The Visual Echoes FX6 Better Beamer Flash Extender
will help increase the reach of your Nikon SB-900 flash and increase the output by about 2 to 3 f/stops. The Better Beamer is designed to be used with lenses 300mm and longer.
Included in this kit is the LensCoat FlashKeeper and BeamerKeeper. These neoprene pouches will protect your flash and BeamKeeper during travel.