A source (19) for multiple energy X-ray generation in particular by field emitting carbon nanotubes (1, 2) is presented. In order to achieve a spatial overlap of the trajectories of the X-ray beams coming from different emitters, a focusing unit (7, 9) is supplied to the emitted electrons (28, 29). A fast switching between the emission of the different carbon nanotubes allows multiple kilovolt imaging. Independent determination of multiple focal spot parameters by the focusing unit leads to the possibilities of fast switching between different spot geometries and spatial resolutions. This might be seen in FIG. 1.