Abstract:
When n is taken as integers of 2 or more, n reflecting systems are constituted by providing reflecting mirrors on opposite (two) side surfaces in 2 n  side surfaces of a transparent body having the shape of a 2 n -sided prism. The n reflecting systems are provided on each pair of opposite side surfaces, and images of an object are formed using each of the n reflecting systems.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an optical element and a picture taking system including the optical element that is particularly suitable for a video camera, a still video camera, and a copying machine. 
     2. Description of the Related Art 
     FIG. 10 schematically illustrates a main part of an optical system disclosed in Japanese Patent Laid-Open No. 8-292371. 
     Referring to FIG. 10, there is provided an optical element  10  including a transparent body formed of glass or plastic, having a plurality of curved reflecting surfaces provided on the surface thereof. 
     On the surface of the optical element  10 , there are formed, in the order of passage of light from an object, a concave refracting surface (incident surface) R 2  having a negative refractive power, four reflecting surfaces of concave mirror R 3 , reflecting mirrors R 4  and R 5 , a concave mirror R 6 , and a convex refracting surface (emergent surface) R 7  having a positive refractive power. In FIG. 10, there are shown a diaphragm (entrance pupil) R 1  disposed on the object side of the optical element  10 , an optical correcting plate  3 , such as a quartz low-pass filter, an infrared filter, or the like, a final image forming surface R 10  on which an image pick-up surface (light receiving surface) of an image pick-up element (image pick-up medium) such as a CCD is located, and a reference axis  5  of the optical system. 
     Both the refracting surfaces R 2  and R 7  are rotary symmetrical spherical surfaces, and all the reflecting surfaces R 3  to R 6  are aspheric surfaces symmetrical with respect to only a YZ plane. 
     An image forming operation of the optical element  10  will now be described. Of the light flux  1  from an object, the amount of incident light is regulated by the diaphragm R 1 , and then enters the incident surface R 2  of the optical element  10 , is reflected by the surfaces R 3  and R 4 , temporarily forms an image near the surface R 4 , is reflected from the surfaces R 5  and R 6 , and is emitted from the emergent surface R 7  to form an image again on the final image forming surface R 10  via the optical correcting plate  3 . As described above, the light from the object temporarily forms an image near the surface R 4 , while the light of the entrance pupil R 1  temporarily forms an image between the surfaces R 5  and R 6 . 
     The direction of the reference axis entering the optical element  10  and that emitting therefrom are parallel to and the same as each other. In addition, all of the reference axes including the incident reference axis and emergent reference axis are given in FIG. 10 (on the YZ plane). 
     The optical element  10  serves as a lens unit having a desired optical performance and a positive refractive power overall by virtue of the refractive power (φ=1/f; φ: power, f: focal length) of the incident and emergent surfaces R 2  and R 7 , and the refractive powers of the concave reflecting mirrors R 3  and R 6 . 
     In addition, the optical element  10  collects light fluxes from the object existing in one direction (left side on the plane of the drawing), and forms the image thereof on the final image forming surface R 10 . 
     It is convenient that pictures of an object located in another direction, for example, in a direction perpendicular to the plane of the drawing (the X direction) can be taken as in the state of FIG. 10 without rotating the optical element  10  around an axis of rotation in the Y direction. 
     In addition, it is also convenient that pictures of objects located in the same direction can be easily taken by substantially one optical element with different magnification. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a convenient optical element and a picture taking system having the convenient optical element. 
     According to an aspect of the present invention, there is provided an optical element including a plurality of curved reflecting portions, the reflecting portions reflecting light entered into the optical element, thereby transmitting the light inside the optical element, wherein the reflecting portions include a plurality of reflecting portion groups, and the reflecting portion groups form optical paths that are different from each other. 
     According to another aspect of the present invention, there is provided an optical element including a plurality of curved reflecting portions, the reflecting portions reflecting light entered into the optical element from a light incident portion, thereby transmitting the light inside the optical element, wherein the reflecting portions include a plurality of reflecting portion groups, and the reflecting portion groups have different optical characteristics. 
     In each of the above optical elements, the reflecting portions may be provided on 2n(n=integers of 2 or more) side surfaces (inner surfaces when body is hollow) of at least one of a solid body and a hollow body having the shape of a 2n-sided prism (n=integers of 2 or more), respectively, and the reflecting portion groups may be constructed by the reflecting portions provided on each pair of opposite side surfaces (inner surfaces when the body is hollow). 
     In addition, in each of the above optical elements, each of the reflecting portion groups may include a light incident portion and a light emergent portion; the reflecting portion groups may include a common reflecting portion and light incident portion, and the common reflecting portion and light incident portion may be rotatable together; and the reflecting portion groups may include a common final reflecting portion and light emergent portion, and the common final reflecting portion and light emergent portion may be rotatable together. 
     Furthermore, in each of the above optical elements, at least one of the light incident portion and the light emergent portion may include a curved surface that forms a spherical lens or an aspheric lens. 
     Still furthermore, in each of the above optical elements, each of the reflecting portions may include a rotary asymmetrical aspheric reflecting surface. 
     According to the present invention, there is provided a picture taking optical system including any one of the above optical elements, and a picture taking apparatus including the picture taking optical system and at least one of an image pick-up element and an image pick-up medium. 
     Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a main part external view of a first embodiment of a picture taking system having an optical element of the present invention; 
     FIG. 2 illustrates the optical element shown in FIG. 1; 
     FIG. 3 illustrates the optical element shown in FIG.  1 : 
     FIG. 4 illustrates another configuration of the embodiment of the optical element of the present invention; 
     FIG. 5 is a main part external view of a second embodiment of a picture taking system having an optical element of the present invention; 
     FIG. 6 is another main part external view of the second embodiment of a picture taking system having an optical element of the present invention; 
     FIG. 7 is a main part external view of a third embodiment of a picture taking system having an optical element of the present invention; 
     FIG. 8 illustrates one cross-sectional view of FIG. 7; and 
     FIG. 9 illustrates another cross-sectional view of FIG. 7; and 
     FIG. 10 schematically illustrates a main part of a conventional optical element. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a main part external view of a first embodiment of a picture taking system including an optical element of the present invention. 
     Referring to FIG. 1, there is provided an optical element  100 , and image pick-up elements  108  and  118  are provided near light emergent surfaces  107  and  117 , respectively, of the optical element  100 . FIG. 2 schematically illustrates an optical path of a first reflecting system R 01  that is set with respect to the XZ plane of the optical element  100  of FIG. 1, and FIG. 3 schematically illustrates an optical path of a second reflecting system R 02  that is set with respect to the XY plane of the optical element  100  of FIG.  1 . The optical element  100  of this embodiment employs a transparent body GP having the shape of a rectangular parallelepiped. The transparent body GP is formed of glass or plastic. 
     As will be understood from FIG. 2, the optical element includes a refracting surface  101  on which light flux is dent, a plurality of (five in FIG. 2, but the number is limited thereto) reflecting surfaces  102  to  106  each having curvature, and a refracting surface  107  from which the light flux reflected by the reflecting surfaces is emitted, provided on the surfaces of the opposite side surfaces  10   a  and  10   b  of the transparent body GP, thereby constructing the first reflecting system R 01  in which light La 1  is on an optical path in the XZ plane. 
     In the first reflecting system R 01  of FIG. 2, the light flux from the object (not shown) located in the Z direction is guided to an image pick-up element  108  via the refracting surface  101 , reflecting surfaces  102  to  106  and the refracting surface  107 , and an object image is formed by the light flux on the image pick-up surface. 
     As will be understood from FIG. 3, the optical element  100  includes a refracting surface  111  on which light flux is incident, a plurality of (five in FIG. 3, but the number is not limited thereto) reflecting surfaces  112  to  116  each having curvature, and a refracting surface  117  from which the light flux reflected by the reflecting surfaces is emitted, provided on the surfaces of the opposite side surfaces  11   a  and  11   b  of the transparent body GP, thereby constructing the second reflecting system R 02  in which light La 2  is on an optical path in the XY plane. 
     In the second reflecting system R 02  of FIG. 3, the light flux from the object (not shown) located in the Y direction is guided to an image pick-up element  118  via the refracting surface  111 , reflecting surfaces  112  to  116  and the refracting surface  117 , and an object image is formed by the light flux on the image pick-up surface. 
     The optical operation of the first reflecting system R 01  shown in FIG.  2  and that of the second reflecting system R 02  are completely separated. Therefore, it is also possible to construct the first and second reflecting systems R 01  and R 02  by optical systems in which optical parameters (optical characteristics) such as focal length, image taking view angle, and the like are different from each other. 
     For example, by allowing the reflecting systems R 01  and R 02  to differ from each other in the focal length, the optical element  100  can be used as a double-focus lens. According to this embodiment, an optical system having a far-reduced size and thickness can be achieved as compared with an optical system of a type of switching an attachment and a turret seen in a conventional coaxial optical system. 
     In addition, by constructing the reflecting surfaces of the reflecting systems R 01  and R 02  so that they have a different reflectance, the reflecting systems R 01  and R 02  may differ from each other in terms of total transmittance. With this construction, selection of either of the reflecting systems according to luminance of the object eliminates the need for mechanical switching such as driving of the diaphragm and insertion of a ND filter, and a combination of either of the reflecting systems and a mechanical shutter or a electrical shutter of the image pick-up element enables pictures to be taken in a wide range of exposures. 
     Further, the F-number at the time of design may be varied between the reflecting systems R 01  and R 02 . In this case, the depth of field can be varied in addition to the effect of the above step-by-step exposure switching, enabling a greater variety of types of pictures to be taken. 
     Still further, image pick-up elements having different aspect ratios may be used for the image pick-up elements  108  and  118 . This allows images of differing aspect ratio to be easily obtained. 
     In this embodiment, one of the image pick-up elements  108  and  118  may be omitted, and the remaining one image pick-up element may be rotated around the axis  110  of the optical element  100 . 
     The shape of the transparent body GP and the number of the reflecting systems provided thereon are not limited to those of the transparent body GP shown in FIG.  1 . For example, first to third reflecting systems may be provided on each of the opposite side surfaces of a transparent body GP having the shape of a hexagonal prism, as shown in FIG.  4 . 
     FIGS. 5 and 6 are main part external views each showing a second embodiment of the picture taking system having the optical element of the present invention. 
     The second embodiment differs from the first embodiment of FIG. 1 in that an optical member  21  is produced by separating the refracting surface  101  and only the reflecting surface  102  from the optical element  100  and by combining these surfaces, and the optical member  21  is rotatably provided with respect to the center axis  210  of the transparent body GP in the direction shown by the arrows in FIGS. 5 and 6. 
     Light flux from the object in the Z direction (FIG. 5) and light flux from the object in the Y direction (FIG. 6) are selectively taken in and guided to the transparent body GP, thereby being guided to the corresponding image pick-up element  203  or  213 . 
     FIGS. 7,  8  and  9  are main part external views each showing a third embodiment of the picture taking system having the optical element of the present invention. 
     Referring to the drawings, numeral  400  denotes an optical element, and first and second reflecting systems  405  and  406  each having a plurality of reflecting mirrors similar to those shown in FIGS. 2 and 3 are provided in a transparent body  40  that constitutes a part of the optical element  400 . 
     In this embodiment, an optical member  4   a  that is a combination of a refracting surface  411  (corresponding to the refracting surface  101  or  111  of FIG. 1) on which the light flux from the object is incident, and a reflecting surface  401  (corresponding to the reflecting surfaces  102  and  112 ) for reflecting the light incident from the refracting surface  411  is rotatably provided with respect to an axis  410  in opposition to one surface of the transparent body  40 . 
     In addition, an optical member  4   b  that is a combination of a reflecting surface  403  (corresponding to the reflecting surfaces  106  and  116  of FIG. 1) for reflecting the light flux emitted from the transparent body  40 , and a refracting surface  421  (corresponding to the refracting surface  107  or  117 ) for emitting the light flux from the reflecting surface  403  is rotatably provided with respect to the axis  410  in opposition to the other surface of the transparent body  40 . 
     Furthermore, one image pick-up element  404  is provided in the emergent direction of the refracting surface  421  so as to be rotated together with the optical member  4   b.    
     In the state shown in FIG. 7, light flux from the object (not shown) located in the Z direction is, as shown in FIG. 8, incident on the transparent body  40  via the refracting surface  411  of the optical member  4   a,  and the reflecting surface  401 , is reflected from a plurality of reflecting mirrors of the first reflecting system  405  provided within the XZ plane in the transparent body  40  similarly to the optical element  100  of FIG. 2, is emitted from the transparent body  40 , and then guided to the image pick-up element  404  via the reflecting surface  403  of the optical member  4   b  and the refracting surface  421 , and an object image is formed on the image pick-up surface by the light flux. 
     FIG. 9 illustrates the optical members  4   a  and  4   b  and the image pick-up element  404  that are rotated 90° in a counterclockwise direction using the axis  410  as an axis of rotation in the state of FIG.  7 . 
     In FIG. 9, light flux from the object (not shown) located in the Y direction is reflected by a plurality of reflecting mirrors of the second reflecting system  406  provided within the XY plane in the transparent body  40  similarly to optical element  100  of FIG. 3 via the refracting surface  411  of the optical member  4   a  and the reflecting surface  401 , is emitted from the transparent body  40 , and then guided to the image pick-up element  404  via the reflecting surface  403  of the optical member  4   b  and the refracting surface  421 , and an object image is formed on the image pick-up surface by the light flux. 
     An optical element having a plurality of reflecting systems as described above offers the following advantages. 
     (A) It is possible to easily take pictures of an object located in any of a plurality of directions. 
     (B) It is possible to easily obtain a plurality of picture-taking modes. 
     (C) Pictures can be taken with different optical characteristics (focal length, total transmittance, F-number, and picture-taking aspect ratio), and various types of images can be obtained. 
     (D) Since pictures can be taken with a plurality of focal lengths, images of different view angles can be obtained without an additional attachment or a complicated zoom mechanism. 
     (E) The optical element has reflecting systems of different total transmittance and F-number, whereby step-by-step exposure control can be easily effected. 
     (F) By varying the picture-taking aspect ratio between the reflecting systems, the optical element can respond to a greater variety of picture-taking formats. 
     (G) The adoption of an off-axis optical system enables an optical system to be reduced in thickness and size, as compared with a coaxial optical system. 
     While the present invention has been described with reference to what are presently considered to be the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.