The defect could not be more obvious than this one:!:
RegardingTony's experience and judging fromanother copy they sent me as replacement, this is a wide spread issueabout Sigma!
As you can read in my next post above: ''Testing the Sigma 17-70; The rest of the story!'' I sent back the lens to the general distributor of Sigma in my country, skipping the dealer I bought from to prevent further loss of time! It took onlya few telephone conversations with the product development manager there who had really a professional mind, plus a few example shotsto hise-mail!
I believe your perfect sigma is awaiting you; )