This post and the reference to gonzogolf is dead on the money. What I thought was diffusion at one time to what it really is was way off. I took some lighting courses, followed the flash forums, studied Neil van Niekerk and realized it is simple physics and there are no magic bullets. The manufacturers and resellers of gimmick diffusers make lot a of money off magic bullets. Not saying the flashes bounce card is a gimmick. It is a just a tool with a specific job.
Yep. Too much mystery
Diffuser and reflections are the same in a way that they must increase the size of the light source. Usually with a diffuser the light is spread is more even light over the modified itself, which can make it "kind of" bigger
and the hotspot is better controlled.





