Patent Publication Number: US-6903885-B2

Title: Light-projecting device

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a light-projecting device provided for indicating a focused point, for example, in a view finder of a single-lens reflex camera. 
   2. Description of the Related Art 
   Conventionally, there is known a single-lens reflex camera provided with a function, in which a plurality of distance-measurement points are set for an image to be photographed, and a point, which is in-focus and included in the distance-measurement points, is indicated and superimposed on a subject image in a view finder, as disclosed in Japanese Unexamined Patent Publication No. 2002-268128. Namely, a focusing glass and a superimpose-plate are superposed on each other, and disposed under a hollow pentagonal mirror, and if the number of the distance-measurement points is seven, seven small focusing marks are formed on the superimpose-plate. A light-projecting optical system is provided in a rear portion or an emergent opening of the hollow pentagonal mirror and above an ocular optical system. In a photographing operation, when any point of the distance-measurement points is in-focus, an illumination light beam is radiated from the light-projecting optical system onto the corresponding focusing mark, so that the photographer can recognize the in-focus point. 
   Each of the focusing marks formed on the superimpose-plate is formed by lots of micro-prisms, which are inclined relative to a surface of the superimpose-plate at an inclination angle that depends upon the position of the focusing mark. Namely, an illumination light beam is obliquely radiated from a light source of the light-projecting optical system provided at a side of the emergent opening of the hollow pentagonal mirror. The radiation angle of the illumination light beam differs depending upon the position of the focusing mark, and the micro-prisms are inclined at an angle such that the illumination light beam is effectively received. 
   Thus, since the inclination angles of the micro-prisms are different from each other, the manufacturing process of the superimpose-plate is complicated, which in turn makes controlling the manufacturing process difficult, resulting in increased manufacturing cost. 
   SUMMARY OF THE INVENTION 
   Therefore, an object of the present invention is to provide a light-projecting device in which the number of different kinds of inclination angles of the micro-prisms is reduced, so that the manufacturing process of the micro-prisms is simplified. 
   According to the present invention, there is provided a light-projecting device for a view finder, comprising a superimpose-plate, a hollow pentagonal mirror, and a light-projecting optical system. 
   The superimpose-plate is put on a focusing glass, on which a subject image obtained through the photographing optical system is formed. The hollow pentagonal mirror is provided above the focusing glass and the superimpose-plate. The light-projecting optical system is disposed close to an emergent opening of the hollow pentagonal mirror. An illumination light beam output from the light-projecting optical system is reflected on the third reflecting plane and the roof reflecting plane of the hollow pentagonal mirror, and is approximately perpendicularly radiated on the superimpose-plate. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The objects and advantages of the present invention will be better understood from the following description, with reference to the accompanying drawings in which: 
       FIG. 1  is a sectional view showing a mirror box and a view finder optical system, to which a first embodiment of the present invention is applied, and in which a light-projecting prism is removed; 
       FIG. 2  is a sectional view showing the mirror box and the view finder optical system, in which an ocular optical system is removed; 
       FIG. 3  is a perspective view in which a hollow pentagonal mirror is viewed from the rear side; 
       FIG. 4  is a view showing an arrangement of focusing marks formed on a superimpose-plate or SI-plate; 
       FIG. 5  is a sectional view showing a light source; 
       FIG. 6  is a perspective view showing a disassembled focusing glass and SI-plate; 
       FIG. 7  is an enlarged perspective view of the SI-plate; 
       FIG. 8  is an enlarged plane view showing a central portion of the SI-plate; 
       FIG. 9  is a cross-sectional view along a line IX—IX of  FIG. 8 ; 
       FIG. 10  is a longitudinal sectional view along a line X—X of  FIG. 8 ; and 
       FIG. 11  is a plane view showing another example of a micro-prism group. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present invention will be described below with reference to the embodiments shown in the drawings. 
   FIG.  1  and  FIG. 2  are sectional views showing a mirror box and a view finder optical system of a single-lens reflex camera,  FIG. 1  indicating a state in which a light-projecting prism is removed,  FIG. 2  indicating a state in which an ocular optical system is removed.  FIG. 3  is a perspective view in which a hollow pentagonal mirror is viewed from the rear side or a side of the ocular optical system. 
   A mirror box  11  has an opening  12  at the front portion thereof (i.e., left side in FIGS.  1  and  2 ), through which light, passing through a photographing optical system (not shown), is made incident. A hollow pentagonal mirror  21  is provided above the mirror box  11 . A quick return mirror  13  is housed in the mirror box  11 , to reflect light entering through the opening  12  to the hollow pentagonal mirror  21 . The quick return mirror  13  is rotatably supported by a pin  14  provided above the rear portion of the mirror box  11 . 
   A focusing glass  31 , on which a subject image obtained through the photographing optical system is formed, and a superimpose-plate (i.e., SI-plate)  32 , on which micro-prisms are formed, are provided in an incident opening formed at a lower portion of the hollow pentagonal mirror  21 , which is disposed in the upper end portion of the mirror box  11 . The SI-plate  32  is put on the focusing glass  31 . A focusing mark, indicated in a picture plane of the view finder, is formed on the SI-plate  32 . The focusing glass  31  and the SI-plate  32  are inclined by a few degrees (e.g., about 5 degrees) in such a manner that the front edges, close to the photographing optical system, of the focusing glass  31  and the SI-plate  32 , are lowered. On the other hand, the ocular optical system  23  faces an emergent opening  22  of the hollow pentagonal opening  21 . The emergent opening  22  is roughly triangular, and a photometry optical system  24  is provided at a portion close to an upper end of the emergent opening  22 . Note that the photometry optical system  24  is omitted in FIG.  3 . 
   The hollow pentagonal mirror  21  has a roof reflecting plane  41 , formed at an upper portion, and a third reflecting plane  42 , formed at a front portion. A light beam B 1 , passing through the photographing optical system and reflected on the quick return mirror  13 , passes through the focusing plate  31  and the SI-plate  32 , is reflected on the roof reflecting plane  41 , and reaches the third reflecting plane  42 . The light beam B 2  reflected on the third reflecting plane  42  passes through the emergent opening  22 , and enters the ocular optical system  23 . 
   Alight source  25  and a light-projecting prism  26 , which form a light-projecting optical system, are provided outside the emergent opening  22 . The light source  25  is disposed beside the photometry optical system  24 , and close to an upper end of the emergent opening  22 . The light-projecting prism  26  is disposed below the light source  25  and beside the ocular optical system  23 , and directly fixed on an attaching portion  43  integrally formed on a frame of the hollow pentagonal mirror  21 . The optical axis A extending between the light source  25  and the light-projecting prism  26  is approximately parallel to the plane of the emergent opening  22 , and does not interfere with the optical path of the photometry optical system  24 . 
   A light-projecting plane  26   a , or an emergent plane of the light-projecting prism  26 , faces a corner of a lower portion of the emergent opening  22 , and is positioned below the optical axis of the ocular optical system  23 . An illumination light beam C 1 , output from the light source  25  to the light-projecting prism  26 , is reflected on the light-projecting prism  26 , and is projected from the light-projecting plane  26   a  toward the emergent opening  22 . The illumination light beam C 1  is directed slightly upward with respect to the horizontal plane, and is led to approximately the center portion of the third reflecting plane  42  through the emergent opening  22 . The illumination light beam C 2  reflected on the third reflecting plane  42  is reflected on the roof reflecting plane  41 , and is approximately perpendicularly radiated onto the SI-plate  32 . 
     FIG. 4  indicates an arrangement of the focusing marks M formed on the SI-plate  32 . In the embodiment, when viewing the ocular optical system  23 , the photographer can observe eleven focusing marks M superposed on the subject image, in a picture plane of the view finder. The photographing optical system can focus at points corresponding to the eleven focusing marks M, with respect to the subject. When an in-focus state is obtained in a photographing operation, a focusing mark M corresponding to the in-focus point lights in red, for example. Namely, when it is sensed by an in-focus sensor that any point on the subject is in-focus, a focusing mark M corresponding to the in-focus point is illuminated by the illumination light beam C 2  projected from the light source  25 . 
   The light source  25  is provided with eleven radiating units or light emitting diodes (LEDs)  27  corresponding to the focusing marks M. Each of the LEDs  27  corresponds to one focusing mark M. Namely, illumination light beams output from the LEDs  27  are radiated on different portions of the SI-plate  32 . As shown in  FIG. 5 , a tapered hole  29  is formed in a frame  28  of the light source  25 , so that illumination light beams output from the LEDs  27  are led to the light-projecting prism  26 . 
     FIG. 6  shows the focusing glass  31  and the SI-plate  32 , which are disassembled. A focusing glass frame  33 , which is a rectangular frame, is pivotally supported by an upper end of the mirror box  11  at the rear end  34  (see FIG.  1 ), and has an engaging portion  35  at a front edge, which can be engaged with a predetermined portion of the mirror box  11 . The focusing glass  31  is fit in the focusing glass frame  33 . The SI-plate  32  is placed on the focusing glass  31  with a channel-shaped focus-adjusting washer  36  intervening therebetween. Namely, space of a predetermined size is formed between the focusing glass  31  and the SI-plate  32  by the channel-shaped focus-adjusting washer  36 . The focusing glass  31 , the channel-shaped focus-adjusting washer  36 , and the SI-plate  32  are superposed on each other, and are supported by the focusing glass frame  33  and fixed to an upper portion of the mirror box  11 . 
     FIG. 7  is an enlarged perspective view showing the SI-plate  32 . The SI-plate  32  is a transparent member formed of a plastic material. The SI-plate  32  has a plane-parallel plate  37  and an outer frame  38  enclosing the plane-parallel plate  37 . The outer frame  38  is mounted on the focus-adjusting washer  36 . A rib  39  is formed on an outer surface of a short side of the outer frame  38 . The plane-parallel plate  37  is inclined by an angle (1-3 degrees, for example) relative to the outer frame  38 . Namely, the plane-parallel plate  37  is inclined so that an edge, close to the photographing optical system (i.e., the left side in FIGS.  1  and  2 ), of the SI-plate is lowered relative to the focusing glass  31 . In other words, the SI-plate  32  is more inclined than the focusing glass  31 . 
     FIG. 8  shows an enlarged view of the central portion of the SI-plate  32 , when viewed from the upper side of the SI-plate  32  and when facing the SI-plate  32  from the side of the photographing optical system, and is also an enlarged view of the central portion of FIG.  4 . Namely, the left side of  FIG. 8  corresponds to the left side of the picture plane of the view finder. 
   Lots of micro-prisms  52   a ,  52   b  are formed to project from the lower surface of the SI-plate  32 . An outline of a micro-prism is a slender trapezoid, when viewing the SI-plate  32  from an upper or lower side. The micro-prism shows a triangle in a cross-section, as described later, and a ridgeline of each of the micro-prisms  51   c ,  52   c , and  53   c  is parallel to the right-left (or horizontal) direction of the picture plane of the view finder. In other words, the longitudinal direction of each of the micro-prisms is coincident with the horizontal direction in the picture plane of the view finder. The micro-prisms form eleven groups, and each of the micro-prism groups  51 - 61  corresponds to the focusing mark M (see  FIG. 4 ) indicated in the picture plane of the view finder. Namely, each of the focusing marks M is formed by an aggregation of a plurality of micro-prisms. 
   In a picture plane of the view finder, the first micro-prism group  51  is located at the leftmost side. The second, third, and fourth micro-prism groups  52 ,  53 , and  54  are positioned at the right side of the first micro-prism group  51 . The fifth, sixth, and seventh micro-prism groups  55 ,  56 , and  57  are located at the center of all the micro-prism groups. The eighth, ninth, and tenth micro-prism groups  58 ,  59 , and  60  are positioned at the right side of the fifth, sixth, and seventh micro-prism groups  55 ,  56 , and  57 , and the eleventh micro-prism group  61  is at the rightmost side. 
   Taking the second micro-prism group  52  as a typical example, the structures of the micro-prism groups  51  through  61  are described below. The second micro-prism group  52  is composed of a plurality of micro prisms, and has relatively large first micro-prisms  52   a  and relatively small second micro-prisms  52   b.    
   The first micro-prisms  52   a  are aligned horizontally in  FIG. 8  in groups of three, to form four first prism rows R 1 . In a first prism row R 1 , the micro-prisms  52   a , which are adjacent, are in contact with each other. Namely, an upper side of the trapezoid of a micro-prism  52   a , positioned at the center of a row, is in contact with a lower side of the trapezoid of the micro-prism  52   a , disposed at the left side of the center micro-prism  52   a . A lower side of the trapezoid of the center micro-prism  52   a  is in contact with an upper side of the trapezoid of the other micro-prism  52   a , disposed at the right side of the center micro-prism  52   a.    
   There are four first prism rows R 1 . In the space formed between the first prism rows R 1 , a second prism row R 2  composed of a second micro-prisms  52   b  is provided. The second micro-prism rows R 2  are constructed by arranging the second micro-prisms  52   b  horizontally in  FIG. 8 , in pairs. A lower side of the trapezoid of the left micro-prism  52   b  is in contact with an upper side of the trapezoid of the right micro-prism  52   b.    
   The second micro-prism  52   b  is located at a position corresponding to a place between the two first micro-prisms  52   a , adjacent to the first prism row R 1 . An oblique side of the trapezoid of the second micro-prism  52   b  is in contact with an end point of the lower side of the trapezoid of the first micro-prism  52   a . Similarly, an end point of the lower side of the trapezoid of the second micro-prism  52   b  is in contact with an oblique side of the trapezoid of the first micro-prism  52   a . Thus, the micro-prisms  52   a  and  52   b  are arranged in a zigzag manner. 
     FIGS. 9 and 10  show the second micro-prism group  52 .  FIG. 9  is a cross-sectional view along line IX—IX of  FIG. 8 , and  FIG. 10  is a longitudinal sectional view along line X—X of FIG.  8 . The cross-section shape of each of the first and second micro-prisms  52   a  and  52   b  is approximately an isosceles triangle, so that an incident light beam radiated from the above reflects on the micro-prisms  52   a  and  52   b , and returns in parallel to the incident light beam. Note that the vertical angle of the triangle of each of the micro-prisms  52   a  and  52   b  is approximately 90 degrees. 
   The ridgeline  52   c  of the reflecting plane of the first micro-prism  52   a  is at a slant relative to the lower surface  32   a  of the SI-plate  32 , as understood from FIG.  10 . The slant angle a is determined in such manner that an illumination light beam C 2  (see FIG.  2 ), radiated from the roof reflecting plane  41  of the hollow pentagonal mirror  21 , is effectively received by the micro-prism  52   a . The illumination light beam C 2  is radiated from a point above the light source corresponding point C 3 , shown in  FIG. 8 , to the SI-plate  32 . Therefore, the angle of inclination of an illumination light beam become greater, as it separates from the light source corresponding point C 3 . 
   Thus, regarding the inclination angle α of the ridgeline of each of the micro-prism groups, the first micro-prism group  51  is the largest. The inclination angles α of the second, third, and fourth micro-prism groups  52 ,  53 , and  54  are equal to each other, and are smaller than that of the first micro-prism group  51 . The inclination angles α of the fifth, sixth, and seventh micro-prism groups  55 ,  56 , and  57  are equal to each other, and are smaller than those of the second, third, and fourth micro-prism groups  52 ,  53 , and  54 . The inclination angles α of the eighth, ninth, and tenth micro-prism groups  58 ,  59 , and  60  are equal to each other, and are smaller than those of the fifth, sixth, and seventh micro-prism groups  55 ,  56 , and  57 . 
   The eleventh micro-prism group  61  is located at the opposite side of the ninth micro-prism  59  with respect to the light source corresponding point C 3 . Accordingly, the inclination angle α of the eleventh micro-prism group  61  is opposite to that of the eighth, ninth, and tenth micro-prism groups  58 ,  59 , and  60 , but is approximately the same amount as that for the eighth, ninth, and tenth micro-prism groups  58 ,  59 , and  60 . 
   As described above, the number of different inclination angles α of the ridgelines of the first through eleventh micro-prism groups  51  through  61 , is five. The inclination angles α differ in accordance with the horizontal positions in a picture plane of the view finder, and the inclination angles α of the ridgelines of the micro-prism groups aligned in a vertical direction in the picture plane (for example, the micro-prism groups  52 ,  53 , and  54 ) are the same. 
   Thus, on a lower surface  32   a  of the SI-plate  32 , the micro-prism groups  51  through  61  are formed at the positions where illumination light beams output from the light source  25  are radiated, and correspond to the focusing marks M. In a photographing operation, when the photographing optical system focuses on any point on the subject, the LED  27  ( FIG. 5 ) corresponding to the point is lit. Due to the illumination light beam C 2  ( FIG. 2 ) output from the LED  27 , the corresponding micro-prism or the focusing mark M shines in red, the photographer can recognize the focused point. 
   Note that, in  FIG. 8 , each of the second through fifth micro-prism groups  52  through  55 , and the seventh through tenth micro-prism groups  57  through  60  are square shaped. The sixth micro-prism group  56  is a frame shaped. Further, the first and eleventh micro-prism groups  51  and  61  are rectangular shaped. These shapes can be changed in accordance with necessity or object. 
   A metal mold for forming a plastic material is used for manufacturing the SI-plate  32  having lots of micro-prisms. Namely, a tip of an edged tool is pressed on the metal mold to form the surface, by which the micro-prisms are formed. The tip of the edged tool has a triangle section, and the surface of the tip is mirror-polished. For example, a portion corresponding to the second micro-prism  52  is formed by pressing an edged tool, which has a tip having the same shape as that of the first micro-prism  52   a , on a metal mold. Namely, the corresponding portion of the first micro-prism  52   a  is pressed by the edged tool to a predetermined depth, and the corresponding portion of the second micro-prism  52   b  is pressed by the edged tool to a shallower depth than the first micro-prism  52   a.    
   As described above, there are five different kinds of inclination angle α of the micro-prisms. Therefore, five kinds of edged tools are sufficient for forming the micro-prisms. For example, regarding the second, third, and fourth micro-prisms  52 ,  53 , and  54 , since the inclination angle α is common, the same edged tool is used. 
     FIG. 11  shows another example of the micro-prism group. As understood from a comparison with the second micro-prism group  52  shown in  FIG. 8 , in the micro-prism group  62 , all of the micro-prisms  62   a  have the same shape and size. Namely, the three micro-prisms  62   a  forming the first prism row R 3  have the same shape and size as the two micro-prisms  62   a  forming a second prism row R 4 . The second prism rows R 4  are provided between two first micro-prism rows R 3  adjacent to each other, and each of the micro-prisms  62   a  of the second micro-prism row R 4  is located at a position corresponding to a place between two adjacent micro-prisms  62   a  of a first prism row R 3 . Namely, the micro-prisms  62   a  are arranged in a zigzag manner. The other constructions are the same as those for the second micro-prism group  52  of FIG.  8 . 
   In the embodiment described above, the light source  25  is provided at an upper portion of the emergent opening  22  of the hollow pentagonal mirror  21 , and the light-projecting prism  26  is provided at a lower portion of the emergent opening  22 , so that the illumination light beam radiated from the light source  25  is reflected on the light-projecting prism  26 , and is projected into the hollow pentagonal mirror  21  through the emergent opening  22 . Therefore, in a photographing operation, when an in-focus sensor senses that any point on the subject is in-focus, and the LED  27  corresponding to the focusing point is turned ON, the illumination light beam is reflected on the third reflecting plane  42  and the roof reflecting plane  41 , and is led to the SI-plate  32 , so that the corresponding micro-prism group is illuminated. 
   In the embodiment, the number of different kinds of inclination angles α of the micro-prisms is five, and therefore, it is not necessary to change the inclination angle for each of the micro-prism groups. Accordingly, the manufacturing process of the SI-plate  32  is simplified, so that controlling the manufacturing process becomes simple, and the manufacturing cost is suppressed. 
   Further, in the embodiment, the light-projecting prism  26  is directly fixed on the attaching portion  43  of the frame of the hollow pentagonal mirror  21 . Therefore, by fixing the light-projecting prism  26  to the attaching portion  43  of the hollow pentagonal mirror  21  with a predetermined level of accuracy, an illumination light beam output from the light source  25  is accurately radiated onto a predetermined portion of the SI-plate  32  without fine-adjustment of the light-projecting prism  26  at its attached position relative to the hollow pentagonal mirror  21 , in an assembling process of a camera. 
   Although the embodiments of the present invention have been described herein with reference to the accompanying drawings, obviously many modifications and changes may be made by those skilled in this art without departing from the scope of the invention. 
   The present disclosure relates to subject matters contained in Japanese Patent Application No. 2003-009566 (filed on Jan. 17, 2003), which is expressly incorporated herein, by reference, in its entirety.