I just got a 550EX for my EOS 3 for no good reason besides the EOS 3 not having a pop-up flash. I quickly realized that I have no idea as to what I can do with it besides turn it on and put it in auto. So I'd appreciate suggestions as to any books, web sites, etc to educate myself on the different uses of a flash. I have the manual and have looked it over and I'd like to know more.