Here I have the Nikon G to Micro 4/3rds helicoid; I also own the Nikon G to NEX helicoid. These allow for direct mounting of Nikon lenses to Micro 4/3rds and NEX; other helicoids require at least another adapter in order to mount Nikon lenses to a mirror less camera. I gather Fotodiox also make a Nikon to mirror less camera helicoid adapter, and I have made enquiries regarding their Nikon-Micro 4/rds helicoid adapter.
Cost: under £30 (from UK)
It extends by 11.18mm in total.
This helicoid has a little arm which extends inside the adapter for manual adjustment of the aperture of Nikon G lenses. In order to use with my Coastal Optics 60mm F4 APO lens which is in Nikon F-mount, I have had to remove this arm and replace it with another screw. I have also epoxied the upper ring of this helicoid which moves for adjustment of the aperture of Nikon G lenses (which I don’t require). There is a little play in this adapter; I am wondering if the Fotodiox version being a Pro adapter will have ‘No play’?
This helicoid has now replaced my previous setup for mounting the Coastal Optics 60mm F4 APO on my Olympus EM-5. The reason for this is that now that I have my new focusing system D|focus v4 focuser, this will reduce the size of my setup and make it easier to shoot subjects which are a little further away, although not quite to infinity (as I have not replaced the ICF in my Olympus E-M5). It is by no means perfect, but it is the best solution I have at the moment.