I have some questions that probably qualify under dummies....please be merciful: given: going from canon xt to t2i & I shoot raw (lots of no flash, low light situations) 1. How, in shooting, do I prevent myself from having to correct for exposure & black point sliders in post processing? (I told you I was a dummy... Be merciful.) 2. Anything above iso 800 too grainy? 3. How big of a raw file do I need to keep? 10mb?