There's also the issue with flange distance – it's impossible to achieve infinity focus on a EF lens on Nikon body without optics in the adapter. The other way round is fine.The Nikkor F mount is very much smaller than the EF mount, so receiving a L lens on a Nikon body is actually deemed to be impossible. It may be a one-off custom converter that you saw, or you eyes may have tricked you. :bsmilie: