I'm using a Nikon D800E with my 24-70 f/2.8 lens. The problem happens in low-light situations using a YN-685N and YN-622N-TX. I shoot at f/5.6 and pics aren't that sharp, but when I use my SB-910 it's all good even on f/2.8. The situation is a little better at f/8 but it's too much for me. I am using YN's AF-assist red grid and I always get focus confirmation. Anyone had a similar issue?