Hi: I recently got a D2Xs and while I was testing it I noticed that the viewfinder's "clarity" changes. I was using it with a 17-55 and the image was crystal clear on the VF, then I tried it with a 200-400VR and the image looks kind of grainy. it seems to be limited to this lens. So being a rookie with this camera, is this normal behavior??? Thanks for any input you can give me!!!