"i" Backs - Next generation: ISO dial on back, 6400 max. setting, 2 stop exposure compensation. Film back exchanges are not possible without inserting a dark slide which cannot be removed from a detached film back. - + Ai 120/220: 6x6cm format, 12 exp/120 roll, 24 exp/220 roll. - ** Film Inserts (120 and 220, 6x6 & 6x4.5 format) and 6x6 & 6x4.5 Film Back Shells (no insert or darkslide included) are available separately.