The Visual Echos FX4 Better Beamer Flash Extender will help to increase the reach of the flash, and increases the flash output by about 2 to 3 f/stops. It focuses and concentrates the output of the flash into a narrow beam via the fresnel screen that gets positioned in front of the flash. This allows shooting at greater distances and shooting with smaller apertures.
The Better Beamer is designed to be used with lenses 300mm and longer. Its rugged injection-molded plastic side supports are attached to the flash head by a sturdy elastic "hook-and-loop" band. The rigid supports hold the Fresnel screen in place in both horizontal and vertical formats. Just weighs 2.5 oz.
The FX6 version is designed to custom fit the Nikon SB-900 flash, without any need for use of additional "shims".