A method for operating an assembly configured to produce electromagnetic radiation, especially X-ray radiation or extreme ultraviolet radiation. Particles, especially electrons, are guided onto a target by way of an adjustable focusing device. The particles produce electromagnetic radiation in the target. At least one object, especially a calibration object, is penetrated by the electromagnetic radiation and a radiogram of the object is recorded. The radiogram or a plurality of radiograms is automatically evaluated and the focusing device is adjusted depending on the evaluation.