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PostPosted: Mon Dec 21, 2009 2:13 pm 
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If I have a flash gun in the hot shoe, what is it the tells the flash to illuminate when I press the shutter?


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PostPosted: Mon Dec 21, 2009 5:53 pm 
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It's basically a small jolt of electricity....not much more to it ;)

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PostPosted: Mon Dec 21, 2009 6:27 pm 
AFAIK the camera shorts the two contacts of the flash (on a simple flash with only two contacts). If you don't mount the flash on anything but just short these contacts it should fire. The trigger voltage between these contacts can be quite high on older flashes, even to the point where a modern digicam can be damaged by it. Check here.

Ben
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PostPosted: Sun May 16, 2010 9:27 am 
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The hot shoe provides the closing switch which fires the trigger tranformer in the flashgun which ionises the Xenon gas in the flash tube allowing the main energy pulse from the energy storage capactor to flow through the flash tube.

As Ben says - in older flash units - firing the trigger transformer means shorting the trigger capacitor across the trigger tranformer primary, and there may be several hundred volts on the little trigger capacitor which may damage the hot shoe switch.

Most modern flashguns discharge the little trigger capacitor through the trigger transfomer using a thyristor, and the hot shoe switch just allows a low voltage pulse to get to the thyristor gate, turning the thyristor on (briefly) and firing the trigger transformer.

Greg

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PostPosted: Sun May 16, 2010 9:44 am 
Does this answer your question or do you mean how do you set up your flash to shoot with it?


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PostPosted: Sun May 16, 2010 2:18 pm 
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Well, this question was asked a while ago (check dates)

But I just really wanted to know how it was triggered, not how to set one up, I don't own an external gun as yet, but when I do, I may ask then, if I'm unsure.

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