When I went from my old Nikon N8008 to a D90 I seem to remember something about D90 changing lens "length". I am interested in using my old Tokina 80-200 2.8 vs Nikon 18-200 DX (3.5-5.6) for the speed but when I compare photos I see more magnification with the 80-200. Can someone explain? And am I running any risk when using the old lens on the D90?