I shoot mainly field sports (lacrosse, football) and ice hockey. I have the 300f2.8 which is superb, and have a Sigma 70-200f2.8 zoom which is pretty good. I was looking for some better low-light capability and sometimes the 300mm is just too long, especially for the indoor lacrosse game and hockey.
I'd seen a lot of good reviews about this lens so took a shot. Out of the box everything was just plain bad - significant back-focusing (not related to the 40D body since the 300mm and Sigma were just fine), poor color rendition, etc...
I took lots of comparison shots and this lens could not compare even with the Sigma zoom at equivalent aperature and focal lengths.
The lens has now been back and forth to the service center 2 times (first time it came back with no improvement) and now the focus appears to be fixed but even when focused, still don't see close to the same sharpness of the 300.
Overall I'm disappointed - maybe the big 300 lens sets the bar too high, but my copy of this lens is perhaps equivalent to the Sigma in terms of sharpness and color, only with less flexibility and a much higher price - it will probably end up for sale. I am considering the 200f2 but am choking over the price tag