Modern cameras take care of exposure metering themselves in the subject and automatic modes, and deliver satisfactory results – even when detachable flash units are used, insofar as the camera and the detachable flash unit can communicate with each other regarding exposure via a data protocol. In the case of external flash units there’s no TTL or E-TTL function, and the camera and the flash unit have to be adjusted manually.
Read more about this issue in an excerpt from a book published by Rheinwerk Verlag.
