I want a flash and I probably wont get one for a few months, (cant afford yet), but I want to start doing my homework. I have some questions that I cant really find anymore... For ex: What is the red thing on the front of all flashes, EXCEPT the Speedlite 270EX??? Speedlite 580EX II vs Speedlite 430EX II What are the major differences? Is there some site that kinda of compares each flash? How do I know what flash is for me?