If you have a camera mounted ST-E3-RT running as master plus any number of radio connected 600EX-RTs is it possible to utilize the AF assist on one of the 600s since the ST-E3-RT doesn't have the capability or is AF assist only possible from the master unit? I like the size of the ST-E3-RT but I also like the AF assist on the 600s and since the ST doesn't have the AF assist built in I have been wondering if there is a way around it. I've been reading around the Internet as well as checking out the product manuals but unable to find an answer to the question (or maybe I missed it?). Thanks in advance!