The Vivitar 500 mm DX is a manual focus ultra-telephoto lens which, due to its mirror design, is extremely compact and lightweight for its focal length. The design of the Vivitar DX lens incorporates the merits of both reflex optics and refraction optics. This combination allows the Vivitar DX lens to offer users an extremely sharp picture with minimum color aberration. This lens is useable on small frame digital SLR cameras as well as 35 mm film cameras that use a T adaptor. The drawback to this Vivitar 500 mm is that only one fixed aperture is possible, and it is useable only in manual focus and manual exposure modes. This Vivitar DX lens is designed for high definition telephoto photography, which offers the capability of shooting crisp, clear pictures. Weighing 1.4 lbs, this ultra-telephoto lens is ideally suited for outdoor photography. It has a fixed aperture of f/6.3.