I have an Ixus 500 and my dad has an Ixus 700 (different names in the US I know, but they are compact digital cameras).

Last night I tried using an external flash to improve on indoor shots to try to get less 'harsh' photos and less red-eye. The flash has a sensor on it that detects the cameras flash and then it fires but the results were strange.

What resulted was an image that looked like no flash was used at all. Why would this be? Is the camera getting confused? I tried different angles and positioned the flash infront and behind the camera but still the problem is there. Theres nothing in the manual about it either.

Canon do sell an external flash for these cameras so I don't see why what I'm doing doesn't work. Does the Canon one perhaps plug into the camera?

Any help would be appreciated!