2nd camera fill flash script? - Script Writing - CHDK Forum
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2nd camera fill flash script?

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Offline J_Hanna

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2nd camera fill flash script?
« on: 15 / April / 2017, 09:40:46 »
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Sorry if this has been addressed before, I searched for existing scripts but possibly didn't use the right search terms.
I'm doing some tabletop semi-macro photography on the cheap and would like to trigger a second camera to flash simultaneously with the primary camera.
I have 3 Canon point and shoot cameras I could use ( A620, A480, S100 ). I have CHDK loaded on the A620 and A480 and I assume there is a version that works on the S100, it's an awesome little camera!

I'm wondering if I could use a version of the lightning capture script for this, the questions being...

1) would the first camera's flash be sufficent to trigger the second camera?
2) Would the second camera respond fast enough?
3) I assume the lightning script doesn't ordinarily trigger a flash, could I set it to do so?

Thanks in advance for any input!
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Offline reyalp

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Re: 2nd camera fill flash script?
« Reply #1 on: 15 / April / 2017, 15:05:53 »
Quote from: J_Hanna on 15 / April / 2017, 09:40:46
1) would the first camera's flash be sufficent to trigger the second camera?
Almost certainly. edit: see below
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2) Would the second camera respond fast enough?
That depends on the length of your exposure. 1 second? No problem. 1/1000th? No way. In between... need to test. The minimum reliable response time for MD is likely to be something around 1/10th of second, though it may be better or worse on some cameras.
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3) I assume the lightning script doesn't ordinarily trigger a flash, could I set it to do so?
You might have to modify this script, but it should be trivial and someone here can probably give you a modified script if you are unable to do it yourself.
« Last Edit: 15 / April / 2017, 16:11:39 by reyalp »
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Offline waterwingz

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Re: 2nd camera fill flash script?
« Reply #2 on: 15 / April / 2017, 16:03:54 »
Quote from: reyalp on 15 / April / 2017, 15:05:53
Quote from: J_Hanna on 15 / April / 2017, 09:40:46
1) would the first camera's flash be sufficent to trigger the second camera?
Almost certainly.
I'd agree that it would be sufficient from a brightness standpoint.  But electronic flash durations are really short.  Possibly too short for an MD script to detect it reliably?
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Offline reyalp

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Re: 2nd camera fill flash script?
« Reply #3 on: 15 / April / 2017, 16:11:21 »
Quote from: waterwingz on 15 / April / 2017, 16:03:54
I'd agree that it would be sufficient from a brightness standpoint.  But electronic flash durations are really short.  Possibly too short for an MD script to detect it reliably?
That's a good point, I wasn't thinking about that. Chance of catching it would depend on the live view exposure time, which varies based on the ambient light level.

A more reliable approach might be to use the USB remote with a delay on the "slave" camera to ensure it fires during the exposure.

edit:
FWIW, I tried triggering MD on my G7X using the flash from my elph130 (with AF assist and red-eye turned off).

One where the G7X used 1/20th, F/1.8, ISO 125, it triggered for ~5 of 9 shots.

I did a second run at where zoom on a darker area, where the G7X used 1/5th, F/2.8 and it triggered for 7 of 7 shots.

So probably not 100% reliable, but possibly enough to be useful in relatively low light.
« Last Edit: 15 / April / 2017, 18:54:29 by reyalp »
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Offline J_Hanna

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Re: 2nd camera fill flash script?
« Reply #4 on: 15 / April / 2017, 19:36:15 »
Thanks for the input!
1/5th second exposures sounds doable since the photo subject will be an inanimate object, I'll set it up in the next day or so and try it with my equipment.
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Offline reyalp

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Re: 2nd camera fill flash script?
« Reply #5 on: 15 / April / 2017, 19:57:59 »
Quote from: J_Hanna on 15 / April / 2017, 19:36:15
Thanks for the input!
1/5th second exposures sounds doable since the photo subject will be an inanimate object, I'll set it up in the next day or so and try it with my equipment.
Just to be clear, the exposure information I gave was only meant as an indication of how bright the scene was. This matters because the exposure the camera uses for live view varies depending on the available light, and to trigger MD, the flash needs to go off during a live view frame.
 
I only tested whether MD was triggered by flash, not the full set up of having the flash from one trigger the other and capturing that in the exposure of the first.

For motion detection, you could use the mdfb2013.lua script (https://chdk.setepontos.com/index.php?topic=10864.0)  with the line

Code: [Select]
    set_prop(props.FLASH_MODE, 2)     -- flash off
removed or commented out by putting  -- at the start

You would still need to enable flash in the Canon settings. Should also make sure AF assist and red eye reduction are turned off on both cameras.
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Offline J_Hanna

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Re: 2nd camera fill flash script?
« Reply #6 on: 16 / April / 2017, 18:37:06 »
I set my A480 as the secondary and ran the mdfb2013.lua script with the flash off command commented out and it worked!

I do have to shoot at 1/5 for it to work fairly consistently and I had to set "trigger threshold" to around 100 for it to ignore the IR red flash.

Thanks again!
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Offline J_Hanna

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Re: 2nd camera fill flash script?
« Reply #7 on: 17 / April / 2017, 13:33:24 »
Since the MD setup is so touchy I went ahead and made a USB cable by splicing a push button switch into a USB extender cable. I tested it with a non-powered USB hub and it works fine on multiple cameras.
Thanks again!
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