vinetting is going to be a problem wide open on a full frame... lens profiles help, but to an extent... You are shooting on auto ISO and manual settings... This is where a lot of people are bitching about AUTO ISO and lack of exposure compensation... It could be that the rebel was over exposing, but keep in mind, with auto settings, it is trying to make your shot 18% gray, middle tone gray. So for the most part, that's what it's doing... making it somewhat muddy, consistently. What I would do since you cannot exposure correct on the fly in manual with auto iso, and you have a shutter requirement, shoot in shutter priority... this will open up exposure compensation with auto ISO, it will allow you to set it at +1 or whatever tickles your fancy, and set your shutter speed and away you go... Also if you learn your exposure really good, since your indoors and light will be consistant... play around with what the appropriate ISO is. Once you got that nailed, you really don't need to change your settings, ever, unless you find something off. As long as the lighting doesn't change, your settings dont need to change... So pregame, find your exposure and away you go. Hope this helps.