IXUS 860 turn flash off - General Discussion and Assistance - CHDK Forum
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IXUS 860 turn flash off

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Offline mr.burns

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IXUS 860 turn flash off
« on: 11 / July / 2009, 17:23:31 »
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Hello,

I use an external USB switch to synchronize two IXUS 860 for 3D photography.
The normal behaviour of the USB switch is:

Press and release USB button 1st time: Focus both cams
Press and hold USB button: Start synchronize (LCD gets black, debug (blue) LED is on)
Release button: Take photo

So far no problem at all. If I turn on the flash on both cameras, and press the USB button 2nd time to start the synchronize function, the flash triggers 1st time for some reason.
Then if I release the USB button the flash triggers 2nd time on taking the photo.

My question now, why the flash triggers 1st time on starting the synchronize function?
How can avoid 1st trigger of flash?

The reason why I want to avoid 1st trigger of flash is that I use an external flash triggered by the flash of the cam. But the external flash is triggered already by the 1st trigger of the built in flash what I need to avoid, because the external flash needs some time to charge again to trigger 2nd time when I release the USB button to take the photo.

Thanks for any ideas.

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2 x IXUS 860IS 100c
2 x Powershot S110 103a
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Offline Microfunguy

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Re: IXUS 860 turn flash off
« Reply #1 on: 11 / July / 2009, 17:54:21 »
Quote from: mr.burns on 11 / July / 2009, 17:23:31
My question now, why the flash triggers 1st time on starting the synchronize function?

That is the preflash that enables the Canon firmware to determine white balance and required flash duration.

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How can avoid 1st trigger of flash?

You cannot.

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The reason why I want to avoid 1st trigger of flash is that I use an external flash triggered by the flash of the cam. But the external flash is triggered already by the 1st trigger

Use a Firefly flash trigger, it will trigger on the second flash.

Or, make a simple circuit using a DIL relay that triggers your main flash after a suitable delay when USB switch released.
Details in files section of Yahoo SDM Group.

Or, wait for a commercial device to become available that not only does that and synch shooting but also allows you to take synchronised time-lapse.
The circuit board design has been sent away for manufacture.
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Offline mr.burns

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Re: IXUS 860 turn flash off
« Reply #2 on: 12 / July / 2009, 07:48:18 »
Hi Microfunguy,

thanks, is the 1st flash trigger really necessary?
My idea is to disable the flash on shutter half press that it could not trigger 1st time.
Then within synchronize function, I can enable flash again to be activated if I release the shutter button to take a photo.

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2 x IXUS 860IS 100c
2 x Powershot S110 103a
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