I saw this posted on another forum and it Parallels something I did not too long ago.



"A few days ago, I will shooting a small party with about 25 guests.


The party was in close quarters and when it came time for a group shot, the DA 16-45 wasn't quite wide enough to get the entire group head on.

So, I dediced to shoot the group at an angle using one flash on camera and one flash off camera.

As I began to shoot, I would preview each shot and they were coming out as if I were using no flash at all and were very dark. I could not figure out what was happening to cause this. Well, for some unkown reason, I decided to repostion both my self and the off camera flash and this did the trick. The photos were coming out nice and bright with good lighting from both flashes.

Later that evening, when I arrive home and started processing the photos, I discovered the problem..

On the wall behind the group was a shall mirror and the off camera flash was coming directly back to the camera which was causing the problem. For simplicity of shooting, I was using picture mode and the camera was adjusting according to the light being received back into the camera.

So, If you're shooting, make sure you don't have a mirror reflecting directly back to the camera.

Obviously, this is a mistake that I will not make again."