Since I am usually taking pictures under low light ambient conditions I have discovered the nifty 1.4 lenses (such as the Sigma 30mm/1.4 or the Canon 50mm/1.4 or also the Canon 85mm/1.8) for my Canon 550D. My main problem is not that there's not enough light to capture images, but that the autofocus – usually with one fixed AF point – is rather slow under those conditions, if it can focus at all.
My main subjects are dancers, who are quite naturally moving, so speed is an issue, especially with the narrow DOF the 1.4 or 1.8 aperture gives.
What can I do?