We discuss a Poincar\'e invariant coupled-channel formalism which is based onthe point-form of relativistic quantum mechanics. Electromagnetic scattering ofan electron by a 2-body bound state is treated as a 2-channel problem for aBakamjian-Thomas-type mass operator. In this way retardation effects in thephoton-exchange interaction are fully taken into account. The electromagneticcurrent of the 2-body bound state is then extracted from theone-photon-exchange optical potential. As an application we calculateelectromagnetic 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 eliminatedin an unambiguous way such that one is left with a current that has all thedesired properties.
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