A camera system having an interchangeable objective lens selectively mountable to at least two different types of camera bodies of a, first type and second type, is involved. The camera system has a ROM located in the interchangeable objective lens for storing a plurality of compensation data: one is suitable for the first type camera body; and the other is suitable for the second type camera body. Each data compensates an error in fully-open aperture light measurement for each type of camera. The compensation data is transmitted from the lens to the camera body. A register is provided in the camera body for storing a selected compensation data which is necessary for the type of camera body mounted with the lens. A device is provided in the camera body for practicing a fully-open aperture light measurement through the interchangeable objective lens to produce a light measuring information including the light measurement error. A calculator is provided in the camera body for calculating a correct exposure information using the compensation data stored in the register and the light measuring signal, whereby the error included in the light measuring signal can be removed.