This 'problem' has bugged me for a while now. There is no clear instruction (or none I found) in the Canon EOS 500D's user manual or manufacturer website on how to turn off the pre-flash.
What is the pre-flash for? The pre-flash helps the camera calculate the flash strenght needed for the shot. It also helps reduce red eye.
The problem is, people mistake it for the actual flash fire and they start to move. Worse, it drains your battery life faster too.
For a while now, I have been searching online to find out how to turn off the pre-flash. Now, thanks to rickjbradbury, I finally know how to do it.
I asked him via his YouTube channel. And he was so nice to respond. He is a really good photographer and I think he should get logo design ideas for his website header.
And you can find those commands here:
Certainly there is a trade-off on image quality if the pre-flash wont fire. But hey, it's your choice. Happy shooting. :)
Related: Here is another camera flash tip.
Update: I jsut recetly tried shooting in the evening with the preflash turned off and it is very hard to auto focus if there is little ambient light. (gabi nga e, so malamang madilim talaga) You'll need to rely on your "manual focusing skillz" if you want the pre flash turned off.