Interchangeable lens barrel structure
BACKGROUND OF THE INVENTION 
     1. Field of the Invention: 
     This invention relates to interchangeable lens barrels which are to be used with motion picture cameras and still cameras, and more particularly to the structure of a composite barrel of the mount for an interchangeable lens which barrel is composed of two distinct sections detachable from each other, one of which is for the mount of a front assembly of a lens system, and the other section which is for the mount of a rear assembly thereof, and which structure permits selection of a plurality of front lens assemblies of different types mounted in the respective front barrel sections for attachment to the rear barrel section provided with a diaphragm drive mechanism incorporated therein. 
     2. Description of the Prior Art: 
     Recently in cameras, iris blades used to form an opening to control the incidence of object light, have been positioned within the incidental optical path of the object light, and the size of opening has been made variable by controlling the iris blades so that the photographing can be made with the appropriate exposure. A method for controlling the iris blades is such that an object brightness is detected and the iris blades are controlled by such iris blades driving means as a motor or a galvanometer controlled by signal afforded by the detecting step. Interchangeable lens units housing both the iris blades and the iris blades driving means for operating the iris blades within one interchangeable lens barrel are known. Such a conventional interchangeable lens unit forms one unit having all the optical elements necessary for photographing within itself. But it is necessary for a photographer to prepare many kinds of interchangeable lenses so different arrangements of interchangeable lenses can be used as desired for attaining different photographing effects. However, a conventional interchangeable lens unit housing both the iris blades driving means within one interchangeable lens barrel will have a complicated lens unit structure as the various parts housed within it cause the manufacturing cost to go up, and the price of one interchangeable lens to become high. Therefore, when a photographer wants to photograph with various effects, he needs a number of high priced interchangeable lens units, which results in a considerable economic burden. Providng iris blades and iris blades driving mechanism within each interchangeable lens unit makes the size of the unit that much bigger and heavier, leaving a problem that the unit is inconvenient for handling. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a novel structure of an interchangeable lens barrel which has overcome these conventional drawbacks. 
     Another object of the present invention is to provide a compact, inexpensive and reliable diaphragm drive mechanism-incorporated interchangeable lens barrel. 
     Still another object of the present invention is to provide an interchangeable lens barrel composite system in which an interchangeable lens barrel attachable to the camera body is divided into two sections, one of which is for the mount of a front assembly of a lens system and the other section which is for the mount of a rear lens assembly thereof, the rear barrel section being constructed as including a main connector arranged at the rear end to be detachably coupled with the connector of the camera body, an intermediate connector arranged at the front end, a number of tandem connection terminals arranged in a space within the main connector for connection with the corresponding number of electric connection terminals of the camera body, a diaphragm device including drive means therefor connected to the tandem connection terminals, and the rear lens assembly including an image-forming optic arranged behind the diaphragm device, and, on the other hand, the front lens barrel section being constructed as including a connector arranged at the rear end to be detachably coupled with the intermediate connector of the rear barrel section and the front lens assembly including a focusing member and the like, so that such construction and arrangement of the front and rear sections of the composite barrel permits not only the attachment and detachment of an interchangeable lens to and from the camera body but also the selection of front lens assemblies of different types in the individual front barrel sections for attachment to the rear barrel section. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the front and rear sections of an interchangeable lens barrel according to the invention which are about to be coupled with each other and with a camera body. 
     FIG. 2 is a schematic sectional view of an interchangeable lens barrel section assembling system in which two front barrel sections having front lens assemblies of different type are illustrated as being adaptable to the same rear barrel section. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIGS. 1 and 2, there is shown a camera body 1 having a window 1a provided through the housing thereof to receive photometric light, an image-forming lens 18 arranged in the window 1a and a sensor circuit. The sensor circuit comprises a photo-conductive elememt 19 arranged behind the image-forming lens 18 which upon exposure to an image of the object to be photographed located outside of the camera body 1 formed by the image-forming lens 18 from light entering through the window 1a produces an electric signal dependent upon the level of brightness of the object being photographed, a variable resistor 20 of which the resistance value is adjustable in accordance with the sensitivity of a photographic film in a magazine 30 associated in the camera body 1 and two fixed resistors 23 and 24, said photoconductive element 19 and said resistors 20, 23 and 24 constituting a Wheatstone bridge circuit of which the output points, a, and a&#39;, are connected to connection terminals 3 and 3&#39; respectively provided in a space within a lens connector portion 2 of the camera body 1. The bridge circuit is connected to a battery 26 through a switch 25 which is operable for selectively connecting and disconnecting the bridge circuit to and from the battery 26. The battery 26 also is connected to terminals of a motor 27 for driving the camera, for example, the shutter mechanism and film transport mechanism through a switch 28 which is operable for selectively connecting and disconnecting the motor 27 to and from the battery 26. These switches are arranged to be accessible to the operator from the outside of the camera. Numeral 29 indicates an eyepiece provided in the view finder not shown. 
     An interchangeable lens barrel is constructed as consisting of a rear section 5 and a front section 14. The rear section 5 is provided with a main connector 4 of the complete interchangeable lens barrel arranged at the rear end thereof to be detachably coupled with the connector 2 of the camera body when the interchangeable lens is attached to the camera body, an intermediate connector 6 arranged at the front end of the rear barrel section 5 for connection of the front barrel section to the rear barrel section, a diaphragm device having blades 12, the rear lens assembly such as a relay lens arranged behind the diaphragm device 12 and fixedly carried in a sleeve 8, and a pair of electric connection terminals 9 and 9&#39; arranged in a space within the main connector to be connected to the connection terminals 3 and 3&#39;, respectively, of the camera body when the rear lens barrel section is attached to the camera body. The rear lens barrel section is further provided with a diaphragm drive device 11 associated with a motor or galvanometer having terminals connected through the respective leads 10&#39; to the electric connection terminals 9 and 9&#39; upon connection of the terminals 9 and 9&#39; to the terminal 3 and 3&#39; to control the diaphragm blades 12 in response to the output signal from the sensor circuit so as to adjust the size of diaphragm aperture in accordance with the light value sensed by the photoconductive element 19. The rear lens assembly-carrying sleeve has an externally screw-threaded portion 8&#39; cooperatively engaged with a screw-thread 5&#39; of the barrel 5 to be interchanged with a different type of rear lens assembly. The rear lens assembly 7 in the rear barrel section 5 may be equipped with a plurality of interchangeable front lens assemblies known in the art such as those of varifocal lens system 16 and unifocal lens system 17 and mounted in their respective front barrel sections 14 and 15 as shown in FIG. 2. Each of the different front barrel sections 14 and 15 is provided with a connector 13, 13&#39;, respectively arranged at the rear end thereof to be detachably coupled with the intermediate connector 6 of the rear barrel section 5. 
     The front and rear barrel sections of the construction described above are coupled with each other at their adjoining connectors 6 and 13, 13&#39; forming an intermediate mount to complete an interchangeable lens which when coupled with the camera body 1 at their adjoining connectors 4 and 2 to effect the connection of the diaphragm drive device 11 to the output terminals of the bridge circuit of the camera body provides an automatic diaphragm control system for the camera. In interchanging the lens system of the camera with another while maintaining the automatic diaphragm control system, the operator needs only to operate the intermediate mount of the connectors 6 and 13. If he desired to use an interchangeable lens with a manual diaphragm mechanism, this interchangeable lens may be attached to the camera body at the connector portion 2. 
     In the embodiment of the present invention which has been described in connection with a schematic example shown in FIGS. 1 and 2, it is preferred that the exposure control circuit associated with the sensor circuit for controlling the diaphragm drive device 11 is incorporated in the camera body. The example can be changed in many ways. For example, instead of incorporating the sensor circuit in the camera body, it is possible to incorporate an exposure control circuit including the sensor circuit in the rear lens barrel section 5 in such a manner that a photoconductive element 19 is arranged in the rear lens barrel section 5 to receive photometric light from the object being photographed, and the sensor circuit is arranged in the diaphragm drive device 11. In this case, it is preferred to utilize the battery 26 in the camera body as a power source of the exposure control circuit incorporated in the rear barrel section 5 through the intermediary of the leads 10 10&#39; and the connection terminals 3, 3&#39;, 9 and 9&#39;. 
     When a camera using the lens barrel structure of the present invention is pointed toward an object, object light outside of the camera is incident on the photoconductive element 19 for photo-sensing through the window 1a. As the object light is incident on the photoconductive element 19, the resistance value is varied. Since the element 19 forms one side of the bridge circuit for determining allowable incident light amount, when the object brightness is different from the reference brightness, the state of equilibrium in the bridge circuit is broken and a corresponding signal is generated at the output terminals a,a&#39;. The output signal from the bridge circuit is inputted into the diaphragm drive device through connection terminals 9,9&#39; and leads 10,10&#39;. The device 11 is operated for a time corresponding to the bridge circuit output signal, and the blades 12 are activated in association with the operation of the diaphragm drive device 11. Thus, the size of the aperture allowing the passage of object light within the lens unit will be the aperture of such size as desired for photographing the object. 
     It will be seen from the foregoing description that the described embodient of the present invention accomplishes the above-mentioned objects by constructing the barrel of the mount for an interchangeable lens associated with a diaphragm mechanism which is automatically controlled as consisting of two distinct sections of which the rear section carries the diaphragm mechanism and the front section which carries no complicated mechanism but a front lens assembly, these barrel sections being detachably coupled with each other so that when interchanging the lens system of the camera, there is no need to operate the hardly-manageable, complicated and expensive rear barrel section, but it is only required to operate the front lens barrel section provided that the interchangeable lenses which are to be used with the camera body have a common rear lens assembly. The provision for interchanging the rear lens assembly is made in the sleeve assembly 8 and 8&#39;, giving to the interchangeable lens barrel system of the invention an additional advantage of permitting the automatically controllable diaphargm device to be unremoved from the rear barrel section when interchanging the rear lens assembly, with another one.