[1, 2], the focal spot size of an X-ray tube was determined
using its image obtained with the aid of a cylindrical
X-ray optical structure of Kumakhov optics.
However, the accuracy provided by such imaging systems
is frequently insufficient for determining the
dimensions of focal spots of the modern microfocus
X-ray tubes, since the error introduced by the usual
polycapillary structure is comparable with the anode
spot size to be determined.