  We provide the general expression of the cross section for exclusive deeply
virtual photon electroproduction from a spin 1/2 target using current
parameterizations of the off-forward correlation function in a nucleon for
different beam and target polarization configurations up to twist three
accuracy. All contributions to the cross section including deeply virtual
Compton scattering, the Bethe-Heitler process, and their interference, are
described within a helicity amplitude based framework which is also
relativistically covariant and readily applicable to both the laboratory frame
and in a collider kinematic setting. Our formalism renders a clear physical
interpretation of the various components of the cross section by making a
connection with the known characteristic structure of the electron scattering
coincidence reactions. In particular, we focus on the total angular momentum,
$J_z$, and on the orbital angular momentum, $L_z$. On one side, we uncover an
avenue to a precise extraction of $J_z$, given by the combination of
generalized parton distributions, $H+E$, through a generalization of the
Rosenbluth separation method used in elastic electron proton scattering. On the
other, we single out for the first time, the twist three angular modulations of
the cross section that are sensitive to $L_z$. The proposed generalized
Rosenbluth technique adds an important constraint for mapping the 3D structure
of the nucleon.
