The Canon EOS 7D body has a built-in Canon "Speedlite Master" controller, which is accomplished through use of the built-in flash to send commands to slave Speedlites.

Since Canon has been offering point-of-sale rebates on Speedlites here through December 31, I decided to take advantage and try out the system, purchasing a pair of 320EX Speedlites from a local dealer at the sale price.

Using the 7D as the controller, with its onboard flash as a fill lamp (or even not used for exposure), the system works very well with the two slave 320EX strobes. Well enough that I'm inclined now to carry one in the bag on future travels for use as an outboard fill lamp and macro strobe. Which is saying a lot, since I've only rarely lugged along an external flash before now.

Canon's Speedlite exposure system has puzzled many (most?) users, myself included. But it begins to make sense once outboard slaves are employed.

Cheers