Conversion lens assembly for an automatic focusing system in a lens

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. The driven member of the exchangeable lens assembly is driven for displacing the focusing optical system through coupling with the intermediate driving member of the conversion lens assembly in response to the movement of the driving output member of the camera body. The data signal is related to a ratio of image plane displacement amount by the adjustment of the focusing optical system to the movement of the driven member. The conversion lens assembly may be provided with a signal transmission system which transmits the above data signal to the control circuit with a predetermined transmission coefficient.