Rare is a constant-aperture ultra wide angle zoom lens. The AT-X 235AF PRO lens uses the latest in lens development technology with two moulded, multicoated aspherical elements. The exclusive "Focus Clutch Mechanism", unique to Tokina, provides manual focus dampening unmatched in autofocus lenses. Like all of Tokina AT-X AF series, the barrel is constructed using all aluminium and a chrome-plated brass mount plate.