I'm guessing there would be some image quality loss with the built in lens adapter. That would also drive the cost up for what is essentially something I'm playing around with.That's really an old thread :smile:
Oddly enough, meanwhile, there are adapters for almost everything.
I have now plenty of them, including those which I searched for when I started this thread.
The reason for loosing infinity focus is that Nikon has a larger registry distance than virtually all other camera brands. I mostly use these adapters to adapt lenses for macro use. Recently, I even managed to find solutions to reverse-mount an EL-Nikkor 75/4 on my D3 and on a Novoflex bellows, respectively. The EL-Nikkor has a 40.5mm filter thread, so I needed altogether two adapters, one step-down ring and the BR-2a to be able to use it on both combinations.
There are special adapters with an additional lens built in that allow you to gain infinity focus but I have never tried those and thus do not know if it has some adverse effect on image quality.