Some years ago I bought a mystery Nikkor from Akira. No specifications were found on the lens, but after some research I consider this to be one of the technical lenses used by the Nikon repair techs to test for infinity focus in a collimator. The lens is set in a solid metal casing and has no aperture control or focusing helicoid. It does indeed focus precisely to infinity on my Df.
Enter the Z generation of Nikons and by adding a focusing helicoid to the lens, it can focus to 1:1 if required. The design is clearly intended for infinity focus so image quality starts to suffer in the closer range, as expected. I can also coax it into being operative on my IR cameras, an example of which is presented below.
