Sodium Bismuth Titanate, Na0.5Bi0.5TiO3 (NBT) is a mixed A-site perovskite. It is both of commercial interest, due to its usage in lead-free piezoelectric solid-solutions; and of fundamental interest, due the richness of length scales over which its structural features are observed. We aim to characterise the long-range, average structure, across a recently observed thermally induced phenomenon: the optical isotropisation point. At a temperature just below the pseudo-rhombohedral to tetragonal phase transition, NBT becomes fleetingly non-birefringent: it appears that all strain and polarization¿at least on the length scale of visible light¿go to zero. High-quality Rietveld refinements around this temperature will reveal the existence of any structural anomalies that occur, including any pseudo-cubic phase, thus revealing the atomic providence of this macroscopic observation.