I don't know what filters were used at Snake Valley star camp. Try PM-ing Wombat if he doesn't reply to this thread. I'm sure he would be happy to tell you all about it.
Otherwise try contacting a competent dealer. I found that AOE are very good at explaining things and very patient with persistent questioning. I just looked at their filters page. I think what you might be after are the Neutral Density and/or the Polarising filter.
