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Old Aug 28, 2006, 1:58 PM   #1
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20D + 580ex

I do not quite understand how to get away from using the flash in P mode which defaults to 1/60th of a second. Is this the shutter AND the sync speed both? I would like to shoot in Av. could someone offer me a hypothetical walk-thru of shooting w/ the 580 in Av or M?

What is the actual range of shutter speeds & applicable rules of thumb?

I am a firm believer in RTFM theorybut I have to say the manual with the 580 might has well been written in penguin hieroglyphics.
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Old Aug 28, 2006, 2:26 PM   #2
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The shutter and sync are two different things:
The shutter is the time the curtain remains open while the sync is what is used to trigger your flash:
1. The sync can be either @ open of the curtain
2. Or the sync can be @ the closing of the curtain

What is the actual range of shutter speeds & applicable rules of thumb?
On most cameras you can sync with any shutter speed below 1/200s, and some cameras will let you sync even up to 1/500s, but this is rarely needed because a flash pulse is usually 1/1000s, or less anyway, and can freeze the action without needing the higher shutter speed... Yes even @ 1/60s!
The reason you want to use a slower shutter (or aperture) is to add-in more ambient light, i.e. not black out the background
-> the ambient light is what blurs the subject motion as a result of the slower shutter speed

Several cameras will enable you to sync at a higher speed than 1/200s (or 1/500s) all the way up to the max shutter value, and this is called the high-speed-shutter sync. This is not used to freeze the actions however, because the flash is actually slowed down to coincide with the traveling of the shutter curtain. This is achieved by lowering the flash output and firing it multiple times hence the flash can only cover relatively short distance only in this mode!

On a 20D, the camera can be set to manual and the 580EX can remain on automatic, in which case you can control both the shutter speed and aperture to anything you like: The EV -2..-1..v..+1..+2 scale in the viewfinder will indicate how much ambient light will be include with your flash which you can vary with the shutter/aperture
-> The flash will automatically balance the rest of the exposure when it fires :idea:
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