i had the HSM mk II and it was front focusing a lot on 50D (i ended with a +16 mfa) and almost perfect on 450D...so the fault is Sigma or Canon? And i have at lest one more person that got the same results... weird; then some months after i got the OS version of the lens , beacuse of a good offer from amazon in eu, and the focus was quite good on both cameras (just a +3 to achieve the maximum sharpness). And dont think sigma did a lot of 70-200 because as far i remember there are four lenses so far
1) 70-200 APO
2) 70-200 HSM
3) 70-200 HSM II (it's not a redesign, it's a rework to make the lens cheaper, so smae perfromance)
4) 70-200 HSM OS (total redesign)
canon did 3.
know peoples that had to exchange the Canon 35L 1.4 twice before they got a good sample and for what i know, canon doesnt offer free calibration for their lenses, at least here in italy, but maybe i am wrong, because i own just a canon lens (a shitty 17-85... +5 for the record); i am not sure it's completly a sigma QC fault the AF problems, because with nikon the problems are not so pronunced as with canon. i think the accuracy of focues with canon camera is more firmware dependant than other brands, but with the new dock, i guess a lot of problems will go away
A +5/-5 micro adjust is quite minor and easily within a lens / lens mount manufacturing tollerences. But a +15/-15 is pretty obviously a lens issue. Especially if it's the same across multiple cameras. I'm currently running a pair of 5DIII's and a 5DII and I had to micro adjust every lens on every camera. None of my lenses were more than +5/-5 adjustment across all three cams. One of cams consistently needs more - adjustment than my other two.
Sigma seem to pop out a new 70-200 fairly regularly:
70-200 f2.8 APO
70-200 f2.8 EX HSM
70-200 f2.8 EX DG HSM (new shell and coatings)
70-200 f2.8 EX DG MACRO
70-200 f2.8 EX DG MACRO II
70-200 f2.8 OS
I dare say the new OS version is about to be re-designed in their new Sport livery and new outer casing.
It's tricky to compare with Canon, because their IS and non IS versions are not replacements but are options.
ef 70-200 f2.8 L, there has only been one.
ef 70-200 f2.8 L IS was a very old lens, the very first 70-200 with IS and predates digital SLR's. This lens was only recently upadated with the 70-200 f2.8 L IS II.
So if you compare Canon non IS, there's only been one lens and if you compare IS lenses...there has only been two.
I'm not saying that Canon don't have QC issues, but in my experiance they are a lot less common and far less sevear than Sigma's QC issues. My Sigma issues were very bad and quite frequent.
Here in the UK, if a Canon lens is out of spec it can be sent in for calibration under warrenty. I belive this is a Europe wide policy. but they will charge if the lens is within expected tollerences. I've only had one lens which has needed this...unfortunatly a lot of people don't think to send it in under the manufacturers warrenty.