Athabasca AF Square Holder for 150mm Glass FiltersThis glass filter holder is designed to mount onto the lens adapter **.This holder accept 2mm thick Square/ Rectangular filters 150x150mm or 150x170mm.It can mount up to 3x glass filters.Note : **To use this item it is recommended to purchase the Athabasca AF Adapter Ring and you will need the exact model/ size lens to be compatible.e.g. Optional to buy Tamron 15-30mm Lens adapter ring