I went out to Bay Area Park to practice with my Canon 100-400 f4.5-5.6 L series IS lens this morning. My friend Tom Beech has one of these. It is truly a great lens. When I first got the lens I was disappointed because I had not found the sweet spot with it and was always shooting ISO 100. My Rebel XT really has very low noise, so I am trying to keep in the mid-f stop ranges. Anyway, this one came out pretty sharp and I can see the improvement in my technique.