Hope you guys out there can help me with this. I just purchase a used Canon 20-35 f2.8L http://www.canon.com/camera-museum/camera/lens/ef/data/ef_20~35_28l.html). By the way, I'm using 350D.
The picture I took with f2.8 is soft but it's sharp on f5.6. I even notice the focus range (the lens indicator) will be different when I focus on a stll object with a tripot. It will go from 0.5m to 0.6m. Is the lens having problem and can I send to Canon for calibration?