Metering flash bulbs with flashmeter

Discussion in 'Lighting' started by BrianShaw, Dec 23, 2006.

  1. BrianShaw

    BrianShaw Member

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    Is there any reason that a flashmeter (Sekonic L-558R) can't be used to accurately measure exposure with flash bulbs? The reason I ask is that all I have ever seen for computing flash bulb exposure is Guide Numbers and tables, as in the Kodak Master Photoguide and Professional Photoguide.
     
  2. Pinholemaster

    Pinholemaster Member

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    Yes because the bulb burns longer than an electronic flash.

    Shutters set on "M" for flash bulbs delay their opening till the bulb is at its peck burn. A flashmeter will measure the entire burn, not the peck when the shutter is open.

    You'll get a false reading.

    Hope that's helpful.
     
  3. fotch

    fotch Member

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    Really? I thought my flash meter measured brightness. Different strobes have different speeds of flash and still meter correctly. My understanding is they measure the peak light output. I will have to try it.:surprised:
     
  4. Dan Fromm

    Dan Fromm Member

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    fotch, with most electronic flashes the entire burn takes place while the shutter is open. But if you're using a studio flash or (sob,cry, it won't do what I want) an Agfatronic 643CS, check the manual to see what full-power flash duration is.
     
  5. Pinholemaster

    Pinholemaster Member

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    A flash bulbs burns so much longer than an electronic flash that a flash meter doesn't know what is the peak of the bulb's burn. Thus the false reading.
     
  6. BrianShaw

    BrianShaw Member

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    Good point about the M-sych -- if the meter measures the full duration, the first 20 ms of the burn is lost due to the sych delay. I should have thought of that myself! For what it's worth, I did remember to the loss factor due to use of higher shutter speeds :wink: I suppose I'll stick with the Kodak guide calculators. It's just that I spent so much money on the meter that I hoped I could use it for everything.