View Full Version : Metering flash bulbs with flashmeter
12-23-2006, 11:25 AM
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.
12-23-2006, 12:46 PM
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.
12-23-2006, 01:05 PM
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.:o
12-23-2006, 03:59 PM
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.
12-23-2006, 04:06 PM
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.
12-23-2006, 06:05 PM
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 ;) 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.