Grex has introduced a new Fan Spray Tip for the Tritium series and XSi / Xgi, airbrushes.  The tips are available for needle sizes, 0.3mm, 0.5mm and 0.7mm.  You simple have to remove the Nozzle Cap and Needle Cap and replace it with the new Fan Spray Cap.  The spray pattern will then be oval in shape.

The Fan Spray Tip is also available  in a conversion kit (Part #TFK-3 to 7), should you need to convert your airbrush to a different size needle.

When using the Fan Spray tip 0.7mm, you will increase the volume of air required to atomize your liquid, and may need a larger compressor.