External flash trigger - page 2 - Script Writing - CHDK Forum

External flash trigger

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Re: External flash trigger
« Reply #10 on: 14 / November / 2015, 21:37:02 »
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I can't find the thread now, but I think several years ago I reported on a test setup to fire a manual remote flash from my A590is.  I mounted a Seagull SYK3 optical slave trigger directly in front of the A590's flash, with a Cowboy Studio radio trigger transmitter mounted on the Seagull's hotshoe.  And it worked.  But that was only because the A590 let me set a manual flash level, which did away with the ETTL pre-flash, and because it had full manual exposure options, so I could take pictures which the camera thought were very underexposed.

But the A590 has a real flash.  If you wanted to fire an LED instead, a Seagull SYK5 (Ebay) might work if the LED will trigger it.  It has a delay adjustable from 70 msec to 1.5 sec.  And you would probably have to depend on the script to do manual exposure.  The A590 was the last entry level Powershot with full manual options and a real iris.  Since then, manual controls have become scarce on all but the high end cameras.

So I have to agree that if the budget permits, using a camera with a hotshoe is a lot more likely to give the results you want.  And it certainly can be a CMOS sensor.  As reyalp said, you won't notice any difference on still pictures.

By the way, the A590 was my first digital camera.  Pure dumb luck, but I bought it on closeout at Staples for $100.  Best photographic purchase I ever made.


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Offline reyalp

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Re: External flash trigger
« Reply #11 on: 14 / November / 2015, 21:40:17 »
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.
Assuming corneliz isn't planning to use flash with video or shoot without the lens hardware, it would seem that way.

SX60 is a digic 6 cam, so CHDK support may be a long way off. Same G16 and all the G*x cams except the original G1x.

Maybe also worth noting there are (IIRC) some unresolved issues with CHDK overrides when the hot shoe is occupied. Don't remember the exact details, https://www.google.com/search?q=site%3Achdk.setepontos.com+hot+shoe may give some starting points.
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Re: External flash trigger
« Reply #12 on: 14 / November / 2015, 22:11:40 »
SX60 is a digic 6 cam, so CHDK support may be a long way off. Same G16 and all the G*x cams except the original G1x.
So his best option might be G15's or SX50's from the Canon refurb site.
Ported :   A1200    SD940   G10    Powershot N    G16

Re: External flash trigger
« Reply #13 on: 14 / November / 2015, 22:13:56 »
I can't find the thread now, but I think several years ago I reported on a test setup to fire a manual remote flash from my A590is.  I mounted a Seagull SYK3 optical slave trigger directly in front of the A590's flash, with a Cowboy Studio radio trigger transmitter mounted on the Seagull's hotshoe.  And it worked.  But that was only because the A590 let me set a manual flash level, which did away with the ETTL pre-flash, and because it had full manual exposure options, so I could take pictures which the camera thought were very underexposed.
I think that trips across his original concern about wearing out the internal flash unit after many exposures? Not that there is any data that i have seen that says that's an issue.
« Last Edit: 14 / November / 2015, 22:16:48 by waterwingz »
Ported :   A1200    SD940   G10    Powershot N    G16


Re: External flash trigger
« Reply #14 on: 14 / November / 2015, 23:21:01 »
Well I just tested the Seagull SYK-3 with the A590's autofocus assist lamp, and it didn't work.  Not enough light, I guess.

Also, the Seagull devices don't have batteries.  They get any needed power from the device they're triggering.  Apparently that's good enough to fire the Cowboy Studio radio trigger, but the delay circuit in the SYK-5 would require ongoing power, and the CS trigger doesn't provide any.  So that combination shouldn't work, although some other cheap trigger might.

I don't think there's any good answer for this unless, as you suggested, WW, you build a circuit for it.  But if he was willing to use the built-in flash as a trigger, and if the camera can be made to NOT pre-flash, then the Seagull SYK-3 and CS trigger combination will work on the A590, and probably other cameras.  If A590s would be good enough (only 8mp), he could probably pick up used ones on Ebay for $40-50.  The Seagull is about $7 on Ebay, and the CS trigger set is $21 on Amazon.  So it wouldn't cost much to try them out.  He would just need to build a rig of some kind to hold the camera and the trigger in the right place.  And, you know, if the flash burns out, you just buy another camera.  But I'm still using old Vivitar flashes from the mid-1980's, so I suspect the built-in flashes will last a long time.


Re: External flash trigger
« Reply #15 on: 16 / November / 2015, 03:30:40 »
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.
Are there numbers?

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.
1/10,000 per pixel, it does not say anything about the total readout procedure.  See for example http://www.bhphotovideo.com/c/find/newsLetter/Comparing-Image-Sensors.jsp

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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.
Ok... Is it possible to force electronic shutter via CHDK?


Re: External flash trigger
« Reply #16 on: 16 / November / 2015, 03:50:12 »
Well I just tested the Seagull SYK-3 with the A590's autofocus assist lamp, and it didn't work.  Not enough light, I guess.

Also, the Seagull devices don't have batteries.  They get any needed power from the device they're triggering.  Apparently that's good enough to fire the Cowboy Studio radio trigger, but the delay circuit in the SYK-5 would require ongoing power, and the CS trigger doesn't provide any.  So that combination shouldn't work, although some other cheap trigger might.

I don't think there's any good answer for this unless, as you suggested, WW, you build a circuit for it.  But if he was willing to use the built-in flash as a trigger, and if the camera can be made to NOT pre-flash, then the Seagull SYK-3 and CS trigger combination will work on the A590, and probably other cameras.  If A590s would be good enough (only 8mp), he could probably pick up used ones on Ebay for $40-50.  The Seagull is about $7 on Ebay, and the CS trigger set is $21 on Amazon.  So it wouldn't cost much to try them out.  He would just need to build a rig of some kind to hold the camera and the trigger in the right place.  And, you know, if the flash burns out, you just buy another camera.  But I'm still using old Vivitar flashes from the mid-1980's, so I suspect the built-in flashes will last a long time.

I have to take a picture every second or two. So for sure the flash device will build up some heat.

So bottom line: My best option is to use a CCD camera with electronic shutter, with CHDK I have to manually set the exposure settings (and disable flash). Next I have to flash a LED on the device, pickup that LED signal by a schema.

But the next question is how to force electronic shutter in photo mode? Can CHDK force that?

Re: External flash trigger
« Reply #17 on: 16 / November / 2015, 05:54:00 »
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.
I'm not sure that the SX60 or recent G series will fit my needs. I capture moving objects, I require shutter times of 1/1000 or a flash duration of 1/1000. Sorry, I haven't said that at first post.
I'm not sure that a whole CMOS sensor is read-out in 1/1000 seconds. Only with a mechanical shutter I think... Because the read-out occurs after the shutter close.

Next is that I will reach 100,000 shots easily and go far beyond that. Replacing the camera every time is not an option.

Somewhat background information: http://hackcanon.com/camera-tricks/exposure/high-speed-photography/.

It seems that all camera's have a mechanical shutter. The CCD ones to shield the sensor from light while readout, it is not clear for my why that is.
In my case the environment is dark, so a the mechanical shutter could be left open. But how to do that is another question...


Re: External flash trigger
« Reply #18 on: 16 / November / 2015, 09:16:40 »
I'm not sure that the SX60 or recent G series will fit my needs. I capture moving objects, I require shutter times of 1/1000 or a flash duration of 1/1000. Sorry, I haven't said that at first post.   I'm not sure that a whole CMOS sensor is read-out in 1/1000 seconds. Only with a mechanical shutter I think... Because the read-out occurs after the shutter close.
As the readout occurs after the mechanical shutter closes, the actual time to do the read-out is irrelevant.

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Next is that I will reach 100,000 shots easily and go far beyond that. Replacing the camera every time is not an option.
There are no guarantees - these are mostly inexpensive cameras designed for taking snap-shots.  But many of the CHDK developers have pushed their cameras well past 100K shots without reports of failures.

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In my case the environment is dark, so a the mechanical shutter could be left open. But how to do that is another question...
You are on your own here.  I do not recall anyone trying this.  However, it is possible to control the shutter mechanism seperately from the actual exposure.   See how it's done in this script  meteor.lua to create "dark frames".   What you want is the opposite effect (i.e. force shutter open rather than closed) but the same approach might work.   Be sure to let us know how it works out if you try it?
Ported :   A1200    SD940   G10    Powershot N    G16

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Offline reyalp

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Re: External flash trigger
« Reply #19 on: 16 / November / 2015, 16:32:09 »
Are there numbers?
I don't know of any official specs, but my d10 has well over 100k and still works (though it may be failing now, I still haven't been able to conclusive determine if the issue encountered in http://chdk.setepontos.com/index.php?topic=12258.0), and other timelapse shooters have reported similar or greater lifetimes.

Lapser suggestion that very short shutter times reduces shutter life. If you are using flash in a dark scene to control your exposure, this should not be a concern, you could easily use something like 1/100th with no impact.

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Ok... Is it possible to force electronic shutter via CHDK?
No. We can open or close the shutter using eventprocs as in the script waterwingz mentioned, but AFAIK no one has tried to override the existing behavior.

Calling these eventprocs will *not* solve your problem: they open or close the shutter immediately when called.

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It seems that all camera's have a mechanical shutter. The CCD ones to shield the sensor from light while readout, it is not clear for my why that is.
The rows of the CCD continue to accumulate charge while they are being shifted out, so if you don't have a shutter, you get smearing, particularly if you are using a simple full frame sensor like these cameras do. See http://www.andor.com/learning-academy/ccd-sensor-architectures-architectures-commonly-used-for-high-performance-cameras

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In my case the environment is dark, so a the mechanical shutter could be left open. But how to do that is another question...
It's possible the shutter could be disabled in software with some reverse engineering.

If you are brave and mechanically inclined, you may be able to physically remove or disable the shutter.

The shutter is also not used when recording video (hence, rolling shutter effects obvious visible on CMOS cameras video), but it's unlikely you would be able to synchronize video frames with flash.

edit:
Related thread discussing effect of shutter failure http://chdk.setepontos.com/index.php?topic=11712.0

Since "broken shutter cable" is a cause of this, it's possible some careful wire cutting could achieve your desired result. However, newer cameras might notice something was wrong and refuse to operate.
« Last Edit: 16 / November / 2015, 16:36:53 by reyalp »
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