60D using onboard flash to trigger a 430EX II. Can you avoid the on camera flash?

Hi Dale, Essentially I agree with you, it is the output from the pop-up that sends the control code and the trigger now signal to the Ex slaves.

The window (nearly black) on Ex slave units covering the Wireless sensor is an 'IR only - pass' filter. So control 'pre-flashes' include what Canon calls 'near-IR'. They mean that it's EMR energy in the 'near visible' part of the IR spectrum.

So the Pre-flashes & Trigger-flashes from a 60D pop-up are White visible light & near IR mixed together. Which explains why Nikon's SG-3IR - suitably modified - works so well to allow the control & trigger signals to 'get through'. The ST-E2 is the only Canon master/Controller (Light based) device that had an IR pass filter placed in front of its Xenon flash tube.