This European standard specifies the checking of focal spot dimensions above 0,5 mm of X-ray systems up to and
including 500 kV tube voltage, by means of radiographs of sharp edges.
The image quality and the resolution of X-ray images depend highly on the characteristics of the focal spot. The
imaging qualities of a focal spot are based on the two dimensional intensity distribution in the object plane.
The edge method is especially useful for the checking of focal spots under field conditions in order to find changes
of the focal spot. It cannot be used for an absolute measurement of the focal spot. For absolute measurements the
method according to Annex A is applied.