I've got a 5d mk1 and in the studio using a 50mm 1.8, 85mm 1.8, or my Tokina 24-75 2.8 I get lovely sharp images up to iso 800 but outdoors it's a very different story. Did a shoot yesterday for a family and it was quite overcast so I pumped the iso up to 500 to allow me to use a faster shutter speed as I like people moving around so I can capture natural shots, not fast moving though. I was shocked when I downloaded the images last night to see how grainy they were. Even ones I shot at 200 had grain in them and I am thinking that that can't be right. Is there something wrong with my 5D?