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Strobe power adjustment - How exactly


JackAllTog e2
5 4.0k 58 United Kingdom
30 Jan 2012 4:49PM
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 7 1.8k 15 England
30 Jan 2012 5:24PM

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
HouseMartin 5 193 1 England
30 Jan 2012 5:52PM
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
HouseMartin 5 193 1 England
30 Jan 2012 6:19PM
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
JackAllTog e2
5 4.0k 58 United Kingdom
30 Jan 2012 6:58PM
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 9 3.7k England
30 Jan 2012 7:36PM

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
oldblokeh 3 922 United Kingdom
30 Jan 2012 7:43PM
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 .
oldblokeh 3 922 United Kingdom
30 Jan 2012 7:55PM
I mean, of course, that the main capacitor is *triggered* from fully charged.

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