hi, thanks for the reply! i weirdly didn't get an email notification like i usually do, but nvm I actually have 70-200 2.8 and used it on the same shoot, it was tack sharp which made me question the sigma even more. Unfortunately i don't get to use it as often, my kids don't like to be so far away from me lol. I will be having a look at that firmware upgrade just incase, and calibrate it to the camera properly to cover all the basis. I'm very happy with my d750 so i think i can live without all the d810 megapixels, especially since i don't do landscapes at all, like ever