Just a thought - if the slave is cheap enough, you've already done the hard work with the flip flop. It may be cheapest to use 2 flashes of the same type in the same position and trigger one on the pre-flash and the second as you do now.

-Skip


------Original Message------
From: Bob Blick
Sender: piclist-bounces@mit.edu
To: piclist@mit.edu
ReplyTo: Microcontroller discussion list - Public.
Subject: [EE] How do modern camera flashes work?
Sent: Nov 25, 2009 3:37 PM

The flash in my Canon Elph is probably a fairly typical example of a
modern flash. It flashes twice in quick succession, the first time is
for exposure and maybe focus. The second time it's for taking the
picture.

In old-fashioned flashes, the flash had an inverter charging a big
capacitor that had a Xenon flash tube across it, and a little SCR that
hit a second, smaller transformer to trigger the flash tube. The big
capacitor is drained pretty heavily and takes time to recharge, it can't
flash twice in a tenth of a second.

Any idea how they get two quick flashes in my camera? I'd love to be
able to use my cheap slave flash to augment the one in the camera, but I
don't see how any of the circuitry can be reused. And I already tried
putting a flip-flop in, so that it would only fire the second time. My
test pictures were overexposed because the first flash(the one that sets
the exposure) wasn't augmented by the slave flash.

Thanks,

Bob

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