A still camera wherein the main diaphragm can be adjusted by a focussing ring is coupled with or incorporates an electric flash unit wherein a photosensitive receiver which measures the amount of light reflected from the subject is located behind an adjustable auxiliary diaphragm. The auxiliary diaphragm is adjustable with the main diaphragm to change the threshold value of the control circuit of the flash unit. The motion transmitting connection between the main diaphragm and the auxiliary diaphragm is separable in response or prior to detachment of a removable flash unit so that the main diaphragm can be adjusted by the focussing ring when the flash unit is detached or when the housing of the camera is connected with a different flash unit.
