Originally Posted by Bambam Ilusorio
I don't calibrate lenses... I can only help you check if the lens that you are planning to get has front focus or back focus problems.
It is true that Sigma lenses has this issue.. I am not sure about the lack of a good QA.. I guess they don't.. Coz if they did, we wouldn't be talking about this here right? That's why I strongly urge you to test the lens thoroughly before you leave the store.. I posted in one my earlier replies how to test it using a measuring tape.
With regards to the 50-150, I must say it is a very practical, decent, lightweight, fast (HSM), and best value for the buck lowlight telephoto lens. I used to have one and I am very happy with how it performed. Until I went for an all Nikon setup, this was my money lens for telephoto shots for lowlight shooting.
So whichever way you plan to go, be it the 50-150 or 70-200 lenses of Sigma, just make sure you test the lens for the FF and BF issues. And if you do get a good copy, I'm sure you won't regret it.