Abstract: Accessories for use in photographic camera systems provide various data that are inherent to the objective lens being used and are transmitted from the objective lens to the camera body, and the various data are processed and the resultant data are used for automatic exposure control, automatic focusing, and various warnings and indications. Such data may include the maximum and minimum F-numbers, the focal length and the shortest photographable distance of the lens, data indicative of the relationship between the direction of the rotation of a motor within the camera body for automatic focusing and the direction of movement of the lens system, and data indicative of the relationship between the amount of rotation of the motor and the amount of the shifting of the image plane.

Abstract: An automatic focusing system in a lens exchangeable camera is adapted to use a conversion lens assembly, in which a drive transmission mechanism is provided between an intermediate driven member capable of being coupled with a driving output member of a camera body and an intermediate driving member capable of being coupled with a driven member of an exchangeable lens assembly, for transmitting movement of the intermediate driven member to the intermediate driving member with a predetermined transmission coefficient .mu.c.In use, the conversion lens assembly is interposed between the camera body and the exchangeable lens assembly. A control circuit of the camera body controls the rotation of a driving motor based on a focus condition signal obtained by focus condition detection and a data signal input from the exchangeable lens assembly for determining the amount and direction of the movement of the driving output member driven by the driving motor.