TPB #23 – Measuring Flash Duration

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This week I show how to measure flash duration using a light sensor and an oscilloscope. I also explain the advantages of xenon flash tubes and their downfall. Lastly I go describe a trick modern speed-lite flashes use to get their short durations.

After all this I measure the flash duration of a Canon 580 EXII and a Yongnuo 460 flash. Much to my surprise the Yongnuo flash had less than half the flash duration. If anyone wants to verify this or write software for the Camera Axe to measure this please leave a comment or a post in the Camera Axe forums.

Update:
There is some really good discussion on this flickr thread about this post. They pointed out that flashes use modern flashes use IGBT and not mosfets to cut off flash duration (this is probably correct). They pointed out that studios don’t actually use resistors anymore to weaken the effect of flashes and instead they use complex circuits to try and keep the a constant light color at different flash powers (my studio flash knowledge is just from what I’ve read and is probably out of date, but studio flashes do tend to be slower). They also made a few other good points so it’s definitely worth checking out that thread. They do have a different perspective though of caring about flash power and light quality that flat out speed that many of us Camera Axe folks care about.

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Maurice is a computer engineer, photographer, and all around renaissance man.

Discussion

  1. Gabriel Marigo  October 21, 2011

    Do both flashes output the same amount of light or they are just set to the same relative power (1/128)?

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  2. Maurice  October 21, 2011

    I was only concerned with flash duration so I didn’t measure light output. That said, I think it’s likely that the Canon flash outputs more light.

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  3. Peter  January 5, 2013

    Hi Maurice,
    I have been trying to replicate your test on flash duration, can you please submit settings you used on rigol scope
    As I have same model scope and still learning thank you regards Peter

    (reply)

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