I have a Cannon XTI with a 430EX Flash. I recently took photo's at a wedding and most of the pictures came out dark. I thought it might be the flash that was not strong enough to light the people, but I was about 8 feet away. I used the ETTL mode and I made sure it was charged before I took a picture. The camera setting was set to automatic or Program mode and I had no success. What could I be doing wrong?