Unpolarised SPF (top), polarised fraction (middle), and polarised SPF (bottom) of two models of compact spheres with a rough irregular surface (Mukai et al. 1982), with size parameters x of 31 (red curve) and 392 (blue curve). For the unpolarised SPF (top graph), we overplotted that derived for HR 4796 in the NIR at 1.6 μm (black curve). At this wavelength, the red and blue model SPFs correspond to particle sizes of 8 and 101 μm, respectively. For the polarised SPF (bottom graph) we overplotted that of HR 4796 as derived in the optical in this study (black curve). At this wavelength, the red and blue model SPFs correspond to particle sizes of 3.7 and 47 μm, respectively.