Binh, maybe its the diopter...this needs to be adjusted before you shoot for the first time, once its focused your pictures should be in focus especially if your using auto focus mode. I also have a 20D and the lens but a 550ex flash, and sometimes mt problem is that the pictures are not as sharp as could be. I still think my problem is the diopter and my eyes, but I don't wear glasses...go figure.
Canon 20D
in Canon EOS Mount
Posted