Abstract: An apparatus for measurement of the thickness of thin layers by means of X-rays using an X-ray tube which emits X-rays which are directed at a layer to be measured, has at least one aperture apparatus arranged between the X-ray tube and the layer to be measured. The apparatus includes an area absorbing X-rays and an aperture opening. At least one aperture opening in the aperture apparatus has a geometric shape which, seen in the beam direction, projects an area which at least in places is matched to the geometry of the layer to be measured.

Abstract: The invention relates to a method of setting a position of an object of measurement in layer thickness measurement by X-ray fluorescence in which a beam of an optical recording device is projected into the beam of the X-radiation and in which the surface of the object of measurement is recorded and output as an image comprising a number of image points, with the distance between the surface and the collimator being changed by an absolute amount of a path of movement, with changes in brightness of the image points being recorded in at least one measuring plane during the at least one change of the distance between the surface and the collimator, with the maximum of the difference in brightness of the image points of an image being ascertained after the at least one change of the absolute amount of the distance, and with the distance between the collimator and the object of measurement being set to the position of the ascertained maximum of the difference in brightness.