I own a BR-2 lens reversing ring. While getting my F4s serviced at NIKON in Torrance, CA I asked what the difference was between a BR-2 and a BR-2A ring. I person returned five minutes later and said none of the technicians knew of a difference between the two(!) I figured they must not have looked at them side by side so I bought a BR-2A ring from B&H and when it arrived I compared the two. Nearly identical. I found two minor differences of no real consequence, and I mean minor! I emailed NIKON through their website and received a reply that said "the BR-2A is for auto focus bodies and the BR-2 is for manual focus bodies. Do not use the older ring on an AF body as damage to the contacts may result." The owner's manuals for my F4s and F100 say to use the newer ring. However, I have been using the BR-2 on my F4s for a while now. It clears the electrical contacts just fine. When I emailed them back and notified them of this here's what they said: "We have found that you already visited Nikon in Torrance and the technicians could not provide information of the differences of the two rings. Therefore, I do not have the information either. However, we still advise to use only the BR-2A ring for autofocus cameras as the instruction manual indicates. The BR-2 is not recommended. The factory would not have replaced the BR-2 with the BR-2A if there was no compatibility issue. If we obtain more information on this issue we will let you know." I know this isn't an earthshaking issue but if someone can answer this question then maybe NIKON should be notified too.