While this is old news for Nikon shooters, this is a new capability for Canon DSLRs. The only other Canon DSLR that has this is the 7D.
The cool thing here is that you don't have to waste a 550EX, 580EX, or 580EXII atop your camera to control your off-camera flashes. OK, OK - the 60D's built-in flash isn't as powerful or as versatile master as one of the dedicated flashes: it can only control 2 groups of flashes, instead of three, and its lower power means less working range, particularly outdoors.
However, it has enough juice for a lot of uses, it's fast to set up and it's always there.
I finally got a chance to put it through some paces, under a reasonably trying set of conditions: outdoors, sunset time under heavy, leaden skies, in a light rain. Hey, it was my only chance to score some shots of the lovely ice covered branches and pine needles from the day's wintery mix.
So, the basic set up is the 60D's builtin flash acting as master, in ratio to a slaved Canon 550EX on a stand. The 550 has a Full CTO gel on it, to make it nice and orange, like late, late afternoon light, and a Honl snoot, to narrow the beam. The narrowed beam does two things: it keeps light from spraying all over the background, giving me a clean black background, and it keeps the light from spraying into the lens causing flares, ghosts and loss of contrast.
I set the ratio between the slave and the master to 8:1, which mean the 550EX was pumping out 3x the light the on camera unit was. I also set the flash exposure compensation to +1 ev, to compensate for the shiny reflective ice. The stand was placed so the 550 would be side lighting or partially rim lighting the subject, creating texture and highlights and shadows, while the built-in flash provided fill in light to ensure detail.
It worked pretty well, I think. :-)
Some more notes - I shot these at ISO 200, with a Canon 100mm F/2.8 L IS Macro lens, at F/11 or F/16. The extremely close range, 1.3 feet or so, was the only reason I got away with such high apertures. The 60D's built in flash doesn't have the juice to even fill in F/16 at standard portrait distances.
The 60D's built-in flash's method of autofocus assist is to pulse flash. It's annoying, but it was effective, especially once I took the lens hood off the 100 Macro.
So, was this better than slapping another 550EX on top of my 60D? Well, for this use, yes. I was working in way close, and the built-in flash actually has a better angle for on axis fill in this situation that 550EX standing tall in the hot shoe would have had.
It also made for a lighter, less bulky camera unit - less protruding things to bump and shake branches attached to the subject. As it was, I had to be careful where I place myself. A big, on-camera flash would have made that even more challenging.
Going all-TTL for this was also a huge help. I normally go all manual, but in the rain, with the light quickly dying, it was a blessing not to be fiddling the with power settings on the 550EX as I moved it around. I was able to work faster than usual, and that maximized my picture making time.
