This item is a Hasselblad 41025 Focusing Screen Adapter. This replaces the film back on an SWC / Superwide and enables you to focus accurately on the ground glass and compose accurately, unlike using the SWC viewfinder which can be a bit hit and miss, especially close up. So it allows you to turn your SWC into a mini view camera. Also great for using grad filters and being able to position them accurately. It will also allow you to fit a prism or WLF to this for easier viewing. It can also be used on any normal Hasselblad 500/2000 series camera in order to check focus at the film plane if your mirror or focussing screen is out of alignment. I used this on my SWC, but I no longer own that camera so this is surplus to requirements.