Abstract:
A photometering apparatus has a photometering apparatus having a plurality of photometering systems for measuring the brightness of an object. photometering system includes:a light receiving device in which different parts of an object are detected by a plurality of split photodetectors whose light receivers each comprise a detection area which is made separate by at least one insensitive area; a photometering optical system for projecting the image of the object onto the light receiving device; wherein the image of the object formed on the at least one insensitive area of one of the plurality of split photodetectors of one of the plurality of photometering systems is formed on the plurality of detection areas of another of the plurality of split photodetectors of another of the plurality of photometering systems.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a photometering apparatus having a split type photodetector. 
     2. Description of the Related Art 
     In a known photometering apparatus in a camera, a light receiving surface of a photo sensor is located in a predetermined focal plane of an object image or in the vicinity thereof, so that the brightness of the object image formed on the light receiving surface can be detected by the photodetector. In a known photometering apparatus having a split type photodetector, the light receiving surface is split into a plurality of detection sections (areas) which detect the brightness of the object image incident thereupon. 
     In a split type photodetector, the light receiving surface is split into a plurality of detection areas corresponding to a desired number of split measurement zones. To prevent ‘crosstalk’, or due to the wiring arrangement of electrical leads, the split measurement zones are separated by an insensitive area. FIG. 6 shows an example of a known split type photodetector. In FIG. 6, the split type photodetector  71  is provided with six split detection areas  73 A through  73 F which are separated by an insensitive band  75 . 
     Hence, it is impossible to detect the brightness of the object image formed on the insensitive band  75 ; if the bright object image is made incident on the insensitive band, the object image cannot be detected, and hence the whole object may be recognized as a dark object. 
     If the insensitive band  75  is narrow, ‘crosstalk’ tends to occur, thus resulting in a reduced measurement accuracy. Namely, the measurement accuracy is reduced by the insensitive band  75  as the split type photodetector  71  becomes small or the number of the split detection areas is increased. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a multi-measurement or split measurement type photometering apparatus in which an immeasurable area is made as small as possible, or at least reduced. 
     To achieve the object mentioned above, according to the present invention, there is provided a photometering apparatus having a plurality of photometering systems for measuring the brightness of an object, wherein each photometering system includes:a light receiving device in which different parts of an object are detected by a plurality of split photodetectors whose light receivers each comprise a detection area which is made separate by at least one insensitive area; a photometering optical system for projecting the image of the object onto the light receiving device; wherein the image of the object formed on the at least one insensitive area of one of the plurality of split photodetectors of one of the plurality of photometering systems is formed on the plurality of detection areas of another of the plurality of split photodetectors of another of the plurality of photometering systems. 
     Preferably, the photometering apparatus includes a pair of photometering systems, wherein the ratios of the vertical and horizontal dimensions of the detection area of the plurality of split photodetectors and at least one insensitive area are the same. 
     Preferably, the photometering optical system of one of the plurality of photometering systems includes a photometering lens which forms an image on the light receiving portion of the one of the plurality of photometering systems at a different magnification to a photometering lens of the photometering optical system of another of the plurality of photometering systems. 
     Preferably, the split photodetectors have the same shape and size. 
     Preferably, the ratios of the vertical and horizontal dimensions of each detection area of the split photodetectors and at least one insensitive area are the same. 
     Preferably, the magnification of each photometering system is such that substantially all of the image of the object formed on the at least one insensitive area of the split photodetector of one of the plurality of photometering systems is formed on at least one the detection area of the other the split photodetector of another of the plurality of photometering systems. 
     According to another aspect of the present invention, there is provided a photometering apparatus having a plurality of photometering systems for measuring the brightness of an object, wherein each photometering system includes: a split photodetector having light receiving portions with comprising a detection area which is made separate by an insensitive area; wherein the photometering optical system of one of the plurality of photometering systems comprises a photometering lens which forms an image on the light receiving portion of the one of the plurality of photometering systems at a different magnification to a photometering lens of the photometering optical system of another of the plurality of photometering systems; and wherein the magnification of each photometering system is such that substantially all of the object image formed on the insensitive area of the split photodetector of one of the plurality of photometering systems is formed on at least one detection area of the other the split photodetector of another of the plurality of photometering systems. 
     Preferably, the split photodetectors have the same shape and size. 
     Preferably, the photometering apparatus includes a pair of photometering systems, wherein the ratios of the vertical and horizontal dimensions of each the detection area of the split photodetectors and the insensitive areas are the same. 
     Preferably, the magnification of one of the plurality of photometering systems is less than the magnification of another of the plurality of photometering systems. 
     Preferably, the photometering apparatus is provided between an image erection system and an eyepiece in a finder optical system of a single lens reflex camera. 
     According to another aspect of the present invention, there is provided a photometering apparatus, having a plurality of photometering systems for measuring the brightness of an object, wherein each the photometering system comprises: a light receiving device which receives light carrying the object image; and a photometering optical system for projecting the object image onto the light receiving device, the light receiving device receiving object light of different portions of the object; wherein the photometering optical systems have different magnifications. 
     According to another aspect of the present invention, photometering apparatus including: a pair of split photodetectors for detecting different parts of an object image each of the split photodetectors being provided with a light receiver having detection areas which are separated by an insensitive area; the ratios of the vertical and horizontal dimensions of the insensitive area of one of the pair of split photodetectors and the detection areas of the other of the pair of split photodetectors are the same. 
     The present disclosure relates to subject matter contained in Japanese Patent Application No. 09-296776 (filed on Oct. 29, 1997) which is expressly incorporated herein by reference in its entirety. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described below in detail with reference to the accompanying drawings, in which: 
     FIG. 1 is an exploded perspective view of a photometering apparatus applied to a single lens reflex camera, according to an embodiment of the present invention; 
     FIG. 2 is an explanatory view of a relationship between a pair of detection areas of a split photodetector and an image surface in the photometering apparatus shown in FIG. 1; 
     FIG. 3 is a schematic view of a pair of detection areas of a split photodetector and an insensitive area, and a object image area which is overlapped at the same magnification of an object image; 
     FIGS. 4A and 4B are schematic views of a detection area and an insensitive area according to another embodiment of the present invention, respectively; 
     FIGS. 5A and 5B are schematic views of a detection area and an insensitive area according to yet another embodiment of the present invention, respectively; and 
     FIG. 6 is an explanatory view of split detection areas and an insensitive area in a known photometering apparatus. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the illustrated embodiment, a photometering apparatus is discussed. The photometering apparatus has a pair of photometering systems  10  and  20  provided with photometering optical systems  113  and  123  (e.g., image forming lenses) that form object images on split photodetectors  11  and  21  at different magnifications. 
     In FIG. 1 which shows a photometering apparatus applied to a single lens reflex camera according to the present invention; light which carries an object image through a photographing lens is reflected by a main mirror  31 , is transmitted through a focusing screen  33  which is located at a position optically equivalent to a film surface and a condenser lens  35 , and is made incident on a trapezoidal prism  37  which forms an image erection optical system which erects the inverted object image. A large part of the object light reflected by and emitted from the trapezoidal prism  37  is transmitted through a finder magnifier (eyepiece)  39  and is received by a photographer&#39;s eye. 
     The first and second split photodetectors  11  and  21  each constitute a photometering system, on opposite sides of the finder magnifier  39 . The split photodetectors  11  and  21  are provided with photometering systems  113  and  123  through which the object light emitted from the trapezoidal prism  37  is made incident on the light receiving surfaces of the photodetectors  11  and  21  to form object images. The photometering optical systems  113  and  123  are each composed of a first photometering lens  115  or  125 , a mirror (not shown) which deflects the light path by 90° in the upward direction (with respect to the camera body), and a second photometering lens  117  or  127  as an image forming lens, in this order from the trapezoidal prism ( 37 ) side. 
     According to one of the most significant features of the embodiment illustrated in FIG. 2, the split photodetectors  11  and  21  are identical and have the same pattern of split detection area. The light receiving surfaces of the split photodetectors  11  and  21  are each provided with six split detection areas which are separated by an insensitive area. Namely, the first split photodetector  11  is composed of a central detection area  13 A, a pair of right and left detection areas  13 B and  13 C on opposite sides of the central detection area  13 A, a pair of upper and lower detection areas  13 D and  13 E on opposite sides of the central detection area  13 A, a peripheral detection area  13 F, and an insensitive area  15  which separates the detection areas  13 A through  13 F. Likewise, the second split photodetector  21  is composed of split detection areas  23 A through  23 F and an insensitive area  25 , identical in shape to the detection areas  13 A through  13 F so and the insensitive area  15 , respectively. 
     FIG. 2 shows a relationship between the picture surface (whole object area)  41  of the camera and the detection areas  43 N and  43 W corresponding to the object area formed on the light receiving surfaces of the split photodetectors  11  and  21 . As can be seen in FIG. 2, the object image within the relatively narrow detection area  43 N of the picture surface  41  is formed on the first photodetector  11 , and the object image within the detection area  43 W which is larger than the detection area  43 N is formed on the second photodetector  21 . The larger detection area  43 W is projected onto the second photodetector  21  at a magnification less than that of the detection area  43 N projected onto the first photodetector  11 . Namely, the object images are formed on the first photodetector  11  and the second photodetector  21  at a high magnification and a low magnification, respectively. Consequently, the magnification of the photometering optical system  113  is higher than the magnification of the photometering system  123 , or the focal length of the photometering optical system  113  is longer than the focal length of the photometering optical system  123 . 
     Among the object images formed on the split photodetectors  11  and  21 , the brightness of the object images formed on the split detection areas  13 A through  13 F and  23 A through  23 F can be detected, but the brightness of the object images formed on the insensitive areas  15  and  25  cannot be detected. In view of this problem, according to one of the most significant features of the illustrated embodiment, the portions of the object images that cannot be detected or measured, within the wide and narrow detection areas  43 W and  43 N, are made as small as possible. 
     FIG. 3 shows a relationship between the detection areas  43 N,  43 W and the split detection areas  13 A through  13 F and  23 A through  23 F of the split photodetectors  11  and  21 , respectively. In FIG. 3, the magnification of the object images formed on the split photodetectors  11  and  21  are modified in accordance with the ratio of the size of the images on the picture surface  41 . As can be seen in FIG. 3, a large part of the insensitive area  25  which cannot be detected by the second split photodetector  21  is covered (overlapped) by the split detection areas  13 A through  13 F of the first split photodetector  11 . Likewise, a large part of the insensitive area  15  which cannot be detected by the first split photodetector  11  is covered (overlapped) by the split detection areas  23 A through  23 F of the second split photodetector  21 . Thus, the insensitive portions which cannot be detected or measured by the split photodetectors are only those hatched in FIG.  3 . 
     As may be understood from the foregoing, according to the illustrated embodiment, since the split detection areas  13 A through  13 F of the first split photodetector are overlapped on the insensitive area  25  of the second split photodetector while the magnifications of the object images to be formed on a pair of split photodetectors are different, the area of the insensitive portions can be reduced by using the measurements of the split detection areas  13 A through  13 F and  23 A through  23 F of the split photodetectors  11  and  21 , thus resulting in a precise and fine measurement. Moreover, since the split photodetectors  11  and  21  are identical, not only can the number of the elements be reduced, but also the structure and the assembling operation of the apparatus can be simplified. 
     In the above-mentioned embodiment, the improvement is chiefly addressed to the shape and arrangement of the split detection areas. FIGS. 4A,  4 B and  5 A,  5 B show different embodiments in which significance is placed on the realization of smaller insensitive areas of a pair of split photodetectors. 
     In FIG. 4A, the split photodetector  60  is a two-split type photodetector which is provided with a central detection area  61 A and a peripheral detection area  63 A which surrounds the central detection area  61 A. The detection areas  61 A and  63 A are isolated by an insensitive area  62 A. The ratios of the vertical and horizontal dimensions of the peripheral detection area  63 A and the insensitive area  62 A are the same. 
     In FIGS. 4A and 4B, a pair of split photodetectors  11  and  21  shown in FIGS. 1 through 3 are replaced with the split photodetectors  60  to show the relationship between the detection areas and the insensitive areas. Assuming that the split photodetector  60  shown in FIG. 4A corresponds to the second split photodetector  21 , the split detection areas and the insensitive area of the split photodetector  60  corresponding to the first split photodetector  11  are as shown in FIG.  4 B. As shown in FIGS. 4A and 4B, the detection area  63 B of high magnification is substantially the same as the insensitive area  62 A of low magnification. Namely, if the magnification of the photometering lens is appropriately set, the object image formed on the insensitive area  62 A on the low magnification side can be substantially overlapped on or identical to the object image formed on the detection area  63 B on the high magnification side. Thus, a split measurement can be carried out, owing to an absence of an immeasurable area. 
     The split photodetector  70  shown in FIGS. 5A and 5B is a three-split type photodetector which constitutes a central detection area  71 A, an intermediate detection area  73 A which surrounds the central detection area  71 A, and a peripheral detection area  75 A which surrounds the intermediate detection area  73 A. The detection areas  71 A and  73 A are isolated by an insensitive area  72 A, and the detection areas  73 A and  75 A are isolated by an insensitive area  74 A. The ratios of the vertical and horizontal dimensions of the peripheral detection area  75 A and the intermediate detection area  73 A are the same as the insensitive areas  74 A and  72 A, respectively. 
     In FIGS. 5A and 5B, a pair of split photodetectors  11  and  21  shown in FIGS. 1 through 3 are replaced with the split photodetectors  70  to show the relationship between the detection areas and the insensitive areas. Assuming that the split photodetector  70  on the low magnification side, shown in FIG. 5A corresponds to the second split photodetector  21 , the split detection areas  71 B,  73 B and  75 B and the insensitive areas  72 B and  74 B of the split photodetector  70  on the high magnification side, corresponding to the first split photodetector  11  are as shown in FIG.  5 B. As shown in FIGS. 5A and 5B, the detection areas  75 B and  73 B of high magnification substantially overlaps, or is identical to, the insensitive areas  74 A and  72 A of low magnification. Namely, if the magnification of the photometering optical systems  113  and  123  is appropriately set, the object image formed on the insensitive areas  74 A and  72 A on the low magnification side can be substantially the same as the object image formed on the detection areas  75 B and  73 B on the high magnification side. Thus, a split measurement can be carried out, owing to an absence of an immeasurable area. 
     As may be understood from the foregoing, in the embodiments illustrated in FIGS. 4A,  4 B and  5 A and  5 B, since the object light incident on the insensitive area of one of the photodetectors is identical to the object light incident on the detection areas of the other photo detector, the entire object light incident on the light receivers of the split photodetector  60  or  70  can be effectively used for the measuring operation. 
     In the embodiments illustrated in FIGS. 4A,  4 B and  5 A,  5 B, the pair of photodetectors are identical to each other, and the magnifications (focal lengths) of the photometering lenses are different, so that there is no insensitive portion. Alternatively, it is possible to eliminate the insensitive portion by making the size of the split photodetectors different from one another as shown in FIGS. 4A,  4 B or  5 A,  5 B. 
     Although two split photodetectors are used in the illustrated embodiments, the number of the photodetectors is not limited to two. More than two photodetectors can be used. The structure of the photometering optical system is not limited to that of the illustrated embodiments. Moreover, the number, arrangement and shape, of the split detection areas of each photodetector are not limited to those in the illustrated embodiments. 
     As may be understood from the above discussion, according to the present invention, since the magnifications of a plurality of split type photometering systems are different, the insensitive area of one of the photometering systems can be detected by the detection areas of another photometering system. Consequently, the brightness of the entire object can be split-measured. 
     Moreover, according to another aspect of the present invention, since the object image portion formed on the insensitive area of one of the split photodetectors having light receiving portions provided with split detection areas separated by the insensitive area is formed on the detection areas of the other split photodetector, almost all of the portions of the object formed on one of the split photodetectors can be measured, thus resulting in a precise and fine measurement of the brightness of the object. 
     Furthermore, since the identical photodetectors can be used, not only can the number of elements be reduced, but also the structure or assembling operation of the apparatus can be simplified. 
     Obvious changes may be made in the specific embodiments of the present invention described herein, such modifications being within the spirit and scope of the invention claimed. It is indicated that all matter contained herein is illustrative and does not limit the scope of the present invention.