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You need a Minolta AF to Sony E/NEX adapter. The MD/MC Minolta mount is different from the AF mount, so the AF lenses don't physically fit the MD-NEX adapter. 

If the gh4 is a micro 4/3rds system then it will work. I have quite a few Nikon and Sigma lenses including the 50mm afs and they all fit and work perfectly. You will have to set your aperture and focus manually but the camera will make all the necessary exposure adjustments itself. Don't forget on a 4/3rds system your 50mm will be 100mm based on a full frame. Make sure your camera is a micro 4/3rds and not a 4/3rds, I have both. 

This adapter fits the Panasonic G85 perfectly. If your lens is a Nikon G lens, then you should have no problems. The version of this adapter I have is M43 (Micro 4/3rd) to M42 lens. Hope this helps. 

Yes, it is indeed Nikon f mount.