  Direct imaging of exoplanets requires the detection of very faint objects
orbiting close to very bright stars. In this context, the SPICES mission was
proposed to the European Space Agency for planet characterization at visible
wavelength. SPICES is a 1.5m space telescope which uses a coronagraph to
strongly attenuate the central source. However, small optical aberrations,
which appear even in space telescopes, dramatically decrease coronagraph
performance. To reduce these aberrations, we want to estimate, directly on the
coronagraphic image, the electric field, and, with the help of a deformable
mirror, correct the wavefront upstream of the coronagraph. We propose an
instrument, the Self-Coherent Camera (SCC) for this purpose. By adding a small
"reference hole" into the Lyot stop, located after the coronagraph, we can
produce interferences in the focal plane, using the coherence of the stellar
light. We developed algorithms to decode the information contained in these
Fizeau fringes and retrieve an estimation of the field in the focal plane.
After briefly recalling the SCC principle, we will present the results of a
study, based on both experiment and numerical simulation, analyzing the impact
of the size of the reference hole.
