From the Manufacturer:
The longest lens in the NIKKOR lineup, delivering 800mm of exceptional full-frame super-telephoto power (1000mm with the included 1.25x teleconverter) and the latest advancements in optical design and lens technology. Suprisingly compact and lightweight with a magnesium-alloy barrel and dust- and moisture-resistant construction, this is the definitive long-reach lens for sports, news and wildlife photographers.
As the longest lens in the NIKKOR lineup, the AF-S NIKKOR 800mm f/5.6E FL ED VR delivers an astounding 800mm (1200mm equivalent on DX-format cameras) of super-telephoto reach with a fast f/5.6 maximum aperture in a rugged, well-balanced design. But for even greater reach, the lens includes a matched 1.25x teleconverter (TC 800-1.25E). This high-performance 1.25x teleconverter has an Extra-low Dispersion (ED) glass element for superior sharpness and color correction, and it increases the lens' overall focal length to 1000mm (1500mm equivalent on DX-format cameras).
The AF-S NIKKOR 800mm f/5.6E FL ED VR is a marvel of NIKKOR optical design. The lens is comprised of 20 elements split into 13 lens groups. The front and second elements are fluorite (a lightweight mono-crystal optical material), which provides superior optical characteristics and reduced weight for balanced handling. Two Extra-low Dispersion (ED) glass elements provide superior sharpness and color correction by minimizing chromatic aberration, and Nano Crystal Coat (N) reduces ghosting and lens flare throughout the visible spectrum.
The AF-S NIKKOR 800mm f/5.6E FL ED VR is an advanced lens for advanced D-SLRs. Autofocus is powered by Nikon's exclusive Silent Wave Motor (SWM), which uses ultrasonic vibrations—instead of a gear system—for ultra-fast, ultra-quiet, ultra-precise focusing. It also allows you to seamlessly override the AF system with no time lag. Nikon's second generation Vibration Reduction enables handheld shooting at up to 4 shutter speeds slower than would otherwise be possible (Based on CIPA Standard)—a huge advantage when the lighting is less than ideal. And for maintaining consistent exposures during high-speed continuous shooting, the lens uses a highly precise 9-blade electromagnetic diaphragm that produces outstanding bokeh under the shallow depth-of-field necessary for separating subjects from the background during peak action photography.