Comparison of input (left) and reconstructed (centre, right) visibilities of a 100 mJy Cygnus A, when observed on-axis in the marginally resolved regime (8 arcsec source size and 12 arcsec beam) with negligible time and bandwidth smearing. The model visibilities in the right hand panel were constrained to only positive source components. The mean visibility error is 0.7% (centre) and 7% (right) relative to the integrated flux of the source.