I have bought the Sigma 150-500 a few weeks ago and am very zufieden. The picture quality hit me almost from the stool, hardly occur to the optical errors at all. The resolution is also on my 50D well. The only real drawback is the OS because this is relatively slow, at least for my taste, as I was, of course nciht used / am a second to wait until the OS accesses. Well, this may not sound like much now, but it may in birds and other animals quickly become a problem, as these unfortunately rarest wait forever. For efficiency of the OS, I can say that I get at least 1/60 at 500mm best results. I recently had the opportunity to test the lens on the floating stage in Bregenz, (AIDA). Neither focus nor exposure times were a problem. (Not least then the OS because I despite ISO 1600 (Canon EOS 400D) could not be shorter than 1/125 expose mostly)
The AF is absolutely great, focuses fast, quiet and above all very precise.
All in all probably the best lens I own. I can further missing only.
