sigma 500 dg on slave mode

[zod]

with the sigma 500 dg super set on optical triggered slave mode, i used my canon both in built flash as well as 420 ex flash to trigger the slave

both worked. both times, the slave fired at the same time as the shutter opened.

why? why isn't the sigma 500 being fooled by the ettl's preflash?
when used with studio strobes, the strobes were fooled by the preflash.

[weg]

i realised that too...
there are some slave flashes out there that have a circuit to account for ettl preflash, perhaps the 500dg super has this circuit inbuilt too?
otherwise, general slaves shld be fooled by it

Originally Posted by zodnm with the sigma 500 dg super set on optical triggered slave mode, i used my canon both in built flash as well as 420 ex flash to trigger the slave both worked. both times, the slave fired at the same time as the shutter opened. why? why isn't the sigma 500 being fooled by the ettl's preflash? when used with studio strobes, the strobes were fooled by the preflash.

[Ah Pao]

What mode did you set the 500DG to? Wireless slave (C1 SL) or optical slave (C0 SL)?

And what camera are you using?

I have a problem using the 500DG as the wireless master (C1) with 420EX as the wireless slave on the 300D. Unless I use FEL, both flashes will 90% of the time fire at full power, thereby ruining the shot.

I am still figuring out how to use the two together. If anyone has experience in this please help!