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Using CHDK on SD800 with slave studio lighting

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Offline nesteryo

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Using CHDK on SD800 with slave studio lighting
« on: 27 / September / 2023, 14:50:03 »
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Hello,

I've recently discovered CHDK and started playing with it in the studio. I tried to use it with external flash lighting as slave and set Ev step value to 1/125. It sets the external light off, however it doesn't seem to sync properly and there is no external light active on the photo, just the camera internal flash. I've attached two photos with 1/125s and 2s exposure times, every visible light was set to slave. Is this the flash speed problem? Thanks in advance!
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Offline reyalp

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Re: Using CHDK on SD800 with slave studio lighting
« Reply #1 on: 27 / September / 2023, 15:51:51 »
Quote from: nesteryo on 27 / September / 2023, 14:50:03
Hello,

I've recently discovered CHDK and started playing with it in the studio. I tried to use it with external flash lighting as slave and set Ev step value to 1/125. It sets the external light off, however it doesn't seem to sync properly and there is no external light active on the photo, just the camera internal flash. I've attached two photos with 1/125s and 2s exposure times, every visible light was set to slave. Is this the flash speed problem? Thanks in advance!
What external flash are you using? It's seems like this probably more of an external flash setup issue than a CHDK issue.

Since the external flash doesn't appear to have fired in the 2s exposure (I'm assume the thing on the stand in the upper left is one of the slaves?), one possibility that comes to mind is it's triggering on the Canon AF assist lamp (or maybe red-eye reduction preflash if that camera has it) rather than the main flash and firing *before* the exposure.
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Offline nesteryo

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Re: Using CHDK on SD800 with slave studio lighting
« Reply #2 on: 27 / September / 2023, 16:50:39 »
Every light is Quadralite MOVE X 400. I have shot without pre-flash, and see all the external lights firing with the camera flash properly on time, however it must be slightly before the photo is taken. I thought maybe I could somehow override flash timing with a script.

Quote from: reyalp on 27 / September / 2023, 15:51:51
Quote from: nesteryo on 27 / September / 2023, 14:50:03
Hello,

I've recently discovered CHDK and started playing with it in the studio. I tried to use it with external flash lighting as slave and set Ev step value to 1/125. It sets the external light off, however it doesn't seem to sync properly and there is no external light active on the photo, just the camera internal flash. I've attached two photos with 1/125s and 2s exposure times, every visible light was set to slave. Is this the flash speed problem? Thanks in advance!
What external flash are you using? It's seems like this probably more of an external flash setup issue than a CHDK issue.

Since the external flash doesn't appear to have fired in the 2s exposure (I'm assume the thing on the stand in the upper left is one of the slaves?), one possibility that comes to mind is it's triggering on the Canon AF assist lamp (or maybe red-eye reduction preflash if that camera has it) rather than the main flash and firing *before* the exposure.
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Offline reyalp

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Re: Using CHDK on SD800 with slave studio lighting
« Reply #3 on: 27 / September / 2023, 18:42:11 »
Quote from: nesteryo on 27 / September / 2023, 16:50:39
Every light is Quadralite MOVE X 400. I have shot without pre-flash, and see all the external lights firing with the camera flash properly on time, however it must be slightly before the photo is taken. I thought maybe I could somehow override flash timing with a script.
I still think something must be triggering the quadralite *before* the main flash. I may be wrong, but it would seem surprising if the Canon flash illuminated long enough before the exposure for the quadralite to fire and not affect it at all. The quadralite site (https://www.quadralite.eu/studio-flashes/343-move-x) does say that the duration depends on the exposure setting (1/800s @1/11/2000s @1/32) so if this were happening, a higher setting might pick up some of the flash.

A second curtain setting would presumably also work if this were what was happening, but I don't see that option in the Canon manual (edit: There's a "slow synchro" setting mentioned in the manual) and the CHDK setting for that does not appear to be implemented.

The Quadralite FAQ (https://www.quadralite.eu/faq) under "How to trigger Quadralite flash without a sync cord?" also says "If you use a camera without the manual flash control mode, you can come across some difficulties when synchronizing your studio flash with a shutter. This is because a camera operating in the auto mode triggers a measuring pre-flash before the actual exposure. To avoid this, you should use a photocell of a studio flash operating in the pre-flash skip mode. This will enable you to properly synchronize the flash and the shutter."

(The click to expand function in their FAQ seems to be broken, I had to use dev tools to see the answer :blink:)
« Last Edit: 27 / September / 2023, 18:51:16 by reyalp »
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Offline nesteryo

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Re: Using CHDK on SD800 with slave studio lighting
« Reply #4 on: 27 / September / 2023, 19:29:01 »
Quote from: reyalp on 27 / September / 2023, 18:42:11
The Quadralite FAQ (https://www.quadralite.eu/faq) under "How to trigger Quadralite flash without a sync cord?" also says "If you use a camera without the manual flash control mode, you can come across some difficulties when synchronizing your studio flash with a shutter. This is because a camera operating in the auto mode triggers a measuring pre-flash before the actual exposure. To avoid this, you should use a photocell of a studio flash operating in the pre-flash skip mode. This will enable you to properly synchronize the flash and the shutter."

(The click to expand function in their FAQ seems to be broken, I had to use dev tools to see the answer :blink:)

Thank you for the guidance! You might be onto the problem, as the product website states under "Features" list:

Quote
by-passing the pre-flash function allowing to synchronize with cameras with pre-flashtrigger system

Will try this tomorrow at the studio, thank you again for your time.
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