The magnification is as large as the ratio between the width of the beam spread on the detector l and the beam footprint on the surface S. in the plane XOZ normal to the axis of a cylinder with a radius R that is perpendicular to the figure plane. h is the offset of the elementary ray rh,i from the beam center r0,i. The angle αi is the effective grazing angle, while αi,h and Δαi,h are the actual grazing angle of rh,i and the difference of this angle from αi, respectively.