Bejersey wrote:
I have the 430 ex II. I will try it
Won't work.
The 430EX II (and all the Canon EX speedlites, afaik) do not have "dumb" optical slave modes (like Nikon's SU-4, or Godox's S1/S2 modes) that work the way that Photato described.
AND there's YA issue, that simple optical triggers like the one picturedtend not to play well with Canon's EX circuitry. Something like a good ol' Wein peanut simply doesn't work with Canon EX speedlites, which drove any Canon readers of the Strobist insane back when Hobby was writing about this stuff from his Nikonian POV. He'd airily assure you your speedlight would have a PC sync port, have a dumb optical slave mode (or you could plug in a Wein peanut), or use the autothyristor mode, and the 580EX had/did none of these things and was a top-of-the-line $400 speedlite.
Also, a lot of add-on optical slaves attach to a PC sync port, which the 430EX II doesn't have (the 580EX II does; it has the Ext. metering modes as well, which kinda/sorta reinstated the autothyristor). And of those, the only optical slaves that worked reliably where the Sonia green-based ones, that flashzebra sells.
Just saying. Might be easiest to simply blow $65 ona Godox TT600, put it in S1 mode (if your pop-up is in M) or S2 (if your pop-up is in TTL) and use that instead. It is manual only, and you won't have any remote control over its settings or TTL/HSS, but you wouldn't have those with "dumb" optical slaving anyway, and it's only $65.
And now you know why when it came time for me to go mirrorless back in the day, I went for a Panasonic G3 instead of an EOS M, because I was already a Strobist. I wanted an EVF and off-camera flash over radio at the same time. (Well, that and the lack of a mode dial on the EOS M).