Well I'm new to photography but I really love. My sister and I are doing collages. Where we take pictures of small sections of some thing and then but them together into one big picture. I know that I could just take one picture and have it blown up but this is more fun. My question is that when I take different sections I get different "shades". The last one we did was of a girl in a wedding dress. When I would take pictures where it was half the wedding dress and half the background, the dress is bright white. When I take a picture where the only thing in the shot is part of the dress, the dress isn't as bright. I realize that the camera is evening out the brightness. What do I have to do to get it so the brightness of the dress is always the same?