The long lens tube is made from a male adapter PVC fitting (the centre piece in the photo) glued to a female adapter with spigot end (avoiding the need for an additional length of pipe to connect the two together). To use it, the male adapter end is screwed into the female adapter thread of the 'standard' lens tube.

Here you can also see the tripod mount, which is an Arca-Swiss type plate bolted onto the bottom of the short lens tube.