I just bought my D30 and should have it by thursday. Obviously, I now need a tele lens. I'm seriously considering a used 80-200 2.8L + kenko convertor. My other options are 70-200 sigma and 100-300 sigma. Or the canon 70-200 f4L. My questions are I'm interested in more than just aviation photography(although that is the main part), will I need the extra F stop. Is there any danger in buying an older lens? Thanks a lot everyone in advance.