I have several questions for you guys. I think I am still confused with how to use my flash properly. I have 550 ex. Here are my questions and please correct me if my assumption/understanding is wrong: 1. If I am not mistaken, E-TTL uses a preflash that will calculate how much power the flash needs to light up the subject properly. That means even if I put filter on my lens, or put diffuser on my flash, it will not matter correct? Since it shoots a preflash, I assume it uses more battery power. HOw do I know what kind of power the shot in ETTL mode was taken? If I am shooting on a tripod on a subject that is always the same distance, I want to be able to just change the flash to manual and copy the ETTL so that I dont shoot preflash and use up the battery power. 2. If I set the flash to high synch, how much power does the flash put out? I assume it doesnt do preflash anymore? Thanks for your help guys!