What does a flash diffuser do?
A diffuser is used to soften the light when using your flash as the primary light source for illuminating your subject. Normally a direct beam of light from your flash is very “hard”, in that shadows created will have sharp edges and create a strong contract that is normally unflattering to the subject. The diffuser works on two levels: First by increasing the surface area of the light source, you get a wider spread of light. The ultimate expression of this is the light box used in studio lighting. When you have a bigger surface area, you soften the shadows because shadowed areas fall off slower as the light source is gradually occluded. Think of it this way, if you move your hand slowly across a laser beam, the light still goes out suddenly when you block it. Move your hand at the same speed over a lantern and the light slowly dims. Big enough lantern and it never really goes dark. Same with increasing the area of the flash unit. If you diffuser does not increase the surface area much
