  We discuss a Poincar\'e invariant coupled-channel formalism which is based on
the point-form of relativistic quantum mechanics. Electromagnetic scattering of
an electron by a 2-body bound state is treated as a 2-channel problem for a
Bakamjian-Thomas-type mass operator. In this way retardation effects in the
photon-exchange interaction are fully taken into account. The electromagnetic
current of the 2-body bound state is then extracted from the
one-photon-exchange optical potential. As an application we calculate
electromagnetic pion and deuteron form factors. Wrong cluster properties,
inherent in the Bakamjian-Thomas framework, are seen to cause spurious
(unphysical) contributions in the current. These are separated and eliminated
in an unambiguous way such that one is left with a current that has all the
desired properties.
