After a brief review of the kinematics of deep inelastic scattering (DIS) w
ithin the so-called Sigma method. we derive the necessary formulae for the
treatment of QED radiative corrections to DIS originating from hard photon
radiation. The results are applied to a calculation of the corrections to D
IS with a tagged photon with next-to-leading logarithmic accuracy under HER
A conditions. It turns out that the next-to-leading logarithmic corrections
are quite important for the Sigma method. We also discuss the dependence o
f the corrections on the longitudinal structure function of the proton, F-L
, in the region of low Q(2) and moderate x.