Use the Metabones SPeedbooster Ultra with aperture ring for Nikon G and the Zhongyi M42 Lens turbo II. Have most of the fast old nikkor primes and a lot of great M42 lenses. The Zhongyi surprised me in good way. It rockks with the Helios 58/2, Fujinon 100mm f2.8 EBC and the Carl Zeiss 180mm f2.8 Sonnar. The Metabones SPeedbooster Ultra is just a tad sharper. But be carefull with using long telephoto lenses on the Metabones. My 400mm f3.5 Nikkor vignettes like crazy on the Metabones. The Metabones makes some of my old nikkor primes render nicer and sharper than on my Nikon Df: especially the 20/f4 ai, 35/1.4 ais, 55/1.2 pre-Ai, 85/1.4 ais, 105/2.5 ais, 105/1.8 ais, 180/2.8 ais and 200mm Nikkor Q f4