Conversion lens assembly for an automatic focusing system in a lens exchangeable camera

Claim 1

In an automatic focusing system for a lens exchangeable camera, in which an exchangeable lens assembly attachable to a camera body includes a focusing optical system, a driven member, a focusing mechanism for adjusting said focusing optical system in response to movement of said driven member and signal means for providing a data signal which is representative of the ratio of the image plane displacement by the adjustment of said focusing optical system to the movement of said driven member, and in which said camera body includes a focus condition detection means for detecting the focus condition of said focusing optical system to generate a focus condition signal, a driving member capable of being coupled with said driven member, a motor rotatable for driving said driving member, and a control circuit for controlling the rotation of said motor in response to said focus condition signal and said data signal so that said focusing optical system is brought into an in-focus condition by said focusing mechanism through the coupling between said driving and driven members, a conversion lens assembly adapted to be interposed between said camera body and said exchangeable lens, comprising: a conversion lens unit having a predetermined magnification power M; an intermediate driven member capable of being coupled with said driving member; an intermediate driving member capable of being coupled with said driven member; drive transmission means for transmitting movement of said intermediate driven member to said intermediate driving member with a predetermined transmission coefficient μc to cause movement of said intermediate driving member the amount of which is the product of said transmission coefficient and the amount of movement of said intermediate driven member, said transmission coefficient μc being larger than 1 when said magnification power M is smaller than 1, while being smaller than 1 when said magnification power M is larger than 1; and, signal transmission means for transmitting said data signal to said control circuit with a predetermined transmission coefficient ηc so that said control circuit receives said data signal multiplied by said transmission coefficient ηc.