Lucky I guess. My 100-400 has been back twice and both times they adjusted it with some improvement. My 24-70 was always a bit soft until I dropped it and sent it to canon. It came back sharper. Honestly I have been frustrated as of late with the sharpness of my Canon stuff. I recently shot some hummers. I used the 5D, 1DsII, and 30D. All were on a tripod with the same settings. I found my 30D to produce the sharpest images and my 1Ds distinctly softer than the other 2 bodies with both the 70-200 and 100-400.
Z, were you on aiservo?
That was my biggest complaint (well 2nd biggest) with my M3. (the first complaint was that it didn't track whites well)




