windshoppe Loc: Arizona

Sorry if this question has been previously answered, but I've done a search and can't find a reference. I've been using BBF on my 5DII for some time and am a believer. Recently I've taken to learning as much as possible about Speedlight use - I have the original Canon 580EX. My understanding is that when using the Speedlight in E-TTL mode that the camera takes a reading of the ambient light when the shutter button is depressed half-way and the pre-flash is triggered by the shutter button being depressed fully, thus determining distance from camera to subject. My question is: Does this still occur in the same way if the camera is set up for BBF and, if so, are there circumstances in which BBF cannot be used effectively with Speedlight? Any light that you can shed on this (pun intended) would be most appreciated.

BigBear Loc: Northern CT

BBF has nothing to do with ETTL. ETTL synchronizes the Speeedlite and the camera, and uses through the lens metering to automatically adjusting the amount of flash it think it needs for the proper exposure. The beam it uses is infra red and can't be seen. My 580ex tends to throw too much light for me, so I step it down 2 - 3 stops depending on where I'm shooting.