Well, I've got myself into a small problem..... I received an "el cheapo" set of extension rings last week, and decided to use them on my Nikon D80 this afternoon. Just tried to remove them, and find that I am unable to seperate the lens from the "adapter". I removed the "grub screw", but no matter how much I twist or turn, the adapter will not separate from the back of the lens.... Any suggestions????? Anyone else had this problem previously???? Thank you for any assistance provided.