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External Flash?? A Raw Idea

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Offline hal.nls

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External Flash?? A Raw Idea
« on: 30 / July / 2009, 14:53:44 »
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hi guys,

i've got sx110is and my goal is to make it cabable of shooting with an external flash.
i have some questions now for you:

1. does an external flash work on a simple pulse? i mean if i will send him a pulse of 3V he will fire?
2. can i use the usb cable for sending a signal ?
3. supose i can make the camera send a signal through the usb port, how can i sync it with the camers's flash?
4. another idea: take out the 2 screws at the inner flash and connect 2 lines to the inner flash and run them outside
the camere to the other flash and when the camera fires the inner flash it will provide the needed pulse


Hadar

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Offline PhyrePhoX

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Re: External Flash?? A Raw Idea
« Reply #1 on: 30 / July / 2009, 15:18:55 »
just use an optical slave. you cannot send data via usb, plus it would be too slow.
screwing around with the internal flash is not a good idea unless you seriously know your way around electronic devices and know the laws that are therin.
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Offline vostok

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Re: External Flash?? A Raw Idea
« Reply #2 on: 31 / July / 2009, 05:30:48 »
If I'm not mistaken the PC sync port that's used to fire an external flash just shorts the two contacts on the line. Not sure about the voltage or current taking place here. Go with Phox's advice. You'll find optical slave sensors for a few dollars at dealextreme.com
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Offline gremmy

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Re: External Flash?? A Raw Idea
« Reply #3 on: 31 / July / 2009, 07:38:15 »
I recently attempted to use the lightning MD script to try and capture the flashes of disposable cameras, (that I had picked up for free from my local camera store ;) ), thinking that the script would be fast enough to be used in the same way as a camera with a synced flash would, but it wasn't a success. The camera would take the shot after seeing the flash and not at the same time. If anyone knows if there's something I could try so that the camera could capture the flash, or if it is impossible to capture light that fast, that'd be great.

Grem.
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Offline Anaglyphic

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Re: External Flash?? A Raw Idea
« Reply #4 on: 31 / July / 2009, 14:07:38 »
Quote from: hal.nls on 30 / July / 2009, 14:53:44
4. another idea: take out the 2 screws at the inner flash and connect 2 lines to the inner flash and run them outside
the camere to the other flash and when the camera fires the inner flash it will provide the needed pulse
You don't mention how skilled you are as an engineer, so I'm approaching this as though you're a hobbyist... I highly suggest against #4. If you're taking the taps from the xenon tube itself, note that the voltage on those wires when the flash capacitor dumps is going to be somewhere between 250 - 400 volts with nothing to impede the current flow. This could prove lethal. (If it uses a transformer, it could be much higher. Most P&S built-in flashes do not have them.) If you screw up, you could end up solving all your problems in life - instantly.

There is a de-facto bible on the internet, Samuel Goldwasser's Sam's Strobe FAQ. Go read it. Especially the part about discharging storage capacitors.
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Offline Anaglyphic

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Re: External Flash?? A Raw Idea
« Reply #5 on: 31 / July / 2009, 14:23:48 »
Quote from: gremmy on 31 / July / 2009, 07:38:15
I recently attempted to use the lightning MD script to try and capture the flashes of disposable cameras

Ah, no, it's never gonna happen. An optical slave strobe detects and reacts in a microsecond or two. MD on it's best day is many thousands of times slower than that. In a recent test using the SX100, MDFB could catch things delayed at 100ms (that's millisecond not microsecond) about 22% of the time. The flash duration from a small disposable camera is going to be pretty long, as flashes go - probably 1/2500th (0.4ms) - 1/1000th (1ms). There's zero chance MD could catch that.

[edit: I forgot my noodles]
« Last Edit: 31 / July / 2009, 14:49:47 by Anaglyphic »
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Offline fvdk

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Re: External Flash?? A Raw Idea
« Reply #6 on: 31 / July / 2009, 17:32:23 »
Quote from: Anaglyphic on 31 / July / 2009, 14:23:48
Quote from: gremmy on 31 / July / 2009, 07:38:15
I recently attempted to use the lightning MD script to try and capture the flashes of disposable cameras

I have no idea what it exactly is that you want to capture but why not set the exposure time of your CHDK camera at a few seconds in a darkened room and than fire your disposable camera while the shutter is open?
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Offline Anaglyphic

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Re: External Flash?? A Raw Idea
« Reply #7 on: 01 / August / 2009, 13:00:45 »
Quote from: gremmy on 31 / July / 2009, 07:38:15
thinking that the script would be fast enough to be used in the same way as a camera with a synced flash would
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Offline PhyrePhoX

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Re: External Flash?? A Raw Idea
« Reply #8 on: 01 / August / 2009, 14:29:35 »
a pm he wrote me:
Quote from: hal.nls on 01 / August / 2009, 13:42:31
hi,

can you please tell me how to use an optical slave?
what exactly should i buy?


thank you

(by the way i hate getting personal messages on public forums asking stuff that deserves to be asked in public).

there are two kinds of optical triggers. the really cheap ones that trigger on every flash they see. and then there are the more expensive ones, that ignore preflashes. or even ones that can be tweaked to your kind of "trigger" flash.
a preflash is fired by your camera everytime the flash is NOT set to manual. which on an ixus is every time, EXCEPT if you use the manual flash override feature i added to chdk a few revisions ago.
by setting the flash to manual power 0 (lowest setting) you can trigger the optical slave plus you dont have the ugly oncamera flash in the picture (since it is so weak).
an example for a cheap trigger is this: http://www.amazon.com/Seagull-SYK-4-Optical-Trigger-Socket/dp/B0028DM1YA/ref=sr_1_2?ie=UTF8&s=electronics&qid=1249151317&sr=8-2
actually most photography shops and electronics markets sell these things.
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Offline gremmy

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Re: External Flash?? A Raw Idea
« Reply #9 on: 01 / August / 2009, 21:16:44 »
Thanks for the informative explanation Anaglyphic, it's thoroughly appreciated.

fvdk: Yes, most of the time I will be using the flashes during long exposures, but for situations that are brighter, where an exposure of longer than a second or two could lead to an overexposed image, that technique wouldn't be usable. That is why I looked into using the MD script to capture the external flash.

Thanks, Grem.
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