We bought an S3 IS and confirmed with a rotating mirror and a laser that CHDK software indeed enables shutter speeds of 50 micro seconds or less.
The trigger pulse to take the shot had to be at least 30 milliseconds, the camera did not respond for shorter trigger pulses.
Is the camera hardware capable of being triggered with microsecond accuracy and how can we do it?
We are also planning to call and ask someone from canon, I don't know how canon feels about CHDK.
I don't know if it's compatible with the S3IS, though.
With a bit of electronics you could create the plasma at the same instant.
...and to clarify a bit: You can get better accuracy with CHDK compared to what you got from your experiments so far. You need to use the SDM build's sync feature. It was written to sync two cameras which get their triggers from a single USB remote wired to both cameras, but it can also help you to trigger a single camera more precisely. I don't know if it's compatible with the S3IS, though.The delay from your remote trigger pulse to the shutter opening doesn't actually get any shorter using the sync feature, but (unlike in the standard Allbest build) the delay will be pretty constant (to almost 50 us for some cameras, quoting Microfunguy above, which could be enough for you to capture some nice images with a greater probability). So, this will only help you if you can predict your plasma events by a couple of tens of ms or so (or whatever the delay is) i.e. if you for instance are actuating them electronically.
it opens its shutter all the way and does somethings then takes the shot at the end of 2 seconds. Is there a way to tell the camera to just take the shot which could make triggering more stable I guess.
Not quite an answer to your question on the 2 second delay
Yes, the s2is and s3is are not recommended for precision stereo synch or precision delay to capture.I cannot answer regarding shutter-speed but your tests suggest that it is 'real'.So far, in terms of the difference in delay times between two cameras before shooting, the A630 performed best but this was a one-off test.Some very inexpensive cameras with modest features (such as the A460) can have very repeatable delays after USB signal goes low.Quoteit opens its shutter all the way and does somethings then takes the shot at the end of 2 seconds. Is there a way to tell the camera to just take the shot which could make triggering more stable I guess.The whole point of this method is to let the camera do whatever pre-exposure operations it needs to and then pause the shoot operation until the USB signal goes low.At that point, the camera presumably has very few other operations to do before firing the shutter.So, the delay should be very consistent from one shot to the next.In SDM you can programme a delay after USB low to a resolution of 100 microseconds.We could increase that resolution to about 0.1 microseconds.I assume that you used a fast-response photodiode ?It will be interesting to hear of any further work.Incidentally, SDM 1.70 is released today.David
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