The present invention relates to a viewing optical system and an image display apparatus using the same. More particularly, the present invention relates to a viewing optical system devised so that a bright image of a display device of the type in which an image is displayed by reflected light, e.g. a reflection type liquid crystal display device, can be observed through an ocular optical system arranged to be compact in size and to minimize the loss of light quality. The present invention also relates to an image display apparatus, e.g. a head-up display, using the viewing optical system.
The present invention also relates to a see-through viewing optical system that allows see-through observation of the outside world or the like in an optical system of an image display apparatus, e.g. a head-up display.
In recent years, with the development of head-up displays and glasses-type displays, compact ocular optical systems have been actively developed. As a result, ocular optical systems using a thin and compact decentered prism have been proposed as disclosed, for example in Japanese Patent Application Unexamined Publication Numbers (hereinafter referred to as xe2x80x9cJP(A)xe2x80x9d) 7-333551, 8-50256 and 8-234137. These are compact ocular optical systems in which reflecting surfaces have a power and the optical path is folded, and in which rotationally asymmetric decentration aberrations produced by decentered reflecting surfaces with a power are corrected by using an anamorphic reflecting surface or a rotationally asymmetric reflecting surface having one plane of symmetry.
Regarding liquid crystal display devices for displaying an image for observation, reflection type liquid crystal display devices have been developed to form images that are brighter and easier to observe. As a reflection type liquid crystal display device including an illumination structure therefor, JP(A) 10-268306 has been laid open to public.
As an ocular optical system using a reflection type image display device that is brighter than the transmission type, e.g. a reflection type liquid crystal display device, U.S. Pat. No. 5,771,124 is known.
However, the ocular optical system disclosed in U.S. Pat. No. 5,771,124 needs to form all the optical members from glass and is therefore heavy in weight. Regarding the arrangement of the ocular optical system, the number of parts is large, and the structure is large in size. In addition, because illuminating light incident on the reflection type image display device is tilted from the direction perpendicular to the image display surface to a considerable extent, brightness is sacrificed undesirably.
Accordingly, it is conceivable to apply illuminating light from a direction approximately perpendicular to the display surface of the reflection type image display device of the viewing optical system according to JP(A) 10-268306. This is, however, unfavorable for U.S. Pat. No. 5,771,124 because the ocular optical system disclosed therein lacks compactness.
Under these circumstances, it is conceivable to construct a bright and compact viewing optical system by combining together an ocular optical system superior in compactness as proposed, for example, in JP(A) 7-333551, 8-50256 and 8-234137 and the reflection type image display device according to JP(A) 10-268306, in which illuminating light is applied to the display surface approximately perpendicularly.
However, the above-described conventional ocular optical system using a decentered prism is based on the assumption that a transmission type image display device is used. Therefore, the distance between the image display device and the entrance surface of the decentered prism is short. For this reason, it is impossible to ensure a space for placing an optical member for illuminating the display surface of the reflection type image display device between the image display device and the decentered prism. Consequently, it is unavoidably necessary to tilt the reflection type image display device with respect to the optical axis to a considerable extent and to dispose a light source so that illuminating light is applied to the display surface from an oblique direction as in the case of U.S. Pat. No. 5,771,124.
When a reflection type image display device is tilted with respect to the optical axis to a considerable extent, particularly when a reflection type liquid crystal display device is used as the reflection type image display device, the brightness of the reflection type image display device cannot be exhibited satisfactorily owing to the viewing angle dependence. Moreover, because the object plane is tilted with respect to the optical axis, an excessively heavy load is imposed on the ocular optical system to allow the image to be observed perpendicularly to the optical axis without curvature and distortion.
To construct a see-through optical system for see-through observation of the outside world or the like by using a thick prism optical system constituting a conventional ocular optical system as stated above, the common practice is to use surfaces of the same configuration as the eye-side surface and the outside world-side surface and to set the power of the see-through optical path to zero.
However, when the eye-side surface of the prism optical system is not a plane surface, even if the power of the see-through optical path is zero, the angular magnification is not 1. Accordingly, in the case of a head-mounted image display apparatus designed for a single eye, in which the user performs observation with one eye through the prism optical system and the other eye being naked, two images seen with the left and right eyes cannot properly be fused into a single image.
In view of the above-described problems with the prior art, an object of the present invention is to provide a compact, bright and high-performance viewing optical system using an ocular optical system, which is formed from a decentered prism, and a reflection type image display device, and also provide an image display apparatus using the viewing optical system.
Another object of the present invention is to provide a viewing optical system in which when the outside world or the like is viewed in a see-through manner through an ocular optical system, e.g. a prism optical system, which forms a displayed image of an image display device, the outside world or the like can be seen in the same way as in the case of viewing with the naked eye.
A first viewing optical system according to the present invention provided to attain the first object includes a reflection type image display device for displaying an image by reflecting an illuminating light beam incident from the front side of a display surface for forming an image for observation. The viewing optical system further includes an ocular optical system for leading the image to a pupil position where an observer""s eyeball is to be placed.
The image display device has an illuminating device and an illuminating light guide optical device for guiding a light beam emitted from the illuminating device so that the light beam can be applied to the display surface from the front side thereof.
The ocular optical system includes a prism member having an entrance surface through which a display light beam reflected from the reflection type image display device enters the prism member after passing through the illuminating light guide optical device. The prism member further has at least one reflecting surface reflecting the light beam in the prism member, and an exit surface through which the light beam exits from the prism member.
The at least one reflecting surface of the prism member is decentered with respect to an optical axis and has a rotationally asymmetric curved surface configuration that corrects decentration aberrations due to the decentration of the reflecting surface and gives a power to the light beam.
The spacing between the entrance surface of the prism member and the display surface of the reflection type image display device satisfies the following condition to lead the image to the pupil position:
0.6 less than L/H less than 3.1
where L is the distance between an image center position where the display surface of the reflection type image display device intersects the optical axis and a position where the entrance surface of the prism member intersects the optical axis, and H is the image height of the reflection type image display device (the diagonal length in a case where the display surface is quadrangular).
A second viewing optical system according to the present invention provided to attain the second object includes an image forming member for forming a first image to be viewed by an observer, and an ocular optical system arranged to lead the image formed by the image forming member to an observer""s eyeball. The viewing optical system further includes a see-through optical element placed closer to a second image, which is different from the first image, than the ocular optical system so as to lead the second image to the observer""s eyeball.
The ocular optical system has at least a reflecting surface with a curved surface configuration arranged to reflect a light beam from the first image and to lead it toward the observer""s eyeball. The reflecting surface has a transmitting action to allow a light beam from the second image to enter the ocular optical system after passing through the see-through optical element.
The see-through optical element is placed closer to the second image than the reflecting surface at a distance from the reflecting surface.
The viewing optical system is arranged so that when the light beam from the second image passes through the see-through optical element and the ocular optical system, the combined optical power P of the see-through optical element and the ocular optical system is approximately zero, and the combined angular magnification xcex2 is approximately 1.
A third viewing optical system according to the present invention provided to attain the second object includes an image forming member for forming a first image to be viewed by an observer, and an ocular optical system arranged to lead the image formed by the image forming member to an observer""s eyeball. The viewing optical system further includes a see-through optical element disposed closer to a second image, which is different from the first image, than the ocular optical system so as to lead the second image to the observer""s eyeball.
The ocular optical system has at least a reflecting surface with a curved surface configuration arranged to reflect a light beam from the first image and to lead it toward the observer""s eyeball. The reflecting surface has a transmitting action to allow a light beam from the second image to enter the ocular optical system after passing through the see-through optical element.
The see-through optical element is placed closer to the second image than the reflecting surface in such a manner as to be in close contact with the reflecting surface.
The viewing optical system is arranged so that when the light beam from the second image passes through the see-through optical element and the ocular optical system, the combined optical power P of the see-through optical element and the ocular optical system is approximately zero.
A fourth viewing optical system according to the present invention provided to attain the second object includes an image forming member for forming a first image to be viewed by an observer, and an ocular optical system arranged to lead the image formed by the image forming member to an observer""s eyeball. The viewing optical system further includes a see-through optical element disposed closer to a second image, which is different from the first image, than the ocular optical system so as to lead the second image to the observer""s eyeball.
The ocular optical system has at least a reflecting surface with a curved surface configuration arranged to reflect a light beam from the first image and to lead it toward the observer""s eyeball. The reflecting surface has a transmitting action to allow a light beam from the second image to enter the ocular optical system after passing through the see-through optical element.
The see-through optical element is placed closer to the second image than the reflecting surface in such a manner as to be in close contact with the reflecting surface.
The viewing optical system is arranged so that when the light beam from the second image passes through the see-through optical element and the ocular optical system, the combined angular magnification xcex2 of the see-through optical element and the ocular optical system is approximately 1.
The reasons for adopting the above-described arrangements in the present invention, together with the functions thereof, will be described below in order.
The first viewing optical system according to the present invention includes a reflection type image display device for displaying an image by reflecting an illuminating light beam incident from the front side of a display surface for forming an image for observation. The viewing optical system further includes an ocular optical system for leading the image to a pupil position where an observer""s eyeball is to be placed. The image display device has an illuminating device and an illuminating light guide optical device for guiding a light beam emitted from the illuminating device so that the light beam can be applied to the display surface from the front side thereof.
Thus, the first viewing optical system according to the present invention has an illuminating light guide optical device for guiding a light beam emitted from the illuminating device so that the light beam can be applied to the display surface of the reflection type image display device from the front side thereof. Accordingly, illuminating light can be applied to the display surface from the front side thereof at approximately right angles to the display surface. Thus, it is possible to construct a bright viewing optical system.
The ocular optical system is formed from a prism member having an entrance surface through which a display light beam reflected from the image display device enters the prism member. The prism member further has at least one reflecting surface reflecting the light beam in the prism member, and an exit surface through which the light beam exits from the prism member. Therefore, it is possible to construct a thin and compact viewing optical system.
The at least one reflecting surface of the prism member is decentered with respect to an optical axis and has a rotationally asymmetric curved surface configuration that corrects decentration aberrations due to the decentration of the reflecting surface and gives a power to the light beam. Therefore, it is possible to construct a high-performance viewing optical system that is compact and lightweight and yet capable of exhibiting high optical performance.
A refracting optical element such as a lens is provided with a power by giving a curvature to an interface surface thereof. Accordingly, when rays are refracted at the interface surface of the lens, chromatic aberration unavoidably occurs according to chromatic dispersion characteristics of the refracting optical element. Consequently, the common practice is to add another refracting optical element for the purpose of correcting the chromatic aberration.
Meanwhile, a reflecting optical element such as a mirror or a prism produces no chromatic aberration in theory even when a reflecting surface thereof is provided with a power, and need not add another optical element only for the purpose of correcting chromatic aberration. Accordingly, an optical system using a reflecting optical element allows the number of constituent optical elements to be reduced from the viewpoint of chromatic aberration correction in comparison to an optical system using a refracting optical element.
At the same time, a reflecting optical system using a reflecting optical element allows the optical system itself to be compact in size in comparison to a refracting optical system because the optical path is folded in the reflecting optical system.
Reflecting surfaces require a high degree of accuracy for assembly and adjustment because they have high sensitivity to decentration errors in comparison to refracting surfaces. However, among reflecting optical elements, prisms, in which the positional relationship between surfaces is fixed, only need to control decentration as a single unit of prism and do not need high assembly accuracy and a large number of man-hours for adjustment as are needed for other reflecting optical elements.
Furthermore, a prism has an entrance surface and an exit surface, which are refracting surfaces, and a reflecting surface. Therefore, the degree of freedom for aberration correction is high in comparison to a mirror, which has only a reflecting surface. In particular, if the prism reflecting surface is assigned the greater part of the desired power to thereby reduce the powers of the entrance and exit surfaces, which are refracting surfaces, it is possible to reduce chromatic aberration to a very small quantity in comparison to refracting optical elements such as lenses while maintaining the degree of freedom for aberration correction at a high level in comparison to mirrors. Furthermore, the inside of a prism is filled with a transparent medium having a refractive index higher than that of air. Therefore, it is possible to obtain a longer optical path length than in the case of air. Accordingly, the use of a prism makes it possible to obtain an optical system that is thinner and more compact than those formed from lenses, mirrors and so forth, which are placed in the air.
In addition, an ocular optical system is required to exhibit favorable image-forming performance as far as the peripheral portions of the image field, not to mention the performance required for the center of the image field. In the case of a general coaxial optical system, the sign of the ray height of extra-axial rays is inverted at a stop. Accordingly, if optical elements are not in symmetry with respect to the stop, off-axis aberrations are aggravated. For this reason, the common practice is to place refracting surfaces at respective positions facing each other across the stop, thereby obtaining a satisfactory symmetry with respect to the stop, and thus correcting off-axis aberrations.
In the first viewing optical system according to the present invention, as stated above, the ocular optical system is formed from a prism member having an entrance surface, at least one reflecting surface, and an exit surface. The at least one reflecting surface is decentered with respect to the optical axis and has a rotationally asymmetric curved surface configuration that corrects decentration aberrations due to the decentration of the reflecting surface and gives a power to the light beam, thereby enabling not only axial aberrations but also off-axis aberrations to be favorably corrected.
With the above-described basic arrangement of the first viewing optical system according to the present invention, it is possible to obtain a compact ocular optical system that has a smaller number of constituent optical elements than in the case of an optical system using a refracting optical system or a rotationally symmetric reflecting optical system and exhibits favorable performance throughout the image field, from the center to the periphery thereof.
When a light ray that passes through the center of the pupil and reaches the center of the display surface of the reflection type image display device in backward ray tracing is defined as an axial principal ray, if at least one reflecting surface of the prism member is not decentered with respect to the axial principal ray, the axial principal ray travels along the same optical path when incident on and reflected from the reflecting surface, and thus the axial principal ray is intercepted in the optical system undesirably. As a result, an image is formed from only a light beam whose central portion is shaded. Consequently, the center of the image is unfavorably dark, or no image is formed in the center of the image field.
It is also possible to decenter a reflecting surface with a power with respect to the axial principal ray.
When a reflecting surface with a power is decentered with respect to the axial principal ray, it is desirable that at least one reflecting surface of the surfaces constituting the prism member should be a rotationally asymmetric surface.
The reason for this will be described below in detail. First of all, a coordinate system used in the following description and rotationally asymmetric surfaces will be described. An optical axis defined by a straight line along which the axial principal ray travels until it intersects the first surface of the optical system is defined as a Z-axis. An axis perpendicularly intersecting the Z-axis in the decentration plane of each surface constituting the ocular optical system is defined as a Y-axis. An axis perpendicularly intersecting the optical axis and also perpendicularly intersecting the Y-axis is defined as an X-axis. Ray tracing will be described by backward ray tracing in which rays are traced from the pupil toward the reflection type image display device, as stated above.
In general, a spherical lens system comprising only a spherical lens is arranged such that aberrations produced by spherical surfaces, such as spherical aberration, coma and curvature of field, are corrected with some surfaces by canceling the aberrations with each other, thereby reducing aberrations as a whole.
On the other hand, rotationally symmetric aspherical surfaces and the like are used to correct aberrations favorably with a minimal number of surfaces. The reason for this is to reduce various aberrations that would be produced by spherical surfaces.
However, in a decentered optical system, rotationally asymmetric aberrations due to decentration cannot be corrected by a rotationally symmetric optical system. Rotationally asymmetric aberrations due to decentration include distortion, curvature of field, and astigmatic and comatic aberrations, which occur even on the axis.
First, rotationally asymmetric curvature of field will be described. For example, when rays from an infinitely distant object point are incident on a decentered concave mirror, the rays are reflected by the concave mirror to form an image. In this case, the back focal length from that portion of the concave mirror on which the rays strike to the image surface is a half the radius of curvature of the portion on which the rays strike in a case where the medium on the image side is air. Consequently, as shown in FIG. 23, an image surface tilted with respect to the axial principal ray is formed. It is impossible to correct such rotationally asymmetric curvature of field by a rotationally symmetric optical system.
To correct the tilted curvature of field by the concave mirror M itself, which is the source of the curvature of field, the concave mirror M is formed from a rotationally asymmetric surface, and, in this example, the concave mirror M is arranged such that the curvature is made strong (refracting power is increased) in the positive direction of the Y-axis, whereas the curvature is made weak (refracting power is reduced) in the negative direction of the Y-axis. By doing so, the tilted curvature of field can be corrected. It is also possible to obtain a flat image surface with a minimal number of constituent surfaces by placing a rotationally asymmetric surface having the same effect as that of the above-described arrangement in the optical system separately from the concave mirror M.
It is preferable that the rotationally asymmetric surface should be a rotationally asymmetric surface having no axis of rotational symmetry in the surface nor out of the surface. Such a rotationally asymmetric surface allows the degree of freedom to increase, and this is favorable for aberration correction.
Next, rotationally asymmetric astigmatism will be described. A decentered concave mirror M produces astigmatism even for axial rays, as shown in FIG. 24, as in the case of the above. The astigmatism can be corrected by appropriately changing the curvatures in the X- and Y-axis directions of the rotationally asymmetric surface as in the case of the above.
Rotationally asymmetric coma will be described below. A decentered concave mirror M produces coma even for axial rays, as shown in FIG. 25, as in the case of the above. The coma can be corrected by changing the tilt of the rotationally asymmetric surface according as the distance from the origin of the X-axis increases, and further appropriately changing the tilt of the surface according to the sign (positive or negative) of the Y-axis.
The ocular optical system according to the present invention may also be arranged such that the above-described at least one surface having a reflecting action is decentered with respect to the axial principal ray and has a rotationally asymmetric surface configuration and further has a power. By adopting such an arrangement, decentration aberrations produced as the result of giving a power to the reflecting surface can be corrected by the surface itself. In addition, the power of the refracting surfaces of the prism is reduced, and thus chromatic aberration produced in the prism can be minimized.
The rotationally asymmetric surface used in the present invention should preferably be a plane-symmetry free-form surface having only one plane of symmetry. Free-form surfaces used in the present invention are defined by the following equation (a). It should be noted that the Z-axis of the defining equation is the axis of a free-form surface.                     Z        =                                            cr              2                        /                          [                              1                +                                                      {                                          1                      -                                                                        (                                                      1                            +                            k                                                    )                                                ⁢                                                  c                          2                                                ⁢                                                  r                          2                                                                                      }                                                              ]                                +                                    ∑                              j                =                2                            66                        ⁢                          xe2x80x83                        ⁢                                          C                j                            ⁢                              X                m                            ⁢                              Y                n                                                                        (        a        )                                                      ∑                          j              =              2                        66                    ⁢                      xe2x80x83                    ⁢                                    C              j                        ⁢                          X              m                        ⁢                          Y              n                                      =                  xe2x80x83                ⁢                                            C              2                        ⁢            X                    +                                    C              3                        ⁢            Y                    +                                    C              4                        ⁢                          X              2                                +                                    C              5                        ⁢            XY                    +                                    C              6                        ⁢                          Y              2                                +                                    C              7                        ⁢                          X              3                                +                                                  xe2x80x83                ⁢                                            C              8                        ⁢                          X              2                        ⁢            Y                    +                                    C              9                        ⁢                          XY              2                                +                                    C              10                        ⁢                          Y              3                                +                                    C              11                        ⁢                          X              4                                +                                    C              12                        ⁢                          X              3                        ⁢            Y                    +                                                  xe2x80x83                ⁢                                            C              13                        ⁢                          X              2                        ⁢                          Y              2                                +                                    C              14                        ⁢                          XY              3                                +                                    C              15                        ⁢                          Y              4                                +                                    C              16                        ⁢                          X              5                                +                                    C              17                        ⁢                          X              4                        ⁢            Y                    +                                                  xe2x80x83                ⁢                                            C              18                        ⁢                          X              3                        ⁢                          Y              2                                +                                    C              19                        ⁢                          X              2                        ⁢                          Y              3                                +                                    C              20                        ⁢                          XY              4                                +                                    C              21                        ⁢                          Y              5                                +                                                  xe2x80x83                ⁢                                            C              22                        ⁢                          X              6                                +                                    C              23                        ⁢                          X              5                        ⁢            Y                    +                                    C              24                        ⁢                          X              4                        ⁢                          Y              2                                +                                    C              25                        ⁢                          X              3                        ⁢                          Y              3                                +                                                  xe2x80x83                ⁢                                            C              26                        ⁢                          X              2                        ⁢                          Y              4                                +                                    C              27                        ⁢                          XY              5                                +                                    C              28                        ⁢                          Y              6                                +                                    C              29                        ⁢                          X              7                                +                                    C              30                        ⁢                          X              6                        ⁢            Y                    +                                                  xe2x80x83                ⁢                                            C              31                        ⁢                          X              5                        ⁢                          Y              2                                +                                    C              32                        ⁢                          X              4                        ⁢                          Y              3                                +                                    C              33                        ⁢                          X              3                        ⁢                          Y              4                                +                                    C              34                        ⁢                          X              2                        ⁢                          Y              5                                +                                                  xe2x80x83                ⁢                                            C              35                        ⁢                          XY              6                                +                                    C              36                        ⁢                          Y              7                        ⁢            …                              
where Cj (j is an integer of 2 or higher) are coefficients.
In general, the above-described free-form surface does not have planes of symmetry in both the XZ- and YZ-planes. In the present invention, however, a free-form surface having only one plane of symmetry parallel to the YZ-plane is obtained by making all terms of odd-numbered degrees with respect to X zero. For example, in the above defining equation (a), the coefficients of the terms C2, C5, C7, C9, C12, C14, C16, C18, C20, C23, C25, C27, C29, C31, C33, C35, . . . are set equal to zero. By doing so, it is possible to obtain a free-form surface having only one plane of symmetry parallel to the YZ-plane.
A free-form surface having only one plane of symmetry parallel to the XZ-plane is obtained by making all terms of odd-numbered degrees with respect to Y zero. For example, in the above defining equation (a), the coefficients of the terms C3, C5, C8, C10, C12, C14, C17, C19, C21, C23, C25, C27, C30, C32, C34, C36, . . . are set equal to zero. By doing so, it is possible to obtain a free-form surface having only one plane of symmetry parallel to the XZ-plane.
Furthermore, the direction of decentration is determined in correspondence to either of the directions of the above-described planes of symmetry. For example, with respect to the plane of symmetry parallel to the YZ-plane, the direction of decentration of the optical system is determined to be the Y-axis direction. With respect to the plane of symmetry parallel to the XZ-plane, the direction of decentration of the optical system is determined to be the X-axis direction. By doing so, rotationally asymmetric aberrations due to decentration can be corrected effectively, and at the same time, productivity can be improved.
It should be noted that the above defining equation (a) is shown as merely an example as stated above, and that the feature of the present invention resides in that rotationally asymmetric aberrations due to decentration are corrected and, at the same time, productivity is improved by using a rotationally asymmetric surface having only one plane of symmetry. Therefore, the same advantageous effect can be obtained for any other defining equation that expresses such a rotationally asymmetric surface.
Incidentally, it is important in the present invention that the spacing between the entrance surface of the prism member and the display surface of the reflection type image display device should satisfy the following condition to lead the image to the pupil position:
0.6 less than L/H less than 3.1xe2x80x83xe2x80x83(1)
where L is the distance between an image center position where the display surface of the reflection type image display device intersects the optical axis and a position where the entrance surface of the prism member intersects the optical axis, and H is the image height of the reflection type image display device (the diagonal length in a case where the display surface is quadrangular).
The condition (1) needs to be satisfied in order to place the illuminating light guide optical device between the entrance surface of the prism member and the display surface of the reflection type image display device. If L/H is not smaller than the upper limit, i.e. 3.1, the spacing between the entrance surface of the prism member and the display surface of the reflection type image display device becomes excessively wide, and it becomes difficult to attain the above-described ocular optical system. In addition, the viewing optical system itself becomes large in size. This goes against the object of the present invention. If L/H is not larger than the lower limit, i.e. 0.6, the spacing becomes excessively narrow, and the tilt of the beam splitter surface of the illuminating light guide optical device with respect to the optical axis becomes excessively small. Consequently, if illuminating light is made incident on the display surface of the reflection type image display device at approximately right angles thereto, it is difficult to illuminate the whole display surface owing to eclipse.
It is more desirable to satisfy the following condition:
0.7 less than L/H less than 2.0xe2x80x83xe2x80x83(1-1)
The meaning of the upper limit of this condition is the same as the above.
It is even more desirable to satisfy the following condition:
0.8 less than L/H less than 1.5xe2x80x83xe2x80x83(1-2)
The meaning of the upper limit of this condition is the same as the above.
As the reflection type image display device in the present invention, for example, a reflection type liquid crystal display device can be used, although the present invention is not necessarily limitative thereto.
Incidentally, chromatic aberration is relatively likely to occur in the viewing optical system according to the present invention because the illuminating light guide optical device is placed in a relatively wide spacing provided between the entrance surface of the prism member and the display surface of the reflection type image display device. Therefore, it is desirable to place a diffractive optical element on the entrance surface side of the prism member to correct the chromatic aberration.
In the viewing optical system according to the present invention, the prism member used as an ocular optical system can be any of various known decentered prisms. However, it is desirable to use a decentered prism of the type which has at least one surface serving as both a refracting surface and a reflecting surface in order to fold the optical path to achieve a reduction in size.
A typical prism of the type described above has an entrance surface through which the display light beam reflected from the reflection type image display device enters the prism after passing through the illuminating light guide optical device, and a first reflecting surface that reflects the light beam entering through the entrance surface. The prism further has a second reflecting surface that reflects the light beam reflected from the first reflecting surface, and an exit surface through which the light beam reflected from the second reflecting surface exits from the prism. The first reflecting surface and the exit surface are formed from a single surface serving as both a refracting surface and a reflecting surface.
Another prism of the type described above has an entrance surface through which the display light beam reflected from the reflection type image display device enters the prism after passing through the illuminating light guide optical device, and a first reflecting surface that reflects the light beam entering through the entrance surface. The prism further has a second reflecting surface that reflects the light beam reflected from the first reflecting surface, and a third reflecting surface that reflects the light beam reflected from the second reflecting surface, and further an exit surface through which the light beam reflected from the third reflecting surface exits from the prism. The second reflecting surface and the exit surface are formed from a single surface serving as both a refracting surface and a reflecting surface.
In the viewing optical system according to the present invention, the illuminating light guide optical device may be a transparent member having a first surface through which the light beam emitted from the illuminating device enters the transparent member, and a second surface that totally reflects the light beam entering through the first surface, and further a third surface that reflects the light beam totally reflected by the second surface. The second surface transmits the light beam reflected from the third surface to illuminate the display surface of the reflection type image display device from the front side thereof and also transmits the display light beam reflected from the display surface of the reflection type image display device. The third surface forms a beam splitter surface that transmits the display light beam passing through the second surface.
In this case, it is desirable that a deviation angle compensating member should be placed on the third surface side of the transparent member to compensate for an angle of deviation caused by the transparent member.
It is not always necessary to place a deviation angle compensating member besides the illuminating light guide optical device. When no deviation angle compensating member is provided, it is desirable to satisfy the condition described below.
Let us define parameters first. FIG. 19 is a ray path diagram showing the axial principal ray passing through the illuminating light guide optical device. The angle a formed between a tangential plane passing through the intersection between the second surface (in general, a curved surface or a plane surface) of the illuminating light guide optical device and the axial principal ray and a tangential plane passing through the intersection between the third surface (in general, a curved surface or a plane surface) of the illuminating light guide optical device and the axial principal ray is defined as an apex angle. The angle xcex8 formed between the axial principal ray entering the second surface and the axial principal ray exiting from the third surface is defined as an angle of deviation.
In general, the minimum angle of deviation xcex8min of a triangular prism (refractive index of which is denoted by n) having an apex angle xcex1 is determined by
xcex8min=2 sinxe2x88x921[nxc2x7sin(xcex1/2)]xe2x88x92xcex1xe2x80x83xe2x80x83(2)
Here, let us define xcex8xe2x88x92xcex8min as xcex94xcex8, where xcex8 is the angle of deviation of the axial principal ray passing through the second and third surfaces of the illuminating light guide optical device, and xcex8min is the minimum angle of deviation of the triangular prism having an apex angle defined by the angle xcex1 formed between a tangential plane passing through the intersection between the second surface and the axial principal ray and a tangential plane passing through the intersection between the third surface and the axial principal ray. In this case, it is important to satisfy the following condition:
xcex94xcex8 less than 20xc2x0xe2x80x83xe2x80x83(3)
If xcex94xcex8 is not smaller than the upper limit of this condition, i.e. 20xc2x0, a light beam at each field angle is refracted at a large angle by the illuminating light guide optical device. Therefore, comatic aberration due to decentration and chromatic aberration occur in excessively large amounts, and it becomes difficult to correct these aberrations by canceling them with the prism member of the ocular optical system.
It is more desirable to satisfy the following condition:
xcex94xcex8 less than 10xc2x0xe2x80x83xe2x80x83(3-1)
The meaning of the upper limit of this condition is the same as the above.
It is even more desirable to satisfy the following condition:
xcex94xcex8 less than 3xc2x0xe2x80x83xe2x80x83(3-2)
The meaning of the upper limit of this condition is the same as the above.
The present invention includes an image display apparatus having the above-described viewing optical system for a right eye or left eye of an observer.
The present invention also includes an image display apparatus having a pair of viewing optical systems arranged as stated above for both right and left eyes of an observer.
Further, the present invention includes an image display apparatus having a support member for supporting the image display apparatus on the observer""s head so that the image display apparatus is positioned in front of the observer""s face.
Next, the second viewing optical system according to the present invention will be described.
FIG. 26 is a ray path diagram of a viewing optical system according to Example 5 (described later). The second viewing optical system will be described below with reference to FIG. 26. The ocular optical system of the viewing optical system includes a prism optical system 210. The prism optical system 210 has a first surface 211, a second surface 212, and a third surface 213 as counted from the exit pupil 201 side in backward ray tracing. The first surface 211 serves as both a transmitting surface and a totally reflecting surface. The second surface 212 is a semitransparent reflecting surface. The third surface 213 is a transmitting surface. Display light from an image display device placed in an image plane 203 enters the prism optical system 210 through the third surface 213. The incident light is reflected by the first surface 211 and further reflected by the second surface 212 to exit from the prism optical system 210 through the first surface 211. Then, the light enters an observer""s eyeball placed so that the pupil is located at the position of the exit pupil 201. Thus, the image displayed at the image plane 203 is observable as an enlarged image.
A see-through optical element 220 is placed in front of the second surface 212 of the prism optical system 210 at a distance therefrom (the on-axis distance between the see-through optical element 220 and the second surface 212 may be zero) . The see-through optical element 220 is formed from another transmission prism member having a first surface 221 and a second surface 222 as counted from the exit pupil 201 side in backward ray tracing. The first surface 221 and the second surface 222 are transmitting surfaces. Light from the outside world passes successively through the second surface 222 and first surface 221 of the see-through optical element 220 and further through the second surface 212 and first surface 211 of the prism optical system 210 and enters the observer""s eyeball, in which the pupil is placed at the position of the exit pupil 201, to form an outside world image. It is possible to selectively observe either of the outside world image and the displayed image of the image display device placed in the image plane 203. It is also possible to observe both the images superimposed on one another. In FIG. 26, reference numeral 202 denotes an axial principal ray.
Thus, the viewing optical system according to the present invention includes an image forming member (the image display device placed in the image plane 203) for forming a first image to be viewed by an observer, and an ocular optical system (including the prism optical system 210 and a diffractive optical element 204 in this case) arranged to lead the image formed by the image forming member to an observer""s eyeball. The viewing optical system further includes the see-through optical element 220 placed closer to a second image (the outside world image in this case), which is different from the first image, than the ocular optical system so as to lead the second image to the observer""s eyeball. The ocular optical system has at least a reflecting surface 212 with a curved surface configuration arranged to reflect a light beam from the first image and to lead it toward the observer""s eyeball. The reflecting surface 212 has a transmitting action to allow a light beam from the second image to enter the ocular optical system after passing through the see-through optical element 220. The see-through optical element 220 is placed closer to the second image than the reflecting surface 212 at a distance from the reflecting surface 212.
In the present invention, the viewing optical system is arranged so that when the light beam from the outside world passes through the see-through optical element 220 and the prism optical system 210, the combined optical power P of the see-through optical element 220 and the prism optical system 210 is approximately zero, and the combined angular magnification xcex2 is approximately 1. The optical power and the angular magnification are those at a position where the axial principal ray 202 passes.
If the optical power P of the see-through optical system is approximately zero and the angular magnification xcex2 is approximately 1 as stated above, the image viewed through the see-through optical system appears to be the same as the image seen with the naked eye. Therefore, the image seen with the naked eye and the image viewed through the see-through optical system are readily fused into a single image. Accordingly, when a head-mounted image display apparatus designed for a single eye is used, for example, it is easy to view the outside world image with both eyes.
The phrase xe2x80x9cthe optical power P is approximately zeroxe2x80x9d means that the optical power P is within the range defined by the following condition:
xe2x88x920.002 less than P less than 0.002(/mm)xe2x80x83xe2x80x83(4)
If the optical power P is not within the range defined by this condition, the image-formation position of the image viewed through the see-through optical system and that of the image seen with the naked eye become excessively different from each other. Accordingly, it becomes difficult to see the outside world image with both eyes.
The phrase xe2x80x9cthe angular magnification xcex2 is approximately 1xe2x80x9d means that the angular magnification xcex2 is within the range defined by the following condition:
0.95 less than xcex2 less than 1.05xe2x80x83xe2x80x83(5)
If the angular magnification xcex2 is not within the range defined by this condition, the image viewed through the see-through optical system and the image seen with the naked eye are not formed with the same size. Accordingly, it is difficult to fuse the two images seen with the left and right eyes into a single image.
The above-described arrangement in which the see-through optical element is placed at a distance from the ocular optical system means a structure in which an optical power (e.g. an air lens) produced between the ocular optical system and the see-through optical element also contributes to the optical performance of the see-through optical system, but not a structure in which the ocular optical system and the see-through optical element are cemented together with an adhesive having a refractive index approximately equal to those of the optical members, so that an optical power produced at the cemented surface can be ignored. The present invention is not necessarily limited to the structure in which the ocular optical system and the see-through optical element are separated by air, but includes a structure in which the ocular optical system and the see-through optical element are cemented together with an adhesive having a refractive index different from those of the optical members, and a structure in which the gap between the ocular optical system and the see-through optical element is filled with a fluid, e.g. a liquid or a gas. It should be noted that a liquid crystal shutter may be disposed between the ocular optical system and the see-through optical element.
It is preferable from the viewpoint of aberration correction that the reflecting surfaces of the ocular optical system should have a rotationally asymmetric curved surface configuration that corrects decentration aberrations.
The reason for this is the same as stated above with reference to FIGS. 23 to 25.
The ocular optical system according to the present invention may also be arranged such that the above-described at least one surface having a reflecting action is decentered with respect to the axial principal ray and has a rotationally asymmetric surface configuration and further has a power. By adopting such an arrangement, decentration aberrations produced as the result of giving a power to the reflecting surface can be corrected by the surface itself. In addition, the power of the refracting surfaces of the prism is reduced, and thus chromatic aberration produced in the prism can be minimized.
The rotationally asymmetric surface used in the present invention should preferably be an anamorphic surface or a plane-symmetry free-form surface having only one plane of symmetry. Free-form surfaces used in the present invention are defined by the above equation (a). It should be noted that the Z-axis of the defining equation is the axis of a free-form surface.
It should be noted that the above defining equation (a) is shown as merely an example, and that the feature of the present invention resides in that rotationally asymmetric aberrations due to decentration are corrected and, at the same time, productivity is improved by using a rotationally asymmetric surface having only one plane of symmetry. Therefore, the same advantageous effect can be obtained for any other defining equation that expresses such a rotationally asymmetric surface.
It is desirable that the see-through optical system should be arranged to cancel the optical power and angular magnification produced by the ocular optical system so that the combined optical power and angular magnification given to the light beam from the second image when it passes through the see-through optical element and the ocular optical system satisfy the following conditions:
xe2x88x920.002 less than Px less than 0.002(1/mm)xe2x80x83xe2x80x83(6)
xe2x80x83xe2x88x920.002 less than Py less than 0.002(1/mm)xe2x80x83xe2x80x83(7)
0.97 less than xcex2x less than 1.03xe2x80x83xe2x80x83(8)
0.95 less than xcex2y less than 1.05xe2x80x83xe2x80x83(9)
where when the decentration direction of the entire optical system is a Y-axis direction, and a plane parallel to the axial principal ray is defined as a YZ-plane, and further a direction perpendicularly intersecting the YZ-plane is defined as an X-axis direction, Px and Py are powers in the X- and Y-axis directions, respectively, of the entire optical system, and xcex2x and xcex2y are angular magnifications in the X- and Y-axis directions, respectively, of the entire optical system.
It should be noted, however, that the above conditions apply in a case where the vertical direction of a man is the Y-axis direction. When the vertical direction of a man is the X-axis direction, the conditions (8) and (9) are as follows:
0.95 less than xcex2x less than 1.05xe2x80x83xe2x80x83(8)
0.97 less than xcex2y less than 1.03xe2x80x83xe2x80x83(9)
The reason why there is a difference in angular magnification between the vertical and horizontal directions is as follows. The human eye can see more finely in the horizontal (X-axis) direction than in the vertical (Y-axis) direction. Therefore, the tolerances on xcex2Y in the Y-axis direction can be somewhat relaxed, and thus there is a difference between the conditions (8) and (9).
The meaning of the upper and lower limits of the conditions (6) to (9) is the same as that of the upper and lower limits of the conditions (4) and (5).
Regarding the powers Px and Py in the X- and Y-axis directions of the entire optical system, it is more desirable to satisfy the following conditions:
xe2x88x920.001 less than Px less than 0.001(1/mm)xe2x80x83xe2x80x83(6-1)
xe2x88x920.001 less than Py less than 0.001(1/mm)xe2x80x83xe2x80x83(7-1)
It is also desirable to satisfy at least either one of the following conditions:
xe2x88x920.0005 less than Px less than 0.0005(1/mm)xe2x80x83xe2x80x83(6-2)
xe2x88x920.0005 less than Py less than 0.0005(1/mm)xe2x80x83xe2x80x83(7-2)
Regarding the angular magnifications xcex2x and xcex2y in the X- and Y-axis directions, respectively, of the entire optical system, it is more desirable to satisfy the following conditions:
0.99 less than xcex2x less than 1.01xe2x80x83xe2x80x83(8-1)
0.99 less than xcex2y less than 1.01xe2x80x83xe2x80x83(9-1)
It is even more desirable to satisfy the following conditions:
0.995 less than xcex2x less than 1.005xe2x80x83xe2x80x83(8-2)
0.995 less than xcex2y less than 1.005xe2x80x83xe2x80x83(9-2)
Let us denote the curvatures of the surfaces as follows. The curvatures in the X- and Y-axis directions of the entrance surface of the eye-side, first prism (the prism optical system 210 in FIG. 26) in backward ray tracing at the intersection between the entrance surface and the visual axis (axial principal ray) are denoted by Cx1 and Cy1, and the curvatures in the X- and Y-axis directions of the exit surface of the first prism at the intersection between the exit surface and the visual axis are denoted by Cx2 and Cy2. Further, the curvatures in the X- and Y-axis directions of the entrance surface of the see-through optical element, which is placed on the object side, at the intersection between the entrance surface and the visual axis are denoted by Cx3 and Cy3, and the curvatures in the X- and Y-axis directions of the exit surface of the see-through optical element are denoted by Cx4 and Cy4. When the first prism and the second prism are placed in close proximity to each other, it is desirable that Cx3/Cx2 and Cy3/Cy2 should satisfy the following conditions:
0.3 less than Cx3/Cx2 less than 1.2xe2x80x83xe2x80x83(10)
0.3 less than Cy3/Cy2 less than 1.2xe2x80x83xe2x80x83(11)
If Cx3/Cx2 or Cy3/Cy2 is not larger than the lower limit of the above conditions, i.e. 0.3, this portion has an excessively strong positive power because of the presence of the air layer sandwiched between the above-described two surfaces. To make the optical power of the entire optical system zero, the exit surface of the second prism unavoidably needs to have a strong negative optical power in order to cancel the power of this portion. Consequently, the angular magnification becomes far less than 1. In order to make the angular magnification approximately 1, the exit surface of the second prism also unavoidably needs to have a strong negative optical power. Consequently, the optical power of the entire optical system undesirably becomes a strong positive power. Accordingly, it becomes impossible to observe a far place.
If Cx3/Cx2 or Cy3/Cy2 is not smaller than the upper limit of the above conditions, i.e. 1.2, this portion has an excessively strong negative power because of the presence of the air layer sandwiched between the above-described two surfaces. To make the optical power of the entire optical system zero, the exit surface of the second prism unavoidably needs to have a strong positive optical power in order to cancel the power of this portion. Consequently, the angular magnification exceeds 1 to a considerable extent. In order to make the angular magnification approximately 1, the exit surface of the second prism also unavoidably needs to have a strong positive optical power. Consequently, the optical power of the entire optical system undesirably becomes a strong negative power. Accordingly, it becomes impossible to observe a near point.
It is more desirable to satisfy the following conditions:
0.4 less than Cx3/Cx2 less than 1xe2x80x83xe2x80x83(10-1)
0.4 less than Cy3/Cy2 less than 1xe2x80x83xe2x80x83(11-1)
Incidentally, the ocular optical system should preferably have at least a prism member filled with a medium having a refractive index larger than 1, as illustrated in FIG. 26. The prism member includes at least three optical surfaces having at least either one of a transmitting optical action and a reflecting optical action. The three surfaces are a first surface, a second surface, and a third surface. The third surface is an entrance surface through which a light beam from the first image enters the prism member. The second surface is disposed to face the see-through optical element at a distance. The second surface has a transmitting action to allow a light beam from the second image to enter the prism member after passing through the see-through optical element. The second surface further has a reflecting action to reflect the light beam from the first image in the prism member. The second surface has at least a curved reflecting surface. The first surface is an exit surface through which the light beam from the first image exits from the prism member.
In this case, it is desirable that at least either the first surface or the third surface should have a rotationally asymmetric curved surface configuration that corrects decentration aberrations, and that the curved surface configuration should be either an anamorphic surface or a plane-symmetry free-form surface having only one plane of symmetry.
It is desirable for the first surface to be arranged to serve as both a reflecting surface and a transmitting surface for the light beam in the prism member.
In this case, the first surface serving as both a reflecting surface and a transmitting surface should preferably be a totally reflecting surface arranged so that the reflected light beam is incident on the first surface at an angle exceeding the total reflection critical angle, and thereafter, the light beam reflected back from the reflecting surface is incident on the first surface at an angle not exceeding the total reflection critical angle to exit from the prism member.
In the viewing optical system according to the present invention, the ocular optical system and the see-through optical element may be arranged so that a first image viewing field range determined by the light beam from the first image as it exits from the ocular optical system is formed within a second image viewing field range determined by the light beam from the second image as it passes through the see-through optical element and a part of the ocular optical system.
Furthermore, the ocular optical system and the see-through optical element may be arranged as follows. The optical diameter of the see-through optical element is set smaller than the reflecting surface of the ocular optical system, which is placed to face the see-through optical element, and the see-through optical element is placed to face a region of the reflecting surface closer to the image forming member so that the light beam transmitting region of the reflecting surface that transmits the light beam entering through the see-through optical element shifts toward the image forming member with respect to the light beam reflecting region of the reflecting surface. In addition, a portion of the reflecting surface that does not directly face the see-through optical element is provided with a light-blocking coating to prevent entrance of flare rays from the outside world.
It is possible to place a light-blocking member capable of switching between transmission and cutoff of the light beam from the outside world image or switching between transmission and dimming of the light beam at at least either one of positions in front of and behind the see-through optical element so that the second image is the outside world image.
In addition, another display device that forms an image different from the first image may be placed on the side of the see-through optical element remote from the ocular optical system so that the second image is formed by the display device.
The viewing optical system may be arranged such that a light-blocking member capable of switching between transmission and cutoff of the light beam from the outside world image or switching between transmission and dimming of the light beam is placed at at least either one of positions in front of and behind the see-through optical element so that the second image is the outside world image, and a display device for displaying a third image is provided between the outside world image and the see-through optical element.
The viewing optical system according to the present invention may have a line-of-sight detecting device for detecting the observer""s line of sight. The line-of-sight detecting device includes a light source for pupil illumination and a light-receiving element for receiving the image of the pupil, which are disposed at respective positions out of the optical path in the ocular optical system for leading the light beam from the first image and the optical path in the see-through optical element for leading the light beam from the second image.
In this case, the line-of-sight detecting device may be arranged such that at least the image of the pupil is passed through the optical path of the ocular optical system and separated from the optical path between the ocular optical system and the first image so as to be led to the light-receiving element. Thus, the optical path of the line-of-sight detecting device is formed by using the viewing optical path. Consequently, it is possible to eliminate the influence of outside world light that may enter through the optical path of the line-of-sight detecting device and also the influence of stray light from the pupil-illuminating light source. It is also possible to eliminate the greater part of the line-of-sight detecting optical system. Accordingly, it is possible to achieve a cost reduction and a size reduction.
It is desirable that the ocular optical system, the see-through optical element and the exit pupil should be positioned so as to satisfy the following condition:
xcex8xe2x89xa660xc2x0
where when the optical axis of the light beam from the first image that exits from the ocular optical system is defined as a visual axis, xcex8 is the angle defined at the exit pupil by the ocular optical system in a direction away from the image forming member with respect to the visual axis.
If the above-described condition is satisfied, it is possible not only to perform observation through the see-through optical path but also to see a keyboard, for example, placed below the viewing optical system directly without looking through the viewing optical system.
It should be noted that the present invention includes a head-mounted viewing optical apparatus having an apparatus body unit including any one of the foregoing viewing optical systems, in which the ocular optical system, the see-through optical element and the image forming member for forming the first image are retained with the required spacings therebetween by a retaining device. The head-mounted viewing optical apparatus further includes a support device for supporting the apparatus body unit on the observer""s head.
Next, the third and fourth viewing optical systems according to the present invention will be described.
FIG. 44 is a ray path diagram of a viewing optical system according to Example 7 (described later). The third and fourth viewing optical systems will be described below with reference to FIG. 44. The ocular optical system of the viewing optical system includes a prism optical system 410. The prism optical system 410 has a first surface 411, a second surface 412, and a third surface 413 as counted from the exit pupil 401 side in backward ray tracing. The first surface 411 serves as both a transmitting surface and a totally reflecting surface. The second surface 412 is a semitransparent reflecting surface. The third surface 413 is a transmitting surface. Display light from an image display device placed in an image plane 403 enters the prism optical system 410 through the third surface 413. The incident light is reflected by the first surface 411 and further reflected by the second surface 412 to exit from the prism optical system 410 through the first surface 411. Then, the light enters an observer""s eyeball placed so that the pupil is located at the position of the exit pupil 401. Thus, the image displayed at the image plane 403 is observable as an enlarged image.
A see-through optical element 420 is placed in front of the second surface 412 of the prism optical system 410 so as to be in close contact with the second surface 412 (the see-through optical element 420 may be cemented to the second surface 412). The see-through optical element 420 is formed from another transmission prism member having a first surface 421 (with the same configuration as that of the second surface 412 of the prism optical system 410) and a second surface 422 as counted from the exit pupil 401 side in backward ray tracing. The first surface 421 and the second surface 422 are transmitting surfaces. Light from the outside world passes successively through the second surface 422 of the see-through optical element 420 and the first surface 421 thereof (=the second surface 412 of the prism optical system 410) and further through the first surface 411 of the prism optical system 410 and enters the observer""s eyeball, in which the pupil is placed at the position of the exit pupil 401, to form an outside world image. It is possible to selectively observe either of the outside world image and the displayed image of the image display device placed in the image plane 403. It is also possible to observe both the images superimposed on one another. In FIG. 44, reference numeral 402 denotes an axial principal ray.
Thus, the third and fourth viewing optical systems according to the present invention each include an image forming member (the image display device placed in the image plane 403) for forming a first image to be viewed by an observer, and an ocular optical system (including the prism optical system 410 and a diffractive optical element 404 in this case) arranged to lead the image formed by the image forming member to an observer""s eyeball. The viewing optical system further includes the see-through optical element 420 placed closer to a second image (the outside world image in this case), which is different from the first image, than the ocular optical system so as to lead the second image to the observer""s eyeball. The ocular optical system has at least a reflecting surface 412 with a curved surface configuration arranged to reflect a light beam from the first image and to lead it toward the observer""s eyeball. The reflecting surface 412 has a transmitting action to allow a light beam from the second image to enter the ocular optical system after passing through the see-through optical element 420. The see-through optical element 420 is placed closer to the second image than the reflecting surface 412 so as to be in close contact with the reflecting surface 412.
The third viewing optical system according to the present invention is arranged so that when the light beam from the outside world passes through the see-through optical element 420 and the prism optical system 410, the combined optical power P of the see-through optical element 420 and the prism optical system 410 is approximately zero. It should be noted that optical power P is the optical power at a position where the axial principal ray 402 passes.
If the optical power P of the see-through optical system is approximately zero as stated above, the outside world image viewed through the see-through optical system and the outside world image viewed with the naked eye are seen at the same position. Therefore, it becomes easy to see the see-through image. Consequently, when a head-mounted image display apparatus designed for a single eye is used, for example, it is easy to view the outside world image, particularly the axial portion of the outside world image, with both eyes. In this case, however, the optical system becomes a two-unit telephoto optical system, which comprises a combination of a positive optical unit and a negative optical unit or a combination of a negative optical unit and a positive optical unit, from the viewpoint of paraxial optical theory. Therefore, it is difficult to arrange the optical system so that the combined angular magnification xcex2 of the see-through optical element 420 and the prism optical system 410 is 1 at the same time as the optical power P of the see-through optical system is made approximately zero. Accordingly, it is difficult to make the magnification of the outside world image viewed through the see-through optical system and the magnification of the outside world image seen with the naked eye equal to each other. For this reason, binocular rivalry occurs between the left and right eyes with respect to the peripheral portion of the image field. Consequently, the image seen with the dominant eye is observed.
The fourth viewing optical system according to the present invention is arranged so that when the light beam from the outside world passes through the see-through optical element 420 and the prism optical system 410, the combined angular magnification xcex2 of the see-through optical element 420 and the prism optical system 410 is approximately 1. It should be noted that the angular magnification xcex2 is the angular magnification at a position where the axial principal ray 402 passes.
If the angular magnification xcex2 of the see-through optical system is approximately 1 as stated above, the outside world image viewed through the see-through optical system and the outside world image seen with the naked eye are of the same magnification. Therefore, when a head-mounted image display apparatus designed for a single eye is used, for example, it is easy to fuse two images seen with the right and left eyes. In this case, however, it is difficult to arrange the optical system so that the combined optical power P of the see-through optical element 420 and the prism optical system 410 is zero at the same time as the angular magnification xcex2 of the see-through optical system is made approximately 1. Accordingly the image-formation position of the outside world image viewed through the see-through optical system and the image-formation position of the outside world image seen with the naked eye are not coincident with each other. Consequently, it is somewhat difficult to observe a far object. However, there is no problem in the case of observing a near object.
The phrase xe2x80x9cthe optical power P is approximately zeroxe2x80x9d means that the optical power P is within the range defined by the following condition:
xe2x88x920.002 less than P less than 0.002(1/mm)xe2x80x83xe2x80x83(12)
If the optical power P is not within the range defined by this condition, the image-formation position of the image viewed through the see-through optical system and that of the image seen with the naked eye become excessively different from each other. Accordingly, it becomes difficult to see the outside world image with both eyes.
The phrase xe2x80x9cthe angular magnification xcex2 is approximately 1xe2x80x9d means that the angular magnification xcex2 is within the range defined by the following condition:
xe2x80x830.95 less than xcex2 less than 1.06xe2x80x83xe2x80x83(13)
If the angular magnification xcex2 is not within the range defined by this condition, the image viewed through the see-through optical system and the image seen with the naked eye are not formed with the same size. Accordingly, it is difficult to fuse the two images seen with the left and right eyes into a single image.
The above-described arrangement in which the see-through optical element 420 is placed in close contact with the reflecting surface 412 of the prism optical system 410 means a structure in which the first surface 421 of the see-through optical element 420 and the second surface 412 of the prism optical system 410 are formed with the same surface configuration and the first surface 421 and the second surface 412 are brought into close contact with or close proximity to each other or cemented together with an adhesive approximately equal in refractive index to these optical members. A structure in which an optical power produced by these surfaces can be ignored is included in the arrangement according to the present invention.
It is preferable from the viewpoint of aberration correction that the reflecting surfaces of the ocular optical system should have a rotationally asymmetric curved surface configuration that corrects decentration aberrations.
The reason for this is the same as stated above with reference to FIGS. 23 to 25.
The ocular optical system according to the present invention may also be arranged such that the above-described at least one surface having a reflecting action is decentered with respect to the axial principal ray and has a rotationally asymmetric surface configuration and further has a power. By adopting such an arrangement, decentration aberrations produced as the result of giving a power to the reflecting surface can be corrected by the surface itself. In addition, the power of the refracting surfaces of the prism is reduced, and thus chromatic aberration produced in the prism can be minimized.
The rotationally asymmetric surface used in the present invention should preferably be an anamorphic surface or a plane-symmetry free-form surface having only one plane of symmetry. Free-form surfaces used in the present invention are defined by the above equation (a). It should be noted that the Z-axis of the defining equation is the axis of a free-form surface.
It should be noted that the above defining equation (a) is shown as merely an example, and that the feature of the present invention resides in that rotationally asymmetric aberrations due to decentration are corrected and, at the same time, productivity is improved by using a rotationally asymmetric surface having only one plane of symmetry. Therefore, the same advantageous effect can be obtained for any other defining equation that expresses such a rotationally asymmetric surface.
In the third viewing optical system according to the present invention, it is desirable that the see-through optical system should be arranged to cancel the optical power produced by the ocular optical system so that the combined optical power given to the light beam from the second image when it passes through the see-through optical element and the ocular optical system satisfies the following conditions:
xe2x88x920.002 less than Px less than 0.002(1/mm)xe2x80x83xe2x80x83(14)
xe2x88x920.002 less than Py less than 0.002(1/mm)xe2x80x83xe2x80x83(15)
where when the decentration direction of the entire optical system is a Y-axis direction, and a plane parallel to the axial principal ray is defined as a YZ-plane, and further a direction perpendicularly intersecting the YZ-plane is defined as an X-axis direction, Px and Py are powers in the X- and Y-axis directions, respectively, of the entire optical system.
The meaning of the upper and lower limits of the conditions (14) to (15) is the same as that of the upper and lower limits of the condition (12).
Regarding the powers Px and Py in the X- and Y-axis directions of the entire optical system, it is more desirable to satisfy the following conditions:
xe2x88x920.001 less than Px less than 0.001(1/mm)xe2x80x83xe2x80x83(14-1)
xe2x88x920.001 less than Py less than 0.001(1/mm)xe2x80x83xe2x80x83(15-1)
It is also desirable to satisfy at least either one of the following conditions:
xe2x88x920.0005 less than Px less than 0.0005(1/mm)xe2x80x83xe2x80x83(14-2)
xe2x88x920.0005 less than Py less than 0.0005(1/mm)xe2x80x83xe2x80x83(15-2)
In the fourth viewing optical system according to he present invention, it is desirable that the see-through optical system should be arranged to cancel the angular magnification produced by the ocular optical system so that the combined optical magnification given to the light beam from the second image when it passes through the see-through optical element and the ocular optical system satisfies the following conditions:
0.97 less than xcex2x less than 1.03xe2x80x83xe2x80x83(16)
0.95 less than xcex2y less than 1.06xe2x80x83xe2x80x83(17)
where when the decentration direction of the entire optical system is a Y-axis direction, and a plane parallel to the axial principal ray is defined as a YZ-plane, and further a direction perpendicularly intersecting the YZ-plane is defined as an X-axis direction, xcex2x and xcex2y are angular magnifications in the X- and Y-axis directions, respectively, of the entire optical system.
It should be noted, however, that the above conditions (16) and (17) apply in a case where the vertical direction of a man is the Y-axis direction. When the vertical direction of a man is the X-axis direction, the conditions (16) and (17) are as follows:
0.95 less than xcex2x less than 1.06xe2x80x83xe2x80x83(16)xe2x80x2
0.97 less than xcex2y less than 1.03xe2x80x83xe2x80x83(17)xe2x80x2
The reason why there is a difference in angular magnification between the vertical and horizontal directions is as follows. The human eye can see more finely in the horizontal (X-axis) direction than in the vertical (Y-axis) direction. Therefore, the tolerances on xcex2Y in the Y-axis direction can be somewhat relaxed, and thus there is a difference between the conditions (16) and (17).
The meaning of the upper and lower limits of the conditions (16) and (17) is the same as that of the upper and lower limits of the condition (13).
Regarding the angular magnifications xcex2x and xcex2y in the X- and Y-axis directions, respectively, of the entire optical system, it is more desirable to satisfy the following conditions:
0.99 less than xcex2x less than 1.01xe2x80x83xe2x80x83(16-1)
0.99 less than xcex2y less than 1.01xe2x80x83xe2x80x83(17-1)
It is even more desirable to satisfy the following conditions:
0.995 less than xcex2x less than 1.005xe2x80x83xe2x80x83(16-2)
0.995 less than xcex2y less than 1.005xe2x80x83xe2x80x83(17-2)
Incidentally, the ocular optical system should preferably have at least a prism member filled with a medium having a refractive index larger than 1, as illustrated in FIG. 44. The prism member includes at least three optical surface having at least either one of a transmitting optical action and a reflecting optical action. The three surfaces are a first surface, a second surface, and a third surface. The third surface is an entrance surface through which a light beam from the first image enters the prism member. The second surface is placed in close contact with the see-through optical element. The second surface has a transmitting action to allow a light beam from the second image to enter the prism member after passing through the see-through optical element. The second surface further has a reflecting action to reflect the light beam from the first image in the prism member. The second surface has at least a curved reflecting surface. The first surface is an exit surface through which the light beam from the first image exits from the prism member.
In this case, it is desirable that at least either the first surface or the third surface should have a rotationally asymmetric curved surface configuration that corrects decentration aberrations, and that the curved surface configuration should be either an anamorphic surface or a plane-symmetry free-form surface having only one plane of symmetry.
It is desirable for the first surface to be arranged to serve as both a reflecting surface and a transmitting surface for the light beam in the prism member.
In this case, the first surface serving as both a reflecting surface and a transmitting surface should preferably be a totally reflecting surface arranged so that the reflected light beam is incident on the first surface at an angle exceeding the total reflection critical angle, and thereafter, the light beam reflected back from the reflecting surface is incident on the first surface at an angle not exceeding the total reflection critical angle to exit from the prism member.
In the third and fourth viewing optical systems according to the present invention, the ocular optical system and the see-through optical element may be arranged so that a first image viewing field range determined by the light beam from the first image as it exits from the ocular optical system is formed within a second image viewing field range determined by the light beam from the second image as it passes through the see-through optical element and a part of the ocular optical system.
Furthermore, the ocular optical system and the see-through optical element may be arranged as follows. The optical diameter of the see-through optical element is set smaller than the reflecting surface of the ocular optical system, which is placed to face the see-through optical element, and the see-through optical element is placed to face a region of the reflecting surface closer to the image forming member so that the light beam transmitting region of the reflecting surface that transmits the light beam entering through the see-through optical element shifts toward the image forming member with respect to the light beam reflecting region of the reflecting surface. In addition, a portion of the reflecting surface that does not directly face the see-through optical element is provided with a light-blocking coating to prevent entrance of flare rays from the outside world.
It is possible to place a light-blocking member capable of switching between transmission and cutoff of the light beam from the outside world image or switching between transmission and dimming of the light beam in front of the see-through optical element so that the second image is the outside world image.
In addition, another display device that forms an image different from the first image may be placed on the side of the see-through optical element remote from the ocular optical system so that the second image is formed by the display device.
The viewing optical system may be arranged such that a light-blocking member capable of switching between transmission and cutoff of the light beam from the outside world image or switching between transmission and dimming of the light beam is placed in front of the see-through optical element so that the second image is the outside world image, and a display device for displaying a third image is provided between the outside world image and the see-through optical element.
The third and fourth viewing optical systems according to the present invention may have a line-of-sight detecting device for detecting the observer""s line of sight. The line-of-sight detecting device includes a light source for pupil illumination and a light-receiving element for receiving the image of the pupil, which are disposed at respective positions out of the optical path in the ocular optical system for leading the light beam from the first image and the optical path in the see-through optical element for leading the light beam from the second image.
In this case, the line-of-sight detecting device may be arranged such that at least the image of the pupil is passed through the optical path of the ocular optical system and separated from the optical path between the ocular optical system and the first image so as to be led to the light-receiving element. Thus, the optical path of the line-of-sight detecting device is formed by using the viewing optical path. Consequently, it is possible to eliminate the influence of outside world light that may enter through the optical path of the line-of-sight detecting device and also the influence of stray light from the pupil-illuminating light source. It is also possible to eliminate the greater part of the line-of-sight detecting optical system. Accordingly, it is possible to achieve a cost reduction and a size reduction.
It is desirable that the ocular optical system, the see-through optical element and the exit pupil should be positioned so as to satisfy the following condition:
xcex8xe2x89xa660xc2x0
where when the optical axis of the light beam from the first image that exits from the ocular optical system is defined as a visual axis, xcex8 is the angle defined at the exit pupil by the ocular optical system in a direction away from the image forming member with respect to the visual axis.
If the above-described condition is satisfied, it is possible not only to perform observation through the see-through optical path but also to see a keyboard, for example, placed below the viewing optical system directly without looking through the viewing optical system.
It should be noted that the present invention includes a head-mounted viewing optical apparatus having an apparatus body unit including any one of the foregoing viewing optical systems, in which the ocular optical system, the see-through optical element and the image forming member for forming the first image are retained with the required spacings therebetween by a retaining device. The head-mounted viewing optical apparatus further includes a support device for supporting the apparatus body unit on the observer""s head.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.
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