I've been using my brand new 16-35mm VR lens with D700 for over a week now. A few times I have got two dark corners. They seem to happen only zooming 20mm - 16mm and do not happen all the time. Also the lens seems to have some black dots (only can be seen by facing it against bright sky). They all seem to be inside the lens as I have tried to clean the lens and it doesn't help. attached is one of the pics. Not sure if the lens's got some sort of defects (not sealing well for dust and moisture) as I was in Venice shooting. thanks.