Get yourself a 37mm series VI adapter ring. They are plentiful and cheap, as are the series VI filters, either on the auction site, or at one of the numerous camera swap meets around the country. The 37mm end slips on the lens. The opposite end is threaded to accept a retaining ring to hold the filter in place, or a lens hood, which can also hold the filter in place. The threaded end is available in various diameters. You can often rummage around in boxes of odds and ends at the swap meets and find them for a dollar or two. I've outfitted two Bessas and an Ikoflex in this manner. There is quite a selection on the auction site right now, though I can't say if there are any 37mm.