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External flash trigger

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External flash trigger
« on: 14 / November / 2015, 12:58:59 »
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For my project I need a camera with CCD sensor (for global shutter). I have to trigger the camera from a computer. So I came across some Canon Powershots and CHDK.
There are no modern Powershot camera's with external flash capabilities like the G12. For example the SX410IS (currently not supported by CHDK) or SX170IS (http://chdk.wikia.com/wiki/SX170IS) are modern CCD camera's, but without external flash capabilities.

Searching for CHDK and external flash I came across http://chdk.wikia.com/wiki/Forum:External_Flash_Control. For my project I do not want to use the internal flash device. I have to take a lot of pictures and that will blow up the internal flash.

I cannot use the USB because the USB is in use by the computer which controls the camera. Or I have to trigger a flash via the computer. But how to sync that? And is that fast enough? The camera is in an almost dark environment. So theoretically I can open de sensor for e relative long time (max 1/50 second) and flash somewhere in that timespan. But this is not my first solution (if working).

I came also across this script: http://chdk.wikia.com/wiki/UBASIC/Scripts:_LED_light. Maybe that idea is part of the solution? Is it possible to flash a LED on the camera in stead of the flash light? And pickup the LED signal by a sensor (or directly connect to the LED power). Next is to trigger the external flash, but that is not a real problem. Should this work?

Re: External flash trigger
« Reply #1 on: 14 / November / 2015, 14:29:46 »
Maybe it is a topic for the Hotwire! subforum?

Re: External flash trigger
« Reply #2 on: 14 / November / 2015, 14:41:14 »
Maybe it is a topic for the Hotwire! subforum?
There are only a few people that respond to posts on this forum and they follow all threads.

Is it possible to flash a LED on the camera in stead of the flash light?
You can script this so that a LED or the AF lamp blinks a few milliseconds prior to the shutter opening.  But it won't be really precise so a slow shutter speed and a few 10's of millisecond delay in your flash interface circuit would be needed.

Too bad you feel the need for a CCD sensor. There are several recent CMOS sensor cameras with a hot shoe.

Or you could buy a used / refurb'd G12?
Ported :   A1200    SD940   G10    Powershot N    G16

Re: External flash trigger
« Reply #3 on: 14 / November / 2015, 14:52:44 »
Is it possible to flash a LED on the camera in stead of the flash light?
You can script this so that a LED or the AF lamp blinks a few milliseconds prior to the shutter opening.  But it won't be really precise so a slow shutter speed and a few 10's of millisecond delay in your flash interface circuit would be needed.

Hmm in that case I need a shutterspeed of 1/20 when I have a delay of 50 milliseconds? And for a shutterspeed of 1/50 something like 20 milliseconds delay. Or is that to short for the camera?

Too bad you feel the need for a CCD sensor. There are several recent CMOS sensor cameras with a hot shoe.

Yeah, I'm afraid that within a few years all new camera's will be CMOS. But I hope that CMOS will have good global shutter capabilities at that time.

Or you could buy a used / refurb'd G12?

I need multiple setups. In the first stage around 3-4. So where to buy multiple camera's?


Re: External flash trigger
« Reply #4 on: 14 / November / 2015, 14:56:08 »
Is it possible to remove the flash tube and connect the output to a device which switches the external flash?

I do not know how such a device is called. But it has to translate the incoming voltage (100-400V?) to the PC sync port of an external flash. If that device does not eat up all energy from the capacitor, the camera should be able to 're-flash' rapidly?

Re: External flash trigger
« Reply #5 on: 14 / November / 2015, 15:52:08 »
Hmm in that case I need a shutterspeed of 1/20 when I have a delay of 50 milliseconds? And for a shutterspeed of 1/50 something like 20 milliseconds delay. Or is that to short for the camera?
What you want to do is a hard thing to do.  So you are going to have to "fiddle" with it to make it work. The delay you suggest will be in the right range.  If I was doing this project I would probably use a cheap Arduino clone board to sense the LED signal from the camera,  insert a delay,  and fire the flash.   With a little bit of electronics knowledge,  you could rig up a 555 circuit to do the same thing with a pot to adjust the delay.  You'll have to find the necessary delay by trial & error - make sure you get the min & max times when you do that.

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Yeah, I'm afraid that within a few years all new camera's will be CMOS. But I hope that CMOS will have good global shutter capabilities at that time.
What does "global shutter capabilities" mean?  That's not an English term I recognize.

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I need multiple setups. In the first stage around 3-4. So where to buy multiple camera's?
eBay.

Or lurk around on the Canon refurb website : http://shop.usa.canon.com/shop/en/catalog/refurbished-powershot-digital-cameras . The selection there varies a lot from week to week.


Is it possible to remove the flash tube and connect the output to a device which switches the external flash?
Yes - it is technically possible to do something like that.  Although you probably would want to work your way back into the circuit and find the signal used to fire the thrystor that triggers the flash tube.  But you really need to know a lot about electronics and circuit design, coupled with some reverse engineering experience before you try something like that.   Even the little flash circuit in a Powershot camera has enough energy to knock you flat on your posterior if you do something wrong.
Ported :   A1200    SD940   G10    Powershot N    G16

Re: External flash trigger
« Reply #6 on: 14 / November / 2015, 16:40:14 »
What does "global shutter capabilities" mean?  That's not an English term I recognize.
That the whole sensor is capturing at once. CMOS sensors capture line by line, so there is a delay between the top line and bottom line. This causes issues named the rolling shutter effects. And when having a very short flash duration, the flash is only visible at the lines which are read during the flash.
A DSLR uses a mechanical shutter to avoid this. But that shutters have a lifetime of ~150.000. Some professional and expesive DSLR's go far beyond that.

Re: External flash trigger
« Reply #7 on: 14 / November / 2015, 18:37:48 »
That the whole sensor is capturing at once. CMOS sensors capture line by line, so there is a delay between the top line and bottom line. This causes issues named the rolling shutter effects. And when having a very short flash duration, the flash is only visible at the lines which are read during the flash.
Interesting!  How long does it actually take to read out the entire CMOS sensor?   Seems like it must be less that 10 uSec given the ability of CHDK to push most cameras up to at least a 1/10,000 shutter time.

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A DSLR uses a mechanical shutter to avoid this. But that shutters have a lifetime of ~150.000. Some professional and expesive DSLR's go far beyond that.
The Canon Powershots have mechanical shutters too AFAIK.
Ported :   A1200    SD940   G10    Powershot N    G16


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Offline reyalp

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Re: External flash trigger
« Reply #8 on: 14 / November / 2015, 20:15:06 »
That the whole sensor is capturing at once. CMOS sensors capture line by line, so there is a delay between the top line and bottom line. This causes issues named the rolling shutter effects.
This is only happen if readout occurs without the shutter being closed. For Canon P&S, this should only be true when recording video, or in case of mechanical failure, or extreme hardware modification.
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And when having a very short flash duration, the flash is only visible at the lines which are read during the flash.
Again, this should only be an issue if the flash happens during readout (at which point the shutter should be closed) rather than during the exposure proper.
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A DSLR uses a mechanical shutter to avoid this. But that shutters have a lifetime of ~150.000. Some professional and expesive DSLR's go far beyond that.
As far as we know, all Canon P&S (both CCD and CMOS) use a mechanical shutter for still shooting. It's a lot simpler than a DSLR shutter, so lifetime should be quite good.
Don't forget what the H stands for.

Re: External flash trigger
« Reply #9 on: 14 / November / 2015, 20:24:01 »
This is only happen if readout occurs without the shutter being closed. For Canon P&S, this should only be true when recording video, or in case of mechanical failure, or extreme hardware modification.
This suggests that the OP look at the SX60 or any of the recent G series,  all of which have a hot shoe.

A lot easier than modifying the flash electronics or tinkering with millisecond delays trying for flash sync.
Ported :   A1200    SD940   G10    Powershot N    G16

 

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