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PC sync port on a camera that doesn't have one

My wife needs a way to control an external flash on her camera, without using the on camera flash. She has a Canon s3 is, and the flashes she needs to use have a PC sync cable? I know nothing about cameras, but I am handy with electronics.

Does anyone know if this is even possible? Even better, if it is possible, does anyone have a teardown guide for this camera?

Any help would be appreciated.

Nick
Sat, 30 Dec 2006 08:10:48 -0800

Hi Nick,

That is a really interesting hack. I haven't thought about it till you mentioned it. I think you can wire it to the shutter release, the same way I wrote about "Building Triggers" in my "Hacking Digital Cameras" book. Then wire wires would go to a PC sync port that you can buy at camera stores.

Of course, you'd have to take the shutter lag into account. Once you figure out how long the shutter lag is, wire up a delay timer (perhaps using a 555 timer chip, which I also shown how to use in my book) between the shutter release and the PC sync port. Then it should trigger the external flash.

Chieh Cheng
Sat, 30 Dec 2006 14:11:03 -0800

That sounds like a plan. While I'm waiting on the book to be shipped to me, how about another approach? This camera has a usb port like all digital cameras. Is there any sort of software that anyone knows of that will test to see if ANY sort of signal is emitted from the usb port when the shutter is depressed. That would be a great shortcut!

Nick
Sun, 31 Dec 2006 09:01:23 -0800

Or what about changing the flash settings on the camera to a single flash, (no preflash, redeye, etc) and hooking something straight up to the flash?

Nick
Sun, 31 Dec 2006 09:33:05 -0800

I think it is unlikely that the USB port will emit a signal when the shutter is released. USB has a complicated handshake protocol and will not communicate until the handshake is proformed.

Hooking up to the flash might be a worthy approach. The flash capacitor carries high voltage and could fry your electronics, so I probably won't try hooking up to that. But if you can find the flash trigger circuitry, it might work pretty well.

Another idea is place a photon detector (forgot what's the electrical terminology for it) in the flash window. The photon detector is connected to a slave flash. Then mask off the window with black electric tape so the flash won't be emitted to the outside world. The internal flash will trigger the detector and in turn, trigger the external slave flash. The easiest way I can think of doing this is to buy a commercial slave flash, pull out the photon detector, and extend the wires.

Chieh Cheng
Sun, 31 Dec 2006 12:52:40 -0800

If memory serves, the hot-shoe flash triggers (~$15 on eBay) are triggered by the IR emitted from your camera's built-in flash. You can use a piece of exposed 35mm film to cover your camera's flash so that its IR light is still emitted in sufficient quantity to trip the flash trigger. Even if they're not triggered by the flash's IR, I suppose that covering the built-in flash with a piece of diffusing plastic or paper will cut the flash output enough so that it trips the trigger w/o over-exposing your photo. If your camera has manual modes to allow you to compensate for the additional light, this can be a non-issue. (The Canon S3 does have this ability)

TIM
Tue, 03 Apr 2007 00:51:56 -0700

Update: I know this is old, but I just found it.

What I did: I got a photo resistor from Radio Shack. I mounted it inside an old 35mm film canister. I cut out a notch so that the canister would completely cover the onboard flash. Now, when the flash fires, its contained in the canister, but still trips the photo diode, sending the flash signal to the lights. I turned off all preflash and set it to a single flash only.

Nick
Tue, 16 Sep 2008 16:36:00 +0000

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