The kirk lp 59n quick release lens plate fits canons 300mm f28 is ii usm and 400mm f4 do is ii usm lenses replacing the existing foot it provides a secure quick release capability with arca style release systems including kirk arca swiss acra tech and wimberley this replacement foot was designed with a longer dove tail in the rear to allow for perfect balance this is the only replacement foot that will allow enough foraft movement for proper balance on all styles of tripod heads