Binocular optical system with automatic focusing mechanism
This application is a continuation of application Ser. No. 245,840, filed 3/20/81, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to binoculars with an automatic focusing mechanism in which each of right and left objectives is provided with a light admitting window close thereto and independent thereof. Light entering through each light admitting window is introduced to a focus detecting element module through a movable reflex structure or a fixed reflex structure and a lens having a long focal length or a non-focus or afocal optical system attachment. 
     In ordinary binoculars, it is troublesome to manually rotate an adjustment ring for oculars to thereby achieve the focusing of the binoculars. Moreover, this manual operation is not accurate. In order to overcome these problems, heretofore auto-focus binoculars have been proposed in which light reflected by a fixed reflex structure and a movable reflex structure is introduced into a focus detecting element module and the oculars are moved in accordance with control signals generated in the module to thereby automatically perform the focusing operation. However, in such binoculars, light entering through the objectives is divided into ocular light and focus detecting element module light. As a result, the intensity of the image viewed through the oculars is reduced and at the same time the light supplied to the focusing detecting element module is insufficient and hence a desired focusing accuracy cannot be obtained in low light situations. 
     With the intention of overcoming these difficulties, the present applicant has proposed, in U.S. Pat. No. 4,262,988 filed on Dec. 28, 1979, binoculars having an automatic focusing mechanism in which, in order to provide both a fixed reflex structure and a movable reflex structure with a sufficient amount of light, right and left object-distance metering windows are formed independent of right and left objectives, respectively. However, in such binoculars, light reflected by the fixed reflecting member and the movable reflecting member is directly introduced to the focus detecting element module. Since the field angle of the binoculars is rather narrow in comparison with that of a camera, light from most of the view field (70% or more) is introduced into the module resulting in incorrect focusing as a whole. Therefore, it is impossible to focus a desired object on the image plane. Namely, if a large object upon which it is not desired to focus is positioned in the same field as a relatively small object upon which focusing is desired to be carried out, most of the view field is occupied by the large object. Even if the desired object is positioned in the middle of the view field, it is difficult to achieve desirable focusing in such a condition. 
     SUMMARY OF THE INVENTION 
     In order to overcome the above noted defects, the present invention provides binoculars in which each of right and left objectives is provided with a light admitting window close thereto and independent thereof. Light entering through each light admitting window is introduced to a focus detecting element module to thereby produce a control signal. The oculars are moved by a control signal. Optical means having a long focal length or afocal optical attachment are disposed between the module and the fixed and movable reflex structures whereby, when the distance to the object to be viewed is varied, only light from the center of the view field of the binoculars is introduced to the module to thereby enable focusing with a high accuracy. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The single FIGURE is a horizontal cross-sectional view of binoculars with an automatic focus detecting mechanism according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be described with reference with the single drawing FIGURE. In the FIGURE, reference numerals 1 and 1&#39; denote left and right objectives, reference numerals 2 and 2&#39; denote prism systems disposed in lens barrels, and reference numerals 3 and 3&#39; denote ocular optical systems, respectively. In each ocular optical system, at the outermost portion of the housing H of the binoculars, a fixed ocular lens 3a or 3a&#39; is provided, and at the inner portion thereof an ocular lens 3b and 3b&#39; movable relative to the housing H is provided. The movable ocular lenses 3b and 3b&#39; are connected to an output shaft of an ocular lens drive motor 5 through drive rods 4 and 4&#39; by a suitable gear structure and are moved by rotation of the drive motor 5 to thereby vary the front focal position of the overall ocular system 3 or 3&#39;. 
     Light admitting windows 6 and 6&#39; for metering the distance from the binoculars to the object are provided beside the left and right objectives 1 and 1&#39; in the binocular housing H. It is desired that, as shown in FIG. 1, the light admitting windows be positioned symmetrically with respect to the center line of the binoculars. In the specific embodiment described, the windows are formed outside of the objectives. However, it is possible to place the windows upward or downward of the objectives or inside of the objectives. 
     Reflex members 7 and 7&#39; are disposed rearward of the light admitting windows 6 and 6&#39;. One of the reflex members is formed as a fixed reflex member 7 and the other is formed as a movable reflex member 7&#39;. With respect to the movable reflex member 7&#39;, a drive motor 9 therefor is provided at an end portion of a drive lever 8. An eccentric cam 10 is fixed to an output shaft of the drive motor 9 and the cam 10 is in contact with an end portion of the lever 8. In addition, the end portion of the drive lever 8 is normally biased toward the eccentric cam 10 by a spring or the like. 
     A focus detecting element module 11 into which light from both reflex members 7 and 7&#39; is received is disposed between the fixed reflex member 7 and the movable reflex member 7&#39;. The focus detecting element module 11 per se is well known and may, for example, be a focus detecting mechanism used in an auto-focus camera. When a focused image is obtained at the module from the light reflected from the left and right reflex members 7 and 7&#39;, a signal is generated to stop the motor 9 coupled to the movable reflex member 7&#39; and simultaneously to stop the drive motor 5 coupled to the oculars cooperating with the drive motor 9. In front of the light admitting windows of the module 11 there are disposed long focus lenses or afocal optical system attachments 13 and 13&#39; for narrowing the view field to a predetermined range. Reference numeral 12 denotes a receiving case for a battery for supplying current to the motors 5 and 9 which is formed within available space in the housing H. 
     The operation of the binoculars thus constructed will now be described. The light entering through the objectives 1 and 1&#39; passes through the prism systems 2 and 2&#39; and is focused by the ocular optical systems 3 and 3&#39;. Initially, the focusing position of the objective lenses and the front focus position of the ocular lenses are generally not the same. However, with the present invention, since the left and right light admitting windows 6 and 6&#39; are provided independently of the objectives, the light passing through the windows is introduced into the housing H through the fixed reflex member 7 or the movable reflex member 7&#39; and the long focus optical systems or afocal optical system attachments 13 and 13&#39;. In this case, since the movable reflex member 7&#39; is always reciprocatingly moved by a mechanism such as the motor 9 and the drive lever 8 or the like, the image from the movable reflex member is caused to overlap with the image of the fixed reflex member 7. The movable reflex member 7&#39; is thus reciprocated until overlap of the images is attained. At the time when the movable reflex member 7&#39; is rotated through an angle in a predetermined proportion to the distance from the binoculars to the object, the above-described images are at identical positions. At that time, a focusing signal is produced by the module 11. 
     In the binoculars of the invention, it is to be noted that the field of the module 11 can be set as desired, such as to a narrow range, by the long focus optical systems or afocal optical systems 13 and 13&#39;. 
     The oculars 3b and 3b&#39; are moved according to the electronic control circuitry which operates in response to the distance to the object, namely, to the position corresponding to the angle of the movable reflex member 7&#39; at the time when the two images are identical with each other, that is, at the same relative positions of the module 11. The ocular lenses are so constructed that the front focal position of the oculars is the same as the image formed by the objectives. Since the movements of the ocular lenses are controlled by the electronic circuitry, it is possible to start their movements immediately after the binoculars are pointed to the desired object or, alternatively, to start them after a certain time lapses using a memory circuitry. 
     Thus, the images focused by the oculars and introduced from the objectives are completely focused. By the repeated operation as above, the focused condition will be maintained even if the distance to the object is varied. 
     As is clear from the discussion above, since the binoculars constructed according to the present invention are provided with the long focus optical systems or afocal optical system attachments 13, 13&#39;, a narrow portion of the center of the binocular field is introduced to the module. With this construction, even if the object to be viewed is displaced within the center of the field and in case of the small object, it is possible to maintain proper focus. The view field control system disclosed herein can be applied to 8 mm cameras and other optical systems although the invention has been described as relating to binoculars.