JJC FX-N910 Flash Multiplier Extender for Nikon SB-900 SB-910,300mm+ Telephoto Lens Use Allows you to shoot at greater distances Excellent for photography on wildlife, birding, wedding, evening party, portraits and more Allows you to shoot at greater distances and shoot with smaller apertures The unit helps increase the flash output by about 2 to 4 f/stops or more Increases the flash output by about 2 to 3 f/stops