The lens is rented permanently from one of my friends in Tokyo. It is quite likely Cosina made with only mono-coating,
it doesn't have the shaved rear element of M42 version, which may not have a true F1.2 speed due to this shaved glass.
317g, filter size = ∅55mm, MFD = 0.5m ... There is MFD = 0.4m version there, it is most likely Tomioka made one if so.