  Differential dynamic microscopy (DDM) can be used to extract mean particle
size from videos of suspensions. However, many suspensions have multimodal
particle size distributions (PSDs), for which this is not a sufficient
description. After clarifying how different particle sizes contribute to the
signal in DDM, we show that standard DDM analysis can extract the mean sizes of
two populations in a bimodal suspension given prior knowledge of the sample's
bimodality. Further, the use of the CONTIN algorithm obviates the need for such
prior knowledge. Finally, we show that by selectively analysing portions of the
DDM images, we can size a trimodal suspension where the large particles would
otherwise dominate the signal, again without prior knowledge of the
trimodality.
