Initially, Mamiya-Sekor Z-series lenses were produced with an aperture ring with full stops only. Later, Mamiya modified these lenses by adding half stops, after which the lens names were supplemented with the letter "W". Optically, Non-W and W lenses were the same. The newer Mamiya APO-Sekor series and Mamiya M-series lenses had half stops from the very beginning of their production.