panel18, LL represents the largest radius of the first lens34, TR represents the throw ratio, which is the quotient of division of the projection distance by the second distance from the optical axis N to the largest image height of the enlarged image projected on the screen S, and NA represents the numerical aperture of the liquid crystal panel18.

In the present example, the values described above are listed below.

TR=0.259 is provided from the table shown above, so that Conditional Expression (1) is satisfied. (OAL/imy)×(LL/imy)×TR×(1/NA)=59 is satisfied, so that Conditional Expression (2) is satisfied.

Effects and Advantages

In the projection system3C according to the present example, the reflection surface40is provided with a reflection coating layer (reflection layer). The projection system3C according to the present example can therefore provide the same effects and advantages as those provided by Example 1.

In the projection system3C according to the present example, the lens L13(second lens) disposed at a position closest to the enlargement side in the first optical system31is formed as a lens separate from the first lens34. The lens L13is disposed between the reflection surface40and the first lens34in the direction of the optical axis N. That is, the lens L13disposed at a position closest to the enlargement side in the first optical system31is disposed inside the second optical system32in the direction of the optical axis N, so that the distance between the lens L13and the reflection surface40decreases. The projection system3C according to the present example can therefore provide the same effects and advantages as those provided by Example 1.

In the projection system3C according to the present example, the first optical system31includes the lens L13(second lens) and the lens L12(third lens), which is disposed adjacent to the lens L13and shifted therefrom toward the reduction side. That is, the lens L13disposed at a position closest to the enlargement side in the first optical system31is disposed inside the second optical system32in the direction of the optical axis N, so that the distance between the lens L13and the reflection surface40decreases. In the projection system3C according to the present example, focusing that causes the projection distance to be changed from the short distance to the long distance is performed by moving the lens L12toward the enlargement side in the direction of the optical axis N. The projection system3C, in which the lens L12, which corrects a variety of aberrations on an image height basis, is moved in the direction of the optical axis N, therefore allows suppression of occurrence of the variety of aberrations during focusing. Furthermore, in a configuration in which a lens having no aspherical shape is moved in the direction of the optical axis N for focusing, an aspherical lens that corrects a variety of aberrations needs to be separately prepared. In contrast, the present example, in which the lens L12, which moves during focusing, has an aspherical shape, allows reduction in the size of the entire projection system.

The lens L13is fixed in the direction of the optical axis N. The lens L13, which is the second lens, is disposed between the reflection surface40and the first lens34. Therefore, when the lens L13is moved in the direction of the optical axis N for focusing, the mechanism that moves the lens L13is complicated, resulting in an increase in manufacturing cost. The manufacturing cost of the projection system3C according to the present example can therefore be suppressed as compared with the manufacturing cost of the projection system3A according to Example 1, in which the lens L17, which is the second lens, is moved in the direction of the optical axis N.

The first optical system31further includes the cemented doublet L22at the enlargement side of the diaphragm51. The chromatic aberrations can therefore be corrected well.

The projection system3C according to the present example, which satisfies Conditional Expressions (1) and (2), can provide the same effects and advantages as those provided by the projection system3A according to Example 1.FIG.13shows the lateral aberrations produced by the projection system3C set at the standard distance.FIG.14shows the spherical aberration, astigmatism, and distortion produced by the projection system3C set at the standard distance.FIG.15shows the spherical aberration, astigmatism, and distortion produced by the projection system3C set at the short distance.FIG.16shows the spherical aberration, astigmatism, and distortion produced by the projection system3C set at the long distance. The projection system3C according to the present example produces an enlarged image having suppressed aberrations, as shown inFIGS.13to16.

FIG.17is a beam diagram showing beams passing through a projection system3D according to Example 4. The projection system3D according to the present example is formed of a first optical system31and a second optical system32sequentially arranged from the reduction side toward the enlargement side, as shown inFIG.17. The second optical system32is disposed on an optical axis N of the first optical system31.

The first optical system31is a refractive optical system. The first optical system31is formed of thirteen lenses L1to L13. The lenses L1to L13are arranged in the presented order from the reduction side toward the enlargement side. A diaphragm51is disposed between the lens L6and the lens L7.

The lens L5has aspherical shapes at opposite sides. The lens L8has aspherical shapes at opposite sides. The lens L12(third lens) has aspherical shapes at opposite sides. The lens L13(second lens) has aspherical shapes at opposite sides. The lens L3and the lens L4are bonded to each other into a cemented doublet L21. The lens L10and the lens L11are bonded to each other into a cemented doublet L22.

The second optical system32includes an optical element33and a first lens34. The optical element33and the first lens34are arranged in the presented order from the reduction side toward the enlargement side. The optical element33has a first surface36, which faces the reduction side, and a second surface37, which faces the side opposite from the first surface36. The optical element33has a reflection coating layer at the second surface37. The first surface36has a concave shape. The second surface37has a convex shape. The optical element33has a first transmission surface41, a reflection surface42, and a second transmission surface43sequentially arranged from the reduction side toward the enlargement side. The first transmission surface41is provided at the first surface36. The first transmission surface41has a concave shape. The reflection surface42is the reflection coating layer and has a concave shape to which the surface shape of the second surface37has been transferred. The reflection surface42reflects light within the optical element33. The second transmission surface43is provided at the first surface36. The second transmission surface43has a concave shape. The first transmission surface41, the reflection surface42, and the second transmission surface43each have an aspherical shape. The first transmission surface41, the reflection surface42, and the second transmission surface43are located at the lower side Y2of the optical axis N, as shown inFIG.17.

The first lens34is located at a position shifted from the optical element33in the first direction Z1and disposed at the upper side Y1of the optical axis N. The first lens34has negative power. The first lens34has a convex enlargement-side surface and a concave reduction-side surface. The first lens34has aspherical shapes at opposite sides.

The liquid crystal panel18of the image formation unit2is disposed in the reduction-side conjugate plane of the projection system3D. The screen S is disposed in the enlargement-side conjugate plane of the projection system3D.

The liquid crystal panel18forms a projection image in an image formation plane perpendicular to the optical axis N of the first optical system31. The liquid crystal panel18is disposed in a position offset from the optical axis N of the first optical system31toward the upper side Y1. The projection image is therefore formed in a position offset from the optical axis N toward the upper side Y1.

The beams from the liquid crystal panel18pass through the first optical system31and the second optical system32in the presented order. Between the first optical system31and the second optical system32, the beams pass through the lower side Y2of the optical axis N. The beams are thus incident on the first transmission surface41of the optical element33, which forms the second optical system32.

The beams having entered the optical element33via the first transmission surface41travel toward the reflection surface42. The beams having reached the reflection surface42are deflected back in the first direction Z1towards the upper side Y1. The beams deflected back by the reflection surface42travel toward the second transmission surface43. The beams having exited via the second transmission surface43cross the optical axis N toward the upper side Y1and travel toward the first lens34. The beams passing through the first lens34are widened by the first lens34and reach the screen S.

The lens L13of the first optical system31is disposed between the reflection surface42and the first lens34in the direction of the optical axis N. An intermediate image30is formed between the lens L13and the reflection surface42.

In the projection system3D, the portion at the reduction side of the first optical system31is a telecentric portion.

The projection system3D has a changeable projection distance. When the projection distance is changed, four lenses of the first optical system31, the lenses L9to L12, are moved along the optical axis N for focusing.

Data on the projection system3D are listed below,

NA0.25imy11.7 mmscy1463 mmPD376.0 mmM125TR0.257OAL175 mmLL40.0 mm
where NA represents the numerical aperture of the liquid crystal panel18, imy represents a first distance from the optical axis N to the largest image height at the liquid crystal panel18, scy represents a second distance from the optical axis N to the largest image height of the enlarged image projected on the screen S, PD represents a projection distance that is the distance from the first lens34to the screen S, M represents a projection magnification that is the quotient of division of the second distance by the first distance, TR represents a throw ratio that is the quotient of division of the projection distance by the second distance, OAL represents the axial inter-surface spacing from the liquid crystal panel18to the reflection surface42, and LL represents the largest radius of the first lens34.

Data on the lenses of the projection system3D are listed below. The surfaces of the lenses are numbered sequentially from the reduction side toward the enlargement side. Reference characters are given to the liquid crystal panel, the dichroic prism, the lenses, the optical element, the first lens, and the screen. Data labeled with a surface number that does not correspond to any of the liquid crystal panel, the dichroic prism, the lenses, the optical element, the first lens, and the screen is dummy data. Reference character R represents the radius of curvature. Reference character D represents the axial inter-surface spacing. Reference character C represents the aperture radius, and twice the aperture radius is the diameter of the lens surface. Reference characters R, D, and C are each expressed in millimeters.

The projection system3D according to the present example has a changeable projection distance selected from a standard distance, a short distance shorter than the standard distance, and a long distance longer than the standard distance. When the projection distance is changed, four lenses of the first optical system31, the lenses L9to L12, are moved along the optical axis N for focusing. When the focusing is performed so as to change the projection distance from the short distance to the long distance, the lens L9moves along the optical axis N toward the reduction side. In the same focusing operation, the lenses L10and L11move along the optical axis N toward the enlargement side. In the same focusing operation, the lens L12moves along the optical axis N toward the enlargement side. In the projection system3D according to the present example, the lens L13is fixed.

The table below shows the variable spacings 1, 2, 3, 4, and 5 at the projection distances where the focusing is performed. The variable spacing 1 is the axial inter-surface spacing between the lens L8and the lens L9. The variable spacing 2 is the axial inter-surface spacing between the lens L9and the lens L10. The variable spacing 3 is the axial inter-surface spacing between the lens L11and the lens L12. The variable spacing 4 is the axial inter-surface spacing between the lens L12and the lens L13. The variable spacing 5 is the projection distance.

The aspherical coefficients are listed below.

The projection system3D according to the present example satisfies all Conditional Expressions (1) and (2) below,

where OAL represents the axial inter-surface spacing from the liquid crystal panel18to the reflection surface42, imy represents the first distance from the optical axis N to the largest image height at the liquid crystal panel18, LL represents the largest radius of the first lens34, TR represents the throw ratio, which is the quotient of division of the projection distance by the second distance from the optical axis N to the largest image height of the enlarged image projected on the screen S, and NA represents the numerical aperture of the liquid crystal panel18.

Furthermore, it is more preferable that the projection system3D satisfies all Conditional Expressions (1) and (2′) below.

In the present example, the values described above are listed below.

TR=0.257 is provided from the table shown above, so that Conditional Expression (1) is satisfied. (OAL/imy)×(LL/imy)×TR×(1/NA)=53 is satisfied, so that Conditional Expression (2) is satisfied.

Effects and Advantages

In the projection system3D according to the present example, the lens L13(second lens) disposed at a position closest to the enlargement side in the first optical system31is formed as a lens separate from the first lens34. The lens L13is disposed between the reflection surface42and the first lens34in the direction of the optical axis N. That is, the lens L13disposed at a position closest to the enlargement side in the first optical system31is disposed inside the second optical system32in the direction of the optical axis N, so that the distance between the lens L13and the reflection surface42decreases. The projection system3D according to the present example can therefore provide the same effects and advantages as those provided by Example 1.

In the projection system3D according to the present example, the first optical system31includes the lens L13(second lens) and the lens L12(third lens), which is disposed adjacent to the lens L13and shifted therefrom toward the reduction side. The lenses L12and L13each have an aspherical shape. In the projection system3D according to the present example, focusing that causes the projection distance to be changed from the short distance to the long distance is performed by moving the lens L12toward the enlargement side in the direction of the optical axis N. The projection system3D, in which the lens L12, which corrects a variety of aberrations on an image height basis, is moved in the direction of the optical axis N, therefore allows suppression of occurrence of the variety of aberrations during focusing. Furthermore, in a configuration in which a lens having no aspherical shape is moved in the direction of the optical axis N for focusing, an aspherical lens that corrects a variety of aberrations needs to be separately prepared. In contrast, the present example, in which the lens L12, which moves during focusing, has an aspherical shape, allows reduction in the size of the entire projection system.

The lens L13is fixed in the direction of the optical axis N. The lens L13, which is the second lens, is disposed between the reflection surface42and the first lens34. Therefore, when the lens L13is moved in the direction of the optical axis N for focusing, the mechanism that moves the lens L13is complicated, resulting in an increase in manufacturing cost. The manufacturing cost of the projection system3D according to the present example can therefore be suppressed as compared with the manufacturing cost of the projection system3A according to Example 1, in which the lens L17, which is the second lens, is moved in the direction of the optical axis N.

The first optical system31further includes the cemented doublet L22at the enlargement side of the diaphragm51. The chromatic aberrations can therefore be corrected well.

The projection system3D according to the present example, which satisfies Conditional Expressions (1) and (2), can provide the same effects and advantages as those provided by the projection system3A according to Example 1.FIG.18shows the lateral aberrations produced by the projection system3D set at the standard distance.FIG.19shows the spherical aberration, astigmatism, and distortion produced by the projection system3D set at the standard distance.FIG.20shows the spherical aberration, astigmatism, and distortion produced by the projection system3D set at the short distance.FIG.21shows the spherical aberration, astigmatism, and distortion produced by the projection system3D set at the long distance. The projection system3D according to the present example produces an enlarged image having suppressed aberrations, as shown inFIGS.18to21.