Dorr GO System Filter Green. This filter easily fits onto the GO Filter Holder (not supplied) then the holder attaches to the adapter ring (not included) & this fits onto the lens for different effects every time. Up to 3 GO Filters can be attached to the holder at a time. This filter is for creative Black & White photography & allows red colours to get darker & blue to get lighter. It also reinforces haze, reduces contrast & produces diffuse & atmosphere.