Patent ID: 7973851

Claim:
An auto-focus system comprising: a picture-taking lens device detachably attached to a camera via a mount; a focus controlling device on the picture-taking lens device for setting an AF area in a display of a view finder of the camera and controlling a focus of a picture-taking lens to focus on an object in the AF area; a view finder controlling device for controlling the display of the view finder displaying an image taken by the camera; an AF area display information outputting device on the camera for outputting AF area display information for displaying AF area information relating to a range of the AF area; an AF area indicating device for indicating a range of an AF area in the display of the view finder; an AF area changing device for changing a range of an AF area to be set in the focus controlling device to a range of an AF area indicated by the AF area indicating device; and a switching device for switching a change of a range of an AF area by the AF area changing device between possible and impossible, wherein the change at least relates to the location of an AF area, and wherein the switching device switches a change of a range of an AF area to impossible when the view finder controlling device has no function of displaying the AF area information on the view finder, wherein said focus controlling device on the picture-taking lens device performs a test to determine if the AF area display information outputting device has requested AF area display information from the focus controlling device, and if the AF area display information outputting device on the camera has requested that the focus controlling device send AF area display information to the AF area display information outputting device, then the focus controlling device determines whether or not that said camera has a function of displaying the AF area information on the view finder, and if the AF area display information outputting device has not requested that the focus controlling device send AF area display information to the AF area display information outputting device, then the focus controlling device determines that said camera has no function for displaying the AF area information on the view finder.