The 52mm drop in gelatine filter holder allows you to fit various gels on your canon telephoto lenses that accepts 52mm filters in their standard holder for example uv skylight gels etc it is compatible with the canon ef 500mm f4l is usm canon ef 400mm f4 do is usm canon ef 300mm f28l is usm canon ef 400mm f28l is usm canon ef 600mm f4l is usm