Actually a Sony lens, but the KM equivalent, exactly the same except for aesthetics. The STF (Smooth Transition Focus) lens is a pretty unique lens. It basically uses two apertures one for DOF the other for out of focus effects. The T 4.5 Aperture denotes a light transmission rating, the actual aperture is 2.8 for DOF. Basically this lens is the king of defocused effects (or bokeh in japanese), smoothness unlike any other.