A camera system according to this invention comprises an interchangeable lens unit, an intermediate adapter, and a camera body unit. An AF sensor detects the defocus amount of the interchangeable lens unit. The interchangeable lens unit incorporates a data storage section. The data storage section stores first AF correction data and second AF correction data. The first AF correction data is determined by the optical characteristic of the interchangeable lens and associated with the type of the light source illuminating the object of photography. The second AF correction data is determined by the optical characteristic of a system composed of the interchangeable lens and the intermediate adapter and associated with the type of the light source illuminating the object of photography.