Arc statistics with a sample of the most x-ray luminous galaxy clusters

We present a sample of 21 medium redshift galaxy clusters selected from the ROSAT Bright Survey. We have chosen the most X-ray luminous clusters because they are the most massive systems. In these massive clusters the probability of finding arcs is particularly high (~45%), therefore they are best suited for arc statistics, mass determinations, studies of the best lensed distant galaxies and even for investigations of merging properties. In this presentation we show the results of optical observations in the R- and V-band and discuss the photometric properties of arc candidates.