There may be another explanation. How do you have the focusing mode set? I suggest you put the camera on a tripod keep the camera aimed at a constant subject, then try setting the camera to Single point focus. Then look and see whether the pictures are clear on the exact point of focus.

My experience is that when I get soft pictures it has more to do with exactly how the camera is focusing. If you have the camera on dynamic area focus, 51 focus points and continuous focusing, I have found that I am likely to have a picture NOT focused on what I want it focused on. It is always focused on something, but not necessarily my target. That is why I almost always use single point focus.

Larry Miller, Annapolis, MD
D700/D800
http://www.pbase.com/lmmiller9
http://lmmillerphotography.smugmug.com/