Using pop-up as a trigger to sigma optical slave

[KarlosDaJackal]

So I keep hearing/reading that you can't really use the on-board flash to trigger optical slaves because the ETTL Pre-Flash will cause the slave to go of on the pre-flash instead of the real exposure.

So when i put my Sigma EF-530 super in optical slave mode on Channel "0", it seems to work correctly when triggered by the on board flash.....

http://farm4.static.flickr.com/3033/2979469316_8741faa9bc.jpg

Can anyone else confirm this works? The documentation from Sigma is lacking to say the least. Usually I only bring one flash with me (the 430EX as its easier to fit in a small bag) but thats limiting, if a sudden opp of a good photo comes up. If this is reasonably reliable, I might bring this instead so I can have more options with less gear in the bag. I know its not the same as Nikon's commander mode on there on board flashes, but its better than nothing.

[transcend]

It will set the flash off, but not at the right time. The flash is being triggered by the pop up pre flash (which helps set exposure and reduce redeye). This happens just before the actual shutter trips and the flash fires.

[KarlosDaJackal]

It will set the flash off, but not at the right time. The flash is being triggered by the pop up pre flash (which helps set exposure and reduce redeye). This happens just before the actual shutter trips and the flash fires.

Yes thats the normal optical slave theory....... but the Sigma apparently can understand and ignore the pre-flash simply by setting the channel in optical slave mode, a so called "smart slave". So channel zero seems to tell the sigma an ETTL pre-flash is coming and you need to ignore it, channels 1 and 2 probably understand i-TTL pre-flashes. From that picture it looks like its going of at the right time for a 1/250 shot.

Do you see something wrong with that picture that I don't?