Phot r 77mm adapter ring is specifically designed to allow the cokin filter holder to attach to lenses with a 77mm filter thread the adapter ring thread allows you to use a minimum number of step up rings otherwise the holder will be pushed away from the lens and vignetting is possible made to fit 77mm lenses and cokin p series filter holder compatible with most camera lenses includingcanon nikon pentax olympus the adapter ring thread allows you to use a minimum number of step up rin