Our imaging session continues by locating the next point source in the image, and modelfitting the cumulative model. This is essentially what CLEAN does, but we are doing it carefully by subracting each component's contribution to the visibility. Finally we self-cal the data, modelfit one last time, then restore the image.

Above L-R: (1) Residual after subtraction of all four point components; (2) Residual after phase-only selfcal; (3) Residual after global amplitude self-cal; (4) Final restored (clean) image.

Final rms noise level - 0.4 mJy per beam! Because of strong sidelobes from the multiple componenets in this object, care must be taken in the deconvolution and self-cal iterations. In this case, modelfitting works wonders and gives us an excellent quantitative model for quadruple gravitational lens system CLASS B1608+656!