Hey i am looking at getting umbrella's for my 580exii on flextt5 i am wondering is it more efficient to get one of them umbrella's with like a back on it. not square like a soft box. i think its Westcott that make them. i know that open normal umbrellas are not efficient as in you cant control yourso is having a "back" on the umbrella more efficient and still have "umbrella" lighting effect?
BTW i am looking for an umbrella around 60inch size.