OK, I'm going to go out on a limb here since I'm not an infrared shooter, but I thought that shooters of infrared used a deep red filter with the film, and I'm sure that any filter used by a 35mm shooter for infrared would be available in the 58mm normal 645 Mamiya lens size. Search a few threads on infrared > filters and you'll get your answer. Btw, isn't infrared in 120 size extremely limited? I looked into this about a year ago or so, and there was one guy I remember rolling the film and charging kind of hefty prices for it. Are you looking to simulate it with a filter? If so, I believe I read a thread somewhere about this, but can't give you any more information; You'll have to do a search. You might also have to go down the digital road for the 120 film size, but then I am unaware of the availabilities.