I wanted to mount a uv filter on the X100 trying to keep out some dust of the lens/body. Not having a 49 mm one around, but with a case ful of old Nikon AIS stuff I opted for a 49 to 52 adapter ring and 52 mm filter. Can't mount the little silver lenshood anymore - but adapter ring and filter should work as a hood as well - but hey add an old Nikon 52 mm lens cap (which actualy stays on without threatening to fall off any moment) and a modern day Nikon S rangefinder is born ;-)
Fuji_Nikon by Lieven Loots, on Flickr