Abstract:
A focus detecting device and a photographic apparatus provided with such a device has an apparatus for setting optic axes thereof with a base length therebetween, and for photoelectrically detecting a focus state thereof, at least one of the optic axes being bent, or reflected, by a fixed reflecting surface, and a focus detection component disposed along the bent optic axis and movable, during a focus detection operation, in a direction intersecting the bent axis.

Description:
This application is a continuation of application Ser. No. 204,969 filed June 8, 1988, now abandoned, which is a continuation of application Ser. No. 829,939 filed Feb. 18, 1986, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a photoelectric focus detecting device of which the driving mechanism can be simplified and to a photographing apparatus provided with such device. 
     2. Related Background Art 
     Photographic cameras and video cameras having an automatic focus detecting device incorporated therein are commonplace, and such focus detecting device is mounted on a camera body or is incorporated in an interchangeable lens. On the other hand, the tendency of cameras and lenses toward compactness is well known and along therewith, it is required to make the detecting device compact and simplify the driving mechanism thereof. 
     As is well known, the automatic focus detecting system is broadly divided into the passive type and the active type. In a typical system of the passive type, photosensor arrays are disposed on two optic axes, respectively, and the correlation between an image signal obtained by driving a pivotable mirror provided on one of the optic axes and scanning the array thereon by the image of an object or by electrically scanning the array and other image signal is taken and the object distance is detected from the scanning angle thereof or the scanning distance thereof. Also, in a system of the active type, an invisible light or the like is projected from one lens side onto an object and the reflected light from the object is received by the remaining lens and directed to a photoelectric element, and in that case, at least one of a light source, a photoelectric element, a projecting lens and a light-receiving lens is moved and scanned. 
     In both of these types, except a few examples in which the array is electrically scanned, some driving mechanism is required and moreover, reciprocal pivotal movement and movement in a direction perpendicular to the photographing optic axis are effected and therefore, converting means such as a cam or an encoder need be provided in a connecting structure for connecting the movement of those movable elements and the movement of the focusing lens of the photo-taking optical system in the direction of the optic axis. Such connecting structure is liable to cause a reduction in accuracy. 
     SUMMARY OF THE INVENTION 
     It is a first object of the present invention to simplify the driving mechanism of a focus detecting device of the active type or the passive type and in particular, to provide a construction which can simplify a mechanism for driving the component of the focus detecting device such as a projection light source, a photoelectric converting element or a converging lens. 
     It is a second object of the present invention to simplify the construction for harmonizing the operation of the focus driving mechanism of an optical apparatus performing the original function, such as photographing apparatus, and the operation of the driving mechanism of a focus detecting device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an optical arrangement illustration showing an embodiment of the present invention. 
     FIGS. 2 and 3 illustrate the optical action. 
     FIGS. 4 and 5 are optical arrangement illustrations showing further embodiments of the present invention. 
     FIG. 6 illustrates the optical action. 
     FIGS. 7 and 8 are optical arrangement illustrations showing still further embodiments of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows an embodiment of the present invention. This Figure is depicted with the distance between an object to be photographed and the apparatus being greatly shortened. In FIG. 1, reference character 0 designates an object, reference numeral 1 denotes the photo-taking lens of the photographing apparatus K, and reference numeral 2 designates an image pickup surface which is the surface of a photographic film or the light-receiving surface of a video image pickup element. Letter A denotes a focus detecting device, reference numeral 3 designates a projecting lens, and reference numeral 4 denotes a projection light source which may preferably be an LED emitting an invisible light, for example, infrared light. The projection light source 4 lies on the focal plane of the projecting lens 3. Reference numeral 5 designates a total reflection mirror for bending the projection optic axis X1 at a right angle. However, the projection light source 4 not only moves in a direction orthogonal to the optic axis, but also finely moves in the direction of the optic axis to absorb blur. Accordingly, in the case of precise measurement, the optic axis may be bent at an angle somewhat greater than a right angle and the amount of movement in the direction of the optic axis may be approximated. Reference numeral 4&#39; designates the mirror image of the projection light source 4, and this also corresponds to the projection light source of the conventional apparatus. 
     In the present embodiment, the introduction of the total reflection mirror 5 enables the projection light source 4 to be disposed at the bent position of the optic axis X1 of the projecting lens 3 and as a result, it has become possible to move the projection light source 4 in the same direction as the direction of movement of the photo-taking lens 1, in contrast with the conventional apparatus in which the light source 4&#39; was moved in the direction of broken line arrow a. That is, in the past, a mechanism for moving the light source in a direction perpendicular to the direction of movement of the photo-taking lens was necessary, whereas in the present embodiment, a mechanism for moving the light source in the same direction as the direction of movement of the photo-taking lens is only required. 
     Reference numeral 6 designates a light-receiving lens provided at a distance equal to the base length, and reference numeral 7 denotes a photoelectric element provided with a light-receiving area vertically divided into two as viewed in FIG. 1 with the optic axis X2 as the boundary. It is to be understood that the photoelectric element 7 lies on the focal plane of the light-receiving lens 6. Reference numeral 8 designates a device for processing the output signal of the photoelectric element 7 and driving the lens. 
     In the above-described construction, the infrared detecting light emitted from the projection light source 4 is projected toward the object 0, and as the projection light source 4 is moved from the optic axis X1 in a direction perpendicular thereto, the projection optic axis becomes inclined as indicated by X1&#39; and intersects the optic axis X2 of the light-receiving lens 6 on the object 0. That is, at this time, the detecting light reflected by the object 0 is imaged by the light-receiving lens 6 and enters the two light-receiving areas of the photoelectric element 7 in equal quantities, an in-focus state is judged, and the photo-taking lens 1 axially moved at the same time is stopped. 
     In the above-described embodiment, the directions of movement of the projection light source and the photo-taking lens are coincident with each other and therefore, the mechanical structure becomes simplified and compact, but if a construction in which the two are moved together is adopted, means for mediating the difference between the amounts of movement of the two will become unnecessary. 
     Description will hereinafter be made of the fact that integral movement is possible in the optical principle. 
     FIG. 2 shows a form in which the focus detecting device provided with the projecting lens 3, the projection light source 4, the light-receiving lens 6 and the photoelectric element 7, but without the total reflection mirror 5, is developed along the optical axis. If the distance between the projection optic axis X1 and the light-receiving optic axis X2, i.e., the base length is D and the distance from the projecting lens to the object is R and the focal length of the projecting lens is f and the scanning distance from the infinity state of the projection light source to the in-focus state is a, the following expression can be made from a geometric similarity relation: 
     
         R/D=f/a. 
    
     Thus, this can be modified into: 
     
         a=D·f/R 
    
     Also, generally, if the distance from the forward focus of the lens depicted in FIG. 3 to the object to be photographed is x and the distance from the rearward focus of the lens to the image point is x&#39; and the focal length of the lens is f, there is a relation that 
     
         xx&#39;=-f.sup.2 
    
     (Newton&#39;s equation). 
     The amount of axial movement of the lines for focusing is -x&#39; and therefore, if the above-mentioned amount of movement a of the projection light source can be made coincident with the amount of axial movement -x&#39;, integral scanning will become possible. 
     Accordingly, if the focal length of the focusing lens of the photo-taking system, for example, a component lens of the entire lens or the single lens, or the focusing lens of a zoom lens, is f F , 
     
         x&#39;=-f.sup.2.sub.F /x, 
    
     where x is the distance from the forward focus of the lens to the object, and if the forward focus position of the focusing lens is made coincident with the principal point position of the projecting lens, x=R. Also, even in a case where they are not made coincident with each other from the problem of disposition or the problem of appearance design, if the distance is sufficiently long like an object in the normal photographing area, 
     
         x&gt;&gt;f.sub.F 
    
     and even if x is regarded as x=R, the accuracy of distance measurement can be sufficiently ensured. 
     Accordingly, in order that a=x&#39;, D·f is determined as per the following equation: 
     
         D·f=f.sup.2.sub.F. 
    
     To further ensure the accuracy, the relation among D, f and f F  may be determined so that a=x&#39; between infinity and the photographing close distance. 
     FIG. 4 shows a second embodiment which is of the type scanning a photoelectric element instead of a projection source. In FIG. 4, components similar to those in FIG. 1 are given similar reference numerals. 
     In the present embodiment, a projection light source 4 is fixed on the optic axis X1 of a projecting lens 3, while the optic axis X2 of a light-receiving lens 6 is bent substantially at a right angle by the reflecting surface of a mirror 5&#39; and a photoelectric element 7 is disposed on the focal plane of the light-receiving lens 6. Reference numeral 10 designates a zoom lens comprising a focusing lens 10a, a variator 10b, a compensator 10c and a relay lens 10d. The focusing lens 10a is moved in the direction of the optic axis for focus adjustment, and the photoelectric element 7 is also moved in the direction of the optic axis of the zoom lens with the focusing lens 10a. 
     FIG. 5 shows still another embodiment in which a projection light source 4 and a photoelectric element 7 are fixed and instead, a projecting lens 3 or a light receiving lens (in the present embodiment, the projecting lens 3) is scanned. One of the projection optic axis and the light-receiving optic axis (in the present embodiment, the light-receiving optic axis X2) is made coincident with the photographing optic axis X3. The projection optic axis X1 is bent by a reflecting mirror 5&#34; at a position more adjacent to the object side than the projecting lens 3, and the projecting lens 3 is moved by the same amount as the amount of movement of a photo-taking lens 1 in a direction orthogonal to the optic axis X1, i.e., the direction of the photographing optic axis X3. Reference numeral 11 designates a half-mirror obliquely disposed on the optic axis X3, and the photoelectric element 7 is disposed on the branched-off optic axis and receives a reflected light imaged by the photo-taking lens 1. At this time, a=D·f(R-f). See FIG. 6. Approximately, if R&gt;&gt;f, D·f=f 2   F . To further enhance the accuracy, the relation among D, f and f F  may be determined so that a=x&#39; between infinity and the close photographing distance. 
     As described above, the projecting lens or the light-receiving lens may be scanned instead of the projection light source or the photoelectric element being scanned. Also, one of the projection optic axis and the light-receiving optic axis may be made coincident with the optic axis of the photo-taking system, or may be disposed through the photo-taking system but with the optic axis being deviated. 
     The above-described embodiments are ones applied to the active type, but they can also be applied to the passive type. In FIG. 7, reference numerals 9 and 10 designate photosensor arrays. It is to be understood that the array 9 is movable with a photo-taking lens, not shown, and the array 10 is stationary. Thus, the array 9 scans the object field, and the correlation between the image signals from the two arrays 9 and 10 is taken and an in-focus state is determined. When scanning is to be effected by the photo-taking lens, the focusing lens is moved, but instead, a holding member for an image pickup surface 2 may be moved. 
     FIG. 8 shows yet still another embodiment which is of the type in which both of the projecting side and the light-receiving side are scanned to eliminate parallax. 
     In the present embodiment, the projection optic axis X1 and the light-receiving optic axis X2 are bent in opposite directions by reflecting mirrors 5 and 5&#39;&#34;, respectively, and a projection light source 4 and a photoelectric element 7 disposed on the optic axis are moved in the same direction as a photo-taking lens 1. 
     Again in this case, the amounts of movement of the photo-taking lens 1, the projection light source 4 and the photoelectric element 7 can be made equal to one another, and if the spacing between the photographing optic axis X3 and the projection optic axis X1 is D1 and the spacing between the photographing optic axis X3 and the light-receiving optic axis X2 is D2, the focal length f 1  of the projecting lens and the focal length f 2  of the light-receiving lens may be determined so as to satisfy D1f 1  =f 2   F  and D2f 2  =f 2   F  which correspond to the result of the development of the aforementioned equation. 
     In the present invention described above with respect to the preferred embodiments thereof, the direction of movement of the focusing system and the direction of movement of the components of the focus detecting device can be made identical to each other and therefore, the interlocking mechanism is simplified and made compact, and this greatly contributes to the compactness of the photographing apparatus, the prevention of troubles and the ease of manufacture and assembly. Further, if the amounts of movement of the focusing system and the components are made equal to each other, means for controlling the amount of movement such as a cam or a lever can be eliminated, and this leads not only to the ease of manufacture but also to the possibility of eliminating all error factors including back-lash that have necessarily existed in the adjusting means, which also leads to a very excellent effect that the accuracy of focusing can be improved.