Hi everyone, I have both a Nikon D80 and a D700 and am considering updating the former with a D7100. I see all kinds of posts on other forums relating to the D7100 and other cameras regarding "auto-focus fine tune." Admittedly I've never used it on my D700 and I don't think I have focus issue problems. Quite simply, what is auto-focus fine tune and how necessary is it to use on the newer Nikon cameras? I really don't want to get involved in shooting wall targets for several hours for each and every lens I have. Thanks for your comments.