Abstract:
Full and minimum aperture information is transmitted to a camera body from an interchangeable lens by coding possible combinations of the two values into various discrete single values and transmitting the single value to a decoder in the camera body. For instance, a projection may be provided on the lens barrel having a height corresponding to a particular combination of full and minimum aperture values.

Description:
BACKGROUND OF THE INVENTION 
     With an interchangeable lens type camera, if information on the full-aperture value and minimum-aperture value of each interchangeable lens can be transmitted to the camera body, it is convenient for the photographer. If this is possible, for instance the full-aperture value and minimum-aperture value of a lens coupled to the camera body can be displayed in the finder. In light metering with a shutter priority type automatic exposure camera, although a lens having a full-aperture value f 4 is coupled to the camera body, sometimes an indication (for instance f 2) brighter than that is made. If a photographing operation is carried out in this state, an exposure error is caused. Therefore, in this case it is necesary to provide a warning means or to transmit the full-aperture value information from the lens to the camera body. The same is true of the minimum-aperture value. However, there is no relationship between the full-aperture value and the minimum-aperture value of a lens and, therefore, heretofore such aperture information transmitting means are formed independently of one another. Furthermore, since there are a number of full-aperture values and minimum-aperture values available, most of the aperture information transmitting means are so designed as to transmit information on the full-aperture value only which is essential for compensation of light metering; that is, they are not so designed as to transmit information on the minimum-aperture value. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of this invention is to provide a means in which two pieces of information on a full-aperture value and a minimum-aperture value are transmitted to a camera body by means of only one aperture information transmitting member provided in a lens barrel. This can be accomplished, for instance, by determining several possible full and minimum aperture value combinations, assigning a discrete value to each combination, and providing a projection on the lens barrel having a height corresponding to a particular value. The camera body includes a detector for determining the proper values from the height of the projection when the lens is mounted. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view showing an embodiment of this invention. 
     FIG. 2 is a Table indicating the combinations of full-aperture values and minimum-aperture values. 
     FIG. 3 is a perspective view illustrating a lens barrel. 
     FIG. 4 is also a perspective view showing an electrical means for electrical division of a full-aperture value and a minimum-aperture value. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     This invention will now be described with reference to its preferred embodiment. 
     In FIG. 1, reference numeral 1 designates a camera mounting; reference numeral 2, a transmission pin; reference numeral 3, a link lever; and reference numeral 4, a slide lever. The slide lever 4 is provided with a full-aperture value cam 4a for the full-aperture value and a minimum-aperture value cam 4b for the minimum aperture value. A first opening lever 5 as a follower is in contact with the full-aperture value cam 4a. One end of a string 6a is tied to one end of the lever 5, and a restoring spring 7 is connected to the other end of the string 6a. A pointer 8a indicating the full-aperture value is fixedly secured to the string 6a in such a manner as to correspond to aperture value indicating numbers 10 in a finder picture frame 9. On the other hand, a second operating lever 11 employed as a follower is brought into contact with the minimum-aperture value cam 4b by a restoring spring 12. Similarly as in the case of the aforementioned full-aperture value indicating means, a pointer 8b is fixedly secured to the string 6b in such a manner as to correspond to the aperture value indicating numbers 10. In FIG. 2, reference number 16 designates a mounting lock pin. The cams 4a and 4b are in certain relation to each other which is defined by codes A through G as indicated in FIG. 2, for instance. The codes A through G mean the combinations of full-aperture values and minimum aperture values of interchangeable lenses as indicated in FIG. 2. 
     A lens barrel is shown in FIG. 3, which comprises a lens mounting 13, an aperture operating member 14, and an aperture value relating protrusion 15. The height of the protrusion 15 is so determined that the combination of the full-aperture value and minimum-aperture value of the lens coincides with one of the combinations or codes A through G. In FIG. 3, reference numberal 17 designates a mounting lock groove. 
     For instance, the height of the protrusion 15 for a lens having a full-aperture value f 2.8 and a minimum-aperture value f 32 corresponds to code F. When this lens is mounted in the body in such a manner that the lock groove 17 is engaged with the mounting lock pin 16, the transmission pin 2 is depressed by the protrusion 15, as a result of which the slide lever 4 is displaced right in FIG. 1 by means of the lever 3. The amount of this displacement is so determined in advance that the cam followers of the first and second operating levers 5 and 11 coincide with the F position of the cam of the slide lever 4. Accordingly, the first operating lever 5 engages the position f 2.8 of the full-aperture value cam 4a, and the string 6a is moved to allow the pointer 8a to indicate &#34;f 2.8&#34;. On the other hand, the second operating lever 11 engages the position f 32 of the minimum-aperture value cam 4b, and the string 6b is moved to cause the point 8b to indicate &#34;f 32&#34;. 
     In the above description, one piece of input information is mechanically divided into two pieces of information representative of the full-aperture and the minimum aperture. One example of a method in which such division is electrically effected will be briefly described. In this method, each of the codes A through G is digitally processed into a 3-bit code. More specifically, the full-aperture values are represented by P 1  and P 2  including a logical high level (&#34;H&#34;) and a logical low level (&#34;L&#34;), while the minimum-aperture values are represented by P 3  including the logical high level and the logical low level, as indicated in FIG. 2. A pattern 18 indicating the high and low levels for P 1 , P 2  and P 3  is provided so as to coincide with the codes A through G. A desired one out of the codes A through G can be picked up by using a slider 19, thus electrically dividing the code into a full-aperture value and a minimum-aperture value (FIG. 4). Furthermore, if data representative of the combinations of full-aperture values and minimum-aperture values are replaced by electrical data such as electrical resistances which are provided for a lens barrel, it is possible to electrically detect aperture values in the camera body. 
     As is apparent from the above description, according to the invention, the inherent data of interchangeable lenses are determined by combining the full-aperture values and minimum-aperture values thereof, respectively, and the aperture value information transmission member corresponding to the inherent data is provided in the lens barrel, while the signal detecting member for detecting the signal from the aperture value transmission member is provided in the camera body. Therefore, two pieces of information on the full-aperture value and minimum-aperture value of an interchangeable lens can be transmitted with only one information transmission member. Accordingly, the mechanism for information transmission is simple, which leads to reduction in manufacturing cost and to improvement in reliability. Thus, the invention has significant advantages.