Jamesino wrote in post #7389868
Does this mean if I tilt my 580 EX downwards and shoot a portraits at a very close distance, the shadows will also be diffused, similar to a beauty dish effect?
Nope. the front lens of your 580 only define "the largest possible" surface source of light. In reality, however, the light from a flash is not intentionally diffused and is ideally more like a point source.
Tracing the outgoing rays of light backwards, you will find an imaginary point source located roughly 5-30 cm behind the Fresnel lens of the flash (for 28-135mm FF coverage).
Now, I have not done the ray tracing myself, nor seen anyone do it, so it may not be a perfect point source, nor exactly at the positions I mentioned, so its all (fairly reasonable) guesstimations. The Fresnel lens is however not the source of light since it refracts light, not diffuse it.
EDIT: Apparently, I'm a moron. Forget about the rambling above. Please.