FWIW, I have a 300 2.8 L that I bought many years ago. Non IS of course. I liked the lens and found it to be very adequate. I was using film for years. I got a digital DSLR and found that I could detect a bit of softness, especially at 2.8. Still a good lens but my 100-400 L was as sharp in the f8 f11 range and much easier to carry around, but when the light was down out came the 300 2.8. Well I got a 7D a few months ago, and it was my first camera with microadjust. So I set it up, and carefully set the adjustment for the 300 and now I have A SUPER LENS in my 300 2.8. Same lens, it just wasn't set quite the same as my cameras were. (too bad I had not sent it in with my camera and got it adjusted years ago. OH Well) It was like buying a new lens when the microfucus of my camera was carefully done. I would suggest the set up should be done at at least 5 or more times the minimum focus distance.