Prototype 1 of the filter cartridge is nearing completion. Here you can see its place just above the tertiary mirror and below the focuser. It will slide quickly into and out of the tertiary housing.
The triangular tab seen in the bottom corner will be textured for two reasons. One is for better grip. The other is that different pairs of cartridges will have distinct texture patterns, enabling the user to distinguish them in the dark by feel. Broadband filters can be assigned to one pattern, narrowband to another, OIII to a third pattern, etc.