Specifications: Size:2 Focal length:20mm Afvo:80 degree ultra wide angle 7 elements/4 groups Superior optics Ultra wide angle 80 degrees, high quality fully multicoated glass. Super sharp, high contrast & excellent aberration correction, extremely high resolution. Fold-down rubber eyecups, filter threads, blackened lens edges, anti-reflection threads for maximum contrast, upper barrels are black anodized aluminum with a rubber grip ring.