Can 580 Wireless Communicate Through People and Perform as a Back Light?

[Peacefield]

The title essentially says it all, but here are the details of what I'm trying to do:

Wedding reception, couple's first dance, two 580 EX II's in wireless ETTL. Master is toned way down, revealing only a hint of the subject. The slave is opposite the couple as they entirely block it from the camera's view so that it essentially creates a rim light around them. The slave will probably be about 20' away from the camera/master, we're in a large crowded ballroom, and there's no direct line of sight. Will it work?

Presently, I go with a single remote flash and Cyberxyncs, but the above approach will greatly simplify how I work through my variety of shots during this important moment in the couple's day so I'd like to introduce it, but I need it to be reliable.

Thanks.

[apersson850]

In this case it depends completely upon how much there is for the master's light to bounce off. If there is a ceiling or walls or things like that, which can bounce light to the slave, then it works.
Shooting in my living room I can trigger the slave even if it's hidden under the sofa, but that room is much smaller than a ballroom (!), so the only way you can be sure is if you try it out.

[BigBlueDodge]

Could be a good reason to buy a PocketWizard MiniTT1 and FlexTT5. Still get ETTL capability, but not have to worry about line of sight issues.

[bobbyz]

Why not have the flash behind the couple in manual mode?

[vadim_c]

Why not have the flash behind the couple in manual mode?
Actually I am not sure that TTL would give any good results in such configuration.

[CliveyBoy]

The ballroom configuration would be marginal, and may or may not work. Even if tested ok, the Canon Wireless communication could fail at a critical time. It is a pity, for the E-TTL can simplify a photographer's work, especially on the run.

RadioPoppers and the new PocketWizards overcome the communication failure, while preserving some or all E-TTL functionality.

[coryparris]

It works great with two things that I do differently. The first is that I use radiopoppers so that the Canon system is no longer line of sight. The second is that I use manual setting on the slave flash. If it shows up in the frame AT ALL with eTTL, it shuts down immediately. To get your slave in manual mode while you have your master doing eTTL (or other slaves in eTTL), press the mode button and hold it down. Then, you can have that one flash in manual while having others in eTTL.