1 Introduction

Instrumental development of adaptive optics and coronagraphic concepts are required for the improvement of image contrast (Malbet et al. 1995; Malbet 1996). Astronomical advances such as circumstellar imaging, substellar objects and exoplanet detection or the study of extragalactic nebulosities would benefit of an increased dynamic range. Limitations come from the light diffracted by the telescope and instrument optics: polishing defects, spider arms, and the wavefront residual bumpiness. The principle of dark-speckle imaging, proposed in 1995 by Labeyrie, and refined since (Boccaletti et al. 1998a) is one of the necessary steps for a better suppression of this scattered light. It requires an efficient adaptive optics and then uses the speckle imaging for freezing the atmospheric turbulence, which further degrades the image. The concept is fully described in the aforesaid papers (Labeyrie 1995; boccaletti et al. 1998a). We here present a recent experimental simulations performed with the dark-speckle coronagraph. They were obtained under good and stable artificial seeing conditions and allowed us to calibrate our instrument in comparison with the classical long-exposure imaging. We stress upon the fact that dark-speckle theory doesn't take into account optical defects of the instrument, and consequently, the results may appear optimistic in some cases. Sections 2 and 3 briefly describe the experiment and data processing. Sections 4 and 5 discuss the results.