The Prizm is designed to give either the Canon 220EX or the Nikon
SB-400 more versatility. The Prizm will help to soften shadows by
scattering the light throughout the room more evenly. Prizm allows
light to travel up towards the ceiling to achieve excellent room light
while simultaneously allowing light to travel forward for a nice fill
flash effect. Previously this was a much harder task with these types
of flash units.