I have just replaced my D800 with the D850. am setting the menus up etc, and for the life of me I cannot get the focus shift to select. It is continually greyed out. When I try to select it says "this option is not available at the current settings or the camera state". I am used to focus stacking, I have it on my Olympus, so am familiar. So what is preventin me from selecting this option on the D850. I have an AF-s lens, I have full battery,i have made slight changes from default, mainly back button focus, so what am I doing wrong?, incidentally I have the same response on the HDR setting ( not that I will use this)