I cannot say this in engraved in stone, but I found out not all extension rigs are equal. Crazy as it may sound they don't all work with the contacts. After much research, I went with, and use KENKO rings on my Nikon lenses. No problems, except last year I thought there was something funny going on with my 80-400 with a ring attached. ?? Hmmmm? I used a micro fiber cloth, of which I keep several on hand, and did a careful wipe down of the contacts bot on the ring, and D 700. Problem, if there was one, solved. I can only relate this to the maybe 'film' you get on your newer car windows, even if you don't smoke-I don't - Has something to do with all the plastic used these days in cars. Who Can say for sure? At any rate, I have had not the hint of a problem since. I got my rings just to cut down the min., focus distance, like from 5 feet to 2. It works.