  We present results on the Omega baryon electromagnetic form factors using
$N_f=2+1$ domain-wall fermion configurations for three pion masses in the range
of about 350 to 300 MeV. We compare results obtained using domain wall fermions
with those of a mixed-action (hybrid) approach, which combine domain wall
valence quarks on staggered sea quarks, for a pion mass of about 350 MeV. We
pay particular attention in the evaluation of the subdominant electric
quadrupole form factor to sufficient accuracy to exclude a zero value, by
constructing a sequential source that isolates it from the dominant form
factors. The $\Omega^-$ magnetic moment, $\mu_{\Omega^{-}}$, the electric
charge and magnetic radius, $\langle r^{2}_{E0/M1} \rangle$, are extracted for
these pion masses. The electric quadrupole moment is determined for the first
time using dynamical quarks.
