While on the road, I was called at the last minute by one of my bosses to do an engagement dinner last night. Long story but I only had a 50D + a nifty 50/1.8 coming from a museum and didn't have time to drive 50 miles to get any gear.
Suffice it to say, photons were pretty scarce. There's nothing worse then shooting a bunch of untanned white people in the dead of winter surrounded by orange-beige colored walls under 5 watt bulbs. 
I'm sifting through photos now. 3200 ISO is unusable even after noise ninja. 1000-1600 is pretty bad to because I was underexposed most of the time even at f/1.8 and some ungodly slow SS.
I had a 580ex with me and those are keepers but you can only disrupt people so many times in a small room. After 100+ shots I can probably salvage 35 or so which is fine.
My question is... how much of a difference would a FF camera have made? (Even something like the 5D classic)


