The invention relates to a diaphragm unit 4 or a diaphragm unit 4 and an associated x-ray emitter 1 with adjustment option for displaying an asymmetrical area under examination, with the diaphragm unit 4 being able to be tilted in accordance with the invention relative to the x-ray emitter 1, preferably by moving it on a rail system 12 attached isocentrically to the tube focus 9 on the tube housing 2 and/or the unit 1;4 made up of diaphragm unit 4 and x-ray emitter 1 being able to be tilted isocentrically to the tube focus 9 of the x-ray tube 2.