I have read on here numerous times (and seen the Offical Canon Instructions) one ofthe disadvantages with the STE-2 is that is must have line of sight with the flash to be able to work. Well at least in my limited testing I would have to say that it is not all true. Take a look at the attached images. I was playing/testing my ST-E2 with my 550ex at work today. I put the flash on a stand with the IR facing the wall behind a cloumn (see 2nd photo). I went to the other side of the room (23 feet away) and lined up almost with the column edge. As you can see in the photo the flash is nowhere to be seen but the flash easily fired. Yes the room had no lights on, but I turned them on increasing the light in the room by almost 2 full stops (1/5-1/30) and the flash still fired. My next test will be outside in the sun to see what results I get.