Projection optical system and projector

The present invention relates to a projection optical system which expands and projects an image of an image display element and is suitable to be incorporated into a projector and the projector using the projection optical system.

In recent years, as a projection optical system which is used for a projector and by which a large screen can be obtained by projecting an image from a short distance, a projection optical system in which a refraction optical system and a concave mirror are used is suggested (for example, see PTL 1 and PTL 2).

However, for example, in PTL 1 (JP-A-2006-235516), although a very wide viewing angle is implemented using the refraction optical system and the concave mirror, the curved mirror is very large and the entire length thereof is very long. In PTL 2 (JP-A-2007-079524), for example, a mirror size is made small by combining a concave mirror and a convex mirror while setting the viewing angle to approximately 60 degrees in an eighth example. However, similar to PTL 1 described above, the entire length is very long. Configured two mirrors are aspherical mirrors and it is very difficult to manufacture the mirrors from a viewpoint of accuracy and assembly.

As described above, in a composite optical system including the refraction optical system and the concave mirror, an ultra-wide viewing angle is obtained while it is difficult to make the entire length small. For that reason, the composite optical system is not fit for, for example, a device that places importance on portability like a front projector.

Patent Literature

PTL 1: JP-A-2006-235516

PTL 2: JP-A-2007-079524

Technical Problem

The invention has been made in view of the background and an object of the invention is to provide a projection optical system capable of covering a wide zooming range while having a relatively small number of lenses and a projector provided with the projection optical system.

Solution to Problem

In order to achieve the object described above, a projection optical system according to an aspect of the invention includes, in order from a reduction side, a first optical group which has positive power and includes a plurality of lenses and a second optical group which includes a single reflection surface having a concave aspherical shape, and the first optical group includes a 1-1 lens group fixed at the time of focusing accompanying magnification change and having positive power and a 1-2 lens group moved at the time of focusing accompanying the magnification change, bordering the widest air spacing, the 1-2 lens group is constituted with three lenses of an F 1 lens which includes a single positive lens having a convex surface to the reduction side, an F 2 lens which includes a single negative meniscus lens having a convex surface to an enlargement side, and an F 3 lens which includes a single negative lens, in order from the reduction side.

In the projection optical system described above, the 1-2 lens group is arranged to the enlargement side among the first optical group and requires a relatively large lens. In the projection optical system, the 1-2 lens group includes the F 1 lens which includes a single positive lens having a convex surface to the reduction side, the F 2 lens which includes a single negative meniscus lens having a convex surface at an enlargement side, and the F 3 lens which includes a single negative lens so that a desired zooming range can be covered. Also, the projection optical system can be compactly configured as a whole.

According to a specific aspect of the invention, the 1-1 lens group includes an aperture diaphragm inside the 1-1 lens group and includes a positive lens having a convex aspherical surface located at a position nearer to the reduction side than the aperture diaphragm. In this case, even in a case where the 1-2 lens group is simply constituted with three lenses, it is possible to obtain an image of small flare and high contrast. The number of configuring lenses is suppressed so that the entire length of the lenses can be shortened.

According to another aspect of the invention, the 1-1 lens group includes an aperture diaphragm inside the 1-1 lens group and includes a lens group including at least one positive lens located at a position nearer to the enlargement n side than the aperture diaphragm and having positive power. In this case, a state of a flux of light beams is adjusted in the 1-1 lens group that is responsible for capturing the flux of light beams emitted from an object side (hereinafter, also referred to as a light flux) and sending the flux of light beams to the 1-2 lens group to thereby make it possible to prepare a proper primary image (intermediate image) in the 1-2 lens group in a wide zooming range.

According to still another aspect of the invention, the 1-1 lens group includes an aperture diaphragm inside the 1-1 lens group and includes two positive lenses, a first cemented lens including a positive lens and a negative lens, and a second cemented lens including a positive lens and a negative lens located at a position nearer to the reduction side than the aperture diaphragm. In this case, the cemented lenses are included in the 1-1 lens group so as to make it possible to prevent, for example, occurrence of chromatic aberration.

According to still yet another aspect of the invention, the 1-1 lens group includes an aperture diaphragm inside the 1-1 lens group and a negative lens having an aspherical shape on at least one surface of the negative lens is arranged in the vicinity of the aperture diaphragm. Here, the lens arranged in the vicinity of the aperture diaphragm means a lens positioned nearest to the aperture diaphragm among the lenses constituting projection optical system. In this case, the lens arranged in the vicinity of the aperture diaphragm is formed by the negative lens having an aspherical shape on at least one surface thereof so that an object side numerical aperture can be made larger.

According to still yet another aspect of the invention, three lenses of the 1-2 lens group are divided into at least two lens groups and the two lens groups are respectively moved. In this case, even in a wide zooming range (for example, 1.5 times or more), it is possible to prepare the primary image (intermediate image) with which a good image can be obtained finally.

According to still yet another aspect of the invention, the F 3 lens includes a both-side aspherical lens molded from resin. According to this configuration, it is easy to prepare a lens, like the F 3 lens, which is arranged to the enlargement side among the first optical group and thus tends to become large and also has the aspherical surface on both side of the lens. There is a possibility that the F 3 lens may be interfered with a light beam returning from a reflection mirror constituting the second optical group. For that reason, although a case where a portion of the lens constituting the F 3 lens needs to be cut occurs, the lens is molded from resin so that it is easy to form the lens in a non-circular shape, or the like.

According to still yet another aspect of the invention, the F 3 lens has a concave shape to the reduction side in the vicinity of the optical axis. In this case, it is easy to form the F 2 lens in a negative meniscus lens shape having a convex surface to the enlargement side.

According to still yet another aspect of the invention, the object side numerical aperture is greater than or equal to 0.3. In this case, it is possible to form a sufficiently bright projection image.

According to still yet another aspect of the invention, the reduction side is substantially telecentric.

According to still yet another aspect of the invention, all of elements constituting the first optical group and the second optical group are rotation symmetry systems.

According to still yet another aspect of the invention, a zooming range is 1.5 times or more.

According to still yet another aspect of the invention, the 1-2 lens group has negative power as a whole.

In order to achieve the object described above, a projector according to the invention includes a light modulating element that modulates light from a light source and forms image light and the projection optical system according to any one of the projection optical systems described above that projects image light from the light modulating element. The projector includes any one of the projection optical systems described above so as to make it possible to cover a desired zooming range while implementing a configuration in which the number of lenses is suppressed.

FIG. 1 is a diagram illustrating a schematic configuration of a projector incorporating a projection optical system of an embodiment.

FIG. 2 is a view of a configuration and light beams from an object surface to a projection surface in a projection optical system of the embodiment or Example 1.

FIG. 3 is a partial enlarged view from object surface to a concave reflection mirror of FIG. 2 .

FIG. 4 is a diagram illustrating a configuration of a projection optical system of Example 1.

FIGS. 5(A) to 5(C) are reduction side aberration diagrams of the projection optical system of Example 1.

FIGS. 6(A) to 6(E) are lateral aberration diagrams of the projection optical system corresponding to FIG. 5(A) .

FIGS. 7(A) to 7(E) are lateral aberration diagrams of the projection optical system corresponding to FIG. 5(B) .

FIGS. 8(A) to 8(E) are lateral aberration diagrams of the projection optical system corresponding to FIG. 5(C) .

FIG. 9 is a diagram illustrating a configuration of a projection optical system of Example 2.

FIGS. 10(A) to 10(C) are reduction side aberration diagrams of the projection optical system of Example 2.

FIGS. 11(A) to 11(E) are lateral aberration diagrams of the projection optical system corresponding to FIG. 10(A) .

FIGS. 12(A) to 12(E) are lateral aberration diagrams of the projection optical system corresponding to FIG. 10(B) .

FIGS. 13(A) to 13(E) are lateral aberration diagrams of the projection optical system corresponding to FIG. 10(C) .

FIG. 14 is a diagram illustrating a configuration of a projection optical system of Example 3.

FIGS. 15(A) to 15(C) are reduction side aberration diagrams of the projection optical system of Example 3.

FIGS. 16(A) to 16(E) are lateral aberration diagrams of the projection optical system corresponding to FIG. 15(A) .

FIGS. 17(A) to 17(E) are lateral aberration diagrams of the projection optical system corresponding to FIG. 15(B) .

FIGS. 18(A) to 18(E) are lateral aberration diagrams of the projection optical system corresponding to FIG. 15(C) .

FIG. 19 is a diagram illustrating a configuration of a projection optical system of Example 4.

FIGS. 20(A) to 20(C) are reduction side aberration diagrams of the projection optical system of Example 4.

FIGS. 21(A) to 21(E) are lateral aberration diagrams of the projection optical system corresponding to FIG. 20(A) .

FIGS. 22(A) to 22(E) are lateral aberration diagrams of the projection optical system corresponding to FIG. 20(B) .

FIGS. 23(A) to 23(E) are lateral aberration diagrams of the projection optical system corresponding to FIG. 20(C) .

In the following, a projection optical system according to an embodiment of the invention will be described in detail with reference to the drawings.

As illustrated in FIG. 1 , a projector 2 incorporating the projection optical system according to an embodiment of the invention includes an optical system portion 50 projecting image light and a circuit device 80 controlling an operation of the optical system portion 50 .

In the optical system portion 50 , a light source 10 is, for example, an ultra-high pressure mercury lamp and emits light including R light beam, G light beam, and B light beam. Here, the light source 10 may be a discharge light source other than the ultra-high pressure mercury lamp and may be a solid light source such as an LED or laser. A first integrator lens 11 and a second integrator lens 12 have a plurality of lens elements arranged in an array shape. The first integrator lens 11 divides light fluxes from the light source 10 into a plurality of light fluxes. Respective lens elements of the first integrator lens 11 condense the light fluxes from the light source 10 in the vicinity of the lens elements of the second integrator lens 12 . The lens elements of the second integrator lens 12 cooperate with a superimposing lens 14 and form images of the lens elements of the first integrator lens on liquid crystal panels 18 R, 18 G, 18 B. By such a configuration, the entire display area of the liquid crystal panels 18 R, 18 G, and 18 B is illuminated with substantially uniform brightness by light from the light source 10 .

A polarization conversion element 13 converts light from the second integrator lens 12 into predetermined linearly polarized light. The superimposing lens 14 superimposes images of respective lens elements of the first integrator lens 11 on the display areas of the liquid crystal panels 18 R, 18 G, and 18 B through the second integrator lens 12 .

A first dichromic mirror 15 reflects R light incident from the superimposing lens 14 and transmits G light and B light beam. R light reflected from the first dichromic mirror 15 is incident onto the liquid crystal panel 18 R which is a light modulating element via a reflection mirror 16 and a field lens 17 R. The liquid crystal panel 18 R modulates R light according to an image signal to form an R color image.

A second dichromic mirror 21 reflects G light from the first dichromic mirror 15 and transmits B light beam. G light reflected from the second dichromic mirror 21 is incident onto the liquid crystal panel 18 G which is the light modulating element via a field lens 17 G. The liquid crystal panel 18 G modulates G light according to an image signal to form a G color image. B light transmitted through the second dichromic mirror 21 is incident onto the liquid crystal panel 18 B which is the light modulating element via relay lenses 22 and 24 , reflection mirrors 23 and 25 , and the field lens 17 B. The liquid crystal panel 18 B modulates B light beam according to an image signal to form a B color image.

A cross dichroic prism 19 is a prism for light synthesization and synthesizes light beams modulated by respective liquid crystal panels 18 R, 18 G, and 18 B and causes synthesized light beams to be propagated as image light to the projection optical system 40 .

A projection optical system 40 is a projection zoom lens that expands and projects image light which is modulated by respective liquid crystal panels 18 G, 18 R, and 18 B and synthesized by the cross dichroic prism 19 on a screen (not illustrated).

The circuit device 80 includes an image processing unit 81 that receives an external image signal such as a video signal, a display driving unit 82 that drives the liquid crystal panels 18 G, 18 R, and 18 B provided in the optical system portion 50 based on the output of the image processing unit 81 , a lens driving unit 83 that operates a driving mechanism (not illustrated) provided in the projection optical system 40 to adjust a state of the projection optical system 40 , and a main control unit 88 that comprehensively controls operations of these circuit portions 81 , 82 , and 83 .

The image processing unit 81 converts the input external image signal into an image signal including gradation of each color or the like. The image processing unit 81 also can perform various image processing such as distortion correction or color correction on the external image signal.

The display driving unit 82 can operate the liquid crystal panels 18 G, 18 R, and 18 B based on the image signal output from the image processing unit 81 and can form an image corresponding to the image signal or an image corresponding to the image obtained by being subjected to image processing in the liquid crystal panels 18 G, 18 R, and 18 B.

The lens driving unit 83 operates under control of the main control unit 88 and appropriately moves some of optical elements constituting the projection optical system 40 along an optical axis OA through an actuator AC to thereby make it possible to perform focusing accompanying zooming (focusing when varying power) in projection of an image onto a screen by the projection optical system 40 . The lens driving unit 83 can change a vertical position of an image to be projected on the screen through tilt adjustment by moving the entirety of projection optical system 40 in the up and down direction perpendicular to the optical axis OA.

In the following, the projection optical system 40 of the embodiment will be described in detail with reference to FIG. 2 and FIG. 3 . The projection optical system 40 illustrated in FIG. 2 or the like has the same configuration as that of the projection optical system 40 of Example 1 which will be described later.

The projection optical system 40 of the embodiment projects the image formed on the liquid crystal panel 18 G ( 18 R, 18 B) on a screen (not illustrated). Here, a prism PR corresponding to the cross dichroic prism 19 of FIG. 1 is arranged between the projection optical system 40 and the liquid crystal panel 18 G ( 18 R, 18 B).

The projection optical system 40 includes a first optical group 40 a including a plurality of lenses in order from the reduction side and having positive power and a second optical group 40 b constituted with a mirror MR that includes a reflection surface having a concave aspherical shape. The first optical group 40 a includes a 1-1 lens group 41 provided at a reduction side and having positive power and a 1-2 lens group 42 provided at an enlargement side and having weak negative power compared to power of the 1-1 lens group 41 bordering the widest air spacing BD among space formed between lenses included in the first optical group.

The 1-1 lens group 41 includes an aperture diaphragm ST inside the 1-1 lens group 41 and includes a lens group E 1 located at position nearer to the reduction side than the aperture diaphragm ST and a lens group E 2 located at position nearer to the enlargement side than the aperture diaphragm ST.

The 1-2 lens group 42 includes an F 1 lens (hereinafter, referred to as lens F 1 ), an F 2 lens (hereinafter, referred to as lens F 2 ), and an F 3 lens (hereinafter, referred to as lens F 3 ) in order from the reduction side. The lens F 1 , the lens F 2 , and the lens F 3 are respectively moved in the optical axis direction at the time of focusing accompanying the magnification change. Among the lenses F 1 to F 3 , the lens F 1 located at a position nearest to the reduction side is a positive lens (lens L 12 ) having a convex surface on the reduction side, the lens F 2 positioned between the lens F 1 and the lens F 3 is a negative meniscus lens (lens L 13 ) having a convex surface on the enlargement side, and the lens F 3 located at a position nearest to the enlargement side is a negative lens (lens L 14 ). The lens F 3 is a both-side aspherical lens molded from resin and has a concave shape to the reduction side in the vicinity of the optical axis. The lenses F 1 to F 3 are moved in a direction A 1 along the optical axis OA by the actuator AC at the time of focusing when varying power. Here, the lenses F 1 and F 2 are made movable integrally with each other and the lens F 3 is made movable independently of the lenses F 1 and F 2 . That is, the lenses F 1 to F 3 are divided into at least two lens groups (a lens group including lenses F 1 and F 2 and a lens group including lens F 3 ) and respective lens groups are movable independently of each other. With this, even in a wide the magnification change range, it is possible to prepare the primary image with which a good image can be obtained finally. For a way of moving the lenses F 1 to F 3 by the actuator AC, various aspects by aspects of focusing when varying power are possible. For example, the lenses F 1 to F 3 may be moved completely and independently of each other and may be moved by being interlocked with each other using a cam mechanism or the like.

In the following, lenses constituting each lens group will be described in order from the reduction side. The lens group E 1 includes lenses L 1 to L 9 and the lens group E 2 includes lenses L 10 and L 11 . The lens F 1 is constituted with the lens L 12 , the lens F 2 is constituted with the lens L 13 , and the lens F 3 is constituted with the lens L 14 . That is, the first optical group 40 a is constituted with fourteen lenses of the lenses L 1 to L 14 as a whole.

Each of the lenses L 2 , L 4 , L 6 , and L 7 is the positive lens and each of the lenses L 3 , L 5 , and L 8 is the negative lens. The lens L 2 and the lens L 3 are the first cemented lens and the lens L 4 and the lens L 5 are the second cemented lens. The lens L 6 has a convex aspherical surface. The lens L 7 and the lens L 8 form a cemented lens. The 1-1 lens group 41 includes at least two sets (here, three sets) of cemented lenses including the positive lens and the negative lens that are provided at a position nearer to the reduction side than the aperture diaphragm ST and at least one positive lens having the convex aspherical surface. Each of the lenses L 1 to L 9 is a lens made of glass and has a circular shape axially symmetrical to the optical axis OA. All lenses other than the lens L 6 are spherical lenses.

The lens L 10 which is a negative meniscus lens and the lens L 11 which is a biconvex positive lens forms a cemented lens. When considering the way of viewing, the lens group E 2 may be referred to as a lens group including at least one positive lens (lens L 11 ) and having positive power. In this case, a state of a flux of light beams is adjusted in the 1-1 lens group 41 that is responsible for capturing a flux of light beams emitted from an object side, that is, panel surface PI and sending the flux of light beams to the 1-2 lens group to thereby prepare a proper primary image (intermediate image) in the 1-2 lens group 42 in a wide zooming range. The lenses L 10 and L 11 are spherical lenses made of glass and have a circular shape axially symmetrical to the optical axis OA.

As described above, the 1-1 lens group 41 is constituted with eleven lenses of the lenses L 1 to L 11 as a whole. The projection optical system 40 according to the present embodiment can reduce chromatic aberration by a relatively small number of lenses. Furthermore, it is possible to make the numerical aperture large. The influence by variation in assembling is small. Furthermore, the aspherical positive lens (L 6 ) made of glass is provided to the reduction side (lens group E 1 ) of the aperture diaphragm ST and thus, it is possible to obtain an image of small flare and of high contrast even when the 1-2 lens group 42 is simply constituted with three lenses of the lenses F 1 to F 3 . The number of configuring lenses of the lens group is suppressed so that the entire length of the lenses can be shortened.

The lens L 12 is the positive lens having a convex surface on at least the reduction side. The lens L 12 is responsible for making the aberration correction by the lens L 13 and the lens L 14 easy at the time of focusing as well as responsible for converting the light flux emitted as divergent light from the 1-1 lens group 41 into a state of being close to parallel light and guiding the converted light to the lens L 13 . In a case where a surface to the reduction side of the lens L 12 is a flat surface or a convex surface, the aberration correction effect in the surface to the reduction side is small and thus, aberration correction by the lens L 13 and the lens L 14 becomes difficult. Accordingly, the F 1 lens is preferably formed by a positive lens having a convex surface to the reduction side. The lens L 12 is a spherical lens made of glass and has a circular shape axially symmetrical to the optical axis OA.

The lens L 13 is a negative meniscus lens having a convex surface to the enlargement side. The lens L 13 cooperates with the lens L 12 to prepare a good primary image at the time of focusing. The lens L 13 has a divergence surface including a concave surface to the reduction side to thereby make it possible to correct aberration with the lens L 12 at the time of focusing with good balance. The lens L 13 has a light condensing surface including a convex surface to the enlargement side to thereby make it possible to suppress divergence of light beams to be incident onto the lens L 14 and to lessen the influence by variation of the lens L 14 which is subjected to strong aspherical surface machining. The lens L 13 is a spherical lens made of glass and has a circular shape axially symmetrical to the optical axis OA.

As described above, the lens L 14 is a both-side aspherical lens having negative power in the vicinity of the optical axis OA and is molded from resin. The lens L 14 , that is, the lens F 3 is an aspherical lens of a shape having a concave surface to the reduction side so that it is easy to form the lens L 13 , that is, the lens F 2 in a negative meniscus lens shape having a convex surface to the enlargement side. The lens L 14 may have a circular shape axially symmetrical to the optical axis OA and may also have a noncircular shape. For instance, the lens L 14 may have a shape in which a portion of an upper side, which is circular and axially symmetrical to the optical axis OA (a side to which video light is projected), is cut.

As previously described, the second optical group 40 b is constituted with the mirror MR having a concave aspherical shape. The mirror MR reflects video light emitted from the first optical group 40 a towards the screen.

As described above, each of the lenses L 1 to L 14 constituting the first optical group 40 a has a circular shape axially symmetrical to the optical axis OA or at least the lens L 14 has a shape in which a portion of an upper side, which is circular and axially symmetrical to the optical axis OA, is cut. Also, the mirror MR constituting the second optical group 40 b has a shape in which a portion, which is axially symmetrical to the optical axis OA, is cut. That is, the respective lenses L 1 to L 14 and the reflection surface formed on the mirror MR are rotation symmetry systems. As illustrated, the reduction side is substantially telecentric in the projection optical system 40 . With this, for example, as described above, in a case where light beams modulated by respective liquid crystal panels 18 R, 18 G, and 18 B are synthesized to be formed into image light in the cross dichroic prism 19 , it is possible to easily absorb variation in assembling.

In a proximity projection optical system, in general, a distance to a screen is very short. In the projection optical system 40 , an image formed on a panel surface PI of the liquid crystal panel 18 G ( 18 R, 18 B) is formed once in front of the mirror of the second optical group 40 b by the first optical group 40 a and the image is formed on the screen by the second optical group 40 b again so that a proximity projection is performed. That is, the first optical group 40 a prepares the primary image (intermediate image) in front of the mirror MR. In the proximity projection optical system described above, variation of aberration when varying power is relatively large and thus, there is a possibility that zooming range cannot be made large. Accordingly, the primary image formed by the first optical group 40 a is preferably optimized so that a good image is obtained even when the projection magnification is changed. In a general proximity projection optical system, reduction in contrast due to variation of astigmatism or image surface curvature is large. Change in distortion aberration when varying power is likely to be higher than that of a normal lens.

However, in the projection optical system 40 of the present embodiment, as described above, although the 1-2 lens group 42 which is a focus lens group is constituted with three lenses (a single positive lens and two negative lenses) and has a simple configuration in which an aspherical lens is only a single negative lens (lens L 14 ) nearest to the enlargement side, the 1-2 lens group 42 is movable along the optical axis OA and thus, a desired zooming range can be covered. Furthermore, the projection optical system can be made compact and is capable of achieving cost reduction. More specifically, three lenses constituting the 1-2 lens group 42 are divided into at least two lens groups and at least the two lens groups are individually movable in order to form a good image in a wide magnification change range, at the time of focusing accompanying the magnification change. In the 1-2 lens group 42 , an angle of a divergent light flux from the 1-1 lens group 41 is gently angled and is made incident onto the next negative lens (lens F 2 , that is, lens L 13 ) by the positive lens (lens F 1 , that is, lens L 12 ) arranged to the reduction side, and the lens F 2 favorably relays the light flux without worsening corrected aberration, an image is formed while diverting further the light flux by the negative lens (lens F 3 , that is, lens L 14 ) arranged to the enlargement side, so that a required primary image (intermediate image) is prepared.

In the present embodiment, in the 1-1 lens group 41 constituting a fixed group which is not moved at the time of focusing, for example, an aspherical surface (lens surface of lens L 6 ) formed of glass is arranged to the reduction side of the aperture diaphragm ST so that variation of aberration is made small even in a wide magnification change range without increasing sensitivity of the aspherical lens made of resin (lens L 14 ). More specifically, first, the plurality of lenses L 1 to L 9 of the 1-1 lens group 41 arranged at a position nearer to the reduction side (lens group E 1 ) than the aperture diaphragm ST, as previously described, efficiently capture a flux of light beams emitted from the panel surface PI. Here, in a case where the 1-1 lens group 41 including the lenses L 1 to L 9 is constituted only with the spherical lenses, the number of lenses is increased. However, in the projection optical system 40 , when the number of lenses is increased, transmittance is reduced and the entire length of the lenses is increased so that the number of lenses of a lens configuration as little as possible is required. Furthermore, in a case where the 1-2 lens group 42 is constituted with three lenses, which are the minimum number of lenses of a lens configuration, as described above, a flux of light beams incident onto the 1-2 lens group 42 also needs to be properly controlled. In contrast, in the present embodiment, the 1-1 lens group 41 includes at least one convex shaped aspherical surface so that occurrence of flare can be suppressed and an image of high contrast can be provided. At least two lenses (L 10 , L 11 ) are arranged to the enlargement n side (lens group E 2 ) of the aperture diaphragm ST in the 1-1 lens group 41 so that a proper intermediate image is more reliably prepared in the 1-2 lens group 42 in a wide zooming range. The lens F 3 constituted with a lens having an aspherical shape while having negative power, among the 1-2 lens group 42 , cooperates with the second optical group 40 b constituted with the mirror MR having the concave aspherical shape to perform a final correction of an amount of aberration. The second optical group 40 b is the reflection surface onto which light fluxes having respective image heights are incident by being separated and the lens F 3 arranged immediately before the second optical group 40 b among the first optical group 40 a is formed by an aspherical lens so that it is possible to effectively perform optimal correction to respective image heights. By adopting the configuration as described above, even in a case where the 1-2 lens group 42 constituting a focus lens group is formed with three lenses, the number of lenses of the entire projection optical system 40 is approximately thirteen or fourteen, and the second optical group 40 b is constituted with a single mirror MR, proper aberration is included in the primary image so as to enable an image, which is to be projected on a screen via the second optical group 40 b , to be a good image having small aberration. That is, in the projector 2 which is a proximity projector, it is possible to cover a wide zooming range and also cope with an image display element of high resolution.

Furthermore, by adopting the configuration as described above, the projection optical system of the present embodiment has performance capable of coping with the image display element of high resolution by securing a high zooming range of 1.5 times or more (furthermore, 1.6 times or more) while setting object side numerical aperture to be greater than or equal to 0.27, that is, having brightness of the extent of the F-number of 1.8. As will be described later in Example 3, the glass aspherical surfaces are properly arranged so as to make it possible to suppress the number of configuring lenses of the lens group and shorten the entire length of the lenses. As will be described later in Example 4, the glass aspherical surfaces are properly arranged in the vicinity of the aperture diaphragm ST so as to make it possible to obtain an image having small flare and high contrast while setting the numerical aperture to be greater than or equal to 0.3, that is, having brightness of the extent of the F-number of 1.6.

In the following, a specific example of the projection optical system 40 will be described. Meaning of specification common to Examples 1 to 4 which will be described in the following is summarized below.

f focal distance of entire system

ω half viewing angle

NA numerical aperture

R curvature radius

D axial surface spacing (lens thickness or lens spacing)

Nd refractive index of d-line

Vd Abbe number of d-line

The aspherical surface is specified by the following polynomial (aspherical expression).

z = ch 2 1 + 1 - ( k + 1 ) ⁢ c 2 ⁢ h 2 + A 4 ⁢ h 4 + A 6 ⁢ h 6 + A 8 ⁢ h 8 + A 10 ⁢ h 10 + A 12 ⁢ h 12 + A 14 ⁢ h 14

Where,

c: curvature (1/R)

h: height from optical axis

k: conical coefficient of aspherical surface

Ai: high-order aspherical coefficient of aspherical surface

The OBJ means the panel surface PI, the STO means the aperture diaphragm ST, and the IMG means an image surface on a screen (a projection surface). A surface for which the mark “*” is described before the surface number is a surface having an aspherical shape.