second curtain flash

<p>I am using my oly e510, with a promaster5750DX flash. I am trying to use second curtain, why does the flash fire twice, once at the beginning, and once at the end of the exposure? I dont see how this could benifit me at weddings as wont both flashes cause confusion of the subject in focus? I would think it would cause a blending of maybe 2 different facial expressions.<br>

Any advice would be appreciated.</p>

<p>I'm not really familiar with the 5750 DX, but assuming that it's working as a TTL flash, the first flash is probably before the shutter acutally opens. The camera is basically measuring how much flash output is required for the exposure, and it uses a test flash to do that. Try using the AE lock functionality to see if it computes the flash exposure as well; if so, you can probably just do that. Or perhaps the 510 has some way of doing a separate flash exposure lock.</p>

<p>If you have your flash set to TTL, there are always two flashes. The Olympus TTL flash system always fires a pre-flash to calculate the flash exposure, then a second flash to actually expose the image. When you are using second-curtain flash, meaning the flash is firing to expose the image at the end of the exposure, the distance between the first (pre-exposure) and second pops is much further than when the two fire virtually at the same time when you are shooting regularly.</p>