Lately, I have been experiencing an oddity when shooting with my D800. When shooting in manual mode with A/M focus, as I twirl the main command dial to center the exposure point on the scale in the viewfinder, the image will sometimes go black and the readout will show f/0. If I release the shutter then, the resulting photo is black. After firing off 1 or 2 more images the picture comes back in the viewfinder and f-stop readout is normal. But, sometimes I have to turn the camera of and on to clear it. So far, this has only happened with my 70-200mm lens. Any idea what’s going on – this is just a recent occurrence.