this could be a really basic question. i've always used generic flash with manual output modes and i have never owned two ETTL flashes until now so i'm playing around with ETTL master/slaves.
i have 580EXII as master, controlling a slave 430EX.
if in a case where i just want slave to fire, i disable master 580EX via disabling master per page 39 in the manual. but the master unit still fires... i dont get why?
it says in a small note in the page 39 that "it will still preflash to transmit wireless signals" to slave but i thought that was what the IR was for? so why does it need to send preflash?