We have carried out both theoretical and experimental studies of the sensitivity of dark hole contrast to the control bandwidth and dark - hole dimensions in high - contrast broadband stellar coronagraphy . We have evaluated the performance of DM actuator solutions in the presence of occulting mask defects using one to five 2 % -wide bands spanning a 10 % bandpass . We have also investigated the dependence of the HCIT contrast performance on the size of dark -hole area including large dark holes formed at the Nyquist limit of the DM .