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    #11
    Senior Member g.l's Avatar
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    Interesting David. So triggering video with a shutter release works? But it doesn't give you reliable low-error sync? Is it at least better than just randomly hitting 'start', ie. is the max error at least less than 1/2 frame that way?

    Displaying the error could be done with an external box that monitors the composite outs. I'm sure they already exist, but I could theoretically build one (I'm a programmer and I've dabbled with microprocessors a bit).


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    #12
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    Quote Originally Posted by g.l View Post
    Interesting David. So triggering video with a shutter release works? ....
    I believe the remote port to be polled, so on it's own it does not work for sync. (It would be the cat's pajamas if the remote port generated an interrupt - but I've yet to find the camera where that happens)

    In any case, it's a one-two punch with our approach. Punch 1 - Power-up the cameras simultaneously, using external power (I'll post details). Punch 2- Send the remote shutter release trigger simultaneously.

    I'm getting a bit ahead of my plan to provide detail on what we've tried, what has worked, what has not, how we're testing and what we plan to try next. I'll try to fill in the blanks with some detailed posts over the next few days.

    Glad to see some interest!!


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    #13
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    If we don't find a hardware or firmware solution to sync, the best you can do is shoot at 50p / 60p, because the maximum error will be smallest (1/25 or 1/30). The GH2 is rumoured to have those rates at Full HD.
    Thats a long shot. The rolling shutter will cause noticable issues without precise sync. Your only hope for a production ready system is to break the cameras open and find the ex sync pulse, if one exists. I hope you got enough cash for two more GH1's.


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    #14
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    Quote Originally Posted by tonpole View Post
    Thats a long shot. The rolling shutter will cause noticable issues without precise sync. Your only hope for a production ready system is to break the cameras open and find the ex sync pulse, if one exists. I hope you got enough cash for two more GH1's.
    Maybe... and the thought of breaking these cameras (open or otherwise) has certainly crossed our minds over the past 2 months! There is, however, a hopeful alternative that may get us the level of performance that can be had from two LANC-sunk cameras.

    To be clear about this: the 1-2 punch approach described above works about 70% of the time. By works I mean sync so tight that the electron gun scanning in a CRT isn't fast enough to show sensor phase disparity between the two cameras. If we can determine why it's a 70% success rate and not 100% - or - if we can predict that we're in the 30% fail zone and try to power-up the cameras again, we'll be golden.

    So - I assert that it is premature to call the efforts to sync by camera surgery, "your only hope." That said, there are two VERY interesting pins on FP9004, on the GH1's main PCB, labeled CMOS HD and CMOS VD - if all else fails.
    Last edited by David Cole; 08-29-2010 at 02:36 PM. Reason: wrong pins


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    #15
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    Here are the details for ganging DC power-in and the shutter release remote control:

    DC Power In:

    Note: This has some risk associated. We've used it a LOT without incident, but, you never know. A good, regulated power supply is a must to avoid potentially damaging surges. Use at your own risk.

    Shutter Release:


    and here both controls are installed in a tripod-mounted box:



    To use:

    1) turn the gang-power switch off,
    2) turn the camera power switches on,
    3) turn the gang-power switch on (at your own risk!),
    4) begin and end recording (in creative movie mode) with the shutter release momentary switch,
    5) power the cameras down using the camera power switches - not the gang-power switch
    ... lather rinse repeat ...
    Last edited by David Cole; 08-29-2010 at 05:21 PM. Reason: Added detail.


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    #16
    Senior Member g.l's Avatar
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    I've just had a thought - if the random missyncs you're seeing are merely the result low-frequency polling, then a simple firmware mod would be to find & up the polling rate.

    Or, your 70% success rate could indicate that polling is running at a lower priority and is occassionly interrupted by something.

    Are your success rates consist over several takes in the same session? Or is it random with every take?


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    #17
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    We've found that second and third takes without cycling the power with the gang controller are more and more likely to have sync drift. We now limit to a single take between power cycles (and still get the 30% sync-drift).

    My hunch is that there is something non-dererministic in the power up / initialization in the cameras that sometimes results in the clocks being off. This is often observed in LANC-controlled stereo camcorder rigs. The solution is to power-cycle again with a LANC controller.


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    #18
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    Quote Originally Posted by David Cole View Post
    Here are the details for ganging DC power-in and the shutter release remote control:

    DC Power In:
    ...
    Note: This has some risk associated. We've used it a LOT without incident, but, you never know. A good, regulated power supply is a must to avoid potentially damaging surges. Use at your own risk.
    My idea is the same, except that I would try to avoid plain switches.

    Quote Originally Posted by David Cole View Post
    Shutter Release:
    ...
    Also similar observation as above.
    You said that you have 70% success rate. What does it mean? How do you define your success rate? Less than .... 1ms missynch, measured by Wimmer's programme?


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    #19
    Senior Member g.l's Avatar
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    Quote Originally Posted by David Cole View Post
    We've found that second and third takes without cycling the power with the gang controller are more and more likely to have sync drift. We now limit to a single take between power cycles (and still get the 30% sync-drift).
    Have you tried powering the cams without memory cards? Not convenient, but worth a try to see if that is causing the randomness.

    Of course the real question is how frame capture start is actually timed internally. Either it's engaged from scratch every time you start a take. Or the relevant clock is initialised once at boot and never changes, ie. regardless of when you begin a take, it may wait for the next internal frame 'pulse' before it actually starts recording.

    In the 2nd case, a synchronised trigger mechanism really plays no useful part (except that you at least don't have to find the frame-level sync in post).

    Anybody know how this usually works?


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    #20
    Senior Member g.l's Avatar
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    Quote Originally Posted by crunchy View Post
    My idea is the same, except that I would try to avoid plain switches.
    What kind of switches would you recommend crunchy?


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