this is a moisture removal plug l have finally got up and running, it goes into the focuser when the scope is not in use and while giving an air tight seal via an O-ring it draws out the moist air trapped inside the scope which can lead to fungal build up.
inside the plug are replaceable Silica Gel sachets.
perfect for all sealed unit scopes like Cassegrains and refractors.
any comments gratefully accepted.
they will only be 2" Andrew, l'm trying to keep the price down to around $75,
some may think it's a bit much, but compared to the price of a good OTA l think it's a good investment in the long term.