Well, I can say I know where you're coming from. If I'm not mistaken, the 220EX flash doesn't have a directional head on it, therefore most of the flash pictures look flat. For shooting in low light, the only way to do it is buy a fast lens. The "nifty fifty" as they call it is the cheapest and is pretty fast at f1.8. Your Sigma EX 50-500 f1.4-6.3 aught to be a good lens for this as long as you keep it at 50mm. I would say to consider investing in at least a 420EX flash. By being able to bounce the flash, you can acheive some amazing results. Otherwise you've got to invest some big money in expensive lenses that have a low aperture value. A good flash comes out cheaper. Anywho, that is a good picture of your child, just under exposed. I hope this helps. . .