  Trajectories of light rays in a static spacetime are described by
unparametrised geodesics of the Riemannian optical metric associated with the
Lorentzian spacetime metric. We investigate the uniqueness of this structure
and demonstrate that two different observers, moving relative to one another,
who both see the universe as static may determine the geometry of the light
rays differently. More specifically, we classify Lorentzian metrics admitting
more than one hyper--surface orthogonal time--like Killing vector and analyze
the projective equivalence of the resulting optical metrics. These metrics are
shown to be projectively equivalent up to diffeomorphism if the static Killing
vectors generate a group $SL(2, \R)$, but not projectively equivalent in
general. We also consider the cosmological $C$--metrics in Einstein--Maxwell
theory and demonstrate that optical metrics corresponding to different values
of the cosmological constant are projectively equivalent.
