AF 600mm F/4 (APO G) – A large aperture, extreme-telephoto lens with an internal focusing design for outstanding telephoto effects.  This lens uses AD (Anomalous-Dispersion) glass to reduce chromatic aberration to a level that places it in the distinguished “apochromat” class.  A focus-hold button is conveniently located on the side of the lens carrel, and adjusting the focusing range is made possible by using the focusing range ring.