We created the Neutral Density Film Pack Filter to enable Polaroid SX-70 shooters to use any Impossible 600 type film in their SX-70 cameras. These reusable ND filters are easy to attach and detach. All you need to do is insert the filter on top of an Impossible 600 type film cartridge - it adjusts 600 type films to around 100 ASA, so they can be used with an SX-70 camera. No changes are required for the camera itself. Each pack contains 2 reusable ND filters.