Wireless Flash for Macro?

I'm planning how I'm going to do a two flash setup for macro work (outdoors, not copy work). I'd rather go with two flashes like the 430ex and 580ex instead of the MT24-EX. My question is, how bright is the flash during the communication between the master and slave. Will it affect a macro exposure being the heads are so close to the subject?

The flash is very bright whenever it goes off, but it won't affect the exposure. It's very quick so I doubt even insects will have time to react to the preflashes.

Thanks for the reply, Tim. Does the communication between the master and slave occur during the exposure? Again my concern with macro and very close working distances between the flash and subject, that it might affect the exposure in a wireless mode.

The communication occurs before the shutter opens. Have a read of the EOS flash bible, which is linked from the forum FAQ.