I am looking for ND filters for my SK35 & SK90. I read Vieri's excellent reviews on filter systems and holders. But then I realized that both the SK 35 and SK 90 have rather small filter threads - 52 mm for the SK35 and 40.5 mm for the SK90. Guess, a 100 mm filter system would be somewhat an overkill. Any suggestions/recommendations for other options?