>>3578666That lens is a single element, vintage glass wide open at about f/2. The main thing is to have the lens wide open so all of the lens space is being used and all the lens aberrations affect the entire image. Adjust the exposure times as needed, so not necessarily +1. After that, it will be up to the lens itself as to how effective it will be in giving you that blur. ISO/ASA also plays a roll, but with digital you get less than stellar results with it.
Hamilton used a Rokkor 50 f/1.7 lens wide open after all. Proper lighting and developing play a huge role. No filters needed.