580 Flash Question

canon400dcanon400d Banned Posts: 2,826 Major grins
edited November 1, 2009 in Technique
Yesterday I did a vintage car rally shoot and the light was not good at times so I dwcidwd to use my 580 flash on my 40D using a 70-200 lens. I was in continuous mode and I am sure there is a simple explanation for this but I have noticed my flash only activates once in continuous. Can anyone please explain this? It would appear that the flash activates on the first image.
Regards
Bob

Comments

  • pathfinderpathfinder Super Moderators Posts: 14,708 moderator
    edited November 1, 2009
    canon400d wrote:
    Yesterday I did a vintage car rally shoot and the light was not good at times so I dwcidwd to use my 580 flash on my 40D using a 70-200 lens. I was in continuous mode and I am sure there is a simple explanation for this but I have noticed my flash only activates once in continuous. Can anyone please explain this? It would appear that the flash activates on the first image.
    Regards
    Bob


    The 580 speedlite is a battery powered device that depends on charging a capacitor to power the flash. If you dump the entire charge of the capacitor for the first frame ( likely if shooting at a significant distance out of doors at a low ISO ) then for the next frames the capacitor is not charged and the flash does not fire.

    Raise your ISO way up, and your flash will perform better for a couple frames, but it will not keep up with high frame rate indefinitely no matter what you do Bob, it only has 4 little AA batteries for power.

    You may need a 220 V power supply for what you want Bob - just joking.thumb.gif
    Pathfinder - www.pathfinder.smugmug.com

    Moderator of the Technique Forum and Finishing School on Dgrin
  • pyrypyry Registered Users Posts: 1,733 Major grins
    edited November 1, 2009
    Pathfinder's right, the 580 has a full power recycle time long enough to only get one pop off per burst, two if you're in half power etc.

    You can get an external battery pack that will improve this performance, but it comes with a bit of catch. If you push the flash too hard an external battery pack will fry it - you will see smoke.
    Creativity's hard.

    http://pyryekholm.kuvat.fi/
  • canon400dcanon400d Banned Posts: 2,826 Major grins
    edited November 1, 2009
    pyry wrote:
    Pathfinder's right, the 580 has a full power recycle time long enough to only get one pop off per burst, two if you're in half power etc.

    You can get an external battery pack that will improve this performance, but it comes with a bit of catch. If you push the flash too hard an external battery pack will fry it - you will see smoke.

    Thanks Pathfinder and Pyry. I fully understand what you are saying and you have fully explained it to me. I was shooting at an ISO of 800 I am pleased to say everything turned out quite well. However, I was somewhat curious why the flash only went off once. Thanks again for your kind help which I truly appreciate.
    Regards
    Bob
  • pathfinderpathfinder Super Moderators Posts: 14,708 moderator
    edited November 1, 2009
    Pyry's comments are pertinent. The flash manual warns against firing too many times too rapidly. You can literally fry your flash by driving it too fast too often.

    I do have the external battery pack and it can help, but I never use flash in High Frame rate mode because as Bob discovered, it really doesn't work that well.

    If you can use you flash at 1/16th power, you might get several shots before the capacitor is fully dumped.
    Pathfinder - www.pathfinder.smugmug.com

    Moderator of the Technique Forum and Finishing School on Dgrin
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