The stellar binary fraction in star clusters is a key factor in understanding the effects of binary stars on the properties and dynamical evolution of the host cluster. Using a very accurate stellar catalogue based on deep Hubble Space Telescope (HST) observations of the young rich Large Magellanic Cloud cluster NGC 1818, we assess its binary content. Based on artificial star tests we have established a method to very efficiently determine the probability of chance blends and superpositions. Combining the measured photometric errors and the superposition statistics, we construct synthetic colour-magnitude diagrams (CMDs) as a function of input binary fraction. The binary fraction of the cluster is then calculated by means of a Kolmogorov-Smirnoff (K–S) test between the synthetic and the observed CMDs. The likely binary fraction for this cluster is 50–70.
