I have a number of Hoya filters. They are square and slot into a carrier which in turn clicks on to an adapter (step down) ring. This ring is a 55mm thread for my old film SLR. My digital camera takes 58mm. The equivalent rings for Cokin filters don't fit the filter carrier and Hoya no longer trade.:( Does anyone know where I might be able to get hold of a second hand Hoya 58mm adapter?