Adapter rings serve to accommodate filters, close-up lenses and other attachments to lenses with differ
-ent filter thread sizes. For example, with a camera outfit that includes lenses with 49 mm and 52 mm filter threads, adapter rings make it possible to use 52 mm filters on both types of lenses. Not only does this save money that can be invested in a greater se
-lection of filter types, it also saves space and weight in the gadget bag. Caution: When a smaller filter is adapted to a lens with a larger filter thread, there is the probability of vignetting!
Find thread pitch for B+W adapter rings here