Chris, measure the outside of the front lens barrel with a ruler (to the nearest 1/16 inch or to the nearest mm). On ebay there are sellers of series adapters. Buy that size adapter. It will either be Series VI or VII... IDK for sure. It should be rather obvious, though, which is available. Make sure you get eitehr a retaining ring or a lens hood -- one or the other is necessary to hold the filters in place. Then look for filters in that size. If you have a choice, Series VI filters seem more easlily available than VII filters.