The reason you can't is because 580exII does not have a conventional slave cell. Just adding simple optical slave doesn't work either because the pre-flash the on-board flash would trigger it.
A cheap radio trigger is the least expensive way to move it off camera, but that just creates harsh unfilled shadows. A better investment in the long-term is buy a second Canon flash (430ex or 580exII) and use the Canon wireless system in a key / fill arrangement.
Search "Wein Peanut" on the B&H site, they make a "digital" version of the slave cell that is supposed to ignore the pre-flash. I can't vouch for how well it works, but it's cheaper than a new 580exII by about $400.
I own a Wein Peanut and vouch that it doesn't work with Canon EX flashes. To recap, Wein Peanut plus Canon EX flash equals darkness, unlimited quantities of dark. Careful testing proved the Wein is very effective with my Profoto packs. Check Strobist for the sad Wein/Canon situation
rico wrote:
I own a Wein Peanut and vouch that it doesn't work with Canon EX flashes. To recap, Wein Peanut plus Canon EX flash equals darkness, unlimited quantities of dark. Careful testing proved the Wein is very effective with my Profoto packs. Check Strobist for the sad Wein/Canon situation
I would like to know for sure if you have the digital version of the peanut. I'm not trying to argue with your experience, I just want to know for certain that that is what you were dealing with so that I and others can make better informed choices if we get the urge to try a similar setup.
Note: I accidentally posted this same comment using my wife's username, then deleted it. Just in case anyone saw it and got confused.
I have the analog Wein, although pre-flash is not the problem per se. My 550EX was operating with pre-flash disabled, and my Contax flashes don't emit pre-flash. Perhaps Wein improved the electrical signalling for their digital model but, as the price is markedly higher, I would simply go PW.
