New to the forum. Joined firstly to share two images and answer the BR2 / 2A difference question definitively, since I can't find an answer anywhere online. I know this is an old topic but thought this might be useful. I've been surprised by people suggesting there's no difference, or that they can't see one. I had my suspicions so I bought a 2A, which arrived today, and compared that with my BR-2, which definitely will not fit my Df. The two rings are very different in whether they clear the internal mechanisms of newer cameras. The bayonet lugs on the 2A have been milled off at 45º to take away the corner that does hit the electrical terminals that connect with AF lenses, and even after removing one of those the ring still doesn't want to go, so there's possibly other stuff going on at the micro level. You might get away with it on some newer cameras but not all of them. Here's the shots - 55mm Macro at f5.6 on a Df to give enough DOF to show the diff. clearly. Look at the top ring. If you have a lathe or know an engineer, it's a simple job to modify a BR-2 to fit anything once you work out where the problem is. I plan to experiment until I crack this one. Hope someone still alive finds this useful - all my glass is ai or ais!