  We demonstrate that perturbative QCD allows one to calculate the absolute
cross section of diffractive exclusive production of photons at large $Q^2$ at
HERA, while the aligned jet model allows one to estimate the cross section for
intermediate $Q^2 \sim 2 GeV^2$.
  Furthermore, we find that the imaginary part of the amplitude for the
production of real photons is larger than the imaginary part of the
corresponding DIS amplitude by about a factor of 2, leading to the prediction
of a significant counting rate for the current generation of experiments at
HERA. We also find a large azimuthal angle asymmetry in $ep$ scattering for
HERA kinematics which allows one to directly measure the real part of the DVCS
amplitude and hence the nondiagonal parton distributions.
