On camera flash triggers it, but does not contribute to the exposure. When you set up the flash settings in your camera you can choose for off camera only, or off camera with pop up flash. If you choose off camera only, the popup will just pulse a split second before the shutter opens to signal the 430. But that pulse has no impact on your exposure. I was worried about the line of sight thing, but so far haven't had any troubles with my 60D. Out of superstition I like to swivel it around so the censor is pointed in the direction of the camera...don't know if I have to or not but it seems to work when I do so I figure why not. It's my first off camera flash, but I'm lovin' it!