I want to use a reversing ring to attach a Nikon 50mm lens to a Nikon 70-300mm lens. Want to attach in such a way that the 70-300 is mounted normally on the D80, then face-to-face attachment of the 70-300mm with the 50mm.

How do I attach a 50mm in reverse manner to a 70-300mm?

What filter thread do I need to attach to both of these, and what are the pros and cons of this type of attachment?