High angular resolution provided by adaptive optics on ground-based telescopes allows detailed study of bright stars environment. The limitation of dectability of faint companions is the diffracted light from the star. The 4Q coronagraph (Rouan et al. 2000; Riaud et al. 2001; Abe et al. 2001) decreases this diffracted halo and provides high contrast imaging. The residual speckle pattern becomes the final limitation for the coronagraphic observations. We present here, a complete study of the 4Q coronagraph in use with an high order adaptive optics on the VLT telescope, within the context of "Planet Finder" ESO project. Practically, a simple solution making use of commercial half waveplates seems well suited for a ground-based coronagraphic device.