Step updown rings are a reliable and economical way to use filters for example a 49 52mm step up ring would allow you to use 52 mm filters on lenses with a 49 mm front filter thread size note step down rings allow smaller sized filters to be used on lenses with larger front filter thread sizes for example a 52 49 mm step down ring would allow a 49mm filter to be used on a lens with a front filter thread size of 52mm care must be taken using step down rings in order to avoid vignettin