the dock lets you make adjustments depending on subject distance and focal range. mine was frontfocusing really bad on the 18mm side at close distances but fine at infinity, on the 35mm side it was ok close but backfocusing at infinity. the dock has 4 distance settings and 4 zoom ranges 18,24,28,and 35 that you can make adjustments. its a lot of trial and error and a lot of lens on and off but it works. the infinity setting was the hardest to get right. try using live view and look at your focus scale, then switch to regular af and refocus, that will give you a starting point to see where it is off