DrSteve:My Oly 5050 gives a flash for focus and then boom does the real thing. That's fine, but the pre-focus flash shows up as a great pic on the LCD and then I moved the camera blurring the actual shot! As someone told me once - shoot until your shutter finger bleeds, and then shoot some more.
Huh, a slight correction here. The preflash that you get is for TTL function ie for the camera to measure the light level so the camera can adjust the flash for proper exposure. There is no photo taken during preflash and you should not see anything on LCD. If I remember correctly (sorry, sold my C5050 quite awhile ago) C5050 has a focus assisting light that is useless underwater as it is blocked by the housing.
And yes, if you move your camera after the preflash, you will definitely get a blurry picture.