Genlock sync of HM700/750 to HM790 at DVinfo.net

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Old February 4th, 2011, 11:15 AM   #1
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Genlock sync of HM700/750 to HM790

I recently shot a series in 3D using a HM700 and HM790 paired together for the 3D rig. The method I used would also work just fine for a multiple camera shoot so I've posted this here instead of the 3D forum.

The HM790 has the ability to genlock to a blackburst or tri-sync signal. However, I simply used a BNC cable and took the "Y" out of the HM700 and fed it into the Genlock in on the HM790. The 790 shows "SYNC LOCKING" for a couple seconds and then you have sync. This is very important if you are using a switcher or 3D muxer.
The sync lock worked great in 1080i60, 720p60 and 1080p25, however there is one caveat with 1080p24 (or 720p24.) With 3D, shutter sync is equally important or there will be a temporal disparity between the eyes. This isn't an issue in 25p, 60i or 60p modes but I found that in 24p mode it was simple luck whether the pulldown pattern started on the same frame. We would have to plug and unplug the genlock a few times until we happened to get perfect 2:3 pulldown sync. In the end we decided it was simpler to just shoot the series in 1080p25 because it was foolproof and our first broadcasters are European anyway.
We will conform the masters to 24p later. They will be a little longer but it is always easy to cut out some content.


I also built a single button trigger system using a couple 8-pin remote connectors wired to a DPST momentary switch (pins E & F for trigger.) Fujinon and Canon lenses use the same pins for start/stop trigger.
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Old February 10th, 2011, 02:27 AM   #2
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Tim, this should also work with the HD-251, yes ?
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Old February 10th, 2011, 10:19 AM   #3
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Yes. The same technique works with the HD250 or HD251 but you will run into the same issue with 24p pulldown in a 60 hertz sync signal.
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Old February 13th, 2011, 03:30 PM   #4
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thanks, Tim - yes, I realise that about 24p - but we're not shooting 3-D (yet...). the issue is rather to keep output pins free - since YUV outputs also double as TC in-out. if we can just blackburst in, we'll have external sound sync when we need it. this leaves the YUV output free for monitors and the SDI for the 4:2:2 signal without tricky pass-throughs. i just need to find out if the wordclock signal is compatible with jvc's sync in. if not, put a blackburst generator in the loop. (this could, I suppose, even be a plain old betacam deck's sync-out, yes ?)
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