I was reading your post on using extension tubes for Nikon D5100.
I own the same camera and bought it couple of months back. I just got Vello extension tubes from B&H. They recommended to get this one.
I tried using the extension tubes. However, the camera says 'Lens Not Attached' when I am using extension tube. Have you (or other forum members) faced this problem before? Can you provide some insight in to this?