The Nikon BR-2 lens reversal ring fits between the lens and the camera body. It allows the lens to be used in a backwards or reversed position. I use it to reverse a 28mm lens so I can taking photos with a reproduction ratio up to 8:1 compared to a reproduction ratio of 1:12 when used in its normal position.
Nikon BR-3 Ring can be used on the reversed lens to allow filters or lens hood to attached to the back end of the lens.
Nikon Macro Set Up by
Narsuitus, on Flickr