Thank you all! The soft focus was done by using the adjustable diffusion ring on the front of the lens. Around half the old Velostigmat Series II lenses have that feature. The real trick is to disassemble the front part of the lens and remove the restraining screw that keeps it in a very conservative (as in "I can't tell the difference") range of soft focus. After you unscrew it past four or five rotations (this one was nine) it starts to come out of its shell...