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With the Canon 580 EXII, there is a custom function to allow a second flash before the flash is fully charged when in anything other than single frame advance. When I use flash, I will shoot at the low speed 3fps. High mah rechargeable batteries help with faster recycle or an external battery pack will really help. You do not want the flash to fire to many times in low or high fps because you could burn out the flash.
The difference with HSS and a standard flash is kind of complex. Think of it this way, when a flash fires normally, you get one quick flash that fires while the shutter is open. As long as your exposure on camera is about 2 stops bellow ambient, the flash acts as the shutter. I.E. shutter speed of 1/250 and flash duration of 1/1000th as long as no ambient light is coming in, it should look like you shot with a shutter speed of 1/1000. With HSS, the flash actually starts firing before the shutter opens and stops after the shutter closes. And it is a bunch of lower powered flash burst during this time frame. So, in a well lit location, with a close subject, HSS adds light to help you achieve faster camera shutter speeds. The standard bullet through a balloon or apple scenario is a great example. Adding 2 or 3 or more flashes in HSS allow you to achieve that 1/8000th shutter speed, but the flash is lighting the scene, not stopping the action. SO, when you are shooting HSS, you are adding light, not stopping action with the flash, and if you look at the back of your flash it will show you the range. Tonight, I have two football games. The first one, starts at 4pm and I should be able to get to the 4th quarter using no flash. As soon as dusk hits, I will set my flash to HSS, just for fill, but still rely on the shutter to stop the action. Normally, as soon as I am no longer getting shutter speeds of at least 1/500th, I will change the strobe to normal, not HSS, drop the ISO to 800 and continue shooting with the flash stopping action. BUT, I tried something last week that I am going to work with tonight some more. I shot a quarter of a game last week in RAW and ISO 12,800, edited in Lightroom and was able to submit to MaxPreps and get the gallery approved. Blew me away that the 7D could create MaxPreps quality shots at 12,800. What I will do tonight is the same thing, except shoot with the flash in HSS just to give the uniforms a little pop and act as a little fill, but Ambient will be my main light source.