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Strobe power adjustment - How exactly

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    JackAllTog
    JackAllTog e2 Member 53629 forum postsJackAllTog vcard United Kingdom58 Constructive Critique Points
    30 Jan 2012 - 4:49 PM

    Hi,

    If i was to make my own flash unit, how would i go about controlling the power level and the duration?

    Is it purly reducing the main DC voltage or would it be by adjusting the effective charge of the main capacitor?
    I'm assiming trigger voltage and duration have no part to play in this.

    As well as power output level should i consider any other output parameters?


    Many thanks for your ideas.
    Stuart

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    lawbert
    lawbert  71713 forum posts England15 Constructive Critique Points
    30 Jan 2012 - 5:24 PM


    Quote:

    As well as power output level should i consider any other output parameters?


    I would suggest a pair of Wellies...(and dont stand in a puddleWink) Blue sparks are dangerous and not to be toyed withWink

    Helpful Post! This post was flagged as helpful
    HouseMartin
    30 Jan 2012 - 5:52 PM

    I think your assumption on duration is wrong Stuart.

    Most flashguns control power by duration, not brightness. The basically charge, splat on trigger, and shut off when sufficient light has fallen on the subject.

    Most speedlights spec. max. duration implying shorter times, and why when doing those clever drip shots people do, less power means shorter light burst means better frozen action.

    HTH

    Paul

    Helpful Post! This post was flagged as helpful
    HouseMartin
    30 Jan 2012 - 6:19 PM

    Just read your OP properly Stuart (should have done that first time).

    You are right, trigger pulse duration does not control flash duration. It just sets things in motion. If you Google flash gun circuits you should get plenty of info e.g. here. The partial Sunpak 383 schematic shows a power control circuit quite nicely.

    Paul

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    JackAllTog
    JackAllTog e2 Member 53629 forum postsJackAllTog vcard United Kingdom58 Constructive Critique Points
    30 Jan 2012 - 6:58 PM

    Many thanks Paul and good wellies hint.
    I'm weighing up an idea, and considering something similar to what bigbri did or maybe using a 30 yoghnu flash as a base.

    MeanGreeny
    30 Jan 2012 - 7:36 PM


    Quote: As well as power output level should i consider any other output parameters?


    Many thanks for your ideas.
    Stuart

    The peak power output level [i.e. 'brightness'] of any actual 'flash' is the same for all 'flashes' from a given flashgun - it's the duration of the flash that varies to give the reduced f stops of illumination.

    e.g.

    580 EX II on full power is approx 1/800 of a second
    580 EX II on 1/64 power is approx 1/4200 of a second

    The longest duration [full power = 1/800] should therefore always be less than the camera sync speed [1/250 on my 30D].

    That's why shutter speed does not affect the flash exposure but aperture does.

    HTH

    Last Modified By MeanGreeny at 30 Jan 2012 - 7:40 PM Helpful Post! This post was flagged as helpful
    oldblokeh
    oldblokeh  3820 forum posts United Kingdom
    30 Jan 2012 - 7:43 PM

    Your main capacitor is always fully charged. If you are wanting to save the unused stored energy you can:

    1. Quench the tube by firing a thyristor that dumps charge into a much smaller capacitor.This can lower the voltage across the tube long enough to quench it. Or...
    2. Use an IGBT.

    Edit: Here's a useful app note from Fairchild.

    Last Modified By oldblokeh at 30 Jan 2012 - 7:51 PM Helpful Post! This post was flagged as helpful
    oldblokeh
    oldblokeh  3820 forum posts United Kingdom
    30 Jan 2012 - 7:55 PM

    I mean, of course, that the main capacitor is *triggered* from fully charged.

    Helpful Post! This post was flagged as helpful
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