Years ago I used a Mamiya 28mm lens with a Mamiya AFD body and Phase One P30+ digital back. I used it so much it was almost like it was welded to the body. As much as I used it, it was very much a love hate relationship. I loved the wide angle field of view, likewise the sharp images. I hated the fact that there was no real way of attaching/using any filter. The lack of filters was due mainly to the front element and fixed lens hood; there just wasn’t any way to attach a filter to the lens. I ended up selling the lens shortly after upgrading my system to a technical camera and hadn’t thought much of it since then.
As much as I liked the 28mm focal length (equivalent to 17mm in full frame 35mm terms) I hated the fact that there were no filters for it. Or so I thought. Seems that Phase One partnered with Lee Filters and their SW150 filter system (150mm filters) to make a system that would work on the Phase One 28mm lens. Sit a Mamiya 28mm D lens side-by-side to a Phase One 28mm LS lens and you cannot see any outward difference. They are both the same size.