What are my options for off camera flash with the Canon XS. I have a 420ex and recently purchased a 3ft cord to allow for off camera flash. Now I want to extend the range of the off camera flash. If I get a 580EX and mount it to the camera, can it force the 420 to flash a few feet away? Is there any other inexpensive options? Im also considering purchasing a simplistic clamp lamp to help.