Wide angle is a tough subject not only for lenses, but for flashes, too... I've done several tests to see how Canon 580EX II covers the frame at every zoom setting. Here are the results: Canon 580EX II test Tthe built-in white card covers about 50mm angle of view If you use a bounce card it's good to know that a narrow side of 580EX II gives you about 1/2 stop more fill light than a wide side. Hope this is useful. Cheers!