I'm renting a 580ex II for a wedding next weekend and using the flash I own as a backup. My flash is off-brand because I bought it before I knew what I was doing.

My question is... I thought I read somewhere that there was a way to set the 580ex to "see" another flash bulb go off and it fire as well. Basically, what I want to do is use my flash on camera and set the 580ex up on a stand as another light source and have them both fire, but I read through the manual for it and didn't see anything about this mode. Anybody know if this is possible?

i believe its only possible on the nikon sb800s

Darn... I'm not Nikon yet :-(

Yes you can, but you need another canon flash. The 580EX II can be a master flash, but you need to turn it on in the flash settings. The older 580EX has a switch on the outside of the flash.

Read this to learn about Canon wireless flash

http://super.nova.org/DPR/Canon/580exFAQ/

and

http://super.nova.org/DPR/Canon/MultiCanon/

its pretty funny b/c it will end up ruining everyone else's point and shoot shots... going off all night wears the batteries out pretty quickly though

Hey what do you know... should have read my own flash's manual. I just assumed it couldn't do it because it was the cheapest one I could find at the time that worked with my 30D (currently I own a Quantaray QDC900WA). I'm going to play around with this... been wanting to do wireless flash for awhile but didn't think I had the necessary equipment.

I can't seem to get it to sync with my popup flash (sorry, don't have a real flash to work with right now). I see it fire through my viewfinder before the shutter goes. I can't figure out how to slow it down. I'm thinking that the popup is doing some red-eye reduction type thing where it pops twice, but I can't find any settings for this. Then again, this may just be an issue with the quantaray flash that I can't get around.

That is not correct. Canon wireless flash will not fire from having a point and shoot flash near it when it fires.

You can also get a Canon ST-E2 transmitter. It requires line of site shooting, unlike Radio slaves, but works well if your REAL careful.
Be careful if using the 580 with standard radio slaves. These puppies throw a lot of electrical interference that cause more accidental pops than useful pops. Mine only work of I have the radio receiver at the end of my intelli-sync cord.
Better yet...get the Radio-popper if you can.

Matt -

That 1st flash you see through the viewfinder is not red-eye reduction, it's the pre-flash (how it "Evaluates" how much light to put out - hence the "E-TTL" - Evaluative Through The Lens flash metering). Put it on second curtain sync and use a loooong shutter speed, and you'll actually be able to see both flashes.

The wireless system actually sends out quite a few of those "pre" flashes to communicate with the other flashes. It's a coded signal, so others can't interfere. You even get 4 separate channels, so you could technically have 4 different optical wireless systems going without interference (love to see that! LOL)

Canon can't use the pop-up flash as a master (Nikon and others can) but Canon 550, 580, 580 II, and ST-E2 all can be masters. Most of the dedicated Sigma flashes can too. The 420, 430, 550, 580, and 580 II can all be "Slaves" (remotes). Again, Sigmas can too.

You could always put your flash in manual mode, and use a radio trigger to try it - the ebay Cactus brand is great for trying it out.

Just thought you might want to know!

Shan