  In this communication are presented rigorous and approximate analytical
expressions of the Point Spread Function (PSF) and Field of View (FoV)
achievable by multi-aperture Fizeau interferometers, either of the imaging or
nulling types. The described formalism can be helpful for dimensioning future
space missions in search of habitable extra-solar planets. Herein the
characteristics of PSF and FoV are derived from simple analytical expressions
that are further computed numerically in order to evidence the critical role of
pupil re-imaging along the interferometer arms. The formalism is also well
suited to simulating pseudo-images generated by a nulling Fizeau
interferometer, and numerical computations demonstrate that it is only
efficient for very short baselines. Finally, two different designs improving
the nulling capacities of such exoplanet observing instruments are briefly
presented and discussed
