The Vivitar 28mm F/2.5 is a wide-angle prime lens with an extremely fast lens speed designed for Nikon AI cameras. Central sharpness and resolution are excellent at f/2.5 and outstanding by f/4. The lens employs anti-reflection coating to increase light transmission, improve color consistency and reduce flare. The lens can even be used on an APS-C sensor as a portrait lens. Its optical construction consist of eight elements in seven groups, six bladed diaphragm, 0.3 meter close focusing distance and 55mm filter thread.