The M1 filter holder from NiSi is designed to allow lenses with a relatively small lens diameter to mount 70mm photo filters (2mm thick). The M1, like all NiSi filter holders, is made of aviation-grade aluminum and given a matte black finish. The opening is wide enough to prevent vignetting in virtually all compatible lenses, and the holder comes with an adapter for 58mm lenses. Other adapters, including those for 37, 39, 40.5, 43, 46, 49, 52, and 55mm lenses, are available seperately.
The M1 comes with a round, rotatable circular polarizer. This filter is geared on the outside, and can be turned without direct contact via geared wheels on the outside of the filter holder. Three more rectangular photo filters (70mm wide) can be mounted on the front of the holder by simply sliding them in.