Top: negative representation of the VISTA H-band image of the cluster NGC 3324 (top) and the VISTA K_s-band image of the cluster G286.38−0.26 (bottom). The positions of the X-ray sources are shown by the green boxes. We note that the X-ray source position uncertainties are in most cases considerably smaller than the size of the box symbols; the rather large 2′′ box size was chosen for a clarity of display.