English: Maps of Strehl ratio (a measure of light concentration) in the case of single conjugated adaptive optics, i.e. as used in present AO systems (SCAO; left) and multi-conjugated (MCAO; right), as measured in images of Omega Centauri. Different colours correspond to different Strehl ratios, from 0 (black) to red (35%). The SCAO map illustrates how inhomogeneous the correction is across the field of view. The peak Strehl ratio is about 30% close to the guide star, to the right, and decreases with the distance to the guide star due to atmospheric anisoplanatism. The MCAO map, however, is much more uniform across the field of view, and peaks close to the location of the three guide stars shown by crosses. A comparison between the two images clearly shows the advantage of MCAO.