1. Field of the Invention
This invention relates to a camera arranged to permit an optical accessory to be mounted thereon.
2. Description of the Related Art
It has been practiced to design a camera system taking into consideration the use of such accessories as a telephoto conversion lens (hereinafter referred to as a tele-converter), etc. For example, the use of a tele-converter which increases the focal length of a photo-taking lens by two or 1.4 times is in great demand. A camera system, therefore, must be designed to permit data correction in anticipation of an extender to be mounted for that purpose. More specifically, in the case of a camera system of the kind performing automatic focusing (hereinafter referred to as AF) and automatic exposure control (hereinafter referred to as AE), information on the lens received by the camera body without the use of any extender must be adjusted and corrected when the extender is used. To meet this requirement, there have been proposed various lens information correcting methods. In one method, the lens information (about its focal length, its aperture value, etc.) is corrected within the extender. In another, the use of an extender is detected and the lens information is corrected as necessary within an interchangable lens.
However, the conventional camera system is arranged to correct the lens information obtained with the tele-converter mounted on the camera system on the assumption that the AF and AE actions are to be performed at a maximum aperture. The conventional camera system, therefore, has presented a problem that accurate control is hardly possible in cases where a video camera system is arranged to perform the AF and AE actions with the aperture in a state of having been stopped down.