#1. "RE: question about extension tubes" In response to In response to 0 Sat 22-Dec-12 11:12 PM by Leonard62
Hi Darlene, I think you're going to have to figure this out by the process of elimination. The first thing I would do is to remove the tubes from your D90 body. Then one by one add the tubes to the lens and see if the focus ring turns freely while it's off the body. You should be able to see if one of the tubes is binding. If everything turns freely off the body then attach the tubes and lens to the D90 and see if it focuses. Make sure the little AF/MF switch is turned to MF.
I have the Kenko tubes and a D80 which should be close enough. But I don't have your lens. My AF 105mm f2.8 lens manually focuses just fine when the lens is set to MF. It turns quite freely with all the tubes attached and mounted on the body. In my case I don't have to set the body switch to MF but you may have to.
edit: I forgot to ask. Is your lens HSM or screw drive? I assumed it was screw drive.