I will guess that either your particular unit is malfunctioning or you are not operating it properly. It is entirely possible that you have a plus or minus exposure chosen on the flash or you have the same chosen on your camera, which would be a global change, affecting not only the flash exposure but the ambient exposure as well. As someone who used strobes back in the seventies, I think I have some experience here and would like to offer you some suggestions. First, don't EVER let the strobe do your thinking for you. No matter how sophisticated, no camera or strobe can successfully make decisions like that. You need to understand how it thinks and constrain its thinking so that it give you an acceptable result. Let me explain: First, set you camera on Tv. Set your shutter at 1/60, or the lowest shutter speed you can reliably handhold. Nest, set your ISO to give you a good exposure at the aperture you would like to shoot at in that location without the strobe. I generally (but not always) set the strobe to +1/3. Now you have constrained its thinking to give you an exposure close to the base exposure in the room. NEVER point the strobe directly at the subject. Bounce it off the ceiling while using a modifier like the Lumiquest 80/20 or the little white card (in my opinion slightly less effective) that you can pull out of the 580EX. In my experience at hundreds of venues, the aperture hovers around f/2.8, the shutter stays at 1/60 and the ISO is 400-1000. What you are aiming at is an exposure looks just like what your eye sees, only better. The bounce light from the strobe + the adequately rendered ambient exposure gives you a good even light that shows the venue properly. The small amount of forward-directed light from the strobe clears up raccoon eyes and cleans up the color. I use a flash bracket that always keeps the flash directly over the lens, so that any shadows fall below and behind the subject. I often use gels over the strobe the match the existing light in the room. This is a choice that only your own experience can inform and of course is the subject of a different and much longer post. Now at each shot you need to think like a strobe: Is there a window behind the subject or in the field of view that will mess up its thinking? If so change your position or exposure. Common at corporate events are group shots involving shiny award plaques. Tell your subjects to angle the plaques slight downward or the reflection off the plaque will cause a severe under-exposure, not to mention Photoshop post production work. These are just 2 examples of things that cause auto-exposure failure. There are many others and your experience should be your guide here. White tablecloths, black walls and glass-covered pictures in the background are others. Of course, you need to be shooting RAW. This will allow you to make nearly every exposure spot-on. That said, flash auto exposure has came a long way since the seventies. It is way more accurate and reliable. Back in the day, you educated yourself by carrying a hand-held meter and measuring exposure and comparing that to what your eye/experience told you was correct. After a while, you would get pretty sharp at guessing exposure. Cameras are not foolproof now and have never been. By properly guiding the instrument, you can produce professional quality work far more easily than was possible in the seventies. Is it stressful? Yes, it is. You are combining your experience and a mechanical/electronic device in an effort to create a perfect record of an event, done in real time. Stress is what causes you to be sharp, not only technically, but also to improve your eye, to recognize good images as they occur and capture them. When all of this works together and you are on your game, it is exhilarating.
Regards,
Tony
