Recently I photographed a teen party with my Canon 50D. I would really like some input about how to do this kind of low-light job right. Here are some of the problems I encountered: Starting out with reasonable light, I used Sigma 50mm 1.4, high ISO and no flash to keep the mood. Autofocus was quite unreliable though. When light levels dropped further, autofocus stopped working, especially the Sigma lens AF was completely useless. Isn't there supposed to be some red AF assist light in these situations? Did manual focus for a while, and then light dropped to very low. Pulled out the 540EX flash, and the 17-85 IS. Was unable to do indirect light with the flash, since the roof was like 8 meters up. So, pointing the flash straight forward, and dialed in -1 in flash level compensation, to try to keep it down, and also -1 in exposure compensation to not aim for "normal" light level in the pictures. The flash refused to do ETTL, simply stating "TTL" in the display instead, and it did not reflect the correct zoom distance of the lens, nor the compensation levels. Insisting on firing the full load everytime, exposure was way off. Normally ETTL serves me well, I often use both one and two flashguns and the ST-E2 master. What happened to my 540EX here? And still AF did not work at all. In the end I stopped using the 540EX, and used the built-in flash instead. The built-in flash gave me pre-flash to help the autofocus, and the exposure was now in accordance with my compensation settings. Probably the most usefull pictures of the night, even though I would normally do much to avoid the flash-on-camera pictures. Are the AF and ETTL problems normal? Why would the 540EX not do at least as good a job as the built-in flash? How do you guys normally handle low-light focusing, and how do you get reasonable pictures retaining just a little bit of the mood when doing nightlife pictures? All advice welcome - thanks, Jesper.