Another question, the Pocket has timelapse functionality right? Could we trigger this simultaneously on both bodies? How is it activated?

I included microcontroller-based timelapse functionality on the custom controller for my GH2 rig: http://www.dvxuser.com/V6/showthread.php?221553-GH1-Stereoscopic-Rig-Collaboration&p=2359206&viewfull=1#post2359206 (that was the old hyper rig, it's all now on a much shorter bar from DealExtreme).

But that was triggering the stills shutter, so the trigger came from an external clock (my controller) and wouldn't drift between two bodies. Would this even work on the Pocket without massively drifting?

Thanks @kavadni. From skimming the datasheet, it seems much more capable than the standard composite sync separators, but it still only deals with analogue signals, correct? The Pocket doesn't have analogue, so the only option would be HDMI.

If going that route I would want to do full image processing on two HDMI inputs to give live anaglyph and other stereo previews on a single HDMI monitor (and you could also display the sync directly on it). But I don't know how to do the HDMI interfacing ...

Thinking about it, you can do most of these tests with your Applied Logic readout. Here I would leave one camera connected and running, and try the above on the other cam. If the sync suddenly changes the capture clock is reset.

You can also try manually start-stop recording one body several times. Does it change the sync?

A quick test with a single BMPCC confirms Marcus's thought that the lens release button resets the camera's clock. At least I can say that the lens release button appears to put the camera though the same protocol as camera start. If I can get a moment this afternoon I will two cameras and the Applied Logic board to see if a common reset with the lens release buttons of two cameras will put them in sync. I have never set up Peter's synctest but hopefully the Applied Logic board's led read-outs will provide some information.

I should point out, however, that the lens reset button understandably only works with an automatic lens.

Very valuable info @crunchy. I don't actually measure sync on my GH2's. I only recently started designing a circuit for it though (with a nice OLED display and everything), but if the Pockets work out I'll use LANC instead of VSYNC extraction.

(on a tanget: Of course what I'd really like is HDMI decoding (you could also measure sync from that), but it's beyond my skillset. The idea is to build a small board that accepts two HDMI ins from cameras, and does custom image processing to a single HDMI out to show eg. anaglyph previews (and other types) on any cheap HDMI monitor. You could extend that with histograms etc. I can do the image processing, but HDMI signal handling seems very complex, and demands high-speed processors and suitable electronics, I have no experience with either.)

Like you I find that with my Panny primes that sync is hit and miss - but when it works, it's usually perfect. As I suspected the lens calibration, I developed a routine where I pre-focus and expose my shot (I always use manual exposure), then power cycle the bodies first before recording. The idea was that as both lenses are already on the same focus & iris, the calibration time on both should be much closer. It seems to be working for me, in that I get good sync more often (which I determine from the audio waveforms of a click at recording start). I also take more time these days after power-up to let everything settle, so it may be a combination of things, or maybe the lenses really have nothing to do with it at all. I should have done scientific sync test on my GHs, but I just never got around to it as it worked well enough-ish (but I will with my Pockets).

@MarcusWolschon, I didn't realise that m43 lenses use SPI (I've just coded SPI comms on an AVR for something else). That might give us another way in. Has anybody reverse-engineered the protocol?

It would be much easier to hack the lens pins with manual lenses (not sure how that works out with a Speedbooster fitted?).

Can someone try the LENS RELEASE to see if it resets the capture clock on a single body? The best way to test it (and dual-body sync) is with an old CRT monitor (has to be CRT) and Peter Wimmer's free software: http://www.3dtv.at/Knowhow/Synctest_en.aspx , you can just see what's happening to sync in real-time.

Try the LENS-RELEASE button in sync to sync the cameras. It does a proper lens shutdown and power-on via the SPI interface to the lens.

OK, maybe there's another way to trick it.

re. lenses I will confirm when I get my bodies. I have the 14mm and 20mm primes here, and I can tape the contacts to simulate manual lenses. (I also have the Lumix 3D lens which I tape up to shoot raw stills, it's mostly awful for video though).

A second idea - as the power button is 'soft', something is already running when the camera is off. It may just be an interrupt that wakes the CPU, but it's possible that the master clock is already running from the moment you connect power. If so, then just delivering juice to the bodies, even when switched off, may be syncing them at that point.

On the GH's, David Cole found that simul-power sync was only reliable with manual lenses. The bodies do some kind of lens calibration at boot with native lenses (probably focus and/or iris), and that probably introduces a random delay (which also suggests that the capture clock is only initialised after this calibration, so the firmware can apparently reset the clock).

We'll need to see if this is true for the Pocket aswell.

Very very good idea to begin this effort. We bought two BMPCCs pretty much as soon as they were released, primarily for stereo work. These are wonderful little cameras. If handled with care, they are capable of making beautiful images. There are, however, certainly limitations to the BMPCC and (at least for our purposes) the ability to control shutter (frame) sync is one of them.

As GL suggests, the form factor of the camera is good for mounting side by side. There are 1/4-20 mounting points directly over and under the lens mount so building a side by side mount for the camera is pretty straight forward. We also have built a beam-splitter rig that works quite well. But the shutter sync issue remains...

Powering the cameras simultaneously does seem to work in our experience and we have produced some quite good results. We have no plans, however, to take the BMPCC stereo rig to the horse-races any time soon.

With regard to GL's thoughts, some things we've observed:

A permanent press on the power button does not work in that a long press on the power button cycles the camera on and then immediately off.

It is certainly possible to start the cameras simultaneously with LANC commands but sadly, the LANC start command does not reset the camera's internal clock. It would be wonderful if BMD were able to write that capability into a future firmware update.

The work-around we have been using for shutter sync is through the use of the Applied Logic DUAL CAMERA LANC CONTROLLER http://www.appliedlogiceng.com/index_files/Page1431.htm.

This board is seems very well conceived, engineered and fabricated and is relatively inexpensive at 240 USD. The board offers control of Zoom out, Zoom in, Focus Auto/Man, Focus Near, Focus Far, Photo Capture, Record Start/Stop, and Power On, and Power Off. Sadly, of course, the Power On, and Power Off does not work with BMPCCs. The board does not shutter-sync the cameras but through a set of LEDs one can tell when the camera is within 5 milliseconds which we find is good for most applications this side of a horse-race.

Very much looking forward to others thoughts and observations on the possibility of syncing these splendid little cameras.