I've had this lens for over twenty years and used to use it on my Linhof. Trying to work out if it's a W or NW so that I can purchase correct step up ring as I've standardised on 77mm filters. I've read that the NW lenses are labeled N which leads me to believe that it stands for New M.... I'm probably wrong. When I measure the filter thread it appears to be around 54mm. The NWs are 55, I believe. I'm thinking it must be the NW....