First time for everything. I've sent a lens back for calibration, my new Sigma 50 mm f/1.4. I escaped that monster with my Sigma 30 mm f/1.4. It's been spot-on since day one. I had hoped to have the same luck with the 50 mm lens, but no such luck. You can click on my name and see sample shots in another thread if you want.
I'm really hoping the 50 is spot on after this calibration. However, if it's not, I'll send it back again. I've decided I'm not accepting anything other than a perfectly focusing lens. If becomes as good as my 30, which I love, I'll be happy. I'll send it back however many times it takes.
There's one thing I'm wondering about. If Sigma can't get a lens calibrated spot-on, do they replace it with another one? That's what a lot of warranty companies do. If they can't fix a device, they replace it. If I end up sending this lens back a bunch of times, I would hope they would get me another one, check its calibration, and just send it to me.
I really hope Sigma handles their quality control issues. They make some excellent lenses. I could not be happier with my 30 mm f/1.4. I would think it would be less costly for Sigma to get the calibration right to begin with than to have to take a bunch of lenses back and then recalibrate them.
If my 50 mm Sigma ends up as good as my 30, it's a slam dunk that I'm keeping it and getting rid of my Canon 50 mm f/1.4. However, straight out of the box, the Canon one wins by a mile.