The present invention relates to an X-ray fluorescence, XRF, spectrometer, for measuring X-ray fluorescence emitted by a target, wherein the XRF spectrometer comprises an X-ray tube with an anode to emit a divergent X-ray beam, a capillary lens that is configured to focus the divergent X-ray beam on the target, an aperture system that is positioned between the anode of the X-ray tube and the capillary lens and comprises at least one pinhole, and a detector that is configured for detecting X-ray fluorescence radiation emitted by the target, wherein the at least one pinhole is configured for being inserted into the divergent X-ray beam and for reducing a beam cross section of the divergent X-ray beam between the anode and the capillary lens. The present invention further relates to an aperture system for a spectrometer, to the use of an aperture system for adjusting the focal depth of a spectrometer and to a method for adjusting the focal depth of as spectrometer.