Does anyone else have this problem? Intermittently the mirror on my D800 does not go back properly. This means when you look through the viewfinder it is darker at the top of the frame and the image is blurred. After taking several pictures the mirror returns, however it then messes up again, this time when looking through the viewfinder the focus is really strange like using a shift lens. The camera has been sent back to Nikon twice, first time they could not find anything wrong and the second time they blamed it on the batteries. The problem is now occuring on every job I do and I can't rely on the camera. Has anyone else had this problem and do you know what to try?