Nikon SB-900 Speedlight
The Nikon SB-900 Speedlight is Nikon's flagship flash unit, and the most advanced in the Speedlight range. As a replacement to the SB-800, the SB-900 shares many of the same functions, but also has some innovative additions and improvements. Its automated zoom head has been expanded to cover 17mm to 200mm lenses (in 35mm/FX format), and can cover this range in just 1.2 seconds. This flash now lets you select from three light distribution patterns: Standard, Center-weighted, and Even. It will also automatically detect if it is connected to a DX or FX format camera, and adjust itself accordingly.
The SB-900 can work as a stand-alone flash, or as part of a wireless group, either in Commander mode or as a slave (remote). The i-TTL system in this flash supports Advanced Wireless Lighting and versatile functions for up to four groups of Speedlights, with 3 remote i-TTL Speedlight groups controlled through the master SB-900. i-TTL Balanced Fill-Flash flash control employs Nikon's Advanced Data Communication system. This system provides an improved method for the monitor pre-flash and wireless operation that marks an evolution in higher precision over Nikon's acclaimed D-TTL Balanced Fill-Flash control system, and forms the core of the Creative Lighting System.
For detailed technical information, please visit the manufacturer site here.