The invention relates to an X-ray apparatus for forming X-ray images, which apparatus includes an X-ray detector (4) for the conversion of X-rays into electrical signals, a detector exposure unit (5) for the emission of electromagnetic radiation in dependence on how first and second exposure parameters, the value of the first exposure parameters being defined by the acquisition mode whereas the second exposure parameters are not defined by the acquisition mode, and also a control unit (13) for changing and controlling at least one second exposure parameter of the detector exposure unit upon a change of the acquisition mode.